UKOOA Drill Cuttings Final Reportrodadas.anp.gov.br/...R7/biblio/UKOOAcascalho.pdfUKOOA Drill Cuttings Initiative Final Report 3 1. Preamble Since the beginning of 2000 the oil industry

UKOOA Drill Cuttings Initiative

Final Report

February 2002

UKOOA Drill Cuttings Initiative Final Report

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Contents Page

1. Preamble 3

2. Initiative Background and Results of Phase I 42.1 Introduction 42.2 Background 42.2.1 What are Cuttings Piles? 52.2.2 Why has UKOOA investigated Cuttings Piles? 52.2.3 Stakeholder Dialogue 52.2.4 Scientific Review Group 62.2.5 Phase I Results 6

3. Phase II Programme and Results 83.1 Phase II Structure 83.2 Phase II Programme Results 83.3 Key Conclusions By Task 93.3.1 Task 1: Cuttings Pile Characterisation 93.3.2 Task 2a: Investigation of the Toxicokinetics of

Water Based Mud Cuttings 113.3.3 Task 2b: Assessment of the Actual Present

Environmental Impacts of Representative Cuttings Piles 113.2.4 Task 2c: Water Column and Food Chain Effects 113.2.5 Task 3: Initial Comparative Time Series Data on

Factors Determining Future Pile Volumes 123.3.6 Task 4: Development and Validation of Mathematical

Model of Short and Long Term Cuttings Pile Fate 143.3.7 Task 5a: Enhanced Bioremediation 163.3.8 Task 5b: Covering 183.3.9 Task 6: Pilot Cuttings Lifting Operation 193.3.10 Task 7: Evaluation of Options for Slurry

(Lifted Pile Material) Handling 22

4. Scientific Conclusions 264.1 Discussion 264.2 Environmental Impact 264.3 Long-term Fate of Piles 264.4 The Management Option 27

5. Dialogue Conclusions 285.1 The Framework 285.2 Aspects of Time 295.3 Completed Assessment Frameworks 295.3.1 Cuttings Pile A: Large pile containing a significant

volume of hydrocarbons 305.3.2 Cuttings Pile B: Medium sized pile containing a small

volume of hydrocarbons 315.4 Comparison of Management Options at the Dialogue Event 32


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6. UKOOA’s Conclusions & Recommendations 336.1 Overall Discussion 336.2 Action Programme 336.3 What is the Best Environmental Strategy? 346.3.1 Rate of Loss of Hydrocarbons 356.3.2 Area of Seabed Contaminated over Time 366.3.3 Summary 36

Annex I Development of the Assessment Framework 38

Annex II Summary of R & D Phase II Findings 40


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1. Preamble

Since the beginning of 2000 the oil industry has, in the UKCS alone investedsome £50 million capital in retro-fitting drill cuttings re-injection equipment and afurther £50 million a year in skip, ship and onshore processing of oil basedcuttings to avoid the discharge of any oil based cuttings to sea. Thisenvironmental mitigation measure has been highly effective and prevents of theorder of 100 Te per new well drilled being discharged into the marineenvironment.

This report is the final report from the United Kingdom Offshore OperatorsAssociation (UKOOA) sponsored scientific Initiative that has addressed the issueof cuttings piles under North Sea production sites created from historic, legaldischarges of oil based cuttings from the early 1970’s through to 2000. Theobjective of the Initiative has been to identify the Best Environmental Practice/Best Available Techniques for the drill cuttings piles. As the eventual frameworkproposed for undertaking a comparison of management options is similar but notidentical to the aforementioned BEP/ BAT frameworks, it is referred to as the‘Best Environmental Strategy’ in this document.

UKOOA wish to thank DNV for the Project Management, TEC for organising andfacilitating the parallel Dialogue Process, the SRG for scientific review andaccreditation, the Researchers for their scientific output and in particular, thewider stakeholding group for their guiding commentary and advice willingly givenat the three consultations.

The next section provides the reader with the background to the Initiative and theresults of Phase I completed in February 2000.

In the third section, the sponsors state what they have learned from the recentlycompleted Phase II Programme in simplified Q&A form.

Section four presents the scientific conclusions.

Section five discusses the assessment framework for management options, whatshould be considered in determining the best environmental strategy andprovides examples of the assessment framework completed comparingmanagement options for two characteristically different cuttings piles.

The sixth and final section concludes the report with recommendations lookingforward.

The final scientific reports from Phase II researchers are included as a CD-ROMattachment. The 2 page management summaries abstracted from theresearchers’ reports are contained as an appendix.

UKOOA Drill Cuttings Initiative Executive CommitteeDecember 2001


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2. Initiative Background and Results of Phase I2.1 Introduction

The United Kingdom Offshore Operators Association (UKOOA) has undertaken aresearch programme to tackle the historical issue of drill cuttings, which haveaccumulated beneath offshore installations in the North Sea. The UKOOA DrillCuttings Initiative was launched in June 1998 and was completed with thepublication of this report in December 2001. The project has been managed byDNV on behalf of a UKOOA Executive Committee. The goal of the Initiative wasto identify the best environmental practice and the best techniques available fordealing with these accumulations in accordance with the principles set out by theOSPAR Convention. A programme combining scientific investigation andstakeholder dialogue at a cost of just under £6 million has now been completed.All UKOOA members operating installations with cuttings piles have financiallysupported the Initiative. The work was executed in two phases; Phase Iessentially being a programme of desktop studies and Phase II including recoveryof cuttings material for laboratory experiments plus some limited offshore fieldtrials to provide data for comparative assessment of different managementoptions. The findings of the programme are summarised in this document.

A review group under the chairmanship of Professor John Shepherd ofSouthampton Oceanography Centre has independently accredited the science.

A great deal more information than contained in this summary report is availableat the UKOOA website (www.oilandgas.org.uk/issues), under ‘EnvironmentIssues’ and then select ‘Drill Cuttings’.

2.2 Background

2.2.1 What are Cuttings Piles?

In the same way that sawdust is produced when a domestic drill drills a hole inwood, small pieces of rock - called cuttings - are created when a well is drilled inrock to reach oil and gas trapped below. These cuttings can vary in size andtexture, from fine silt to gravel. The cuttings are carried back to the surface by thedrilling “mud”, a special fluid used to lubricate and cool the drill bit, and tomaintain pressure in the well to prevent blow-outs of oil and gas. At the rig thecuttings are separated from the mud; as much mud as possible is recycled to beused again and the small rock cuttings are discharged to the seabed, takenashore for treatment or re-injected into wells.

Where cuttings are discharged to the seabed an accumulation of cuttings materialmay form. Cuttings have not accumulated around installations in the southernNorth Sea, where the stronger ocean currents and wave action have rapidlydispersed them, enhancing natural degradation (the breakdown of any tracehydrocarbons). The rapid dispersal exposes more surface area on the chips ofrock, making the breakdown of any hydrocarbons more effective. However,cuttings have accumulated beneath drilling installations in the central andnorthern areas of the North Sea, in the British and Norwegian sectors, becauseseabed currents in these much deeper waters are far weaker. The cuttingsaccumulate on top of each other, so that top layers prevent oxygen and otherseawater constituents from penetrating to those below. The lack of oxygen within


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these accumulations means that bio-degradation is much slower and as a result,any trace hydrocarbons take much longer to break down.

2.2.2 Why has UKOOA investigated Cuttings Piles?

All products used in making and maintaining drilling mud and all discharges ofmud-coated cuttings from offshore installations and mobile drilling units havebeen made legally under the prevailing regulations of the day. Whilst there havebeen many changes to these regulations over the last 25 years, perhaps the mostsignificant in the context of this Initiative is the cessation of discharge of any oilbased cuttings containing oil at concentrations greater than 1% which came in toforce via OSPAR in 2000. At the same time as these regulations were beingdeveloped, industry was beginning to tackle early decommissioning programmeswhich required operators to address the cuttings piles both directly and indirectlythrough the need to undertake jacket and template removal activity in and aroundthem. Ahead of the UKOOA Initiative, knowledge about the legacy accumulationsand their impact on the environment on the UK continental shelf was limited. Thislinkage lead to a common concern amongst UKOOA members that insufficientinformation was available to understand the environmental impact of theseactivities and further the long-term fate of oil based cuttings material.

The research has added to our understanding of the physical and chemicalcharacteristics of the accumulations as well as the feasibility of variousmanagement options for dealing with the piles and the impact that these optionswould have on the environment.

The overarching principle driving the Initiative was to determine what would bebest for the environment, and what technology would be required to deliver it.Would it be better overall to leave the accumulations undisturbed on the seabedor to remove them and dispose of them elsewhere? To answer this, the Industryhad to consider the possible long-term effects of leaving the piles undisturbed aswell as the risks involved in lifting them and disposing of the material elsewhere.Scientists have not only studied the environmental impacts on marine habitats,but also those associated with landfill, discharges and atmospheric emissions.

2.2.3 Stakeholder Dialogue

The Initiative has been founded on a twin-track approach. This is believed to beimportant to understanding the environmental fate and impact of cuttingsaccumulations and determining practicable management options that are bothscientifically sound and accepted by a wide range of interested parties. This hasinvolved conducting a dialogue with stakeholders in tandem with the programmeof scientific research.

With the support of UKOOA, a group of some 70 people have been invited by theindependent UK charity, the Environment Council, to take part in the stakeholderdialogue. They include government officials from the European Commission,Germany, the Netherlands, Norway and the UK, representatives from the OSPARSecretariat and the oil and fishing industries as well as environmental NGOs andscientists both from the UK and abroad.

The consultation programme’s aims are:• To encourage a common understanding of the issues


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• To prioritise key issues• To identify research requirements• To identify criteria for the selection of management options• To review the ongoing process• To aid the making of judgements between different management options

The first workshop for participants was held on 13 November 1998 in London andattracted a high level of interest. The debate was constructive and there wasagreement that the issue was complex and that all potential solutions warrantedfurther investigation. The results of the first phase of the research anddevelopment programme were discussed at a second meeting of stakeholders on2 February 2000, attended by over 70 delegates. The third and final session washeld on 20 November 2001 in London. 60 delegates met to review the scientificoutput of the Phase II programme and to review assessment frameworks forestablishing how to make judgements between cuttings pile management options.No single management option was considered to be the best environmentalstrategy under all circumstances, with natural degradation and recovery beingcited by most stakeholders as the two preferred options.

2.2.4 Scientific Review Group

A Scientific Review Group (SRG) has been established as an independentworking party to validate the UKOOA Drill Cuttings Initiative research programme,review its findings and report back to stakeholders. It has been created to ensuretransparency and integrity in the initiative’s activities. A summary report on theInitiative from the SRG will be published in January 2002.

Professor John Shepherd, the former director of the Southampton OceanographyCentre and currently director of the Earth System Modelling Initiative inSouthampton has chaired the group.

The full listing of the SRG members is contained below:• Professor John Shepherd MA, PhD, CMath, FIMA, FRS• Professor William Dover, FIMechE, CEng, FINDT• Dr Brian McCartney, BSc, PhD, FIEE, CEng• Professor Bruce Sellwood, BSc, Dphil, FGS, CGeol• Dr Hans Temmink• Professor Dr Jürgen Rullkötter, Dipl.-Chem., Dr. rer. nat. habil., AAPG,

DGMK, DGMS, EAOG, GDCh, GS• Research Scientist Torgeir Bakke, Cand.real. (MSc equiv.) Marine Biology• Professor Brian Wilkinson BscEng, BscGeol, PhD, FICE, FCIWEM, FGS, C

Eng, C Geol, F Russ Acad.Nat.Sci.

2.2.5 Phase I Results

Key findings from Phase I published in early 2000 included:

• Cuttings piles are highly heterogeneous and their content and volume are bothdifficult to forecast from drilling/ discharge records. This finding suggestedthat surveying and sampling would be required in order to undertake anymeaningful environmental impact assessment (Phase II Task 1).


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• Total hydrocarbon concentrations in cuttings piles containing oil-based mudwere found to be greatly in excess of the ‘no effect concentration’ for typicalmarker species such as mud shrimp. However, pathways from the cuttingspiles to marine life species in their vicinity, necessary for there to be anyenvironmental impact, remained subject of further research (see Phase IITask 2c).

• Experimental evidence demonstrated low bioavailability of heavy metalelements within a cuttings pile and very low levels of heavy metal leachingfrom a cuttings pile (heavy metals originate from impurities within weightingagents used in muds). (Further work undertaken in Phase II Task 2a.)

• Hydrocarbons within the surface layer of cuttings piles (top 5mm) degrade orleach naturally and re-colonisation was observed. Further work was requiredto quantify rates and end points of these processes for hydrocarbon materialoriginating from drilling mud (Phase II Task 3).

• Recovery to surface of drill cuttings appeared technically feasible, but thedegree of pollution through re-suspension would be key in the environmentalassessment of this option (Phase II Task 6).

• Models were constructed to enable assessment of the environmental impactof disturbances to cuttings piles (including recovery), but still requiredcalibration with field data (Phase II Task 6).

• On recovery, injection of the ground cuttings and the entrained waterappeared technical feasible where reservoir/ wells/ facilities would permit,although not presently legal (Phase II Task 6).

• Onshore treatment and disposal of the recovered cuttings appearedtechnically feasible, but further work was required to investigate transportationto shore and the most appropriate disposal route for the large volumes ofcontaminated water recovered with the cuttings (Phase II Task 7).

• Enhanced bioremediation did not appear to be practical, with key concernsidentified around reaction end-points and timescales (Phase II Task 5a).

• In determining the technical feasibility of the above management options inPhase I safety aspects, energy balances and economic and social issueswere not considered.

• On the available data from Phase I natural degradation was not ruled out as acandidate best environmental strategy in any assessment process.


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3 Phase II Programme and Results

3.1 Phase II Structure

Following the completion of Phase I and the second stakeholder dialoguesession, a second and concluding programme of research was designed,tendered and launched to close the remaining science and technology gaps. Thesecond Phase was more focused on understanding the management options andtheir impact on the environment. The management options studied in Phase I ofthe project meriting further work in Phase II included:

• Removal either by suction dredging from specially designed underwatervehicles, with subsequent treatment and disposal either offshore or onshore.[Alternative removal schemes involving conventional dredging or trackedvehicles were ruled out in the Task 6 tender exercise and have not beenconsidered by this Initiative.]

• In-situ treatment on the seabed, involving capping the cuttings with deposits ofsand, gravel and rock armour, or bio-remediation in which natural microbialbreakdown of hydrocarbons is artificially accelerated.

• Leaving the piles to degrade naturally.

UKOOA has now completed the second phase of the research programme at acost of £4.4 million. Again UKOOA members funded the programme, the projectmanaged by DNV and the independent accreditation role of the SRG wasretained. In addition, the DTI, OLF and NOGEPA (the latter two are theNorwegian and Dutch oil industry trade associations respectively) all joined theInitiative as observers.

The offshore element of the Phase II programme comprised testing the feasibility/environmental performance of recovery technologies, calibration of disturbancemodelling, and gathering further data on rates of natural degradation, re-colonisation and the environmental impact of undisturbed cuttings piles. Thelaboratory element of the programme has included further ecotoxicological testingto better understand any in-situ environmental impact (source/ pathways/receptors) of cuttings piles, flume testing to determine pile erosion rates and thedevelopment of a new longer term disturbance model with a capability to includenatural degradation, erosion and faunal colonisation over time. This longer-termmodel would then be able to predict the physical and biological persistence ofindividual cuttings piles. A summary of the findings of the Phase II programme isincluded below.

3.2 Phase II Programme Results

Phase II was constructed to answer a series of 80 questions, key to determiningthe best environmental strategy asked by the UKOOA EC, the SRG and thestakeholders at the end of Phase I. The findings from Phase II below arepresented in Q&A form, with the questions listed under the particular Taskinvestigating that knowledge gap. The answers are based on individual Taskresearchers’ reports. The researchers’ reports are included in full, together with a2 page Management Summary as a CD-ROM attachment to this report.


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3.3 Key Conclusions By Task

3.3.1 Task 1: Cuttings Pile Characterisation

1. Does the OLF protocol provide all the information needed to characterise acuttings pile?

Generally the OLF protocol, as revised, is comprehensive and provides abasis for systematic characterisation studies.

Task 1 measured the following physical parameters: cone penetration; shearstrength; grain size distribution and porosity. CPT measurements wereunsuccessful in the soft material of the sampled piles, and could notdistinguish between the material in different layers of the Beryl A and Ekofisk2/4 A cuttings pile. Shear strength measurements (using a Wing tool) on thematerial from the cores showed small differences. Detailed geotechnicalmeasurements are needed to support assessment of management options, inparticular covering (preferably consistent with a recognised standard such asBS1377: 1990, i.e. full particle size distribution, water content, particledensities, Atterberg limits, consolidation characteristics, see Task 5b report).

“Whole sediment” assays – including toxicity and Endocrine Disruptor (ED)assays – provide a useful screen for potential biological effects of re-suspension of pile material, although it is unlikely that effects can be relateddirectly to individual contaminants.

The discovery of significant concentrations of PCBs at Ekofisk was notexpected, and future characterisation studies should therefore include PCBanalysis. However no PCB’s were detected in the Beryl pile.

2. Do the available sampling methods and survey designs provide the necessaryinformation?

The sampling locations in Task 1 were positioned, based on previousmapping, to enable full penetration of the pile material into underlyingsediments. Sampling locations in the deepest parts of the piles were alsoplanned if those parts of the piles were accessible. However, samplingunderneath the platforms were not possible, so the deepest parts of the pile atBeryl and Ekofisk 2/4-A were therefore not sampled. Obtaining good coresamples from underneath jacket structures remains difficult.

Problems were experienced with obtaining deep cores, due partly to weather;and with the high degree of spatial variability within individual piles (thesehave also been common issues in previous pile investigations). A relativelyheavy (2 tonne) Vibrocorer proved the most successful device for deep coring,although a lighter instrument may be more useful in marginal weatherconditions. Such an instrument was not available to be tested at this survey.This remains a technology gap, which needs addressing in order to fullycharacterise thick piles.

Box coring proved an effective method of obtaining bulk samples of pilematerial. However, spatial variability in physical properties and contaminant


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concentrations was generally more evident in toxicity, small-scale andmesocosm studies (Tasks 2, 3 and 5) using box core samples from thesampled piles, than in the Task 1 characterisation data. The need for accuracywas thought higher with the experimental work of tasks 2,3 and 5. However,future characterisation studies should give particular attention to this issueduring the planning stages (e.g. consideration of required replication, stratifiedsampling). A limitation of using box coring for bulk samples was that only thesurface 20-50cm of the pile could be sampled.

3. Was the understanding of generic cuttings pile structure / composition fromPhase 1 confirmed ?

Key conclusions of Phase I were that hydrocarbon concentrations (in OBMpiles) were around 30,000 mg/kg (3%); that the surface top 5mm decomposesrapidly; and that the bulk of a pile remains inert.

Task 1 conclusions were that THC concentrations at Beryl ranged from 0.2%to 20%, while up to nearly 8% (mainly of esters from SBM) were found atEkofisk 2/4-A in the surface layers, and virtually no hydrocarbons beneaththese. In general, little evidence of degradation in a surface-active layer wasfound, possibly due in part to erosion and exposure of undegraded material.The NPD profile at Beryl corresponded relatively well with recorded drillingdischarges. Hydrocarbon and metal concentrations within both piles indicatelittle, if any, degradation or leaching of contaminants.

The presence of surface crust at Ekofisk, although reported previously fromother piles, was unexpected and required additional investigation. Afteridentification of crystalline phases and microscopic studies of the crust it wasfound to have originated from discharged grout.

4. Is there a clear distinction between OBM and WBM cuttings piles; and is thisdistinction relevant for management purposes?

The major difference between the Beryl and Ekofisk piles was mainly due tothe nature of the drilling fluids used at the two sites, and in the crust layer,which was only seen at Ekofisk. Cuttings material from Ekofisk 2/4-A reflectedrecent substantial discharges of SBM coated cuttings (both esters and polyalpha olefins) and could not be considered representative of a WBM pile.

Overall, the range of hydrocarbon concentrations and compositions recordedfrom different cuttings piles does not support a simple distinction betweenOBM and WBM piles (at least for multi-well development locations). Theresearch suggests that sampling and surveying are essential forcharacterising a cuttings pile.

5. Are there indications of anaerobic degradation within the bulk of the pilematerial?

Qualitative (i.e. presence / absence) sulphide measurements directly on thecores suggested the presence of anoxic processes within both cuttings piles,i.e. sulphide accumulation. Indications of anoxic processes, sulphideproduction, were also seen from small-scale degradation studies (Task 3) and


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by the presence of components assumed to be anaerobic degradationproducts. Parallel work at the University of Oklahoma supports this finding.

3.3.2 Task 2a: Investigation of the Toxicokinetics of Water Based Mud Cuttings

6. ‘Can contaminants other than oil be demonstrated as having no significantenvironmental impact?’

Given the lack of any measurable toxic response from the WBM samples, itwas impossible to demonstrate that contaminants other than oil werecontributing to environmental impacts.

3.3.3 Task 2b: Assessment of the Actual Present Environmental Impacts ofRepresentative Cuttings Piles

7. What is the environmental impact of cuttings piles at present, compared withother environmental management problems faced by the North Sea?

The calculated contaminant burden for 194 extant piles in the UK andNorwegian sectors of the North Sea has been estimated using the bestavailable data.

Hydrocarbons present in piles represent up to 4% of the total mass of piles,and in UK the six largest oil-based mud piles account for 24% of the totalmass of oil in piles. The rate of release oil from all North Sea piles is relativelylow and thought to be of the order of 330 Te/ year, which equates to less than0.5% of the total annual input of hydrocarbon from all other sources.

Barium, zinc and lead are the most abundant metals in piles. The total massof lead in piles is equivalent to about 0.15 (15%) of the total annual input tothe North Sea from non-pile sources. The total mass of zinc is equivalent toabout 0.056 (6%) of the total annual input to the North Sea from non-pilesources. Annual inputs of these metals from cuttings piles are thereforeconsidered to be negligible.

After 30 years of discharges, the total area of seabed resulting in biologicaldisturbance due to cuttings piles was estimated to be 1,605km2 or 0.23% ofthe total area of the North Sea. This compares with an area of seabed that isaffected by fishing, dredging and spoil dumping of approximately 130,000 to369,000km2 per year (up to 50%).

3.3.4 Task 2c: Water Column and Food Chain Effects

8. Can cuttings pile impact, if any, on the food chain be quantified?

The potential food chain effects of the OBM sediment seen during thebioaccumulation study are generally very slight and do not vary greatly fromthe accumulation seen in reference sediment from the southern North Sea.

However, the toxicity results indicate that potential for water column effects,albeit on a very minor scale in volumetric terms, exists if the OBM sedimentsare disturbed. Practically, rapid dilution from bottom currents and the lack of


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established communities in and around the pile reduces this potential to nosignificant impact.

3.3.5 Task 3: Initial Comparative Time Series Data on Factors DeterminingFuture Pile Volumes

9. What is the rate of natural degradation in the surface layers of the cuttingspiles?

Degradation processes of the organic fraction of drill cuttings material, bothaerobic and anaerobic, have been examined. It has been shown, both throughsmall-scale and meso-scale experiments that biodegradation processes areslow, that they mainly take place in the oxygenated surface active layer (SAL),and that they probably are little influenced by macrofaunal presence andbioturbation activity. However, bioturbation activity may influence the effectivethickness of the SAL.

Degradation rates for hydrocarbons (THC) of cuttings pile material at aerobicconditions are estimated to 3 mg/kg THC per day with Beryl cuttings (OBM)and 11 mg/kg THC per day with Ekofisk cuttings (PBM/ WBM). Thiscorresponds to half-lives of 120 days for Beryl (initial concentration about 750mg/kg THC) and 750 days for Ekofisk (initial concentration 74,000 mg/kgTHC). There are considerable variability in the THC data and hence in thepresented rates and half-lives. Presented data must hence be taken only asindications of degradation. This has been discussed in detail by the sub-reports.

There is some evidence of toxic conditions or inhibition that limits degradationat Beryl at concentrations above 2,000 mg/kg. Similar degradation patternsand rates observed with the Ekofisk cuttings were also evident with Frøycuttings (PBM). Only aerobic degradation processes take place to a significantextent.

10. What is the rate of erosion to the surface layers of the cuttings piles?

The current speed at which significant erosion was observed was around 35cm/s for both Beryl and Ekofisk (no waves applied). This value represents a 1-year (i.e. to be expected only once per year) current speed at Ekofisk.

The maximum measured erosion rate of the Ekofisk cuttings (PBM/ WBM)was about 6 kg/m2 per day at the maximum shear stress tested of (12 N/m2).With the Beryl cuttings (OBM) a similar shear stress gave erosion rates 40-100 times higher (up to 600 kg/m2). This difference is not thought to be due tothe mud type alone, as Beryl material contained a much higher fraction offines. The conditions at which these erosion rates were measured represent acombination of a 100-year current speed and a 10-year significant waveheight, conditions that are rather extreme.

At a maximum shear stress of 3 N/m2, the erosion rate of Beryl material was12 kg/m2. No erosion was observed at Ekofisk at the same conditions.


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11. Does degradation influence the rate of erosion?

Although this has not been addressed directly, THC concentrations mayinfluence erosion, and hence degradation processes may indirectly have animpact. Based on the two piles investigated, it seems that at the highest THCconcentration in the surface layer (Ekofisk), erosion is lower. However, theremay be other parameters responsible for the differences observed (like e.g.protection from the platform itself, localised differences in current and wavesetc).

12. What is the rate of re-colonisation of the OBM contaminated sites?

Colonisation, or macrofaunal activity (settling, burrowing behaviour, survivaletc.), of drill cuttings material by two species (Capitella capitata and Abra alba)has been examined in experimental systems.

Re-colonisation of cuttings piles is of interest for two main reasons. Firstly re-colonisation is a sign of the cuttings pile surface becoming healthier thusallowing macrofaunal species to settle and thrive. Secondly, re-colonisation isa necessary precursor for bioturbation to occur.

Re-colonisation processes are known from other situations to be slow, i.e.considerable time, maybe years, are needed for a macrofaunal community toestablish on a “new” surface. In areas with significant and regular erosion, re-colonisation of the pile is therefore expected to be practically absent.Bioturbation as a result of macrofaunal activity is thus assumed to be limited.In cases where a macrofaunal community is established, bioturbation is onlyexpected to affect the top few centimetres of the pile surface.

An estimation of the thickness of the SAL has been provided based onmeasured redox profiles of the cuttings, apparent burying depths of Capitellaand Abra, and from what layers depletion/degradation apparently hasoccurred:• In the mesocosm experiments, the main depletion/degradation processes

were restricted to the top 4-5mm.• In the macrofaunal colonisation mesocosm, burial depths down to about

20-30 mm was observed by Capitella capitata. The burrowing depth wasdependent on the cuttings concentration (THC), the depth decreasing toonly the top 5-10 mm at the 100% cuttings samples of both Beryl andEkofisk. At the lower concentrations tested (20% cuttings), the burial depthextended to 20-30 mm on both cuttings types.

13. What is the rate of sedimentation?

Rates of background sedimentation have not been established directly. Otherstudies show that in some cases significant sedimentation has occurred,covering the cuttings layer, while at the two piles of the study, no evidence ofnet sedimentation is seen. Sedimentation is not now thought a significantmechanism when considering the long-term fate of cuttings piles in the NorthSea.


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14. Are there differences between oil types with regard to natural degradationrates?

Oil type determines when degradation inhibitory conditions apply. The oil typefound at Beryl (OBM) appeared to inhibit degradation at concentrationsgreater than 2,000 mg/ kg. Whereas the oil type (PBM) found on the surfaceof Ekofisk was found to degrade at concentrations as high as 74,000 mg/ kg.When an oil type is present in a concentration where degradation is enabled,the type did not overly appear to affect the degradation rate.

3.3.6 Task 4: Development and Validation of Mathematical Model of Short andLong Term Cuttings Pile Fate

15. What is the environmental impact of trawling events over 10 and say 50years?

Task 4 modelling and the short-term modelling from Phase I suggests that thedisturbance impact of trawling is secondary when compared with thedisturbance due to episodic storm events. Whilst trawling will elevate cuttingsmaterial into the water column, the model predicts settlement withincontaminated footprint. Further, hydrocarbons are closely associated with theparticles and the release of free oil to the water column from a trawling eventis considered very small.

16. What would be the impact of jacket removal?

The modelling capability for assessing the potential environmental impact ofcutting and removing a jacket surrounding by cuttings pile material has beendeveloped by the Initiative. Factors that would influence the impact includewater depth, jacket configuration (number of legs, wall thickness, groutpresence etc.), cutting technology (shaped charge, diamond wire etc), waveand current data at the time of removal, physical properties of the cuttingsmaterial, volume and arrangement of cuttings around the cut location and theTHC levels within those cuttings. Suffice to say that a specific assessmentwould need to be undertaken in each and every case in order to quantify thepotential environmental impact.

Task 6 results indicate that cuttings can be recovered in and around thebottom of a jacket structure, and also that cuttings can be recovered andtherefore physically removed from a cut location should this be necessary. Itis therefore reasonable to assume that the removal of a jacket and the bestmanagement option for a cuttings pile are independent of each other andwhere there is potential for inter-dependence technology has been developedby the Initiative to both mitigate and model the potential environmental impactof the preferred course of action.

17. How would cuttings piles, if left to degrade naturally, be characterised in 50and 200 years time?

Task 4 suggests that the long-term fate of cuttings piles is determined by thephysics of cuttings dispersion, which then enables subsequent degradation ofhydrocarbons and re-colonisation to take place.


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The frequency and strength of physical disturbance is related to water depth -in deeper water (e.g. beyond 70m) it is relatively rare for there to be sufficientwave/ current energy to significantly move pile material; nevertheless, eventhe deepest parts of the North Sea seabed will experience disturbance underextreme storm conditions.

The presence of hydrocarbons from the pile material is likely to be measuredin decadal timescales e.g. 10 to 50 years in water depths of around 70m. Forwater depths over 120 m, the presence of hydrocarbons from the pile materialis likely to be measured in centennial timescales e.g. 500 to 1,500 years.

A specific assessment would be required to fully understand the long-term fateof any cuttings pile.

18. How would a cuttings pile site following retrieval be characterised in 50 and200 years time?

Again a specific assessment would be required to fully understand the long-term fate of the remains of any cuttings pile post recovery. Some preliminarymodelling undertaken in Task 4 for a large pile in deep water (150 m)indicated that the 5% of material that would remain post recovery is likely tocause elevated THC profiles for a period of up to 100 years. Thecorresponding THC persistence for the case where the pile was left todegrade naturally was of the order of 1,000 years.

19. What would be the appropriate monitoring programme for a naturaldegradation situation?

A monitoring program for a natural degradation solution should be based onthe protocol used for seabed monitoring at producing field sites, but shouldalso include sampling and analysis of the pile itself. A minimum of twomonitoring surveys should be undertaken at an interval of 3 years. Theoutcome of these surveys should then be used as basis for considering theneed for any further survey.

20. How much would natural degradation cost (in terms of monitoring etc.)?

Under UK law an operator would remain liable for the production site inperpetuity. Costs relating to natural degradation will be for the monitoringprogramme, and be driven by the number of surveys and the number ofsampling stations. Based on experience from previous monitoring surveys ofthe seabed at field sites in the North Sea area, the cost would be in the rangeof £ 50 - 200 K per field, including field sampling, laboratory analysis, andreporting. Two monitoring surveys over a period of 6 years followingdecommissioning of a field could then amount to maximum £400K. For thepurposes of the comparative assessment costs should be estimated at £25 to£100/ m3 in-situ pile material.


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21. Would there be any energy consumption associated with natural degradation?

Energy consumption for natural degradation option would be related andessentially limited to the use of survey vessel during sampling at the field site.Field sampling will normally be undertaken over a period of one to two days,using a survey vessel or supply-boat. Both CO2 emissions and energyconsumption are negligible when compared with other management options.

3.3.7 Task 5a: Enhanced Bioremediation

22. What would be the dimensions and design of the bioreactor?

The proposed reactor vessel would have a nominal volume of 280 m3, thuswhen 50% full of solids during the reaction phase of the experiment,approximately 140 m3 drill cuttings would be treated in one batch.

23. What would it be made of?

The reactor vessel would be made of carbon steel, lined on the inside andinsulated on the outside. There is a variety of equipment required for the de-watering processes (which occur onboard ship or on a platform) to ensure thatall the contamination is returned back to the reaction vessel for treatment.

24. Could the bioreactor be deployed from a platform?

The system has been designed to be deployed from a supply ship andsupported thereafter from the platform.

If a decision is made that the platform should be removed before treatment ofdrill cuttings can take place then this will have an effect, primarily on the costof the process. Provision would need to be made for the costs of a supportvessel fitted with dynamic positioning equipment and suitable manpower tosupport it. Whilst the utility requirements for the bioreactor system couldpotentially be serviced from a support vessel, they would be more easilyserviced from the platform.

25. What mechanism would be required to deploy the bioreactor?

The bioreactor itself will be deployed from a supply ship using an A-Framewith a capacity of up to 60 tonnes dry weight.

26. What manpower effort would be required to deploy and service thebioreactor?

Once in place, it is estimated that the reactor system will require a team of 10to operate. As the reactor is required to operate 24 hours a day therefore ateam of 20 operators will be required for a period of 30-50 weeks, to treat apile of 6,000 m3 with two-three reactors operating continuously. No weatheror operational downtime has been assumed in this calculation, so in practice itwould take longer.


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27. What would be the impact of jacket removal prior to remediation?

After moving away from the reactor design that relied on a single vessel beingmoved around to different pile locations, the removal of the jacket now has amuch more limited effect on the efficacy of the technique but would increasecosts. Without the platform being present a support vessel would need to be inplace while treatment was occurring. Although technically feasible, this wouldrepresent a major cost increase and therefore it is considered best that thesystem is used with the platform installation intact. However, it should benoted that the timescales of this option are so long that the retention andoperation of platform to support bioremediation would also incur verysignificant costs.

28. How would the bioreactor manage pile debris?

A movable reactor as envisaged in the Phase 1 report would not have handledpile debris well especially large pieces of debris. The use of the currentreactor design that allows for the transport of cuttings material from the pile tothe reactor should work well with most debris. Smaller pieces of debris shouldbe able to be moved out of piles once identified by the ROV, whilst the cuttingmaterial should be able to be removed from around larger immovable piecesof debris.

29. Could the platform footprint be bioremediated with the platform in place?

The reactor design has been specially selected to allow the platform to remainin place while bioremediation takes place. The re-design of the main reactorvessel to become a static feature with the cuttings delivered to the vessel froman ROV means that the platform can stay in place while treatment of thecuttings takes place. Indeed for ease of utility supply and to host theassociated equipment we have assumed that it is preferable for the platform tostay in place. The optimal approach to clean up of cuttings piles may bemultiple reactors (2-3) deployed around the platform operated in parallel andserviced by a single set of equipment held on the platform.

30. What would the energy consumption be for bioremediation process?

There are three main energy consumptive processes with the operation of thebioremediation system as we have designed it here, the ROV, the pumpsassociated with the system and principally the heater to circulate warm wateraround the reactor to raise its temperature. Based on the ratings of theequipment the energy consumption is very high at 122GJ/ m3, leading toemissions of 9,040 CO2 Te/ 1,000 m3 cuttings treated.

31. How much would bioremediation cost?

Based on 2 months remediation time, 3 reactors each of cuttings volume140m3 and an up time of 100% throughout the year, the cost is estimated at£2,350/m3. However, a factor of two should be applied given the relativelylow level of maturity of this option and for any comparative assessment arange of £2,350 to £4,700 /m3 should be considered.


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32. How long will it take to treat a typical pile?

Based on 100% uptime and 4 season working, the duration of the remediationfor a 6,000 m3 pile is 31 months.

More realistically the process would operate summer only in which case theduration would be 5 years for a 6,000 m3 pile and some 20 years for some ofthe larger piles.

33. To what depth would bioremediation be effected?

The bioremediation scheme proposed moves the pile material to the reactorand hence is able to remediate through to the bottom of the pile.

34. Would the bio-reactor work effectively for both OBMs and WBMs?

The bio-reactor remediates the hydrocarbons in the pile, which are at a nearzero concentrations in water-based muds, hence the management option isnot appropriate for water-based muds.

3.3.8 Task 5b: Covering

35. What would be the minimal thickness for a cover

A minimum thickness of 1m of granular material will absorb any leachate withoverlying larger stone armour of 1-2m for protection against storm anddamage.

36. What would the cover be constructed from?

The most appropriate material from practical installation and effectivenesspoint of view is sand/gravel and stone.

37. What would be the maximum gradient for stability?

This will vary for different pile types and for steeper sloped piles an infill sandlayer to reduce slope to about 18deg is recommended, where for smaller pilesa slope of 1-5deg is more typical.

38. How would the cover be constructed?

Using conventional proven methods and vessels with fall pipe vesselspreferred.

39. How do you know it is working over the long term?

Monitoring would be required to check performance and repair any damage ifcontainment is crucial.

40. What kind of monitoring would be required?

Details of monitoring would depend on detailed studies of the degree ofcontainment but some regular inspection is to be expected.


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41. What would be the impact of jacket footings removal prior to covering?

Depending on the pile characteristics disturbing the pile to remove maychange the stability and limit the potential to cover.

42. What would be the impact of storms and trawling to the cover?

The armour layer can be designed to withstand extreme storm events andshort /medium term trawling events but would be impractical to design forindefinite protection against repeated trawling and anchor impacts.

43. How much would the cover cost?

Depending on size of pile the cost is estimated to be from £240-400/m3 forlarge piles to over £1,000/m3 for smaller deposits.

44. What would the energy consumption be?

Depending on armour thickness and pile size the energy consumption ofcovering will be in the range 50,000GJ – 200,000+GJ i.e. 5 GJ/ m3 withemissions of 371 CO2 Te/ m3.

3.3.9 Task 6: Pilot Cuttings Lifting Operation

45. What is the typical rate at which cuttings can be removed from the sea-bed?

From the trial results, the dredging system utilised could recover cuttings fromthe seabed at an average rate of 10m3/Hr and potentially this system may beable to achieve higher rates (see 46-47 below for discussion on associatedwater). Significantly higher rates are possible if larger system size is used,however in many circumstances it may be difficult to install or utilisesignificantly larger systems due to platform limitations.

46. What is the range of composition of the slurry as it arrives at the surface?

During the trials the water percentage in the recovered slurry was high, theshort trial duration limited the ability to achieve the systems optimumperformance, however steady state ratios were in the range of 10:1 to 20:1water to solids. However it is considered that a system similar to that used atNW Hutton could achieve an overall ration of 10:1 water to solids for a fullrecovery operation.

47. What determines the ratio of solids to water and how can it be minimised?

This is determined by equipment design and dredge technique & experienceplus the properties of the cuttings. With regard to equipment design andselection the dredge head, pump and dredge vehicle are all important. Theimprovements between Blyth and NW Hutton trials indicate that the improveddredging instrumentation assist with obtaining and maintaining good systemoperation.


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48. What is the degree of secondary pollution (i.e. water column impact and area /thickness of cuttings re-settlement) due to re-suspension caused by thedredge-head and the ROV / crawler? What is the environmental impact ofsecondary pollution?

Dredging by suction produces little secondary pollution or plume; a largerlocalised plume is produced by cutter suction dredging (using the Breebotcrown cutter). The dredging ROV created a localised plume by its movementduring dredging. The largest plume was created by back flushing the hoses toclear blockages. Little secondary pollution was discernable at a distance of100 metres from the dredging operations, and no effects were seen on thesea surface. Nevertheless it is clear that material is displaced from thecuttings pile to the water column, particularly during back flushing followinghose blockages.

49. How much would removal to surface cost?

The cost of removing a typical 25,000m3 pile depends on the system selectedbut could range from over £5 million to £7.5 million for recovery of the cuttingsfrom seabed to surface. These estimates include allowances for a number ofitems that are highly variable and likely to be platform specific (e.g. structuralmodifications). These estimates do not include any cost to cover storage,transport and disposal of the recovered solids and water (covered by Task 7of the Initiative). The estimates also assume significant gains on the trialexperience from optimisation and improved techniques and are unlikely to besufficient to cover the cost of any early attempted pile recoveries.

Therefore, £300 /m3 cuttings recovered appears a reasonable estimateshould recovery become common practice.

50. What is the energy consumption for removal (Operation)?

The subsea system requires approximately 200kW to power the ROV and thedredge pump, this would equate to approximately 500MW hours for lifting thecuttings pile to an elevation of +70m. This equates to a modest 1,800 GJ forthe pile and 0.07 GJ/ m3 cuttings lifted. Further processing and disposalwould be required and this energy consumption in not included here.

51. What is the condition of the seabed under a cuttings pile?

The trial did not dredge through the cuttings down to the seabed so noinformation was gained on this.

52. How do you know when removing seabed rather than cuttings i.e. can you seeat dredge head or do you need to sample slurry at surface?

The trial did not test this, however it is envisaged that there will be a change ofconsistency once the seabed is reached, and bathymetry data would alsoprovide information on the depth through the pile that may be supplementedwith coring results. In practice to remove all the cuttings it may be necessaryto remove some of the seabed beneath the cuttings. The pre-installationbathymetry is unlikely to be exact and there may have been seabedsettlement that may complicate identifying the interface.


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53. Can the ROV / crawler operate / be controlled reliably within the jacketfootprint?

From the trial it is clear that the jacket structure does not provide anyrestrictions on access of dredging vehicles except in the vicinity of theconductors. A large tracked system would also be able to operate within thejacket footprint; however crossing the jacket members once the cuttings havebeen cleared would require further development as would work around thepipeline tie-ins in and around the jacket.

54. What are typical downtimes for weather and system reliability (i.e. debrisblockages etc.)?

ROV’s can achieve 90-95% reliability for 24 hour operations once they havepassed through the initial settling in period. Provided sufficient spares arecarried offshore a dredging system should be able to achieve 90% reliability.This may not be achieved if the system suffers damage from large amounts ofdebris or if the cuttings are abrasive. Weather downtime is very specific to themethod of launching the equipment and the routing of hoses and umbilicalsthrough the splashzone. An initial estimate of around 20% weather downtimeis considered reasonable for year round operations.

It should be noted that experience of Task 6 was well below these figures andthey are based on what might be achievable through optimisation and learningshould recovery become common practice. This assessment does notconsider the reliability and availability of the disposal route which, if requiringthe backloading of cuttings/ slurry is likely to be far more weather sensitiveand would dictate the overall reliability of the management option given thatstorage space for lifted cuttings/ slurry on an installation be severely limited.

55. What is the best way to clear new debris as it is uncovered by pile removal?

Working around debris as it is exposed is possible given good visibility, asfound at NW Hutton. Once debris is excavated it would be moved into abasket for recovery to surface. Potentially this activity could be undertaken bya second ROV that is also used for monitoring the dredging andenvironmental monitoring. Practically, any large debris would be workedaround and would provide a hazard to recovery operations.

56. Is it possible to remove a large ‘conical’ pile without major slumping, if sohow?

Dredging from the side would cause slumping if properties were similar to NWHutton, however it is probably possible for an ROV dredging system byworking from top down depending on its properties. Tracked vehicles may notbe suitable for working at the top of the pile dependent on the pilecharacteristics.


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3.3.10 Task 7: Evaluation of Options for Slurry (Lifted Pile Material) Handling

Relating to injecting slurry offshore

57. How much would injecting back cuttings into the hole cost?

Task 6 indicates that £300/ m3 is the cost of lifting plus £250 to £900/ m3 forinjection dependent whether wells need to be worked over to inject thecuttings. Therefore costs for this option are in the range £550 to £1,200/ m3.

58. What is the energy consumption for injection?

The energy consumption for this option is of the order of 1.7 GJ/ m3.

Relating to injecting water offshore and shipping solids to shore

59. How would water be best separated from solids offshore?

Conventional technology of mud shakers and screens would appear to besufficient, however relatively few of the piles are located under installationswhere this equipment could be provided.

60. How would solids be shipped back to shore e.g. skip and ship vs. bulk loadingto dedicated vessel?

Currently, skip and ship is the only proven marine transport method and againthis would appear to be feasible. However, the cuttings material being waterwet is very different to the material presently shipped back via this technology.

Relating to shipping slurry to shore, treating and disposing water

61. How would water be best separated from solids onshore?

Conventional technology of mud shakers and screens would appear to besufficient.

62. How would the water be treated?

Onshore production/ ballast water treatment facilities e.g. Nigg Oil terminal(Cromarty Firth) may be able to handle the water. This could only beconfirmed once an inventory of the water was known. This is likely to varyconsiderably between piles.

63. What are the discharge standards for the separated water?

This is dependent on individual facility license agreement (typically 5 - 15 ppmfor hydrocarbons).

64. How would slurry be shipped back to shore e.g. skip and ship vs bulk loadingto dedicated vessel?

Trailer dredgers (range from 1,000 - 30,000 m3 capacity) are designed totransport slurry and liquids although it would require to be equipped with a


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dynamic positioning system to enable close enough location to a platform.This concept is yet to be tested for offshore cuttings slurry.

65. How much would shipping slurry to shore, separating, treating and dischargingthe water cost?

This element of the process costs around £735/m3, this excludes recovery at£300/ m3 and onshore treatment and disposal of solids at £430/ m3, giving anall up cost for this option of +£1,500/ m3. Given the immaturity of all theelements of this process, a further factor of 2 increase is required to define therange of possible costs (i.e. up to £3,000/ m3).

66. What is the energy consumption for shipping slurry to shore, separating,treating and discharging the water?

The energy consumption would be around 6.7 GJ/ m3.

Relating to disposal of oily solids

67. Where, today, could the oily solids be landfilled?

In the North East of Scotland currently, Stoney Hill landfill near Peterheadmight be licensed to receive the oil solids, other site licenses are reported asbeing under review for provision of this facility.

68. Could a purpose built special waste landfill facility be constructed?

A site with suitable geology and management could be dedicated for specialwaste, subject to licence requirements eg Stoney Hill

69. What would be the long-term impact of the oily solids in the land-fill site?

Providing the facility is correctly maintained, contamination outside the sitefrom the oily solids is thought unlikely.

70. How much would disposing of the oily solids onshore cost?

This would cost approximately £250/ m3 for landfilling untreated cuttings(includes transport costs from quayside to landfill facility).

Relating to treatment and disposal of solids

71. What processes could treat the oily solids?

Direct/indirect thermal desorption or solvent extraction onshore and, grindingwith thermal desorption offshore. However, none of these processes havebeen tested with wet cuttings recovered from the seabed. The Rotomillprocess selected for offshore solids treatment is presently limited to 1m3/ hrprocess rate, which raises practical difficulties for the treatment of any pile ofsignificant size.


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72. What existing plants could treat the oily solids?

Total Waste Management Alliance and Oil Tools (Aberdeen, Peterhead andLerwick), Maersk and Scotoil (Aberdeen) appear to be possibilities for onshoresolid treatment. However, the cuttings being water wet and in slurry form arelikely to have a significant impact on the efficiency and effectiveness of theirprocesses which are designed for a different feedstock specification.

73. How is the oil disposed of? Can the oil be re-used?

Oil is currently reused as fuel for the thermal treatment process, as a base forfresh drilling muds (oil from residual cuttings will probably be weathered andunsuitable for reuse in drill muds), or reconditioned for use as fuel for powerstations and quarry operations.

The quantity of oil recovered at 3.5% of pile mass amounts to some 1,470tonnes, for the study pile in question. The energy consumed to recover this oilamounts to up to 6 GJ/ m3 of cuttings processed for a benefit of 2.5 GJ/ m3 ofcuttings processed.

74. What would be the long-term impact of the cleaned solids in the land-fill site?

The solids post-cleaning are still likely to be classified as special waste.Providing the landfill facility is correctly maintained, contamination outside ofthe site is unlikely and so the long-term impact is thought similar to that forlandfilled oily solids.

75. How much would treating and disposing of the cleaned solids cost onshore?

Costs are thought to be approximately £430/m3 (includes treatment, transportto landfill from quayside and disposal costs). This does not include the costsof recovering the cuttings and transporting to shore and disposing of thewater.

76. What are the throughput capacities of existing facilities (compared with thevolume to be treated)?

Currently, treatment capacity is greater than volume to be treated so someullage is potentially available for this new feedstock (noting the potentiallimitations of process suitability for a water wet cuttings feedstock). However,should recovery to shore prove a BEP, new capacity would be required oralternatively the recovery and processing operations would be executed overa very slow 20 year plus timescale.

77. What is the energy consumption for treating and disposing of the cleanedsolids?

The consumption for cleaning and disposing of the solids at shore is 3.8 GJ/m3 (includes treatment and transport to landfill, but not recovery from theseabed and ship to shore)


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Relating to treatment, disposal of oil and re-use of solids

78. What re-use opportunities are there for cleaned solids?

Cleaned solids are currently used as a liner and cell wall building material inlandfill sites. Scotoil propose to use the cleaned cuttings as an absorbentbase material for cat litter. The exact nature of cleaned cuttings pile materialis not yet known, and so this question remains a knowledge gap.

Relating to overall comparative analysis of slurry disposal options

79. Which of the slurry treatment and disposal options studied merit furtherconsideration against the other managmement options (i.e. Cover,Bioremediation, Natural Degradation)?

Options 2, 5 and 6 appear to merit further consideration. Option 2 separatesand treats liquids offshore and solids onshore. Option 5 injects the slurryoffshore. Option 6 transports the slurry to shore in a trailer dredger andprocesses liquids and solids thereafter. Options 2 and 5 have relativelyproven technology, although the onshore treatment of the solids under Option2 remains a gap. Option 6 is immature and yet to be proven at all.

80. What are the relative costs and energy consumption for the 3 preferredoptions?

Option 2: separate and treat liquids offshore and solids onshore, includingrecovery costs between £1,000 and £1,500 /m3 and consumes 6.7 GJ/ m3cuttings. 2.5 GJ/ m3 cuttings could offset energy consumption if oil isrecovered and re-used.

Option 5: inject the slurry offshore, including recovery costs between £750 and£1,200 /m3 and consumes 1.7 GJ/ m3 cuttings.

Option 6: transport the slurry to shore in a trailer dredger and process liquidsand solids thereafter, including recovery costs between £1,000 and £2,000/m3 and consumes 5.8 GJ/ m3 cuttings. 2.5 GJ/ m3 cuttings could offsetenergy consumption if oil is recovered and re-used.


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4 Scientific Conclusions

4.1 Discussion

Reviewing the Q&A’s in the previous section, UKOOA has collated key scientificstatements from the research. These statements incorporate the comments ofthe SRG and were broadly accepted when highlighted at the final stakeholderdialogue session.

4.2 Environmental Impact

• Cuttings piles differ significantly in terms of volume, extent, and particle sizeand contaminant inventory. This degree of heterogeneity, suggests that allpiles should be sampled and surveyed in accordance with a revised OLFprotocol ahead of determining best environmental strategy.

• Hydrocarbons and hydrocarbon containing materials (e.g. PBM’s) have beenidentified as the prime contaminant. Potential impacts of other contaminantsincluding heavy metals are very small in comparison with the hydrocarbonsand very small in absolute terms too.

• Hydrocarbons when present are closely associated to the particles/ fines andwhere a pile is not disturbed very little hydrocarbon leaches to the marineenvironment. The rate of loss of hydrocarbons from an entire pile to the watercolumn is of the order of 5 Te/ year in the piles investigated. (To providesome context for this rate of loss, it equates to rather less than a drippingkitchen tap at up to 10 Te/ year.)

• The cumulative impact for all North Sea cuttings piles is small compared withother inputs to the North Sea, e.g., annual input of hydrocarbons from all pilesat 330 Te to the water column in the North Sea equates to 0.5% of that fromother sources at circa 65,000 Te. However, the total volume of hydrocarbonsestimated to be contained within all the North Sea cuttings piles is significantat around 160,000 Te (from 30 years of discharge).

• After 30 years of discharges, the total area of seabed resulting in biologicaldisturbance due to cuttings piles was estimated to be 1,605km2 or 0.23% ofthe total area of the North Sea. This compares with an area of seabed that isaffected by fishing, dredging and spoil dumping of approximately 130,000 to369,000km2 per year (up to 50%).

4.3 Long-term Fate of Piles

• The long-term fate of cuttings piles is determined by the physics of dispersion,which will enable subsequent degradation of hydrocarbons and re-colonisationto take place.

• The frequency and strength of physical disturbance is related to water depth -in deeper water (e.g. beyond 70m) it is relatively rare for there to be sufficientwave/ current energy to significantly move pile material; nevertheless, eventhe deepest parts of the North Sea seabed will experience disturbance underextreme storm conditions.


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• The presence of significant contamination, i.e. the hydrocarbons from the pilematerial that can be discerned in water depth around 70m, is likely to bemeasured in decadal timescales e.g. 10 to 50 years. For water depths over120 m, the presence of hydrocarbons from the pile material is likely to bemeasured in centennial timescales e.g. 500 to 1,500 years.

4.4 The Management Options

• Selection of the best management option is influenced by the nature andvolume of the THC within the particular pile, the local hydrographical situation,and the local facilities available for supporting a particular managementoption. Selecting the best management option for a particular pile on itsmerits is likely to require a specific assessment.

• The bioremediation scheme investigated is not attractive, with reservationsidentified around the timescale, endpoint hydrocarbon concentrations andpracticalities of this management option. It must be borne in mind that thisscheme was identified as being the most promising bioremediation scheme inPhase I of the Initiative.

• Covering appears practicable in some instances and would preventcontamination from the piles, and if properly maintained, would effectivelyensure that hydrocarbons do not spread or indeed enter the water column.

• Retrieve and dispose appears possible. Significant technical issues around liftefficiency, onshore processing of wet oily solids and lift water treatment anddisposal have been identified. Further, secondary pollution associated withrecovery may have a greater potential impact than natural degradation.

• Some of the sub-options for slurry treatment and disposal following recoverywere not practicable when compared with the other sub-options and threedisposal routes were recommended including slurry injection for furtherconsideration. The only disposal option post recovery that is presently legal isto return the slurry to shore, but this is not considered best environmentally.

• Natural degradation is worthy of further consideration. Natural degradationwould require an extensive monitoring programme to demonstrate that therecovery of the site is happening as per the hypothesis from the long-termmodelling work. The monitoring data would need to be collated centrally toverify and further improve the industry’s short-term and long-term disturbancemodelling capability.


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5 Dialogue Conclusions

Three dialogue sessions were held during the Initiative. The first in November1998 introduced the parallel science and dialogue process that was proposed to avaried group of stakeholders and provided an opportunity for the participants toraise any issues surrounding the identified management options before the PhaseI study scopes were finalised.

This was followed in February 2000 by the second event to present and discussthe findings of Phase I at which participants could comment on the outputs andprovide their input into the content of the Phase II studies.

The final session was held in November 2001, where the results of the totalscientific programme were presented and the participants contributed their viewson the research conclusions and the different management options and how thebalance of the best environmental strategy assessment could be judged.

5.1 The Framework

A draft framework for management option assessment was provided tostakeholders via an interactive web-based exercise ahead of the third and finaldialogue session (see Appendices). Following incorporation of Stakeholders’comments via the web event, and from the discussion at the third Dialogue eventitself, a framework broadly acceptable to most participants was agreed.

The framework is introduced in this section incorporating comments from both thedialogue session and the web event.

The framework enables one to make an assessment of the management optionsfor drill cuttings accumulations taking a number of criteria into account;

a. impacts on the marine environment of the management option, includingexposure of biota to contaminants contained within the accumulation, otherbiological impacts arising from physical/ habitat effects and interference withother legitimate uses of the sea;

b. impacts of the management option on the atmosphere e.g. emissions andenergy;

c. impacts of the management option on the land e.g. leaching to groundwater,discharges to surface fresh water and effects on the soil and consumption ofnatural resources;

d. health and safety considerations associated with the management optionboth direct and indirect e.g. other users of the sea;

e. social impacts on amenities, jobs and the activities of communities of themanagement option and other consequences to the physical environmentwhich may be expected to result from undertaking the management option(e.g. aesthetics, transport, littering);

f. technical and engineering aspects of the management option, including thedegree of re-use and recycling;

g. any legal implications of the management option;h. ongoing liabilities associated with the management option e.g. the nature,

volume and persistence of the drill cuttings contaminants and the scope andscale of any monitoring that would be required for the management option;


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i. any cumulative impacts should this management option be selected at for anumber sites;

j. economic aspects of the management option;k. public acceptability of the management option.

5.2 Aspects of Time

It follows that best environmental practice for drill cuttings accumulations maychange with time in the light of technological advances, economic and socialfactors, as well as changes in scientific knowledge and understanding.

If the reduction of impacts resulting from the use of best environmental practicedoes not lead to environmentally acceptable results, additional measures have tobe applied and best environmental practice redefined.

5.3 Completed Assessment Frameworks

Two Assessment Frameworks have been completed by UKOOA following theresults from Phase II research for two characteristically different piles.

Cuttings Pile A: 150 m water depth, Northern North Sea, East of Shetlands,large producing platform with cuttings re-injection capability.

25,000 m3 volume, history of OBM cuttings discharges of alltypes, hydrocarbon concentrations vary from < 100 mg/ kg to100,000 mg/ kg and average 40,000 mg/ kg, i.e. 1,250 Tehydrocarbons total load. Oil is considered the primecontaminant of concern. Metal contaminants are below SFTremediation thresholds for harbours. Trace ED’s have beenmeasured, no PCB’s have been detected. The contaminatedarea is estimated from survey to be less than 10 km2

Cuttings Pile B: 70 m water depth, Central North Sea, small producing platformwithout cuttings re-injection capability or mud-handling system.

5,000 m3 volume, history of WBM cuttings discharges, but withsome recent PBM (synthetics) hydrocarbon concentrationsvary from < 50 mg/ kg through most of the pile to 75,000 mg/kg in certain strata and average 4,000 mg/ kg, i.e. 36 Tehydrocarbons total load. Oil is considered the primecontaminant of concern. Metal contaminants are below SFTremediation thresholds for harbours. Trace ED’s have beenmeasured, no PCB’s have been detected. The contaminatedarea is estimated from survey to be less than 5km2

5.3.1 Cuttings Pile A: Large pile containing a significant volume of hydrocarbons

Pile Location150 m water depth, Northern North Sea, East of Shetlands, large producing platform with cuttings re-injection capability

PileDescription

25,000 m3 volume, history of OBM cuttings discharges of all types, hydrocarbon concentrations vary from < 100 mg/ kg to 100,000 mg/ kg and average 40,000 mg/ kg, i.e. 1,250 Te hydrocarbons total load. Oil is considered theprime contaminant of concern. Metal contaminants are below SFT remediation thresholds for harbours. Trace than 10 km2

Retrieve (6)ManagementOption Cover (5b) Solids to Shore Only (7.2) Inject Slurry (7.5)

Assessment Criteria

Marine Covering prevents naturaldegradation of oil, thus increasespersistence.Negligible impact, rock armourlikely to increase biodiversity.Gravel assumed to be quarried.

Contaminated site likely to recover over100 years.Processed lift water if returned to sea islikely to meet present standards for oil.Metals & ED’s?

Contaminated site likely torecover over 100 years

Atmosphere(4,000 car miles= 1 Te CO2)

Energy is small; 9,000 Te CO2.Dust from quarrying has minor/local impact.

Energy is small; 12,000 Te CO2 Energy is very small; 3,000Te CO2

Land Impact limited to quarry & transportactivity

Solids land-filled (25,000 m3) No impact

HSE Exposure limited to quarrying/transport / marine operations (c.10,000 hours, PLL = 0.0005)

Exposure mainly subsea and transportc. 100 boat loads & 1,500 truck loads,(c. 150,000 hours, PLL = 0.0055)

Exposure mainly drillingcrew for processing andinjection & subseaoperations (c. 100,000hours, PLL = 0.0034)

Social Possible local Heavy GoodsVehicle increase for cover materialtransportation

Local Heavy Goods Vehicle increaseforecast at 10% for duration of landfilling.No significant re-use benefits.

No significant impact onlocal communities.

Technical Geotechnics of pile main technicalconcern i.e. is it firm enough tocover?

Technical issues around onshoreprocessing of wet oily solids.Lifted water volumes/ efficiency?20 offshore beds for a prolonged periodof time.

Need assurance thatinjection zone is secure.Lifted water volumes/efficiency?40 offshore beds for aprolonged period of time.

Legal Presently legal, Food andEnvironment Protection Act (FEPA)license required

Legal issues if liquids aredischarged.Presently legal if liquids are injectedfor reservoir support.

Not presently legal.

Liabilities Operator remains liable inperpetuity for a UK site.Option may require ongoingmaintenance.

Liability for contaminated site offshoreand land-fill

Liability for contaminatedsite offshore

CumulativeImpacts, i.e. forall piles

Increased quarrying and roadtransport.PLL = 0.024

Expansion of oily wastes processingand landfill required.Movement of waste to England?PLL = 0.28

No cumulative effectsanticipated; note that optionis not applicable to all piles.PLL = 0.18

Economic £6 – £10 million£5,000 - £8,000/ Te Oil

£25 - £35 million£20,000 - £28,000/ Te Oil

£14 - £20 million£11,000 - £16,000/ Te Oil

PublicAcceptability

Duration of cover, and irreversibilityraised as concerns at dialogue

Well supported at dialogue, secondarypollution & onshore processingconcerns raised

Well supported at dialogue,secondary pollution &injection concerns raised

Aspects ofTime

This option is irreversible.Very long term coverperformance not known.

No temporal effects.This option is irreversible, but oily wasteis controlled onshore.

This option is irreversible.No temporal effects providedthat injection zone is secure.


5.3.2 Cuttings Pile B: Medium sized pile containing a small volume of hydrocarbons

Pile Location70 m water depth, Central North Sea, small steel jacket producing platform without cuttings re-injection capability or mud-handling system

PileDescription

5,000 m3 volume, history of WBM cuttings discharges, but with some recent PBM (synthetics) hydrocarbon concentrations vary from < 50 mg/ kg through most of the pile to 75,000 mg/ kg in certain strata and average 4,000 mg/kg, i.e. 36 Te hydrocarbons total load. Oil is considered the prime contaminant of concern. Metal contaminants are below SFT remediation thresholds for harbours. Trace The contaminated area is estimated from survey to be less than 5 km2.

Retrieve (6)ManagementOption Cover (5b) Solids Only to Shore (7.2) Inject Slurry (7.5)

Assessment Criteria

Marine Covering prevents naturaldegradation of oil, thus increasespersistence.Negligible impact, rock armourlikely to increase biodiversity.Gravel assumed to be quarried.

Contaminated site likely to recoverwithin a few years.Processed lift water if returned to sea islikely to meet present standards for oil.Metals & ED’s?

Atmosphere(4,000 car miles= 1 Te CO2)

Energy is very small; 2,000 TeCO2.Dust from quarrying has minor/local impact.

Energy is very small; 2,000 Te CO2

Land Impact limited to quarry & transportactivity

Solids land-filled (5,000 m3)

HSE Exposure limited to quarrying/transport / marine operations (c.3,000 hours, PLL = 0.0001)

Exposure mainly subsea and transportc. 20 boat loads & 300 truck loads, (c.30,000 hours, PLL = 0.0011)

Social Possible local Heavy GoodsVehicle increase for cover materialtransportation

No impacts/ no re-use benefits.

Technical Geotechnics of pile main technicalconcern i.e. is it firm enough tocover?

Technical issues around onshoreprocessing of wet oily solids.Lifted water volumes/ efficiency?

Legal Presently legal, Food andEnvironment Protection Act (FEPA)license required

Legal issues if liquids are discharged.Presently legal if liquids are injected forreservoir support.

Liabilities Operator remains liable inperpetuity for a UK site.Option may require ongoingmaintenance.

Liability for contaminated site offshoreand land-fill

CumulativeImpacts, i.e. forall piles

Increased quarrying and roadtransport.PLL = 0.024

Expansion of oily wastes processingand landfill required.Movement of waste to England?PLL = 0.28

Economic £2 – £5 million£60,000 - £140,000/ Te Oil

£5 - £7 million£140,000 - £190,000/ Te Oil

PublicAcceptability

Duration of cover, and irreversibilityraised as concerns at dialogue

Well supported at dialogue, secondarypollution & onshore processingconcerns raised

Aspects ofTime

This option is irreversible.Very long term cover performancenot known.

No temporal effects, this option isirreversible, but oily waste is controlledonshore.

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5.4 Comparison of Management Options at the Dialogue

The completed assessment frameworks for the two characteristically differentcuttings piles, as completed by UKOOA, were presented to the stakeholdersat the third and final dialogue session to see if a clear best environmentalstrategy could be identified for both or either.

Selecting the best environmental strategy for either of the two examples at thedialogue session appeared to be very difficult due to different views on /priority of technical assumptions, legality and the subjective nature of suchvalue judgements.

However, stakeholders rejected the bioremediation scheme studied in PhaseII as it offered no advantages on environmental performance and benefitswhen compared with other options.

Covering received a mixed response, with some scientific advocacy in favourof covering resisted by others’ concerns with regard to its irreversibility andpotentially very long-term maintenance requirements.

Many stakeholders were still concerned about secondary pollution of anycuttings recovery effort. Should cuttings be recovered, many favoureddisposal by injection, although some stakeholders also voiced concernsagainst this practice. Knock on effects on land of recovery were a concern,particularly onshore processing and land filling of oily wastes, transport issuesand treatment and discharge of the entrained lift water.

The stakeholders broadly supported natural degradation for both case studies.Discussion on values indicated that any reservations around naturaldegradation were mainly focused on peer acceptability and industrialresponsibility to restore the work site, rather than environmental impact assuch. Long-term liability was also raised as a concern particularly for the morepersistent pile in case study A.

Stakeholders supported the industry’s conclusion that a comprehensiveprogramme of surveying, sampling, analysis and long-term fate modelingwould be required in order to complete the management option assessmentframework supported at the dialogue session, and that such information wasnecessary in order to make environmentally sound decisions.

Further, given the diversity of views regarding management optionsrepresented within the stakeholding group, UKOOA concluded that thecontinued incorporation of public consultation should be embedded in anyapproval process.


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6 UKOOA’s Conclusions & Recommendations

6.1 Overall Discussion

The Task 4 modelling and independent research in Norway* and theNetherlands# indicates that the cessation of discharge of oil-based cuttings in2000 has been a highly appropriate and effective management action forimproving the quality of the North Sea marine environment. This action hasnot come without burden to industry which has, in the UKCS alone investedsome £50 million capital in retro-fitting drill cuttings re-injection equipment anda further £50 million a year in skip, ship and onshore processing of water dryoily cuttings as they come straight off the drilling mud shakers.

The UKOOA Initiative has addressed the issue of drill cuttings piles to see ifany additional environmental management actions are appropriate, and if sounder what circumstances.

* Environmental status of the Norwegian Offshore Sector Based on the Petroleum Regional MonitoringProgramme, 1996 – 1998, prepared for OLF by Akvaplan-niva, Unilab & DNV 2000

# Daan, R., Booij, K., Mulder, M., Van Weerlee, E. M. 1996. Environmental Effects of a Discharge ofDrill Cuttings Contaminated with Ester-Based Drilling Muds in the North Sea

6.2 Recommended Action Programme

UKOOA concludes that a comprehensive action programme of surveying,sampling and analysis (in accordance with revised OLF guidelines), and long-term fate modeling is required in order to complete the management optionassessment framework contained in this document, and that such informationis necessary in order to select an environmentally sound management optionfor any particular cuttings pile.

Given that the impact of cuttings pile in the marine environment appears to bestatic or reducing over oil field production timescales, it is recommended thatselection and execution of the best environmental strategy for the cuttingspiles is undertaken as part of the installation decommissioning programme atend of field life. A post-implementation monitoring plan for the cuttings sitewould be required. Historical survey data demonstrating the extent andmovement of a contaminated zone during the operator’s period of tenurewould be insightful in any such science based best environmental strategyselection process undertaken at the end of field life.

Addressing cuttings within a decommissioning plan would also ensure publicconsultation, which is essential if the operator is to make its value judgementas to the best environmental strategy in keeping with broadly held public viewsof the day.

Management options that may be considered as being the best environmentalstrategy include:

• Covering,• Retrieval & ship ‘solids only to shore’/ ’inject’/ ‘ship slurry to shore’, and• Natural degradation.


34

Each option has its limitations, and no one option appears best under allcircumstances.

The results from Phase II and the feedback from the dialogue sessionsindicate that determination of a lasting best environmental strategy willrequire value judgements to be made around industrial responsibilitytogether with consideration of the science of environmental impact.UKOOA believes that these judgements are best made following aspecific public consultation around a completed assessment frameworkfollowing a comprehensive sampling and surveying programme andpossibly as part of an overall installation decommissioning programme.

6.3 What is the Best Environmental Strategy?

Acknowledging the stakeholders’ desire for firm closure on this question,UKOOA offer some ideas for determining whether specific managementoptions can be considered scientifically best under certain situations. Thisexercise is not intended to replace the Recommended Action Programmeabove but to provide an insight to what the likely outcome of such action mightbe.

Focusing on the science of environmental impact is helpful and enables theidentification of situations where impact by cuttings pile material on the marineenvironment could broadly and demonstrably be shown as beinginsignificant. Where the impact can be demonstrated as being insignificant,a purely scientific assessment of the management options would concludethat natural degradation is the best environmental strategy. (Noting that theUKOOA commitment to an open and transparent process incorporating thepublic consultation proposed above would ensure that any issues surroundingindustrial responsibility would have been adequately addressed too.)

Conversely, when the impact by cuttings pile material on the marineenvironment is considered as being significant, a management optionpreventing hydrocarbons entering the water column e.g. cover or recoverwould be considered the best environmental strategy.

From the scientific results from Phase II, hydrocarbons and hydrocarboncontaining materials (e.g. PBM’s) have been identified as the primecontaminant; while the long-term fate of cuttings is determined by the physicsof dispersion. Building on these findings, three questions have beenidentified which when combined will describe the overall potential forenvironmental impact of individual cuttings piles to be considered significant orinsignificant:

1. What is the rate of loss of hydrocarbons to the water column?

2. What is the area of the seabed where the biological impact from thecuttings can be discerned (e.g. THC footprint above 50 mg/ kg as proxy)?

3. What is the rate of change of this contaminated area and specifically, in theperiod of tenure of the operator, is it getting larger or smaller?


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These questions have been selected in consultation with the SRG to reflectboth the absolute contribution of a particular pile to the contaminant burden ofthe North Sea, and the contribution of non-persistent organic contaminantsrelative to the assimilative capacity of the local environment.

6.3.1 Rate of loss of hydrocarbons (Question 1)

Considering the first question, rate of loss of hydrocarbons, and comparing thepiles’ situation with offshore industry oil to sea data may provide a usefulstarting point:

• Cuttings historically discharged overboard from a single oil based mud wellmay amount to some 150 Te of oil to sea over a period of say 4 months,hence for a full drilling programme on a single installation some 450 Te/year of oil to the marine environment would have been discharged prior tothe change in regulations in 2000.

• A large UK field producing 100 Kbd oil with a 50 % watercut, discharging100 Kbd produced water at 40 mg/ ltr (current OSPAR performancestandard requirement) amounts to 232 Te/ year. This will reduce to annual174 Te in accordance with new OSPAR performance standard to beimplemented by 2006.

• A small oil producing field with a production of 25 Kbd oil with a watercut of25% (8.3 Kbd PW) and performance of 20 mg/ ltr in discharged water (wellbelow average performance in the North Sea) would representapproximately10 Te/ year oil to sea.

Setting an environmental limit of insignificance of 10 Te/ year rate of loss ofhydrocarbons from an individual cuttings pile to the water column wouldestablish a number considerably lower than the target hydrocarbon input inproduced water from for the vast majority of North Sea oil installations, andgreatly below the historical oil to sea rate from oil based cuttings discharge forwhich mitigating measures have already been passed by OSPAR (ban oncuttings discharges of greater than 1% THC).

To put this number in wider context, 10 Te/ year is equivalent to one fourhundredth of the rate of oil discharge from all North Sea shipping operations.

The question of significance should be considered also. Again looking at theoil industry data above, a level of 100 Te/ year rate of loss of hydrocarbonsfrom an individual cuttings pile to the water column is selected as the limit ofsignificance, as it is at this level of oil input that mitigation measures havealready been implemented by the industry to address cuttings and producedwater discharge.

Rates of loss of hydrocarbons from an individual cuttings pile to the watercolumn in between the limits of 10 and 100 Te/ year cannot from a scientificperspective be conclusively considered either significant of insignificant.

The long-term modeling capability developed under Task 4 is able to estimatethe rate of oil loss to the water column over time. Further, the short termmodeling capability developed in Phase I is able to estimate the oil to sea fromdisturbances such as jacket removal, trawling and cuttings recovery.


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6.3.2 Area of seabed contaminated over time (Questions 2 & 3)

Considering the second and third questions above together by evaluating thetotal area of contamination over time may provide more insight thandiscussing them individually. It should be noted however that this ‘totalexposure’ approach only addresses potential and not actual impacts and is anapproach rooted more in theoretical deduction than in scientific data.Therefore, setting a scientifically defensible limit of significance is more difficultthan for hydrocarbons loss.

Following some sensitivity work 500 km2years has been selected as the limit,as it would ensure that to be under such a limit, and hence of insignificantenvironmental impact, a particular pile would have to be either:

• virtually free of any hydrocarbons, e.g. water based cuttings piles;

• of small area extent; or

• recovering and able to be demonstrated as such within the period oftenancy of the operator.

With regard to the last bullet point above, the suggested assessment againstan insignificance limit of 10 Te/ year would be essential to ensure that arapidly eroding/ degrading pile was not over-burdening the local environmentwith the rate of loss of its hydrocarbons to the water column.

Should a pile be determined as having a footprint greater than 500 km2years,this is not necessarily an indication that the environmental impact issignificant, but more a statement that demonstration of recovery within theperiod of tenancy of the operator is likely to be more difficult.

Again, the long-term modeling provides data on the movement of thecontaminated area boundary over time.

6.3.3 Summary

In an effort to remove some of the subjectivity around the three questions insection 6.3 above, limits of potential environmental insignificance/ significancehave been investigated. The limits identified by UKOOA are:

• If the rate of loss of hydrocarbons to the water column from a cuttings pileis greater than 100 Te/ year, then the potential environmental impact isconsidered significant.

• The potential environmental impact of a cuttings pile is consideredinsignificant if the rate of loss of hydrocarbons to the water column is lessthan 10 Te/ year, and the area of seabed at greater than 50mg/kg overtime, is less than 500km2year.

Should a scientific investigation as recommended in the Action Programme insection 6.2 above, suggest that the site is of insignificant potentialenvironmental impact then UKOOA believe that natural degradation wouldappear to be the best environmental strategy. Noting that public consultationproposed in the Action Programme above would be needed to ensure that any


37

issues surrounding industrial responsibility had been adequately addressed bythe operator, and that the scientific investigation would need to address localissues such as spawning grounds etc.

Should a scientific investigation as recommended in the Action Programme insection 6.2 above, suggest that the site is of significant potentialenvironmental impact i.e. > 100 Te hydrocarbons/ year to the water column,then UKOOA believe that covering or recovery would appear to be the bestenvironmental strategy.

Should the scientific investigation suggest that either or both of the limits ofinsignificance are expected to be exceeded by a particular site but remainbelow the significance boundary then the best environmental strategy is lessclear. Exceeding the limits does not imply that significant environmentalimpact is taking place but more that insignificance cannot be demonstratedbeyond reasonable doubt within the period of tenure of the operator. Aspecific assessment of the management options of cover, recover and naturaldegradation, together with a programme public consultation is recommendedfor selecting lasting and environmentally sound solutions under thesecircumstances.

This is summarised pictorially below:

Likely Best Environmental Strategy outcome following execution of theAction Programme recommended in Section 6.2

0

10

20

30

40

50

60

70

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90

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0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000

Area of seabed at greater than 50 mg/kg over time, in km2years

Rate of oil loss in Te/ year

Potential environmental impact can bedemonstrated as insignificant in this zone,

hence natural degradation is considered theBest Environmental Strategy

Potential Environmental Impact is considered a significant concern in this zone,hence recover or cover are considered the Best Environmental Strategy

Potential Environmental Impact cannot be demonstrated as insignificant in thiszone, hence Best Environmental Strategy is less clear and all options I.e. recover,

cover and natural degradation should be considered

UKOOA Drill Cuttings Initiative Final Report Annex IDevelopment of the Assessment Framework

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Annex 1: Development of the Assessment Framework

Preamble

Thank you for taking the time to contribute to the framework review. We had a goodresponse which we have read, digested and hopefully reflected where possible in theattached update. This will be presented for comment at the Dialogue session on the20th.

Overall the main feedback suggested that the criteria proposed were relevant ,although clarifications and expansions on specifics were identified. There was alsothe clear indication that many of the stakeholders wanted to discuss the judgmentsbetween and relative importance of different aspects which will be part of the processand which we shall get into more on Nov 20th.There were also some additional criteria identified.

The framework is intended to identify the key components that need to be quantifiedand then considered in an assessment. It is important that the framework is not seenin isolation as a mechanistic tool but rather part of a larger process aimed atidentifying and assembling the data in a rational and transparent way such thatassessment can be carried out.

Perhaps this assessment could be carried out as part of the overall DecommissioningPlan for an installation and then be subject to the range of inputs and consultationrequirements that such submissions receive, namely scientific data, stakeholderviews, peer group reviews and consultation on the recommendation.That maybe something worth considering further in our Nov 20th discussions: ieWhat consultation safeguards should be included within any future guidance?

Revised DRILL CUTTINGS ASSESSMENT FRAMEWORK –

Reflecting guidance contained in OSPAR appendices on BEP/BAT selection.Included in that guidance is that the BEP/BAT has a dynamic element which maychange as more knowledge and improved technology becomes available.

STEP 1Characterise each existing pile in accordance with OLF guidance. This guidance isspecific protocol on the scope and activities to be carried out to sample andcharacterise drill cuttings accumulations and has been developed to ensure aconsistent approach to pile characterisation.

STEP 2Determine which management options are applicable to this pile

Assemble Impacts of Various Options within the following Framework to conduct aspecific assessment for this pile.

UKOOA Drill Cuttings Initiative Final Report Annex IDevelopment of the Assessment Framework

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CATEGORY OptionA

OptionB

Option..i..

What are the MarineImpacts ? eg• Impacts on the marine environment of the

management option, including exposure of biota tocontaminants contained within the accumulation,

• biological effects arising from physical/ habitateffects.

• Area affected by presence and time related effects.• Impacts on other legitimate users of the sea. And

environmental sensitivity of location.

What Are the Atmospheric Impacts? eg– Energy &emissions

What are the land impacts? eg Disposal sites, secondary pollution;

What are the personnel Health & safety risks &exposures?• Mitigation measures against identified exposures.• Personnel involved in the operation and other sea-

users

What are the societal/community impacts? eg

• Re-use/recycling potential• Noise, disturbance;• Job creation• Aesthetics• Cost/benefit

What are the technical uncertainties?

What are the costs of carrying out the option?• Now & future

Are there any legal issues?Assess any legal limitations of identified options.Movement of waste etc. What are the ongoing liabilities?• Scope and scale of monitoring

Are there any cumulative impacts for the area notaddressed from assessing a specific pile inisolation?

STEP 3Assess significance and ranking in each category – considered as part of atransparent and inclusive process.

STEP 4Assess Overall BEP/BAT from the above completed table.

STEP 5Execute option.

UKOOA Drill Cuttings R&D Initiative Annex IISummary of R & D Phase II Task Findings

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Annex II: Summary of R & D Phase II Task Findings

Task 1Characterisation of the Cuttings Piles at the Beryl A and Ekofisk 2/4 A platform

The objective of Task 1, conducted by Rogaland Research, was to conduct achemical, physical and biological characterisation of a water-based (WBM) and anoil-based (OBM) cuttings piles, based on the OLF Guidelines for characterisation ofcutting piles (OLF, 2000). Within the UKOOA phase II programme thecharacterisation task gives important input to short-term and long-term modelling ofcuttings piles, as well as to other tasks investigating cuttings pile changes andimpacts with time.

Two piles were investigated - Beryl A (OBM) and Ekofisk 2/4 A – both of which werepreviously mapped and classified as being ‘fairly large’. The Ekofisk pile wasintentionally chosen to represent a water based pile (WBM). However, in the laterperiod of drilling activity at Ekofisk, synthetic drilling fluids containing esters and poly-alfa-olefines were used in addition to WBM at the 2/4 A platform. Although themajority of cuttings discharges at 2/4 A (about 90%) were WBM, the characteristicsof the pile is clearly different from that expected with a purely WBM pile.

Task 1 was undertaken in three parts, the main part (PART 1) dealing with planningof survey and sampling locations, offshore sample collection, and analysis andinterpretation of data. The offshore survey also included collection of samples (bulkmaterial) for several other tasks within the UKOOA phase II program. The offshoresurvey took place late September 2000.

Contour mapping from recent surveys was used to plan the sampling program duringthe fieldwork. The selected parameters investigated included:

• Geotechnical parameters: cone penetration (CPT), shear strength, grain sizedistribution and density,

• Mineralogy and main constituents,• Hydrocarbons and other organic contaminants, including total hydrocarbons

(THC), polycyclic aromatic hydrocarbons (PAH); napthenes, phenantrenes anddibenzothiophenes (NPDs); decalines and selected polychlorinated biphenylcongeners 28, 52, 101, 118, 153, 180 (PCBs; the so-called “Dutch 7”),

• Metals: Aluminium, Vanadium, Manganese, Iron, Barium, Chromium, Cobalt,Nickell, Copper, Zinc, Arsenic, Strontium, Cadmium, Lead and Mercury,

• Other chemical characteristics: Total Organic Carbon (TOC), Total OrganicNitrogen (TON), pH, Redox potential (eH) and sulphide concentration,

• Biological parameters: macrofaunal composition, endocrine disrupting effects(screening test with yeast cells).

• In addition to Task 1 analyses, concentrations of Naturally Occurring RadioactiveMaterial (NORM, present in scale) and alkylated nonylphenol ethoxylates(potential endocrine disrupters) were analysed as part of UKOOA Task 2c.

The listed parameters were analysed on core samples from both cuttings piles. AtEkofisk 2/4A, a previous investigation in 1998 provided additional data which wereassessed in the characterisation work. The experience obtained from fieldwork has


41

been evaluated with regard to selection of appropriate cuttings pile samplingmethods

PART 2 of Task 1 investigated speciation of metals and the (bio)availability of tracemetals in cuttings material. These aspects were investigated using a sequentialextraction approach followed by subsequent ICP-MS analyses.

PART 3 examined endocrine disruption (ED) caused by components of cuttingsmaterial, and potential effects related to the presence of low quantities of PCBs. Thedirect measurement of endocrine disruption is very complex and has not beenconducted on drill cuttings material previously. The objectives of Part 3 weretherefore to assess available methods, and to provide pilot screening data on theoccurrence of endocrine disruptive chemicals (EDCs) in drill cuttings material fromthe North Sea. Other potential impacts of PCBs were examined, also by a screeningapproach, and interpreted in relation to endocrine disruption effects.

The main conclusions and observations of Task 1 are summarised below:

PART 1 - Major findings and conclusions:

• The nature of the cuttings piles made traditional coring work difficult. Theexperience at both the cuttings piles sampled was that the coring equipmentmust be carefully selected to be able to retrieve samples and to reduce thenumber of failed attempts.

• The material found in both cuttings pile was extremely soft. CPT and shearstrength measurements on Beryl A and Ekofisk 2/4 A cuttings material gave verysimilar results.

• The mineralogy results showed that barite is one of the main constituents. Pyrite(iron sulphide) was one of the crystalline phases found.

• Sulphide measurements directly on cores indicated that anoxic conditionsoccurred within both cuttings piles. Redox conditions in the piles were variable,with no consistent differences between the two piles.

• Both cutting piles contain significant amounts of hydrocarbons (THC),although the total load at Beryl pile was considerably higher than at Ekofisk.Clear differences in the types and spatial distribution of hydrocarbons could beseen between the two piles:

At Beryl, THC levels were high (between 0.2 and 20%) throughout the pile,and tended to increase vertically into the pile. The hydrocarbon source wasmainly mineral oils.

At Ekofisk, the highest concentrations (up to 8%) of hydrocarbons werefound in the surface layer (to about 20cm depth), and were dominated byesters. Deeper in the pile, THC levels decreased considerably, reflecting theuse of WBM in earlier drilling activity.

• The PAH concentration was high at Beryl, although the concentration of thecarcinogenic PAH component B(a)P was rather low compared to the sum PAH


42

measured. The vertical distribution of PAHs clearly reflected early use of dieselbased drilling fluids, and later use of lower toxicity base oils with lower aromaticcontent.

At Ekofisk 2/4 A, the concentration of the sum of PAH components was moderateand B(a)P was low. This reflects the different origin of the THC in this pile.

• No PCB was detected in the Beryl pile. In the Ekofisk pile, relatively highconcentrations of PCB were found in some layers (up to 1500 µg/kg sediment ina thin layer). The PCB contaminated layer was found in the oldest part of thecutting pile and was covered with cuttings layers in which no PCB was detected.

• Both cuttings piles show very similar contamination patterns for metals.The largest increase over background concentrations was for lead. Both pilesalso contained concentrations of copper, zinc, cadmium and mercury indicativeof moderate contamination.

• A hard crust layer was found on parts of the Ekofisk pile surface. Afteridentification of crystalline phases and microscopic studies of the crust it wasfound to be comprised of discharged cement. No such observations were madeon the Beryl pile.

• Both cuttings piles showed a similar composition and distribution ofbenthic fauna. The number of taxa found was in line with what could be expectedin this area of the North Sea. The dominating species in both piles was Capitellacapitata, which is indicative of disturbed or contaminated seabed habitats.

• Analyses of alkylphenols (nonylphenol, 4-tert.octylphenol and alkylphenolethoxylates) were carried out on surface layer cuttings from Beryl (0-40 cm) andin southern North Sea reference sediment, by TNO as part of Task 2c. Noconcentrations above the detection limits (20, 20 and 200µg/kg respectively)were measured in either sample set.

• The NORM analysis (also by TNO) showed elevated concentrations of allisotopes measured in surface layers (0-40 cm) for both Ekofisk and Beryl whencompared to a North Sea reference station. However, the levels measured werenot significantly higher than reported background levels for the North Sea moregenerally. Only for Ra-226 was there a clear difference between Beryl andEkofisk, Beryl having twice the concentration measured at Ekofisk.

Overall, the major differences between the piles are the types and vertical distributionof organic contamination, which is mainly due to the nature of the drilling fluids usedat the two sites; and in the crust layer which was only seen at Ekofisk.



43

• Metals of high environmental concern (mercury, lead and cadmium) are to aconsiderable extent bound in fractions of high mobility (with regard togeochemical processes). However, at the higher metal contamination levels, thefraction (%) of the total pool of these metals in the most bioavailable fractions arereduced. Potential impacts to the environment therefore do not increase linearlywith the total concentration of these metals.

• The attempt to apply multivariate analysis (Principal Component Analysis, PCA)to relate the different metals to particular fractions did not enable a generalisedinterpretation of the results with respect to the distribution of metals betweenspecific fractions, location of the sample within the piles, or between differentpiles.

• Data from related studies indicate that cadmium in the cuttings may be potentiallybioavailable for biota.

• Metals generally associated with uptake by different biota (bioaccumulation), e.g.zinc, copper, cadmium and mercury can be found in the more bioavailablefractions.


• Using a number of separate cell culture-based assay techniques (YES/YAS, ER-CALUX, AR-LUX and DR-CALUX), indications of potential estrogenic, anti-estrogenic, androgenic and anti-androgenic activities were detected in drillcuttings pile samples from various oilfields in the North Sea (including Ekofisk2/4A and Beryl A). Generally however, the effects found were weak and variable,and as such the conclusions that can be drawn from the results are limited. Thestudy was therefore not conclusive with regard to the environmental risksassociated with endocrine disruptive chemicals in the cuttings piles material.

• The present investigation represents a first step into the very complex issue ofevaluating possible ED activities of chemicals occurring in the numerous drillcuttings piles in the North Sea. This task is particularly challenging due to samplevariability, not only between piles but also within piles. Prior identification ofpotential EDCs is important as a basis for selection of ED related test parametersand for interpretation of results. However, due to the chemical complexity andheterogeneous nature of the piles, this task could not be fully accomplished in thepresent study.

• Integrative cell-culture tests each indicating estrogenic, androgenic and dioxinrelated effects of the cuttings piles extracts were used. The study suggested thatthe occurrence of dioxin type toxicity in some cuttings samples can be related tohigh levels of PCBs. In addition, a partial correlation of high BaP levels and anti-estrogenic effects was also indicated.

• These preliminary bioassay studies were hampered by the presence of cytotoxiccomponents in many of the cuttings samples.

• Further studies are recommended to establish clear evidence with regard to theenvironmental significance of EDCs in drill cuttings. Such studies must putconsiderable emphasis in experimental design in order to minimise the influence


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of cytotoxicity, including selection of appropriate test systems and the use ofsublethal exposure doses. Long-term studies addressing low-dose and chroniceffects of EDs are also suggested.

6 Task 2aInvestigation of the toxicokinetics of water based mud cuttings

ERT (Scotland) Ltd was contracted to carry out toxicokinetic studies on cuttingsdrilled with water-based muds. It was planned to conduct exposure and uptakestudies using the same methods previously used to study oil based mud cuttingsundertaken as part of phase I of the drill cuttings initiative (ERT, 1999). The objectiveof the study was to obtain information to form the basis of a direct comparison of theeffects of discharged cuttings generated from oil-based and water-based drillingmuds.

Sediment-phase exposures were carried out in accordance with the publishedOSPAR method (using the amphipod Corophium volutator) for assessing sedimenttoxicity; water-phase exposures were carried out in accordance with OSPARmethods (using the phytoplankton Skeletonema costatum) for assessing aqueoustoxicity.

WBM cuttings samples, collected from seabed cuttings piles, exhibited a relativelyflat and limited acute toxic response in the sediment phase at concentrations rangingup to the relatively high addition rate of 60% weight/weight. The toxicity of the WBMcuttings was found to be much lower than the acute toxicity of the previouslyanalysed OBM cuttings. The responses were consistent with what would beexpected for material containing the relatively low level of hydrocarbons found in theWBM samples tested (approximately 100 mg.kg-1 dry weight). It was not possible toconclusively rule out the presence of other non-hydrocarbon components whichcould have contributed to the overall acute toxicity of the samples, however theresults of the chemical and toxicity analyses undertaken provided no evidence toindicate significant toxicity due to other components.

The results obtained from the water phase algal tests indicated the absence ofsignificant quantities of soluble toxicant in the WBM samples supplied. In addition, itshould be noted that the test concentrations used in this study were relatively high(up to 10% weight/volume WAF preparation), it is therefore very unlikely thatsignificant effects on phytoplankton productivity would occur during a short termexposure if this type of material were re-suspended in the water column.

This study assessed the acute toxicity of samples collected from only two waterbased mud cuttings piles. It is known that water based drilling mud composition willvary from site to site, with most of the variation being due to differing proportions ofcommon drilling fluid additives. In addition to differing composition and dischargeconditions, variations in the particle size of drill cuttings and the length of time thecuttings have been present in the environment may have some influence on thetoxicity of the material present in individual piles. In the case of most WBM cuttingsthese factors will probably not have a very substantial effect on acute toxicity.

The data obtained from this study together with data previously obtained for OBMcuttings suggests that the total hydrocarbon content of cuttings pile material may


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prove useful in estimating the likely acute sediment phase toxicity of the cuttings.However there were also indications that the type of hydrocarbons present could bean important influencing factor. The uptake of hydrocarbons by the test Corophiumfrom the WBM test material appeared to be lower than the uptake of hydrocarbonsmeasured during the previous OBM test. This observation could be due to differingphysical/chemical partitioning properties of the mixture of hydrocarbon componentspresent in each sample. In this case an increased relative proportion of highermolecular weight compounds was present in the WBM material compared with theOBM cuttings. Therefore, in addition to total hydrocarbon concentration, data on theuptake of different hydrocarbon types from the sediment phase (such as existingbioaccumulation factor data) would have to be taken into account when estimatingacute toxicity of the cuttings.

7 Task 2bAssessment of Present Impacts of Cuttings Piles

Task 2b was undertaken by Cordah Limited in association with Aquaplan Niva, toassess the existing load of hydrocarbons and metals within historic cuttings piles,and compare this with the present input of such contaminants to the North Sea fromother sources.

The scope of work was to:

• Estimate the existing contaminant load in historic piles: All the piles in theUK and Norwegian sectors were classified into one of four categories, based onthe predominant type of mud used during drilling and the volume of the pile.Using data on absolute and unit contaminant loading for piles representative ofeach type, the total extant contaminant loading in piles in the North Sea wascalculated.

• Estimate annual input of contaminants to the North Sea from other sources:A range of data sources were used to calculate an estimate of the total inputs ofcontaminant into the North Sea

• Comparison of contaminant loading in plies with annual inputs from allother sources: The above data were then examined to provide an overview ofthe relative total load of contaminants in piles and the annual input of thosecontaminants from other sources.

It is estimated that cuttings piles in the UK and Norwegian sectors contain a total ofapproximately 161,500 tonnes of oil (103,000te, 64% UK: 58,500te, 36% Norway).Hydrocarbons present in piles represent up to 4% of the total mass of piles, and onthe UKCS the six largest oil-based mud piles account for 24% of the total mass of oilin piles. The average mass of oil in each UK pile is 860 tonnes, and in Norway 693tonnes.

The metals with high concentrations in piles are barium, zinc and lead, and the totalmass of these contaminants in UK and Norway, respectively, are barium 9,251tonnes and 1,664 tonnes; zinc 911 tonnes and 332 tonnes; and lead 527 tonnes and254 tonnes. The total mass of lead in piles is equivalent to about 0.15 (15%) of thetotal annual input to the North Sea from other sources. The total mass of zinc is


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equivalent to about 0.056 (6%) of the total annual input to the North Sea from othersources.

The area of seabed where hydrocarbons concentration exceeded 50ppm wasdetermined from historical data. This threshold was selected because it haspreviously been shown to be a concentration at which effects on seabed invertebrateorganisms can be detected. The area of seabed around cuttings piles in whichbiological disturbance would accordingly be expected was estimated at 1056 km2 inthe UKCS and 549 km2 in the NCS. The total area affected represents 0.23% of thetotal area of the North Sea. It is expected that this area should decrease slowly ashydrocarbons are broken down and other components become dispersed.

The selected contaminants found in drill cuttings piles also enter the North Sea byother routes, including refineries and terminals, dredged material, produced waterfrom offshore platforms, accidental discharges from ships, spills from oil and gasoperations offshore, illegal discharges from ships, rivers, and the atmosphere.

A direct comparison between the effects of cuttings piles and other inputs wasrestricted to those which directly impacted the seabed viz, dredging, spoil dumpingand fishing. An area of the North Sea of between 130,000 and 369,000 km2 istrawled annually, resulting in a direct impact on seabed living organisms by physicaldamage and disruption to habitats.

Aggregate extraction in the UKCS alone disturbs a further 238 km2 and spoil dumpingfrom all states a further 5 km2. Both of these activities create physical impactsthrough smothering and loss of habitat. Dredge spoil may also create an impact fromassociated contaminants if they leach from the disposal site.

Task 2cWater Column and Food Chain Impacts

Task 2C, designed to investigate the water column and food chain impacts of drillcuttings piles, was carried out by Dames & Moore in collaboration with TNO. Theobjectives were to:

• Determine the exposure/uptake/ toxicity relationship for OBM cuttings derivedcontaminants eluted into the water phase,

• Develop trials (in-situ and lab based) to sample and analyse or to exposeindicator species to OBM-cuttings to determine any uptake into the food chain,

• To verify the null hypothesis ‘Cuttings piles impacts are localised and limited tothe sediment (assuming no disturbance) with no effects on the water column orthe food chain’.

These objectives were investigated using a laboratory based bioaccumulation study,sediment analysis and toxicity testing. It was intended that the lab-based work wouldbe backed up by chemical analysis on the tissue of biota collected during thesampling cruise. However, the sampling cruise yielded insufficient field biota foranalysis. The OBM sample was collected from the cuttings pile at the Beryl Aplatform in the North Sea, the reference sediment was collected five miles offshore


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the Dutch coast. A sample was also taken from the WBM cuttings pile from theEkofisk 2/4 A cuttings pile, however, as it was not part of the scope, only toxicitytesting and initial sediment analysis were carried out on this sample.

The bioaccumulation study utilised an artificial ecosystem (mesocosm) representingthe sediment (either OBM drill cuttings material or reference North Seas sediment)and overlying water. Uptake of contaminants was investigated using the musselMytilus edulis, the ragworm Nereis virens, and the turbot Scophthalmus maximus.Chemical analysis of contaminants within the sediments and animals tissue wascarried out on a range of chemicals believed to be the most toxic or harmful elementswithin the cuttings piles. These included 16 USEPA Priority Polycyclic AromaticHydrocarbons (PAHs), metals, endocrine disruptors, and naturally occurringradioactive material (NORM). Standard toxicity tests using Corophium volutator,Echinocardium cordatum, and Acartia tonsa were used to investigate the toxicity ofthe sediment and sediment elutriate to biota.

The findings are summarised below:

• Concentrations of PAHs, metals, endocrine disruptors and NORM weremeasured in OBM sediments, both before and after the mesocosmexperiments. By comparison with known effects ranges, none of theconcentrations appeared likely to result in an adverse effect on biota.

• Mytilus edulis were observed to bioaccumulate lead, zinc, cadmium andmercury and alkylphenol ethoxylate in the OBM mesocosm. However, agenerally similar pattern was observed in the reference mesocosm,suggesting that no incremental effect is present in the water column withOBM versus reference sediment.

• In Nereis, several PAHs were observed to bioaccumulate in both the OBMand reference mesocosms. However, of these only fluorene, phenanthrene,anthracene and pyrene were significantly greater in the OBM compare to thereference mesocosms. Several metals were additionally accumulated in bothOBM and reference animals, though no significant difference was observedbetween the two sediment types.

• Turbot were seen to accumulate several metals, alkylphenol ethoxylate andradium-226 in the OBM sediment. A similar pattern was observed in thereference mesocosms with the exception of radium-226. However of these,only lead was significantly different in the OBM than in the reference.

• No biomagnification of the PAHs, heavy metals, or NORM material wasdemonstrated. Biomagnification of the endocrine disruptor, alkylphenolethoxylate was shown in the OBM but at smaller rates than wasdemonstrated in the reference sediment. However the biomagnificationcalculation used does not take into account the possibility that contaminantsmay have undergone uptake from any source other than food.

• A toxic response is clearly demonstrated in the OBM sediments, relative tothe reference sediment, in all three types of toxicity tests. This provides


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strong evidence that contaminant(s) associated with the OBM are responsiblefor the toxic effect. No toxic response was detected in the WBM sediment.

• It appears unlikely that any of the measured contaminants are responsible forthe observed toxic effects. This conclusion is based on both the results of thesediment assessment criteria screening process and the predominantabsence of any incremental bioaccumulation or biomagnification effects in theOBM compared to the reference sediment. Irrespective of the cause of thetoxic response, it should be stressed that the laboratory toxicity tests are notdirectly analogous to the in-situ conditions. In particular, it may be noted thatthe laboratory test investigate disturbed sediment which is not necessarily thecase in the field.

• It is postulated that the primary factor in determining the toxic effects causedby the OBM is THC. A parallel research study undertaken by RogalandResearch to characterise the OBM and WBM showed that the OBMcontained very high concentrations of THC, in a mineral oil form. It ispossible that this mineral oil may have a deleterious physical effect on the testorganisms, acting through a ‘smothering’ effect, rather than any physiologicaleffects. This would explain the acute responses observed. The absence ofthe toxic effects in WBM may be explained by the different physiochemicalproperties associated with the THC, which are in contrast predominatelyesters, and are of a lower concentration.

The potential food chain effects of the OBM sediment seen during thebioaccumulation study are generally very slight and do not vary greatly from theaccumulation seen in the reference sediment mesocosm. However, the toxicityresults indicate that the potential for water column effects, albeit on a very minorscale in volumetric terms, exist if the OBM sediments are disturbed.

Task 3Factors Determining Future Pile Characteristics

Task 3 focuses on factors that may cause cuttings pile changes (e.g. pile size andcomposition) with time, primarily due to natural processes. Task 3 has beenorganised in several sub-tasks that separately and combined seek to give input to themain objectives of the study. This report summarises the findings of these sub-tasks,produced jointly by the project participants: Rogaland Research, SINTEF, ERT(S)Land AEAT.

The main objective has been to generate time series data on factors that affectcuttings pile characteristics, feeding relevant data into a mathematical model (Task 4)that predicts the fate of cuttings piles with time.

More specifically, relevant objectives addressed include:

• To define essential factors to be used as numerical model input data, and definedata sets to be handled by the model tool,

• To visualise how cuttings piles are eroded, depending on the conditions in andaround the pile,

• To measure rates and impacts of biodegradation, microbial processes,bioturbation and re-colonisation, and to assess how these factors are affected by,and affect, pile characteristics and contaminant concentration.


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Basically, two main processes have been addressed in this project, namely erosion,and depletion of THC. Associated processes and their impact on these mainprocesses have further been addressed. The main findings of the task 3 project aresummarised, addressing the questions raised in the scope as presented below. Thestudy was based on samples from two cuttings piles, the oil-based pile Beryl A, andthe Ekofisk 2/4 A pile that has part pseudo-oil based (PBM; esters, poly-alphaolefines) and water based cuttings. The work planning and progression hasbeen a dynamic process, increasingly so as the complexity of the processes underinvestigation has become clearer. Hence, not all of the scoped objectives have beenaddressed to the same extent, as the most relevant issues have been prioritised.

A major conclusion of Task 3 is that for the two piles investigated, and with theconditions prevalent in the areas where they are situated, erosion will be the majorfactor affecting the piles. Degradation processes and other processes that mayinfluence these will, in comparison, be of limited importance.

Degradation processes of the organic fraction of drill cuttings material were shown,both through small-scale and meso-scale experiments that biodegradation processesunder in-situ conditions are slow, that they mainly take place in the oxygenatedsurface active layer (SAL), and that they probably are little influenced by macrofaunalpresence and bioturbation activity. However, bioturbation activity may influence theeffective thickness of the SAL.

Degradation rates for hydrocarbons (THC) of cuttings pile material at aerobicconditions were estimated at 3 mg/kg THC per day with Beryl cuttings (OBM) and 11mg/kg THC per day with Ekofisk cuttings (PBM/WBM). This corresponds to half-livesof 120 days for Beryl (initial concentration about 750 mg/kg THC) and 750 days forEkofisk (initial concentration 74,000 mg/kg THC). There was considerableinconsistency in the THC data and hence in the presented rates and half-lives.

There is some evidence of toxic conditions or inhibition that limits degradation ofBeryl at concentrations above 2000 mg/kg. Similar degradation patterns and ratesobserved with the Ekofisk cuttings were also evident with Frøy cuttings (PBM), withonly aerobic degradation processes taking place to a significant extent.

The erosion rate of the Ekofisk cuttings (PBM/WBM) was about 6 kg/m2 per day atthe maximum shear stress tested (12 N/m2). With the Beryl cuttings (OBM) a similarshear stress gave erosion rates 40-100 times higher (up to 600 kg/m2). Theconditions at which these erosion rates were measured represent a combination of a100 year current speed (constant current direction) and a 10 year significant waveheight (orbital current direction), conditions that are rather extreme.

The current speed at which significant erosion started was around 35 cm/s for bothBeryl and Ekofisk (no waves applied). This value represent a 1-year return currentspeed at the bottom of Ekofisk. At a maximum shear stress of 3 N/m2, the erosionrate of Beryl material was 12 kg/m2. No erosion was observed at Ekofisk at the sameconditions.

An estimation of the thickness of the surface active layer has been provided basedon measured redox profiles of the cuttings, apparent burying depths of Capitella andAbra, and from what layers depletion/degradation apparently has occurred:


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• In the mesocosm experiments, the main depletion/degradation processes wererestricted to the top 4-5mm.

• In the macrofaunal colonisation mesocosm, burial depths down to about 20-30mm were observed by Capitella capitata. The burrowing depth was dependent onthe cuttings concentration (THC), the depth decreasing to only the top 5-10 mm atthe 100% cuttings samples of both Beryl and Ekofisk. At the lower concentrationstested (20% cuttings), the burial depth extended to 20-30 mm on both cuttingstypes.

“True” water-based piles, defined as those at multi-well development locationscontaining no discharges other than WBM cuttings, are infrequent on the UK andNorwegian continental shelves. Such piles will most likely contain low levels of THC(100-600 mg/kg), the THC in such WBM piles likely having similar degradationcharacteristics as the THC in the OBM piles. In that respect, there would seem to belittle differences between natural degradation in WBM and OBM piles, as the totalTHC concentration will be the determining factor. There will however be a majordifference between WBM and OBM piles in that the concentration of oil will beconsiderably higher in an oil-based pile.

Given that erosion processes are likely to be the main factor in the long-term fate ofcuttings piles, a monitoring programme should address the mass balance of materialin the pile, in addition to contaminant concentrations within the pile, “fraying edge”and surrounding seabed.

The appropriate extent and frequency of a monitoring programme will be site-dependent, and should be assessed on the basis of long-term fate modelling andreviewed in light of emerging experience.

Task 4Adaptation and Evaluation of Mathematical Model

Task 4 objective of this task has been to develop a model capable of simulating thenecessary processes to predict the evolution and fate of legacy cuttings piles overtimescales of decades to millennia. To achieve this objective a new model has beendeveloped using the principles of diagenetic modelling.

Modelling has focused on prediction of the persistence of cuttings piles, in particularthe persistence of total petroleum hydrocarbons associated with the solid phasecuttings material. The physical removal of pile material has been simulated initiallyusing the Short Term Model (STM) developed by BMT under Phase I of the DrillCuttings Initiative. This model has been used to simulate a range of hydrodynamicforcing scenarios (tidal currents and waves) acting on piles defined by thecharacteristics of the cuttings material. This has allowed prediction oferosion/deposition fluxes and deposition patterns that have been provided as input tothe Long Term Model (LTM) as statistical distributions according to the wave climateat the geographical location of interest.

The LTM is a diagenetic model that consists of a grid of 1-D processors thatrepresent a vertical section of the cuttings pile at that location. The LTM allows thesimulation of bioturbation, biodegradation, migration and surface loss of oil, andvertical advection. The initialization of the model is in the form of a physicochemical


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description of the pile in three dimensions. There is very significant uncertaintyassociated with a number of the key constants that are required in the LTM. Tounderstand the importance of these parameters and their impact on the prediction ofpersistence, a sensitivity analysis was conducted. The analysis gave confidence inthe parameters used in predicting natural physical removal. The two key constants inthe diagenetic process were the Surface Loss Rate and the Bioturbation Coefficient.There is no reliable and relevant literature or experimental data presently availablefor these parameters and best estimates were required for use in the subsequentmodelling.

A number of case studies were conducted to illustrate the performance of the modeland provide indicative predictions of cuttings pile persistence. The case studyscenarios ranged from a large deep water oil-based pile (25000m3 in 145m) to amedium synthetic-based pile in shallow water (3600m3 in 70m). Persistencies rangedfrom c.1500 years for a pile that received very little hydrodynamic forcing, to 12 yearsfor a small low concentration pile. A scenario representing cuttings outside of thedefined physical pile showed relatively rapid removal of oil content and rapidreduction of area contaminated. A scenario including trawling concluded that thiswould have limited effect on persistence, and a scenario simulating a pile that hadbeen 95% recovered showed disproportionately rapid recovery times compared withthe original pile.

Although the model appears to be simulating the physical and biochemical processessensibly according to intuition, the extent to which the model has been validated isvery limited. A comparison with surveys of N. Sea cuttings piles was severely limitedby the data quality and uncertainties although modelling results could be interpretedas comparable. There was more confidence in the validation of the crucialhydrodynamic forcing and erosion rates that are critical for physical removalprediction. There was also a positive comparison between modelled removal rates,and those estimated from surveys of the Ekofisk pile.

Notwithstanding the critical need for better input data, and if possible, validation data,the project has been able to deliver a model capable of application for decision-making provided input data is adequate and precautions are taken in defining andpresenting scenarios.

Task 5aBioremediation solutions

Task 5a, conducted by AEAT, investigated the potential and cost of treating contaminateddrill cuttings on the sea bed using a sub-surface bioreactor, a process called in situbioremediation. During the early phases of this stage of the study, the initial concept wasmodified. Moving the sub-sea bioreactor from place to place was concluded to beimpractical and only possible after the platform jacket had been removed. A more practicalapproach of performing the operation from an existing platform (during the production tail-down period) was pursued, and this is described in outline below.

Process OverviewThe basic philosophy would be to transport the cuttings to a stationary reactor vessel onthe sea bed for treatment by combined cuttings scrubbing and bioremediation. AEAT haveproposed an operating procedure for the bioreactor which would be as follows:-


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• Install the reactor vessel(s) (RV) on the seabed and place equipment at a suitablelocation on the platform (e.g. redundant drilling areas).

• Use an ROV and dredging pump to transport the cuttings from the pile to the RV.Debris would be removed by the ROV and recovered for appropriate disposal.

• Treat the water used to transport the cuttings (to remove solids and oil) usingequipment installed at the sea surface on the platform or a ship, and dischargeassuming treatment to an acceptable standard can be achieved.

• The solid drill cuttings are treated in the bioreactor on the sea bed. The rate ofbiodegradation is encouraged by the circulation of warm water, bacteria, and oxygenfrom topsides facilities into the reactor.

• After completion of scrubbing/bioremediation, and confirmation by analysis ofacceptable contaminant concentrations, the RV is emptied using solids transportationdevices, and the clean solids are placed in a specified location on the sea bed.

AEAT have presented a very preliminary time scale for the operation of the bioreactorbased on the results of the limited laboratory experiment that was conducted as part ofthis scoping study. As this was only a single experiment these timescales are onlyindicative and have significant uncertainties within. Timescales can only be properlyestablished in field trials of this approach.

Clearly the operation of the bioreactor at sea may entail the resolution of problems thatcannot be identified in a desktop evaluation such as this. A detailed review of thepracticality of the approach can only be achieved through further work and field trials.

EquipmentThe size of the RV has been based on limiting factors such as ease of manufacture, abilityto transport to site, and deployment to the sea bed. However, maximising the size of theRV and hence minimising the number of processes required was a key design feature.These investigations suggest that a pressure vessel of approximately 6 meters indiameter and 10 meters high may be suitable. The vessel could be made from carbonsteel, lined on the inside and insulated on the outside.

This size of vessel could be transported to site on deck of a supply boat that has an A-frame lift at stern. This equipment is readily available on support vessels. The vesselwould be lowered into position on the seabed using an A-frame and using air in thereactor as ballast.

It is assumed that topsides treatment and water and air re-circulation could be performedwith tried and tested equipment commonly used in the clean up of produced water. Thebioreactor could be connected to the surface with flexible hoses. Installation of the hosesand the topsides equipment on a suitable platform could be achieved using an existingplatform crane, or alternatively the process could be run from a ship. It is also assumedthat the ROV and associated equipment could be deployed in a conventional manner fromthe platform.

Key features of the described treatment process include:

Use of existing platform infrastructure.During the production decline and pre-decommissioning period, space, utilities andcapacity may be available and could be used to operate the more than 1 sea bedbioreactors. This approach would overcome the need for costly rental associated with aboat operation. It could also allow for interchangeability and the plan would be that


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equipment would pass from platform to platform in order to clean up sea bed cuttingsdeposits at each site. This would be an ideal, but would clearly have to be tested in thefield and AEAT have indicated in the conclusion to the report that testing would berequired to confirm that this is a feasible approach.

Residual cleanliness of the treated cuttings pile can be determined.The proposed design allows sampling from the circulation stream to ensure that thereaction time is adjusted to ensure the required clean up is achieved.

The controllable treatment of cuttings piles around the jacket legs and braces.AEAT have modified the original design for the bioreactor proposed in Phase 1 of the JIPsuch that a fixed reactor is proposed with cuttings material being brought to the reactor byan ROV. The thoroughness of the ROV controlled suction amongst the jacket braces andsurrounding areas can be controlled and removal of drill cuttings from around the jacketlegs will also enable easier jacket removal. The use of an ROV allows cuttings piles to betreated even if they contain non-cuttings debris such as metal structures and cement asthis approach allows debris to be separated from cuttings material

The in situ treatment of cuttings.We have provided an indicative timescale for the treatment of cuttings material in thebioreactor based on our laboratory experiment and other limited work. With theseassumptions and using a single RV the system would require ~1 year to clean up a pile of6,000m3. By using 3 RVs it will be possible to fill one while treatment is occurring in theother reactor(s), making the operation virtually continuous. While these timescales areconsistent with the available limited laboratory data, there is significant uncertainty inthese treatment times. The clean up of oil cuttings will be dependent on the compositionand concentration of the contaminants in any pile. If UKOOA wished to proceed with thistechnology a full field evaluation would be required to establish the relative contribution ofphysical (scrubbing) and biological (biodegradation) processes to the cuttings piletreatment. It would also enable the practicality of the approach to be assessed.

AEAT have concluded that treatment of cuttings piles in situ is potentially practical andfeasible using tried and tested equipment, and have provided budget and time estimatesfor use in comparative assessment with other management options. The most cost-effective bioremediation treatment is likely to involve using existing platforms to basesurface equipment. The approach may potentially be used to treat piles containing debrisand those deposited around platform legs. However, all of these assertions need furtherevaluation under realistic field conditions.

A preliminary estimate, based on a very limited data set, suggests the cost of treatmentmay be in the range of £650-1300 per m3 of treated material. This cost depends on thereaction time for removing contamination in the cuttings material being 1-2 months.Further experimentation is necessary to determine if this is the case and further researchhas been proposed to understand the potential of this approach under more realisticconditions. Other areas of further work include the environmental impact of the treatmentsystem (pile disturbance, and release of heavy metals as a result of bioremediation) andlegal issues around the re-discharge of cuttings material into the environment.


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Task 5bIn-situ solutions: Covering

The Phase I preliminary review of in situ covering of drill cuttings concluded that theoption was practical and that covers could be constructed using natural granularmaterials such as sand, gravel and armour stone. This Phase II study has beenundertaken, by Dredging Research Ltd, in order to identify the limitations of thetechnique.

This Phase II assessment has confirmed that covers can be placed using provenconstruction methods. They should comprise an initial layer of sand followed by agravel filter layer and an outer protective layer of armour stone. Alternative materials,such as membranes, mattresses, concrete and various resinous and bituminousformulations would be costly and very difficult to place. They have few, if any,advantages over natural materials. However, at present, there is no proven methodof construction underneath existing installations although it is likely that methodscould be developed. Covering may not be appropriate for concrete installations thatare fully removed but is a practical option for fully and partly removed steel structuresand, possibly, partly removed concrete structures.

Uncertainty about the in situ properties of drill cuttings prevents confidentidentification of the geotechnical constraints to covering. Additional work is requiredin this area but indicative designs have been developed on the basis that many pilesmay be only marginally stable. These envisage the need to ‘build-out’ steep concavepile slopes and to reduce the slopes of steep conical piles by varying the thickness ofthe initial sand layer to ensure pile stability and to provide a suitable slope for armourstone of a size which can be placed using existing plant. An alternative approachmay be to remove the tops of some piles prior to covering.

The armour layer will provide adequate short term protection against the impacts ofsevere storms, trawling and collapse of parts of partially-removed structures but it isnot practical to provide guaranteed long-term protection against the cumulativeeffects of trawling, emergency anchoring by large vessels and repeated structurecollapse events, particularly in the case of part-removed concrete structures.Monitoring and maintenance will therefore be required, the details of which,particularly the required duration, can only be defined when other studies havedetermined the extent to which the cuttings must be isolated, taking intoconsideration possible time-dependent changes of the nature and degree ofcontamination.

The sand layer can be designed to accommodate all the pore water that will beexpelled from the cuttings due to consolidation. In the long term, contaminants willbe released due to chemical migration and by pore water exchange caused by apumping action induced by waves but these losses are predicted to be negligible.Potentially more significant, short-term releases may occur during construction due tocuttings disturbance when placing the initial sand layer. Leachate analyses andecotoxicology tests using samples recovered from the Ekofisk and Beryl A piles, incombination with estimates of potential rates of release during construction, indicatethat dilution of the released leachate will be rapid and that the risk of acute or chronictoxic effects will be very low. Limited data from other cuttings piles suggests that thisconclusion may apply to a majority of piles but additional analyses and diffusion


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modelling are required to increase the knowledge database before firm conclusionscan be drawn concerning the number of piles for which this finding is valid.

A risk review has concluded that, as long as the cuttings are physically isolated forthe period during which they pose a threat to the environment, covering is a generallylow-risk option which can be achieved using proven methods of construction and withlittle or no adverse impact on the marine environment. However, adoption of thisoption represents a potential liability due to the possibility of damage of the coverresulting in release of contamination and a risk to fishing activities. Covering may beviewed adversely by the general public and stakeholder groups such as fishermen’sassociations.

Task 6Cuttings recovery and reinjection

Task 6, carried out by BP, comprised development and field deployment of cuttingsrecovery equipment with an extensive environmental monitoring programme(conducted by CEFAS) to evaluate the impacts of the operation.

Management of the project involved significant development and testing ofcomponents and systems, a major onshore test and a full scale mobilisation to theoffshore testing location (The North West Hutton platform) located 130 km north eastof the Shetland Islands.

The main aim of the project was to develop an in-depth understanding of thepracticalities, physical parameters and environmental impacts of drill cuttingsrecovery in the marine environment. The project also provided important informationregarding the physical properties of a cuttings pile in-situ and implications fordisposal of the material (Task 7).

A major tender exercise was implemented to identify a dredging system suitable for achieving the trialobjectives. The exercise confirmed many of the findings of the phase I study but also indicated that manysystems required more development time and funding to reach maturity than had been previously indicated.

The system selected consisted of a heavy-duty work class ROV with a variety ofdredge heads and a standard centrifugal dredging pump that was electrically drivenand located on the seabed. Cuttings were transferred to the platform via a fixedhose. Design flow rate was 100m3 per hour with a theoretical maximum water: solidsratio of 3:1.

Onshore TrialA significant onshore trial was implemented at the EEST dry dock facility in Blyth,Northumberland. This exercise proved invaluable and demonstrated that allcomponents of the system could meet the design criteria. In particular, the ability topump the material to the delivery point 65m above sea level at the platform and theability to deploy, connect and manoeuvre the subsea hoses with the ROV whilstdredging. The areas of concern from the onshore trial were the low ratio of solidsachieved (worse than 20:1). This was determined as being due to a combination ofsynthetic samples, dredge-head design, and operator skill. Extremely poor visibilitywas a major problem.

Following the onshore trial a series of modifications were made to improve thesystem. A cutter type dredge head was manufactured to handle material of a


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cohesive nature and improvements were made to the deployment system. The othermajor outcomes were the need for the dredge head to maintain contact with thematerial at all times and confirmation that the system should be able to achieve thedesired ratios.

Offshore TrialAside from the operation itself, the offshore trial indicated the major impact that suchan operation would have on the day to day running of an offshore productionplatform. In addition to the recovery equipment a large amount of equipment andpersonnel were required for the treatment and disposal operations. In all 40 peoplewere involved in running the operation with major operations at four separate worksites on the platform of which approximately 20 personnel were dedicated to thesubsea equipment. The topside processing system included options for disposal byre-injection or ship to shore by skips.

Apart from the scale of the work, the deployment and operation of the equipmentwas relatively straightforward with all aspects operating largely as planned.

Limitations in the disposal system limited the maximum running time but it wassufficient to gain confidence in all the major areas tested. The rotating cutter headcreated a visible but relatively small plume during operation. The majority of the trialwas implemented with a suction dredge head that proved effective. No significantplume was observed from this dredge head. The ROV thrusters and the ROV hullmoving through the pile created small plumes.

The most effective dredging technique appeared to result from driving the ROVforward thrusting the dredge-head deeply into the pile. The system appeared to copewell with debris. Stopping the pump and or backflushing cleared several blockagesduring the operation. Shutting down the operation and backflushing did result insignificant visible re-suspension of cuttings material from the delivery hose.

Water to solids ratios improved with operator experience and several samples below10:1 were noted with 6:1 (by volume of wet cuttings) being the best instantaneousresult. Steady operational ratios were between 10:1 and 20:1 with an overall trialaverage of approximately 4% of wet cuttings including stopping and starting thedredging operation. Frequent starting and stopping the system significantlyincreased the volume of water recovered.

Environmental MonitoringResults from the environmental monitoring arrays confirm that plume generation anddrifting of re-suspended material was low during the operations. There were novisible indications of an oil sheen being created at surface.

Water and solids analysis for oil content indicates oil contamination of the cuttings atthe levels that would have been expected from generic oil on cuttings sampling. Itappears that the majority of the oil remains bound to the cuttings. The level of oil inthe associated dredged water is low which may be associated with the high ratio ofrecovered water to solids.

Contaminant analysis confirmed that the background levels of barium and totalhydrocarbons were not significantly increased in seawater samples as a result of the


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dredging operation. Levels of alkyl phenolethoxylates and barium were higher in therecovered water at the platform topsides. LSA levels in the recovered cuttingsmaterial were low and similar to background levels. There was no detectable oil inthe plumes generated during the trial.

ConclusionsRecovery of contaminated drill cuttings from the seabed to the surface appears to beoperationally feasible and indications are that secondary pollution is relatively lowbased on the equipment utilised in the trial operation.

The levels of oil recorded in the material suggest that previous estimates ofcontamination were representative of the trial site selected. The oil in generalremains bound to the drill cuttings with a relatively small amount migrating into thedredged water.

The practical application of cuttings recovery on an operational platform wouldappear to be limited to a few installations capable of supporting the operation. Theoperation would be challenging with a significant duration, significant costimplications and a major impact on routine platform operations. In the event that aplatform had ceased operating then the operation would have to address theadditional cost of maintaining platform operations for the duration of the operation.

The direct cost of the dredging operation from an existing operational platform islikely to be in the range of £200/m3 to £300/m3 to lift the material to the surface (for a25,000m3 pile) and possibly higher for smaller piles. This equates to at least£4000/m3 of oil removed assuming 5% contamination. Note that this does notinclude offshore processing, storage, transport or disposal costs which will besignificant.

Task 7Assessment of Offshore and Onshore Handling, Transport and TreatmentOptions for Lifted Cuttings Material.

Task 7, carried out by ERM, considered the various options for treatment of removedcuttings and associated water. Both offshore and onshore treatment options wereconsidered.

In total, six treatment options were identified from the previous UKOOA JIP Phase Ireports and consultations with industry as follows:

Option 1: Separation offshore, treatment and disposal of solids and liquidsoffshore.Option 2: Separation, treatment of liquids offshore, transport and treatment of

solids onshore.Option 3: Separation, treatment of solids offshore, transport and treatment of

liquids onshore.Option 4: Separation offshore, transport onshore treatment of both solids andliquids.Option 5: Injection of cuttings.Option 6: Transport of slurry to shore, separation and treatment onshore.


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These options were compared using a high level Best Practical EnvironmentalOptions Study assessments method, which is based on technical, environmental,cost and health and safety performance.

The results of this assessment suggested that no one option was obviously superiorand all had some significant drawbacks.

Options 1 and 3 were not considered viable due to the deposition of treated solids onthe seabed and restrictions on offshore solids treatment equipment. Option 4 islogistically complex and is considered impracticable.

Option 5, cuttings injection was overall the most attractive option which is estimatedto be viable at 25% of UKCS installations. However, the injection of lifted cuttings isnot currently legal in UKCS waters. Option 2 is logistically complex and likely to beconstrained by weather but was considered potentially viable providing legalconstraint can be resolved.

Option 6 was the only option which is viable and legal (under current regulations), butsome aspects of the technology have not yet been proved in the context of cuttingsrecovery and removal. Onshore impacts due to cuttings treatment and theavailability of treatment facilities are major constraints provided the rate of cuttingsgeneration is managed to avoid excess demand.

The viability of Options 2, 5 and 6 could be improved by the following:

• changes to legislation;• development and testing of offshore water treatment and cuttings handling

equipment, and• investment in onshore cuttings treatment facilities for the separation of solids and

liquids.

The specific circumstances of pile removal and treatment operation would be verydifferent and a Best Practical Environmental Option (BPEO) study would be requiredin each case.

Documents

UKOOA Drill Cuttings Final Reportrodadas.anp.gov.br/...R7/biblio/UKOOAcascalho.pdfUKOOA Drill Cuttings Initiative Final Report 3 1. Preamble Since the beginning of 2000 the oil industry