Deepwater geohazards: How significant are they?

Who wants to have rigs delayed or even lose a well in4000 ft of water because of tophole drilling problems? Orfind out after drilling a deepwater discovery well that siteconditions will make development unexpectedly expen-sive or economically unfeasible altogether? Or learn late inthe exploration development sequence that the cost of anexport pipeline will be significantly more expensive thanoriginally budgeted because of difficult route conditions?

No one, of course. But all of these costly problems havebeen experienced by operators working the deepwater Gulfof Mexico. And, as deepwater activity continues to increaseworldwide, more costly mistakes are expected. Those whodo not appreciate and adequately plan for deepwater geo-hazards will be especially at risk.

Conditions at most sites on the continental shelves aresimple, as shown in Figure 1. With a few important excep-tions (mostly associated with large river deltas whereseafloor instability on the delta front is common), geohaz-ards have rarely been a significant issue. And yet it has beenon the shelves where the vast majority of offshore oil indus-try activity has taken place during the past 50 years.Consequently, as the industry moves into deeper and deeperwaters, few think much about geohazards. At least not untilthey have a costly lesson in reality. In sharp contrast, Figures2-4 illustrate how conditions in the deepwater Gulf ofMexico can be complex and difficult.

To avoid or reduce the adverse effects of deepwatergeohazards, I believe that anyone involved in deepwaterexploration or development should have a basic apprecia-tion of the geohazards issue. Whether you are an explorer,driller, planner, manager, economic analyst, pipeliner, facil-ities designer, or landman, you need to have a basic knowl-edge of deepwater geohazards and how they can affectyour project.

This paper summarizes deepwater geohazards and theirpotential significance to exploration and development oper-ations. Case histories illustrate the problems some opera-tors have experienced. Some technology used to investigatedeepwater geohazards is briefly discussed, and concepts to

effectively deal with deepwater geohazards are introduced.

Case histories. The following case histories illustrate howlack of knowledge of seafloor conditions can cause unex-pected budget overruns and, potentially, costly delays indelivering first oil. All examples involve deepwater Gulf ofMexico sites in less than 3500 ft of water. These examplesrepresent the “tip of the iceberg,” as it were. For the mostpart, as an industry overall, we’ve barely begun dealing withthe many difficult areas in the deepwater Gulf. As moreexploration and development is done in deeper and deeperwater, the number and severity of “geohazard” problemsis likely to noticeably increase.

1) A discovery well was drilled in about 1000 ft of waterwith no problems. The operator decided to develop thefield and commissioned production facility design. Thedesign concept was that of a conventional pile-supportedjacket structure, similar to Shell’s Cognac platformdesign. The base dimensions were to be about 300 × 300ft. After design was well under way, deep soil boringswere requested to define soil conditions needed to com-plete final design.

1) As part of the final design effort to confirm site suit-ability, the existing geohazards data were reviewed. Twoseparate surveys, the original drilling hazards survey anda postdiscovery pipeline route survey, had been com-pleted. Review of these geohazards data suggested anirregular seafloor at the proposed platform location.However, because the survey lines were 1000 ft apart(meeting MMS minimum requirements) and the pro-posed platform location was between survey lines, theseafloor topography could not be defined at the level ofdetail required for siting and design.

1) As a result of this severe limitation of the geohazardsdata, the production 3-D exploration seismic data (withbin spacing about 66 × 41 ft) were used to prepare thedetailed but preliminary bathymetric map (Figure 5).This map and the seafloor profile (Figure 6) show that

514 THE LEADING EDGE APRIL 1999 APRIL 1999 THE LEADING EDGE 0000

Deepwater geohazards: How significant are they?

KERRY J. CAMPBELL, Fugro GeoServices, Houston, Texas, U.S.

Figure 1. 3.5 kHz subbottom profiler record showingsimple conditions typical of the Gulf of Mexico conti-nental shelf.

Figure 2. 3.5 kHz deep-tow subbottom profiler recordshowing complex conditions typical of many Gulf ofMexico continental slope sites.

Dow

nloa

ded

07/0

3/14

to 1

28.8

3.63

.20.

Red

istr

ibut

ion

subj

ect t

o SE

G li

cens

e or

cop

yrig

ht; s

ee T

erm

s of

Use

at h

ttp://

libra

ry.s

eg.o

rg/

with the center of the platform base resting on theseafloor near the discovery well, the four corners wouldhave a “water gap” (height of the platform base abovethe mud line) of 6, 4, 35, and 17 ft, respectively. Thus,upon generation of this map, it was immediately obvi-ous that the proposed platform location was unsuitablefor the planned design concept. At last report, after hav-ing already spent considerable money on platform designand field development, the project was on hold and theprojected date of first oil remained uncertain while alter-native development scenarios were being evaluated.

1) There were no hazards to drilling the well; it’s just thatapparently no one bothered to think ahead to possibledevelopment. Early in the exploration/developmentsequence, the explorationist identifies prospects. Thedrilling engineer drills wells. Typically the foundationand structural specialists haven’t been brought into thepicture yet. And may not be for a year or more. The think-ing is “Why bring them in? We don’t even have a dis-

covery!” So, who’s looking at the big picture to see if thewhole deal will work technically and economically? Alltoo often, apparently, no one. Or, the economic analysisis based on economic models that, other than increasedwater depth and distance to market, assume simple siteconditions as are typical of the shelf. The result is that a$15-20 million well may be unknowingly drilled at a siteunfavorable for development when more favorable sitesnearby are also acceptable from the drilling target stand-point.

2) Field development planning was well under way for alarge deepwater field in the Gulf of Mexico. Several sub-sea completions with a tie back to a central FPS site wereplanned. Water depths ranged between about 2000 and3000 ft. Soil borings were requested for several locationsto confirm soil conditions and allow the foundationdesign work to be completed.

1) As part of the planning effort prior to drilling thefoundation borings, the several drilling hazards reportsand geohazards data sets available for the planned devel-opment area were reviewed. But this was authorized onlyafter extensive and repeated explanations to the skepti-cal operator as to why this minimal-cost effort was animportant step. “Why do we need to spend money onthis? We’ve never had to do this before!” Similar thoughtsare often expressed by those with little or no deepwaterexperience.


Figure 3. Seafloor rendering showing complex seafloorconditions in northern Green Canyon lease area, Gulfof Mexico. Color represents water depth, which is amaximum of about 5800 ft in south-central part ofimage. Original image generated from NOAA multi-beam data by Shell E&P Technology Co.

Figure 4. Seafloor rendering showing complex seafloorfault patterns in northern Keathley Canyon lease area,Gulf of Mexico. Color represents water depth, which isa maximum of about 5700 ft in eastern part of image.Original image generated from NOAA multibeam databy Shell E&P Technology Co.

Figure 5. Bathymetric map of proposed platform site indeepwater Gulf of Mexico. Discovery well apparentlywas located without regard to irregular seafloor topogra-phy. Contours were generated from seafloor pick on 3-Dexploration seismic data because available site-surveydata were too widely spaced to define bathymetricdetails. Figure 6 is seafloor profile along line A-A′.

Figure 6. Seafloor profile A-A′ across proposed plat-form site shown in Figure 5. Note that horizontal baseof proposed platform would be as much as 35 ft aboveirregular seafloor at this unfavorable location.

Dow

nloa

ded

07/0

3/14

to 1

28.8

3.63

.20.

Red

istr

ibut

ion

subj

ect t

o SE

G li

cens

e or

cop

yrig

ht; s

ee T

erm

s of

Use

at h

ttp://

libra

ry.s

eg.o

rg/

1) Initial review of the geohazards information suggestedconditions unfavorable for development. As a result,the planned soil-boring work was put on hold while com-prehensive engineering-geologic remapping and assess-ment of site conditions were carried out. This detailedassessment confirmed complex and difficult site condi-tions, including seafloor fault scarps 10-40 ft high;rugged, rocky seafloor; and steep slopes with landslides.

1) The proposed FPS site was subsequently moved to amore favorable site several miles away and in about30% deeper water. This move presumably resulted incostly project delay while the field layout and otherdetails were redesigned, and ultimately to delay in deliv-ery of first oil. Other unexpected costs presumably werealso incurred, including increased cost for the riser andother components required for the new site in muchdeeper water.

1) This is another good example of how the business-as-usual (irreverently referred to as the “shelf mentality”)approach can be very expensive in deepwater.Specifically, the operator began design and assumed butdidn’t confirm that site conditions were favorable fordevelopment. Incredibly, site-survey data had been avail-able several years before design was started but appar-ently were used only to get the MMS-required drillingpermit.

3) A pipeline route survey was conducted for a deepwaterdevelopment after preliminary route selection and designhad been completed based on assumed conditions.Results of the survey showed unexpectedly rugged, andin places, rocky topography. Analysis of 14 differentroutes showed that unacceptable spans would resultalong each of the 14 routings if conventional steel pipewas used as planned. Additional survey and design workwas carried out to develop an acceptable solution.

1) Ultimately, about 10 miles of (expensive and unbud-geted) flexible steel pipe was installed by snaking itthrough patches of rugged and rocky seafloor. The oper-ator concluded that if seafloor conditions had beenknown before the pipeline design concept had beenselected, planning would have been optimized and over-all project costs reduced. And the embarrassing costoverrun would have been avoided.

Deepwater geohazards. The engineering geology of theupper continental slope in the northern Gulf of Mexico isprobably among the most complex of any offshore area inthe world. Most, if not all, geohazards described below alsoare found in other deepwater regions now being exploredand developed, including those off Scotland, Norway, WestAfrica, Brazil, China, and Australia, among others. However,in my experience, few if any other deepwater areas exhibitconditions as dynamic and complex over such a wide areaas are found in the northern Gulf of Mexico. And the fre-quency-of-occurrence of geohazards appears to be higherin the Gulf than is typical in most other deepwater areas.

Shallow geologic conditions in the deepwater Gulf ofMexico (water depths typically >500 ft) result from several,partly interdependent, processes, some of which are stillactive. These processes include: high rates of sedimentation;movement of underlying salt or shale masses; landslidingand density current flows; faulting; hydrocarbons leakingthrough the seafloor; seafloor current scouring; and bio-logical and geochemical activity.

Specific conditions on the continental slope that cancause engineering difficulties include:

1) steep and potentially unstable slopes ranging up to 45° ormore;

2) irregular, sometimes rocky, topography with sharp reliefranging from a few feet to several tens of feet;

3) overpressured sands at relatively shallow depths (thatsometimes cause unexpected, expensive shallow-waterflows and loss of wells);

4) active faults with seafloor scarps ranging up to more than200 ft high;

5) both modern and ancient landslides, some covering largeareas;

6) gas hydrates (solid, icelike mixtures of gas and water) thatmay be subject to reduced shear strength and thaw set-tlement when heated by warm oil flowing through con-ductors or pipelines;

7) seafloor erosion of tens to hundreds of feet of sediment;8) ground conditions ranging from weak, underconsolidated

soils to rock; and9) locally corrosive soils that could require special design and

maintenance of conductors and foundation members.

The actual significance of each type of hazard dependson the current degree of geologic activity as well as the engi-neering activity at hand. For example, an inactive fault withgas migrating along it may be a drilling hazard, whereasan active but gas-free fault may not be because of the veryslow rate of offset relative to the time required to drill thewell. On the other hand, if the exploratory well laterbecomes a production well, then fault movement will even-tually sever the casing, in which case the fault would be aserious hazard. Similarly, scattered patches of irregular,rocky seafloor may not be a serious problem for drilling anexploratory well with a DP rig but could be a major prob-lem for siting production facilities or routing an exportpipeline. In any case, careful definition and assessment ofall potential geohazards are needed to determine theirpotential engineering significance in any given situation.

A particular word of warning to everyone involved indeepwater operations in the Gulf of Mexico: Shallow over-pressured zones, and the potential for shallow-water flows(SWF) during drilling, are perhaps the most intractable geo-hazard encountered in that region. Shallow-water flow isan uncontrollable flow from shallow reservoirs with returnsto the seafloor resulting from natural or induced overpres-sures in the tophole section. SWF typically occurs when theoverpressured sandy zones are penetrated and a poor


Figure 7. Section from deepwater Gulf of Mexico high-resolution 3-D seismic volume. Frequency content isabout 140-150 Hz; limit of separability is less than 10 ftat assumed velocity of 5300 ft/s.

Dow

nloa

ded

07/0

3/14

to 1

28.8

3.63

.20.

Red

istr

ibut

ion

subj

ect t

o SE

G li

cens

e or

cop

yrig

ht; s

ee T

erm

s of

Use

at h

ttp://

libra

ry.s

eg.o

rg/

cement job is done.In fact, some operators feel that SWF is the single biggest

risk and the only potential “showstopper” to deepwaterdevelopment. A vice president of one of the smaller oper-ators that has recently started exploratory drilling in thedeepwater Gulf said that his company “would be history”if they experience a major SWF disaster similar to the recentone in Mississippi Canyon.

Mark Alberty with BP reported at last year’s joint indus-try SWF forum that of 123 wells drilled in the deepwaterGulf, 97 (79%) experienced SWF to some degree, and 30(24%) did not reach their drilling objectives because of SWFproblems. Alberty also reported that an estimated $31 mil-lion had been spent on preventing SWF, and $137 millionhad been spent on remediating SWF problems.

Geohazards technology. Geohazards survey technologyhas seen dramatic improvements over the past 10-15 years.This has been largely in response to the requirements of theoperators who pioneered the push into the deepwater Gulfof Mexico. Afew of the most noteworthy developments aresummarized here. Other important deepwater survey toolsnot discussed here include various swath bathymetric,deep-tow, and 2-D digital survey systems. And autonomousunderwater survey vehicles (AUVs) are expected to becomeroutinely available for deepwater survey work within thenext few years. These preprogrammed survey robots will“fly” just above the seafloor, thus avoiding the several geo-physical and weather-related problems that affect near-sur-face tools.

The appropriateness of any given tool or combinationof tools should be based on various factors including waterdepth and seafloor topography, the nature and complexityof the tophole geology, and the specific objectives of the sur-vey.

3-D seismic data. The widespread availability of 3-D explo-ration seismic data now provides opportunity for doingmore reliable and faster screening, preliminary engineer-ing-geologic, and in some cases MMS-required predrillinghazards assessments of deepwater sites. Only in the pastfew years have the many advantages of 3-D data beenapplied to shallow geohazards assessment. Time and hori-zon slices, surface and volume amplitude maps, and seafloorrenderings are routinely being prepared as part of geohaz-ards studies. Time and horizon slices are being used to mapburied channels and shallow failure zones, and volumeamplitudes are being used to detect gas zones.

Many of the same or similar 3-D seismic techniquesapplied to prospect and reservoir evaluation are nowapplied to shallow geohazards assessment as well. Forexample, to help assess SWF potential, PC-based worksta-tions now analyze seismic stratigraphy and identify shal-low lowstand and highstand sequences as one basis foridentifying possible sand-prone reservoirs and shale seals,respectively. Analyses are robust and areal sampling pointsare typically a few tens of feet apart in all directions (com-pared to typical MMS-required 2-D geohazards data, wheresurvey lines are typically 1000 ft apart).

Seafloor renderings. Seafloor renderings (such as Figures3 and 4) generated from multibeam bathymetric or 3-Dexploration seismic data are an important part of screen-ing and preliminary engineering assessments, as well aspredrilling hazards studies. For example, renderings from3-D seismic data are used to detect subtle seafloor landslidesand flow zones undetectable on the relatively low-resolu-

tion (vertical) seismic sections. By displaying amplitudevariations of seafloor reflections on seafloor renderings,rocky areas, hydrate mounds, and seafloor vents can oftenbe detected and mapped.

High-resolution 3-D seismic data. High-resolution 3-D seis-mic data are collected for special geohazards studies in theGulf of Mexico. Data quality is typically excellent (Figure7). Although various acquisition configurations have beenused, the typical configuration for a geohazards survey issix 100-m, 8-channel streamers and a single 80 or 160 in3

air-gun array. Sail-line spacing is 75 m with streamer spac-ing of 25 m. Collected bin spacing is 6.25 × 12.5 m, inter-polated to 6.25 x 6.25 m for the final 3-D volume. Samplingrate during recording and processing is 0.5 ms, with result-ing frequencies in the final volume typically being 150-300Hz. Vertical resolution (strata discrimination) is on the orderof 4-10 ft; gas sands less than 3 ft in thickness are believeddetectable in some cases. Total record length in deepwaterhas typically been 3-4 s, with penetration below the mudline of 1-2 s.

Use of high-resolution 3-D data is a developing trendthat will accelerate, and collection of high-resolution 3-Ddata will become more common for geohazards surveywork in complex deepwater areas during the next fewyears. The exceptionally high resolution and flexibility ofdisplay and analysis available with high-resolution 3-Ddata makes these data useful for multiple applicationsincluding: well planning and shallow-water-flow assess-ment, drilling hazards analysis, development planning,foundation zone investigations and, in some areas, shallowexploration.

Reducing the impact of deepwater geohazards. Given thepotentially costly impact of deepwater geohazards, what’sthe best approach to avoid them or reduce their impact?Several key steps can greatly reduce the adverse impactsof geohazards: (1) look before you leap (i.e., make geohaz-ards assessment a priority and begin the assessment earlyin the exploration/development sequence); (2) use the inte-grated team approach to provide technical continuity; and(3) follow a fit-for-purpose approach by using the rightgeohazards survey tools.

Look before you leap. This is the first and perhaps most


Figure 8. Generalized drilling favorability map forpart of Green Canyon lease area, Gulf of Mexico. Inthis case, the map shows drilling favorability withrespect to seafloor geohazards only.

Dow

nloa

ded

07/0

3/14

to 1

28.8

3.63

.20.

Red

istr

ibut

ion

subj

ect t

o SE

G li

cens

e or

cop

yrig

ht; s

ee T

erm

s of

Use

at h

ttp://

libra

ry.s

eg.o

rg/

important step. Make it a priority to do at least a prelimi-nary assessment of geohazards early in theexploration/development sequence. Increasingly, this isbeing done based on 3-D seismic exploration data, eitherbefore the lease sale or before drilling. Don’t proceed assum-ing that site conditions are favorable, as they often are not.

There’s no argument that oil prospectivity is the primarydriver for leasing blocks and locating exploratory wells. Butdeepwater site conditions can be an important secondaryconcern and can have a major impact on exploration strat-egy and cost. Why spend limited lease money on blocksthat will be difficult to drill or develop if equally prospec-tive but less challenging blocks are available? Similarly,why first drill prospects that will be difficult to develop if“easy” prospects are available in your stable of prospects?All else being equal, why not start with the easy sites, andget a (relatively) quick return on investment before tack-ling the tough sites? Or, at the very least, wouldn’t it makesense to know up front that drilling or development maybe difficult? This approach would then allow appropriatebudgeting and planning.

Operators need to be asking these questions and beginevaluating geohazards when developing bidding anddrilling strategies. Figure 8 is an example of a regionaldrilling favorability map developed for part of GreenCanyon and intended for general planning purposes. Onlyseafloor conditions that could affect drilling operationswere considered in constructing this particular map.Subsurface favorability can also be taken into account if ade-quate data are available. The concept is largely independ-ent of scale, and detailed favorability maps are oftendeveloped for individual blocks as well.

Integrated teams. As the case studies show, deepwatergeohazards can have major and sometimes costly implica-tions for development. Consequently, another developingtrend is the early formation of multidisciplinary projectteams including explorers, drillers, and permitting people.No surprises here. In addition, the teams increasingly alsoinclude geotechnical and structural engineers concernedwith siting and design, and both internal and external geo-hazards experts. And this is before the first exploratory wellhas been drilled, not after a discovery well has hit the payzone.

Team members meet in one or more prespud meetings

to consider the acceptable surface locations from a reser-voir standpoint and compare these locations with the geo-hazards assessment and drilling favorability map. Theobjective is to select a well site that eliminates concerns ofall interested parties, from the explorationist to the drillerto the facilities people. The investment in meeting time issmall, but the savings can be millions of dollars consider-ing the possible consequences of not coordinating the needsof each activity required to get oil to market. Can you affordto lose a deepwater well, or site it at a location unfavorablefor development? Can you afford to not do it right the firsttime around?

The right tools. Do you think that deepwater geohazardswill be adequately imaged and correctly identified as partof routine, MMS-required geohazards work? Think again.Historically, standard geohazards survey tools and analy-ses often have not adequately defined deepwater geohaz-ards. Typically, the deeper the water and the more ruggedthe seafloor, the poorer the data quality. Geohazards assess-ment can be particularly difficult when only analog dataare available for these complex areas (yes, low-quality ana-log data are still being used for some deepwater predrillinghazards studies). Or if 2-D digital high-resolution data arecollected, to save money it is often not processed, with thethinking being “the analog monitor records are good enoughto get a drilling permit.” The emphasis is clearly on gettinga permit at the lowest immediate cost, without regard fordrilling performance issues. For example, reduced per-formance could include expensive rig delays or lost wellsbecause geohazards were not identified as a result of inad-equate data. The old adage, “penny-wise, pound-foolish,”applies here.

Fit-for-purpose approach. So, what’s a reasonable approachto deepwater geohazards assessment? Clearly, the mostreliable technical approach to minimize the geohazards riskwould be to use 3-D exploration seismic data for a prelim-inary geohazards assessment, followed by a detailed sitesurvey using high-resolution tools designed for deepwateruse. The survey tools would be some combination of swathbathymetric, deep-tow, digital 2-D high-resolution, andhigh-resolution 3-D tools, depending on water depth, topog-raphy, overall site complexity, drilling experience in theregion, and other factors.

In practice, several approaches have been developed bythe more aggressive deepwater operators. One approachgaining popularity is a modification of the ideal technicalapproach described above. This “fit-for-purpose” approachprovides reliable technical results, gives maximum opera-tional flexibility, and reduces the cost of the geohazardswork. This approach includes two principal phases:

1) 3-D exploration seismic data is first used for geohazardsscreening of the area of interest. A geohazards data ade-quacy map is developed based principally on geologiccomplexity of the area and 3-D data quality (which ulti-mately defines limits of vertical resolution, includingboth strata separability and visibility of gas zones). Thismap shows what types of data are judged to be adequatefor drilling hazards assessment at any given site. Figure9 is a hypothetical example of a geohazards data ade-quacy map. This example map is representative of thosebeing prepared from 3-D seismic exploration data as abasis for planning the optimum approach to deepwatergeohazards assessment.

1) The data adequacy map is independent of scale andcan be prepared for a single block or tens of contiguousblocks. At a minimum, this approach helps organize


Figure 9. Hypothetical example of geohazards dataadequacy map. This example map is representative ofthose being prepared from 3-D seismic explorationdata as a basis for planning the optimum approach todeepwater geohazards assessment.

Dow

nloa

ded

07/0

3/14

to 1

28.8

3.63

.20.

Red

istr

ibut

ion

subj

ect t

o SE

G li

cens

e or

cop

yrig

ht; s

ee T

erm

s of

Use

at h

ttp://

libra

ry.s

eg.o

rg/

thinking and allows an operator to prepare a realistic geo-hazards plan. For example, the type and amount of geo-hazards data needed will partly determine how long itwill take to have geohazards reports prepared and readyfor submittal to the MMS. No one wants to risk havinga deepwater rig waiting on a drilling permit.

1) For areas where the tophole geology is simple, therehas been some drilling experience in the region, and 3-Ddata quality is good, the 3-D data alone may be adequatefor drilling hazards assessment. The MMS has been issu-ing drilling permits under these circumstances on a case-by-case basis. Sometimes, data are reprocessed to ashort-offset volume to improve vertical resolution andfault imaging before being used for geohazards assess-ment.

1) As geologic complexity increases, limited 2-D high-resolution data may be needed to supplement the 3-Ddata. In still more complex areas, a full-blown geohaz-ards survey using a combination of deepwater geohaz-ards survey tools may be needed to adequately assessgeohazards. In either case, the results of the geohazardsdata interpretation should be integrated with the inter-pretation of the 3-D data. Finally, in the most complexareas, or where shallow-water flow is a particular con-cern, a high-resolution 3-D survey may be warranted.Alternatively, the operator may simply decide to avoiddrilling wells in the complex areas, thus eliminating theneed for dedicated geohazards data acquisition.

2) Phase 2 is simply the implementation of the geohazardsplan developed in Phase 1. If a geohazards survey is car-ried out, the data may be adequate for both drilling haz-ards assessment and for later facilities siting and design,depending on the specific tools operated. If only 3-Dexploration seismic data are used for the drilling haz-ards assessment, then additional site-survey data will beneeded if development eventually proceeds.

A question of risk. Within the bounds of any applicableregulations, the decision to use 3-D data alone for deep-water predrilling geohazards assessment is not simply aquestion of technical adequacy but is a question of finan-cial risk. In the end, a business decision must be made asto how much risk is acceptable. “How much insurance doI want to buy?” Thus, the limitations and benefits of 3-Ddata versus other options must be considered on a case-by-case basis and coupled with an operator’s risk philos-ophy to make a decision.

Concluding comments. Complex conditions at many deep-water sites and the potential for costly delays if these con-ditions are not identified and planned for in a timelymanner will result in more emphasis on integrated geo-science/geo-technical site investigations in general, andscreening/preliminary geohazards assessments in partic-ular, than has historically been the case. Because of the highstakes, geohazards will be assessed rigorously and quan-titatively. Increas-ingly, the technology applied to geo-hazards assessment will be essentially the same as thetechnology being applied to prospecting and reservoirevaluation.

Multidisciplinary teams, incorporating exploration geo-scientists, drilling engineers, geotechnical engineers, andsite investigation specialists, working together closelythroughout an exploration/ development sequence, willbe essential to identifying and planning for or avoidingdifficult deepwater conditions, and thus minimizing devel-

opment time and cost.3-D exploration seismic data and high-resolution 3-D

site-survey seismic data will play increasingly importantroles in engineering-geologic and hazard assessment ofdeepwater sites. 3-D exploration seismic data, in particu-lar, will be used for most screening/preliminary assess-ments. High-resolution 3-D data for detailed surveys oftarget sites in complex deepwater areas will become morecommon, especially for facilities siting and design.

Yes, there are real geohazards out there in the deep.But, for the most part, the offshore industry has just begunto deal with difficult deepwater sites, and many hard andexpensive lessons are yet to be learned by those who chargeahead in ignorance of geohazards. Can we really afford tonot do it right the first time?

Suggestions for further reading. “Mechanisms of shallowwater flows and drilling practices for intervention” byAlberty et al. (OTC Proceedings, 1997). “Identification of‘flowing water sand’ drilling hazards in the deepwater Gulfof Mexico” by Byrd et al. (OTC Proceedings, 1996). “Deep-water engineering geology and production structure sit-ing, northern Gulf of Mexico” by Campbell and Hooper(in Advances in Underwater Technology, Ocean Science andOffshore Engineering, Offshore Site Investigation andFoundation Behaviour, Society for Underwater Technology,1993). “Fast-track development: the evolving role of 3-Dseismic data in deepwater hazards assessment and siteinvestigation” by Campbell (OTC Proceedings, 1997). “Drillsite geohazard identification facilitated by rework of suit-able existing 3-D seismic data volumes” by Cowlard (OTCProceedings, 1996). “The use of exploration 3-D data in geo-hazard assessment: Where does the future lie?” by Hill(OTC Proceedings, 1996). “DeepStar’s evaluation of shal-low water flow problems in the Gulf Of Mexico” by Nationsand Medley (OTC Proceedings, 1997). “3-D seismic ampli-tude analysis of the seafloor: an important interpretivemethod for improved geohazards evaluations” by Robertset al. (OTC Proceedings, 1996). “The integration of deepwatergeohazard evaluations and geotechnical studies” by Doyle(OTC Proceedings, 1998). LE

Corresponding author: K. Campbell, [email protected]


Dow

nloa

ded

07/0

3/14

to 1

28.8

3.63

.20.

Red

istr

ibut

ion

subj

ect t

o SE

G li

cens

e or

cop

yrig

ht; s

ee T

erm

s of

Use

at h

ttp://

libra

ry.s

eg.o

rg/

Documents

Deepwater geohazards: How significant are they?