Removal of mud components from reservoir sandstone rocks mud... · Removal of mud components from reservoir sandstone rocks Ingebret Fjelde University of Stavanger and IRIS Lunch

Removal of mud components from reservoir sandstone rocks

Ingebret Fjelde

University of Stavanger and IRIS

Lunch & learn

University of Stavanger, 25 November 2016

Lunch&learn - 251116-UiS/IRIS-IF - 2

Outline

› Background

› Water-based mud (WBM)

› Oil-based mud (OBM)

› Conclusions


Reservoir rock sampling

› Pressure and temperature reduced

• Change of solubility (minerals and fluid components),

adsorption, phase partitioning

• Gas phase formed

› Mud invasion can alter rock properties, e.g.

• Wettability alteration

• Permeability reduction

Lab experiments

?

Marle, C.M. 1991. Oil entrapment and mobilization. In Basic Concepts in Enhanced Oil Recovery Processes. Critical Reports on Applied Chemistry. Volume 33. Ed. Baviere, M. SCI. Elsevier Applied Science.


Representative conditions in lab experiments

› If reference potential (e.g. water flooding) not correct, EOR-potential not correct

› Reservoir temperature and pressure

› Reservoir fluids

• Formation water

• Crude oil

› Injection fluid composition (e.g. water)

› Reservoir rock

• Ideally no contaminations


Water-based mud, example

Component Function Description

Bentonite clay Rheology and filtration control Impure clay mostly montmorillonite

Barite Weight material BaSO4

Fluid loss additives Reduce fluid loss Acid soluble particlesCarbon-based particlesModified starchPolymers (e.g. polyanionic cellulose)

Xanthan Rheology and suspension of particles Biopolymer

Potassium chloride Stabilize formation KCl

pH, brine composition Optimize properties of components, reduce corrosion Lime, Ca(OH)2

Soda ash, Na2CO3

Sodium bicarbonate, NaHCO3

Other Inhibitors, shale, H2S scavenger, biocide, defoamer, lubricant


KCl-mud / High permeability reservoir sandstone

• Cleaning

• Synthetic formation water (SFW) flooding

• Methanol/toluene flooding cycles until colourless effluent

• SFW flooding

• Effluent analysed for elements by Inductively Coupled Plasma (ICP)

• Cleaned reservoir rock

• Wettability characterization by spontaneous imbibition + forced imbibition using synthetic oil

• Crushed rock

• Scanning Electron Microscopy (SEM)

• Dichloromethane extracts analysed to characterize oil residue


KCl-mud / SFW before solvent cleaning

Effluent potassium (K) concentration Effluent sodium (Na) concentration

K first much higher than in SFW Na first much lower than in SFW

Similar profiles Ca and Mg

Element First FW injection Second FW injection

a. K

b. S

c. Ca

d. Mg

e. Na


a. K

b. S

c. Ca

d. Mg

e. Na

Core plugs contaminated by KCl-mud

Fjelde, I., Omekeh, A.O. and Minde, M.W. 2015. Removal of Mud Components from Reservoir Sandstone Rocks. SCA2015-016. International Symposium of the Society of Core Analysts


KCl-mud / SFW after solvent cleaning

Effluent K concentration

› Many PV of SFW required

› Usually not verified by analysis

› Change in brine composition can’t be detected by differential pressure

› K higher in beginning

› At the end Na, Ca and Mg also as in SFW


a. K

b. S

c. Ca

d. Mg

e. Na

Fjelde, I., Omekeh, A.O. and Minde, M.W. 2015. SCA2015-016.


KCl-mud / SEM cleaned reservoir rock

• Invasion particles and polymers can reduce permeability

• Invasion particles, especially clay, will increase surface area and may affect established wettability

Element Inlet Mid Outlet

O 36.3 37.7 38.5

Na 1.2 0.6 0.4

Mg 0.1 0.1 0.2

Al 6.9 6.6 5.4

Si 45.5 43.6 45.2

S 1.0 0.9 1.0

K 3.8 5.3 4.0

Ba 3.7 3.5 3.5

Fe 1.5 1.8 1.8

Element composition EDS-spectra



KCl-mud / After water flood - SEM

Barite and clay Barite and clay



KCl-mud / Oil residue

Core plug crushed and extracted

GC STO GC outlet

All crude oil not removed

Sample

id

Extracted material

(mg/kg Rock)

Inlet 62

Mid 132

Outlet 604



KCl mud / Wettability characterization

Cleaned core plugs prepared with Isopar H (synthetic oil)

› Water-wet rock

• Spontaneous imbibition of SFW

– Rather high and fast

• Forced imbibition

– No additional oil produced

– No capillary end effects

› Invasion of particles may still affect wettabilityestablished during aging with crude oil



Oil adsorption lower for KCl than FW

Injection of STO to reservoir rock saturated with brine

Fjelde, I., Polanska, A.P., Taghiyev, F.T., and Asen, S.M. 2013. Low Salinity Water Flooding: Retention of Polar Oil Components in Sandstone Reservoirs.

A24. 17th European Symposium on Improved Oil Recovery, St. Petersburg, Russia, 16-18 April.

KCl earlier breakthrough of polar oil components


Bentonite rather oil-wet

0

10

20

30

40

50

60

70

Kaolinite Calcite Quartz Bentonite

oil-

wet

(%

)

Crude oil 1

Crude oil 2

Wettability characterized by flotation (%oil-wet particles)

Invasion of bentonite can give too oil-wet rock

Kirkhus, H., 2015. Effect of Oil Composition on Wettability Characterized by Flotation. MSc-thesis. University of Stavanger


Oil-based mud, example

Component Function Description

Organoclay Rheology together with water phase and emulsifiers Modified bentonite, impure clay mostly montmorillonite

Barite Weight material BaSO4

Emulsifiers(primary and secondary)

Emulsification and wetting agents Fatty acid derivates, polyamide

Fluid loss additives (primary and secondary)

Polymer, resins and/or particles

CaCl2 Water activity control

Lime Activate emulsifiers, reduce corrosion Ca(OH)2

Base oil Continuous phase Petroleum distillate or synthetic oil

Water Internal brine phase


Organoclay stabilized emulsion

Fjelde, I. 2009. Formation Damage Caused By Emulsions During Drilling With Emulsified Drilling Fluids.

SPE 105858. SPE Drilling & Completion, June: 222-228.

Without organoclay

25m

With organoclay

25m

Interference contrast microscopy

5m


OBM / STO injection

• Sandstone rock (100-200mD)

• STO aging at Swi

• OBM filtrate aging

• STO injection until constand ΔP

• Emulsifier production by interfacial tension (IFT)

• Wettability characterized by spontaneous imbibition of SFW


OBM STO injection / IFT

a. IFT between effluent samples and FW b. Spontaneous imbibition of formation water

Spontaneous imbibition SFW

Core plugs exposed to MF less water-wet

a. IFT between effluent samples and FW b. Spontaneous imbibition of formation water

IFT between effluent samples and SFW

MFM = Mud Filtrate Mineral base oilMFS = Mud Filtrate Synthetic base oil



OBM / Capillary desaturation curve

Water-wet rock expected in project Methanol cleaning: Unexpected CDC

Methanol/toluene, acetic acid and ethanol cleaning: As expected CDC

Rock composition probablyaltered by acetic acid



CDC Mixed-wet sandstones

› Today many sandstone rocks characterized as mixed-wet

› Atypical CDC wetting phase (Chukwudeme et al., 2014)

› Atypical CDC mixed-wet reservoir rock (Fjelde, Lohne and Abeysinghe, 2015)

Recommended to interpolate between kr(Nc)-curves

0,0

0,1

0,2

0,3

0,4

0,5

0,6

1,E-8 1,E-6 1,E-4 1,E-2

RO

S (

Fra

ctio

n o

f P

V)

Nc = νμ/σ

SF Core 1M

SF Core 2M

SF Core 3M

SF Core 4M

WF Core 2a

SF Core 2a

Chukwudeme, E.A., Fjelde, I., Abeysinghe, K.P., and Lohne, A. 2014. Effect of Interfacial Tension on Water/Oil Relative Permeability

on the Basis of History Matching to Coreflood Data. SPE-143028-PA SPE Reservoir Evaluation & Engineering. Vol 17 (01): 37-48.

Fjelde, I., Lohne, A. and Abeysinghe, K. P. 2015. Critical Aspects in Surfactant Flooding Procedure at Mixed-wet Conditions. SPE-

174393-MS. The EUROPEC 2015, Madrid, Spain, 1-4 June.


Representative rock samples

› Ideally all mud components should be removed

› Differential pressure can’t confirm mud contaminations removed

› Effluent analyses

• Colourless effluent can’t confirm all mud components removed

• Challenge many components in muds

• If mud components easiest to remove still present, rock probably not representative

› Cleaning efficiency

• Additional plugs or after flooding experiments


Conclusions

› WBM contamination

• High permeability sandstone reservoir rock

– Mud contaminations can be difficult to remove, especially particles

– Cleaned reservoir rock water-wet, but clay particle invasion may affect established wettability

› OBM contamination

• Slow release of emulsifiers during STO injection, and core plugs exposed to OBM filtrate less water-wet

• CDC measured for reservoir sandstone rock found to depend on cleaning procedure


Conclusions cont.

› Mud components with potential to affect flow conditions should be removed during cleaning of reservoir core plugs,

otherwise, ideally, these core plugs should not be used

› Recommended to analyse effluent samples for mud components to confirm removal, at least the easiest removable

components

› If not all mud contamination removed, recommended to investigate whether presence of mud components may have

affected the results

› Method for determination of cleaning efficiency should be developed


Acknowledgements

› Lundin Norway for financing and supporting the work on water-based mud presented in this paper.

› National IOR Centre of Norway for support

• Research Council of Norway and the industry partners; ConocoPhillips Skandinavia AS, Aker BP ASA, Eni Norge AS,

Maersk Oil Norway AS, DONG Energy A/S Denmark, Statoil Petroleum AS, ENGIE Norge, Lundin Norway AS,

Halliburton AS, Schlumberger Norge AS and Wintershall Norge AS.

Documents

Removal of mud components from reservoir sandstone rocks mud... · Removal of mud components from reservoir sandstone rocks Ingebret Fjelde University of Stavanger and IRIS Lunch