Removal of mud components from reservoir sandstone rocks
Ingebret Fjelde
University of Stavanger and IRIS
Lunch & learn
University of Stavanger, 25 November 2016
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Outline
› Background
› Water-based mud (WBM)
› Oil-based mud (OBM)
› Conclusions
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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.
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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
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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
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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
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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
Element First FW injection Second FW injection
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
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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
Element First FW injection Second FW injection
a. K
b. S
c. Ca
d. Mg
e. Na
Fjelde, I., Omekeh, A.O. and Minde, M.W. 2015. SCA2015-016.
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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
Fjelde, I., Omekeh, A.O. and Minde, M.W. 2015. SCA2015-016.
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KCl-mud / After water flood - SEM
Barite and clay Barite and clay
Fjelde, I., Omekeh, A.O. and Minde, M.W. 2015. SCA2015-016.
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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
Fjelde, I., Omekeh, A.O. and Minde, M.W. 2015. SCA2015-016.
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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
Fjelde, I., Omekeh, A.O. and Minde, M.W. 2015. SCA2015-016.
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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
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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
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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
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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
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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
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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
Fjelde, I., Omekeh, A.O. and Minde, M.W. 2015. SCA2015-016.
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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
Fjelde, I., Omekeh, A.O. and Minde, M.W. 2015. SCA2015-016.
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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.
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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
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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
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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
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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.