NIOR Core plug preparation procedures

Transcription

1 NIOR Core plug preparation procedures

2 Introduction Reservoir rock state changed during sampling, mud contamination, storage and cleaning Representative wettability conditions in SCAL and EOR-experiments Water flooding (WF) experiments often reference for EOR flooding experiments Lab experiments? Ingebret Fjelde CorePreparation

3 Gullfaks First Later ROS estimates up to 0.35 and surfactant flooding (SF) extensively studied (Maldal et al. 1998) Sandstone rocks water-wet For several reasons, SF not implemented in the field ROS < 0.20 in high permeability zones of Gullfaks and Statfjord (Maldal et al. 1998) Too high ROS-estimates because original wettability not preserved or restored in experiments or results not correctly scaled (Maldal et al., 1999) Incorrect input from experiments could have led to a costly EOR project, which would not have been approved with correct data Ingebret Fjelde CorePreparation

4 Ingebret Fjelde CorePreparation Ekofisk First Pressure depletion estimate 18 OOIP% Based on experiments, concluded that WF would not improve recovery Later Tor formation Water-wet, confirmed in WF-pilot and implemented (1987) Ekofisk formation Pilots much higher recovery than estimated Increased suspicion against laboratory results (Sylte et al., 1988; Sulak, 1991) Low sulphate concentration as in real FW more water-wet conditions (Fjelde and Asen, 2015) Current recovery estimate 50 %OOIP If first conclusion final, income due to WF would have been lost

5 Objectives Phase 1 Identify critical steps in core preparation procedures and work out proposal for next phases Phase 2 Main objectives 2017 Developing methods to determine whether core plugs are contaminated by mud Investigate oxidation of iron-mineral and effect on wettability Investigate effect of oxygen scavengers (including sequester and buffer) on wettability Ingebret Fjelde CorePreparation

6 Summary Critical steps identified and proposal for next phases worked out (Report IRIS-2015/230 ) Compositions of rock, reservoir fluids and mud system important input to selection of core preparation procedure Mud contamination During preparation, effluent analyses to determine whether core plugs contaminated Difficult to remove mud particles during cleaning Non-destructive methods for determination of cleaning efficiency should be developed Core plugs with mud components that can affect flow properties should ideally not be used Oxidation Wettability of clay altered to less water-wet by low Fe 3+ concentration in FW Ingebret Fjelde CorePreparation

7 Report and publications Fjelde, I Core plug preparation procedure. Technical report IRIS-2015/230 Mud contamination Fjelde, I., Omekeh, A.O. and Minde, M.W Removal of Mud Components from Reservoir Sandstone Rocks. SCA International Symposium of the Society of Core Analysts, St. John s Newfoundland and Labrador, Canada. Fjelde, I Effect of Mud Invasion on the Determined Low Salinity Water Flooding Potential. 19 th European Symposium on IOR, Stavanger, Norway. Oxidation (Preliminary study) Fjelde, I., Omekeh, A.V., and Haugen, P.E Effect of ferrous ion on wettability: Oxidation and cation bridging. SPE Europec at the 79 th EAGE Annual Conference & Exhibition, Paris, France. Ingebret Fjelde CorePreparation

8 Result examples Mud contamination Oxidation Ingebret Fjelde CorePreparation

9 Water-based KCl mud, example Component Function Description Bentonite clay Rheology and filtration control Impure clay mostly montmorillonite Barite Weight material BaSO 4 Fluid loss additives Reduce fluid loss Acid soluble particles Carbon-based particles Modified starch Polymers (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, Na 2 CO 3 Sodium bicarbonate, NaHCO 3 Other Inhibitors, shale, H 2 S scavenger, biocide, defoamer, lubricant Ingebret Fjelde CorePreparation

10 Minerals and rocks Mineral Composition Cation exchange capacity (meq/kg) Bentonite (Na,Ca) 0.33 (Al,Mg) 2 (Si 4 O 10 )(OH) b (mainly montmorillonite) Glauconite (K,Na)(Fe 3+,Al,Mg) 2 (Si,Al) 4 O 10 (OH) a Kaolinite Al 2 Si 2 O 5 (OH) a Quartz SiO 2 Calcite CaCO 3 Reservoir rock 1 (Flotation experiments) 19.8 Reservoir rock 2 (Core flooding experiments) 10 Bentonite high cation exchange capacity Fjelde th European Symposium on IOR. Stavanger, Norway. Ingebret Fjelde CorePreparation

11 Flotation experiments Affinity of minerals to their respective fluid phases Mainly determined by wettability particle, particle size, temperature and interfacial tension Experiments at same temperature and interfacial tension Reference with n-decane to isolate effect of wettability Ingebret Fjelde CorePreparation

12 KCl-mud Flotation experiments Bentonite more oil-wet than dominating minerals in reservoir rock (Glauconite, kaolinite and quartz) Fjelde, I th European Symposium IOR. Stavanger, Norway. Ingebret Fjelde CorePreparation

13 SFW injection before solvent cleaning K effluent concentration High K concentration showed that core plugs contaminated by KCl mud Concentration of other element confirmed contamination Fjelde, Omekeh and Minde SCA St. John s, Newfoundland and Labrador, Canada. Ingebret Fjelde CorePreparation

14 SFW-injection after solvent cleaning K effluent concentration Confirmed K concentration became as in injected FW Concentration of other elements confirmed effluent composition similar as injected FW Fjelde th European Symposium on Improved Oil Recovery. Stavanger, Norway. Ingebret Fjelde CorePreparation

15 SEM after solvent cleaning Mud particles and polymers not removed during cleaning (injection SFW and solvents) Fjelde, Omekeh and Minde SCA St. John s Newfoundland and Labrador, Canada. Element composition EDS-spectra Element Inlet Mid Outlet O Na Mg Al Si S K Ba Fe Ingebret Fjelde CorePreparation

16 SEM after water flooding Mud particles still in rock after water flooding Fjelde, I th European Symposium on Improved Oil Recovery. Stavanger, Norway. Ingebret Fjelde CorePreparation

17 Oil-based mud example Component Function Description Organoclay Rheology together with water phase and emulsifiers Modified bentonite, impure clay mostly montmorillonite Barite Weight material BaSO 4 Emulsifiers (primary and secondary) Fluid loss additives (primary and secondary) CaCl 2 Emulsification and wetting agents Polymer, resins and/or particles Water activity control Lime Activate emulsifiers, reduce corrosion Ca(OH) 2 Fatty acid derivates, polyamide Base oil Continuous phase Petroleum distillate or synthetic oil Water Internal brine phase Ingebret Fjelde CorePreparation

18 OBM STO injection / IFT IFT a. a. between IFT IFT between effluent effluent samples samples and SFW and FW Spontaneous b. Spontaneous imbibition imbibition SFW of formation water MFM = Mud Filtrate Mineral base oil MFS = Mud Filtrate Synthetic base oil Core plugs exposed to MF less water-wet Fjelde, I., Omekeh, A.O. and Minde, M.W SCA Ingebret Fjelde CorePreparation

19 Oxidation Ions Fe 2+ Fe 3+ Effect of Fe 3+ on wettability Oil components Minerals EOR-chemicals Ingebret Fjelde CorePreparation

20 Flotation experiments Glauconite FWs with 50ppm Fe 3+ gave less water-wet glauconite than FWs without Fe 3+ Fjelde, Omekeh and Haugen SPE MS. SPE Europec, Paris, France. Ingebret Fjelde CorePreparation

21 Fraction of surface occupied by multivalent cations Geochemical simulations Minor change in concentration of multivalent cations on clay I.e. no increase in potential for cationbridging on clay surfaces Fe 3+ -hydroxides and/or oxides rather oil-wet Precipitation of Fe 3+ -hydroxides and/or oxides on clay possible reason Fjelde, Omekeh, and Haugen SPE MS. SPE Europec, Paris, France. Ingebret Fjelde CorePreparation

22 Representative rock samples Differential pressure can t confirm that mud contaminations removed Colourless effluent can t confirm that contaminations removed Effluent analyses to determined whether contaminated by mud Type of analysis depends on mud composition Oxidation products affecting wettability should be removed, but without affecting original mineral composition and distribution Cleaning efficiency Non-destructive method not available Analyses of additional plugs or after flooding experiments Ingebret Fjelde CorePreparation