Pore-Fluid Composition and Mechanical Properties of the Reservoir

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1 Pore-Fluid Composition and Mechanical Properties of the Reservoir Understanding the Geomechanical Effects of EOR Fluids Reidar I. Korsnes, Ph.D., Mona Wetrhus Minde, Udo Zimmermann, Professor and Merete Vadla Madland, Professor University of Stavanger, The National IOR Centre of Norway, Norway;

2 Introduction Chalk important reservoir rock in the Danish and Norwegian Continental Shelf Seawater is used as pressure support and as an enhanced oil recovery (EOR) method to produce more oil from existing and future reservoirs Great success at the Ekofisk field Initial estimate 18% recovery Today estimate is above 50%

3 Why is seawater injection a success in chalk reservoirs? Experimental studies show that seawater contains divalent ions that enhances oil recovery in chalk reservoirs SO 4 2-, Mg 2+ and Ca 2+ Elevated temperatures improve EOR potential Zhang et al. 2007; Wettability alteration and improved oil recovery by spontaneous imbibition of seawater into chalk: Impact of the potential determining ions Ca 2+, Mg 2+ and SO 4 2-

4 Important to study rock mechanical effects when optimizing brines for EOR Optimized brine studies for EOR purposes are performed in Amott and Hassler cells Spontaneous and/or forced imbibition tests Incremental or no incremental oil production Ambient and reservoir temperature Not performed at reservoir stresses Do not measure core deformation Nagel, 2001

5 Divalent ions are important for oil recovery How do they affect geomechanical properties? Important to perform triaxial tests with EOR brines at realistic stresses and temperatures to evaluate any effects on geomechanical properties Study divalent ions; SO 2-4, Mg 2+ and Ca 2+ How do divalent ions affect rock properties? Adsorption of ions on the chalk surface Dissolution and precipitation of new mineral phases

6 Triaxial testing Simulate reservoir conditions with independent control of pore pressure, vertical and horizontal stresses. Any temperature. Axial and radial strains can be measured Inject brines/oil of desired chemistry and rate Analyze effluent water and rock mineralogy to quantify chemical re-emplacement processes

7 Results from selected experimental studies Triaxial tests with seawater and modified seawater Test temperature Study the effect of individual ions Sulfate, magnesium, calcium and more Chalk mineralogy Non-carbonate minerals Long term testing Flooding rate Porosity and permeability evaluation Simulating reservoir conditions High pore pressure Re-pressurization CO 2 injection Wettability and rock strength Fractures and permeability Micro and nano-analytical studies Rock-brine interactions studied by SEM, MLA, XRD, SSA, density etc.and many more

8 Results from selected experimental studies Triaxial tests with seawater and modified seawater Test temperature Study the effect of individual ions Sulfate, Magnesium, Calcium and more Chalk mineralogy Non-carbonate minerals Long term testing Flooding rate Porosity and permeability evaluation Simulating reservoir conditions High pore pressure Re-pressurization CO 2 injection Wettability and rock strength Fractures and permeability Micro and nano-analytical studies Rock-brine interactions studied by SEM, MLA, XRD, SSA, density etc.and many more

9 Test temperature and brine composition

10 The effect of temperature on mechanical strength (yield & bulk modulus) Example: Un-aged & hydrostatic loaded at 20 C Example: Aged and hydrostatic loaded at 130 C NaCl, MgCl 2, SSW and Na 2 SO 4 NaCl and MgCl 2 SSW and Na 2 SO 4 Yield stress Yield stress Nermoen et al., (2018). Incorporating electrostatic effects into the effective stress relation Insights from chalk experiments. Geophysics. ISSN Volume 83. Issue 3. s DOI: /GEO

11 Why does SO 4 2- result in reduced Adsorption process mechanical strength? Tracer tests: SO 4 2- has a strong affinity towards chalk surface Creates a negative surface charge Megawati et al. (2013): surface charge gives rise to a disjoining pressure between two charged surfaces, which is large enough to affect mechanical properties Megawati M, Hiorth A, Madland MV. The impact of surface charge on the mechanical behaviour of high-porosity chalk. Rock Mechan Eng. (2013) 46:

12 Brine composition affect creep rates Test temperature 130 C SSW and MgCl 2 : highest strain rates NaSO 4,NaCl and CaCl 2 : lowest strain rates

13 Low creep rates Effluent compositions are unchanged during creep SO 4 2- conc. back to original after 2 PV s Strain rate decreases when conc. is back to original

14 High creep rates Injected divalent ions interact with rock Magnesium is retained in all tests and equal concentration of calcium is produced from the rock Sulfate adsorb on chalk surface and/or precipitate as anhydrite (CaSO 4 ) Continuous dissolution - precipitation process

15 The reactive Mg 2+ Magnesium triggers dissolution of calcite, precipitation of secondary minerals and enhanced compaction Could we reduce the effect of magnesium and thus lower the total creep?

16 YES! Excess of Ca 2+ less creep and no net dissolution

17 Chalk mineralogy

18 Chalk type affect compaction behavior Porosity=43.3% Mons core >99 wt% CaCO 3, T=130 C Porosity=43.6% Liege core wt% CaCO 3, T=130 C Important to perform long term tests to detect chemical effects

19 Wettability and rock strength

20 Wetting state affect yield strength Mixed wet cores Water wet cores Kansas chalk Hydrostatic test at 130 C Aging fluids: Heidrun oil and 1.1 M NaCl Jaspreet et al., HOW THE PRESENCE OF OIL AND WATER AFFECTS CHALK MECHANICS AT ISOTROPIC STRESSES, EAGE Conference, Copenhagen 2018

21 Wetting state has limited impact on creep during MgCl 2 injection K1 and K2 Water wet Results similar for seawater K3 and K4 Mixed wet Jaspreet et al., HOW THE PRESENCE OF OIL AND WATER AFFECTS CHALK MECHANICS AT ISOTROPIC STRESSES, EAGE Conference, Copenhagen 2018

22 Micro- and nano-analytical studies

23 From core to pore to field 4 µm Flooding impacts reservoir geo-mechanical parameters Mineralogical alterations at sub-micron-scale Important input to our simulators 10 September 2018

24 Our methodologies Optical petrography FEG-SEM (Field Emission Gun Scanning Electron Microscopy) EMPA (electron microprobe analysis for quantitative chemical analyses) Semi-quantitative mapping with QEMSCAN/MLA (mineral liberation analyser) Focused ion beam scanning electron microscopy (FIB-SEM) Transmission Electron Microscopy (TEM) nanosims (nano secondary ion mass spectrometry) X-ray diffraction (XRD) for mineralogical determination Whole-rock geochemistry (ICP-MS) C-O stable isotope geochemistry on carbonates Si-H/D-O isotope geochemistry on silica 87 Sr- 86 Sr isotope geochemistry on carbonates Identification and quantification of mineral phases with micro- and nanoraman applications SSA

25 Joining forces to recover more IRIS, UiS and IFE CoE: Institute for Planetary Materials (former ISEI), Okayama University Misasa, Japan, Prof Eizo Nakamura (TEM, nanoraman). Research assistant Nina Egeland Luxembourg Institute of Science and Technology (LIST) Luxembourg, Dr. Jean-Nicolas Audinot (NanoSIMS, ionprobe) CoE: Helmholtz Institute Freiberg for Resource Technology, TU Bergakademie Freiberg Germany, Prof Bernhard Schultz, Prof Jens Gutzmer (MLA, microprobe) École Polytechnique Paris, France, Prof Razvigor Ossikovski (nanoraman) University of Münster Münster, Germany, Dr. Christian Vollmer (TEM) Saarland University Saarbrücken, Germany, Dominik Britz (FIB-SEM) Università Bicocca Milano Milano, Italy, Dr. Sergio Andó (MicroRaman) University of Edinburgh Edinburgh, Scotland, Dr. Colin Chilcott (Stable Isotope geochemistry) University of Houston Houston, USA, Dr. Thomas Lapen (Whole-rock and isotope geochemistry)

26 Dissolution and precipitation Field Emission Gun Scanning Electron Microscopy Imaging: Textural changes X-ray analyses (EDS): chemical alterations Unflooded Flooded Liège chalk flooded with MgCl 2 for 1090 days (Minde et al., EAGE - 19th European Symposium on Improved Oil Recovery/IOR Norway 2017)

27 Altered mineralogy Minde et al., September 2018 Liège chalk flooded for 718 days with MgCl 2 and CaCl 2 at 130º C

28 Pore-scale mineralogical investigations 10 µm FIB-SEM Thickness: 100 nm 10 µm 20 µm 4 µm (Minde et al., EAGE - 19th European Symposium on Improved Oil Recovery/IOR Norway 2017)

29 a) b) Pore-scale mineralogical investigations STEM on FIB-SEM samples Liège chalk flooded for 718 days with MgCl 2 and CaCl 2 at 130º C Calcium Magnesium (Minde et al., EAGE - 19th European Symposium on Improved Oil Recovery/IOR Norway 2017)

30 Permeability and mineralogy Mg-carbonate Mg-silicate Clean chalk (Stevns Klint) Silica-rich chalk (Aalborg) (Andersen et al., Comparative Study of Five Outcrop Chalks Flooded at Reservoir Conditions: Chemo-mechanical Behaviour and Profiles of Compositional Alteration. Transport in Porous Media 121.)

31 Permeability and mineralogy Fracture 400 µm Fractured Liège chalk flooded with seawater, 130 C, 34 days Healed? (Minde et al., SCA annual symposium, Snowmass Colorado, 2016)

32 Wetting state has limited impact on mineralogical alterations during MgCl 2 injection Water wet Mixed wet Comparison of water wet and mixed wet cores of Kansas chalk after flooding with MgCl 2 Minde et al., (2018). Mineral alterations in water wet and mixed wet chalk due to flooding of seawater-like brines. IOR NORWAY 18

33 Conclusions Temperature is important Elevated temperatures - brine composition affect geomechanical properties Sulphate adsorption causes reduction in rock strength Creates a disjoining pressure large enough to affect mechanical properties Magnesium enhances compaction during creep Continuous interactions between injected ions and rock at 130 C Precipitation of new mineral phases Ion exchange

34 Conclusions Differences in primary mineralogy and texture affects rock mechanical behavior at similar test conditions Wettability alteration affect yield strength Mixed wet core higher yield strength No difference in creep behaviour between mixed wet and water wet cores Micro- and nano-analytical studies Water flooding causes changes in rock mineralogy Mineralogical alterations are verified by effluent profiles Important input to all models

35 The 2018 user partners and observers:

36 Acknowledgement: The authors acknowledge the Research Council of Norway and the industry partners, ConocoPhillips Skandinavia AS, Aker BP ASA, Eni Norge AS, Total E&P Norge AS, Equinor ASA, Neptune Energy Norge AS, Lundin Norway AS, Halliburton AS, Schlumberger Norge AS, Wintershall Norge AS, and DEA Norge AS, of The National IOR Centre of Norway for support.

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