Water Weakening of Chalk insight from lab experiments and numerical modelling

Transcription

1 Water Weakening of Chalk insight from lab experiments and numerical modelling Aksel Hiorth 25. April 2016 University of Stavanger

2 Work supported by Ekofisk & Valhall license BP Norge AS and the Valhall co- venturer; Amerada Hess Norge AS, AND ConocoPhillips and the Ekofisk co- venturers, including TOTAL, ENI, StatoilHydro and Petoro Norwegian research council IOR Centre of Norway ( )

3 Research Team Rock mechanics Merete V. Madland (UiS), Reidar I. Korsnes (UiS), Anders Nermoen, Kim Andre N. Vorland (UiS) MegawaX MegawaX (UiS, now Statoil), Ola KeXl Siqveland et al. La=ce Boltzman- reacave flow modelling Espen Je[estuen, Jan Ludvig, Janne Pedersen, Olav Aursjø, Aksel Hiorth et al. SEM- Sub micron Mona Minde (UiS- IRIS), Tania Hildebrand- Habel (IRIS, now at the Norgwegian Petroleum department), Udo Zimmermann, Wenxia Wang (UiS) Field Scale simulaaon (IORSim) Jan Sagen ( IFE), Jarle Haukås(Schlumberger), Arild Lohne(IRIS), Jan Nossen(IFE), Jan Ludvig Vinningland(IRIS), Terje Sira (IFE), Aksel Hiorth et al.

4 LocaAon of the Ekofisk Field Ekofisk

5 Recovery

6 Ekofisk compacaon IniXal: T=130C σ v =62 MPa p res =8 MPa σ eff 1MPa During primary deplexon: p res 2MPa σ eff 38MPa

7 ProducAon History (*) Production and injection, thousand bbl/d Average reservoir pressure Subsidence rate Oil Water injection Oil Subsidence rate, cm/yr Pressure, hundred psi Year Ekofisk field production history. The oil rate (green) declined until large-scale water injection (blue) (*)Doornhof D., KrisXansen T. G., Nagel N., Pakllo P., Sayers S. CompacXon and Subsidence, Oilfield Review (2006)

8 Field observaaons of Water Weakening (*) 6yrs CumulaAve CompacAon before water front 2yrs CumulaAve CompacAon aser water front (*) Doornhof D., KrisXansen T. G., Nagel N., Pakllo P., Sayers S. CompacXon and Subsidence, Oilfield Review (2006)

9 CompacAon in lab experiments d P σ r σ a Isotropic pressure Strain ε = Stress L0 L L 0 Water injecxon L HydrostaXc tests 1. Saturate with injecxon fluid 2. p=0.8, σ A, σ r =1.3MPa 3. Heat to 130C. Raise σ A, σ r to ~10MPa 5. Observe creep at const. stress 6. Pass fluid through core

10 σ a Chalk strength depends on pore fluid σ r R. Risnes Deforma)on and Yield in High Porosity Outcrop Chalk, Vol. 26, No. 1-2, pp , 2001 Generalized shear stress, q (MPa) q= σ a σ r ( 0 hydrostatic) Water Glycol and water are fully miscible fluids Oil & Methanol HydrostaXc test Glycol "Dry" chalk Average effective stress, p' (MPa) p = 1/3 ( σ a + 2σ r ) p p ( σ v p p hydrostatic )

11 Why are the cores weaker in water? The principal mechanism causing the water weakening effect is apparently related to the added pressure on the grains caused by a[racxon of water molecules to the chalk surface. The adsorpxon pressure acts like an increase in pore pressure, and thus decreasing the cohesion of the chalk R. Risnes, M. Madland et al. J. Pet. Sci Eng (2005) Water weakening of chalk Mechanical effects of water glycol mixtures

12 AdsorpAon pressure & surface tension Pore collapse à creaxng new surfaces Yield ~ γ cc ( Yiel d dry /Yiel d wet )= 18MPa/10MPa =1.8 ( γ dry / γ wet )= 0.32J/ m 2 /0.15J/ m 2 =2.1 A. Røyne, J. Bisschop, D. Dysthe, Experimental investigation of surface energy and subcritical crack growth in calcite, J. Geophys. Res. 116 (2011)

13 ExplanaAon for field water weakening? 20 Generalized shear stress, q (MPa) Water Glycol and water are fully miscible fluids Methanol Oil & Glycol "Dry" chalk Average effective stress, p' (MPa)

14 Seawater weakens at high T and weaker than NaCl Axial stress [MPa] ~25% reducxon in Yield 0 0,0 0,5 1,0 1,5 2,0 2,5 3,0 Axial strain [%] Axial stress [MPa] ,0 0,2 0, 0,6 0,8 1,0 1,2 1, Axial strain [%]

15 Axial Strain (%) 1,8 1,6 1, 1,2 1,0 0,8 0,6 0, 0,2 Seawater affects creep Seawater DW 0,0 0,0 5,0 10,0 15,0 20,0 25,0 PV

16 What can we learn from geochemical modelling? HKF EOS (*) makes it possible to predict logk, Gibbs free energy, Enthalpy, heat capacity at high P & T Seawater in equilibrium with 25C and 130C (*) Johnson et al. SUPCRT92: A soxware package for calculaxng the standard molal thermodynamic properxes of minerals, gases, aqueous species, and reacxons from 1 to 5000 bar and 0 to 1000 C, Comp. Geo. Sci., 1992

17 Seawater chemistry Ion Molality Na Mg Ca K Cl SO HCO CO Sulphate species, similar equaxons for other species NaSO KSO MgSO CaSO 0 0 Na K + Mg Ca + SO SO , K + SO + SO 2, K 2 KSO, K, K NaSO = CaSO a MgSO = K a = a a KSO = a Na a SO Ca a NaSO a Mg a a a CaSO SO SO a MgSO SO

18 Ion Result, 25 C and 1 bar Molality (Total) Free Ion (percent) Me-SO Pair (percent) Me-HCO 3 Pair (percent) Me-CO 3 Pair (percent) Na Mg Ca K Ion Molality (Total) Free Ion (percent) Ca-anion Pair (percent) Mg-anion Pair (percent) Na-anion Pair (percent) K-anion Pair (percent) SO HCO CO Cl

19 Result, 130 C and 8 bar Ion Molality (Total) Free Ion Me-SO (percent) Pair (percent) Me-HCO 3 Pair (percent) Me-CO 3 Pair (percent) Me-Cl Pair (percent) Na Mg Ca K Ion Molality (Total) Free Ion (percent) Ca- anion Pair (percent) Mg- anion Pair (percent) Na- anion Pair (percen t) K- anion Pair (percent) SO HCO E CO E Cl

20 Mg, SO in seawater alter mineralogy in core Mineral Dolomite CaMg(CO 3 ) 2 Dolomite(ordered) CaMg(CO 3 ) 2 Dolomite(disord.) CaMg(CO 3 ) 2 Huntite CaMg 3 (CO 3 ) Brucite Mg(OH) 2 Magnesite MgCO 3 Anhydrite CaSO Calcite CaCO 3 SSW Q/K SSW wo/so 2- Q/K SSW wo/so 2-,Mg 2+ Q/K SSW wo/mg 2+ Q/K A Chemical Model for the seawater- CO 2 - carbonate system- aqueous and surface chemistry, Hiorth, Cathles et al. SCA, Abu Dhabi, 2008

21 Flow through models Seawater M1 M2 M3 M M Effluent

22 Seawater flooding dissolves calcite and precipitate Mg- carbonates & CaSO wt_calcite wt_dolomite wt_anhydrite dpor_tot dpor_calcite dpor_dolomite dpor_anhydrite Concentration [mol/l] Ca Cl Mg SO SO Mg Ca Cl Distance[m] Distance[m] Time [days] 0.08%/PV dissolve & 0.07%/PV precipitates 0.01%/PV net change Hiorth, A., Je[estuen, E., Cathles L. M., Madland M. PrecipitaXon, dissoluxon, and ion exchange processes coupled with a lakce Boltzmann advecxon diffusion solver GCA, 10 (2013)

23 0.219M MgCl2 flooding à ~0.07 wt% alteraxon per PV à 100/0.07= 129 PV replace all calcite w Mg- carbonates Hypothesis: InjecAon water induces chemical alteraaon and affects Yield and Creep CalculaXons: If Mg and SO is removed from seawater à no(very li[le) chemical alteraxon Seawater (Io=0.657) 0.219M MgCl 2 (Io=0.657) 0.219M Na 2 SO (Io=0.657) Dolomite, hunxte, magnesite, precipitaxon Some dissoluxon of calcite (comparable with NaCl brine)

24 MgCl2 flooding of Liege Flood sequence: M NaCl brine 1-7 days M MgCl days DisXlled water (DW) days M MgCl days 1-3PV /day à ~1880PV Data: Nermoen, A., Korsnes, R. I., Hiorth, A.,Madland M. V. Porosity and permeability development in compacxng chalks during flooding of nonequilibrium brines: Insights from long- term experiment J. Geo. Res. Solid Earth, 120 (2015) Pore Scale Modelling: Pedersen, J., Je[estuen E., Madland, M. V., Hildebrand- Habel, Korsnes, R., Vinningland J. L., Hiorth A. A dissoluxon model that accounts for coverage of mineral surfaces by precipitaxon in core floods Adw. Wat. Res. 87 (2016)

25 Mg loss and Ca gain during flooding Mg 2+ Cl - Ca 2+ Modelling highlight (Pedersen et al.): Literature dissoluxon rates too high only match first week Explained by dynamic reacxve surface area Precipitated minerals partly covers primary minerals

26 10% deformaaon and permeability = f(φ, diss.) compacaon Strain Perm compacaon = dissoluaon k CK (t)= φ(t) 3 /2 τ (1 φ(t)) 2 S(t) 2 φ(t)= φ ε (t)+ φ c (t) Increase in specific surface area explains drop in perm DissoluXon explains increase in porosity Measured: φ(t f ) φ(0) 0%

27 Unflooded Textural changes obvious Axer 1072 days

28 Specific surface area increases! explains perm behavior k CK (t)= φ(t) 3 / 2 τ (1 φ(t)) 2 S(t) 2 ( k( t f )/k(0) )= 1.05mD/0.15mD m 2 /g 3.8 m 2 /g ρ(0) 2.69g/c m 3 ρ(t) 2.9g/c m m 2 /g 8.85 m 2 /g

29 Pore scale simulaaon of alteraaon nm = (6.25 μm)3 350 voxels =. μm Currently working with Sandia NaXonal Lab to obtain high resoluxon of chalk

30 IS IT POSSIBLE TO CONTROL PERMEABILITY BY CHANGING THE CHEMISTRY?

31 Adding Ca stops creep and perm decline Axial creep strain [%] permeabili ty 8,5 8,0 7,5 7,0 6,5 6,0 5,5 5,0,5 Mg 2+ Ca 2+, Creep time [days] 0,30 0,25 0,20 0,15 0,10 0,05 0,00 Ion concentration [mol/l] M MgCl2 ph= M MgCl M CaCl2 + NaOH ph= M MgCl2 + NaOH ph=9.02 Calcium concentration Original Ca2+ in M M CaCl2 + NaOH Magnesium concntration Original magnesium concentration

32 Can Mg- alteraaon explain field water weakening? AlteraXon propagaxon is slow at high T Temperature gradients in field will slow down kinexcs What about SO?

33 12 SO affects Yield (Mg less) Axial stress [MPa] C Na 2 130C L1, NaCl aged 130C L33, NaCl aged 130C L, MgCl2 aged 130C L9, MgCl2 aged 130C L10, Na2SO aged 130C L17, Na2SO aged 130C L6, SSW aged 130C L13, SSW aged 130C 0 0,0 0,5 1,0 1,5 2,0 2,5 3,0 Axial strain [%] Liege chalk, Porosity = %

34 Sulphate adsorbes 0.219M Na 2 SO Increasing adsorption & ionic strength SO Megawati, M., Hiorth, A., Madland, M.V., (2012), The impact of surface charge on the mechanical behaviour of highporosity chalk, Rock Mechanics and Rock Engineering-Springer

35 Sulphate adsorpaon! neg surface charge Surface complexaxon model (*) à predict ψ from adsorpxon ξ 0 e Fψ/RT (*) Hiorth, A., L. M. Cathles, Madland M. V. (2010). "The Impact of Pore Water Chemistry on Carbonate Surface Charge and Oil We[ability." Transport in Porous Media 85(1): 1-21.

36 Weakening effect by disjoining pressure Disjoining pressure: I 1/2 Z i 2 m i Results from (*) shows that reducxon in Yield follows formula obove Megawati, M., Hiorth, A., Madland, M.V., (2012), The impact of surface charge on the mechanical behaviour of high-porosity chalk, Rock Mechanics and Rock Engineering-Springer

37 Summarize Water Weakening Pore collapse due to Lower cohesion Surface tension (adsorpxon pressure) Chemical effects Textural changes (dissoluxon/ precipitaxon) (slow) (Mg- carbonates) Surface charge (fast) (SO - absorpxon) physical

38 Next crucial steps Can chemical water weakening explain Ekofisk compacxon? Need to Xe chemical alteraxon to field data IOR Center project Add geochemistry to reservoir simulaxon Predict alteraxon Compare with Ekofisk data

39 IORSim (*) - An add on tool to ECLIPSE for fast and accurate simula=on of mul= phase geochemical interac=ons at the field scale Eclipse Reservoir simulator Restart Files Sw, Po, Pw, qw IORSim (*) advect components Geo- chemistry Oil Rate Mg Water Rate SO (*) Hiorth, A., Sagen J., Lohne L., Nossen J., VinninglandJ., Sira, T.IEA, Sapporo, Japan (2015)

40 Simulated Ekofisk sector INJ I Produced water composiaon Mg ions INJ II PRD I INJ III Reservoir ph SO Model Temp Gradients SO Model Constant Temp

41 IORSim Backward coupling Eclipse Reservoir simulator Files Geo- chemistry IORSim Temp First step use Ocean technology Schlumberger

42 Example core flood Run Eclipse Δt Stop Eclipse process Run IORSim Δt,, calc X Update SATNUM

43 Summarize Lab Water weakening can be explained by: Change in surface energy (lower cohesion) Chemical dissoluxon InteracXon energy (disjoining pressure) Field water weakening: Need to couple flow and geochemistry Predict chemical alteraxon speed & compacxon Compare with field data (IOR Centre)

44 IOR NORWAY 2016 April For more informaxon: uis.no/ior

45 Monitoring CompacAon. Results from compacxon monitoring tool can prove to be crixcal to understanding the nature of the compacxon phenomenon The water weakening effect on reservoir compacxon and seabed subsidence has been verified by direct field measurements including reservoir compacxon, water saturaxon and pressure profiles in a verxcal monitoring well Depth (ft) C-11A Cumulative Compaction Rate Cumulative Compaction Rate (cm/year) N. B. Nagel Jun9-Jan95 Jan95-Jun95 Jun95-Nov95 Nov95-Jun96 Jun96-Mar97 Mar97-Jun97 Jun97-Feb98 5 Feb98-Oct98 Oct98-Apr99 Apr99-Jan00

46 Sulphate adsorbes Increasing adsorption SO Megawati, M., Hiorth, A., Madland, M.V., (2012), The impact of surface charge on the mechanical behaviour of highporosity chalk, Rock Mechanics and Rock Engineering-Springer

47 Discuss water weakening Highlight Pore fluid important for rock strength Ekofisk field vs lab Explained by Physical effects Surface tension Chemical effects Upscaling DissoluXon, precipitaxon, adsorpxon TranslaXng core data to field