Geomechanics at Weyburn, Redwater and Zama

Transcription

1 Geomechanics at Weyburn, Redwater and Zama Chris Hawkes University of Saskatchewan, Canada (With thanks to sponsors and collaborators named herein) IEAGHG Combined Modelling and Wellbore Integrity Networks Meeting April 27 29, 2011 Perth, Australia

2 Geomechanics Workflow CCS Site selection Site characterization Performance prediction Monitoring Geomechanical Analysis (Semi ) Analytical Modeling Numerical Modeling (2D 3D; Uncoupled Coupled) Field Testing, Logging, Sampling Field Testing, Logging, Sampling

3 Overview Analytical modelling tools Case 1 (Zama): Probablistic modelling to address uncertainties Case 2 (HARP): Full modelling workflow Case 3 (Weyburn): Analytical model aids risk (performance) assessment; refinement of site characterization from ongoing field operations

4 Fluid production or in injection induces stress change within/around reservoir Stress change in surrounding rock (during production) Stress change within reservoir (during production)

5 Induced stress Failure? Matthias et al. (2009)

6 (Semi ) Analytical Models for Stress Change Induced by Fluid Injection or Withdrawal Segall (1985): A plane strain solution for Coalinga reservoir, California Segall et al. (1994): An axisymmetric solution for Lacq gas reservoir, France Rudnicki (1999): Using theory of inhomogeneities to analyze an ellipsoidal reservoir in a full space with elastic properties different from the surrounding rock Fault reactivation analysis Soltanzadeh and Hawkes (2007, 2008): Theory of inclusions and inhomogeneities for stress analysis Coulomb Failure Stress Change (ΔCFS) for fault reactivation analysis; induced fracturing

7 Cross sectional Model Geometry Results may be cast as normalized stress arching ratios: W T e / = ) 2 n = W /( D W D T Solutions expressed in terms of normalized reservoir dimensions: ; ; ; ) ( 2 2) ( 1 1) ( P P P V V H H H H Δ Δ = Δ Δ = Δ Δ = α σ γ α σ γ α σ γ α α α

8 Within the reservoir: Examples of Some Models Reservoir Geometry Induced Stresses Inclusion Theory Induced Stresses Inhomogeneity Theory γ γ α ( H ) α ( V ) γ γ γ α ( H ) α ( h ) α ( V ) = γ α ( h) 1 1 2ν 1 = ν 1 e 1 1 2ν ecos e = 2 3/ 1 ν (1 e ) 1 2ν 1 = 1 ν 1+ e 1 2ν = 1 ν 1 2ν e = 1 ν 1+ e 2 2 e 1 e ecos e 2 3 / (1 e ) 2 γ α ( H ) = γ α ( h) = A1 / A3, γ = α ( V ) A2 / A3 A1 = ( 1+ ν )(1 X 2 + (1 Rμ ) X1) + Rμ ( X 3 + νx 4) A2 = ( 1+ ν )[1 ( Rμ 1) X1 X 2] + Rμ[(1 ν ) X 4 + 2ν X 3 2 A3 = ( 1+ ν )[( Rμ 1) X1 + ( Rμ 1) X 2 + 1] X 1 = S S1122 ) S ( S S X + X γ = S S1122 S3333 X 3 = S3333 S = S S1122 2S3311 α ( H ) = C1 C4, γ α ( h) = C2 / C4, γ α ( V ) = C3 / ; / C * C 1 = (1 2ν )[ R [ e(1 2ν ) + 2(1 ν )] + e] μ * 2 C 2 = (1 2ν )[ Rμ[ Rμe(3 4ν ) + 2(1 + e )(1 ν )] + e] * C = (1 2ν )[ R [2e(1 ν ) + 1 2ν ] 1] e C 3 μ + 4 = R μ 2 * [2(1 + e) (1 ν )(1 ν ) * 2eν (1 2ν ) + R μ * * e(3 4ν )] + e(1 2ν ) 4 ]

9 Outside the reservoir: Examples of Some Models Reservoir Geometry Stress Discontinuity Inclusion Theory Stress Discontinuity Inhomogeneity Theory Dis ( ) γ α (Tangential) 1 2ν = 1 ν These models can be adapted to predict temperature induced stress change Discontinuity Shear moduli ratio (R μ) Along Axis 1 Along Axis 2 Along axis 3 General (inhomogeneity) 0 2 ** * 2(1 + ν ) ( * ** ε N ( 1) + νε N (3)) ε N (1) 1 ν 1 ν Dis (γα(11)) 1 2ν 1 2ν Rμ =1 (inclusion) 0 1 ν 1 ν General (inhomogeneity) 2 ** * 2(1 + ν ) ( * ** ε N ( 1) + νε N (3)) 0 ε N (1) 1 ν 1 ν Dis (γ α(22)) 1 2ν 1 2ν R μ =1 (inclusion) 0 1 ν 1 ν General (inhomogeneity) 2 2 ** * ** * ( νε * ( νε * N ( 1) + ε N (3)) N ( 1) + ε N(3) ) 0 1 ν 1 ν Dis (γ α(33)) 1 2ν 1 2ν Rμ =1 (inclusion) 0 1 ν 1 ν 2 Dis γ α = ε 1 ν Dis ** ( ( H ) ) 1 N ( H ) 2 γ α 1 ν ** ( ( V ) ) = ε N ( V )

10 Case study 1: Acid Gas Injection in the Zama Oil Field

11 Case study 1: Acid Gas Injection in the Zama Oil Field 1967 Discovery Depth ~1500 m Initial P ~14 MPa Oil production: P ~4 MPa Waterflood: P ~24 Mpa

12 Case study 1: Acid Gas Injection in the Zama Oil Field Acid Gas Injection: EOR Disposal / storage 90 m 320 m

13 Geomechanical Characterization Smith et al. (2009)

14 Smith et al. (2009) Numerical Modelling: Response to acid gas injection

15 Idealized Reservoir Shape Zama F Pool 90 m 320 m

16 Idealized Reservoir Shape Zama F Pool

17 Analytical Consistent with Numerical Modelling Results Sideburden σ Hmax direction Sideburden σ Hmin direction Potential for failure IF optimally oriented fractures are present

18 Probabilistic Input Parameters Truncated normal PDF s used in all cases

19 Cumulative distribution of critical pressure change for fracture reactivation in sideburden historical production 1 Prob. Reactivation

20 Cumulative distribution of critical pressure change for fracture reactivation in sideburden injection Prob. Reactivation Results bring focus to future site characterization Presence / orientation of fractures / faults in sideburden

21 Case study 2: Heartland Area Redwater CO 2 Storage Project (HARP)

22 Case study 2: HARP Devonian reef (6 units; 8 facies) 275 m thick; 1000 m depth (shallowest) Storage project focussed on injection into deeper, saline portion of reef Pilot t/d (2012) Commercial scale 1 Mt/yr (2015) Bachu et al. (2010)

23 Phase 1: 1D Mechanical Earth Model Log derived mechanical properties, spliced together using data from three wells In situ stresses from regional data & 1 local estimate Used as input for plane strain geomechanical modelling scenarios, based on assumed uniform pressure increase from 7.5 to 13.6 MPa Ireton Leduc

24 N Plane of cross sections used for plane strain geomechanical analyses σ Hmin

25 4,000 m A 200 m B C Analysis points: A caprock B sideburden C reservoir Plane strain cross section CO 2 plume predicted by preliminary reservoir simulations (Fekete Associates)

26 8,000 m 200 m Plane strain cross section

27 20,000 m 200 m Plane strain cross section

28 Title Results for a point in the caprock, immediately above the centre of the injection zone Dashed lines show initial stress state Low potential for induced fracturing Some potential for reactivation of fractures IF weak and optimally oriented

29 HARP: Preliminary Ground Sfc Uplift Modelling ~ 3 4 cm uplift, depending on dimension of pressurized zone Horizontal Vertical Deformation (m) 8 km 4 km Distance from the reservoir center (km) 20 km

30 A three dimensional cross section of the geological model of the HARP study area, developed by AITF HARP Phase 2

31 100/ W4/0 Title Development of a 3D MEM using data from nearly 100 wells Thanks to Seungjoo Lee (UofA) for work on 67 of these wells

32 100/ W4/0 Title Grad σ v E s Grad σ Hmin Grad σ Hmax

33 3 D perspective view of the distribution of Young s modulus in the 3D MEM GPa N

34 Cross sectional views of the distribution of Young s modulus in the 3D MEM GPa N

35 3D Geomechanical Model Domain Ground Surface Caprock & Reservoir Overburden Underburden

36 3D Geomechanical Model Mesh

37 Leduc Formation Mesh Redwater Reef

38 View of Caprock and Reef from Beneath Leduc Redwater Leduc Reef Leduc Ireton (Primary seal)

39 Preliminary Results Uniform pressure increase throughout reef Horizontal Stress Change in Ireton Formation Compressive Stress Change in Sideburdens Tensile Stress Change Above Reef

40 Next: Export of Pressure Distribution from Reservoir Simulator to Geomechanical Model (1 way coupling) kpa Pressure margin: P limit P Simulation output generated by Fekete Associates

41 Anticipated Modeling Outcomes Assessment of: Primary seal integrity Ground surface deformation Sensitivity to mechanical properties & in situ stresses and some of the following Practical balance between model complexity and simplifications Capabilities / limitations of (semi ) analytical models Effects of cool CO 2 injection

42 Case study 3: Weyburn Project

43 Weyburn Oil Field: The Reservoir - Discovered ~1.4 billion barrels (BBLs) oil - Mississippian carbonates; Midale Member (Charles Fm); Upper Marly ; lower Vuggy ; ~ 20 m thick, fractured - ~ 1500 m depth - 16 Mt injected as of spring 2010

44 IEA GHG Weyburn (- Midale) CO 2 Project Launched in July 2000 by PTRC in collaboration with EnCana (Cenovus) Assess technical and economic feasibility of CO 2 geological storage Funded by 15 industry and government sponsors (Canada, USA, Japan, European Union) Employed 24 technology organizations and some eighty specialists in six countries Phase I: completed September 2004 Final (2 nd ) Phase: Near conclusion download:

45 3D of Numerical Modelling Geometry based on Phase 1 geological model; pressures based on compilation of reservoir pressure history; results indicated upper limit for p res dictated by frac gradient FLAC3D mesh Vertical scale exaggerated J. Jimenez (2006 U. Alberta PhD)

46 Geomechanical properties for Weyburn reservoir and surrounding rock (after Jimenez, 2006) Unit Midale Evaporite Young mod. (GPa) Soft properties Poisson ratio Shear mod. (GPa) Young mod. (GPa) Stiff properties Poisson ratio Shear mod. (GPa) Frict. angle Coulomb properties C (MPa) Marly Upper Vuggy Lower Vuggy Frobisher Evaporite

47 Known that fractures reduce stiffness but difficult to quantify

48 Different scenarios for in situ stresses in the Weyburn field (after Jimenez, 2006) In situ Stress Regime scenario Vertical stress gradient (kpa/m) Minimum horizontal stress gradient (kpa/m) Maximum horizontal stress gradient (kpa/m) Strike slip** Isotropic Normal Thrust ** Base case scenario

49 Containment Risk Workshop: Potential for reactivation of Souris River Fault? Whittaker et al. (2004) Projected plane of Souris River fault (20x vertical exaggeration)

50 Contours of critical pressure for fault reactivation; strike slip stress regime scenario. Lower hemisphere stereographic projection for poles to fault plane. φ fault = 30. Uniform pressure change in flat sheet reservoir Critical Pressures for Souris River Fault Actual Reservoir << Critical Pressure Pressure

51 Microseismic Event Locations Weyburn (plan view) Injection wells Monitoring well Prod. wells Verdon et al. (2011)

52 Microseismic Event Locations Weyburn (cross sectional view) Events clustered temporally (some days with up to 10 events, then weeks with no events). Eventsclusteredspatially,withclusterscenteredonthe production wells to NW and SE, rather than around the injector. Many events appear to be located in the overburden (although depth errors are large up to 100m).

53 Passive Seismic Monitoring and Geomechanical Modelling of CO2 Storage at Weyburn Geomechanical model (ELFEN): Stiff material properties % Change in shear fracture potential, in plan view % change in f p % change in f p Reservoir Overburden Injection wells Prod. wells Model details flat reservoir layer with vertical injector with horizontal producers on either side. Period of depletion before injection begins. We plot fracture potential (f p ) closeness of deviatoric stress to the shear failure envelope a proxy for likelihood of microseismic activity. f p increases around the production wells in the reservoir. Little change in f p in the overburden. This model doesn t help explain why there are events in the overburden.

54 Passive Seismic Monitoring and Geomechanical Modelling of CO2 Storage at Weyburn Geomechanical model (ELFEN): Soft reservoir properties Reservoir Overburden With reduced stiffness of the reservoir in this second geomechanical model, fracture potential increases in the overburden above the producing wells. This may explain why microseismic events are located in the overburden above the producers.

55 Opportunity Strikes Mini-frac Stress Test March 2011 well integrity field program access to Weyburn s regional seal (Watrous Fm.) H p p L. Watrous 1. Create two slots ~2.3 m apart 2. Isolate using packers. 3. Inject fluid into upper slot. 4. Monitor pressure response below middle packer. 5. Interpret system perm. from pressure-time data. t 6. Insert straddle-packer & run a mini-frac! Helps constrain Jimenez (2006) s in-situ stress scenarios.

56 σ Hmin Final ISIP = 22.2 MPa σ Hmin Gradient 16.4 kpa/m

57 THE END Thanks for your attention