Presentation to GNS Workshop on Environmental Impacts of Geothermal Development by Michael S. Bruno, PhD, PE GeoMechanics Technologies (formerly Terralog Technologies USA) Subsurface and Surface Deformation Analysis Simulation Methods Calibration with Field Observations Surface Displacement Measurements Subsurface Well Deformation Measurements Inversion of Measured Surface Deformations to Evaluate Subsurface Source Mechanisms Discussion
The weight of sediments overlying an oil or gas reservoir is supported partially by the rock matrix and partially by the pore fluid pressure. When fluid or gas is produced more of the overburden load is transferred to the rock matrix, resulting in reservoir compaction. Changing temperature will create additional compaction or expansion proportional p to the temperature change times the coefficient of thermal expansion. The subsurface dilation (or compaction), H, of a reservoir element of initial thickness, H, can therefore be estimated as: DH = * T*H H + Cm* P*H
Lost Hills, California Interferogram 3D or 2D Geomechanical Modeling to assess overburden stress and deformation details are best when calibrated against field data
Compaction and shear strains in a reservoir and resulting surface deformations can be estimated by techniques of varying complexity: 1. Relatively simple analytical models and spreadsheets 2. 3D influence function models (tied to reservoir simulation) 3. 2D cross-section geomechanical models (typically in parametric mode) 4. 3D geomechanical reservoir models and wellbore models Simple analytical estimates: S = 2 (1- )[H (R 2 +(D+H) 2 ) 0.5 + (R 2 +D 2 ) 0.5 ](Cm P+ T) ( subsidence ) c = 05(1 0.5(1+cos2 ) (Cm P+ T) ; (casing compression) c = 0.5(sin2 ) (Cm P+ T) ; ( casing shear )
Three-dimensional elastic models: Reservoir production layers can be discretized into a 3-D assembly of elements, which can often match reservoir simulation grids. Analytical solutions are then available to estimate displacements and strains induced on any well trajectory or on any horizon due to the combined influence all compacting reservoir cells. ij (x,y,z) = F ij (x-x x n,y-y y n,z-z z n, V n ) Layer Thickness (ft) 0 20 40 60 80 100 120 140 160 180 200 220 240 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 3514000 3514000 Northing 3513000 3513000 3512000 3512000 3511000 3511000 619000 620000 621000 622000 623000 624000 625000 Easting 619000 620000 621000 622000 623000 624000 625000
Apply geomechanical reservoir models or simple analytic equations to estimate t compression and shear along well trajectories 0 2000 Strain Plot Easting (ft) 2230000 2235000 2240000 2245000 2250000 2255000 2260000 2265000 2270000 2275000 2280000 0 4000 6000 8000 5000 Depth 10000 12000 10000 14000 Z Depth (ft) 16000 18000 15000 B45 B2 B3 B4 20000-0.01 0.00 0.01 0.02 0.03 0.04 0.05 Strain 20000 25000
Y X Influence Function Technique Applied to Deepwater Gulf of Mexico Compaction Y 9500 10000 10500 11000 Strain exx Strain eyy Strain ezz X De epth (fttvdss) 11500 12000 12500 13000 13500 14000 Sigh(D)-122 perforation: 13243-13409ftTVDss 14500 15000 15500 16000 compression tension -2.00% -1.50% -1.00% -0.50% 0.00% 0.50% 1.00% 1.50% MI623-C1 Strain (1986-2000)
2D FE Cross-Section Models to analyze Subsidence/Heave, Faulting, and Bedding Plane Slip 0.0 m 0.1 m 0.2 m Block Group Tertiary Cretaceous Jurassic Kungurian Reservoir Early_Paleozoic Vertical Displacement Within Model Total Vertical Displacement due to Pressure + Temperature Change (m)
Geomechanical Issues in Thermal Operations - Reservoir compaction and expansion - Bedding plane slip and associated well damage - Induced fracturing and faulting in caprock - Non uniform, anisotropic changes in permeability and mobility
Recommended Modeling Approach for Subsidence and Caprock Integrity Analysis 1. Start with detailed reservoir simulation model (if available) 2. Embed this grid into 3D influence function and/or FE type geomechanical model 3. Use log and core data and well test data to define geomechanical properties 4. Apply pressure and temperature results from reservoir simulation as input to geomechanical model (essentially one-way coupling) 5. Perform combined geomechanics/thermal simulation to assess induced stresses and deformation in overburden formations 6. Calibrate model against historical surface deformation data (if available) 7. Assess shear and tensile stresses induced in the reservoir and caprock by thermal injection and production operations. 8. History match for period over which field data is available, then perform forward simulations (with periodic updates).
Types of Field Measurements for Deformation 1. Precision level surveying of benchmarks with field crews 2. GPS monitoring (valuable for combined vertical and horizontal movements) 3. Satellite interferometry 4. Surface and shallow wellbore tiltmeters 5. Well deformation and damage surveys
Reservoir Compaction and Expansion: H/H = Cm P+ T Lost Hills, California Interferogram
+285 mm +200 Cold Lake Cyclic steam +100 +260-210 +130 mm Vertical displacements (mm) over 86 days km -165 heave subsidence mod. Stancliffe & van der Kooij, AAPG 2001
WELL AGI1 DEPTH (m) 120 Mudstone & Sand 140 Oil Sand WELL AGI3 160 Limestone Phase A I -20-10 0 10 Deflection (mm) 180-10 0 10 20 Deflection (mm) ref Collins (1994); ref. Ito & Suzuki (1996)
Some Challenges and Approaches to Geomechanical/Thermal Simulation In general, there are no adequate models for fully coupled multiphase flow simulation and geomechanical simulation Therefore, a combination of models with one-way coupling provides better accuracy Detailed pressure/temperature simulation generally only available for reservoir formations ( primarily because that is where history matching can be done ) Therefore, only heat conduction simulation applied to overburden Detailed geomechanical data rarely available for overburden formations and full 3D modeling of formation and overburden problematic ( ~ 1,000,000 grid elements) Therefore, apply a limited full 3D model (1/4 of field), or a series of 2D sections in combination with influence function modeling.
3D Geomechanical Model Created to Simulation Steam Injection and Production for NE Quadrant of Pad 40 (where surface deformation data is available) Reservoir Sections
-650-550 -650-550 Surface and Subsurface Deformation Modeling -450-450 TVD from Surface (m) -350-250 TVD from Surface (m) -350-250 -150-150 -50-50 50 1000 1500 2000 2500 3000 3500 Bulk Density (kg/m^3) 50 100 200 300 400 500 600 700 Acoustic Velocity (micro-sec/m) 650 550 450 Bulk density log and Sonic log from well 1AA031 and the resulting estimated Young s Modulus ace (m) TVD from Surfa 350 250 150 50-50 0 5 10 15 20 25 30 E (GPa)
FLAC3D 2.10 Step 5701 Model Perspective 11:17:58 Tue Feb 27 2007 Center: Rotation: X: 3.602e+002 X: 20.000 Y: 3.142e+002 Y: 0.000 Z: 2.919e+002 Z: 30.000 Dist: 2.374e+003 Mag.: 0.7 Ang.: 22.500 Plane Origin: Plane Normal: X: 0.000e+000 000e+000 X: 0.000e+000 000e+000 Y: 0.000e+000 Y: 0.000e+000 Z: 5.100e+001 Z: 1.000e+000 Job Title: pad50_inj_jan30.dat: Peace River Pad_50 NE Section 3D Reservoir Modeling + 650 m Block Group Axes quaternary base_fish paddy_cadotte notikewin falher wilrich_sandstone wilrich_shale bluesky_sandstone detrital dblt debolt Linestyle Contour of Temperature (518943, 6243807) Y Z X 0 sea level - 100 m (519543, 6243207) Terralog Technologies USA, Inc. Arcadia, CA, 91006, USA (518943, 6243207) Geomechanical model for Pad 50 NE Sector with dimension shown. Also showing sample contour plot of temperature distributions at reservoir level during injection period.
FLAC3D 2.10 Step 5501 Model Perspective 14:37:10 Thu Feb 15 2007 Job Title: inj_198-140_sh-sv_jan22: Peace River Pad_40 NE Section 3D Reservoir Modeling Center: Rotation: X: 6.859e+002 X: 0.000 Y: 6.383e+002 Y: 0.000 Z: 1.619e+002 Z: 30.000 Dist: 4.583e+003 Mag.: 1.25 Ang.: 22.500 Block Group quaternary base_fish paddy_cadotte notikewin Axes falher wilrich_sandstone wilrich_shale bluesky_sandstone detrital debolt Linestyle Y Z X Terralog Technologies USA, Inc. Arcadia, CA, 91006, USA Contour of reservoir dilation due to steam injection from 10-20-2002 to 12-15-2002 (deformed mesh magnified by a factor of 100).
Measured surface changes during 1 st production period from 2002-12-15 to 2003-06-13 6246513.5 6246413.5 6246313.5 6246213.5 10 5 0 Coordinate Y 6246113.5 6246013.5 6245913.5 6245813.5 6245713.5-5 -10-15 -20-25 -30-35 -40 6245613.5 6245513.5 515220.5 515420.5 515620.5 515820.5 516020.5 Coordinate X
6246513.5 6246413.5 6246513.5 6246413.5 mm 2 0 6246313.5 10 5 6246313.5-2 -4 Coordinate Y 6246213.5 6246113.5 6246013.5 6245913.5 0-5 -10-15 -20-25 Y - Coordinate (m) 6246213.5 6246113.5 6246013.5 6245913.5-6 -8-10 -12-14 -16-18 6245813.5 6245713.5 6245613.5-30 -35-40 6245813.5 6245713.5 6245613.5-20 -22-24 -26-28 6245513.5 515220.5 515420.5 515620.5 515820.5 516020.5 Coordinate X 6245513.5 515220.5 515420.5 515620.5 515820.5 516020.5 X - Coordinate (m) Measured Simulated
QA-9 QA-13 QA-8 Water treatment and Steam Raising Plant QA-2 Aa Ab Ac Ad Ba Bb Flowline QA-17 QA-15 Dd Bc QA-10 fractu ture GOC 238 mss QA-20 QA-19 QA-18 QA-14 QA-16 QA-7 Steam injector Producer Observation well Monitoring well Dc Db Da Cd Cc Ca Cb Bd
Well QA-1H Sonic Log -20-40 -60-80 TVDss (m) -100-120 -140 100-160 TVDss (m m) 0-100 -200-300 -400-500 Upper UER Middle UER Base UER Natih C Natih D Natih E Natih F Natih G Nahr Umr Shuaiba Kharaib Lekhwair Habshan -180 0 100 200 300 400 500 600 700 800 Acoustic (ms/m) -600-700 12000 10000 8000 6000 4000 2000 0 Lateral Distance (m)
FLAC3D 2.10 Step 10100 Model Perspective 11:28:35 Thu Jan 19 2006 Job Title: Yr25-Yr00_dT_Jan18: Qarn Alam Caprock Integrity Study, NE-SW X-Section Center: Rotation: X: 6.555e+003 X: 0.000 Y: 1.000e+001 Y: 0.000 Z: -2.825e+002 Z: 180.000 000 Dist: 3.319e+004 Mag.: 3.05 Ang.: 22.500 Block Group fars upper_uer middle_uer base_uer natih_c natih_d natih_e natih_f natih_g nahr_umr shuaiba kharaib lekhwair habshan reservoir 12000 m 0 m
0 0.20 200 0.18 0.16 2D Geomechanical Model 3D Geomechanical Model 400 0.14 Depth (m) 600 800 ace Displacement (m) Surfa 0.12 0.10 0.08 0.06 0.04 1000 0.02 0.00 1200 507000 508000 509000 510000 511000 512000 513000 514000 515000 X - Easting (m) -0.02 12000 11000 10000 9000 8000 7000 6000 5000 Lateral Distance (m) 4000 3000 2000 1000 0 Ang.: 22.500 Contour of Z-Displacement Magfac = 1.000e+003 Exaggerated Grid Distortion -1.5034e-002 to 0.0000e+000 0.0000e+000 to 2.5000e-002 2.5000e-002 to 5.0000e-002 5.0000e-002 to 7.5000e-002 7.5000e-002 to 1.0000e-001 1.0000e-001 001 to 1.2500e-001 001 1.2500e-001 to 1.5000e-001 1.5000e-001 to 1.7500e-001 1.7500e-001 to 1.9304e-001 Interval = 2.5e-002
16 1.20E+04 14 1.00E+04 12 Field Data 8.00E+03 Displacement (mm) 10 8 6 Model Results Sxz (kpa) 6.00E+03 4.00E+03 2.00E+03 0.00E+00 4-2.00E+03 2-4.00E+03 0-6.00E+03-400 -300-200 -100 0 100 200 300 400-8.00E+03 E-W Field Coordinates (m) -1.00E+04 12000 10000 8000 6000 4000 Lateral Distance (m)
Surface Deformation Analysis/Inversion Provides Good Estimates for the Location and Geometry of Subsurface Compaction Sources Bruno, M.S., (1998): Identifying Source Mechanisms Responsible for Subsidence Through Inversion of Measured Surface Displacements, Current Research and Case Studies of Land Subsidence, J. Borchers (ed), Land Subsidence, Case Studies and Current Research, Special Pub. No 8, Association of Engineering Geologist, 1998, pp. 441-450. Bruno, M.S. and Bilak, R.A., (1994): Cost-effective monitoring of injected steam migration using surface deformation analysis, SPE 2788, Proc. West. Reg. Mtg. of the Soc. Pet. Eng., March 23-25, 1994, pp. 397-411 Shape and extent of surface deformation indicates depth and extent of subsurface source mechanism
General Inversion Approach: 1. Discretize subsurface compaction (dilation) zone into source elements, which may be grid volumes (for distributed temp and pressure) or planes (for fractures or faults). 2. Develop 3D influence functions (or FE model) to predict surface deformation due to subsurface effects U i = f( P, T, x, y, z); U i,j = g( P, T, x, y, z); 3. Measure surface deformations (ideally vertical, horizontal, and tilt) 4. Iterate over a range of constrained subsurface parameters and pressure/temperature distributions to minimize error between measured and predicted values, identifying subsurface source mechanisms.
Contour of Z-Displacement Magfac = 0.000e+000-7.0000e-002 to -7.0000e-002-6.5000e-002 to -6.2500e-002-5.7500e-002 to -5.5000e-002-5.0000e-002 to -4.7500e-002-4.2500e-002 to -4.0000e-002-3.5000e-002 to -3.2500e-002-2.7500e-002 to -2.5000e-002-2.0000e-002 to -1.7500e-002-1.2500e-002 to -1.0000e-002-5.0000e-003 to -2.5000e-003 2.5000e-003 to 5.0000e-003 5.0000e-003 to 5.0000e-003 Interval = 2.5e-003 Terralog Technologies USA, Inc. Arcadia, CA 91006 Simulated vertical displacement contours with slipping fault Simulated vertical displacement contours with slipping fault extending through Cretaceous
0.005 0-0.005 Eleva ation Change (m) -0.01-0.015015-0.02 Benchmarks: May 01 - Sep 02 No-fault Model Truncated Fault Model -0.025 Surface Fault Model -0.03-1000 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Distance (m) Comparison of measured and simulated subsidence patterns for period from May, 2001 to September, 2002
Recommended Modeling Approach for Subsidence and Caprock Integrity Analysis 1. Start with detailed reservoir simulation model (if available) 2. Embed this grid into 3D influence function and/or FE type geomechanical model 3. Use log and core data and well test data to define geomechanical properties 4. Apply pressure and temperature results from reservoir simulation as input to geomechanical model (essentially one-way coupling) 5. Perform combined geomechanics/thermal simulation to assess induced stresses and deformation in overburden formations 6. Calibrate model against historical surface deformation data (if available) 7. Assess shear and tensile stresses induced in the reservoir and caprock by thermal injection and production operations. 8. History match for period over which field data is available, then perform forward simulations (with periodic updates).