Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

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CHAPTER 6. GENERATING ANISOTROPIC SEISMIC MODELS BASED ON GEOMECHANICAL SIMULATION 4000 σ33 3500 Velocity (m/s) 3000 2500 σ11 2000 1500 0 5 10 15 20 25 30 35 Hydrostatic Pressure (σ 11 = σ 22 = σ 33 ) (MPa) 40 σ33 > σ11= σ22 = 0 (a) (b) 150 4000 Shear Stress (σ 33 − σ 11 ) (MPa) 100 50 0 5 10 15 20 25 30 35 Confining Stress (σ 11 ) (MPa) 40 45 (c) Velocity (m/s) 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 0 5 10 15 20 25 30 Confining Stress (σ 11 ) (MPa) 35 40 (d) Figure 6.9: Panel (a) shows observed and back-calculated P- and S-wave velocities for hydrostatic compression of Berea sandstone. The best fit parameters (ξ 0 and a 0 ) for the hydrostatic case are used to model the uniaxial case (d). The details of the uniaxial experiment are shown in (b) and (c). Experimental data (symbols) from Scott and Abousleiman (2004). Red - V P z green - V P y , black - V P 45 , cyan - V Sxy , yellow - V Syz . due to the fact that cores generally sample more competent zones of a reservoir, and that they may miss larger scale fractures which could increase stress sensitivity, it is of interest to consider how to account for the damage due to coring (or other mechanisms) within the framework of my model. MacBeth and Schuett (2007) demonstrate the effect that damage can have on a sample, though in this case the damage is caused not by coring but by thermal expansion of grains during heating. Figure 6.10 shows measurements of ultrasonic P- and S-wave velocities from samples before and after they have been damaged by heating. Assuming the isotropic background compliance given by MacBeth and Schuett (2007), and an isotropic α, we use (6.37) and (6.38) to find the optimum values of ξ 0 and a 0 that minimise misfit between observed and modelled velocities. Table 6.4 shows the values of ξ 0 and a 0 used to calculate the modelled velocities in Figure 6.10. It is clear that the differences between damaged and undamaged samples can be accounted for solely 124
6.3. A MICRO-STRUCTURAL MODEL FOR NONLINEAR ELASTICITY 4500 4000 3500 10V V undamaged P V undamaged S V damaged P V damaged S 4500 4000 3500 6H V undamaged P V undamaged S V damaged P V damaged S Velocity (m/s) 3000 2500 Velocity (m/s) 3000 2500 2000 2000 1500 0 10 20 30 40 50 60 Pressure (MPa) 1500 0 10 20 30 40 50 60 70 Pressure (MPa) Figure 6.10: Ultrasonic P- and S-wave velocities measured before (black) and after (red) the sandstone samples 6H and 10V (from MacBeth and Schuett (2007)) have been damaged by heating. Damaged samples show a much larger stress sensitivity at low pressures. Best fit initial aspect ratio and crack densities (Table 6.4) are chosen to model the observed variation of velocity with stress. Sample a 0 ξ 0 6H undamaged 0.005 0.07 6H damaged 0.005 0.27 10V undamaged 0.005 0.065 10V damaged 0.005 0.3 Table 6.4: Best fit initial average crack aspect ratios (a 0 ) and densities (ξ 0 ) to used to generate predicted velocities in Figure 6.10. Damaged samples show similar initial aspect ratios but much larger initial crack densities. by the increase in the initial crack density; thus the potential exists to remove the effects of coring damage from the estimates of stress dependent elasticity for in situ rocks. At present, however, I am not able to estimate how much damage the coring process will cause, and hence by how much I should decrease my estimates for ξ 0 when upscaling from lab measurements to in situ rocks. The treatment of SPO anisotropy and core damage serve as an indication of how we might interpret the physical meaning of crack density and aspect ratio. I note at this point that these terms have been developed as theoretical parameters to model stress dependent elasticity. However, they do appear to have a correlation, if only in a qualitative sense, with physical observations such as alignment of elongate or platy grains, or the degree of damage done to a sample. This correlation strengthens my confidence in the conceptual validity of the micro-structural approach for modelling nonlinear stress dependent velocities. It is an interesting and as yet unanswered question as to whether there are any petrofabric analysis techniques might be able to develop quantitative estimates of micro-structural parameters independently from velocity observations. 125
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Microseismic Monitoring and Geomech
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Abstract Capture of CO 2 produced a
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Author’s Declaration I declare th
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Acknowledgments There are many thin
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Table of Contents Abstract Author
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TABLE OF CONTENTS 5.4 Results . . .
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Preface ‘Research is not an end i
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6. D. Angus, J-M. Kendall, J.P. Ver
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1 Introduction A technology push ap
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1.2. CCS OVERVIEW Figure 1.2: CCS s
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1.3. THESIS OVERVIEW for CO 2 to be
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1.3. THESIS OVERVIEW as microseismi
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2 The Weyburn CO 2 injection projec
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2.2. WEYBURN GEOLOGICAL SETTING Fig
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2.2. WEYBURN GEOLOGICAL SETTING N F
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2.4. EVENT TIMING AND LOCATIONS 500
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2.4. EVENT TIMING AND LOCATIONS 500
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2.4. EVENT TIMING AND LOCATIONS Nor
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2.4. EVENT TIMING AND LOCATIONS Fig
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2.5. DISCUSSION 500 1000 1100 North
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2.6. SUMMARY 2.6 Summary • CO 2 s
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3 Inverting shear-wave splitting me
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3.2. INVERSION METHOD the additiona
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3.2. INVERSION METHOD 1. P-wave inc
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3.2. INVERSION METHOD 180 160 140 C
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3.2. INVERSION METHOD 2800 2800 260
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3.2. INVERSION METHOD Loop over γ,
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20 10 5 5 1 20 30 40 80 100 60 40 1
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3.4. SWS MEASUREMENTS AT WEYBURN th
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3.4. SWS MEASUREMENTS AT WEYBURN ei
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3.4. SWS MEASUREMENTS AT WEYBURN ξ
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3.4. SWS MEASUREMENTS AT WEYBURN da
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4 2 2 3.4. SWS MEASUREMENTS AT WEYB
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1 1 1 1 1 1 1 1 1 1 3.5. DISCUSSION
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3.6. SUMMARY 3.6 Summary • I have
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4 A comparison of microseismic moni
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4.2. EVENT LOCATIONS 2400 Velocity
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4.2. EVENT LOCATIONS 200 150 Northi
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4.3. EVENT MAGNITUDES Pressure (MPa
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4.3. EVENT MAGNITUDES 160 140 120 N
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4.4. SHEAR WAVE SPLITTING 50 −3 E
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4.5. INITIAL S-WAVE POLARISATION In
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4.5. INITIAL S-WAVE POLARISATION 6
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4.5. INITIAL S-WAVE POLARISATION of
Page 91 and 92: 4.6. INTERPRETATION OF SHEAR WAVE S
Page 93 and 94: 1 1 5 5 30 4.6. INTERPRETATION OF S
Page 95 and 96: 80 4.6. INTERPRETATION OF SHEAR WAV
Page 97 and 98: 2 3 3.5 4 5 2 1.8 1.4 4 4.6. INTERP
Page 99 and 100: 4.7. DISCUSSION 4.7 Discussion The
Page 101 and 102: pressure, P fl σ ′ ij = σ ij
Page 103 and 104: 5.2. EFFECTIVE STRESS AND STRESS PA
Page 105 and 106: 5.3. NUMERICAL MODELLING 5.3.1 Flui
Page 107 and 108: 5.3. NUMERICAL MODELLING MORE FLUID
Page 109 and 110: 5.3. NUMERICAL MODELLING (a) (b) Fi
Page 111 and 112: 5.4. RESULTS 0 500 1000 Depth (m) 1
Page 113 and 114: 5.4. RESULTS 1 0.9 0.8 Soft Med Sti
Page 115 and 116: 5.4. RESULTS Overburden Extension i
Page 117 and 118: 5.4. RESULTS 1z:100x:100y 1z:100x:5
Page 119 and 120: 5.5. SURFACE UPLIFT 1 0.9 0.8 Soft
Page 121 and 122: 5.5. SURFACE UPLIFT Figure 5.17: Ma
Page 123 and 124: 6 Generating anisotropic seismic mo
Page 125 and 126: 6.2. STRESS-SENSITIVE ROCK PHYSICS
Page 127 and 128: 6.3. A MICRO-STRUCTURAL MODEL FOR N
Page 141: 6.3. A MICRO-STRUCTURAL MODEL FOR N
Page 145 and 146: 6.4. CALIBRATION WITH LITERATURE DA
Page 147 and 148: 6.4. CALIBRATION WITH LITERATURE DA
Page 149 and 150: 6.5. COMPARISON OF ROCK PHYSICS MOD
Page 151 and 152: 6.5. COMPARISON OF ROCK PHYSICS MOD
Page 153 and 154: 7 Forward modelling of seismic prop
Page 155 and 156: 7.2. SEISMODEL c⃝ WORKFLOW time s
Page 157 and 158: 7.3. RESULTS FROM SIMPLE GEOMECHANI
Page 163 and 164: 7.4. SUMMARY 7.4 Summary • I have
Page 165 and 166: 8 Linking geomechanical modelling a
Page 167 and 168: 8.2. MODEL DESCRIPTION Layer Thickn
Page 169 and 170: 8.2. MODEL DESCRIPTION Unit E (GPa)
Page 171 and 172: 8.3. RESULTS Marl Vugg 0.8 0.8 Norm
Page 173 and 174: 8.3. RESULTS 15 10 Injector Produce
Page 175 and 176: 8.3. RESULTS 2000 15 2000 15 1500 1
Page 177 and 178: 8.4. A SOFTER RESERVOIR 8.4 A softe
Page 179 and 180: 8.4. A SOFTER RESERVOIR 2000 15 200
Page 181 and 182: 8.4. A SOFTER RESERVOIR 2000 Max SW
Page 183 and 184: 8.5. DISCUSSION pore-pressure being
Page 185 and 186: 8.6. SUMMARY 8.6 Summary • I appl
Page 187 and 188: 9 Conclusions Geological storage wi
Page 189 and 190: calibrate. This model has been cali
Page 191 and 192: 9.1. NOVEL CONTRIBUTIONS techniques
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9.2. FUTURE WORK Finally, the compa
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Bibliography Abt, D. L., Fischer, K
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BIBLIOGRAPHY Gassmann, F., 1951. Ub
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BIBLIOGRAPHY Kendall, J.-M., Pilido
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BIBLIOGRAPHY Sayers, C. M., 2002. S
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BIBLIOGRAPHY White, D., 2009. Monit
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A List of Symbols The table below l
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B In Support of Carbon Capture and
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Both China and India are aggressive
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Utsira rock properties vary signifi
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