Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

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CHAPTER 6. GENERATING ANISOTROPIC SEISMIC MODELS BASED ON GEOMECHANICAL SIMULATION 2.0 1.8 1.6 1.4 1.2 B N /B T for Clair samples 1784 1788 1909 1950 2194 B N /B T 1.0 0.8 0.6 0.4 0.2 0.0 0 5 10 15 20 25 30 35 40 45 Pressure (MPa) Figure 6.5: Best fit B N /B T as a function of pressure for the Clair samples. 1.0 Bere 4200 Bere 1.0 Penr 4500 Penr 0.8 4000 3800 0.8 4000 Normalized crack density 0.6 0.4 0.2 Velocity (m/s) 3600 3400 3200 3000 2800 Normalized crack density 0.6 0.4 0.2 Velocity (m/s) 3500 3000 0.0 2600 2400 0.0 2500 −0.2 0 50 100 Pressure (MPa) 2200 0 50 100 Pressure (MPa) −0.2 0 20 40 60 Pressure (MPa) 2000 0 20 40 60 Pressure (MPa) Figure 6.6: Second and fourth order crack density components and back calculated velocities for the literature samples. In the same format as Figure 6.4. 2.0 1.8 1.6 1.4 1.2 B N /B T for literature samples Berea sst Penrith sst B N /B T 1.0 0.8 0.6 0.4 0.2 0.0 0 20 40 60 80 100 Pressure (MPa) Figure 6.7: Best fit B N /B T as a function of pressure for the literature samples. 118
6.3. A MICRO-STRUCTURAL MODEL FOR NONLINEAR ELASTICITY 6.3.4 Effects of stress on crack density We know from micro-structural analysis (e.g., Batzle et al., 1980) that cracks and discontinuities are complex features, with rough walls, nonlinear geometry, irregular intersections, and clay or diagenetic infill; however, in the previous section I have shown that by modelling them as highly simplified, rotationally invariant, smooth (penny-shaped), empty features we can still approximate the effective rock properties to a reasonable degree of accuracy. I use this observation to my advantage in order to predict how the effective properties will be influenced by an applied stress field. In effect, this model assumes that the microcracks within the rock will respond to the long duration, high strain, finite strain-rate deformation imposed by geomechanical effects in the same manner as they do to the short duration, infinitesimal strain, high strain-rate deformation imposed by the passage of a seismic wave. Therefore this assumption will only be appropriate as long as the rock doesn’t undergo any plastic or brittle failure during geomechanical deformation. Hudson (2000) and Tod (2002) present analytical models where the aspect ratio and number density of cracks is dependent upon applied stress and fluid pressure. This model considers elastic deformation only, where the permanent deformation of pores into cracks and the development of new cracks is not considered; hence, when the stress state is returned to its original magnitude, the material will relax to its reference state. Hudson (2000) derives an expression for the change in aspect ratio, δa, of a penny-shaped crack due to a change in applied stress and/or fluid pressure, δa = − 2(1 − νr ) πµ r (δσ ij n i n j − β w δP fl ) − a K r β wδP fl , (6.33) where δσ and δP fl are the change in applied stress tensor and fluid pressure, β w is the Biot-Willis parameter, assumed here for simplicity to be unity, n is the crack normal, and µ r , ν r and K r are respectively the shear modulus, Poisson’s ratio and bulk modulus of the matrix in the absence of compliant porosity. The right-hand term a K r β w δP fl of equation 6.33 is small in comparison with the other terms and can be neglected (Hudson, 2000). Integrating equation 6.33 gives a = a 0 − 2(1 − νr ) πµ r σ c(n) , (6.34) where a 0 is the aspect ratio in the absence of an applied stress (or at a pre-defined reference stress). The effects of applied stress and pore pressure combine to give the effective crack normal stress σ c(n) = σ ij n i n j − β w P fl . (6.35) For a crack with an initial aspect ratio a 0 , there will be a critical stress where a 0 = 2(1 − νr ) πµ r σ c(n) , (6.36) and the crack can be considered as closed. Tod (2002) assumes an exponential distribution of initial aspect ratios. If this is the case, then crack density will decrease exponentially with pressure due to crack closure (van der Neut et al., 2007), so that ξ(σ c ) = ξ 0 exp (−c r σ c(n) ), (6.37) 119
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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
Page 85 and 86: 4.5. INITIAL S-WAVE POLARISATION In
Page 87 and 88: 4.5. INITIAL S-WAVE POLARISATION 6
Page 89 and 90: 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 135: 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
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9 Conclusions Geological storage wi
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calibrate. This model has been cali
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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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Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

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