Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

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C in In Chapter 6 (and Angus et al., 2009) we have found that the aspect ratio rarely varies between CHAPTER 7. FORWARD MODELLING OF SEISMIC PROPERTIES 7.2.2 Initialisation In order to ensure that the relative velocities computed using our rock physics model match the relative stiffnesses of the materials used in the geomechanical modelling, I use an initialisation procedure such that the initial stiffness is set to be equal to that used to compute the geomechanical deformation, C mech =C in . These values can be increased by a specified percentage to represent the fact that dynamic stiffness (the stiffness used to calculate seismic velocities, which are low strain and high strain rate) is generally observed empirically to be larger than static stiffness (used to calculate geomechanical deformation, which has high strain at a low strain rate). By doing so I preserve the relative stiffness differences between reservoir and non-pay units, although absolute values are increased for the dynamic stiffness. I will refer to the stiffness used to compute the initial seismic velocities as C in , while recognising that it may be equal to, or tied to, the geomechanical stiffness C mech . Alternatively, where the seismic velocities of layers are known, these can be used to define sedimentary rocks, so I specify that the initial average aspect ratio a 0 is fixed. This means that there are two parameters that can be varied to ensure that the dynamic stiffness tensor, C, at the initial ρ d ρ fl Φ K fl P fl C mech C in σ ij β w ξi 0 a 0 ξ f a f θ f ϕ f ω M g Results from MORE-ELFEN Density of the dry rock Effective density of the multiphase pore fluid Porosity Effective bulk modulus of the multiphase pore fluid Pore fluid pressure Elastic stiffness used to compute geomechanical deformation Elastic stiffness used to compute the initial seismic velocities Stress tensor User-defined inputs Biot-Willis parameter Initial crack density tensor at zero stress Initial crack aspect ratio Number density of any user-defined fracture sets Aspect ratio of any user-defined fracture sets Azimuth of normals to user-defined fracture sets Inclination of normals to user-defined fracture sets Dominant frequency of incident seismic energy, used to compute squirtflow effects Characteristic grain size, used to compute squirt-flow effects Table 7.1: List of SeisModel c⃝ input parameters 136
7.2. SEISMODEL c⃝ WORKFLOW time step, is equal to C in . These are the stiffness of the background rock C r (which corresponds to the idealised case of the rock mass without any compliant porosity); and the initial crack density tensor ξi 0 at zero stress. Hence I have two options for assigning suitable values for these parameters: to fix an initial C r and compute the ξi 0 tensor that produces a stiffness that matches Cin ; or to fix the ξ 0 i tensor, and compute the appropriate C r tensor that when combined with the assigned ξ 0 i tensor matches C in . Fixed C r To initialise using a fixed background stiffness, I must first assign this stiffness. This stiffness will be greater than C in , but less than that of the minerals making up the rock, as the effects of stiff, spherical pores must still be accounted for. In order to approximate this stiffness I use C in , and increase it by multiplying by (1 − Φ) −1 , such that C r = Cin 1 − Φ . (7.1) Having approximated C r I compute ξi 0 such that the computed stiffness matches C in at the initial timestep. In order to do this I first compute the requisite crack density at the initial stress conditions. This will be given by the difference in compliance between S r and S in , as by rearranging equation 6.7 we have ∆S = S in − S r . (7.2) In order to compute the unnormalised crack density terms I use the inversion procedure outlined in Chapter 6 to compute the crack density based on an observed stiffness and a background compliance using a Newton-Raphson approach, having first rotated both into a coordinate system defined by the principle stress directions. In this case the ‘observed stiffness’ is C in . The computed crack densities are then normalised using the h i parameter given in equation 6.13. Having computed the normalised crack density at the initial stress conditions, I rearrange equation 6.37, so that the crack density at zero stress, ξ 0 i , is given by ξ 0 i = ξ(σ i ) exp (−c r σ i ) . (7.3) The initial crack density tensor is then rotated back into global (ENZ) coordinates to be used in predicting stress dependent stiffnesses at future timesteps. Fixed ξ 0 i To initialise using a fixed initial crack density, I must compute the crack density at the initial stress conditions, and then remove this additional compliance from S in to give S r . The unnormalised crack density at the initial stress conditions is given by ⎛ ⎞ 0 0 ξ1 0 exp(−c r σ 1 )/h 1 0 0 α = ⎜ ⎝ 0 ξ2 0 exp(−c r σ 2 )/h 2 0 ⎟ ⎠ , (7.4) assuming that the initial crack density tensor has been rotated into the coordinate system of the initial principle stress directions. The second and fourth order crack density tensors are used to 137
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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
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4.6. INTERPRETATION OF SHEAR WAVE S
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1 1 5 5 30 4.6. INTERPRETATION OF S
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80 4.6. INTERPRETATION OF SHEAR WAV
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2 3 3.5 4 5 2 1.8 1.4 4 4.6. INTERP
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4.7. DISCUSSION 4.7 Discussion The
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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 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: 7 Forward modelling of seismic prop
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
Page 193 and 194: 9.2. FUTURE WORK Finally, the compa
Page 195 and 196: Bibliography Abt, D. L., Fischer, K
Page 197 and 198: BIBLIOGRAPHY Gassmann, F., 1951. Ub
Page 199 and 200: BIBLIOGRAPHY Kendall, J.-M., Pilido
Page 201 and 202: BIBLIOGRAPHY Sayers, C. M., 2002. S
Page 203 and 204: 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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