Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

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100 5 1 20 1 5 60 80 40 CHAPTER 3. INVERTING SHEAR-WAVE SPLITTING MEASUREMENTS FOR FRACTURE PROPERTIES 330° 0° 30° Anisotropy [%] 5 300° 60° 4 3 270° 90° 2 240° 120° 1 210° 180° 150° 0 (a) 0.2 0.18 0.16 100 100 80 60 40 0.2 0.18 0.16 100 60 80 0.14 0.14 40 30 30 10 20 60 80 80 20 40 γ 0.12 0.1 0.08 0.06 0.04 0.02 60 80 100 80 60 40 40 30 20 30 0 0 20 40 60 80 100 120 140 160 180 Fracture Strike (α) 5 10 20 10 1 30 40 30 40 60 60 δ 0.12 0.1 0.08 0.06 0.04 0.02 100 80 80 100 100 60 30 20 30 0 0 20 40 60 80 100 120 140 160 180 Fracture Strike (α) 10 5 1 5 10 20 20 30 40 (b) 0.2 0.18 (c) 0.16 40 10 5 10 30 0.14 0.12 20 10 5 10 20 30 δ 0.1 1 0.08 0.06 1 5 10 20 30 40 60 0.04 40 0.02 5 20 30 0 0 0.05 0.1 0.15 0.2 γ (d) Figure 3.6: Inversion results for the second synthetic example, with subvertical arrivals, in the same format as Figure 3.5. The initial elastic model is also the same. In this case, there is a trade-off between γ and δ, meaning that neither is well constrained. 60 80 40
3.4. SWS MEASUREMENTS AT WEYBURN the different parameters are. In the case with subhorizontal arrivals (Figure 3.5). Fracture strike and γ are well constrained. However, from the elongation of the misfit contours along the δ axis, I infer that this parameter is not as well constrained. This is because splitting of subhorizontal shear waves is not significantly affected by the size of δ, and therefore it does not have an influence on the inversion. For the case with subvertical arrivals (Figure 3.6), there is a trade-off in the inversion between δ and γ, meaning that neither is well constrained. Essentially, for a set of splitting measurements on subvertical S-waves, any modelled value of γ, with the appropriate value of δ, can produce splitting patterns that match well with the actual splitting. For the case with obliquely arriving waves (Figure 3.7) there is still some trade-off between γ and δ, though both are better constrained than with the subvertical arrivals. In all the examples the fracture strike and density are both well imaged. This is because I use a full range of arrival azimuths from 0 - 180 ◦ . Much as horizontal fabrics are most sensitive to the range of arrival inclinations, vertical fabrics (such as fractures) will be most sensitive to the range of azimuths available. As can be seen in Chapter 4, constraints on fracture strike and density will be dependent on the azimuthal range of S-wave arrivals. This section does not intend to cover every possible source-receiver geometry, these will obviously be specific to the problem being investigated. However, I have outlined how synthetic modelling can guide the interpretation of SWS results, and highlight what real data is likely to identify, and what it cannot. This capacity may well be of use to field engineers when selecting sites to place geophones because geophones sites can be selected to maximise the structures that SWS can constrain. In subsequent sections I will construct further synthetic models that are appropriate to the actual problems being investigated. However, before I do so I will first discuss the SWS measurements made at Weyburn. 3.4 SWS measurements at Weyburn 3.4.1 Method In order to analyse SWS, the seismograms must first be rotated into the ray frame coordinates. I do this using the P-wave particle motion orientation to indicate the direction of ray propagation, using the protate algorithm described by Al-Anboori (2006). Where the P-wave has not been picked, or where this does not produce a satisfactory rotation, the events are rotated using the azimuth of the located event from the receivers and the inclination assuming a straight source-receiver path. If SWS has occurred, the S-wave particle motion will be elliptical. However, a rotation of the components by ψ and a time-shift of δt will remove the effects of splitting and leave the particle motion linearised. I use the methodology of Silver and Chan (1991), performing a grid search over ψ and δt to find values that best linearise S-wave particle motion (indicated by a minimised second eigenvalue of the covariance matrix). To ensure a stable and reliable result, the analysis is conducted over a range of windows centred on the S-wave arrivals. This ensures that the result is not dependent on S-wave picking accuracy. 100 picked windows are automatically generated on which to perform the 41
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Microseismic Monitoring and Geomech
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Abstract Capture of CO 2 produced a
Page 7 and 8: Author’s Declaration I declare th
Page 9 and 10: Acknowledgments There are many thin
Page 11 and 12: Table of Contents Abstract Author
Page 13 and 14: TABLE OF CONTENTS 5.4 Results . . .
Page 15 and 16: Preface ‘Research is not an end i
Page 17 and 18: 6. D. Angus, J-M. Kendall, J.P. Ver
Page 19 and 20: 1 Introduction A technology push ap
Page 21 and 22: 1.2. CCS OVERVIEW Figure 1.2: CCS s
Page 23 and 24: 1.3. THESIS OVERVIEW for CO 2 to be
Page 25 and 26: 1.3. THESIS OVERVIEW as microseismi
Page 27 and 28: 2 The Weyburn CO 2 injection projec
Page 29 and 30: 2.2. WEYBURN GEOLOGICAL SETTING Fig
Page 31 and 32: 2.2. WEYBURN GEOLOGICAL SETTING N F
Page 33 and 34: 2.4. EVENT TIMING AND LOCATIONS 500
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Page 37 and 38: 2.4. EVENT TIMING AND LOCATIONS Nor
Page 39 and 40: 2.4. EVENT TIMING AND LOCATIONS Fig
Page 41 and 42: 2.5. DISCUSSION 500 1000 1100 North
Page 43 and 44: 2.6. SUMMARY 2.6 Summary • CO 2 s
Page 45 and 46: 3 Inverting shear-wave splitting me
Page 47 and 48: 3.2. INVERSION METHOD the additiona
Page 49 and 50: 3.2. INVERSION METHOD 1. P-wave inc
Page 51 and 52: 3.2. INVERSION METHOD 180 160 140 C
Page 53 and 54: 3.2. INVERSION METHOD 2800 2800 260
Page 55 and 56: 3.2. INVERSION METHOD Loop over γ,
Page 57: 20 10 5 5 1 20 30 40 80 100 60 40 1
Page 61 and 62: 3.4. SWS MEASUREMENTS AT WEYBURN ei
Page 63 and 64: 3.4. SWS MEASUREMENTS AT WEYBURN ξ
Page 65 and 66: 3.4. SWS MEASUREMENTS AT WEYBURN da
Page 67 and 68: 4 2 2 3.4. SWS MEASUREMENTS AT WEYB
Page 69 and 70: 1 1 1 1 1 1 1 1 1 1 3.5. DISCUSSION
Page 71 and 72: 3.6. SUMMARY 3.6 Summary • I have
Page 73 and 74: 4 A comparison of microseismic moni
Page 75 and 76: 4.2. EVENT LOCATIONS 2400 Velocity
Page 77 and 78: 4.2. EVENT LOCATIONS 200 150 Northi
Page 79 and 80: 4.3. EVENT MAGNITUDES Pressure (MPa
Page 81 and 82: 4.3. EVENT MAGNITUDES 160 140 120 N
Page 83 and 84: 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
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5.3. NUMERICAL MODELLING (a) (b) Fi
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5.4. RESULTS 0 500 1000 Depth (m) 1
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5.4. RESULTS 1 0.9 0.8 Soft Med Sti
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5.4. RESULTS Overburden Extension i
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5.4. RESULTS 1z:100x:100y 1z:100x:5
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5.5. SURFACE UPLIFT 1 0.9 0.8 Soft
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5.5. SURFACE UPLIFT Figure 5.17: Ma
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6 Generating anisotropic seismic mo
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6.2. STRESS-SENSITIVE ROCK PHYSICS
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6.3. A MICRO-STRUCTURAL MODEL FOR N
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6.4. CALIBRATION WITH LITERATURE DA
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6.4. CALIBRATION WITH LITERATURE DA
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6.5. COMPARISON OF ROCK PHYSICS MOD
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6.5. COMPARISON OF ROCK PHYSICS MOD
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7 Forward modelling of seismic prop
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7.2. SEISMODEL c⃝ WORKFLOW time s
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7.3. RESULTS FROM SIMPLE GEOMECHANI
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7.4. SUMMARY 7.4 Summary • I have
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8 Linking geomechanical modelling a
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8.2. MODEL DESCRIPTION Layer Thickn
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8.2. MODEL DESCRIPTION Unit E (GPa)
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8.3. RESULTS Marl Vugg 0.8 0.8 Norm
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8.3. RESULTS 15 10 Injector Produce
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8.3. RESULTS 2000 15 2000 15 1500 1
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8.4. A SOFTER RESERVOIR 8.4 A softe
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8.4. A SOFTER RESERVOIR 2000 15 200
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8.4. A SOFTER RESERVOIR 2000 Max SW
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8.5. DISCUSSION pore-pressure being
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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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