Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

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CHAPTER 3. INVERTING SHEAR-WAVE SPLITTING MEASUREMENTS FOR FRACTURE PROPERTIES Sh Sv P Sr (before) P S St (before) Sr (after) P S St (after) P S P S P S P S P S (a) (b) Before After (c) (d) Figure 3.8: An example of SWS analysis. (a) shows the input seismograms rotated into the ray frame. (b) shows the radial and transverse components both before and after correction. A good correction will minimise the energy on the St component. (c) shows the fast and slow waveforms, and S-wave particle motion. A good correction will linearise particle motion and leave the fast and slow waveforms looking similar. (d) shows the error surface and cluster analysis. A good result will have one clearly defined error minimum. 44
3.4. SWS MEASUREMENTS AT WEYBURN ξ 1 α 1 ξ 2 α 2 γ δ Inversion for 1 fracture set 0.14 138 ◦ NA NA 0.03 0.0 Inversion for 2 fracture sets 0.3 150 ◦ 0.21 42 ◦ NA NA From Brown (2002) 1.0 - 1.6 m −1 148 ◦ 2.3 - 3.8 m −1 40 ◦ NA NA Table 3.3: Results for the inversion of Weyburn SWS measurements assuming 1 and then 2 fracture sets are present. I also give the results of core and borehole analysis at Weyburn provided by Brown (2002). The fracture densities in this study are given by Hudson (1981)’s non-dimensional fracture density term, but in Brown (2002) they are written as the number of fractures per meter of rock. separate fully. The presence of P-wave coda arriving coincident with the S-wave will contaminate the SWS analysis, leading to unreliable results. Although it is common practise to include only the class A results in analysis, the lack of good quality events means that I include class A and B events in the subsequent discussions. The events recorded during Phase IB are located at reservoir depths, and occur between December 2003 and July 2004. The events recorded during Phase II occur above the reservoir during October 2005. Given their differing temporal and spatial distributions, I will analyse the Phase IB and II results separately. 3.4.3 Phase IB I invert the 30 successful SWS measurements from Phase IB, assuming a VTI fabric and one set of fractures. The results are plotted in Figure 3.9 and the best fit results are listed in Table 3.3. The inversion suggests that there is little VTI, and images a fracture set striking at 138 ◦ (NW-SE) with a density ξ=0.14. When we consider the RMS misfit surface in Figure 3.9, the 90% confidence interval is large, suggesting that the inversion has not found a particularly well constrained result. Core analysis and borehole image logs at Weyburn have imaged the presence of aligned fracture sets in the Weyburn reservoir (Bunge, 2000; Brown, 2002). Two of the fracture sets identified by these studies are listed in Table 3.3. These sets have strikes of 40 ◦ and 148 ◦ , with the set at 40 ◦ being the more pervasive. However, our SWS inversion has identified the apparently weaker set at 138 ◦ . One reason for this may be the geometry of the arrivals available to conduct the inversion. My initial interpretation was that perhaps although the NE-SW set had a greater fracture density when unstressed core samples were considered, stress evolution during production has kept this set closed at depth, while opening the NW-SE set, making it more ‘visible’ to the shear waves. An alternative explanation for why the supposedly stronger NE-SW fracture set is not imaged can be provided by synthetic models. To test this possibility I generated an elastic model containing two vertical fracture sets aligned orthogonally with strikes NW-SE and NE-SW, as observed from Weyburn cores. I assign a higher fracture density to the NE-SW set, as is believed to be the case at Weyburn. I then perform a synthetic inversion using the range of arrivals observed in the real 45
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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
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
Page 35 and 36: 2.4. EVENT TIMING AND LOCATIONS 500
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 and 58: 20 10 5 5 1 20 30 40 80 100 60 40 1
Page 59 and 60: 3.4. SWS MEASUREMENTS AT WEYBURN th
Page 61: 3.4. SWS MEASUREMENTS AT WEYBURN ei
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
Page 109 and 110: 5.3. NUMERICAL MODELLING (a) (b) Fi
Page 111 and 112: 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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