Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

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CHAPTER 4. A COMPARISON OF MICROSEISMIC MONITORING OF FRACTURE STIMULATION DUE TO WATER VERSUS CO 2 INJECTION 4.8 Summary • A lack of seismicity observed at Weyburn has lead to the suggestion that CO 2 has an inherently lower seismic deformation efficiency than water, with obvious implications for the feasibility of using microseismics events to monitor CCS sites. • In order to test this assertion, I compared the microseismic response of CO 2 and water injection into the same reservoir - a North American oil field undergoing hydraulic fracture stimulation. • Event locations image the formation of fractures trending away from the injection well. Events during CO 2 injection are observed well above the injection depth, possibly as a result of the increased buoyancy and mobility of CO 2 . • Event magnitudes show correlation with injection pressures for both water and CO 2 . The event magnitudes and rates of seismicity for both fluids are similar. This indicates that, for this case at least, there is no difference in the amount of deformation induced by CO 2 and water injection. • Shear-wave splitting successfully images the fractures, but within the limits imposed by the source-receiver geometry there is no evidence to suggest a lower degree of fracturing during CO 2 injection. • A method is developed to test the sensitivity of splitting measurements to the initial S-wave polarisation. I find that SWS measurements are reliable so long as the fast direction and initial polarisation are greater than 10 ◦ apart. I also find that the selection criteria outlined by Teanby et al. (2004b) are sufficient to pick up and remove these inaccurate results. 82
pressure, P fl σ ′ ij = σ ij − β w I ij P fl , (5.1) 5 Geomechanical simulation of CO 2 injection Even the self-assured will raise their perceived self-efficacy if models teach them better ways of doing things. Albert Bandura 5.1 Introduction Microseismic monitoring provides information about the geomechanical deformation occurring in and around the reservoir. As such, the interpretation of microseismic activity can be greatly improved by geomechanical modelling. Geomechanical models commonly use finite element techniques to simulate the deformation caused by pore pressure changes in the reservoir. Injection of CO 2 will increase the pore pressure in the reservoir. This represents the loading for the geomechanical model, which computes the deformation both inside and around the reservoir. By examining the stress evolution it is possible to identify areas in and around the reservoir where fractures are likely to form or be reactivated. In this chapter I use a relatively novel technique where a geomechanical model is coupled to a fluid-flow simulator. This allows changes in pore pressure to be passed directly to the geomechanical model, and changes in porosity and permeability to be returned to update the fluid model. The modelling method has been developed by the Integrated Petroleum Engineering, Geomechanics and Geophysics (IPEGG) consortium. In this chapter I introduce the modelling technique and demonstrate it with several simple numerical simulations. I use these to examine how factors such as the reservoir geometry and material properties affect the stress evolution during CO 2 injection. 5.2 Effective stress and stress path parameters The concept of effective stress was introduced by Terzaghi (1943). When a stress is applied to a porous material, part of the stress will be supported by the matrix material, and part will be supported by the fluid in the pores. The part of the stress supported by the matrix is termed the effective stress, given in tensorial form as σ ′ ij . It is the effective stress that will determine the deformation of the rock frame. The effective stress is a function of the external stress applied to the rock, σ ij , and the pore where I ij is a 3×3 identity matrix, and β w is the Biot-Willis parameter (e.g., Mavko et al., 1992), assumed here to be 1. The magnitudes of the principle effective stresses are given by the eigenvalues of σ ′ ij , and when referring to these I will use only one subscript, e.g., σ′ 1. The corresponding eigenvectors give the orientations of the principal effective stresses. One of the principal stresses is usually orientated 83
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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
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,
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Page 59 and 60: 3.4. SWS MEASUREMENTS AT WEYBURN th
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: 4.7. DISCUSSION 4.7 Discussion The
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
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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
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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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