Tony Siggins - Academia.edu (original) (raw)
Papers by Tony Siggins
Energy Procedia, 2011
Seismicity induced by fl uid injection and extraction is a widely observed phenomenon. These eart... more Seismicity induced by fl uid injection and extraction is a widely observed phenomenon. These earthquakes can exceed magnitudes of M 6 and have the potential to impact on the containment, infrastructure and public perceptions of safety at CO 2 storage sites. We examine induced seismicity globally using published data from 75 sites dominated by water injection and hydrocarbon extraction to estimate the timing (relative to injection/extraction), locations, size range and numbers of induced earthquakes. Most induced earthquakes occur during injection/extraction (~70%) and are clustered at shallow depths in the region of the reservoir. The rates and maximum magnitudes of induced earthquakes generally increase with rising reservoir pressures, total fluid volumes and injection/extraction rates. The likelihood of an earthquake greater than or equal to a given magnitude being induced during injection is approximately proportional to the total volume of fluid injected/extracted, which appears to provide a proxy for changes in rock dynamics. If this observation holds for C O 2 storage sites, then we can expect the rates and maximum magnitudes of induced earthquakes to be significantly higher for commercial-scale operations (e.g., 50 Mt) than for pilot projects (e.g., 50 kt). In accord with these results the risks associated with induced seismicity may also rise with project size. Mitigation and monitoring measures at commercial-size sequestration sites, including installation of microseismic networks, public education on the expected seismicity and pressure relief wells, will be key for risk reduction.
EAGE Shale Workshop 2010, 2010
We used undrained multi-stage triaxial tests to evaluate how the ultrasonic wave velocities and t... more We used undrained multi-stage triaxial tests to evaluate how the ultrasonic wave velocities and their anisotropy changed with increasing isotropic and differential stress conditions. In addition, the impact of stress orientation with respect to fabric orientation was evaluated. An array of ultrasonic transducers allowed to measure five independent wave velocities which were used to calculate the elastic properties of the shale. Results indicate that in this shale P- and S-wave velocities vary with stress in a different manner dependent on the maximum stress orientation with respect to the fabric orientation. Where the maximum stress is normal to bedding, Vpv and Vs1 increase monotonically with increasing effective stress. However Vph and Vsh decrease during individual loading stages but increase from stage to stage as confining pressure increases. The reverse occurs when the microfabric is parallel to the maximum principal stress. Where the maximum stress is bedding normal, velocity anisotropy decreases as differential stress increases; when maximum stress is fabric parallel, anisotropy increases. Intrinsic anisotropy is related to the initial composition and fabric of the sediment, while changes in elastic anisotropy result from the applied stresses, their orientation to the rock fabric and the degree of stress anisotropy
GEOPHYSICS, 2011
Anisotropy of velocity in shaly overburden is known to cause significant problems for geophysical... more Anisotropy of velocity in shaly overburden is known to cause significant problems for geophysical interpretation, including depth conversion and fluid identification. In addition, mechanical and dynamic elastic shale behavior is not well understood because few tests have been performed on well-preserved samples. Multiple stage triaxial tests were performed upon horizontal core plugs of a shale from the Norwegian Sea with a view to evaluating rock strength and the evolution of ultrasonic response during rock deformation. In addition, standard rock physical properties were characterized as well as composition. The shale microfabric is seen to be strongly laminated, with alternating thick clay-rich laminae and thin silt-rich laminae. Occasional microfractures are also noted parallel to these laminations. The shale has low friction coefficient and cohesive strength, and shows anisotropy of these parameters when the maximum principal stress is oriented parallel to and at 45° to the micro...
Geophysical Journal International, 2010
Exponential increase of seismic velocities with effective stress has usually been explained by pr... more Exponential increase of seismic velocities with effective stress has usually been explained by presence of pores with a broad distribution of aspect ratios. More recently, a stress-related closure of soft pores with a narrow distribution of compliances (e.g. grain contacts) has been suggested to be sufficient to explain such exponential stress dependency. This theoretical interpretation has been verified here using laboratory measurements on dry sandstones. On the basis of these experimental data, linear dependency of elastic compressibility on soft porosity and exponential decay of soft porosity and elastic compressibility with effective stress up to 60 MPa is confirmed. Soft porosity, estimated from the fitting coefficients of elastic compressibilities, is on the same order of magnitude but slightly lower than obtained from strain measurements. The results confirm applicability of the previously proposed stress sensitivity model and provide justification for using this approach to model stress dependency of elastic properties.
Exploration Geophysics, 2006
Injection of CO2 into underground saline formations, due to their large storage capacity, is prob... more Injection of CO2 into underground saline formations, due to their large storage capacity, is probably the most promising approach for the reduction of CO2 emissions into the atmosphere. CO2 storage must be carefully planned and monitored to ensure that the CO2 is safely retained in the formation for periods of at least thousands of years. Seismic methods, particularly for offshore reservoirs, are the primary tool for monitoring the injection process and distribution of CO2 in the reservoir over time provided that reservoir properties are favourable. Seismic methods are equally essential for the characterisation of a potential trap, determining the reservoir properties, and estimating its capacity. Hence, an assessment of the change in seismic response to CO2 storage needs to be carried out at a very early stage. This must be revisited at later stages, to assess potential changes in seismic response arising from changes in fluid properties or mineral composition that may arise from c...
ASEG Extended Abstracts, 2007
SEG Technical Program Expanded Abstracts 2007, 2007
No single system is available to ground truth the full frequency range of geophysical and petroph... more No single system is available to ground truth the full frequency range of geophysical and petrophysical electromagnetic measurements. We have combined a number of instruments and different measurement principles to obtain truly wide band (mHz to GHz) spectra of conductivity and permittivity of earth materials. We have designed several new cells and fixtures, and implemented a number of novel procedures for measurement and calibration. Several of our cells operate at overburden pressures (35 MPa). Our guarded parallel plate cells can be connected to more than one measurement system to cover the cross-over region adequately. The four electrode cells can be configured for time domain and electrokinetic measurements. To aid in calibration we have also implemented resonant methods giving highly accurate dielectric measurements at spot frequencies that compliment swept frequency data.
ASEG Extended Abstracts, 2007
Abstract Although shales comprise a large proportion of the sedimentary pile in many hydrocarbon-... more Abstract Although shales comprise a large proportion of the sedimentary pile in many hydrocarbon-rich regions, their behaviour is not well understood from basin scales right down to the microscopic physics of particle interactions. Shale properties impact ...
Energy Procedia, 2013
ABSTRACT Seismicity produced by human activities (i.e. induced seismicity) has been widely report... more ABSTRACT Seismicity produced by human activities (i.e. induced seismicity) has been widely reported over the last 40 years. To date few induced earthquakes have been recorded at CO2 storage sites, however, the volumes of injected CO2 and the number of operational sites are small. A review of induced seismicity from different types of fluid injection and extraction sites confirms that these events are typically magnitude (M) and in many cases have no reported earthquakes. Although the size (and associated risks) of induced earthquakes at CO2 storage sites is most likely to be small, these events could decrease seal integrity or raise public concerns, while rare larger events (>M5) could also have ramifications for CCS beyond a single site. These risks can be reduced by careful site selection and development of site-specific risk reduction and mitigation programmes. Forecasts of induced seismicity using physical and statistical models and real-time monitoring will be key planning and decision making tools. The utility of monitoring and mitigation programmes will be maximized by establishing prior to injection, site performance and management guidelines for acceptable levels of induced seismicity, and agreed control measures. Further improvements to risk management practices, understanding induced seismicity processes and stakeholder confidence may be achieved by; a) increasing the number of publically available induced earthquake catalogues for development and testing of physical and statistical models, b) undertaking more systematic studies of individual sites populated by well constrained sub-surface geomechanical information and seismicity data complete down to small magnitudes (e.g., M-3), c) enhancing the physical reality of numerical dynamic models, d) studying the scaling effects of seismicity associated with moving from pilot projects to full commercial implementation of CO2 storage, e) developing standard risk management procedures and guidelines for induced seismicity at CCS sites and, f) filling induced seismicity knowledge gaps in the CCS community by collaborating with seismologists and modellers working in other industries. (auth)
GEOPHYSICS, 2011
Anisotropy of velocity in shaly overburden is known to cause significant problems for geophysical... more Anisotropy of velocity in shaly overburden is known to cause significant problems for geophysical interpretation, including depth conversion and fluid identification. In addition, mechanical and dynamic elastic shale behavior is not well understood because few tests have been performed on well-preserved samples. Multiple stage triaxial tests were performed upon horizontal core plugs of a shale from the Norwegian Sea with a view to evaluating rock strength and the evolution of ultrasonic response during rock deformation. In addition, standard rock physical properties were characterized as well as composition. The shale microfabric is seen to be strongly laminated, with alternating thick clay-rich laminae and thin silt-rich laminae. Occasional microfractures are also noted parallel to these laminations. The shale has low friction coefficient and cohesive strength, and shows anisotropy of these parameters when the maximum principal stress is oriented parallel to and at 45 to the microfabric. The orientation of the maximum principal stress parallel to the intrinsic fabric and microcracks was seen to significantly impact on velocity normal to the fabric as stress parallel to the fabric increased. S-wave anisotropy was significantly affected by the increasing stress anisotropy. Stress orientation with respect to fabric orientation was therefore found to be an important control on the degree of anisotropy of dynamic elastic properties in this shale.
The Leading Edge, 2008
Abstract Despite decades of research, current understanding of elastic properties of shales is in... more Abstract Despite decades of research, current understanding of elastic properties of shales is insufficient as it is based on a limited number of observations caused by the time-consuming nature of testing resulting from their low permeability. Though it is well known that shales are highly anisotropic and assumed to be transversely isotropic (TI) media, few laboratory experiments have been carried out for measuring the five elastic constants that define TI media on well-preserved shales. Many previous measurements were made ...
Energy Procedia, 2011
Seismicity induced by fl uid injection and extraction is a widely observed phenomenon. These eart... more Seismicity induced by fl uid injection and extraction is a widely observed phenomenon. These earthquakes can exceed magnitudes of M 6 and have the potential to impact on the containment, infrastructure and public perceptions of safety at CO 2 storage sites. We examine induced seismicity globally using published data from 75 sites dominated by water injection and hydrocarbon extraction to estimate the timing (relative to injection/extraction), locations, size range and numbers of induced earthquakes. Most induced earthquakes occur during injection/extraction (~70%) and are clustered at shallow depths in the region of the reservoir. The rates and maximum magnitudes of induced earthquakes generally increase with rising reservoir pressures, total fluid volumes and injection/extraction rates. The likelihood of an earthquake greater than or equal to a given magnitude being induced during injection is approximately proportional to the total volume of fluid injected/extracted, which appears to provide a proxy for changes in rock dynamics. If this observation holds for C O 2 storage sites, then we can expect the rates and maximum magnitudes of induced earthquakes to be significantly higher for commercial-scale operations (e.g., 50 Mt) than for pilot projects (e.g., 50 kt). In accord with these results the risks associated with induced seismicity may also rise with project size. Mitigation and monitoring measures at commercial-size sequestration sites, including installation of microseismic networks, public education on the expected seismicity and pressure relief wells, will be key for risk reduction.
EAGE Shale Workshop 2010, 2010
We used undrained multi-stage triaxial tests to evaluate how the ultrasonic wave velocities and t... more We used undrained multi-stage triaxial tests to evaluate how the ultrasonic wave velocities and their anisotropy changed with increasing isotropic and differential stress conditions. In addition, the impact of stress orientation with respect to fabric orientation was evaluated. An array of ultrasonic transducers allowed to measure five independent wave velocities which were used to calculate the elastic properties of the shale. Results indicate that in this shale P- and S-wave velocities vary with stress in a different manner dependent on the maximum stress orientation with respect to the fabric orientation. Where the maximum stress is normal to bedding, Vpv and Vs1 increase monotonically with increasing effective stress. However Vph and Vsh decrease during individual loading stages but increase from stage to stage as confining pressure increases. The reverse occurs when the microfabric is parallel to the maximum principal stress. Where the maximum stress is bedding normal, velocity anisotropy decreases as differential stress increases; when maximum stress is fabric parallel, anisotropy increases. Intrinsic anisotropy is related to the initial composition and fabric of the sediment, while changes in elastic anisotropy result from the applied stresses, their orientation to the rock fabric and the degree of stress anisotropy
GEOPHYSICS, 2011
Anisotropy of velocity in shaly overburden is known to cause significant problems for geophysical... more Anisotropy of velocity in shaly overburden is known to cause significant problems for geophysical interpretation, including depth conversion and fluid identification. In addition, mechanical and dynamic elastic shale behavior is not well understood because few tests have been performed on well-preserved samples. Multiple stage triaxial tests were performed upon horizontal core plugs of a shale from the Norwegian Sea with a view to evaluating rock strength and the evolution of ultrasonic response during rock deformation. In addition, standard rock physical properties were characterized as well as composition. The shale microfabric is seen to be strongly laminated, with alternating thick clay-rich laminae and thin silt-rich laminae. Occasional microfractures are also noted parallel to these laminations. The shale has low friction coefficient and cohesive strength, and shows anisotropy of these parameters when the maximum principal stress is oriented parallel to and at 45° to the micro...
Geophysical Journal International, 2010
Exponential increase of seismic velocities with effective stress has usually been explained by pr... more Exponential increase of seismic velocities with effective stress has usually been explained by presence of pores with a broad distribution of aspect ratios. More recently, a stress-related closure of soft pores with a narrow distribution of compliances (e.g. grain contacts) has been suggested to be sufficient to explain such exponential stress dependency. This theoretical interpretation has been verified here using laboratory measurements on dry sandstones. On the basis of these experimental data, linear dependency of elastic compressibility on soft porosity and exponential decay of soft porosity and elastic compressibility with effective stress up to 60 MPa is confirmed. Soft porosity, estimated from the fitting coefficients of elastic compressibilities, is on the same order of magnitude but slightly lower than obtained from strain measurements. The results confirm applicability of the previously proposed stress sensitivity model and provide justification for using this approach to model stress dependency of elastic properties.
Exploration Geophysics, 2006
Injection of CO2 into underground saline formations, due to their large storage capacity, is prob... more Injection of CO2 into underground saline formations, due to their large storage capacity, is probably the most promising approach for the reduction of CO2 emissions into the atmosphere. CO2 storage must be carefully planned and monitored to ensure that the CO2 is safely retained in the formation for periods of at least thousands of years. Seismic methods, particularly for offshore reservoirs, are the primary tool for monitoring the injection process and distribution of CO2 in the reservoir over time provided that reservoir properties are favourable. Seismic methods are equally essential for the characterisation of a potential trap, determining the reservoir properties, and estimating its capacity. Hence, an assessment of the change in seismic response to CO2 storage needs to be carried out at a very early stage. This must be revisited at later stages, to assess potential changes in seismic response arising from changes in fluid properties or mineral composition that may arise from c...
ASEG Extended Abstracts, 2007
SEG Technical Program Expanded Abstracts 2007, 2007
No single system is available to ground truth the full frequency range of geophysical and petroph... more No single system is available to ground truth the full frequency range of geophysical and petrophysical electromagnetic measurements. We have combined a number of instruments and different measurement principles to obtain truly wide band (mHz to GHz) spectra of conductivity and permittivity of earth materials. We have designed several new cells and fixtures, and implemented a number of novel procedures for measurement and calibration. Several of our cells operate at overburden pressures (35 MPa). Our guarded parallel plate cells can be connected to more than one measurement system to cover the cross-over region adequately. The four electrode cells can be configured for time domain and electrokinetic measurements. To aid in calibration we have also implemented resonant methods giving highly accurate dielectric measurements at spot frequencies that compliment swept frequency data.
ASEG Extended Abstracts, 2007
Abstract Although shales comprise a large proportion of the sedimentary pile in many hydrocarbon-... more Abstract Although shales comprise a large proportion of the sedimentary pile in many hydrocarbon-rich regions, their behaviour is not well understood from basin scales right down to the microscopic physics of particle interactions. Shale properties impact ...
Energy Procedia, 2013
ABSTRACT Seismicity produced by human activities (i.e. induced seismicity) has been widely report... more ABSTRACT Seismicity produced by human activities (i.e. induced seismicity) has been widely reported over the last 40 years. To date few induced earthquakes have been recorded at CO2 storage sites, however, the volumes of injected CO2 and the number of operational sites are small. A review of induced seismicity from different types of fluid injection and extraction sites confirms that these events are typically magnitude (M) and in many cases have no reported earthquakes. Although the size (and associated risks) of induced earthquakes at CO2 storage sites is most likely to be small, these events could decrease seal integrity or raise public concerns, while rare larger events (>M5) could also have ramifications for CCS beyond a single site. These risks can be reduced by careful site selection and development of site-specific risk reduction and mitigation programmes. Forecasts of induced seismicity using physical and statistical models and real-time monitoring will be key planning and decision making tools. The utility of monitoring and mitigation programmes will be maximized by establishing prior to injection, site performance and management guidelines for acceptable levels of induced seismicity, and agreed control measures. Further improvements to risk management practices, understanding induced seismicity processes and stakeholder confidence may be achieved by; a) increasing the number of publically available induced earthquake catalogues for development and testing of physical and statistical models, b) undertaking more systematic studies of individual sites populated by well constrained sub-surface geomechanical information and seismicity data complete down to small magnitudes (e.g., M-3), c) enhancing the physical reality of numerical dynamic models, d) studying the scaling effects of seismicity associated with moving from pilot projects to full commercial implementation of CO2 storage, e) developing standard risk management procedures and guidelines for induced seismicity at CCS sites and, f) filling induced seismicity knowledge gaps in the CCS community by collaborating with seismologists and modellers working in other industries. (auth)
GEOPHYSICS, 2011
Anisotropy of velocity in shaly overburden is known to cause significant problems for geophysical... more Anisotropy of velocity in shaly overburden is known to cause significant problems for geophysical interpretation, including depth conversion and fluid identification. In addition, mechanical and dynamic elastic shale behavior is not well understood because few tests have been performed on well-preserved samples. Multiple stage triaxial tests were performed upon horizontal core plugs of a shale from the Norwegian Sea with a view to evaluating rock strength and the evolution of ultrasonic response during rock deformation. In addition, standard rock physical properties were characterized as well as composition. The shale microfabric is seen to be strongly laminated, with alternating thick clay-rich laminae and thin silt-rich laminae. Occasional microfractures are also noted parallel to these laminations. The shale has low friction coefficient and cohesive strength, and shows anisotropy of these parameters when the maximum principal stress is oriented parallel to and at 45 to the microfabric. The orientation of the maximum principal stress parallel to the intrinsic fabric and microcracks was seen to significantly impact on velocity normal to the fabric as stress parallel to the fabric increased. S-wave anisotropy was significantly affected by the increasing stress anisotropy. Stress orientation with respect to fabric orientation was therefore found to be an important control on the degree of anisotropy of dynamic elastic properties in this shale.
The Leading Edge, 2008
Abstract Despite decades of research, current understanding of elastic properties of shales is in... more Abstract Despite decades of research, current understanding of elastic properties of shales is insufficient as it is based on a limited number of observations caused by the time-consuming nature of testing resulting from their low permeability. Though it is well known that shales are highly anisotropic and assumed to be transversely isotropic (TI) media, few laboratory experiments have been carried out for measuring the five elastic constants that define TI media on well-preserved shales. Many previous measurements were made ...