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Papers by Stephen Bourne

Journal of Geophysical Research: Solid Earth, 2019

The Groningen gas reservoir, situated in the northeast of the Netherlands is western Europe's lar... more The Groningen gas reservoir, situated in the northeast of the Netherlands is western Europe's largested gas reservoir. Due to gas production measureable subsidence and seismicity has been detected across this region, attributed to the deformations induced by reservoir pore pressure depletion. We investigate the surface displacement history using a Principal Component Analysisbased Inversion Method (PCAIM) to combine a diverse set of Optical Leveling, InSAR and GPS data to better constrain reservoir compaction and subsidence history. The generated compaction model is then used in combination with prior pressure depletion models to determine a reservoir uniaxial compressibility. The best fitting model of uniaxial compressibility is timeindependent but spatially variable. The absence of evidence for any significant time-delay between changes in depletion and compaction rates supports an instantaneous poroelastic reservoir response. The absence of non-linear yielding at the largest compaction strains suggests anelastic deformations are a minor part of reservoir compaction.

Geophysical Journal International, 2021

SUMMARY A number of recent modelling studies of induced seismicity have used the 1994 rate-and-st... more SUMMARY A number of recent modelling studies of induced seismicity have used the 1994 rate-and-state friction model of Dieterich 1994 to account for the fact that earthquake nucleation is not instantaneous. Notably, the model assumes a population of seismic sources accelerating towards instability with a distribution of initial slip speeds such that they would produce earthquakes steadily in the absence of any perturbation to the system. This assumption may not be valid in typical intraplate settings where most examples of induced seismicity occur, since these regions have low stressing rates and initially low seismic activity. The goal of this paper is twofold. First, to derive a revised Coulomb rate-and-state model, which takes into account that seismic sources can be initially far from instability. Second, to apply and test this new model, called the Threshold rate-and-state model, on the induced seismicity of the Groningen gas field in the Netherlands. Stress changes are calcula...

64th EAGE Conference & Exhibition, 2002

The studied field is located in the onshore area of the Arabian Peninsula. The trap is formed by ... more The studied field is located in the onshore area of the Arabian Peninsula. The trap is formed by a gentle faulted anticline, trending SW-NE, and contains sweet, 39° API crude oil. It was discovered in the sixties in Early Cretaceous carbonate reservoirs, the Thamama Zones B & C. The volume of oil in place (STOIIP) in the field is several billions barrels. Since the seventies, the oil is recovered with water injection schemes including dozens of injector wells and hundreds of producer wells. The current production is exceeding hundred thousand oil barrels per day.

Proceedings of Abu Dhabi Interntional Petroelum Exhibition and Conference, 2000

To optimise recovery in naturally fractured reservoirs, the field-scale distribution of fracture ... more To optimise recovery in naturally fractured reservoirs, the field-scale distribution of fracture properties must be understood and quantified. We present a semi-deterministic method to systematically predict the spatial distribution of natural fractures and their effect on flow simulations. This approach enables the calculation of field-scale fracture models. These are calibrated by geological, well test and field production data to constrain the distributions of fractures within the inter-well space. First, we calculate the stress distribution at the time of fracturing using the present-day structural reservoir geometry. This calculation is based on geomechanical models of rock deformation such as elastic faulting. Second, the calculated stress field is used to govern the simulated growth of fracture networks. Finally, the fractures are upscaled dynamically by simulating flow through the discrete fracture network per grid block, enabling field-scale multi-phase reservoir simulation. Uncertainties associated with these predictions are considerably reduced by constraining and validating the models with seismic, borehole, well test and production data. This approach is able to predict physically and geologically realistic fracture networks. Its successful application to outcrops and reservoirs demonstrates there is a high degree of predictability in the properties of natural fracture networks. Several examples show the success of the method in singleand multi-phase fields. In cases of limited data-where stochastic models typically fail-this method remains robust.

Geophysical Journal International, 2020

SUMMARYThe Groningen gas reservoir, situated in the northeast of the Netherlands, is western Euro... more SUMMARYThe Groningen gas reservoir, situated in the northeast of the Netherlands, is western Europe’s largest producing gas field and has been in production since 1963. The gas production has induced both subsidence and seismicity. Seismicity is detected and located using the Koninklijk Nederlands Meteorologisch Instituut shallow-borehole array for the period 2015–2017, incorporating the back projection techniques of QuakeMigrate and the nonlinear location procedure to constrain earthquake locations and depths. The uncertainties on the estimated depths are estimated taking into account velocity model, changes in station array geometry and uncertainties in the measurement of arrival times of the P and S waves. We show that the depth distribution of seismicity is consistent with nucleation within the reservoir (28 per cent) or in the overburden (60 per cent) within ∼500 m from the top of the reservoir. Earthquakes with hypocentres in the overburden likely originate from overlying Zech...

Computational Geosciences, 2021

The Groningen gas field in the Netherlands is experiencing induced seismicity as a result of ongo... more The Groningen gas field in the Netherlands is experiencing induced seismicity as a result of ongoing depletion. The physical mechanisms that control seismicity have been studied through rock mechanical experiments and combined physical-statistical models to support development of a framework to forecast induced-seismicity risks. To investigate whether machine learning techniques such as Random Forests and Support Vector Machines bring new insights into forecasts of induced seismicity rates in space and time, a pipeline is designed that extends time-series analysis methods to a spatiotemporal framework with a factorial setup, which allows probing a large parameter space of plausible modelling assumptions, followed by a statistical meta-analysis to account for the intrinsic uncertainties in subsurface data and to ensure statistical significance and robustness of results. The pipeline includes model validation using e.g. likelihood ratio tests against average depletion thickness and st...

Journal of Geotechnical and Geoenvironmental Engineering, 2020

The operator of the Groningen gas field is leading an effort to quantify the seismic hazard and r... more The operator of the Groningen gas field is leading an effort to quantify the seismic hazard and risk of the region due to induced earthquakes, including overseeing one of the most comprehensive liquefaction hazard studies performed globally to date. Due to the unique characteristics of the seismic hazard and the geologic deposits in Groningen, efforts first focused on developing relationships for a Groningenspecific liquefaction triggering model. The liquefaction hazard was then assessed using a Monte Carlo method, wherein a range of credible event scenarios were considered in computing liquefaction damage-potential hazard curves. This effort entailed the use of a regional stochastic seismic source model, ground motion prediction equation, site response model, and geologic model that were developed as part of the broader regional seismic hazard assessment. No to minor surficial liquefaction manifestations are predicted for most sites across the study area for a 2475-year return period. The only sites where moderate surficial liquefaction manifestations are predicted are in the town of Zandeweer, with only some of the sites in the town being predicted to experience this severity of liquefaction for this return period.

Netherlands Journal of Geosciences, 2017

This paper reviews the evolution of a sequence of seismological models developed and implemented ... more This paper reviews the evolution of a sequence of seismological models developed and implemented as part of a workflow for Probabilistic Seismic Hazard and Risk Assessment of the seismicity induced by gas production from the Groningen gas field. These are semi-empirical statistical geomechanical models derived from observations of production-induced seismicity, reservoir compaction and structure of the field itself. Initial versions of the seismological model were based on a characterisation of the seismicity in terms of its moment budget. Subsequent versions of the model were formulated in terms of seismic event rates, this change being driven in part by the reduction in variability of the model forecasts in this domain. Our approach makes use of the Epidemic Type After Shock model (ETAS) to characterise spatial and temporal clustering of earthquakes and has been extended to also incorporate the concentration of moment release on pre-existing faults and other reservoir topographic ...

Netherlands Journal of Geosciences, 2017

Earthquakes associated with gas production have been recorded in the northern part of the Netherl... more Earthquakes associated with gas production have been recorded in the northern part of the Netherlands since 1986. The Huizinge earthquake of 16 August 2012, the strongest so far with a magnitude of ML = 3.6, prompted reassessment of the seismicity induced by production from the Groningen gas field. An international research programme was initiated, with the participation of many Dutch and international universities, knowledge institutes and recognised experts.The prime aim of the programme was to assess the hazard and risk resulting from the induced seismicity. Classic probabilistic seismic hazard and risk assessment (PSHA) was implemented using a Monte Carlo method. The scope of the research programme extended from the cause (production of gas from the underground reservoir) to the effects (risk to people and damage to buildings). Data acquisition through field measurements and laboratory experiments was a substantial element of the research programme. The existing geophone and acc...

Geophysical Journal International, 2018

SUMMARY Induced seismicity typically arises from the progressive activation of recently inactive ... more SUMMARY Induced seismicity typically arises from the progressive activation of recently inactive geological faults by anthropogenic activity. Faults are mechanically and geometrically heterogeneous, so their extremes of stress and strength govern the initial evolution of induced seismicity. We derive a statistical model of Coulomb stress failures and associated aftershocks within the tail of the distribution of fault stress and strength variations to show initial induced seismicity rates will increase as an exponential function of induced stress. Our model provides operational forecasts consistent with the observed space–time–magnitude distribution of earthquakes induced by gas production from the Groningen field in the Netherlands. These probabilistic forecasts also match the observed changes in seismicity following a significant and sustained decrease in gas production rates designed to reduce seismic hazard and risk. This forecast capability allows reliable assessment of alternat...

Bulletin of the Seismological Society of America, 2015

A Monte Carlo approach to Probabilistic Seismic Hazard Assessment (PSHA) is developed for induced... more A Monte Carlo approach to Probabilistic Seismic Hazard Assessment (PSHA) is developed for induced seismicity associated with a compacting gas reservoir. The geomechanical foundation for the method is the work of Kostrov (1974) and McGarr (1976) linking total strain to summed seismic moment in an earthquake catalogue. Our Monte Carlo method simulates future seismic hazard consistent with historical seismic and compaction datasets by sampling probability distributions for total seismic moment, event locations and magnitudes, and resulting ground motions. Ground motions are aggregated over an ensemble of simulated catalogues to give a probabilistic representation of the ground-motion hazard. This approach is particularly well suited to the specific nature of the time-dependent induced seismicity considered. We demonstrate the method by applying it to seismicity induced by reservoir compaction following gas production from the Groningen gas field. A new ground motion prediction equation (GMPE) tailored to the Groningen field, has been derived by calibrating an existing GMPE with local strong motion data. For 2013 to 2023 we find a 2% chance of exceeding a peak ground acceleration of 0.57g and a 2% chance of exceeding a peak ground velocity of 22 cm/s above the area of maximum compaction. Disaggregation shows that earthquakes of magnitude 4-5, at the shortest hypocentral distances of 3 km, and ground motions two standard deviations above the median make the largest contributions to this hazard. Uncertainty in the hazard is primarily due to uncertainty about the future fraction of induced strains that will be seismogenic and how ground motion and its variability will scale to larger magnitudes.

A seismological model is developed for earthquakes induced by subsurface reservoir volume Q2 chan... more A seismological model is developed for earthquakes induced by subsurface reservoir volume Q2 changes. The approach is based on the work of Kostrov (1974) and McGarr (1976) linking total strain to the summed seismic moment in an earthquake catalog. We refer to the fraction of the total strain expressed as seismic moment as the strain partitioning function,. A probability distribution for total seismic moment as a function of time is derived from an evolving earthquake catalog. The moment distribution is taken to be a Pareto Sum Distribution with confidence bounds estimated using approximations given by Zaliapin et al. (2005). In this way available seismic moment is expressed in terms of reservoir volume change and hence compaction in the case of a depleting reservoir. The Pareto Sum Distribution for moment and the Pareto Distribution underpinning the Gutenberg-Richter Law are sampled using Monte Carlo methods to simulate synthetic earthquake catalogs for subsequent estimation of seismic ground motion hazard. We demonstrate the method by applying it to the Groningen gas field. A compaction model for the field calibrated using various geodetic data allows reservoir strain due to gas extraction to be expressed as a function of both spatial position and time since the start of production. Fitting with a generalized logistic function gives an empirical expression for the dependence of on reservoir compaction. Probability density maps for earthquake event locations can then be calculated from the compaction maps. Predicted seismic moment is shown to be strongly dependent on planned gas production.

A Monte Carlo approach to probabilistic seismic-hazard analysis is developed for a case of induce... more A Monte Carlo approach to probabilistic seismic-hazard analysis is developed for a case of induced seismicity associated with a compacting gas reservoir. The geomechanical foundation for the method is the work of Kostrov (1974) and McGarr (1976) linking total strain to summed seismic moment in an earthquake catalog. Our Monte Carlo method simulates future seismic hazard consistent with historical seismic and compaction datasets by sampling probability distributions for total seismic moment, event locations and magnitudes, and resulting ground motions. Ground motions are aggregated over an ensemble of simulated catalogs to give a prob-abilistic representation of the ground-motion hazard. This approach is particularly well suited to the specific nature of the time-dependent induced seismicity considered. We demonstrate the method by applying it to seismicity induced by reservoir com-paction following gas production from the Groningen gas field. A new ground-motion prediction equation (GMPE) tailored to the Groningen field, has been derived by calibrating an existing GMPE with local strong-motion data. For 2013–2023, we find a 2% chance of exceeding a peak ground acceleration of 0:57g and a 2% chance of exceeding a peak ground velocity of 22 cm=s above the area of maximum compaction. Disaggregation shows that earthquakes of M w 4–5, at the shortest hypocentral distances of 3 km, and ground motions two standard deviations above the median make the largest contributions to this hazard. Uncertainty in the hazard is primarily due to uncertainty about the future fraction of induced strains that will be seismogenic and how ground motion and its variability will scale to larger magnitudes.

Measurements of the strains and earthquakes induced by fluid extraction from a subsurface reservo... more Measurements of the strains and earthquakes induced by fluid extraction from a subsurface reservoir reveal a transient, exponential-like increase in seismicity relative to the volume of fluids extracted. If the frictional strength of these reactivating faults is heterogeneously and randomly distributed, then progressive failures of the weakest fault patches account in a general manner for this initial exponential-like trend. Allowing for the observable elastic and geometric heterogeneity of the reservoir, the spatiotemporal evolution of induced seismicity over 5 years is predictable without significant bias using a statistical physics model of poroelastic reservoir deformations inducing extreme threshold frictional failures of previously inactive faults. This model is used to forecast the temporal and spatial probability density of earthquakes within the Groningen natural gas reservoir, conditional on future gas production plans. Probabilistic seismic hazard and risk assessments based on these forecasts inform the current gas production policy and building strengthening plans. Plain Language Summary On rare occasions industrial activities create earthquakes that are sufficiently big and frequent to cause concern about the possibility of building damage and injury. One such example is Western Europe's largest producing natural gas field located next to the city of Groningen in the northeast of the Netherlands. If the physical processes that induce these earthquakes can be understood, then it might be possible to reduce the risks to acceptable levels by reducing the amount of natural gas extracted from below ground each year or by selectively strengthening buildings. A new theory was created to describe how extracting fluids, such as natural gas, from under the ground may distort the surrounding rocks in such a way that they occasionally and abruptly slide past each other forming an earthquake. Using this theory, the timing, location, and number of previous earthquakes within the Groningen gas field may be properly explained and the chance of further earthquakes in the coming few years can be reliably forecasted. These earthquake forecasts are now used to inform choices about how to safely extract the remaining gas from the Groningen field which is capable of supplying the European gas market for at least another 40 years.

S U M M A R Y Induced seismicity typically arises from the progressive activation of recently ina... more S U M M A R Y Induced seismicity typically arises from the progressive activation of recently inactive geological faults by anthropogenic activity. Faults are mechanically and geometrically heterogeneous, so their extremes of stress and strength govern the initial evolution of induced seismicity. We derive a statistical model of Coulomb stress failures and associated aftershocks within the tail of the distribution of fault stress and strength variations to show initial induced seismicity rates will increase as an exponential function of induced stress. Our model provides operational forecasts consistent with the observed space–time–magnitude distribution of earthquakes induced by gas production from the Groningen field in the Netherlands. These probabilistic forecasts also match the observed changes in seismicity following a significant and sustained decrease in gas production rates designed to reduce seismic hazard and risk. This forecast capability allows reliable assessment of alternative control options to better inform future induced seismic risk management decisions.

Journal of Geophysical Research: Solid Earth, 2019

The Groningen gas reservoir, situated in the northeast of the Netherlands is western Europe's lar... more The Groningen gas reservoir, situated in the northeast of the Netherlands is western Europe's largested gas reservoir. Due to gas production measureable subsidence and seismicity has been detected across this region, attributed to the deformations induced by reservoir pore pressure depletion. We investigate the surface displacement history using a Principal Component Analysisbased Inversion Method (PCAIM) to combine a diverse set of Optical Leveling, InSAR and GPS data to better constrain reservoir compaction and subsidence history. The generated compaction model is then used in combination with prior pressure depletion models to determine a reservoir uniaxial compressibility. The best fitting model of uniaxial compressibility is timeindependent but spatially variable. The absence of evidence for any significant time-delay between changes in depletion and compaction rates supports an instantaneous poroelastic reservoir response. The absence of non-linear yielding at the largest compaction strains suggests anelastic deformations are a minor part of reservoir compaction.

Geophysical Journal International, 2021

SUMMARY A number of recent modelling studies of induced seismicity have used the 1994 rate-and-st... more SUMMARY A number of recent modelling studies of induced seismicity have used the 1994 rate-and-state friction model of Dieterich 1994 to account for the fact that earthquake nucleation is not instantaneous. Notably, the model assumes a population of seismic sources accelerating towards instability with a distribution of initial slip speeds such that they would produce earthquakes steadily in the absence of any perturbation to the system. This assumption may not be valid in typical intraplate settings where most examples of induced seismicity occur, since these regions have low stressing rates and initially low seismic activity. The goal of this paper is twofold. First, to derive a revised Coulomb rate-and-state model, which takes into account that seismic sources can be initially far from instability. Second, to apply and test this new model, called the Threshold rate-and-state model, on the induced seismicity of the Groningen gas field in the Netherlands. Stress changes are calcula...

64th EAGE Conference & Exhibition, 2002

The studied field is located in the onshore area of the Arabian Peninsula. The trap is formed by ... more The studied field is located in the onshore area of the Arabian Peninsula. The trap is formed by a gentle faulted anticline, trending SW-NE, and contains sweet, 39° API crude oil. It was discovered in the sixties in Early Cretaceous carbonate reservoirs, the Thamama Zones B & C. The volume of oil in place (STOIIP) in the field is several billions barrels. Since the seventies, the oil is recovered with water injection schemes including dozens of injector wells and hundreds of producer wells. The current production is exceeding hundred thousand oil barrels per day.

Proceedings of Abu Dhabi Interntional Petroelum Exhibition and Conference, 2000

To optimise recovery in naturally fractured reservoirs, the field-scale distribution of fracture ... more To optimise recovery in naturally fractured reservoirs, the field-scale distribution of fracture properties must be understood and quantified. We present a semi-deterministic method to systematically predict the spatial distribution of natural fractures and their effect on flow simulations. This approach enables the calculation of field-scale fracture models. These are calibrated by geological, well test and field production data to constrain the distributions of fractures within the inter-well space. First, we calculate the stress distribution at the time of fracturing using the present-day structural reservoir geometry. This calculation is based on geomechanical models of rock deformation such as elastic faulting. Second, the calculated stress field is used to govern the simulated growth of fracture networks. Finally, the fractures are upscaled dynamically by simulating flow through the discrete fracture network per grid block, enabling field-scale multi-phase reservoir simulation. Uncertainties associated with these predictions are considerably reduced by constraining and validating the models with seismic, borehole, well test and production data. This approach is able to predict physically and geologically realistic fracture networks. Its successful application to outcrops and reservoirs demonstrates there is a high degree of predictability in the properties of natural fracture networks. Several examples show the success of the method in singleand multi-phase fields. In cases of limited data-where stochastic models typically fail-this method remains robust.

Geophysical Journal International, 2020

SUMMARYThe Groningen gas reservoir, situated in the northeast of the Netherlands, is western Euro... more SUMMARYThe Groningen gas reservoir, situated in the northeast of the Netherlands, is western Europe’s largest producing gas field and has been in production since 1963. The gas production has induced both subsidence and seismicity. Seismicity is detected and located using the Koninklijk Nederlands Meteorologisch Instituut shallow-borehole array for the period 2015–2017, incorporating the back projection techniques of QuakeMigrate and the nonlinear location procedure to constrain earthquake locations and depths. The uncertainties on the estimated depths are estimated taking into account velocity model, changes in station array geometry and uncertainties in the measurement of arrival times of the P and S waves. We show that the depth distribution of seismicity is consistent with nucleation within the reservoir (28 per cent) or in the overburden (60 per cent) within ∼500 m from the top of the reservoir. Earthquakes with hypocentres in the overburden likely originate from overlying Zech...

Computational Geosciences, 2021

The Groningen gas field in the Netherlands is experiencing induced seismicity as a result of ongo... more The Groningen gas field in the Netherlands is experiencing induced seismicity as a result of ongoing depletion. The physical mechanisms that control seismicity have been studied through rock mechanical experiments and combined physical-statistical models to support development of a framework to forecast induced-seismicity risks. To investigate whether machine learning techniques such as Random Forests and Support Vector Machines bring new insights into forecasts of induced seismicity rates in space and time, a pipeline is designed that extends time-series analysis methods to a spatiotemporal framework with a factorial setup, which allows probing a large parameter space of plausible modelling assumptions, followed by a statistical meta-analysis to account for the intrinsic uncertainties in subsurface data and to ensure statistical significance and robustness of results. The pipeline includes model validation using e.g. likelihood ratio tests against average depletion thickness and st...

Journal of Geotechnical and Geoenvironmental Engineering, 2020

The operator of the Groningen gas field is leading an effort to quantify the seismic hazard and r... more The operator of the Groningen gas field is leading an effort to quantify the seismic hazard and risk of the region due to induced earthquakes, including overseeing one of the most comprehensive liquefaction hazard studies performed globally to date. Due to the unique characteristics of the seismic hazard and the geologic deposits in Groningen, efforts first focused on developing relationships for a Groningenspecific liquefaction triggering model. The liquefaction hazard was then assessed using a Monte Carlo method, wherein a range of credible event scenarios were considered in computing liquefaction damage-potential hazard curves. This effort entailed the use of a regional stochastic seismic source model, ground motion prediction equation, site response model, and geologic model that were developed as part of the broader regional seismic hazard assessment. No to minor surficial liquefaction manifestations are predicted for most sites across the study area for a 2475-year return period. The only sites where moderate surficial liquefaction manifestations are predicted are in the town of Zandeweer, with only some of the sites in the town being predicted to experience this severity of liquefaction for this return period.

Netherlands Journal of Geosciences, 2017

This paper reviews the evolution of a sequence of seismological models developed and implemented ... more This paper reviews the evolution of a sequence of seismological models developed and implemented as part of a workflow for Probabilistic Seismic Hazard and Risk Assessment of the seismicity induced by gas production from the Groningen gas field. These are semi-empirical statistical geomechanical models derived from observations of production-induced seismicity, reservoir compaction and structure of the field itself. Initial versions of the seismological model were based on a characterisation of the seismicity in terms of its moment budget. Subsequent versions of the model were formulated in terms of seismic event rates, this change being driven in part by the reduction in variability of the model forecasts in this domain. Our approach makes use of the Epidemic Type After Shock model (ETAS) to characterise spatial and temporal clustering of earthquakes and has been extended to also incorporate the concentration of moment release on pre-existing faults and other reservoir topographic ...

Netherlands Journal of Geosciences, 2017

Earthquakes associated with gas production have been recorded in the northern part of the Netherl... more Earthquakes associated with gas production have been recorded in the northern part of the Netherlands since 1986. The Huizinge earthquake of 16 August 2012, the strongest so far with a magnitude of ML = 3.6, prompted reassessment of the seismicity induced by production from the Groningen gas field. An international research programme was initiated, with the participation of many Dutch and international universities, knowledge institutes and recognised experts.The prime aim of the programme was to assess the hazard and risk resulting from the induced seismicity. Classic probabilistic seismic hazard and risk assessment (PSHA) was implemented using a Monte Carlo method. The scope of the research programme extended from the cause (production of gas from the underground reservoir) to the effects (risk to people and damage to buildings). Data acquisition through field measurements and laboratory experiments was a substantial element of the research programme. The existing geophone and acc...

Geophysical Journal International, 2018

SUMMARY Induced seismicity typically arises from the progressive activation of recently inactive ... more SUMMARY Induced seismicity typically arises from the progressive activation of recently inactive geological faults by anthropogenic activity. Faults are mechanically and geometrically heterogeneous, so their extremes of stress and strength govern the initial evolution of induced seismicity. We derive a statistical model of Coulomb stress failures and associated aftershocks within the tail of the distribution of fault stress and strength variations to show initial induced seismicity rates will increase as an exponential function of induced stress. Our model provides operational forecasts consistent with the observed space–time–magnitude distribution of earthquakes induced by gas production from the Groningen field in the Netherlands. These probabilistic forecasts also match the observed changes in seismicity following a significant and sustained decrease in gas production rates designed to reduce seismic hazard and risk. This forecast capability allows reliable assessment of alternat...

Bulletin of the Seismological Society of America, 2015

A Monte Carlo approach to Probabilistic Seismic Hazard Assessment (PSHA) is developed for induced... more A Monte Carlo approach to Probabilistic Seismic Hazard Assessment (PSHA) is developed for induced seismicity associated with a compacting gas reservoir. The geomechanical foundation for the method is the work of Kostrov (1974) and McGarr (1976) linking total strain to summed seismic moment in an earthquake catalogue. Our Monte Carlo method simulates future seismic hazard consistent with historical seismic and compaction datasets by sampling probability distributions for total seismic moment, event locations and magnitudes, and resulting ground motions. Ground motions are aggregated over an ensemble of simulated catalogues to give a probabilistic representation of the ground-motion hazard. This approach is particularly well suited to the specific nature of the time-dependent induced seismicity considered. We demonstrate the method by applying it to seismicity induced by reservoir compaction following gas production from the Groningen gas field. A new ground motion prediction equation (GMPE) tailored to the Groningen field, has been derived by calibrating an existing GMPE with local strong motion data. For 2013 to 2023 we find a 2% chance of exceeding a peak ground acceleration of 0.57g and a 2% chance of exceeding a peak ground velocity of 22 cm/s above the area of maximum compaction. Disaggregation shows that earthquakes of magnitude 4-5, at the shortest hypocentral distances of 3 km, and ground motions two standard deviations above the median make the largest contributions to this hazard. Uncertainty in the hazard is primarily due to uncertainty about the future fraction of induced strains that will be seismogenic and how ground motion and its variability will scale to larger magnitudes.

A seismological model is developed for earthquakes induced by subsurface reservoir volume Q2 chan... more A seismological model is developed for earthquakes induced by subsurface reservoir volume Q2 changes. The approach is based on the work of Kostrov (1974) and McGarr (1976) linking total strain to the summed seismic moment in an earthquake catalog. We refer to the fraction of the total strain expressed as seismic moment as the strain partitioning function,. A probability distribution for total seismic moment as a function of time is derived from an evolving earthquake catalog. The moment distribution is taken to be a Pareto Sum Distribution with confidence bounds estimated using approximations given by Zaliapin et al. (2005). In this way available seismic moment is expressed in terms of reservoir volume change and hence compaction in the case of a depleting reservoir. The Pareto Sum Distribution for moment and the Pareto Distribution underpinning the Gutenberg-Richter Law are sampled using Monte Carlo methods to simulate synthetic earthquake catalogs for subsequent estimation of seismic ground motion hazard. We demonstrate the method by applying it to the Groningen gas field. A compaction model for the field calibrated using various geodetic data allows reservoir strain due to gas extraction to be expressed as a function of both spatial position and time since the start of production. Fitting with a generalized logistic function gives an empirical expression for the dependence of on reservoir compaction. Probability density maps for earthquake event locations can then be calculated from the compaction maps. Predicted seismic moment is shown to be strongly dependent on planned gas production.

A Monte Carlo approach to probabilistic seismic-hazard analysis is developed for a case of induce... more A Monte Carlo approach to probabilistic seismic-hazard analysis is developed for a case of induced seismicity associated with a compacting gas reservoir. The geomechanical foundation for the method is the work of Kostrov (1974) and McGarr (1976) linking total strain to summed seismic moment in an earthquake catalog. Our Monte Carlo method simulates future seismic hazard consistent with historical seismic and compaction datasets by sampling probability distributions for total seismic moment, event locations and magnitudes, and resulting ground motions. Ground motions are aggregated over an ensemble of simulated catalogs to give a prob-abilistic representation of the ground-motion hazard. This approach is particularly well suited to the specific nature of the time-dependent induced seismicity considered. We demonstrate the method by applying it to seismicity induced by reservoir com-paction following gas production from the Groningen gas field. A new ground-motion prediction equation (GMPE) tailored to the Groningen field, has been derived by calibrating an existing GMPE with local strong-motion data. For 2013–2023, we find a 2% chance of exceeding a peak ground acceleration of 0:57g and a 2% chance of exceeding a peak ground velocity of 22 cm=s above the area of maximum compaction. Disaggregation shows that earthquakes of M w 4–5, at the shortest hypocentral distances of 3 km, and ground motions two standard deviations above the median make the largest contributions to this hazard. Uncertainty in the hazard is primarily due to uncertainty about the future fraction of induced strains that will be seismogenic and how ground motion and its variability will scale to larger magnitudes.

Measurements of the strains and earthquakes induced by fluid extraction from a subsurface reservo... more Measurements of the strains and earthquakes induced by fluid extraction from a subsurface reservoir reveal a transient, exponential-like increase in seismicity relative to the volume of fluids extracted. If the frictional strength of these reactivating faults is heterogeneously and randomly distributed, then progressive failures of the weakest fault patches account in a general manner for this initial exponential-like trend. Allowing for the observable elastic and geometric heterogeneity of the reservoir, the spatiotemporal evolution of induced seismicity over 5 years is predictable without significant bias using a statistical physics model of poroelastic reservoir deformations inducing extreme threshold frictional failures of previously inactive faults. This model is used to forecast the temporal and spatial probability density of earthquakes within the Groningen natural gas reservoir, conditional on future gas production plans. Probabilistic seismic hazard and risk assessments based on these forecasts inform the current gas production policy and building strengthening plans. Plain Language Summary On rare occasions industrial activities create earthquakes that are sufficiently big and frequent to cause concern about the possibility of building damage and injury. One such example is Western Europe's largest producing natural gas field located next to the city of Groningen in the northeast of the Netherlands. If the physical processes that induce these earthquakes can be understood, then it might be possible to reduce the risks to acceptable levels by reducing the amount of natural gas extracted from below ground each year or by selectively strengthening buildings. A new theory was created to describe how extracting fluids, such as natural gas, from under the ground may distort the surrounding rocks in such a way that they occasionally and abruptly slide past each other forming an earthquake. Using this theory, the timing, location, and number of previous earthquakes within the Groningen gas field may be properly explained and the chance of further earthquakes in the coming few years can be reliably forecasted. These earthquake forecasts are now used to inform choices about how to safely extract the remaining gas from the Groningen field which is capable of supplying the European gas market for at least another 40 years.

S U M M A R Y Induced seismicity typically arises from the progressive activation of recently ina... more S U M M A R Y Induced seismicity typically arises from the progressive activation of recently inactive geological faults by anthropogenic activity. Faults are mechanically and geometrically heterogeneous, so their extremes of stress and strength govern the initial evolution of induced seismicity. We derive a statistical model of Coulomb stress failures and associated aftershocks within the tail of the distribution of fault stress and strength variations to show initial induced seismicity rates will increase as an exponential function of induced stress. Our model provides operational forecasts consistent with the observed space–time–magnitude distribution of earthquakes induced by gas production from the Groningen field in the Netherlands. These probabilistic forecasts also match the observed changes in seismicity following a significant and sustained decrease in gas production rates designed to reduce seismic hazard and risk. This forecast capability allows reliable assessment of alternative control options to better inform future induced seismic risk management decisions.