Injection-induced seismicity has been a focus of industry for decades as it poses great challenges to the associated risk mitigation and hazard assessment.The response surface methodology is integrated into the geo-me...Injection-induced seismicity has been a focus of industry for decades as it poses great challenges to the associated risk mitigation and hazard assessment.The response surface methodology is integrated into the geo-mechanical model to analyze the effects of multiple factors on induced seismicity during the post shut-in period.We investigate the roles of poroelastic stress and pore pressure diffusion and examine the differences in the controlling mechanism between fault damage zones and the fault core.A sensitivity analysis is conducted to rank the selected factors,followed by a Box‒Behnken design to form response surfaces and formulate prediction models for the Coulomb stress and its components.Reservoir properties significantly affect the potentials of induced seismicity in the fault by changing pore pressure diffusion,which can be influenced by other factors to varying degrees.Coulomb stress is greater in pressurized damage zones than in fault cores,and the seismicity rate exhibits a consistent variation.Poroelastic stress plays a similar role to pore pressure diffusion in the stability of the fault within the pressurized damage zones.However,pore pressure diffusion dominates in the fault core due to the low rigidity,which limits the accumulation of elastic energy caused by poroelastic coupling.The slip along the fault core is a critical issue to consider.The potential for induced seismicity is reduced in the right damage zones as the pore pressure diffusion is blocked by the low-permeability fault core.However,poroelastic stressing still occurs,and in deep basements,the poroelastic effect is dominant even without a direct increase in pore pressure.The findings in this study reveal the fundamental mechanisms behind injection-induced seismicity and provide guidance for optimizing injection schemes in specific situations.展开更多
Anthropogenic induced seismicity has been widely reported and investigated in many regions,including the shale gas fields in the Sichuan basin,where the frequency of earthquakes has increased substantially since the c...Anthropogenic induced seismicity has been widely reported and investigated in many regions,including the shale gas fields in the Sichuan basin,where the frequency of earthquakes has increased substantially since the commencement of fracking in late 2014.However,the details of how earthquakes are induced remain poorly understood,partly due to lack of high-resolution spatial-temporal data documenting the evolution of such seismic events.Most previous studies have been based on a diffusive earthquake catalog constructed by routine methods.Here,however,we have constructed a high resolution catalog using a machine learning detector and waveform cross-correlation.Despite limited data,this new approach has detected one-third more earthquakes and improves the magnitude completeness of the catalog,illuminating the comprehensive spatial-temporal migration of the emerging seismicity in the target area.One of the clusters clearly delineates a potential unmapped fault trace that may have led to the Mw 5.2 in September 2019,by far the largest earthquake recorded in the region.The migration of the seismicity also demonstrates a pore-pressure diffusion front,suggesting additional constraints on the inducing mechanism of the region.The patterns of the highly clustered seismicity reconcile the causal link between the emerging seismicity and the activity of hydraulic fracturing in the region,facilitating continued investigation of the mechanisms of seismic induction and their associated risks.展开更多
From December 3, 2005 to May 18, 2006, a water injection-induced seismicity test was conducted on DuPont test well 1# for about six months by China Earthquake Administration. To the vertical injected well, 11 water in...From December 3, 2005 to May 18, 2006, a water injection-induced seismicity test was conducted on DuPont test well 1# for about six months by China Earthquake Administration. To the vertical injected well, 11 water injection processes were conducted on four depth intervals, including middle Shahejie3, the top of the upper Shahejie3, the bottom of the upper Shahejie3 and Shahejie2, with the vertical span from 1464 m to 3 034 m. Monitoring stations has been run throughout the procedure. From the recorded data, there were 5 090 events being picked out manually, 274 events located. It indicates that the energy of seismic signal is very small, and the largest magnitude is no more than ML0.5. And also, the major energy is centered on the vertical component, while amplitude of the other horizontal components is very small. From the start of water injection, the number of seismic events varied with time. And the event was most frequent in the period of upper Shahejie3 injection. The distribution of events extended from the injected well to the outside with time, and the direction of events distribution rotated in different injected interval. Of which, in the low permeability interval, events trend close to the direction of principal compressive stress direction; while in higher permeability interval, they trend close to the predominant seepage direction.展开更多
Fluid pressurization within the fault zone generates increasing pore pressure and stress change which is liable to create shear and/or brittle fractures within the reservoir volumes and subsequently generating earthqu...Fluid pressurization within the fault zone generates increasing pore pressure and stress change which is liable to create shear and/or brittle fractures within the reservoir volumes and subsequently generating earthquakes of varying magnitudes.Here,we explored time-dependent fault weakening processes in the fault zone which are dependent on several factors,including the rate of cold-water injection,modes of injection(hydromechanical(HM)and thermo-hydro-mechanical(THM)interactions),and changing fault spatial configurations using data from Niger Delta Basin.The variation in the stability of different fault models in withstanding stresses induced by HM and THM fluid interactions is evident.Fault permeability enhancement and the behaviour of slip event under isothermal and non-isothermal conditions revealed that stress and pore pressure perturbations have a first order control on the rate of fault dilation and compression.It is observed that the progressive cooling of the reservoir induced thermal stress which induced the timing of slip by unloading the fault to earlier seismic rupture in the non-isothermal case,and accelerates the magnitude of the fault reactivation and the accompanied induced seismicity.Owing to increased tendency of shear failure during injection,fracture opening through shear dilation is more enhanced in THM simulation as the fracture permeability is significantly higher than in HM.This effect becomes increasingly more dominant with intermediate fault angle and joint orientation.Certain fault/joint configurations which were resistant to shear failure under isothermal injection had their frictional resistance broken by thermal stress.The results also indicate that there is higher pore pressure build-up in THM than in HM as the injection rate increases and reservoir temperature drops during cold injections..This study has demonstrated the importance of fully characterizing the fracture geometries and configurations of normal faulting regime in addition to fluid injection conditions when developing fractured reservoirs to mitigate seismic risks and hazards that could result from early fault reactivation.展开更多
This study aims to understand the effect of injection rate on injection-induced fracture activation in granite.We performed water injection-induced slip tests on samples containing either a smooth or a rough fracture ...This study aims to understand the effect of injection rate on injection-induced fracture activation in granite.We performed water injection-induced slip tests on samples containing either a smooth or a rough fracture at four different injection rates under undrained conditions and monitored the acoustic emission(AE)signals during the tests.Experimental results reveal that the critical activation fluid pressure is related to the injection rate,pressure diffusion rate,stress state,and fracture roughness.For the smooth fracture,as the injection rate increases,the critical activation fluid pressure increases significantly,while the injection rate has little effect on the critical activation fluid pressure of the rough fracture.The quasi-static slip distance of fractures decreases as the injection rate increases,with rough fractures exhibiting a greater overall slip distance compared to smooth fractures.The number of AE events per unit sliding distance increases with the injection rate,while the global b value decreases.These results indicate that higher injection rates produce more large-magnitude AE events and more severe slip instability and asperity damage.We established a linkage between fluid injection volume,injection rate,and AE events using the seismogenic index(Σ).The smooth fracture exhibits a steadily increasingΣwith the elapse of injection time,and the rate of increase is higher at higher injection rates;while the rough fracture is featured by a fluctuatingΣ,signifying the intermittent occurrence of large-magnitude AE events associated with the damage of larger fracture asperities.Our results highlight the importance of fracture surface heterogeneity on injection-induced fracture activation and slip.展开更多
In this study,a high-confining pressure and real-time large-displacement shearing-flow setup was developed.The test setup can be used to analyze the injection pressure conditions that increase the hydro-shearing perme...In this study,a high-confining pressure and real-time large-displacement shearing-flow setup was developed.The test setup can be used to analyze the injection pressure conditions that increase the hydro-shearing permeability and injection-induced seismicity during hot dry rock geothermal extraction.For optimizing injection strategies and improving engineering safety,real-time permeability,deformation,and energy release characteristics of fractured granite samples driven by injected water pressure under different critical sliding conditions were evaluated.The results indicated that:(1)A low injection water pressure induced intermittent small-deformation stick-slip behavior in fractures,and a high injection pressure primarily caused continuous high-speed large-deformation sliding in fractures.The optimal injection water pressure range was defined for enhancing hydraulic shear permeability and preventing large injection-induced earthquakes.(2)Under the same experimental conditions,fracture sliding was deemed as the major factor that enhanced the hydraulic shear-permeability enhancement and the maximum permeability increased by 36.54 and 41.59 times,respectively,in above two slip modes.(3)Based on the real-time transient evolution of water pressure during fracture sliding,the variation coefficients of slip rate,permeability,and water pressure were fitted,and the results were different from those measured under quasi-static conditions.(4)The maximum and minimum shear strength criteria for injection-induced fracture sliding were also determined(μ=0.6665 andμ=0.1645,respectively,μis friction coefficient).Using the 3D(three-dimensional)fracture surface scanning technology,the weakening effect of injection pressure on fracture surface damage characteristics was determined,which provided evidence for the geological markers of fault sliding mode and sliding nature transitions under the fluid influence.展开更多
The occurrence time and magnitude of injection-induced seismicity are influenced by engineering factors,such as wellhead pressure,injection location,injection volume,and injection rate.Understanding the relationship b...The occurrence time and magnitude of injection-induced seismicity are influenced by engineering factors,such as wellhead pressure,injection location,injection volume,and injection rate.Understanding the relationship between injection operations and seismic magnitude is of great significance for optimizing industrial production and reducing earthquake disasters.Numerical simulation of hydromechanical coupling is a crucial method for studying injection-induced seismicity.However,few studies have explored the risk management measures for injection-induced seismicity from the perspective of engineering.How seismic magnitudes can be reduced through reasonable adjustments to injection operations in engineering remains unclear.Therefore,in this study,a 3D hydro-mechanical coupling model involving multiple faults and injection wells was established based on the geological background and well location of Fox Creek,Canada.Different injection schemes under multi-well and multi-fault conditions were studied,and a traffic light system was used to simulate and control the magnitudes under a multi-well injection scheme.Specifically,we simulated injection scenarios involving up to three wells and analyzed the response of five faults.We compared the maximum moment magnitude of different scenarios by controlling the same injection volume.The results revealed the effect and advantage of the multi-well scheme in reducing seismic magnitude.To reduce the risk of induced seismicity,utilizing far-fault operational wells to compensate for the effects of near-fault operational wells proves to be an efficient and cost-effective method,with potential for wide practical applications.展开更多
Late at night on 17 June 2019,a magnitude 6.0 earthquake struck Shuanghe Town and its surrounding area in Changning County,Sichuan,China,becoming the largest earthquake recorded within the southern Sichuan Basin.A ser...Late at night on 17 June 2019,a magnitude 6.0 earthquake struck Shuanghe Town and its surrounding area in Changning County,Sichuan,China,becoming the largest earthquake recorded within the southern Sichuan Basin.A series of earthquakes with magnitudes up to 5.6 occurred during a short period after the mainshock,and we thus refer to these earthquakes as the Changning M6 earthquake sequence(or swarm).The mainshock was located very close to a salt mine,into which for^3 decades fresh water had been extensively injected through several wells at a depth of 2.7–3 km.It was also near(within^15 km)the epicenter of the 18 December 2018 M5.7 Xingwen earthquake,which is thought to have been induced by shale gas hydraulic fracturing(HF),prompting questions about the possible involvement of industrial activities in the M6 sequence.Following previous studies,this paper focuses on the relationship between injection and seismicity in the Shuanghe salt field and its adjacent Shangluo shale gas block.Except for a period of serious water loss after the start of cross-well injection in 2005–2006,the frequency of earthquakes shows a slightly increasing tendency.Overall,there is a good correlation between the event rate in the Shuanghe area and the loss of injected water.More than 400 M≥3 earthquakes,including 40 M≥4 and 5 M≥5 events,had been observed by the end of August 2019.Meanwhile,in the Shangluo area,seismicity has increased during drilling and HF operations(mostly in vertical wells)since about 2009,and dramatically since the end of 2014,coincident with the start of systematic HF in the area.The event rate shows a progressively increasing background with some fluctuations,paralleling the increase in HF operations.More than 700 M≥3 earthquakes,including 10 M≥4 and 3 M≥5 in spatially and temporally clustered seismic events,are correlated closely with active fracturing platforms.Well-resolved centroid moment tensor results for M≥4 earthquakes were shown to occur at very shallow depths around shale formations with active HF,in agreement with some of the clusters,which occurred within the coverage area of temporary or new permanent monitoring stations and thus have been precisely located.After the Xingwen M5.7 earthquake,seismic activity in the salt well area increased significantly.The Xingwen earthquake may have created a unidirectional rupture to the NNW,with an end point close to the NW-trending fault of the Shuanghe earthquake.Thus,a fault in the Changning anticline might have terminated the fault rupture of the Xingwen earthquake,possibly giving the Xingwen earthquake a role in promoting the Changning M6 event.展开更多
Water reinjection into the formation is an indispensable operation in many energy engineering practices.This operation involves a complex hydromechanical(HM)coupling process and sometimes even causes unpredictable dis...Water reinjection into the formation is an indispensable operation in many energy engineering practices.This operation involves a complex hydromechanical(HM)coupling process and sometimes even causes unpredictable disasters,such as induced seismicity.It is acknowledged that the relative magnitude and direction of the principal stresses significantly influence the HM behaviors of rocks during injection.However,due to the limitations of current testing techniques,it is still difficult to comprehensively conduct laboratory injection tests under various stress conditions,such as in triaxial extension stress states.To this end,a numerical study of HM changes in rocks during injection under different stress states is conducted.In this model,the saturated rock is first loaded to the target stress state under drainage conditions,and then the stress state is maintained and water is injected from the top to simulate the formation injection operation.Particular attention is given to the difference in HM changes under triaxial compression and extension stresses.This includes the differences in the pore pressure propagation,mean effective stress,volumetric strain,and stress-induced permeability.The numerical results demonstrate that the differential stress will significantly affect the HM behaviors of rocks,but the degree of influence is different under the two triaxial stress states.The HM changes caused by the triaxial compression stress states are generally greater than those of extension,but the differences decrease with increasing differential stress,indicating that the increase in the differential stress will weaken the impact of the stress state on the HM response.In addition,the shear failure potential of fracture planes with various inclination angles is analyzed and summarized under different stress states.It is recommended that engineers could design suitable injection schemes according to different tectonic stress fields versus fault occurrence to reduce the risk of injection-induced seismicity.展开更多
Observations of surface displacements are expected to aid in geomechanical analyses of injectioninduced seismicity.However,the controlling factors of the displacement magnitude remain poorly understood except the elas...Observations of surface displacements are expected to aid in geomechanical analyses of injectioninduced seismicity.However,the controlling factors of the displacement magnitude remain poorly understood except the elastic modulus of the fluid-bearing reservoir.Here,an experiment scheme of numerical simulation based on fully-coupled poroelasticity is designed to investigate the displacements induced by deep underground fluid injection.According to the sealing ability of deep reservoirs,the numerical experiments are classified into two scenarios:injection into open and sealed reservoirs.Potential effects from both geological and operational parameters are considered during the experiments,which include the hydromechanical properties,the reservoir geometry,injection rates and volumes.Experimental results reveal that in addition to the reservoir depth and Young’s modulus,the porosity also has significant influences on the surface displacements.Geodetic modeling of injection-induced displacements should include the parameter of reservoir porosity.When the reservoir is characterized by a good sealing ability,fluid injection is prone to induce larger horizontal displacements than vertical uplifts.Most of injection activities including hydraulic fracturing can probably induce detectable surface displacements.Geodetic surveying,especially using Global Navigation Satellite System(GNSS)with both horizontal and vertical observations,should become an essential monitoring task for anthropogenic fluid injection/production activities,which is conducive to assess and mitigate some geohazards including earthquakes.展开更多
This study investigated the fault nucleation and rupture processes driven by stress and fluid pressure in finegrained granite by monitoring acoustic emissions (AEs). Through detailed analysis of the spatiotemporal distr...This study investigated the fault nucleation and rupture processes driven by stress and fluid pressure in finegrained granite by monitoring acoustic emissions (AEs). Through detailed analysis of the spatiotemporal distribution of the AE hypocenter, P-wave velocity, stress-strain, and other experimental observation data underdifferent confining pressures for stress-driven fractures and under different water injection conditions for fluiddriven fractures, it was found that fluid has the following effects: 1) complicating the fault nucleation process,2) exhibiting episodic AE activity corresponding to fault branching and the formation of multiple faults, 3)extending the spatiotemporal scale of nucleation processes and pre-slip, and 4) reducing the dynamic rupturevelocity and stress drop. The experiments also show that 1) during the fault nucleation process, the b-value for AEschanges from 1 to 1.3 to 0.5 before dynamic rupture, and then rapidly recovers to around 1–1.2 during aftershockactivity and 2) the hydraulic diffusivity gradually increases from an initial pre-rupture order of 0.1 m2/s to10–100 m2/s after dynamic rupture. These results provide a reasonable fault pre-slip model, indicating thathydraulic fracturing promotes shear slip before dynamic rupture, as well as laboratory-scale insights into ensuringthe safety and effectiveness of hydraulic fracturing operations related to activities such as geothermal development, evaluating the seismic risk induced by water injection, and further researching the precursory preparationprocess for deep fluid-driven or fluid-involved natural earthquakes. The publicly available dataset is expected tobe used for various purposes, including 1) as training data for artificial intelligence related to microseismic dataprocessing and analysis, 2) predicting the remaining time before rock fractures, and 3) establishing models andassessment methods for the relationship between microseismic characteristics and rock hydraulic properties,which will deepen our understanding of the interaction mechanisms between fluid migration and rock deformation and fracture.展开更多
基金the Major Project of Inner Mongolia Science and Technology(Grant No.2021ZD0034)National Natural Science Foundation of China(Grant No.41872210)Creative Groups of Natural Science Foundation of Hubei Province(Grant No.2021CFA030).
文摘Injection-induced seismicity has been a focus of industry for decades as it poses great challenges to the associated risk mitigation and hazard assessment.The response surface methodology is integrated into the geo-mechanical model to analyze the effects of multiple factors on induced seismicity during the post shut-in period.We investigate the roles of poroelastic stress and pore pressure diffusion and examine the differences in the controlling mechanism between fault damage zones and the fault core.A sensitivity analysis is conducted to rank the selected factors,followed by a Box‒Behnken design to form response surfaces and formulate prediction models for the Coulomb stress and its components.Reservoir properties significantly affect the potentials of induced seismicity in the fault by changing pore pressure diffusion,which can be influenced by other factors to varying degrees.Coulomb stress is greater in pressurized damage zones than in fault cores,and the seismicity rate exhibits a consistent variation.Poroelastic stress plays a similar role to pore pressure diffusion in the stability of the fault within the pressurized damage zones.However,pore pressure diffusion dominates in the fault core due to the low rigidity,which limits the accumulation of elastic energy caused by poroelastic coupling.The slip along the fault core is a critical issue to consider.The potential for induced seismicity is reduced in the right damage zones as the pore pressure diffusion is blocked by the low-permeability fault core.However,poroelastic stressing still occurs,and in deep basements,the poroelastic effect is dominant even without a direct increase in pore pressure.The findings in this study reveal the fundamental mechanisms behind injection-induced seismicity and provide guidance for optimizing injection schemes in specific situations.
基金supported by the National Key R&D Program of China(2018YFC1504501)the Hong Kong Research Grants Council(No.14303721 and N_CUHK430/16)the Faculty of Science,CUHK。
文摘Anthropogenic induced seismicity has been widely reported and investigated in many regions,including the shale gas fields in the Sichuan basin,where the frequency of earthquakes has increased substantially since the commencement of fracking in late 2014.However,the details of how earthquakes are induced remain poorly understood,partly due to lack of high-resolution spatial-temporal data documenting the evolution of such seismic events.Most previous studies have been based on a diffusive earthquake catalog constructed by routine methods.Here,however,we have constructed a high resolution catalog using a machine learning detector and waveform cross-correlation.Despite limited data,this new approach has detected one-third more earthquakes and improves the magnitude completeness of the catalog,illuminating the comprehensive spatial-temporal migration of the emerging seismicity in the target area.One of the clusters clearly delineates a potential unmapped fault trace that may have led to the Mw 5.2 in September 2019,by far the largest earthquake recorded in the region.The migration of the seismicity also demonstrates a pore-pressure diffusion front,suggesting additional constraints on the inducing mechanism of the region.The patterns of the highly clustered seismicity reconcile the causal link between the emerging seismicity and the activity of hydraulic fracturing in the region,facilitating continued investigation of the mechanisms of seismic induction and their associated risks.
基金Collaborative Project between China and America "Temporary Seismic Activity Monitoring and Analysis for DuPont Test Well 1#, Dongying, Shandong Province"
文摘From December 3, 2005 to May 18, 2006, a water injection-induced seismicity test was conducted on DuPont test well 1# for about six months by China Earthquake Administration. To the vertical injected well, 11 water injection processes were conducted on four depth intervals, including middle Shahejie3, the top of the upper Shahejie3, the bottom of the upper Shahejie3 and Shahejie2, with the vertical span from 1464 m to 3 034 m. Monitoring stations has been run throughout the procedure. From the recorded data, there were 5 090 events being picked out manually, 274 events located. It indicates that the energy of seismic signal is very small, and the largest magnitude is no more than ML0.5. And also, the major energy is centered on the vertical component, while amplitude of the other horizontal components is very small. From the start of water injection, the number of seismic events varied with time. And the event was most frequent in the period of upper Shahejie3 injection. The distribution of events extended from the injected well to the outside with time, and the direction of events distribution rotated in different injected interval. Of which, in the low permeability interval, events trend close to the direction of principal compressive stress direction; while in higher permeability interval, they trend close to the predominant seepage direction.
文摘Fluid pressurization within the fault zone generates increasing pore pressure and stress change which is liable to create shear and/or brittle fractures within the reservoir volumes and subsequently generating earthquakes of varying magnitudes.Here,we explored time-dependent fault weakening processes in the fault zone which are dependent on several factors,including the rate of cold-water injection,modes of injection(hydromechanical(HM)and thermo-hydro-mechanical(THM)interactions),and changing fault spatial configurations using data from Niger Delta Basin.The variation in the stability of different fault models in withstanding stresses induced by HM and THM fluid interactions is evident.Fault permeability enhancement and the behaviour of slip event under isothermal and non-isothermal conditions revealed that stress and pore pressure perturbations have a first order control on the rate of fault dilation and compression.It is observed that the progressive cooling of the reservoir induced thermal stress which induced the timing of slip by unloading the fault to earlier seismic rupture in the non-isothermal case,and accelerates the magnitude of the fault reactivation and the accompanied induced seismicity.Owing to increased tendency of shear failure during injection,fracture opening through shear dilation is more enhanced in THM simulation as the fracture permeability is significantly higher than in HM.This effect becomes increasingly more dominant with intermediate fault angle and joint orientation.Certain fault/joint configurations which were resistant to shear failure under isothermal injection had their frictional resistance broken by thermal stress.The results also indicate that there is higher pore pressure build-up in THM than in HM as the injection rate increases and reservoir temperature drops during cold injections..This study has demonstrated the importance of fully characterizing the fracture geometries and configurations of normal faulting regime in addition to fluid injection conditions when developing fractured reservoirs to mitigate seismic risks and hazards that could result from early fault reactivation.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFB2390300)the National Natural Science Foundation of China(Grant No.42172292)Yinlin Ji is grateful for the support by the Helmholtz Association's Initiative and Networking Fund for the Helmholtz Young Investigator Group ARES(Contract No.VH-NG-1516).
文摘This study aims to understand the effect of injection rate on injection-induced fracture activation in granite.We performed water injection-induced slip tests on samples containing either a smooth or a rough fracture at four different injection rates under undrained conditions and monitored the acoustic emission(AE)signals during the tests.Experimental results reveal that the critical activation fluid pressure is related to the injection rate,pressure diffusion rate,stress state,and fracture roughness.For the smooth fracture,as the injection rate increases,the critical activation fluid pressure increases significantly,while the injection rate has little effect on the critical activation fluid pressure of the rough fracture.The quasi-static slip distance of fractures decreases as the injection rate increases,with rough fractures exhibiting a greater overall slip distance compared to smooth fractures.The number of AE events per unit sliding distance increases with the injection rate,while the global b value decreases.These results indicate that higher injection rates produce more large-magnitude AE events and more severe slip instability and asperity damage.We established a linkage between fluid injection volume,injection rate,and AE events using the seismogenic index(Σ).The smooth fracture exhibits a steadily increasingΣwith the elapse of injection time,and the rate of increase is higher at higher injection rates;while the rough fracture is featured by a fluctuatingΣ,signifying the intermittent occurrence of large-magnitude AE events associated with the damage of larger fracture asperities.Our results highlight the importance of fracture surface heterogeneity on injection-induced fracture activation and slip.
基金supported by the National Natural Science Foundation of China (Grant No.52122405)Science and Technology Major Project of Shanxi Province,China (Grant No.202101060301024)Science and Technology Major Project of Xizang Autonomous Region,China (Grant No.XZ202201ZD0004G0204).
文摘In this study,a high-confining pressure and real-time large-displacement shearing-flow setup was developed.The test setup can be used to analyze the injection pressure conditions that increase the hydro-shearing permeability and injection-induced seismicity during hot dry rock geothermal extraction.For optimizing injection strategies and improving engineering safety,real-time permeability,deformation,and energy release characteristics of fractured granite samples driven by injected water pressure under different critical sliding conditions were evaluated.The results indicated that:(1)A low injection water pressure induced intermittent small-deformation stick-slip behavior in fractures,and a high injection pressure primarily caused continuous high-speed large-deformation sliding in fractures.The optimal injection water pressure range was defined for enhancing hydraulic shear permeability and preventing large injection-induced earthquakes.(2)Under the same experimental conditions,fracture sliding was deemed as the major factor that enhanced the hydraulic shear-permeability enhancement and the maximum permeability increased by 36.54 and 41.59 times,respectively,in above two slip modes.(3)Based on the real-time transient evolution of water pressure during fracture sliding,the variation coefficients of slip rate,permeability,and water pressure were fitted,and the results were different from those measured under quasi-static conditions.(4)The maximum and minimum shear strength criteria for injection-induced fracture sliding were also determined(μ=0.6665 andμ=0.1645,respectively,μis friction coefficient).Using the 3D(three-dimensional)fracture surface scanning technology,the weakening effect of injection pressure on fracture surface damage characteristics was determined,which provided evidence for the geological markers of fault sliding mode and sliding nature transitions under the fluid influence.
基金funded by the Joint Funds of the National Natural Science Foundation of China(U23A20671)the Major Project of Inner Mongolia Science and Technology(2021ZD0034)the Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering(No.Z021003)。
文摘The occurrence time and magnitude of injection-induced seismicity are influenced by engineering factors,such as wellhead pressure,injection location,injection volume,and injection rate.Understanding the relationship between injection operations and seismic magnitude is of great significance for optimizing industrial production and reducing earthquake disasters.Numerical simulation of hydromechanical coupling is a crucial method for studying injection-induced seismicity.However,few studies have explored the risk management measures for injection-induced seismicity from the perspective of engineering.How seismic magnitudes can be reduced through reasonable adjustments to injection operations in engineering remains unclear.Therefore,in this study,a 3D hydro-mechanical coupling model involving multiple faults and injection wells was established based on the geological background and well location of Fox Creek,Canada.Different injection schemes under multi-well and multi-fault conditions were studied,and a traffic light system was used to simulate and control the magnitudes under a multi-well injection scheme.Specifically,we simulated injection scenarios involving up to three wells and analyzed the response of five faults.We compared the maximum moment magnitude of different scenarios by controlling the same injection volume.The results revealed the effect and advantage of the multi-well scheme in reducing seismic magnitude.To reduce the risk of induced seismicity,utilizing far-fault operational wells to compensate for the effects of near-fault operational wells proves to be an efficient and cost-effective method,with potential for wide practical applications.
基金the State Scholarship Fund of China (No. 201804190004)
文摘Late at night on 17 June 2019,a magnitude 6.0 earthquake struck Shuanghe Town and its surrounding area in Changning County,Sichuan,China,becoming the largest earthquake recorded within the southern Sichuan Basin.A series of earthquakes with magnitudes up to 5.6 occurred during a short period after the mainshock,and we thus refer to these earthquakes as the Changning M6 earthquake sequence(or swarm).The mainshock was located very close to a salt mine,into which for^3 decades fresh water had been extensively injected through several wells at a depth of 2.7–3 km.It was also near(within^15 km)the epicenter of the 18 December 2018 M5.7 Xingwen earthquake,which is thought to have been induced by shale gas hydraulic fracturing(HF),prompting questions about the possible involvement of industrial activities in the M6 sequence.Following previous studies,this paper focuses on the relationship between injection and seismicity in the Shuanghe salt field and its adjacent Shangluo shale gas block.Except for a period of serious water loss after the start of cross-well injection in 2005–2006,the frequency of earthquakes shows a slightly increasing tendency.Overall,there is a good correlation between the event rate in the Shuanghe area and the loss of injected water.More than 400 M≥3 earthquakes,including 40 M≥4 and 5 M≥5 events,had been observed by the end of August 2019.Meanwhile,in the Shangluo area,seismicity has increased during drilling and HF operations(mostly in vertical wells)since about 2009,and dramatically since the end of 2014,coincident with the start of systematic HF in the area.The event rate shows a progressively increasing background with some fluctuations,paralleling the increase in HF operations.More than 700 M≥3 earthquakes,including 10 M≥4 and 3 M≥5 in spatially and temporally clustered seismic events,are correlated closely with active fracturing platforms.Well-resolved centroid moment tensor results for M≥4 earthquakes were shown to occur at very shallow depths around shale formations with active HF,in agreement with some of the clusters,which occurred within the coverage area of temporary or new permanent monitoring stations and thus have been precisely located.After the Xingwen M5.7 earthquake,seismic activity in the salt well area increased significantly.The Xingwen earthquake may have created a unidirectional rupture to the NNW,with an end point close to the NW-trending fault of the Shuanghe earthquake.Thus,a fault in the Changning anticline might have terminated the fault rupture of the Xingwen earthquake,possibly giving the Xingwen earthquake a role in promoting the Changning M6 event.
基金funded by the National Natural Science Foundation of China(Grant Nos.41872210 and 41902297)IRSMGFZ Subsurface Utilization of Captured Carbon and Energy Storage System and the Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering(Grant No.Z018004).
文摘Water reinjection into the formation is an indispensable operation in many energy engineering practices.This operation involves a complex hydromechanical(HM)coupling process and sometimes even causes unpredictable disasters,such as induced seismicity.It is acknowledged that the relative magnitude and direction of the principal stresses significantly influence the HM behaviors of rocks during injection.However,due to the limitations of current testing techniques,it is still difficult to comprehensively conduct laboratory injection tests under various stress conditions,such as in triaxial extension stress states.To this end,a numerical study of HM changes in rocks during injection under different stress states is conducted.In this model,the saturated rock is first loaded to the target stress state under drainage conditions,and then the stress state is maintained and water is injected from the top to simulate the formation injection operation.Particular attention is given to the difference in HM changes under triaxial compression and extension stresses.This includes the differences in the pore pressure propagation,mean effective stress,volumetric strain,and stress-induced permeability.The numerical results demonstrate that the differential stress will significantly affect the HM behaviors of rocks,but the degree of influence is different under the two triaxial stress states.The HM changes caused by the triaxial compression stress states are generally greater than those of extension,but the differences decrease with increasing differential stress,indicating that the increase in the differential stress will weaken the impact of the stress state on the HM response.In addition,the shear failure potential of fracture planes with various inclination angles is analyzed and summarized under different stress states.It is recommended that engineers could design suitable injection schemes according to different tectonic stress fields versus fault occurrence to reduce the risk of injection-induced seismicity.
基金who provided financial support for this studysupported by the CUHK Research Fellowship Scheme(4200555)NSFC/RGC joint Research Scheme(NCUHK418/15)。
文摘Observations of surface displacements are expected to aid in geomechanical analyses of injectioninduced seismicity.However,the controlling factors of the displacement magnitude remain poorly understood except the elastic modulus of the fluid-bearing reservoir.Here,an experiment scheme of numerical simulation based on fully-coupled poroelasticity is designed to investigate the displacements induced by deep underground fluid injection.According to the sealing ability of deep reservoirs,the numerical experiments are classified into two scenarios:injection into open and sealed reservoirs.Potential effects from both geological and operational parameters are considered during the experiments,which include the hydromechanical properties,the reservoir geometry,injection rates and volumes.Experimental results reveal that in addition to the reservoir depth and Young’s modulus,the porosity also has significant influences on the surface displacements.Geodetic modeling of injection-induced displacements should include the parameter of reservoir porosity.When the reservoir is characterized by a good sealing ability,fluid injection is prone to induce larger horizontal displacements than vertical uplifts.Most of injection activities including hydraulic fracturing can probably induce detectable surface displacements.Geodetic surveying,especially using Global Navigation Satellite System(GNSS)with both horizontal and vertical observations,should become an essential monitoring task for anthropogenic fluid injection/production activities,which is conducive to assess and mitigate some geohazards including earthquakes.
文摘This study investigated the fault nucleation and rupture processes driven by stress and fluid pressure in finegrained granite by monitoring acoustic emissions (AEs). Through detailed analysis of the spatiotemporal distribution of the AE hypocenter, P-wave velocity, stress-strain, and other experimental observation data underdifferent confining pressures for stress-driven fractures and under different water injection conditions for fluiddriven fractures, it was found that fluid has the following effects: 1) complicating the fault nucleation process,2) exhibiting episodic AE activity corresponding to fault branching and the formation of multiple faults, 3)extending the spatiotemporal scale of nucleation processes and pre-slip, and 4) reducing the dynamic rupturevelocity and stress drop. The experiments also show that 1) during the fault nucleation process, the b-value for AEschanges from 1 to 1.3 to 0.5 before dynamic rupture, and then rapidly recovers to around 1–1.2 during aftershockactivity and 2) the hydraulic diffusivity gradually increases from an initial pre-rupture order of 0.1 m2/s to10–100 m2/s after dynamic rupture. These results provide a reasonable fault pre-slip model, indicating thathydraulic fracturing promotes shear slip before dynamic rupture, as well as laboratory-scale insights into ensuringthe safety and effectiveness of hydraulic fracturing operations related to activities such as geothermal development, evaluating the seismic risk induced by water injection, and further researching the precursory preparationprocess for deep fluid-driven or fluid-involved natural earthquakes. The publicly available dataset is expected tobe used for various purposes, including 1) as training data for artificial intelligence related to microseismic dataprocessing and analysis, 2) predicting the remaining time before rock fractures, and 3) establishing models andassessment methods for the relationship between microseismic characteristics and rock hydraulic properties,which will deepen our understanding of the interaction mechanisms between fluid migration and rock deformation and fracture.
