This study elucidates the findings of a computational investigation into the stimulation characteristics of natural reservoir systems enhanced by high-voltage electropulse-assisted fluid injection.The presented method...This study elucidates the findings of a computational investigation into the stimulation characteristics of natural reservoir systems enhanced by high-voltage electropulse-assisted fluid injection.The presented methodology delineates the comprehensive rock-fracturing process induced by electropulse and subsequent fluid injection,encompassing the discharge circuit,plasma channel formation,shockwave propagation,and hydro-mechanical response.A hydromechanical model incorporating an anisotropic plastic damage constitutive law,discrete fracture networks,and heterogeneous distribution is developed to represent the natural reservoir system.The results demonstrate that high-voltage electropulse effectively generates intricate fracture networks,significantly enhances the hydraulic properties of reservoir systems,and mitigates the adverse impact of ground stress on fracturing.The stimulationenhancing effect of electropulse is observed to intensify with increasing discharge voltage,with enhancements of 118.0%,139.5%,and 169.0%corresponding to discharge voltages of 20 kV,40 kV,and 60 kV,respectively.Additionally,a high-voltage electropulse with an initial voltage of U_(0)=80 kV and capacitance C=5μF has been shown to augment the efficiency of injection activation to approximately 201.1%compared to scenarios without electropulse.Under the influence of high-voltage electropulse,the fluid pressure distribution diverges from the conventional single direction of maximum stress,extending over larger areas.These innovative methods and findings hold potential implications for optimizing reservoir stimulation in geo-energy engineering.展开更多
An unusual increase in seismicity rate near the development and production sites of unconventional energy(e.g.,natural gas and geothermal fluids)has been attributed to subsurface fluid injection.Damaging and hazardous...An unusual increase in seismicity rate near the development and production sites of unconventional energy(e.g.,natural gas and geothermal fluids)has been attributed to subsurface fluid injection.Damaging and hazardous earthquakes in many countries(e.g.,China,South Korea,and the United States)have motivated tremendous effort to understand the complexity of fault slip behaviors in response to fluid pressurization.This study reviews key characteristics of injection-induced fault slip and highlights prediction and mitigation strategies relevant to unconventional energy projects.This capability relies on adequate understanding and characterization of first-and second-order friction and stability behaviors of faults as well as impacts of fluid pressurization and its role in triggering aseismic,seismic,and transitional slip behaviors.Suitable methods of investigation and characterization are noted together with typical examples together with scientific advances in our understanding towards forewarning and mitigation.Present challenges are addressed relating to the understanding of complex secondorder friction behaviors and the location and characterization of blind faults.These needs are aided in the integration of multi-scale and multi-physical data obtained from laboratory,numerical,and field studies to offer crucial information for induced hazard preparedness and rapid run-up assessment.Finally,emerging technologies contributing to an improved understanding,such as data analytics and machine learning,are discussed in heralding the next frontier for injection-induced seismicity research.展开更多
Stress changes due to changes in fluid pressure and temperature in a faulted formation may lead to the opening/shearing of the fault.This can be due to subsurface(geo)engineering activities such as fluid injections an...Stress changes due to changes in fluid pressure and temperature in a faulted formation may lead to the opening/shearing of the fault.This can be due to subsurface(geo)engineering activities such as fluid injections and geologic disposal of nuclear waste.Such activities are expected to rise in the future making it necessary to assess their short-and long-term safety.Here,a new machine learning(ML)approach to model pore pressure and fault displacements in response to high-pressure fluid injection cycles is developed.The focus is on fault behavior near the injection borehole.To capture the temporal dependencies in the data,long short-term memory(LSTM)networks are utilized.To prevent error accumulation within the forecast window,four critical measures to train a robust LSTM model for predicting fault response are highlighted:(i)setting an appropriate value of LSTM lag,(ii)calibrating the LSTM cell dimension,(iii)learning rate reduction during weight optimization,and(iv)not adopting an independent injection cycle as a validation set.Several numerical experiments were conducted,which demonstrated that the ML model can capture peaks in pressure and associated fault displacement that accompany an increase in fluid injection.The model also captured the decay in pressure and displacement during the injection shut-in period.Further,the ability of an ML model to highlight key changes in fault hydromechanical activation processes was investigated,which shows that ML can be used to monitor risk of fault activation and leakage during high pressure fluid injections.展开更多
The problem of magnetohydrodynamic （MHD） flow on a moving surface with the power-law velocity and special injection/blowing is investigated. A scaling group transformation is used to reduce the governing equations t...The problem of magnetohydrodynamic （MHD） flow on a moving surface with the power-law velocity and special injection/blowing is investigated. A scaling group transformation is used to reduce the governing equations to a system of ordinary differen- tial equations. The skin friction coefficients of the MHD boundary layer flow are derived, and the approximate solutions of the flow characteristics are obtained with the homotopy analysis method （HAM）. The approximate solutions are easily computed by use of a high order iterative procedure, and the effects of the power-law index, the magnetic parameter, and the special suction/blowing parameter on the dynamics are analyzed. The obtained results are compared with the numerical results published in the literature, verifying the reliability of the approximate solutions.展开更多
Fracture/fault instability induced by fluid injection in deep geothermal reservoirs could not only vary the reservoir permeability but also trigger hazardous seismicity.To address this,we conducted triaxial shear expe...Fracture/fault instability induced by fluid injection in deep geothermal reservoirs could not only vary the reservoir permeability but also trigger hazardous seismicity.To address this,we conducted triaxial shear experiments on granite fractures with different architected roughnesses reactivated under fluid injection,to investigate the controls on permeability evolution linked to reactivation.Our results indicate that the fracture roughness and injection strategies are two main factors affecting permeability evolution.For fractures with dif-ferent roughnesses,a rougher fracture leads to a lower peak reactivated permeability(k_(max)),and varying the fluid injection strategy(in-cluding the confining pressure and injection rate)has a less impact on kmax,indicating that the evolution of permeability during fluid pressurization is likely to be determined by the fracture roughness along the shear direction.Both the fracture roughness and injection strategies affect the average rates of permeability change and this parameter also reflects the long-term reservoir recovery.Our results have important implications for understanding the permeability evolution and the injection-induced fracture/fault slips in granite reser-voirs during the deep geothermal energy extraction.展开更多
With the advancement of fracturing technologies in deeper and more geologically complex formations,fault reactivation and induced seismicity have attracted increasing attention.The increasing frequency and magnitude o...With the advancement of fracturing technologies in deeper and more geologically complex formations,fault reactivation and induced seismicity have attracted increasing attention.The increasing frequency and magnitude of these events underscore the need for a robust understanding of the governing physical mechanisms.Elevated pore pressure,modified fault-loading conditions,and aseismic slip are widely acknowledged as the primary drivers.Recent studies have explored these mechanisms under varying factors,including fluid properties,rock ductility,poroelastic responses,and evolving fault stress states,thereby offering critical insights into model refinement.Probabilistic forecasting approaches,which combine statistical analyses of historical data with real-time monitoring,are being increasingly adopted in seismic risk assessments.In parallel,machine learning techniques are employed to process large seismic datasets and identify key patterns.However,their predictive capabilities remain limited by geological heterogeneity,subsurface complexity,and scarce observational data.Moreover,fluid–rock interactions further complicate the development of universally applicable models,thereby constraining the generalizability of mitigation strategies.This review synthesizes the current understanding of induced seismicity mechanisms,evaluates the prevailing prediction and mitigation methods,and identifies major challenges and future research directions.Advancements in these areas are essential to enhancing seismic risk management and ensuring the safe,sustainable development of deep-subsurface energy resources.展开更多
In order to improve our understanding of rock fracture and fault instability driven by high-pressure fluid sources, the authors carried out rock fracture tests using granite under a confining pressure of 80 MPa with f...In order to improve our understanding of rock fracture and fault instability driven by high-pressure fluid sources, the authors carried out rock fracture tests using granite under a confining pressure of 80 MPa with fluid injection in the laboratory. Furthermore, we tested a number of numerical models using the FLAC;modeling software to find the best model to represent the experimental results. The high-speed multichannel acoustic emission（AE） waveform recording system used in this study made it possible to examine the total fracture process through detailed monitoring of AE hypocenters and seismic velocity.The experimental results show that injecting high-pressure oil into the rock sample can induce AE activity at very low stress levels and can dramatically reduce the strength of the rock. The results of the numerical simulations show that major experimental results, including the strength, the temporal and spatial patterns of the AE events, and the role of the fluid can be represented fairly well by a model involving（1） randomly distributed defect elements to model pre-existing cracks,（2） random modification of rock properties to represent inhomogeneity introduced by different mineral grains, and（3）macroscopic inhomogeneity. Our study, which incorporates laboratory experiments and numerical simulations, indicates that such an approach is helpful in finding a better model not only for simulating experimental results but also for upscaling purposes.展开更多
Natural fractures are generally well developed in most hydrocarbon and geothermal reservoirs,which can produce complex fracture networks due to the activation of fractures during hydraulic stimulation.The present pape...Natural fractures are generally well developed in most hydrocarbon and geothermal reservoirs,which can produce complex fracture networks due to the activation of fractures during hydraulic stimulation.The present paper is devoted to developing a method to investigate the activation characteristics of fracture under injection-shearing coupled condition at laboratory scale.The fluid is injected into the single-fractured granite until the fracture is activated based on the triaxial direct shear tests.The results show that injection process can significantly influence the shear stress distribution field,resulting in release of shear stress and relative slip between the opposite sides of the fractured surface.The injectioninduced activation of fracture is strongly dependent on the stress states.When the normal stress increases,the injection-induced activation pressure increases,and the comparatively high normal stress can restrain the fracture activation.The fracture deformation mechanisms during fluid injection are also discussed preliminarily with the experimental data.The sensitivity of shear stress to fluid injection increases with increase of shear stress level,while it decreases under high normal stress.The results can facilitate our understanding of the natural fracture activation behavior during fluid pressure stimulation.展开更多
São Paulo State has witnessed CO_(2)storage-based investigations considering the availability of suitable geologic structures and proximity to primary CO_(2)source sinks related to bioenergy and carbon capture an...São Paulo State has witnessed CO_(2)storage-based investigations considering the availability of suitable geologic structures and proximity to primary CO_(2)source sinks related to bioenergy and carbon capture and storage(BECCS)activities.The current study presents the hydrocarbon viability evaluations and CO_(2)storage prospects,focusing on the sandstone units of the Rio Bonito Formation.The objective is to apply petrophysical evaluations with geochemical inputs in predicting future hydrocarbon(gas)production to boost CO_(2)storage within the study location.The study used data from eleven wells with associated wireline logs(gamma ray,resistivity,density,neutron,and sonic)to predict potential hydrocarbon accumulation and fluid mobility in the investigated area.Rock samples(shale and carbonate)obtained from depths>200 m within the study location have shown bitumen presence.Organic geochemistry data of the Rio Bonito Formation shale beds suggest they are potential hydrocarbon source rocks and could have contributed to the gas accumulations within the sandstone units.Some drilled well data,e.g.,CB-1-SP and TI-1-SP,show hydrocarbon(gas)presence based on the typical resistivity and the combined neutron-density responses at depths up to 3400 m,indicating the possibility of other hydrocarbon members apart from the heavy oil(bitumen)observed from the near-surface rocks samples.From the three-dimensional(3-D)model,the free fluid indicator(FFI)is more significant towards the southwest and southeast of the area with deeper depths of occurrence,indicating portions with reasonable hydrocarbon recovery rates and good prospects for CO_(2)injection,circulation and permanent storage.However,future studies based on contemporary datasets are required to establish the hydrocarbon viability further,foster gas production events,and enhance CO_(2)storage possibilities within the region.展开更多
Five sequences of deep fluid injections at the Pohang Enhanced Geothermal System(EGS)triggered an ML 5.4 earthquake on November 15,2017.The foreshock-mainshock-aftershock sequence was monitored using dense seismic net...Five sequences of deep fluid injections at the Pohang Enhanced Geothermal System(EGS)triggered an ML 5.4 earthquake on November 15,2017.The foreshock-mainshock-aftershock sequence was monitored using dense seismic networks.Between November 14,2017,and May 31,2023,this study detected 5,169 earthquakes and determined the relative locations of 4,902 earthquakes,including seven foreshocks.A heterogeneous subsurface fault model is proposed,in which the fault is reactivated by induced and triggered earthquakes.The earthquake frequency decreased after the mainshock,with a temporary increase after the ML 4.6 event on February 10,2018.The magnitude-frequency b-values are significantly lower than those for the background seismicity in the Korean Peninsula and those for the 2016 Gyeongju earthquake sequence.The aftershock decay rate p-values are within the range of typical values,regardless of decreasing over time.The earthquake focal mechanisms exhibit a predominance of strike-slip components,whereas the slip tendency indicates a higher value in reverse faulting geometry,implying stress redistribution after the mainshock.The seismic landscape with ongoing aftershock activity after the 2017 Pohang earthquake underscores the importance of sustained,long-term seismic monitoring to comprehensively grasp the implications of the new seismic environment for seismic hazards in the area.展开更多
This paper uses a fully coupled framework of thermal-hydraulic-mechanical processes to investigate how the injection and extraction of fluid within a geothermal reservoir impacts on the distributions of temperature, p...This paper uses a fully coupled framework of thermal-hydraulic-mechanical processes to investigate how the injection and extraction of fluid within a geothermal reservoir impacts on the distributions of temperature, pore pressure, and deformation within the rock formations. Based on this formulation, a numerical model is developed in light of the thermodynamics of porous materials. The proposed procedure relies on the derivation of dissipative flow rules by postulating proper storage and dissipation functions. This approach opens new horizons for several resource engineering applications. Since it allows for full coupling, this formulation can play a key role in predicting risks when used for reservoir simulation. The results indicate that the injection-extraction process and temperature change have a definite impact on altering the in-situ properties of the reservoir.展开更多
Post-fracturing evaluation by using limited data is of great significance to continuous improvement of the fracturing programs.In this paper,a fracturing curve was divided into two stages(i.e.,prepad fluid injection a...Post-fracturing evaluation by using limited data is of great significance to continuous improvement of the fracturing programs.In this paper,a fracturing curve was divided into two stages(i.e.,prepad fluid injection and main fracturing)so as to further understand the parameters of reservoirs and artificial fractures.The brittleness and plasticity of formations were qualitatively identified by use of the statistics of formation fracture frequency,and average pressure dropping range and rate during the prepad fluid injection.The composite brittleness index was quantitatively calculated by using the energy zones in the process of fracturing.It is shown from the large-scale true triaxial physical simulation results that the complexity of fractures is reflected by the pressure fluctuation frequency and amplitude in the main fracturing curve,and combined with the brittleness and plasticity of formations,the fracture morphology far away from the well can be diagnosed.Well P,a shale gas well in SE Chongqing,was taken as an example for post-fracturing evaluation.It is shown that the shale beds are of stronger heterogeneity along the extension directions of horizontal wells,and with GR 260 API as the dividing line between brittleness and plasticity in this area,complex fracture systems tend to form in brittleness-prone formations.In Well P,half of the fractures are single fractures,so it is necessary to carry out fine subsection and turnaround fracturing so as to improve development effects.This paper provides a theoretical basis for improving the fracturing well design and increasing the effective stimulated volume in this area.展开更多
Experiments were conducted on a lab-scale fluidized bed to study the distribution of liquid ethanol injected into fluidized catalyst particles. Electrical capacitance measurements were used to study the liquid distrib...Experiments were conducted on a lab-scale fluidized bed to study the distribution of liquid ethanol injected into fluidized catalyst particles. Electrical capacitance measurements were used to study the liquid distribution inside the bed, and a new method was developed to determine the liquid content inside fluidized beds of fluid catalytic cracking particles. The results shed light on the complex liquid injection region and reveal the strong effect of superficial gas velocity on liquid distribution inside the fluidized bed, which is also affected by the imbibition of liquid inside particle pores. Particle internal porosity was found to play a major role when the changing mass of liquid in the bed was monitored. The results also showed that the duration of liquid injection affected liquid-solid contact inside the bed and that liouid-solid mixin~ was not homogeneous durin~ the limited liouid injection time.展开更多
lronmaking using an oxygen blast furnace is an attractive approach for reducing energy consumption in the iron and steel industry. This paper presents a numerical study of gas-solid flow in an oxygen blast fur- nace b...lronmaking using an oxygen blast furnace is an attractive approach for reducing energy consumption in the iron and steel industry. This paper presents a numerical study of gas-solid flow in an oxygen blast fur- nace by coupling the discrete element method with computational fluid dynamics. The model reliability was verified by previous experimental results. The influences of particle diameter, shaft tuyere size, and specific ratio （X） of shaft-injected gas （51G） flowrate to total gas flowrate on the SIC penetration behavior and pressure field in the furnace were investigated. The results showed that gas penetration capacity in the furnace gradually decreased as the particle diameter decreased from 100 to 40 mm. Decreasing particle diameter and increasing shaft tuyere size both slightly increased the SIG concentration near the furnace wall but decreased it at the furnace center. The value of X has a significant impact on the SIG distribution. According to the pressure fields obtained under different conditions, the key factor affecting SIG penetration depth is the pressure difference between the upper and lower levels of the shaft tuyere. If the pressure difference is small, the SIG can easily penetrate to the furnace center.展开更多
In the Sichuan Basin,seismic activity has been low historically,but in the past few decades,a series of moderate to strong earthquakes have occurred.Especially since 2015,earthquake activity has seen an unprecedented ...In the Sichuan Basin,seismic activity has been low historically,but in the past few decades,a series of moderate to strong earthquakes have occurred.Especially since 2015,earthquake activity has seen an unprecedented continuous growth trend,and the magnitude of events is increasing.Following the M5.7 Xingwen earthquake on 18 Dec.2018,which was suggested to be induced by shale gas hydraulic fracturing,a swarm of earthquakes with a maximum magnitude up to M6.0 struck Changning and the surrounding counties.Questions arose about the possible involvement of industrial actions in these destructive events.In fact,underground fluid injection in salt mine fields has been occurring in the Sichuan Basin for more than70 years.Disposal of wastewater in natural gas fields has also continued for about 40 years.Since 2008,injection for shale gas development in the southern Sichuan Basin has increased rapidly.The possible link between the increasing seismicity and increasing injection activity is an important issue.Although surrounded by seismically active zones to the southwest and northwest,the Sichuan Basin is a rather stable region with a wide range of geological settings.First,we present a brief review of earthquakes of magnitude 5 or higher since 1600 to obtain the long-term event rate and explore the possible link between the rapidly increasing trend of seismic activity and industrial injection activities in recent decades.Second,based on a review of previous research results,combined with the latest data,we describe a comprehensive analysis of the characteristics and occurrence conditions of natural and injection-induced major seismic clusters in the Sichuan Basin since 1700.Finally,we list some conclusions and insights,which provide a better understanding of why damaging events occur so that they can either be avoided or mitigated,point out scientific questions that need urgent research,and propose a general framework based on geomechanics for assessment and management of earthquake-related risks.展开更多
It has long been known that human activities such as waste fluid disposal and reservoir impoundment may cause earthquakes. Recently, anthropogenic activities to tackle the increasing energy demand and to address clima...It has long been known that human activities such as waste fluid disposal and reservoir impoundment may cause earthquakes. Recently, anthropogenic activities to tackle the increasing energy demand and to address climate change issues are also reported to induce earthquakes. These activities have a common attribute in that fluids are injected and extracted underground and induce spatiotemporal changes of pore pressure and stress, which may cause slip on faults. Induced earthquakes not only pose significant impacts on seismic hazard assessment and preparation, but also raise the question to the society as how to balance the economic needs of resources development and the public's concerns about potential environmental impacts. Here we review the observations of fluid-injection/extraction induced earthquakes, ground deformation associated with these activities, and their physical mechanisms. Furthermore, we discuss the influences of induced earthquakes on seismic hazard models, regulatory policies on these anthropogenic activities, and current development of academic, industrial and government initiatives and collaborations in order to understand this intriguing phenomenon and address associated challenges.展开更多
基金the National Nature Science Foundation of China(Grant Nos.42077435 and 42377171).
文摘This study elucidates the findings of a computational investigation into the stimulation characteristics of natural reservoir systems enhanced by high-voltage electropulse-assisted fluid injection.The presented methodology delineates the comprehensive rock-fracturing process induced by electropulse and subsequent fluid injection,encompassing the discharge circuit,plasma channel formation,shockwave propagation,and hydro-mechanical response.A hydromechanical model incorporating an anisotropic plastic damage constitutive law,discrete fracture networks,and heterogeneous distribution is developed to represent the natural reservoir system.The results demonstrate that high-voltage electropulse effectively generates intricate fracture networks,significantly enhances the hydraulic properties of reservoir systems,and mitigates the adverse impact of ground stress on fracturing.The stimulationenhancing effect of electropulse is observed to intensify with increasing discharge voltage,with enhancements of 118.0%,139.5%,and 169.0%corresponding to discharge voltages of 20 kV,40 kV,and 60 kV,respectively.Additionally,a high-voltage electropulse with an initial voltage of U_(0)=80 kV and capacitance C=5μF has been shown to augment the efficiency of injection activation to approximately 201.1%compared to scenarios without electropulse.Under the influence of high-voltage electropulse,the fluid pressure distribution diverges from the conventional single direction of maximum stress,extending over larger areas.These innovative methods and findings hold potential implications for optimizing reservoir stimulation in geo-energy engineering.
基金supported by National Research Foundation,Singapore under its Intra-CREATE Thematic Grant(Award No.NRF2019-THE001-0002).
文摘An unusual increase in seismicity rate near the development and production sites of unconventional energy(e.g.,natural gas and geothermal fluids)has been attributed to subsurface fluid injection.Damaging and hazardous earthquakes in many countries(e.g.,China,South Korea,and the United States)have motivated tremendous effort to understand the complexity of fault slip behaviors in response to fluid pressurization.This study reviews key characteristics of injection-induced fault slip and highlights prediction and mitigation strategies relevant to unconventional energy projects.This capability relies on adequate understanding and characterization of first-and second-order friction and stability behaviors of faults as well as impacts of fluid pressurization and its role in triggering aseismic,seismic,and transitional slip behaviors.Suitable methods of investigation and characterization are noted together with typical examples together with scientific advances in our understanding towards forewarning and mitigation.Present challenges are addressed relating to the understanding of complex secondorder friction behaviors and the location and characterization of blind faults.These needs are aided in the integration of multi-scale and multi-physical data obtained from laboratory,numerical,and field studies to offer crucial information for induced hazard preparedness and rapid run-up assessment.Finally,emerging technologies contributing to an improved understanding,such as data analytics and machine learning,are discussed in heralding the next frontier for injection-induced seismicity research.
基金supported by the US Department of Energy (DOE),the Office of Nuclear Energy,Spent Fuel and Waste Science and Technology Campaign,under Contract Number DE-AC02-05CH11231the National Energy Technology Laboratory under the award number FP00013650 at Lawrence Berkeley National Laboratory.
文摘Stress changes due to changes in fluid pressure and temperature in a faulted formation may lead to the opening/shearing of the fault.This can be due to subsurface(geo)engineering activities such as fluid injections and geologic disposal of nuclear waste.Such activities are expected to rise in the future making it necessary to assess their short-and long-term safety.Here,a new machine learning(ML)approach to model pore pressure and fault displacements in response to high-pressure fluid injection cycles is developed.The focus is on fault behavior near the injection borehole.To capture the temporal dependencies in the data,long short-term memory(LSTM)networks are utilized.To prevent error accumulation within the forecast window,four critical measures to train a robust LSTM model for predicting fault response are highlighted:(i)setting an appropriate value of LSTM lag,(ii)calibrating the LSTM cell dimension,(iii)learning rate reduction during weight optimization,and(iv)not adopting an independent injection cycle as a validation set.Several numerical experiments were conducted,which demonstrated that the ML model can capture peaks in pressure and associated fault displacement that accompany an increase in fluid injection.The model also captured the decay in pressure and displacement during the injection shut-in period.Further,the ability of an ML model to highlight key changes in fault hydromechanical activation processes was investigated,which shows that ML can be used to monitor risk of fault activation and leakage during high pressure fluid injections.
基金Project supported by the National Natural Science Foundation of China(Nos.51276014 and 51406008)
文摘The problem of magnetohydrodynamic （MHD） flow on a moving surface with the power-law velocity and special injection/blowing is investigated. A scaling group transformation is used to reduce the governing equations to a system of ordinary differen- tial equations. The skin friction coefficients of the MHD boundary layer flow are derived, and the approximate solutions of the flow characteristics are obtained with the homotopy analysis method （HAM）. The approximate solutions are easily computed by use of a high order iterative procedure, and the effects of the power-law index, the magnetic parameter, and the special suction/blowing parameter on the dynamics are analyzed. The obtained results are compared with the numerical results published in the literature, verifying the reliability of the approximate solutions.
基金the National Natural Science Foundation of China(Grant Nos.42077247 and 42107163)the Fundamental Research Funds for the Central Universities.
文摘Fracture/fault instability induced by fluid injection in deep geothermal reservoirs could not only vary the reservoir permeability but also trigger hazardous seismicity.To address this,we conducted triaxial shear experiments on granite fractures with different architected roughnesses reactivated under fluid injection,to investigate the controls on permeability evolution linked to reactivation.Our results indicate that the fracture roughness and injection strategies are two main factors affecting permeability evolution.For fractures with dif-ferent roughnesses,a rougher fracture leads to a lower peak reactivated permeability(k_(max)),and varying the fluid injection strategy(in-cluding the confining pressure and injection rate)has a less impact on kmax,indicating that the evolution of permeability during fluid pressurization is likely to be determined by the fracture roughness along the shear direction.Both the fracture roughness and injection strategies affect the average rates of permeability change and this parameter also reflects the long-term reservoir recovery.Our results have important implications for understanding the permeability evolution and the injection-induced fracture/fault slips in granite reser-voirs during the deep geothermal energy extraction.
基金supported in part by the National Key Research and Development Project of China(No.2022YFC3004602)in part by the National Natural Science Foundation of China(Nos.52121003 and 52442406)。
文摘With the advancement of fracturing technologies in deeper and more geologically complex formations,fault reactivation and induced seismicity have attracted increasing attention.The increasing frequency and magnitude of these events underscore the need for a robust understanding of the governing physical mechanisms.Elevated pore pressure,modified fault-loading conditions,and aseismic slip are widely acknowledged as the primary drivers.Recent studies have explored these mechanisms under varying factors,including fluid properties,rock ductility,poroelastic responses,and evolving fault stress states,thereby offering critical insights into model refinement.Probabilistic forecasting approaches,which combine statistical analyses of historical data with real-time monitoring,are being increasingly adopted in seismic risk assessments.In parallel,machine learning techniques are employed to process large seismic datasets and identify key patterns.However,their predictive capabilities remain limited by geological heterogeneity,subsurface complexity,and scarce observational data.Moreover,fluid–rock interactions further complicate the development of universally applicable models,thereby constraining the generalizability of mitigation strategies.This review synthesizes the current understanding of induced seismicity mechanisms,evaluates the prevailing prediction and mitigation methods,and identifies major challenges and future research directions.Advancements in these areas are essential to enhancing seismic risk management and ensuring the safe,sustainable development of deep-subsurface energy resources.
基金supported by State Key Laboratory of Earthquake Dynamics,China
文摘In order to improve our understanding of rock fracture and fault instability driven by high-pressure fluid sources, the authors carried out rock fracture tests using granite under a confining pressure of 80 MPa with fluid injection in the laboratory. Furthermore, we tested a number of numerical models using the FLAC;modeling software to find the best model to represent the experimental results. The high-speed multichannel acoustic emission（AE） waveform recording system used in this study made it possible to examine the total fracture process through detailed monitoring of AE hypocenters and seismic velocity.The experimental results show that injecting high-pressure oil into the rock sample can induce AE activity at very low stress levels and can dramatically reduce the strength of the rock. The results of the numerical simulations show that major experimental results, including the strength, the temporal and spatial patterns of the AE events, and the role of the fluid can be represented fairly well by a model involving（1） randomly distributed defect elements to model pre-existing cracks,（2） random modification of rock properties to represent inhomogeneity introduced by different mineral grains, and（3）macroscopic inhomogeneity. Our study, which incorporates laboratory experiments and numerical simulations, indicates that such an approach is helpful in finding a better model not only for simulating experimental results but also for upscaling purposes.
基金The financial support by the National Key Research and Development Program of China(Grant No.2018YFC0809601)the National Natural Science Foundation of China(Grant No.51779252)+1 种基金the Major Technological Innovation Projects of Hubei,China(Grant No.2017AAA128)the Key Projects of the Yalong River Joint Fund of the National Natural Science Foundation of China(Grant No.U1865203)for this work are gratefully acknowledged。
文摘Natural fractures are generally well developed in most hydrocarbon and geothermal reservoirs,which can produce complex fracture networks due to the activation of fractures during hydraulic stimulation.The present paper is devoted to developing a method to investigate the activation characteristics of fracture under injection-shearing coupled condition at laboratory scale.The fluid is injected into the single-fractured granite until the fracture is activated based on the triaxial direct shear tests.The results show that injection process can significantly influence the shear stress distribution field,resulting in release of shear stress and relative slip between the opposite sides of the fractured surface.The injectioninduced activation of fracture is strongly dependent on the stress states.When the normal stress increases,the injection-induced activation pressure increases,and the comparatively high normal stress can restrain the fracture activation.The fracture deformation mechanisms during fluid injection are also discussed preliminarily with the experimental data.The sensitivity of shear stress to fluid injection increases with increase of shear stress level,while it decreases under high normal stress.The results can facilitate our understanding of the natural fracture activation behavior during fluid pressure stimulation.
基金sponsored by Fundação de Amparoa Pesquisa do Estado de São Paulo(FAPESP)(2014/50279-4,2020/15230-5,2021/06158-1)Shell Brasil.
文摘São Paulo State has witnessed CO_(2)storage-based investigations considering the availability of suitable geologic structures and proximity to primary CO_(2)source sinks related to bioenergy and carbon capture and storage(BECCS)activities.The current study presents the hydrocarbon viability evaluations and CO_(2)storage prospects,focusing on the sandstone units of the Rio Bonito Formation.The objective is to apply petrophysical evaluations with geochemical inputs in predicting future hydrocarbon(gas)production to boost CO_(2)storage within the study location.The study used data from eleven wells with associated wireline logs(gamma ray,resistivity,density,neutron,and sonic)to predict potential hydrocarbon accumulation and fluid mobility in the investigated area.Rock samples(shale and carbonate)obtained from depths>200 m within the study location have shown bitumen presence.Organic geochemistry data of the Rio Bonito Formation shale beds suggest they are potential hydrocarbon source rocks and could have contributed to the gas accumulations within the sandstone units.Some drilled well data,e.g.,CB-1-SP and TI-1-SP,show hydrocarbon(gas)presence based on the typical resistivity and the combined neutron-density responses at depths up to 3400 m,indicating the possibility of other hydrocarbon members apart from the heavy oil(bitumen)observed from the near-surface rocks samples.From the three-dimensional(3-D)model,the free fluid indicator(FFI)is more significant towards the southwest and southeast of the area with deeper depths of occurrence,indicating portions with reasonable hydrocarbon recovery rates and good prospects for CO_(2)injection,circulation and permanent storage.However,future studies based on contemporary datasets are required to establish the hydrocarbon viability further,foster gas production events,and enhance CO_(2)storage possibilities within the region.
基金funded by the Korea Institute of Energy Technology Evaluation and Planning(KETEP)grant from the Ministry of Trade,Industry and Energy(MOTIE)(No.20198210100030,20208310100020)the Nuclear Safety Research Program through the Korea Foundation of Nuclear Safety(KoFONS)grant from the Nuclear Safety and Security Commission(NSSC)(No.071610)of the Republic of Korea.
文摘Five sequences of deep fluid injections at the Pohang Enhanced Geothermal System(EGS)triggered an ML 5.4 earthquake on November 15,2017.The foreshock-mainshock-aftershock sequence was monitored using dense seismic networks.Between November 14,2017,and May 31,2023,this study detected 5,169 earthquakes and determined the relative locations of 4,902 earthquakes,including seven foreshocks.A heterogeneous subsurface fault model is proposed,in which the fault is reactivated by induced and triggered earthquakes.The earthquake frequency decreased after the mainshock,with a temporary increase after the ML 4.6 event on February 10,2018.The magnitude-frequency b-values are significantly lower than those for the background seismicity in the Korean Peninsula and those for the 2016 Gyeongju earthquake sequence.The aftershock decay rate p-values are within the range of typical values,regardless of decreasing over time.The earthquake focal mechanisms exhibit a predominance of strike-slip components,whereas the slip tendency indicates a higher value in reverse faulting geometry,implying stress redistribution after the mainshock.The seismic landscape with ongoing aftershock activity after the 2017 Pohang earthquake underscores the importance of sustained,long-term seismic monitoring to comprehensively grasp the implications of the new seismic environment for seismic hazards in the area.
文摘This paper uses a fully coupled framework of thermal-hydraulic-mechanical processes to investigate how the injection and extraction of fluid within a geothermal reservoir impacts on the distributions of temperature, pore pressure, and deformation within the rock formations. Based on this formulation, a numerical model is developed in light of the thermodynamics of porous materials. The proposed procedure relies on the derivation of dissipative flow rules by postulating proper storage and dissipation functions. This approach opens new horizons for several resource engineering applications. Since it allows for full coupling, this formulation can play a key role in predicting risks when used for reservoir simulation. The results indicate that the injection-extraction process and temperature change have a definite impact on altering the in-situ properties of the reservoir.
基金Project supported by the National Natural Science Funds“Mechanism of dynamic stochastic fracture control and theory of waterless fracturing for shale formations”(Grant No.51490653)the Sinopec S&T Researches“Optimal stimulation technology for shale gas formations in Fuling Block”(Grant No.P14091)the National Major S&T Projects“Demonstration of shale gas exploration and development under normal pressure in Pengshui region”(Grant No.2016ZX05061)。
文摘Post-fracturing evaluation by using limited data is of great significance to continuous improvement of the fracturing programs.In this paper,a fracturing curve was divided into two stages(i.e.,prepad fluid injection and main fracturing)so as to further understand the parameters of reservoirs and artificial fractures.The brittleness and plasticity of formations were qualitatively identified by use of the statistics of formation fracture frequency,and average pressure dropping range and rate during the prepad fluid injection.The composite brittleness index was quantitatively calculated by using the energy zones in the process of fracturing.It is shown from the large-scale true triaxial physical simulation results that the complexity of fractures is reflected by the pressure fluctuation frequency and amplitude in the main fracturing curve,and combined with the brittleness and plasticity of formations,the fracture morphology far away from the well can be diagnosed.Well P,a shale gas well in SE Chongqing,was taken as an example for post-fracturing evaluation.It is shown that the shale beds are of stronger heterogeneity along the extension directions of horizontal wells,and with GR 260 API as the dividing line between brittleness and plasticity in this area,complex fracture systems tend to form in brittleness-prone formations.In Well P,half of the fractures are single fractures,so it is necessary to carry out fine subsection and turnaround fracturing so as to improve development effects.This paper provides a theoretical basis for improving the fracturing well design and increasing the effective stimulated volume in this area.
文摘Experiments were conducted on a lab-scale fluidized bed to study the distribution of liquid ethanol injected into fluidized catalyst particles. Electrical capacitance measurements were used to study the liquid distribution inside the bed, and a new method was developed to determine the liquid content inside fluidized beds of fluid catalytic cracking particles. The results shed light on the complex liquid injection region and reveal the strong effect of superficial gas velocity on liquid distribution inside the fluidized bed, which is also affected by the imbibition of liquid inside particle pores. Particle internal porosity was found to play a major role when the changing mass of liquid in the bed was monitored. The results also showed that the duration of liquid injection affected liquid-solid contact inside the bed and that liouid-solid mixin~ was not homogeneous durin~ the limited liouid injection time.
基金We gratefully acknowledge the support of the National Basic Research Program of China （973 Program） （No. 2012CB720401 ） and the Key Project of National Natural Science Foundation of China （No. 51134008）.
文摘lronmaking using an oxygen blast furnace is an attractive approach for reducing energy consumption in the iron and steel industry. This paper presents a numerical study of gas-solid flow in an oxygen blast fur- nace by coupling the discrete element method with computational fluid dynamics. The model reliability was verified by previous experimental results. The influences of particle diameter, shaft tuyere size, and specific ratio （X） of shaft-injected gas （51G） flowrate to total gas flowrate on the SIC penetration behavior and pressure field in the furnace were investigated. The results showed that gas penetration capacity in the furnace gradually decreased as the particle diameter decreased from 100 to 40 mm. Decreasing particle diameter and increasing shaft tuyere size both slightly increased the SIG concentration near the furnace wall but decreased it at the furnace center. The value of X has a significant impact on the SIG distribution. According to the pressure fields obtained under different conditions, the key factor affecting SIG penetration depth is the pressure difference between the upper and lower levels of the shaft tuyere. If the pressure difference is small, the SIG can easily penetrate to the furnace center.
基金support of the State Scholarship Fund of China(Grant No.201804190004)。
文摘In the Sichuan Basin,seismic activity has been low historically,but in the past few decades,a series of moderate to strong earthquakes have occurred.Especially since 2015,earthquake activity has seen an unprecedented continuous growth trend,and the magnitude of events is increasing.Following the M5.7 Xingwen earthquake on 18 Dec.2018,which was suggested to be induced by shale gas hydraulic fracturing,a swarm of earthquakes with a maximum magnitude up to M6.0 struck Changning and the surrounding counties.Questions arose about the possible involvement of industrial actions in these destructive events.In fact,underground fluid injection in salt mine fields has been occurring in the Sichuan Basin for more than70 years.Disposal of wastewater in natural gas fields has also continued for about 40 years.Since 2008,injection for shale gas development in the southern Sichuan Basin has increased rapidly.The possible link between the increasing seismicity and increasing injection activity is an important issue.Although surrounded by seismically active zones to the southwest and northwest,the Sichuan Basin is a rather stable region with a wide range of geological settings.First,we present a brief review of earthquakes of magnitude 5 or higher since 1600 to obtain the long-term event rate and explore the possible link between the rapidly increasing trend of seismic activity and industrial injection activities in recent decades.Second,based on a review of previous research results,combined with the latest data,we describe a comprehensive analysis of the characteristics and occurrence conditions of natural and injection-induced major seismic clusters in the Sichuan Basin since 1700.Finally,we list some conclusions and insights,which provide a better understanding of why damaging events occur so that they can either be avoided or mitigated,point out scientific questions that need urgent research,and propose a general framework based on geomechanics for assessment and management of earthquake-related risks.
基金supported by the NSFC/RGC Joint Research Scheme sponsored by the Research Grants Council of the Hong Kong Special Administrative Region, China (Grant Nos. N_CUHK418/15, N_CUHK430/16)CUHK-University of Manchester Research Fund (Grant No. 4930227)+4 种基金United States National Science Foundation (Grant No. OCE-1357433)Natural Sciences and Engineering Research Council of Canada (Grant No. STPGP 494141-16)Japan Society for the Promotion of Science (Grant Nos. KAKENHI 2624004, 26280006)National Natural Science Foundation of China (Grant No. 41474033)the Summer School Program of Peking University
文摘It has long been known that human activities such as waste fluid disposal and reservoir impoundment may cause earthquakes. Recently, anthropogenic activities to tackle the increasing energy demand and to address climate change issues are also reported to induce earthquakes. These activities have a common attribute in that fluids are injected and extracted underground and induce spatiotemporal changes of pore pressure and stress, which may cause slip on faults. Induced earthquakes not only pose significant impacts on seismic hazard assessment and preparation, but also raise the question to the society as how to balance the economic needs of resources development and the public's concerns about potential environmental impacts. Here we review the observations of fluid-injection/extraction induced earthquakes, ground deformation associated with these activities, and their physical mechanisms. Furthermore, we discuss the influences of induced earthquakes on seismic hazard models, regulatory policies on these anthropogenic activities, and current development of academic, industrial and government initiatives and collaborations in order to understand this intriguing phenomenon and address associated challenges.
