Hydraulic fracturing then fluid circulation in enhanced geothermal system(EGS)reservoirs have been shown to induce seismicity remote from the stimulation-potentially generated by the distal projection of thermoporoela...Hydraulic fracturing then fluid circulation in enhanced geothermal system(EGS)reservoirs have been shown to induce seismicity remote from the stimulation-potentially generated by the distal projection of thermoporoelastic stresses.We explore this phenomenon by evaluating stress perturbations resulting from stimulation of a single stage of hydraulic fracturing that is followed by thermal depletion of a prismatic zone adjacent to the hydraulic fracture.We use Coulomb failure stress to assess the effect of resulting stress perturbations on instability on adjacent critically-stressed faults.Results show that hydraulic fracturing in a single stage is capable of creating stress perturbations at distances to 1000 m that reach 10^(-5)-10^(-4)MPa.At a closer distance,the magnitude of stress perturbations increases even further.The stress perturbation induced by temperature depletion could also reach 10^(-3)-10^(-2)MPa within 1000 m-much higher than that by hydraulic fracturing.Considering that a critical change in Coulomb failure stress for fault instability is 10^(-2)MPa,a single stage of hydraulic fracturing and thermal drawdown are capable of reactivating critically-stressed faults at distances within 200 m and 1000 m,respectively.These results have important implications for understanding the distribution and magnitudes of stress perturbations driven by thermoporoelastic effects and the associated seismicity during the simulation and early production of EGS reservoirs.展开更多
Thermal fracturing could occur during cold CO2 injection into subsurface warm rock formations.It can be seen in a variety of fields such as carbon geo-sequestration,unconventional gas development,enhanced oil recovery...Thermal fracturing could occur during cold CO2 injection into subsurface warm rock formations.It can be seen in a variety of fields such as carbon geo-sequestration,unconventional gas development,enhanced oil recovery,geothermal energy extraction,and energy geological storage systems.In CO2 geosequestion,limited degree of thermal fracturing due to the cooling effects of cold CO2 injection will enhance well injectivity,especially for those storage formations of low permeability.Thermal fracturing can therefore potentially enhance the injection efficiency and make positive impact on commercialization of CO2 geological storage.However,excessively developed fractures could break down the caprock and cause potential CO2 leakage into overlying rock formations.Risk analysis has to be done based on thermal fracturing simulation in order to maintain caprock integrity.Simulation of thermal fracturing during cold CO2 injection involves the coupled processes of heat transfer,mass transport,rock deforming as well as fracture propagation.To model such a complex coupled system,a fully coupled finite element framework for thermal fracturing simulation is presented.This framework is based on the theory of non-isothermal multiphase flow in fracturing porous media.It takes advantage of recent advances in stabilized finite element and extended finite element methods.The stabilized finite element method overcomes the numerical instability encountered when the traditional finite element method is used to solve the convection dominated heat transfer equation,while the extended finite element method overcomes the limitation with traditional finite element method that a model has to be remeshed when a fracture is initiated or propagating and fracturing paths have to be aligned with element boundaries.展开更多
基金funded by the National Natural Science Foundation of China(Grant Nos.42107163 and 42320104003)support from the G.Albert Shoemaker endowment.
文摘Hydraulic fracturing then fluid circulation in enhanced geothermal system(EGS)reservoirs have been shown to induce seismicity remote from the stimulation-potentially generated by the distal projection of thermoporoelastic stresses.We explore this phenomenon by evaluating stress perturbations resulting from stimulation of a single stage of hydraulic fracturing that is followed by thermal depletion of a prismatic zone adjacent to the hydraulic fracture.We use Coulomb failure stress to assess the effect of resulting stress perturbations on instability on adjacent critically-stressed faults.Results show that hydraulic fracturing in a single stage is capable of creating stress perturbations at distances to 1000 m that reach 10^(-5)-10^(-4)MPa.At a closer distance,the magnitude of stress perturbations increases even further.The stress perturbation induced by temperature depletion could also reach 10^(-3)-10^(-2)MPa within 1000 m-much higher than that by hydraulic fracturing.Considering that a critical change in Coulomb failure stress for fault instability is 10^(-2)MPa,a single stage of hydraulic fracturing and thermal drawdown are capable of reactivating critically-stressed faults at distances within 200 m and 1000 m,respectively.These results have important implications for understanding the distribution and magnitudes of stress perturbations driven by thermoporoelastic effects and the associated seismicity during the simulation and early production of EGS reservoirs.
基金The author gratefully acknowledges the support of Department of Energy(DE-FE0026825).
文摘Thermal fracturing could occur during cold CO2 injection into subsurface warm rock formations.It can be seen in a variety of fields such as carbon geo-sequestration,unconventional gas development,enhanced oil recovery,geothermal energy extraction,and energy geological storage systems.In CO2 geosequestion,limited degree of thermal fracturing due to the cooling effects of cold CO2 injection will enhance well injectivity,especially for those storage formations of low permeability.Thermal fracturing can therefore potentially enhance the injection efficiency and make positive impact on commercialization of CO2 geological storage.However,excessively developed fractures could break down the caprock and cause potential CO2 leakage into overlying rock formations.Risk analysis has to be done based on thermal fracturing simulation in order to maintain caprock integrity.Simulation of thermal fracturing during cold CO2 injection involves the coupled processes of heat transfer,mass transport,rock deforming as well as fracture propagation.To model such a complex coupled system,a fully coupled finite element framework for thermal fracturing simulation is presented.This framework is based on the theory of non-isothermal multiphase flow in fracturing porous media.It takes advantage of recent advances in stabilized finite element and extended finite element methods.The stabilized finite element method overcomes the numerical instability encountered when the traditional finite element method is used to solve the convection dominated heat transfer equation,while the extended finite element method overcomes the limitation with traditional finite element method that a model has to be remeshed when a fracture is initiated or propagating and fracturing paths have to be aligned with element boundaries.
