The coupling effect of temperature and confining pressure on fracture toughness is a critical issue in deep shale gas development that cannot be overlooked.Field and laboratory studies have shown that this coupling ef...The coupling effect of temperature and confining pressure on fracture toughness is a critical issue in deep shale gas development that cannot be overlooked.Field and laboratory studies have shown that this coupling effect significantly alters shale fracture toughness,but the underlying mechanisms of it remain poorly understood.To investigate the mechanisms of the temperature-pressure coupling effect on the fracture toughness of transversely isotropic shale,this study develops a thermal-mechanical DEM(discrete element method)model that integrates a customized thermal algorithm and a shining-lamp algorithm.The model validity is verified by using experimental results from high-temperature SCB(semi-circular bend)tests.Additionally,a series of SCB tests under different temperatures and confining pressures are simulated based on this model.The loading curves,fracture toughness evolution,crack morphology,and microcrack statistics results obtained from simulations are analyzed to provide insights into the mechanisms of the temperature-pressure coupling effect.The simulation results indicate that the stimulation of thermal-induced microcracks on crack propagation may be the primary microscopic mechanism behind the thermal-induced weakening of shale fracture toughness.Meanwhile,confining pressure has an inhibitory influence on the thermal effect of shale fracture toughness.The activation of shear microcracks under the application of confining pressure is identified as the leading microscopic mechanism of confining pressure inhibition.The findings in this study enhance the understanding of the fracture property evolution of deep shale reservoirs and provide guidance for site selection,engineering design,and reservoir stability assessment in deep shale gas development.展开更多
基金supported by the National Natural Science Foundation of China(No.42320104003).
文摘The coupling effect of temperature and confining pressure on fracture toughness is a critical issue in deep shale gas development that cannot be overlooked.Field and laboratory studies have shown that this coupling effect significantly alters shale fracture toughness,but the underlying mechanisms of it remain poorly understood.To investigate the mechanisms of the temperature-pressure coupling effect on the fracture toughness of transversely isotropic shale,this study develops a thermal-mechanical DEM(discrete element method)model that integrates a customized thermal algorithm and a shining-lamp algorithm.The model validity is verified by using experimental results from high-temperature SCB(semi-circular bend)tests.Additionally,a series of SCB tests under different temperatures and confining pressures are simulated based on this model.The loading curves,fracture toughness evolution,crack morphology,and microcrack statistics results obtained from simulations are analyzed to provide insights into the mechanisms of the temperature-pressure coupling effect.The simulation results indicate that the stimulation of thermal-induced microcracks on crack propagation may be the primary microscopic mechanism behind the thermal-induced weakening of shale fracture toughness.Meanwhile,confining pressure has an inhibitory influence on the thermal effect of shale fracture toughness.The activation of shear microcracks under the application of confining pressure is identified as the leading microscopic mechanism of confining pressure inhibition.The findings in this study enhance the understanding of the fracture property evolution of deep shale reservoirs and provide guidance for site selection,engineering design,and reservoir stability assessment in deep shale gas development.
