The development of geological lamination in shale reservoirs influences fracture propagation during hydraulic stimulation,and the fracture generation mechanism as it propagates through the laminated interface is close...The development of geological lamination in shale reservoirs influences fracture propagation during hydraulic stimulation,and the fracture generation mechanism as it propagates through the laminated interface is closely related to fracturing effects.In this paper,the laminated shale was selected to conduct three-point bending experiments using digital image correlation(DIC)and acoustic emission(AE)techniques,which revealed that the propagation path of cross-layer fractures exhibits dislocation features.The cohesive fracture mechanism of cross-layer fractures is investigated from the viewpoint of the fracture process zone(FPZ),which displays the characteristics of intermittence and dislocation during fracture development.A computational criterion for predicting the dislocation of cross-layer fracture at the interface is proposed,which shows that the maximum dislocation range does not exceed 72%of the FPZ length.Considering the mechanical differences between adjacent layers of laminated shale,the cohesive zone model of cross-layer fracture is discussed,from which the constitutive relationship and fracture energy during FPZ development are characterized,and the discontinuous nature of the constitutive relationship is found.This study improves the understanding of the geometry and cohesive fracture mechanism of the cross-layer fracture and provides valuable insights for field fracturing in shale reservoirs.展开更多
The continental shale reservoirs of Jurassic Lianggaoshan Formation in Sichuan Basin contain thin lamina,which is characterized by strong plasticity and developed longitudinal shell limestone interlayer.To improve the...The continental shale reservoirs of Jurassic Lianggaoshan Formation in Sichuan Basin contain thin lamina,which is characterized by strong plasticity and developed longitudinal shell limestone interlayer.To improve the production efficiency of reservoirs by multi-cluster fracturing,it is necessary to consider the unbalanced propagation of hydraulic fractures and the penetration effect of fractures.This paper constructed a numerical model of multi-fracture propagation and penetration based on the finite element coupling cohesive zone method;considering the construction cluster spacing,pump rate,lamina strength and other parameters studied the influencing factors of multi-cluster fracture interaction propagation;combined with AE energy data and fracture mode reconstruction method,quantitatively characterized the comprehensive impact of the strength of thin interlayer rock interfaces on the initiation and propagation of fractures that penetrate layers,and accurately predicted the propagation pattern of hydraulic fractures through laminated shale oil reservoirs.Simulation results revealed that in the process of multi-cluster fracturing,the proportion of shear damage is low,and mainly occurs in bedding fractures activated by outer fractures.Reducing the cluster spacing enhances the fracture system's penetration ability,though it lowers the activation efficiency of lamina.The high plasticity of the limestone interlayer may impact the vertical propagation distance of the main fracture.Improving the interface strength is beneficial to the reconstruction of the fracture height,but the interface communication effect is limited.Reasonable selection of layers with moderate lamina strength for fracturing stimulation,increasing the pump rate during fracturing and setting the cluster spacing reasonably are beneficial to improve the effect of reservoir stimulation.展开更多
Laminated continental shale oil reservoirs have the potential for commercial development.In this paper,a new simulation method for interlayer and intra-layer coupled flow in laminated shale reservoirs is established.T...Laminated continental shale oil reservoirs have the potential for commercial development.In this paper,a new simulation method for interlayer and intra-layer coupled flow in laminated shale reservoirs is established.This method simulates the structural characteristics of shale-sandstone longitudinal interlayer distribution by dual-porositysystem,and combines with chemical reaction model to characterize the desorption process of ad-/absorbed oil from kerogen in shale layers.Then,the intra-layer and interlayer interfacial flow mechanism in the depletion process is investigated,and the contribution of interfacial flow and desorption is analyzed.The results indicate that the sandstone layer is the main oil-producing layer,accounting for over 90%of the total oil production.However,the interlayer flow and kerogen desorption in the shale layers make significant contributions,resulting in an enhancement of 13.41%and 42.64%in the total oil production,respectively.Additionally,the desorption of ad-/absorbed oil from kerogen enhances the energy of both the shale and sandstone layers,significantly increasing their production.Moreover,higher pressure drawdown,total organic carbon(TOC)content,desorption rate,and horizontal permeability of sandstone layers are advantageous for the exploitation of shale oil.展开更多
基金financiallysupported by the Excellent Young Fund of Sinopec Petroleum Exploration and Production Research Institute(Grant No.YK2024009)the National Natural Science Foundation of China(Grant Nos.U23B6004 and 51925405).
文摘The development of geological lamination in shale reservoirs influences fracture propagation during hydraulic stimulation,and the fracture generation mechanism as it propagates through the laminated interface is closely related to fracturing effects.In this paper,the laminated shale was selected to conduct three-point bending experiments using digital image correlation(DIC)and acoustic emission(AE)techniques,which revealed that the propagation path of cross-layer fractures exhibits dislocation features.The cohesive fracture mechanism of cross-layer fractures is investigated from the viewpoint of the fracture process zone(FPZ),which displays the characteristics of intermittence and dislocation during fracture development.A computational criterion for predicting the dislocation of cross-layer fracture at the interface is proposed,which shows that the maximum dislocation range does not exceed 72%of the FPZ length.Considering the mechanical differences between adjacent layers of laminated shale,the cohesive zone model of cross-layer fracture is discussed,from which the constitutive relationship and fracture energy during FPZ development are characterized,and the discontinuous nature of the constitutive relationship is found.This study improves the understanding of the geometry and cohesive fracture mechanism of the cross-layer fracture and provides valuable insights for field fracturing in shale reservoirs.
基金financial support by the National Key Research and Development Program of China (No.2022YFE0129800)the National Natural Science Foundation of China (No.52074311)。
文摘The continental shale reservoirs of Jurassic Lianggaoshan Formation in Sichuan Basin contain thin lamina,which is characterized by strong plasticity and developed longitudinal shell limestone interlayer.To improve the production efficiency of reservoirs by multi-cluster fracturing,it is necessary to consider the unbalanced propagation of hydraulic fractures and the penetration effect of fractures.This paper constructed a numerical model of multi-fracture propagation and penetration based on the finite element coupling cohesive zone method;considering the construction cluster spacing,pump rate,lamina strength and other parameters studied the influencing factors of multi-cluster fracture interaction propagation;combined with AE energy data and fracture mode reconstruction method,quantitatively characterized the comprehensive impact of the strength of thin interlayer rock interfaces on the initiation and propagation of fractures that penetrate layers,and accurately predicted the propagation pattern of hydraulic fractures through laminated shale oil reservoirs.Simulation results revealed that in the process of multi-cluster fracturing,the proportion of shear damage is low,and mainly occurs in bedding fractures activated by outer fractures.Reducing the cluster spacing enhances the fracture system's penetration ability,though it lowers the activation efficiency of lamina.The high plasticity of the limestone interlayer may impact the vertical propagation distance of the main fracture.Improving the interface strength is beneficial to the reconstruction of the fracture height,but the interface communication effect is limited.Reasonable selection of layers with moderate lamina strength for fracturing stimulation,increasing the pump rate during fracturing and setting the cluster spacing reasonably are beneficial to improve the effect of reservoir stimulation.
基金financially supported by the National Natural Science Foundation of China(Project No.42090024).
文摘Laminated continental shale oil reservoirs have the potential for commercial development.In this paper,a new simulation method for interlayer and intra-layer coupled flow in laminated shale reservoirs is established.This method simulates the structural characteristics of shale-sandstone longitudinal interlayer distribution by dual-porositysystem,and combines with chemical reaction model to characterize the desorption process of ad-/absorbed oil from kerogen in shale layers.Then,the intra-layer and interlayer interfacial flow mechanism in the depletion process is investigated,and the contribution of interfacial flow and desorption is analyzed.The results indicate that the sandstone layer is the main oil-producing layer,accounting for over 90%of the total oil production.However,the interlayer flow and kerogen desorption in the shale layers make significant contributions,resulting in an enhancement of 13.41%and 42.64%in the total oil production,respectively.Additionally,the desorption of ad-/absorbed oil from kerogen enhances the energy of both the shale and sandstone layers,significantly increasing their production.Moreover,higher pressure drawdown,total organic carbon(TOC)content,desorption rate,and horizontal permeability of sandstone layers are advantageous for the exploitation of shale oil.
