Determining reasonable fracturing stage spacing is the key to horizontal well fracturing.Different from traditional stage spacing optimization methods based on the principle of maximum stimulated reservoir volume,in t...Determining reasonable fracturing stage spacing is the key to horizontal well fracturing.Different from traditional stage spacing optimization methods based on the principle of maximum stimulated reservoir volume,in this paper,by considering the integrity of the wellbore interface,a fracture propagation model was established based on displacement discontinuity method and the competition mechanism of multifracture joint expansion,leading to the proposal of an unequal stage spacing optimization model.The results show that in the first stage,the interfacial fractures spread symmetrically along the axis of the central point during that stage,while in the second and subsequent stages,the interfacial fractures of each cluster extend asymmetrically along the left and right sides.There are two kinds of interface connectivity behaviour:in one,the existing fractures first extend and connect within the stage,and in the other,the fractures first extend in the direction close to the previous stage,with the specific behaviour depending on the combined effect of stress shadow and flow competition during hydraulic fracture expansion.The stage spacing is positively correlated with the number of fractures and Young’s modulus of the cement and formation and is negatively correlated with the cluster spacing and horizontal principal stress difference.The sensitivity is the strongest when the Young’s modulus of the cement sheath is 10-20 GPa,and the sensitivity of the horizontal principal stress difference is the weakest.展开更多
In the last years,shale gas has gradually substituted oil and coal as the main sources of energy in the world.Compared with shallow shale gas reservoirs,deep shale is characterized by low permeability,low porosity,str...In the last years,shale gas has gradually substituted oil and coal as the main sources of energy in the world.Compared with shallow shale gas reservoirs,deep shale is characterized by low permeability,low porosity,strong heterogeneity,and strong anisotropy.In the process of multi-cluster fracturing of horizontal wells,the whole deformation process and destruction modes are significantly influenced by loading rates.In this investigation,the servo press was used to carry out semi-circular bend(SCB)mixedmode fracture experiments in deep shales(130,160,190℃)with prefabricated fractures under different loading rates(0.02,0.05,0.1,0.2 mm/min).The fracture propagation process was monitored using acoustic emission.The deformation characteristics,displacementeload curve,and acoustic emission parameters of shale under different loading rates were studied during the mixed-mode fracture propagation.Our results showed that during the deformation and fracture of the specimen,the acoustic emission energy and charge significantly increased near the stress peak,showing at this point the most intense acoustic emission activity.With the increase in loading rate,the fracture peak load of the deep shale specimen also increased.However,the maximum displacement decreased to different extents.With the increase in temperature,the effective fracture toughness of the deep shale gradually decreased.Also,the maximum displacement decreased.Under different loading rates,the deformation of the prefabricated cracks showed a nonlinear slow growthelinear growth trend.The slope of the linear growth stage increased with the increase in loading rate.In addition,as the loading rate increased,an increase in tension failure and a decrease in shear failure were observed.Moreover,the control chart showing the relationship between tension and the shear failure under different temperatures and loading rates was determined.展开更多
We investigate the Rashba and Dressehaus spin-orbit(SO)couplings in an ordinary GaAs/AlGaAs asymmetric double well,which favors the electron occupancy of three subbands v=1,2,3.Resorting to an external gate,which adju...We investigate the Rashba and Dressehaus spin-orbit(SO)couplings in an ordinary GaAs/AlGaAs asymmetric double well,which favors the electron occupancy of three subbands v=1,2,3.Resorting to an external gate,which adjusts the electron occupancy and the well symmetry,we demonstrate distinct three-level SO control of both Rashba(αv)and Dresselhaus(βv)intraband terms.Remarkably,as the gate varies,the first-subband SO parametersα1 andβ1 comply with the usual linear behavior,whileα2(β2)andα3(β3)respectively for the second and third subbands interchange the values,triggered by a gate controlled band swapping.This provides a pathway towards fascinating selective SO control in spintronic applications.Moreover,we observe that the interband Rashba(ημv)and Dresselhaus(Lμv)terms also exhibit contrasting gate dependence.Our results should stimulate experiments probing SO couplings in multi-subband wells and adopting relevant SO features in future spintronic devices.展开更多
With the increasing demand for the development of unconventional oil and gas resources,hydraulic fracturing has become a key technology for enhancing reservoir permeability.However,achieving controlled propagation of ...With the increasing demand for the development of unconventional oil and gas resources,hydraulic fracturing has become a key technology for enhancing reservoir permeability.However,achieving controlled propagation of fracture networks remains a significant challenge under complex geological conditions.This study integrates theoretical analysis and finite-discrete element method(FDEM)simulations to investigate mixed-mode mechanisms,plastic zone evolution at fracture tips,and anisotropic mechanical responses of shale.Modified fracture criteria-including a T-stress-integrated Mohr-Coulo mb criterion and maximum circumferential tensile stress criterion are derived and validated through uniaxial compression and Brazilian splitting tests on Longmaxi Formation shale.Results demonstrate that the modified Mohr-Coulomb criterion effectively predicts anisotropic fracture propagation by characterizing tensile-compressive strength differences,while the plastic zone evolution under maximum circumferential tensile stress is significantly influenced by T-stress:positive T-stress(45°-90°)expands the plastic zone,whereas negative T-stress(0°-45°)contracts it.Lower tensile-to-compressive strength ratios lead to larger plastic zones.An FDEM-based horizontal well fracturing model reveals vertical fracture propagation dominated by bedding plane and interbed fracture extension,forming complex networks,while horizontal fractures initially grow independently before deflecting and inte rconnecting under maximum principal stress.Sensitivity analysis of perforation spacing identifies 62.5 mm(16holes/m)as the optimal configuration,achieving ModeⅡ-dominated fracture networks with superior connectivity and stimulation efficiency.Larger spacings(71.4-83.3 mm)result in reduced efficiency or isolated fractures.By coupling stress interference and fluid pressure field dynamics,this study establishes a methodology to balance fracture network complexity and reservoir stimulation efficacy.The findings provide theoretical insights and engineering guidelines for optimizing hydraulic fracturing designs in anisotropic shale gas reservoirs through advanced fracture criteria and FDEM-based multiphysics simulations.展开更多
基金This work was supported by the Natural Science Foundation of Heilongjiang Province of China(YQ2021E005)the National Natural Science Foundation of China(No.51774094)+2 种基金the Youth Fund Project of National Natural Science Foundation of China(52004065)the Heilongjiang Natural Science Foundation Project(excellent youth project)(YQ2021E006)"Reveal the top"Science and Technology Project of Heilongjiang Province(2021ZZ10-04).
文摘Determining reasonable fracturing stage spacing is the key to horizontal well fracturing.Different from traditional stage spacing optimization methods based on the principle of maximum stimulated reservoir volume,in this paper,by considering the integrity of the wellbore interface,a fracture propagation model was established based on displacement discontinuity method and the competition mechanism of multifracture joint expansion,leading to the proposal of an unequal stage spacing optimization model.The results show that in the first stage,the interfacial fractures spread symmetrically along the axis of the central point during that stage,while in the second and subsequent stages,the interfacial fractures of each cluster extend asymmetrically along the left and right sides.There are two kinds of interface connectivity behaviour:in one,the existing fractures first extend and connect within the stage,and in the other,the fractures first extend in the direction close to the previous stage,with the specific behaviour depending on the combined effect of stress shadow and flow competition during hydraulic fracture expansion.The stage spacing is positively correlated with the number of fractures and Young’s modulus of the cement and formation and is negatively correlated with the cluster spacing and horizontal principal stress difference.The sensitivity is the strongest when the Young’s modulus of the cement sheath is 10-20 GPa,and the sensitivity of the horizontal principal stress difference is the weakest.
基金supported by the National Natural Science Foundation of China(No.52204007)the Natural Science Foundation of Heilongjiang Province of China(YQ2021E005)+1 种基金New Era Longjiang Outstanding Master's and Doctoral Thesis Project(LJYXL2022-002)Key Laboratory of Enhanced Oil and Gas Recovery,Ministry of Education(NEPU-EOR-2022-04).
文摘In the last years,shale gas has gradually substituted oil and coal as the main sources of energy in the world.Compared with shallow shale gas reservoirs,deep shale is characterized by low permeability,low porosity,strong heterogeneity,and strong anisotropy.In the process of multi-cluster fracturing of horizontal wells,the whole deformation process and destruction modes are significantly influenced by loading rates.In this investigation,the servo press was used to carry out semi-circular bend(SCB)mixedmode fracture experiments in deep shales(130,160,190℃)with prefabricated fractures under different loading rates(0.02,0.05,0.1,0.2 mm/min).The fracture propagation process was monitored using acoustic emission.The deformation characteristics,displacementeload curve,and acoustic emission parameters of shale under different loading rates were studied during the mixed-mode fracture propagation.Our results showed that during the deformation and fracture of the specimen,the acoustic emission energy and charge significantly increased near the stress peak,showing at this point the most intense acoustic emission activity.With the increase in loading rate,the fracture peak load of the deep shale specimen also increased.However,the maximum displacement decreased to different extents.With the increase in temperature,the effective fracture toughness of the deep shale gradually decreased.Also,the maximum displacement decreased.Under different loading rates,the deformation of the prefabricated cracks showed a nonlinear slow growthelinear growth trend.The slope of the linear growth stage increased with the increase in loading rate.In addition,as the loading rate increased,an increase in tension failure and a decrease in shear failure were observed.Moreover,the control chart showing the relationship between tension and the shear failure under different temperatures and loading rates was determined.
基金Supported by the National Natural Science Foundation of China(Grant Nos.11874236 and 11004120)the QFNU Research Fundthe Research Program of JNXY。
文摘We investigate the Rashba and Dressehaus spin-orbit(SO)couplings in an ordinary GaAs/AlGaAs asymmetric double well,which favors the electron occupancy of three subbands v=1,2,3.Resorting to an external gate,which adjusts the electron occupancy and the well symmetry,we demonstrate distinct three-level SO control of both Rashba(αv)and Dresselhaus(βv)intraband terms.Remarkably,as the gate varies,the first-subband SO parametersα1 andβ1 comply with the usual linear behavior,whileα2(β2)andα3(β3)respectively for the second and third subbands interchange the values,triggered by a gate controlled band swapping.This provides a pathway towards fascinating selective SO control in spintronic applications.Moreover,we observe that the interband Rashba(ημv)and Dresselhaus(Lμv)terms also exhibit contrasting gate dependence.Our results should stimulate experiments probing SO couplings in multi-subband wells and adopting relevant SO features in future spintronic devices.
基金financially supported by the First-Class Discipline Collaborative Innovation Program of Heilongjiang Province(Grant No.LJGXCG2024-F02)the Key Research and Development Program of Heilongjiang Province(Grant No.2024ZX09C01)+1 种基金The Postdoctoral Special Funding of Heilongjiang Province(LBH-TZ2301)supported by Heilongjiang Provincial Natural Science Foundation of China(LH2022E020)。
文摘With the increasing demand for the development of unconventional oil and gas resources,hydraulic fracturing has become a key technology for enhancing reservoir permeability.However,achieving controlled propagation of fracture networks remains a significant challenge under complex geological conditions.This study integrates theoretical analysis and finite-discrete element method(FDEM)simulations to investigate mixed-mode mechanisms,plastic zone evolution at fracture tips,and anisotropic mechanical responses of shale.Modified fracture criteria-including a T-stress-integrated Mohr-Coulo mb criterion and maximum circumferential tensile stress criterion are derived and validated through uniaxial compression and Brazilian splitting tests on Longmaxi Formation shale.Results demonstrate that the modified Mohr-Coulomb criterion effectively predicts anisotropic fracture propagation by characterizing tensile-compressive strength differences,while the plastic zone evolution under maximum circumferential tensile stress is significantly influenced by T-stress:positive T-stress(45°-90°)expands the plastic zone,whereas negative T-stress(0°-45°)contracts it.Lower tensile-to-compressive strength ratios lead to larger plastic zones.An FDEM-based horizontal well fracturing model reveals vertical fracture propagation dominated by bedding plane and interbed fracture extension,forming complex networks,while horizontal fractures initially grow independently before deflecting and inte rconnecting under maximum principal stress.Sensitivity analysis of perforation spacing identifies 62.5 mm(16holes/m)as the optimal configuration,achieving ModeⅡ-dominated fracture networks with superior connectivity and stimulation efficiency.Larger spacings(71.4-83.3 mm)result in reduced efficiency or isolated fractures.By coupling stress interference and fluid pressure field dynamics,this study establishes a methodology to balance fracture network complexity and reservoir stimulation efficacy.The findings provide theoretical insights and engineering guidelines for optimizing hydraulic fracturing designs in anisotropic shale gas reservoirs through advanced fracture criteria and FDEM-based multiphysics simulations.
