Coal seams in China are typically characterized by high coal seam gas content and low permeability,posing challenges for efficient coal seam gas extraction.However,achieving successful boreholes,especially in soft coa...Coal seams in China are typically characterized by high coal seam gas content and low permeability,posing challenges for efficient coal seam gas extraction.However,achieving successful boreholes,especially in soft coal formations,remains a challenge.The mechanisms underlying permeability improvement in different coal structures need further exploration.Therefore,this paper is focused on the fundamental principles of permeability improvement in soft coal through hydraulic punching,and in hard coal via hydraulic jet fracturing.Firstly,borehole instability results from a dynamic interplay of four factors:in situ stress,coal structure,mechanical properties of coal with fluid,and drilling technology.While borehole instability is inevitable,enhancing drilling tools,drilling media,and drilling processes can mitigate risks associated with buried and stuck drill pipes by ensuring effective discharge of drill cuttings through critical flow velocity and displacement.Secondly,permeability improvement in soft coal through hydraulic punching aims at pressure relief and capacity increase,while in hard coal,hydraulic jet fracturing induces crack formation within the coal seam.Finally,this study illustrates the dynamics of the granular arch in soft coal after hydraulic punching,shedding light on the complex processes involved.展开更多
This paper comprehensively reviews the application and research progress of CO_(2) fracturing fluids in China,highlights the existing issues and puts forward suggestions for future development.Three types of fracturin...This paper comprehensively reviews the application and research progress of CO_(2) fracturing fluids in China,highlights the existing issues and puts forward suggestions for future development.Three types of fracturing fluid systems containing CO_(2),namely,CO_(2) dry fracturing fluid,CO_(2) energized fracturing fluid,and CO_(2) foam fracturing fluid,are categorized based on the mass ratio and process difference between CO_(2),water,and treatment agents.Field applications in China reveal several problem to be resolved:(1)The application scope of CO_(2) fracturing fluids is restricted to depleted reservoirs,re-fracturing of old wells,and medium-deep reservoirs with low formation pressure coefficients;(2)different types of CO_(2) fracturing fluids require different processes and ground supporting equipment;(3)optimization of CO_(2) compatibility,functionality,temperature and salt tolerance,as well as the cost of treatment agents is necessitated;(4)existing CO_(2) fracturing fluid system fail to perform well with low friction,low filtration,and high sand-carrying capacity.(5)there lacks a targeted industry standard for evaluation of performance of CO_(2) fracturing fluid system and treatment agents.Therefore,in order to meet the goals of CCUS-EOR,CCUS-EGR,or integration of fracturing,displacement and burial by CO_(2),efforts should be made in the aspects that followed,including in-depth investigation of the mechanism of CO_(2) fracturing fluids,the adaptability and compatibility between existing equipment,different CO_(2) fracturing fluid systems and processes,and construction of treatment agents,low-density proppants and highperformance systems of recyclability and industrial-grade.In addition,optimization of CO_(2) fracturing fluid system based fracturing design is also crucial taking such related factors such as overall reservoir geological conditions,petrophysical properties,CO_(2) transportation,and well site layout into consideration.展开更多
基金supported by the National Natural Science Foundation of China(42072193,42230804,Xianbo Su)the National Overseas Top Talents Program of China(JXRSB02001,Zhenjiang You).
文摘Coal seams in China are typically characterized by high coal seam gas content and low permeability,posing challenges for efficient coal seam gas extraction.However,achieving successful boreholes,especially in soft coal formations,remains a challenge.The mechanisms underlying permeability improvement in different coal structures need further exploration.Therefore,this paper is focused on the fundamental principles of permeability improvement in soft coal through hydraulic punching,and in hard coal via hydraulic jet fracturing.Firstly,borehole instability results from a dynamic interplay of four factors:in situ stress,coal structure,mechanical properties of coal with fluid,and drilling technology.While borehole instability is inevitable,enhancing drilling tools,drilling media,and drilling processes can mitigate risks associated with buried and stuck drill pipes by ensuring effective discharge of drill cuttings through critical flow velocity and displacement.Secondly,permeability improvement in soft coal through hydraulic punching aims at pressure relief and capacity increase,while in hard coal,hydraulic jet fracturing induces crack formation within the coal seam.Finally,this study illustrates the dynamics of the granular arch in soft coal after hydraulic punching,shedding light on the complex processes involved.
基金support for this work from National Natural Science Foundation of China (Grants No,U21B2071).
文摘This paper comprehensively reviews the application and research progress of CO_(2) fracturing fluids in China,highlights the existing issues and puts forward suggestions for future development.Three types of fracturing fluid systems containing CO_(2),namely,CO_(2) dry fracturing fluid,CO_(2) energized fracturing fluid,and CO_(2) foam fracturing fluid,are categorized based on the mass ratio and process difference between CO_(2),water,and treatment agents.Field applications in China reveal several problem to be resolved:(1)The application scope of CO_(2) fracturing fluids is restricted to depleted reservoirs,re-fracturing of old wells,and medium-deep reservoirs with low formation pressure coefficients;(2)different types of CO_(2) fracturing fluids require different processes and ground supporting equipment;(3)optimization of CO_(2) compatibility,functionality,temperature and salt tolerance,as well as the cost of treatment agents is necessitated;(4)existing CO_(2) fracturing fluid system fail to perform well with low friction,low filtration,and high sand-carrying capacity.(5)there lacks a targeted industry standard for evaluation of performance of CO_(2) fracturing fluid system and treatment agents.Therefore,in order to meet the goals of CCUS-EOR,CCUS-EGR,or integration of fracturing,displacement and burial by CO_(2),efforts should be made in the aspects that followed,including in-depth investigation of the mechanism of CO_(2) fracturing fluids,the adaptability and compatibility between existing equipment,different CO_(2) fracturing fluid systems and processes,and construction of treatment agents,low-density proppants and highperformance systems of recyclability and industrial-grade.In addition,optimization of CO_(2) fracturing fluid system based fracturing design is also crucial taking such related factors such as overall reservoir geological conditions,petrophysical properties,CO_(2) transportation,and well site layout into consideration.
