In order to improve efficiency of coal seam gas drainage, many fracturing techniques, such as waterjet fracturing, hydraulic fracturing and explosive fracturing, etc, have been developed and widely used in China coal ...In order to improve efficiency of coal seam gas drainage, many fracturing techniques, such as waterjet fracturing, hydraulic fracturing and explosive fracturing, etc, have been developed and widely used in China coal mining industry. How- ever, during the engineering applications, it is observed that the efficiency of gas drainage initially improves, but reduces there- after. Thus, it is speculated that the contrasts in coalbed methane drainage efficiency may reflect variation of the closure be- havior of the artificial fracture created. Based on comprehensive gas drainage monitoring data in underground coal mines, the work presented herein uses numerical simulation to show the behavior of the time-dependent closure of coal seam fractures as- sociated with various levels of waterjet fracturing parameters and geomechanical conditions.展开更多
Deep and ultra-deep reservoirs have gradually become the primary focus of hydrocarbon exploration as a result of a series of significant discoveries in deep hydrocarbon exploration worldwide.These reservoirs present u...Deep and ultra-deep reservoirs have gradually become the primary focus of hydrocarbon exploration as a result of a series of significant discoveries in deep hydrocarbon exploration worldwide.These reservoirs present unique challenges due to their deep burial depth(4500-8882 m),low matrix permeability,complex crustal stress conditions,high temperature and pressure(HTHP,150-200℃,105-155 MPa),coupled with high salinity of formation water.Consequently,the costs associated with their exploitation and development are exceptionally high.In deep and ultra-deep reservoirs,hydraulic fracturing is commonly used to achieve high and stable production.During hydraulic fracturing,a substantial volume of fluid is injected into the reservoir.However,statistical analysis reveals that the flowback rate is typically less than 30%,leaving the majority of the fluid trapped within the reservoir.Therefore,hydraulic fracturing in deep reservoirs not only enhances the reservoir permeability by creating artificial fractures but also damages reservoirs due to the fracturing fluids involved.The challenging“three-high”environment of a deep reservoir,characterized by high temperature,high pressure,and high salinity,exacerbates conventional forms of damage,including water sensitivity,retention of fracturing fluids,rock creep,and proppant breakage.In addition,specific damage mechanisms come into play,such as fracturing fluid decomposition at elevated temperatures and proppant diagenetic reactions at HTHP conditions.Presently,the foremost concern in deep oil and gas development lies in effectively assessing the damage inflicted on these reservoirs by hydraulic fracturing,comprehending the underlying mechanisms,and selecting appropriate solutions.It's noteworthy that the majority of existing studies on reservoir damage primarily focus on conventional reservoirs,with limited attention given to deep reservoirs and a lack of systematic summaries.In light of this,our approach entails initially summarizing the current knowledge pertaining to the types of fracturing fluids employed in deep and ultra-deep reservoirs.Subsequently,we delve into a systematic examination of the damage processes and mechanisms caused by fracturing fluids within the context of hydraulic fracturing in deep reservoirs,taking into account the unique reservoir characteristics of high temperature,high pressure,and high in-situ stress.In addition,we provide an overview of research progress related to high-temperature deep reservoir fracturing fluid and the damage of aqueous fracturing fluids to rock matrix,both artificial and natural fractures,and sand-packed fractures.We conclude by offering a summary of current research advancements and future directions,which hold significant potential for facilitating the efficient development of deep oil and gas reservoirs while effectively mitigating reservoir damage.展开更多
To study the influence of construction interfaces on dynamic characteristics of roller compacted concrete dams(RCCDs),mechanical properties of construction interfaces are firstly analyzed. Then, the viscous-spring art...To study the influence of construction interfaces on dynamic characteristics of roller compacted concrete dams(RCCDs),mechanical properties of construction interfaces are firstly analyzed. Then, the viscous-spring artificial boundary(VSAB) is adopted to simulate the radiation damping of their infinite foundations, and based on the Marc software, a simplified seismic motion input method is presented by the equivalent nodal loads. Finally, based on the practical engineering of a RCC gravity dam, effects of radiation damping and construction interfaces on the dynamic characteristics of dams are investigated in detail. Analysis results show that dynamic response of the RCC gravity dam significantly reduces about 25% when the radiation damping of infinite foundation is considered. Hot interfaces and the normal cold interfaces have little influence on the dynamic response of the RCC gravity dam.However, nonlinear fracture along the cold interfaces at the dam heel will occur under the designed earthquake if the cold interfaces are combined poorly. Therefore, to avoid the fractures along the construction interfaces under the potential super earthquakes,combination quality of the RCC layers should be significantly ensured.展开更多
The Fuling shale gas field in the Sichuan Basin,as a national shale gas demonstration area,is the largest commercially developed shale gas field in the world except those in North America.The fracturing technology in ...The Fuling shale gas field in the Sichuan Basin,as a national shale gas demonstration area,is the largest commercially developed shale gas field in the world except those in North America.The fracturing technology in the mode of“well factory”has been applied widely in the gas field,but it is necessary to perform further investigation on the way to evaluate effectively the fracturing effect of multi-well platform“well factory”and the distribution laws of its induced fracture networks.In this paper,the fractures induced by the“well factory”at the JY 48 platform were real-time monitored by a surfaceedownhole combined microseismic monitoring technology.The geometric size and extension direction of artificial fractures induced in the model of“well factory”fracturing in the Jiaoshiba block of Fuling Shale Gas Field were preliminarily un-derstood.Moreover,the fracturing parameters under the mode of“well factory”were recognized by using the comprehensive interpretation results of surfaceedownhole combined microseismic monitoring technology,together with the SRV fracturing prediction chart.Eventually,the distribution laws of artificial fractures during the“well-factory-zipper”fracturing in the Fuling Shale Gas Field were clarified definitely.This paper provides guidance for the optimization of fracturing parameters at the later stage.展开更多
Outcrop coal samples from the Shizhuang South Block of the Qinshui Basin,Shanxi Province,China,were subjected to true triaxial hydraulic fracturing experiments to simulate fracture propagation.Combined with CT scannin...Outcrop coal samples from the Shizhuang South Block of the Qinshui Basin,Shanxi Province,China,were subjected to true triaxial hydraulic fracturing experiments to simulate fracture propagation.Combined with CT scanning and three-dimensional fracture reconstruction,the study examined fracture propagation patterns and bedding activation behaviors under variable pumping-rate fracturing in coal reservoirs.Results indicate that the variable pumping-rate fracturing technique effectively overcomes the strong trapping effect of coal bedding.Micro-fractures are initiated at multiple weak points along bedding planes,leading to multi-point fracture initiation and competitive propagation of fractures toward the far field,thereby generating a more complex three-dimensional fracture network.The geometry and aperture of the induced fracture network are primarily controlled by the ramp-up rate of injection flowrate.A gradual ramp-up favors the development of a more complex fracture network,though at the expense of lower breakdown pressure,insufficient initiation,and narrower apertures.In contrast,a rapid ramp-up produces wider fractures and larger propped lengths,but results in more pronounced aperture fluctuations.For coal reservoirs with relatively high rock strength,a moderately higher ramp-up rate is recommended to avoid excessively narrow fractures and potential proppant bridging.Different coal lithotypes necessitate tailored ramp-up strategies to optimize fracture morphology and stimulation effectiveness.展开更多
文摘In order to improve efficiency of coal seam gas drainage, many fracturing techniques, such as waterjet fracturing, hydraulic fracturing and explosive fracturing, etc, have been developed and widely used in China coal mining industry. How- ever, during the engineering applications, it is observed that the efficiency of gas drainage initially improves, but reduces there- after. Thus, it is speculated that the contrasts in coalbed methane drainage efficiency may reflect variation of the closure be- havior of the artificial fracture created. Based on comprehensive gas drainage monitoring data in underground coal mines, the work presented herein uses numerical simulation to show the behavior of the time-dependent closure of coal seam fractures as- sociated with various levels of waterjet fracturing parameters and geomechanical conditions.
基金Dao-Bing Wang was supported by the Beijing Natural Science Foundation Project(No.3222030)the National Natural Science Foundation of China(No.52274002)+1 种基金the PetroChina Science and Technology Innovation Foundation Project(No.2021DQ02-0201)Fu-Jian Zhou was supported by the National Natural Science Foundation of China(No.52174045).
文摘Deep and ultra-deep reservoirs have gradually become the primary focus of hydrocarbon exploration as a result of a series of significant discoveries in deep hydrocarbon exploration worldwide.These reservoirs present unique challenges due to their deep burial depth(4500-8882 m),low matrix permeability,complex crustal stress conditions,high temperature and pressure(HTHP,150-200℃,105-155 MPa),coupled with high salinity of formation water.Consequently,the costs associated with their exploitation and development are exceptionally high.In deep and ultra-deep reservoirs,hydraulic fracturing is commonly used to achieve high and stable production.During hydraulic fracturing,a substantial volume of fluid is injected into the reservoir.However,statistical analysis reveals that the flowback rate is typically less than 30%,leaving the majority of the fluid trapped within the reservoir.Therefore,hydraulic fracturing in deep reservoirs not only enhances the reservoir permeability by creating artificial fractures but also damages reservoirs due to the fracturing fluids involved.The challenging“three-high”environment of a deep reservoir,characterized by high temperature,high pressure,and high salinity,exacerbates conventional forms of damage,including water sensitivity,retention of fracturing fluids,rock creep,and proppant breakage.In addition,specific damage mechanisms come into play,such as fracturing fluid decomposition at elevated temperatures and proppant diagenetic reactions at HTHP conditions.Presently,the foremost concern in deep oil and gas development lies in effectively assessing the damage inflicted on these reservoirs by hydraulic fracturing,comprehending the underlying mechanisms,and selecting appropriate solutions.It's noteworthy that the majority of existing studies on reservoir damage primarily focus on conventional reservoirs,with limited attention given to deep reservoirs and a lack of systematic summaries.In light of this,our approach entails initially summarizing the current knowledge pertaining to the types of fracturing fluids employed in deep and ultra-deep reservoirs.Subsequently,we delve into a systematic examination of the damage processes and mechanisms caused by fracturing fluids within the context of hydraulic fracturing in deep reservoirs,taking into account the unique reservoir characteristics of high temperature,high pressure,and high in-situ stress.In addition,we provide an overview of research progress related to high-temperature deep reservoir fracturing fluid and the damage of aqueous fracturing fluids to rock matrix,both artificial and natural fractures,and sand-packed fractures.We conclude by offering a summary of current research advancements and future directions,which hold significant potential for facilitating the efficient development of deep oil and gas reservoirs while effectively mitigating reservoir damage.
基金Projects(20120094110005,20120094130003)supported by the Research Fund for the Doctoral Program of Higher Education of ChinaProjects(51379068,51139001,51279052,51209077,51179066)supported by the National Natural Science Foundation of China+1 种基金Project(NCET-11-0628)supported by the Program for New Century Excellent Talents in University,ChinaProjects(201201038,201101013)supported by the Public Welfare Industry Research Special Fund Project of Ministry of Water Resources of China
文摘To study the influence of construction interfaces on dynamic characteristics of roller compacted concrete dams(RCCDs),mechanical properties of construction interfaces are firstly analyzed. Then, the viscous-spring artificial boundary(VSAB) is adopted to simulate the radiation damping of their infinite foundations, and based on the Marc software, a simplified seismic motion input method is presented by the equivalent nodal loads. Finally, based on the practical engineering of a RCC gravity dam, effects of radiation damping and construction interfaces on the dynamic characteristics of dams are investigated in detail. Analysis results show that dynamic response of the RCC gravity dam significantly reduces about 25% when the radiation damping of infinite foundation is considered. Hot interfaces and the normal cold interfaces have little influence on the dynamic response of the RCC gravity dam.However, nonlinear fracture along the cold interfaces at the dam heel will occur under the designed earthquake if the cold interfaces are combined poorly. Therefore, to avoid the fractures along the construction interfaces under the potential super earthquakes,combination quality of the RCC layers should be significantly ensured.
基金Supported by the Sinopec Key Science and Technology Projects“Fuling shale gas stimulations”(Grant No.P14092)“Fuling shale gas development techniques”(Grant No.P13053).
文摘The Fuling shale gas field in the Sichuan Basin,as a national shale gas demonstration area,is the largest commercially developed shale gas field in the world except those in North America.The fracturing technology in the mode of“well factory”has been applied widely in the gas field,but it is necessary to perform further investigation on the way to evaluate effectively the fracturing effect of multi-well platform“well factory”and the distribution laws of its induced fracture networks.In this paper,the fractures induced by the“well factory”at the JY 48 platform were real-time monitored by a surfaceedownhole combined microseismic monitoring technology.The geometric size and extension direction of artificial fractures induced in the model of“well factory”fracturing in the Jiaoshiba block of Fuling Shale Gas Field were preliminarily un-derstood.Moreover,the fracturing parameters under the mode of“well factory”were recognized by using the comprehensive interpretation results of surfaceedownhole combined microseismic monitoring technology,together with the SRV fracturing prediction chart.Eventually,the distribution laws of artificial fractures during the“well-factory-zipper”fracturing in the Fuling Shale Gas Field were clarified definitely.This paper provides guidance for the optimization of fracturing parameters at the later stage.
基金Supported by China National Petroleum Corporation North China Oilfield Company Medium-to-Long-Term Research Project:“Key Technologies for Efficient Fracturing and Enhanced Production in Coalbed Methane”.
文摘Outcrop coal samples from the Shizhuang South Block of the Qinshui Basin,Shanxi Province,China,were subjected to true triaxial hydraulic fracturing experiments to simulate fracture propagation.Combined with CT scanning and three-dimensional fracture reconstruction,the study examined fracture propagation patterns and bedding activation behaviors under variable pumping-rate fracturing in coal reservoirs.Results indicate that the variable pumping-rate fracturing technique effectively overcomes the strong trapping effect of coal bedding.Micro-fractures are initiated at multiple weak points along bedding planes,leading to multi-point fracture initiation and competitive propagation of fractures toward the far field,thereby generating a more complex three-dimensional fracture network.The geometry and aperture of the induced fracture network are primarily controlled by the ramp-up rate of injection flowrate.A gradual ramp-up favors the development of a more complex fracture network,though at the expense of lower breakdown pressure,insufficient initiation,and narrower apertures.In contrast,a rapid ramp-up produces wider fractures and larger propped lengths,but results in more pronounced aperture fluctuations.For coal reservoirs with relatively high rock strength,a moderately higher ramp-up rate is recommended to avoid excessively narrow fractures and potential proppant bridging.Different coal lithotypes necessitate tailored ramp-up strategies to optimize fracture morphology and stimulation effectiveness.
