With the increasing demand for energy,traditional oil resources are facing depletion and insufficient supply.Many countries are rapidly turning to the development of unconventional oil and gas resources.Among them,sha...With the increasing demand for energy,traditional oil resources are facing depletion and insufficient supply.Many countries are rapidly turning to the development of unconventional oil and gas resources.Among them,shale oil and gas reservoirs have become the focus of unconventional oil and gas resources exploration and development.Based on the characteristics of shale oil and gas reservoirs,supercritical CO_(2) fracturing is more conducive to improving oil recovery than other fracturing technologies.In this paper,the mechanism of fracture initiation and propagation of supercritical CO_(2) in shale is analyzed,including viscosity effect,surface tension effect,permeation diffusion effect of supercritical CO_(2),and dissolution-adsorption effect between CO_(2) and shale.The effects of natural factors,such as shale properties,bedding plane and natural fractures,and controllable factors,proppant,temperature,pressure,CO_(2) concentration and injection rate on fracture initiation and propagation are clarified.The methods of supercritical CO_(2) fracturing process,thickener and proppant optimization to improve the efficiency of supercritical CO_(2) fracturing are discussed.In addition,some new technologies of supercritical CO_(2) fracturing are introduced.The challenges and prospects in the current research are also summarized.For example,supercritical CO_(2) is prone to filtration when passing through porous media,and it is difficult to form a stable flow state.Therefore,in order to achieve stable fracturing fluid suspension and effectively support fractu res,it is urge nt to explo re new fracturing fluid additives or improve fracturing fluid formulations combined with the research of new proppants.This paper is of great significance for understanding the behavior mechanism of supercritical CO_(2) in shale and optimizing fracturing technology.展开更多
Low temperature and low permeability are the challenges for the development of hydrate reservoirs in permafrost.The ice produced around the production well caused by high depressurization driving force reduces the gas...Low temperature and low permeability are the challenges for the development of hydrate reservoirs in permafrost.The ice produced around the production well caused by high depressurization driving force reduces the gas production,and it is necessary to reduce the effect of ice production on gas production.In this work,a new combination of fracturing technology and depressurization method was proposed to evaluate the gas production potential at the site DK-2 in Qinghai-Tibet Plateau Permafrost.A relatively higher intrinsic permeability of the fracture zone surround the horizontal production well was created by the fracturing technology.The simulation results showed that the fracture zone reduced the blocking of production ice to production wells and promoted the propagation of production pressure.And the gas production increased by 2.1 times as the radius of the fracture zone increased from 0 to 4 m in 30 years.Nearly half of the hydrate reservoirs were dissociated in 30 years,and greater than 51.7%of the gas production was produced during the first 10 years.Moreover,production behaviours were sensitive to the depressurization driving force but not to the thermal conductivity.The growth of gas production was not obvious with the intrinsic permeability of the fracture zone higher than 100 m D.The effect of ice production on gas production by fracturing technology and depressurization method was limited.展开更多
Limited by serious heterogeneity both horizontally and vertically, water driving of low-permeability layers in Qiaokou oilfield appears to be very difficult. As the classⅠ layer reaches the stage of high water-conten...Limited by serious heterogeneity both horizontally and vertically, water driving of low-permeability layers in Qiaokou oilfield appears to be very difficult. As the classⅠ layer reaches the stage of high water-content too early, the level of exploitation became worse with low-recovery. Regarding the serious heterogeneity and low recovery in layers class Ⅱand Ⅲ, composite fracturing technology suitable for this kind of reservoir was applied. Its basement was a lab study of indoor water driving efficiency and fracturing experiment. Perfect result has achieved by using the technology.展开更多
Shale gas is a kind of environmentally friendly energy difference between the conventional natural gas, shale gas in shale interlayer containing mineral machine quality, most distributed in the basin topography, shale...Shale gas is a kind of environmentally friendly energy difference between the conventional natural gas, shale gas in shale interlayer containing mineral machine quality, most distributed in the basin topography, shale interlayer thickness is bigger, is because between rock and rock cracks and voids, save for a long time, biological decomposition, degradation. There is also a very small amount of shale gas dissolved in asphaltenes and kerogen. Domestic shale gas resources are very rich, and its utilization can reduce the emission of other polluting gases, but there are certain risks in the exploitation of shale gas. For this, this paper makes a detailed study on the pressure technology and the performance of fracturing oil for the exploitation of shale gas at home and abroad, and analyzes in detail the characteristics, application methods and application scope of various fracturing technologies, which also briefly describes the current development status of shale gas.展开更多
There are abundant tight sandstone gas resources in the Sichuan Basin,which are the important objects of reserve and production increase and large-scale development.Due to their discontinuous sandbody distribution,nar...There are abundant tight sandstone gas resources in the Sichuan Basin,which are the important objects of reserve and production increase and large-scale development.Due to their discontinuous sandbody distribution,narrow channels,and strong horizontal and vertical heteroge-neity,however,conventional fracturing technologies cannot achieve the ideal stimulation effect here.In order to address this difficulty,this paper dissects the geology engineering characteristics of tight sandstone gas reservoirs in the western Sichuan Basin.Starting from the seepage mechanics theory,the concept of“multi-scale high-density”tight gas fracturing technology is put forward by fully referring to the experience of previous multi-round reservoir stimulation in the western Sichuan Basin and the idea of unconventional volume fracturing technology.In addition,its conceptual connotation,key technologies and implementation effects are illustrated.The following research results are obtained.First,the seepage characteristics make it necessary for the efficient production of tight gas reserves to increase fracture density and stimulated reservoir volume(SRV).Second,the“multi-scale high-density”fracturing technology emphasizes the rationality of high-density hydraulic fracture creation and the matching of multi-scale fractureflow capacity,and aims at establishing a multi-level fracture system with effective and steady gasflow in tight reservoirs through fracturing.Third,the“wide,dense,support,stable,and precise”fracturing technology is applied to improve single well production and estimated ultimate recovery(EUR).Fourth,the engineering practice of“multi-scale high-density”fracturing technology in the tight reservoirs of Jurassic Shaximiao Formation and Triassic Xujiahe Formation in the ZJ Gas Field realizes the average single well production rate of 15.6104 m3/d,which is 1.96 times higher than that before the stimulation.Obviously,it provides powerful support for the operation of the ZJ Gas Field into a giant gasfield with the reserves of 100 billion cubic meters.In conclusion,the formation of the concept and key technologies of“multi-scale high-density”fracturing technology effectively supports the efficient development of tight gas in the western Sichuan Basin and points out the following research direction of tight gas reservoir stimulation.The research results provide reference and guidance for the large-scale benefit development of tight gas in China.展开更多
The Self-Propping Phase-transition Fracturing Technology(SPFT)represents a novel and environmentally friendly approach for a cost-effective and efficient development of the world’s abundant unconventional resources,e...The Self-Propping Phase-transition Fracturing Technology(SPFT)represents a novel and environmentally friendly approach for a cost-effective and efficient development of the world’s abundant unconventional resources,especially in the context of a carbon-constrained sustainable future.SPFT involves the coupling of Thermal,Hydraulic,Mechanical,and Chemical(THMC)fields,which makes it challenging to understand the mechanism and path of hydraulic fracture propagation.This study addresses these challenges by developing a set of THMC multifield coupling models based on SPFT parameters and the physical/chemical characteristics of the Phase-transition Fracturing Fluid System(PFFS).An algorithm,integrating the Finite Element Method,Discretized Virtual Internal Bonds,and Element Partition Method(FEM-DVIB-EPM),is proposed and validated through a case study.The results demonstrate that the FEM-DVIB-EPM coupling algorithm reduces complexity and enhances solving efficiency.The length of the hydraulic fracture increases with the quantity and displacement of PFFS,and excessive displacement may result in uncontrolled fracture height.Within the parameters considered,a minimal difference in fracture length is observed when the PFFS amount exceeds 130 m^(3),that means the fracture length tends to stabilize.This study contributes to understanding the hydraulic fracture propagation mechanism induced by SPFT,offering insights for optimizing hydraulic fracturing technology and treatment parameters.展开更多
Hydraulic fracturing technology has played an important role in the exploitation of unconventional oil and gas resources,however,its application to gas hydrate reservoirs has been rarely studied.Currently,there is sti...Hydraulic fracturing technology has played an important role in the exploitation of unconventional oil and gas resources,however,its application to gas hydrate reservoirs has been rarely studied.Currently,there is still limited understanding of the propagation and extension of fractures around the wellbore during the fracturing process of horizontal wells in hydrate reservoirs,as well as the stress interference patterns between fractures.This study simulates hydraulic fracturing processes in hydrate reservoirs using a fluidsolid coupling discrete element method(DEM),and analyzes the impacts of hydrate saturation and geological and engineering factors on fracture extension and stress disturbance.The results show that hydraulic fracturing is more effective when hydrate saturation exceeds 30%and that fracture pressure increases with saturation.The increase in horizontal stress differential enhances the directionality of fracture propagation and reduces stress disturbance.The distribution uniformity index(DUI)reveals that injection pressure is directly proportional to the number of main fractures and inversely proportional to fracturing time,with fracturing efficiency depending on the spacing between injection points and the distance between wells.This work may provide reference for the commercial exploitation of natural gas hydrates.展开更多
The first fractured shale gas well of China was constructed in 2010.After 10 years of development,China has become the second country that possesses the core technology of shale gas development around the world,realiz...The first fractured shale gas well of China was constructed in 2010.After 10 years of development,China has become the second country that possesses the core technology of shale gas development around the world,realized the shale gas fracturing techniques from zero to one and from lagging to partially leading,and constructed the fracturing theory and technology system suitable for middle-shallow marine shale gas exploitation.In order to provide beneficial guidance for the efficient exploitation of shale gas in China in the future,this paper comprehensively reviews development history and status of domestic fundamental theories,optimized design methods,fluid systems,tools and technologies of shale gas fracturing and summarizes the research results in fundamental theories and optimized design methods,such as fracturing sweet-spot cognition,fracture network propagation simulation and control,rock hydration and flowback control,and SRV(stimulated reservoir volume)evaluation and characterization.The development and application of slick-water fracturing fluid system and new fracturing fluid with little or no water is discussed.The development and independent research&development level of multi-stage fracturing tools are evaluated,including drillable composite plug,soluble plug,large-diameter plug and casing cementing sleeve.The implementation situations of field technologies and processes are illustrated,including the early conventional multi-stage multi-cluster fracturing and the current“dense cluster”fracturing and temporary plugging fracturing.Based on this,the current challenges to domestic shale gas fracturing technologies are analyzed systematically,and the development direction of related technologies is forecast.In conclusion,it is necessary for China to continuously research the fracturing theories,technologies and methods suitable for domestic deep and ultra-deep marine shale gas,terrestrial shale gas and transitional shale gas to facilitate the future efficient development of shale gas in China.展开更多
Based on radon gas properties and its existing projects applications, we firstly attempted to apply geo- physical and chemical properties of radon gas in the field of mining engineering, and imported radioac- tive mea...Based on radon gas properties and its existing projects applications, we firstly attempted to apply geo- physical and chemical properties of radon gas in the field of mining engineering, and imported radioac- tive measurement method to detect the development process of the overlying strata mining-induced fractures and their contained water quality in underground coal mining, which not only innovates a more simple-fast-reliable detection method, but also further expands the applications of radon gas detection technology in mining field. A 3D simulation design of comprehensive testing system for detecting strata mining-induced fractures on surface with radon gas (CTSR) was carried out by using a large-scale 3D solid model design software Pro/Engineer (Pro/E), which overcame three main disadvantages of ''static design thought, 2D planar design and heavy workload for remodification design'' on exiting design for mining engineering test systems. Meanwhile, based on the simulation design results of Pro/E software, the sta- bility of the jack-screw pressure bar for the key component in CTSR was checked with a material mechan- ics theory, which provided a reliable basis for materials selection during the latter machining process.展开更多
With the rapid development of shale gas exploration and development in China,casing deformation in shale gas horizontal wells happens frequently,which directly impacts the development efficiency and benefits of shale ...With the rapid development of shale gas exploration and development in China,casing deformation in shale gas horizontal wells happens frequently,which directly impacts the development efficiency and benefits of shale gas.In order to explore casing deformation prediction,prevention and treatment methods,this paper analyzes the geological and engineering causes of casing deformation in shale-gas horizontal wells through laboratory work,such as the casing resistance to internal pressure alternating test,the ground simulation test and systematical casing deformation characteristic analysis of MIT24 caliper logging,and the large-scale physical simulation test and numerical simulation of casing deformation.Then,combined with the generalized shear activity criterion,a new method for evaluating casing deformation risk points and some technical measures for preventing casing deformation were formulated.And the following research results were obtained.First,the deformation characteristics of 119 casing deformation points in 23 wells interpreted by MIT24 caliper logging are consistent with the mechanical behaviors of shear compression deformation test.Second,the large-scale physical simulation test shows that natural fault-fractures slip obviously under the state of strike-slip stress.Third,numerical simulation shows that the compression stress on casing increases with the increase of fault-fracture slip.When the fault-fracture slip is between 7.5 mm and 9.0 mm,the casing reaches the critical yield strength and begins to undergo plastic deformation.The“temporary fracture plugging+long segment and multi-cluster”and other technologies are field tested in 28 wells in Weiyuan area of southern Sichuan Basin.The casing deformation rate decreases from 54%(before this research)to 14.3%,and the segment loss rate decreases from 7.8%to 0,which reveals remarkable achievements in casing deformation treatment.In conclusion,the shear slip of fault and macro fractures(referred to as fault-fracture)is the main cause of casing deformation in shale gas horizontal wells,and some measures(e.g.“temporary fracture plugging+long segment and multi-cluster”,reducing fracturing scale and releasing wellbore pressure properly)shall be taken in advance to reduce the fault-fracture activity before the risk point of casing deformation is fractured,so as to reach the goal of casing deformation prevention.展开更多
Normal-pressure shale gas is an important object of shale gas reserves and production increasewith broad resource prospects in China,but its large-scale benefit development is still confronted with technical bottlenec...Normal-pressure shale gas is an important object of shale gas reserves and production increasewith broad resource prospects in China,but its large-scale benefit development is still confronted with technical bottlenecks.To promote the large-scale benefit development of normal-pressure shale gas,this paper systematically sorts out and summarizes the research achievements and technological progresses related to normal-pressure shale gas from the aspects of accumulation mechanism,enrichment theory,percolation mechanism,development technology,and low-cost engineering technology,and points out the difficulties and challenges to the benefit development of normal-pressure shale gas in the complex structure zones of southern China,by taking the shale gas in the Southeast Chongqing Area of the Sichuan Basin as the research object.In addition,the research direction of normal-pressure shale gas exploration and development is discussed in terms of sweet spot selection,development technology policy,low-cost drilling technology and high-efficiency fracturing technology.And the following research results are obtained.First,the accumulation mechanism of normal-pressure shale gas is clarified from the perspective of geological exploration theory;the hydrocarbon accumulation model of generation,expulsion,retention and accumulation is established;the enrichment theory of“three-factor controlling reservoir”is put forward;and the comprehensive sweetspot target evaluation system is formed.Second,as for development technology,the development technology policies of“multiple series of strata,variable well spacing,long horizontal section,small included angle,low elevation difference,strong stimulation and pressure difference controlling”are formulated.Third,as for drilling engineering,the optimal fast drilling and completion technology with“secondary structureþradical parameterþintegrated guidanceþunpressured leak-proof cementing”as the core is formed.Fourth,as for fracturing engineering,the low-cost and high-efficiency fracturing technology with“multi-cluster small-stageþlimited-entry perforatingþdouble temporary blockingþhigh-intensity sand injectionþfully electric”as the core is formed.Fifth,normal-pressure shale gas is characterized by complex geological conditions,low pressure coefficient and gas content,poor resource endowment and so on,but its resource utilization still faces a series of challenges,such as uncertain productivity construction positions,low single-well productivity and ultimate recoverable reserve,high investment cost and poor economic benefit.In conclusion,the key research directions to realize the large-scale benefit development of low-grade normal-pressure shale gas are to deepen the research on the enrichment and high yield mechanism and sweet spot selection of normal-pressure shale gas,strengthen the research on the benefit development technology policy based on percolation mechanism and the key technologies for low-cost drilling,accelerate the research and devel-opment of the key technologies for low-cost and high-efficiency fracturing,and implement cost reduction and efficiency improvement continuously.展开更多
文摘With the increasing demand for energy,traditional oil resources are facing depletion and insufficient supply.Many countries are rapidly turning to the development of unconventional oil and gas resources.Among them,shale oil and gas reservoirs have become the focus of unconventional oil and gas resources exploration and development.Based on the characteristics of shale oil and gas reservoirs,supercritical CO_(2) fracturing is more conducive to improving oil recovery than other fracturing technologies.In this paper,the mechanism of fracture initiation and propagation of supercritical CO_(2) in shale is analyzed,including viscosity effect,surface tension effect,permeation diffusion effect of supercritical CO_(2),and dissolution-adsorption effect between CO_(2) and shale.The effects of natural factors,such as shale properties,bedding plane and natural fractures,and controllable factors,proppant,temperature,pressure,CO_(2) concentration and injection rate on fracture initiation and propagation are clarified.The methods of supercritical CO_(2) fracturing process,thickener and proppant optimization to improve the efficiency of supercritical CO_(2) fracturing are discussed.In addition,some new technologies of supercritical CO_(2) fracturing are introduced.The challenges and prospects in the current research are also summarized.For example,supercritical CO_(2) is prone to filtration when passing through porous media,and it is difficult to form a stable flow state.Therefore,in order to achieve stable fracturing fluid suspension and effectively support fractu res,it is urge nt to explo re new fracturing fluid additives or improve fracturing fluid formulations combined with the research of new proppants.This paper is of great significance for understanding the behavior mechanism of supercritical CO_(2) in shale and optimizing fracturing technology.
基金support of the Key Program of National Natural Science Foundation of China(51736009)National Natural Science Foundation of China(51676196,51976228)+4 种基金Guangdong Special Support Program(2019BT02L278)Frontier Sciences Key Research Program of the Chinese Academy of Sciences(QYZDJSSW-JSC033,QYZDB-SSW-JSC028,ZDBS-LY-SLH041)Science and Technology Apparatus Development Program of the Chinese Academy of Sciences(YZ201619)the National Key R&D Program of China(2017YFC0307306)Special Project for Marine Economy Development of Guangdong Province(GDME-2018D002,GDME-2020D044)。
文摘Low temperature and low permeability are the challenges for the development of hydrate reservoirs in permafrost.The ice produced around the production well caused by high depressurization driving force reduces the gas production,and it is necessary to reduce the effect of ice production on gas production.In this work,a new combination of fracturing technology and depressurization method was proposed to evaluate the gas production potential at the site DK-2 in Qinghai-Tibet Plateau Permafrost.A relatively higher intrinsic permeability of the fracture zone surround the horizontal production well was created by the fracturing technology.The simulation results showed that the fracture zone reduced the blocking of production ice to production wells and promoted the propagation of production pressure.And the gas production increased by 2.1 times as the radius of the fracture zone increased from 0 to 4 m in 30 years.Nearly half of the hydrate reservoirs were dissociated in 30 years,and greater than 51.7%of the gas production was produced during the first 10 years.Moreover,production behaviours were sensitive to the depressurization driving force but not to the thermal conductivity.The growth of gas production was not obvious with the intrinsic permeability of the fracture zone higher than 100 m D.The effect of ice production on gas production by fracturing technology and depressurization method was limited.
文摘Limited by serious heterogeneity both horizontally and vertically, water driving of low-permeability layers in Qiaokou oilfield appears to be very difficult. As the classⅠ layer reaches the stage of high water-content too early, the level of exploitation became worse with low-recovery. Regarding the serious heterogeneity and low recovery in layers class Ⅱand Ⅲ, composite fracturing technology suitable for this kind of reservoir was applied. Its basement was a lab study of indoor water driving efficiency and fracturing experiment. Perfect result has achieved by using the technology.
文摘Shale gas is a kind of environmentally friendly energy difference between the conventional natural gas, shale gas in shale interlayer containing mineral machine quality, most distributed in the basin topography, shale interlayer thickness is bigger, is because between rock and rock cracks and voids, save for a long time, biological decomposition, degradation. There is also a very small amount of shale gas dissolved in asphaltenes and kerogen. Domestic shale gas resources are very rich, and its utilization can reduce the emission of other polluting gases, but there are certain risks in the exploitation of shale gas. For this, this paper makes a detailed study on the pressure technology and the performance of fracturing oil for the exploitation of shale gas at home and abroad, and analyzes in detail the characteristics, application methods and application scope of various fracturing technologies, which also briefly describes the current development status of shale gas.
基金supported by the key project of the United Foun-dation of National NaturalScience Foundation of China“Basic Research on Volumetric Acid Fracturing of Deep Sulfur-bearing Carbonate Gas Reservoirs in Sichuan Basin”(No.U21A20105)CNPC Science and Technology Innovation Project"Research on the Mechanism of Complex Fracture Propagation and Control Measures of Temporary Plugging Fracturing of Shale Gas Reservoir"(No.2020D-5007-0208).
文摘There are abundant tight sandstone gas resources in the Sichuan Basin,which are the important objects of reserve and production increase and large-scale development.Due to their discontinuous sandbody distribution,narrow channels,and strong horizontal and vertical heteroge-neity,however,conventional fracturing technologies cannot achieve the ideal stimulation effect here.In order to address this difficulty,this paper dissects the geology engineering characteristics of tight sandstone gas reservoirs in the western Sichuan Basin.Starting from the seepage mechanics theory,the concept of“multi-scale high-density”tight gas fracturing technology is put forward by fully referring to the experience of previous multi-round reservoir stimulation in the western Sichuan Basin and the idea of unconventional volume fracturing technology.In addition,its conceptual connotation,key technologies and implementation effects are illustrated.The following research results are obtained.First,the seepage characteristics make it necessary for the efficient production of tight gas reserves to increase fracture density and stimulated reservoir volume(SRV).Second,the“multi-scale high-density”fracturing technology emphasizes the rationality of high-density hydraulic fracture creation and the matching of multi-scale fractureflow capacity,and aims at establishing a multi-level fracture system with effective and steady gasflow in tight reservoirs through fracturing.Third,the“wide,dense,support,stable,and precise”fracturing technology is applied to improve single well production and estimated ultimate recovery(EUR).Fourth,the engineering practice of“multi-scale high-density”fracturing technology in the tight reservoirs of Jurassic Shaximiao Formation and Triassic Xujiahe Formation in the ZJ Gas Field realizes the average single well production rate of 15.6104 m3/d,which is 1.96 times higher than that before the stimulation.Obviously,it provides powerful support for the operation of the ZJ Gas Field into a giant gasfield with the reserves of 100 billion cubic meters.In conclusion,the formation of the concept and key technologies of“multi-scale high-density”fracturing technology effectively supports the efficient development of tight gas in the western Sichuan Basin and points out the following research direction of tight gas reservoir stimulation.The research results provide reference and guidance for the large-scale benefit development of tight gas in China.
基金supported by the National Natural Science Foundation of China(52179112)the Open Fund of National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Southwest Petroleum University)(PLN2023-02)Fundamental Research Funds for the Central Universities(2021FZZX001-14).
文摘The Self-Propping Phase-transition Fracturing Technology(SPFT)represents a novel and environmentally friendly approach for a cost-effective and efficient development of the world’s abundant unconventional resources,especially in the context of a carbon-constrained sustainable future.SPFT involves the coupling of Thermal,Hydraulic,Mechanical,and Chemical(THMC)fields,which makes it challenging to understand the mechanism and path of hydraulic fracture propagation.This study addresses these challenges by developing a set of THMC multifield coupling models based on SPFT parameters and the physical/chemical characteristics of the Phase-transition Fracturing Fluid System(PFFS).An algorithm,integrating the Finite Element Method,Discretized Virtual Internal Bonds,and Element Partition Method(FEM-DVIB-EPM),is proposed and validated through a case study.The results demonstrate that the FEM-DVIB-EPM coupling algorithm reduces complexity and enhances solving efficiency.The length of the hydraulic fracture increases with the quantity and displacement of PFFS,and excessive displacement may result in uncontrolled fracture height.Within the parameters considered,a minimal difference in fracture length is observed when the PFFS amount exceeds 130 m^(3),that means the fracture length tends to stabilize.This study contributes to understanding the hydraulic fracture propagation mechanism induced by SPFT,offering insights for optimizing hydraulic fracturing technology and treatment parameters.
基金financially supported by the National Key Research and Development Plan(2023YFC2811001)the National Natural Science Foundation of China(42206233)the Taishan Scholars Program(tsqn202312280,tsqn202306297)。
文摘Hydraulic fracturing technology has played an important role in the exploitation of unconventional oil and gas resources,however,its application to gas hydrate reservoirs has been rarely studied.Currently,there is still limited understanding of the propagation and extension of fractures around the wellbore during the fracturing process of horizontal wells in hydrate reservoirs,as well as the stress interference patterns between fractures.This study simulates hydraulic fracturing processes in hydrate reservoirs using a fluidsolid coupling discrete element method(DEM),and analyzes the impacts of hydrate saturation and geological and engineering factors on fracture extension and stress disturbance.The results show that hydraulic fracturing is more effective when hydrate saturation exceeds 30%and that fracture pressure increases with saturation.The increase in horizontal stress differential enhances the directionality of fracture propagation and reduces stress disturbance.The distribution uniformity index(DUI)reveals that injection pressure is directly proportional to the number of main fractures and inversely proportional to fracturing time,with fracturing efficiency depending on the spacing between injection points and the distance between wells.This work may provide reference for the commercial exploitation of natural gas hydrates.
文摘The first fractured shale gas well of China was constructed in 2010.After 10 years of development,China has become the second country that possesses the core technology of shale gas development around the world,realized the shale gas fracturing techniques from zero to one and from lagging to partially leading,and constructed the fracturing theory and technology system suitable for middle-shallow marine shale gas exploitation.In order to provide beneficial guidance for the efficient exploitation of shale gas in China in the future,this paper comprehensively reviews development history and status of domestic fundamental theories,optimized design methods,fluid systems,tools and technologies of shale gas fracturing and summarizes the research results in fundamental theories and optimized design methods,such as fracturing sweet-spot cognition,fracture network propagation simulation and control,rock hydration and flowback control,and SRV(stimulated reservoir volume)evaluation and characterization.The development and application of slick-water fracturing fluid system and new fracturing fluid with little or no water is discussed.The development and independent research&development level of multi-stage fracturing tools are evaluated,including drillable composite plug,soluble plug,large-diameter plug and casing cementing sleeve.The implementation situations of field technologies and processes are illustrated,including the early conventional multi-stage multi-cluster fracturing and the current“dense cluster”fracturing and temporary plugging fracturing.Based on this,the current challenges to domestic shale gas fracturing technologies are analyzed systematically,and the development direction of related technologies is forecast.In conclusion,it is necessary for China to continuously research the fracturing theories,technologies and methods suitable for domestic deep and ultra-deep marine shale gas,terrestrial shale gas and transitional shale gas to facilitate the future efficient development of shale gas in China.
基金support for this work provided by the Fundamental Research Funds for the Central Universities(China University of Mining & Technology) (No. 2010ZDP02B02)the State Key Laboratory of Coal Resources and Safe Mining(No. SKLCRSM08X02)
文摘Based on radon gas properties and its existing projects applications, we firstly attempted to apply geo- physical and chemical properties of radon gas in the field of mining engineering, and imported radioac- tive measurement method to detect the development process of the overlying strata mining-induced fractures and their contained water quality in underground coal mining, which not only innovates a more simple-fast-reliable detection method, but also further expands the applications of radon gas detection technology in mining field. A 3D simulation design of comprehensive testing system for detecting strata mining-induced fractures on surface with radon gas (CTSR) was carried out by using a large-scale 3D solid model design software Pro/Engineer (Pro/E), which overcame three main disadvantages of ''static design thought, 2D planar design and heavy workload for remodification design'' on exiting design for mining engineering test systems. Meanwhile, based on the simulation design results of Pro/E software, the sta- bility of the jack-screw pressure bar for the key component in CTSR was checked with a material mechan- ics theory, which provided a reliable basis for materials selection during the latter machining process.
基金supported by the Scientific Research and Technology Development Project of CNPC“Research and field test of key technologies for effective exploitation of deep shale gas”(No.2019F-31JT).
文摘With the rapid development of shale gas exploration and development in China,casing deformation in shale gas horizontal wells happens frequently,which directly impacts the development efficiency and benefits of shale gas.In order to explore casing deformation prediction,prevention and treatment methods,this paper analyzes the geological and engineering causes of casing deformation in shale-gas horizontal wells through laboratory work,such as the casing resistance to internal pressure alternating test,the ground simulation test and systematical casing deformation characteristic analysis of MIT24 caliper logging,and the large-scale physical simulation test and numerical simulation of casing deformation.Then,combined with the generalized shear activity criterion,a new method for evaluating casing deformation risk points and some technical measures for preventing casing deformation were formulated.And the following research results were obtained.First,the deformation characteristics of 119 casing deformation points in 23 wells interpreted by MIT24 caliper logging are consistent with the mechanical behaviors of shear compression deformation test.Second,the large-scale physical simulation test shows that natural fault-fractures slip obviously under the state of strike-slip stress.Third,numerical simulation shows that the compression stress on casing increases with the increase of fault-fracture slip.When the fault-fracture slip is between 7.5 mm and 9.0 mm,the casing reaches the critical yield strength and begins to undergo plastic deformation.The“temporary fracture plugging+long segment and multi-cluster”and other technologies are field tested in 28 wells in Weiyuan area of southern Sichuan Basin.The casing deformation rate decreases from 54%(before this research)to 14.3%,and the segment loss rate decreases from 7.8%to 0,which reveals remarkable achievements in casing deformation treatment.In conclusion,the shear slip of fault and macro fractures(referred to as fault-fracture)is the main cause of casing deformation in shale gas horizontal wells,and some measures(e.g.“temporary fracture plugging+long segment and multi-cluster”,reducing fracturing scale and releasing wellbore pressure properly)shall be taken in advance to reduce the fault-fracture activity before the risk point of casing deformation is fractured,so as to reach the goal of casing deformation prevention.
基金supported by the National Science and Technology Major Project of China"Demonstrative project of normal-pressure shale gas exploration and development in the Pengshui area"(No.2016ZX05061)the Sinopec Scientific Research Projects"Evaluation of normal-pressure shale gas enrichment and production mechanisms and targets in Nan-chuan-Wulong"(No.P21087-6)"Evaluation of shale gas enrichment and targets in the East China exploration area in Sichuan Basin and its periphery"(No.P20059-6).
文摘Normal-pressure shale gas is an important object of shale gas reserves and production increasewith broad resource prospects in China,but its large-scale benefit development is still confronted with technical bottlenecks.To promote the large-scale benefit development of normal-pressure shale gas,this paper systematically sorts out and summarizes the research achievements and technological progresses related to normal-pressure shale gas from the aspects of accumulation mechanism,enrichment theory,percolation mechanism,development technology,and low-cost engineering technology,and points out the difficulties and challenges to the benefit development of normal-pressure shale gas in the complex structure zones of southern China,by taking the shale gas in the Southeast Chongqing Area of the Sichuan Basin as the research object.In addition,the research direction of normal-pressure shale gas exploration and development is discussed in terms of sweet spot selection,development technology policy,low-cost drilling technology and high-efficiency fracturing technology.And the following research results are obtained.First,the accumulation mechanism of normal-pressure shale gas is clarified from the perspective of geological exploration theory;the hydrocarbon accumulation model of generation,expulsion,retention and accumulation is established;the enrichment theory of“three-factor controlling reservoir”is put forward;and the comprehensive sweetspot target evaluation system is formed.Second,as for development technology,the development technology policies of“multiple series of strata,variable well spacing,long horizontal section,small included angle,low elevation difference,strong stimulation and pressure difference controlling”are formulated.Third,as for drilling engineering,the optimal fast drilling and completion technology with“secondary structureþradical parameterþintegrated guidanceþunpressured leak-proof cementing”as the core is formed.Fourth,as for fracturing engineering,the low-cost and high-efficiency fracturing technology with“multi-cluster small-stageþlimited-entry perforatingþdouble temporary blockingþhigh-intensity sand injectionþfully electric”as the core is formed.Fifth,normal-pressure shale gas is characterized by complex geological conditions,low pressure coefficient and gas content,poor resource endowment and so on,but its resource utilization still faces a series of challenges,such as uncertain productivity construction positions,low single-well productivity and ultimate recoverable reserve,high investment cost and poor economic benefit.In conclusion,the key research directions to realize the large-scale benefit development of low-grade normal-pressure shale gas are to deepen the research on the enrichment and high yield mechanism and sweet spot selection of normal-pressure shale gas,strengthen the research on the benefit development technology policy based on percolation mechanism and the key technologies for low-cost drilling,accelerate the research and devel-opment of the key technologies for low-cost and high-efficiency fracturing,and implement cost reduction and efficiency improvement continuously.
