Based on the drilling, logging, experimental and testing data of Well PD1, a shallow normal-pressure shale gas well in the Laochangping anticline in southeastern Sichuan Basin, the shallow shale gas reservoirs of the ...Based on the drilling, logging, experimental and testing data of Well PD1, a shallow normal-pressure shale gas well in the Laochangping anticline in southeastern Sichuan Basin, the shallow shale gas reservoirs of the Ordovician Wufeng Formation to Silurian Longmaxi Formation (Wufeng-Longmaxi) were investigated in terms of geological characteristics, occurrence mechanism, and adsorption-desorption characteristics, to reveal the enrichment laws and high-yield mechanism of shallow normal-pressure shale gas in complex structure areas. First, the shallow shale gas reservoirs are similar to the medium-deep shale gas reservoirs in static indicators such as high-quality shale thickness, geochemistry, physical properties and mineral composition, but the former is geologically characterized by low formation pressure coefficient, low gas content, high proportion of adsorbed gas, low in-situ stress, and big difference between principal stresses. Second, shallow shales in the complex structure areas have the gas occurrence characteristics including low total gas content (1.1-4.8 m3/t), high adsorbed gas content (2.5-2.8 m3/t), low sensitive desorption pressure (1.7-2.5 MPa), and good self-sealing. Third, the adsorbed gas enrichment of shales is mainly controlled by organic matter abundance, formation temperature and formation pressure: the higher the organic matter abundance and formation pressure, the lower the formation temperature and the higher the adsorption capacity, which is more beneficial for the adsorbed gas occurrence. Fourth, the shallow normal-pressure shale gas corresponds to low sensitive desorption pressure. The adsorbed gas can be rapidly desorbed and recovered when the flowing pressure is reduced below the sensitive desorption pressure. Fifth, the exploration breakthrough of Well PD1 demonstrates that the shallow complex structure areas with adsorbed gas in dominance can form large-scale shale reservoirs, and confirms the good exploration potential of shallow normal-pressure shale gas in the margin of the Sichuan Basin.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
The southeastern Sichuan Basin and its basin-margin transition zone(hereinafter referred to as“the basin-margin transition zone of SE Chongqing”)is the focus of normal-pressure shale gas exploration in China.In orde...The southeastern Sichuan Basin and its basin-margin transition zone(hereinafter referred to as“the basin-margin transition zone of SE Chongqing”)is the focus of normal-pressure shale gas exploration in China.In order to summarize the geological characteristics and enrichment laws of shale gas in the basin-margin transition zone of SE Chongqing,we analyzed the geological characteristics of shale gas reservoirs in the Nanchuan-Wulong area of this transition zone from the aspects of sedimentary formation,tectonic reworking and production characteristics by using geophysical,drilling,logging and testing data,and then we compared it with the overpressure shale gas reservoirs in the Jiaoshiba Block.Finally,we explored the main factors controlling the enrichment&high yields of normal-pressure shale gas in this transition zone and their hydrocarbon accumulation patterns.And the following research results were obtained.(1)Different from the over-pressure shale gas reservoirs in Jiaoshiba Block,the normal-pressure shale gas reservoirs in this transition zone are characterized by lower organic porosities,more developed micro-fractures,higher ratios of adsorbed gas,greater differences of stresses in two directions,lower geothermal gradients,lower formation pressure coefficients,higher initial fluid production rates and higher fluid flowback rates.(2)The enrichment&high yields of normal-pressure shale gas in this area is mainly controlled by three factors,i.e.,carbon-rich,silicate-rich and graptolite-rich shale,organic pores,and tectonic stress field,among which,the first factor controlled by deepwater continental shelf facies is the basis of shale gas enrichment,the second is the main controlling factor of shale gas enrichment,and the third is the key factor of high-yield shale gas.(3)The hydrocarbon accumulation patterns of normal-pressure shale gas reservoirs in the transition zone can be divided into four types,including the anticline type,the syncline type,the slope type and the reverse fault type.And the enrichment&high-yield characteristics of shale gas in different hydrocarbon accumulation patterns are also clarified.In conclusion,the research results enrich the geological theory of enrichment&high-yield laws of normal-pressure shale gas and provide a support for the exploration and development of normal-pressure shale gas in complex structures.展开更多
The shale gas accumulation conditions in the basin-margin transition zone of southeastern Chongqing in SW China are complex.In order to improve single-well productivity in this area,the geologic characteristics,major ...The shale gas accumulation conditions in the basin-margin transition zone of southeastern Chongqing in SW China are complex.In order to improve single-well productivity in this area,the geologic characteristics,major factors controlling the occurrence of sweet spots,and drilling/fracturing optimization were investigated in this study.The sweet spot evaluation system and criteria were established,and the horizontal-well-design technology was developed.The following three conclusions were drawn.First,the accumulation and high-productivity-oriented approaches for sweet spot evaluation are proposed and the criteria are established based on screened key indicators.Second,the horizontal well was designed based on:(1)the“six-map”method,to identify both the geology and engineering sweet spots for well locations;and(2)seismic attributes,to predict the development of fractures and cavities,and thus,avoid mud loss and improve the drilling efficiency.The target window,well-azimuth optimization,and the curvature were forecasted to improve the fracturing performances.Third,the Pingqiao anticline,Dongsheng anticline,Jinfo slope,and Wulong syncline were selected as Type I sweet spots.Currently,shale gas has been successfully discovered in the basin-margin transition zone and is being commercially developed.展开更多
基金Supported by the Sinopec Scientific Research Project(P21087-6).
文摘Based on the drilling, logging, experimental and testing data of Well PD1, a shallow normal-pressure shale gas well in the Laochangping anticline in southeastern Sichuan Basin, the shallow shale gas reservoirs of the Ordovician Wufeng Formation to Silurian Longmaxi Formation (Wufeng-Longmaxi) were investigated in terms of geological characteristics, occurrence mechanism, and adsorption-desorption characteristics, to reveal the enrichment laws and high-yield mechanism of shallow normal-pressure shale gas in complex structure areas. First, the shallow shale gas reservoirs are similar to the medium-deep shale gas reservoirs in static indicators such as high-quality shale thickness, geochemistry, physical properties and mineral composition, but the former is geologically characterized by low formation pressure coefficient, low gas content, high proportion of adsorbed gas, low in-situ stress, and big difference between principal stresses. Second, shallow shales in the complex structure areas have the gas occurrence characteristics including low total gas content (1.1-4.8 m3/t), high adsorbed gas content (2.5-2.8 m3/t), low sensitive desorption pressure (1.7-2.5 MPa), and good self-sealing. Third, the adsorbed gas enrichment of shales is mainly controlled by organic matter abundance, formation temperature and formation pressure: the higher the organic matter abundance and formation pressure, the lower the formation temperature and the higher the adsorption capacity, which is more beneficial for the adsorbed gas occurrence. Fourth, the shallow normal-pressure shale gas corresponds to low sensitive desorption pressure. The adsorbed gas can be rapidly desorbed and recovered when the flowing pressure is reduced below the sensitive desorption pressure. Fifth, the exploration breakthrough of Well PD1 demonstrates that the shallow complex structure areas with adsorbed gas in dominance can form large-scale shale reservoirs, and confirms the good exploration potential of shallow normal-pressure shale gas in the margin of the Sichuan Basin.
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.
基金supported by the National Major Science and Technology Project“Pilot project for Pengshui District Normal Pressure Shale Gas Exploration and Development”(No.2016ZX05061)Sinopec Science&Technology Development Dept.project“Studies on the Main Factors of Normal-Pressure Shale Gas Enrichment of the Basin-Margin Transition Zone in SE Chongqing”(No.P18057-2).
文摘The southeastern Sichuan Basin and its basin-margin transition zone(hereinafter referred to as“the basin-margin transition zone of SE Chongqing”)is the focus of normal-pressure shale gas exploration in China.In order to summarize the geological characteristics and enrichment laws of shale gas in the basin-margin transition zone of SE Chongqing,we analyzed the geological characteristics of shale gas reservoirs in the Nanchuan-Wulong area of this transition zone from the aspects of sedimentary formation,tectonic reworking and production characteristics by using geophysical,drilling,logging and testing data,and then we compared it with the overpressure shale gas reservoirs in the Jiaoshiba Block.Finally,we explored the main factors controlling the enrichment&high yields of normal-pressure shale gas in this transition zone and their hydrocarbon accumulation patterns.And the following research results were obtained.(1)Different from the over-pressure shale gas reservoirs in Jiaoshiba Block,the normal-pressure shale gas reservoirs in this transition zone are characterized by lower organic porosities,more developed micro-fractures,higher ratios of adsorbed gas,greater differences of stresses in two directions,lower geothermal gradients,lower formation pressure coefficients,higher initial fluid production rates and higher fluid flowback rates.(2)The enrichment&high yields of normal-pressure shale gas in this area is mainly controlled by three factors,i.e.,carbon-rich,silicate-rich and graptolite-rich shale,organic pores,and tectonic stress field,among which,the first factor controlled by deepwater continental shelf facies is the basis of shale gas enrichment,the second is the main controlling factor of shale gas enrichment,and the third is the key factor of high-yield shale gas.(3)The hydrocarbon accumulation patterns of normal-pressure shale gas reservoirs in the transition zone can be divided into four types,including the anticline type,the syncline type,the slope type and the reverse fault type.And the enrichment&high-yield characteristics of shale gas in different hydrocarbon accumulation patterns are also clarified.In conclusion,the research results enrich the geological theory of enrichment&high-yield laws of normal-pressure shale gas and provide a support for the exploration and development of normal-pressure shale gas in complex structures.
基金supported by the National Science and Technology Major Project(No.2016ZX05061)the Project of Sinopec Science&Technology Department(No.P18057-2).
文摘The shale gas accumulation conditions in the basin-margin transition zone of southeastern Chongqing in SW China are complex.In order to improve single-well productivity in this area,the geologic characteristics,major factors controlling the occurrence of sweet spots,and drilling/fracturing optimization were investigated in this study.The sweet spot evaluation system and criteria were established,and the horizontal-well-design technology was developed.The following three conclusions were drawn.First,the accumulation and high-productivity-oriented approaches for sweet spot evaluation are proposed and the criteria are established based on screened key indicators.Second,the horizontal well was designed based on:(1)the“six-map”method,to identify both the geology and engineering sweet spots for well locations;and(2)seismic attributes,to predict the development of fractures and cavities,and thus,avoid mud loss and improve the drilling efficiency.The target window,well-azimuth optimization,and the curvature were forecasted to improve the fracturing performances.Third,the Pingqiao anticline,Dongsheng anticline,Jinfo slope,and Wulong syncline were selected as Type I sweet spots.Currently,shale gas has been successfully discovered in the basin-margin transition zone and is being commercially developed.
