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
In this paper, the effect of pre-existing discrete fracture network(DFN) connectivity on hydraulic fracturing is numerically investigated in a rock mass subjected to in-situ stress. The simulation results show that DF...In this paper, the effect of pre-existing discrete fracture network(DFN) connectivity on hydraulic fracturing is numerically investigated in a rock mass subjected to in-situ stress. The simulation results show that DFN connectivity has a significant influence on the hydraulic fracture(HF) & DFN interaction and hydraulic fracturing effectiveness, which can be characterized by the total interaction area, stimulated DFN length, stimulated HF length, leak-off ratio, and stimulated total length. In addition, even at the same fluid injection rate, simulation models exhibit different responses that are strongly affected by the DFN connectivity. At a low injection rate, total interaction area decreases with increasing DFN connectivity; at a high injection rate, total interaction area increases with the increase of DFN connectivity. However, for any injection rate, the stimulated DFN length increases and stimulated HF length decreases with the increase of connectivity. Generally, this work shows that the DFN connectivity plays a crucial role in the interaction between hydraulic fractures, the pre-existing natural fractures and hydraulic fracturing effectiveness; in return, these three factors affect treating pressure, created microseismicity and corresponding stimulated volume. This work strongly relates to the production technology and the evaluation of hydraulic fracturing effectiveness. It is helpful for the optimization of hydraulic fracturing simulations in naturally fractured formations.展开更多
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the National Natural Science Foundation of China(Grant Nos.41227901,41502294&41330643)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grants Nos.XDB10030000,XDB10030300&XDB10050400)
文摘In this paper, the effect of pre-existing discrete fracture network(DFN) connectivity on hydraulic fracturing is numerically investigated in a rock mass subjected to in-situ stress. The simulation results show that DFN connectivity has a significant influence on the hydraulic fracture(HF) & DFN interaction and hydraulic fracturing effectiveness, which can be characterized by the total interaction area, stimulated DFN length, stimulated HF length, leak-off ratio, and stimulated total length. In addition, even at the same fluid injection rate, simulation models exhibit different responses that are strongly affected by the DFN connectivity. At a low injection rate, total interaction area decreases with increasing DFN connectivity; at a high injection rate, total interaction area increases with the increase of DFN connectivity. However, for any injection rate, the stimulated DFN length increases and stimulated HF length decreases with the increase of connectivity. Generally, this work shows that the DFN connectivity plays a crucial role in the interaction between hydraulic fractures, the pre-existing natural fractures and hydraulic fracturing effectiveness; in return, these three factors affect treating pressure, created microseismicity and corresponding stimulated volume. This work strongly relates to the production technology and the evaluation of hydraulic fracturing effectiveness. It is helpful for the optimization of hydraulic fracturing simulations in naturally fractured formations.
