The Study On Sedimentary Characteristics And Shale Gas Accumulation Conditions In The Fifth Member Of The Xujiahe Formation At The Longmenshan Foreland Basin

The continental black shale is one of the main source rocks,and it is a key factor to study the formation and distribution of conventional oil and gas.At the same time,shale is also an unconventional reservoir of oil and gas,so the study of continental black shale is very important in the process of unconventional oil and gas exploration and development.At present,China and the world,the study of continental black shale is relatively low,the lack of systematic induction and transformation of results.It is urgent to carry out the theoretical research of typical sedimentary body and combine the exploration in prospecting area,For the unconventional oil and gas exploration and development work in China and the world.In this paper,the sedimentary environment analysis and sedimentary model of the black shale for the fifth member of the Xujiahe formation in the southern part of the Longmenshan foreland basin are discussed from the field sections,the sedimentary structure of the drilling core and the elemental analysis.Geochemical tests and drilling wells were analyzed for selected key areas to clarify the shale gas enrichment in this area.According to the comprehensive geological evaluation index of shale gas,it is the best exploration area for shale gas exploration in the southern part of Longmenshan foreland basin.The study shows that the formation environment of the fifth member of the Xujiahe formation black shale is shallow lake facies,deep lake facies and delta facies.Due to the abundant supply of debris in the Longmenshan foreland basin,the deposition rate is very rapid,which leads to the fact that the sedimentary structure in the sediments is not very developed and no more clay minerals in shale.The sedimentary model of the continental black shale in the fifth member of the Xujiahe formation in the Longmenshan foreland basin is the foreland basin sedimentary model,In this mode,the fine-grained sediments are deposited in the lake invaded and the stratified environment,The different areas of the foreland basin has a great influence on the distribution and preservation of shale.By shale gas accumulation research and organic geochemical testing,the fifth member of Xujiahe formation in this area's average floor strata buried depth in the3600m,the northwestward more deeper,to southeastward shallowing,the organic-rich shale accumulated effective thickness more than 200m,Sangyuan area in central much more thickener than other areas.The average TOC in the study area is greater than 2%and the average Ro is greater than 1.25%.Most of the landforms in the region are plains and hills,which are conducive to the implementation of exploration and development work.It is the most favorable exploration and development area in the fifth member of Xujiahe formation shale gas.In order to achieve the optimal exploration of shale gas,we introduce the comprehensive geological evaluation index.In the study area,the comprehensive geological evaluation index is more than 80 for favorable area,and the main favorable area is located in the Pujiang-sangyuan,and its distribution covers the Sansuchang,Pingluoba,Hanwangchang range et al.structurest,more than 4000km~2.