Controlling Factors For Shale Gas Enrichment Of Permian Shale In Southern North China Basin

As the typical representation to marine-continental transitional shale gas exploration potential favorable area in our country,the research to shale gas accumulation conditions of the Permian Shanxi and Taiyuan formations in the southern north china basin is of great significance.With the purpose of analyzing the enrichment of marine-continental transitional shale gas,we applied multiple research methods,including the analysis to formation geological background of the black shale,characterization of organic geochemistry,physical property of the reservoir and the quantity of shale gas content,the main control factors of the shale gas enrichment is also be discussed.The sedimentary environment of the southern North China Basin in Late Paleozoic from early to late has changed from epicontinental sea to paralic environment then to inland environment.The carbonate platform sedimentary system is mainly formed in the bottom of the vertical direction.Central is the delta depositional system and the fluvial and lacustrine depositional systems is formed in the top.The special sedimentary environment made the organic matter types of the Permian shale is dominated by type III.The organic matter is higher in abundance.Taiyuan formation shale organic carbon content is slightly better than that of Shanxi formation,and has strong heterogeneity in the vertical.At the end of the Triassic Paleogene have twice tectonic subsidence movement which made maximum buried depth of up to 5000 m.The organic matter is in the mature and over mature stage.Then it is beneficial to the enrichment of shale gas.The special sedimentary environment made the formation of Shanxi and Taiyuan in Permian generally contain gas and Taiyuan formation is greater than that of Shanxi formation.There has complex lithofacies assemblage in Permian.The formation of natural gas from source rocks has a short distance migration in addition to the in-situ formation in the process of shale gas accumulation.It form a unique reservoir system which has sand,shale,coal and limestone.The rich organic shale as the main force of the Department for the gas formation.The total organic carbon content,Ro,density,porosity,permeability and the content of clay minerals,quartz content of the Permian shale have a certain influence to the shale gas content.TOCand Ro is the most important factor which affecting the gas content of shale.With the comprehensive analysis of the main controlling factor to the Permian shale in the southern north china basin,it include: Organic-rich shale developed in this special ancient depositional environment of marine-continental transitional is the base of shale gas enrich.During diagenetic process,the composition and thermal evolution degree of shale,the combination of pores and fractures,is the important guarantee for the accumulation of shale gas.The history of hydrocarbon generation and tectonic subsidence at different stages are the key to control the hydrocarbon generation evolution and forming process of shale gas.