Study On Formation Conditions And Enrichment Rules Of Continental Shale Gas In Northeast Of Sichuan Basin

China's shale gas resources rank among the top in the world.The Sichuan Basin is one of the key areas for shale gas exploration in China.The exploration of marine shale in the basin has made great breakthroughs,and Jurassic continental shale with huge natural gas reserves is also becoming a key layer of development.In this paper,based on the field survey,drilling core observation,logging data,geochemical analysis,and rock microscopic observation,the formation conditions and enrichment rules of continental shale gas in the Lower Jurassic Ziliujing Formation in northeastern Sichuan are analyzed and studied.The following conclusions are drawn: The shale of the Ziliujing Formation in the study area is lacustrine sedimentary.It can be subdivided into the lakeside subfacies,shallow lake subfacies and semi-deep lake subfacies.The main sedimentary microfacies include shallow lake mud,shell beach and semi-deep lake mud.The shallow lake and semi-deep lake environment with large water depth and lack of oxygen is conducive to the development of organic-rich continental shale.The organic matter abundance of Da'anzhai section and Dongyuemiao section is good.The type of kerogen is mainly type II2 and type III.The degree of organic matter evolution is moderate.From the point of view of the gas production,the geochemical indicators of the mud shale in the Da'anzhai section and the Dongyuemiao section are relatively favorable.In the reservoir mineral composition,the brittle minerals and clay minerals in the study area are high,the clay mineral content is over 50% on average,and the brittle mineral content is on average 39.3%.Compared with the marine shale,the total content of clay minerals in continental shale is slightly higher than that of marine shale,while the content of brittle minerals is lower than that of marine shale.On the whole,continental shale and marine shale have similar gas storage conditions.There is a lack of tectonic movement in the northeastern part of Sichuan,and the stratum uplift is small,there is no large-scale fracture,and the preservation conditions are good.The roof conditions of the Da'anzhai section and the Dongyuemiao section are relatively good,and the floor conditions of the Da'anzhai section are better than the Dongyuemiao section.The pressure coefficient of the continental shale formation in the study area is between 1.40 and 1.90,the thickness is large,and the self-sealing condition is better.The shale gas in the study area is mainly composed of adsorbed gas and free gas.The enrichment of shale gas is controlled by formation temperature,shale layer thickness,organic matter abundance,organic matter maturity(Ro),permeability,pore pressure,mineral composition,reservoir characteristics and other factors.These factors combine to control shale gas enrichment.