Shale Gas Portential Of Carboniferous And Permian In Yanchang Dominate Blocks

Shale gas potential in China is positively great.The explorations of shale gas of both marine and continental facies in China have made a big breakthrough.Shale of transitional facies in Carboniferous and Permian is widely developed in China.Represented in Ordos basin,transitional facies shale gas is a significant field to break through.This paper used transitional facies shale as the main study object,which is of Benxi and Shanxi Formations in Yanchang dominant blocks.Using field geological survey,core observation and description and sample test methods comprehensively,we analyzed shale gas development geological conditions,improved recourse calculation method,optimized parameters standards of shale gas favorable selection,and predicted shale gas potential.Shale of Carboniferous and Permian is developed in transitional facies.The thickness and distribution of shale,type and content of organic matter,as well as Rock mineralogical characteristics are all influenced and controlled by sedimentary facies.Shale is mainly developed in the layers of lagoon and coastal swamp,with significant effective thickness.Organic matter's type is III.TOC of shale in Shanxi Formation is 2.0%,higher than in Benxi Formation,which is 1.2%.Ro is about 2.0-3.5%.Shale is in high-over mature stage.Clay mineral content is high.Shale gas content is about 1 m~3/t,dominant by adsorbed gas.Different from the marine and continental strata,we improved the favorable selection method and standard.Taking multi-factor progressive superposition method,considering the geological condition of shale gas development,we used sedimentary facies,development and distribution of shale,geochemistry,reservoir condition and gas content as parameters,and selected the favorable areas according to formations.The favorable area of Benxi Formation is in north part of transitional zone and southeast part of Xiasiwan,while of Shanxi Formation is in east part of Yunyan and south part of Xiasiwan.By assigning the square,thickness,density,gas content of shale probabilistically,we take probability volume method to calculate the shale gas resources.The results are:Geological resources of shale gas in Shanxi Formation are 15018.4838×108m~3,recoverable resources are 3304.0664×108m~3;Geological resources in Benxi Formation are 1221.4932×108m~3,recoverable resources are 268.7285×108m~3.At present,researches of transitional facies shale gas are relatively weak in both domestic and foreign.This paper not only provided direct instruction of shale gas development in study area,but also made a good reference for other area with same geological conditions.