Lithofacies And Gas Bearing Property Of Taiyuan Formation In Southern North China

South North China basin as a typical representative of the potential favorable area of shale gas exploration in transition facies,previous study of shale gas.In this paper,the geological conditions,mineral characteristics and petrographic geologic characteristics of the Taiyuan Formation are studied under the premise of discussing the geological background of the whole shale development in the South North China basin,and then the gas content of the Taiyuan Formation is analyzed.The Taiyuan Formation in the South North China Basin is dominated by the lagoon facies and the platform facies,and there are also cliffs and tidal flat facies.The sedimentary water medium conditions are the reducing environment.The formation pressure is atmospheric pressure to high pressure.The maximum buried depth is mainly concentrated in the Kaifeng depression in the north of the basin and the Zhoukou depression in the middle and its vicinity,and the buried depth of the Bengbu depression in the southeast part of the basin is also depth.The results showed that the type of organic matter in Taiyuan Formation was mainly type?,TOC was between 0.4%and 11.89%,with an average of 2.78%.The maturity was more than 2.0%(3.0%-3.8%),with an average of 3.5%.The mineral composition of shale reservoirs in Taiyuan Formation is mainly composed of clay minerals and quartz.The reservoir properties of Taiyuan Formation were studied by means of mercury intrusion,N₂ adsorption and CO₂ adsorption.The porosity permeability of Taiyuan Formation is lower.Pore types are intergranular pores,dissolution holes and organic holes,mainly in the form of fine-sized body ink bottle hole and parallel plate hole.micropores and mesopores exceed the total specific surface area of 98%,the total pore volume of 78%mesopores with pore sizes less than 50 nm provide the primary pore specific surface and pore volume.There are five types of lithofacies in the Taiyuan Formation of the South North China Basin,including siliceous clay shale,calcareous siliceous shale,siliceous shale,sandstone and limestone.The calcareous siliceous shale and siliceous clay shale are the main lithofacies types.The geological characteristics of different lithofacies are described in detail by comparing the organic matter types,mineral composition,organic matter content,pore permeation condition,pore form and pore structure of different lithofacies.At present,the most direct and accurate way to obtain shale gas is to analyze the shale gas content.Shale gas content can be divided into loss of gas,desorption and residual gas,in which desorption and residual gas can be accurately tested by the relevant equipment,and the loss of gas due to its escape process by drilling process temperature and pressure conditions comprehensive impact,so the loss of gas content is difficult to accurately obtain.Based on the analysis of the conditions such as the change of core temperature and pressure during the drilling process,and the more common lossy gas fitting relationship,a new way to loss of gas is obtained by using the loss meter of China University of Geosciences(Beijing)Through the analysis of the geologic conditions and analytical curves of different lithofacies,the loss law of the loss of gas in different rock facies is obtained.Then,the appropriate fitting model is used to obtain the loss gas,and the gas ratio of Taiyuan Formation is analyzed.