Shale Reservoir Characteristics And Gas-bearing Properties Of The Shanxi Formation

The Ordos Basin is one of the large-scale oil and gas basins in China.The inland shale gas resources in the basin account for more than half of the total continental shale gas resources in China,and have good exploration and development prospects.The Shanxi Formation in the Yanchang exploration area is rich in hydrocarbon-generating components,and many gas wells have obtained high-yield industrial gas flow.Among them,the Yun Y-P4well can reach 6.3×10⁴m³/d high-yield gas flow,and the Yun Y-P5-1 well reaches 6.0×10⁴m³/d.The dolomite area shows good shale gas exploration prospects.Therefore,this study takes the Shanxi Formation shale in the dolomite area as the research object,analyzes and tests the organic geochemical characteristics,mineral composition,pore characteristics,gas content,gas composition,etc.,systematically studies the reservoir characteristics,pore qualitative and quantitative characterization and influencing factors,and discusses the Shanxi Formation shale in the dolomite area.Gas-bearing characteristics and main controlling factors and enrichment rules.Mainly obtained the following understanding:（1）The mineral composition of Shanxi Formation shale in Yunyan area is complex,rich in clay minerals,followed by quartz,feldspar,pyrite,siderite and other secondary minerals.The clay minerals are mainly kaolinite and illite,followed by illite mixed layer and chlorite.The shale in the study area has a high abundance of organic matter,with an average TOC content of 2.12%.It has a high maturity of organic matter,with an average Ro of 2.6%.It has entered the stage of over-mature evolution,which is conducive to the pyrolysis of organic matter.The organic kerogen type is type III kerogen with sufficient burial depth,which is a favorable source of gas generation in the study area.The reservoir in the study area is dense and heterogeneous,with an average porosity of 1.98%.The average permeability is0.0580×10^-3μm².（2）The pore throat distribution of the Shanxi Formation shale in the dolomite area is fine,and the sorting is biased.The micropores and mesopores are well developed.The pores are mainly open pores and semi-closed pores,among which inorganic pores are more developed.The pore specific surface area and total volume of shale samples are positively correlated with total organic carbon content and quartz volume fraction,and negatively correlated with the integral number of clay minerals.（3）The average isothermal adsorption gas content of shale gas in dolomite area is2.18m³/t;the average total gas content in the field is 1.52cm³/g.High gas content is usually obtained in the samples of coal seam and coal line.Carbonaceous mudstone or carbonaceous sandstone can also obtain good gas content,and the recoverable coefficient is high,with an average of 81.4%.The natural gas is mainly composed of hydrocarbons,and the drying coefficient is greater than 0.99,which is mainly due to organic coal-type gas.The gas content of shale in the study area has a good positive correlation with the total organic carbon content and a weak positive correlation with the content of clay minerals.The porosity and permeability of shale have a significant positive correlation with the total gas content and desorption gas content,which has a direct control effect on the gas content of shale.The enrichment degree of shale gas is mainly controlled by the development degree of TOC and sandy interlayer.