Analysis Of Shale Reservoir Characteristics And Gas-bearing Control Factors Of Longmaxi Formation In Jingmen Area

This paper chooses the shale of Longmaxi Formation of Lower Silurian in Jingmen Area as the research object for the research on reservoir characteristics and the effect factors of the gas enrichment of Longmaxi Formation under the direction of the correlative theory of tectonic geology,petroleum geology,sedimentary petrology,reservoir geology,element geochemical theory,by using the methods of observation on the field outcrops,cores and integrated analysis with the laboratory test data comprehensively.The strata of Longmaxi and its distribution characteristics of strata thickness are summarized by observation on the cores and wafer and combined with the previous research results.According to the characteristics of rocks,Logging response and biological combination,the strata of Longmaxi Formation is divided into two pieces,the upper and the lower.The strata thickness of Longmaxi Formation,on the whole,presents a thinning trend from the east,southeast to northwest.The sedimentary environment of the study area is Shelf facies:the shale of the top Longmaxi Formation is the shallow-water shelf,the shale of the bottom Longmaxi Formation is the deep-water shelf,pointed out that anaerobic muddy deep-water shelf microfacies was the favorable facies belt for high quality mud shale.Lithologic association of Longmaxi Formation consists of shale,carboniferous shale,mudrock/shale with siltstone,Argillaceous siltstones;The minerals in the shale of Longmaxi Formation are mainly composed of clay minerals and quartz,which has high brittleness and can be pressed;the amount of illite is the largest in the clay minerals.The average value of The TOC of Longmaxi Formation in the study area is 2.24%,the shale,on the whole is good gas-bearing shale,and the content of TOC increased wavelike with the increase of buried depth;the main type of organic carbon can be defined as II type,with a high degree of thermal evolution,generally greater than 2.47%,and increased by the increase of buried depth.The main pore types developed in Longmaxi shale include intercrystal pore between microcrystaline grains of pyrite framboide,mineral mold pore,intercrystal pore between clay minerals and organic pore;the cracks are high angle cracks,low angle cracks and foliation cracks between layers;the porosity of shale peaked in 1%?3%,the permeability of shale was range from 0.00036?0.85×10-3?m2,with an average of 0.06753×10-3?m2,the reservoir of shale has lower porosity and permeability,and there is no obvious relationship between the porosity and the permeability.Through scene desorption gas content,the methane isothermal adsorption simulation experiment and contrasting and abserving logs,We investigate the characteristics of the shale gas gather in the Longmaxi Formation and the effect factors of the gas enrichment.The isothermal sdsorption experiments show that the organic-rich shale of Longmaxi Formation has good adsorption ability.The controlling facors include mineral composition,organic matter content,thermal maturity,shale density,permeability of shale,temperature and pressure and storage conditions.