Controlling Factors And Evaluation Of Gas Bearing Property Of Continental Shale Of Qianfoya Formation In Northeast Sichuan

Compared with marine shale series,continental shale in northeastern Sichuan Basin also has good development potential.However,due to a series of characteristics of continental shale series,such as rapid sedimentary facies change,complex sedimentary structure and structure,low thermal evolution degree,large lithofacies difference and strong heterogeneity,the research on shale gas occurrence state and its proportion and gas bearing control factors in this area is relatively weak.In this paper,the continental shale of Qianfoya Formation in northeastern Sichuan Basin Basin is taken as the research object.Through literature research,field observation of outcrop actual profile,combined with organic carbon content test,scanning electron microscope observation,gas adsorption experiment,high pressure mercury injection experiment,field desorption and isothermal adsorption experiment,the basic characteristics of shale reservoir,shale gas content characteristics,controlling factors of shale gas content in different occurrence states and quantitative evaluation of gas content are analyzed.The results show that:（1）The lithology of Qianfoya Formation in Northeast Sichuan is mainly gray-black shale and gray silty mudstone.Organic matter abundance is high,organic matter type is mainly II₂and III,thermal evolution degree is mature to high mature.Shale clay mineral content is relatively high,mainly illite-montmorillonite mixed layer.This set of shale series mainly develops reservoir spaces such as clay mineral pores,corrosion pores,organic matter pores and micro-fractures;（2）Under shale drying conditions,the average theoretical maximum adsorption gas volume is 1.56 m³/t,the average free gas volume is 2.20 m³/t,the proportion of free gas in shale gas is 59%,and the proportion of adsorbed gas is 41%;（3）The controlling factors of shale gas adsorption in Qianfoya Formation include TOC content,clay mineral content,pore specific surface area,temperature and pressure.The control factors of free gas content include TOC content,clay mineral content,pore volume and gas saturation;（4）The overall gas content of Qianfoya Formation is good,and the average gas content can reach 1.678 m³/t.Vertically,well Yuanye 2 is divided into 10comprehensive favorable zones and well Yuanye 3 is divided into 6 comprehensive favorable zones.This study has reference significance for the development of terrestrial shale industry of Qianfoya Formation in Northeast Sichuan Basin.