Logging Evaluation Of Gas-bearing Properties Of Shale Rich In Organic Matter In Typical Areas Of Sichuan Basin

Logging is an indispensable means for oil and gas resources exploration.However,logging prediction of shale is still relatively weak,restricting the exploration and development of shale gas.In this paper,shales rich in organic matter from 3 marine shale gas wells in Southern Sichuan Basin(H201 Well,L202 Well,H202 Well)and 1continental shale gas well in Northeastern Sichuan Basin(YL4 Well)were chosen as the research objects,through various experiments such as the TOC analysis test and methane isothermal adsorption experiment,the controlling factors of gas-bearing properties and logging responses characteristics of shale with high gas content were clarified.The models of TOC,porosity,water saturation(S_w)and gas content were established by using regression analysis method,kerogen correction method,dual water model and classification method respectively.The main achievements and understandings are as follows.(1)The content of adsorption gas of Longmaxi Formation is mainly controlled by TOC and organic matter types.While,that of Ziliujing Formation is mainly controlled by TOC and S_w.Besides,the content of free gas of both is mainly controlled by pores,temperature and pressure.(2)The gas-bearing shale with high gas content of Longmaxi Formation and Ziliujing Formation both show low density,high radioactivity and high acoustic time difference.(3)Using?log R method and regression analysis method to predict TOC,due to high maturity and pyrite,for shale of Longmaxi Formation,the accuracy of regression analysis is higher.While these two methods have similar accuracy for shale of Ziliujing Formation.Organic matter affects the prediction of porosity,so the corrected density of kerogen was used to predict the porosity.Due to the high content of mud of shale,additional conductivity of mud should be considered.Therefore,dual water model was used to predict S_w.(4)Gas content was predicted by classification method.Shale of H201 Well is dominated by adsorption gas(60%?71%),and shale of L202 Well is dominated by free gas(50%?70%).The shale of H202 Well is dominated by free gas(53%?65%).The section with high gas content of these 3 wells are all lower parts of Longmaxi Formation.The shale of YL4 Well is dominated by free gas(50%?80%)and contains dissolved gas(3%?9%).The gas content of upper and lower shale is similar.Logging evaluation study is of great theoretical and practical significance to conduct the exploration and development of shale gas.