A Quantitative Evaluation of Shale Gas Content in Different Occurrence States of the Longmaxi Formation: A New Insight from Well JY-A in the Fuling Shale Gas Field, Sichuan Basin

摘要

Comprehensive quantitative evaluation of shale gas content and the controlling factors in different occurrence states is of great significance for accurately assessing gas-bearing capacity and providing effective well-production strategies.A total of 122 core samples from well JY-A in the Fuling shale gas field were studied to reveal the characteristics of S1l shale,15 of which were selected to further predict the shale gas content in different occurrence states,which are dependent on geological factors in the thermal evolution process.Geological parameters were researched by a number of laboratory programs,and the factors influential in controlling shale gas content were extracted by both PCA and GRA methods and prediction models were confirmed by the BE method using SPSS software.Results reveal that the adsorbed gas content is mainly controlled by TOC,Ro,SSA,PD and pyrite content,and the free gas content is mainly controlled by S2,quartz content,gas saturation and formation pressure for S1lin well JY-A.Three methods,including the on-site gas desorption method,the empirical formula method,and the multiple regression analysis method were used in combination to evaluate the shale gas capacity of well JY-A,all of which show that the overall shale gas content of well JY-A is in the range of 2.0-5.0 m3/t and that the free gas ratio is about 50％,lower than that of well JY-1.Cause analysis further confirms the tectonics and preservation conditions of S1l in the geological processes,especially the influence of eastern boundary faults on well JY-A,as the fundamental reasons for the differences in shale gas enrichment in the Jiaoshiba area.