Multiple parameter evaluation of shale gas reservoirs based on a fuzzy entropy weight and coefficient variation method:A case of well F-2 in Wulong Area,Sichuan Basin

ZHANG Jiaming; ZHAO Difei; GUO Yinghai; ZHANG Qing; GUAN Xin; JIAO Weiwei; WANG Shengxiu

doi:10.16186/j.cnki.1673-9787.2022100009

Abstract：Due to the complex geological conditions,insufficient economic costs and mining technology and other factors,it is necessary to evaluate the quality of shale reservoir before exploiting the shale gas.Objec-tives In order to explore the key parameters that affect the shale reservoir quality,Methods taking clay min-erals,brittleness index,TOC,porosity and gas content as evaluation indexes,the entropy weight method and variation coefficient method were used to calculate the combination weight,and the fuzzy theory combined with TOPSIS method and RSR method was used to evaluate the reservoir quality of Wufeng Formation-Long11 subsection(Long 111,Long 112,Long 113,Long 114)of well F-2.Results The results showed the shale mineral components of Wufeng Formation-Long 11 subsection of well F-2 in Wulong Area were mainly quartz and clay minerals,and the vertical heterogeneity of material components and physical properties was significant.The average content of quartz in Wufeng Formation-Long 111 subsection was the highest.Its aver-age content of TOC was more than 4%,and its porosity was greater than 4%.A relatively downward trend of these elements had been shown in the upward direction,and they dropped to the lowest in Long114 subsec-tion.The gas content was relatively high in Wufeng Formation-Long 111 subsection,and also showed a down-ward trend in the upward direction,and in Long 114 subsection the gas content decreased to less than 2%.The Long 111 subsection with relatively deep water body and high static degree formed the best material composition ratio and the highest organic matter content during the sedimentation period.Its bedding was well developed and rich in biogenic silica,and its organic pores were developed to a high degree.Therefore,its reservoir quality was optimal.The sedimentary environment of Long 112 subsection and Long 113 subsection was relatively shallow.The input of terrigenous detritus to these two sections was increased,and the reservoir quality was inferior.In the sedimentary period of Wufeng Formation,the reservoir was developed in a detention basin environment,and the heterogeneity of some intervals was relatively stronger due to the influence of terrigenous input,and the overall quality was relatively lower.The reservoir quality of Long 114 subsection was the worst.Conclusions Therefore,it was recommended to give priority to the exploitation of Long 111 subsection,and the exploitation of Long 112 sub-section,Long 113 subsection and other parts of the Wufeng Formation was the second choice.