ZHANG J M,  ZHAO D F,  GUO Y H, et al.Multiple-parameter evaluation of shale gas reservoirs using a fuzzy entropy-weighted and coefficient variation method：A case study of well F-2 in the Wulong Area, Sichuan Basin[J]. Journal of Henan Polytechnic University (Natural Science) , 2024, 43(6): 57-68.

doi：10.16186/j.cnki.1673-9787.2022100009

Received:2022/10/06

Revised:2022/12/15

Online:2024/09/24

Multiple-parameter evaluation of shale gas reservoirs using a fuzzy entropy-weighted and coefficient variation method：A case study of well F-2 in the Wulong Area, Sichuan Basin

ZHANG Jiaming1,2,  ZHAO Difei3,  GUO Yinghai1,2,  ZHANG Qing3,  GUAN Xin4,  JIAO Weiwei5,  WANG Shengxiu6

1. School of Resources and Geosciences，China University of Mining and Technology，Xuzhou  221116，Jiangsu，China；2. Key Laboratory of Coalbed Methane Resources & Reservoir Formation Process，Ministry of Education，Xuzhou  221008，Jiangsu，China；3. Artificial Intelligence Research Institute，China University of Mining and Technology，Xuzhou  221000，Jiangsu，China；4. School of Safety Engineering，China University of Mining and Technology，Xuzhou  221116，Jiangsu，China；5. School of Architectural Engineering，Chongqing Industry Polytechnic Institute，Chongqing  401120，China；6. Shale Gas Branch，Chongqing Institute of Geology and Mineral Resources，Chongqing  401120，China

Abstract: Due to complex geological conditions, economic costs, mining technologies, and other factors, it is necessary to evaluate the quality of shale reservoirs before exploiting shale gas. Objectives This study aims to identify the key parameters that affect shale reservoir quality. Methods  Clay minerals, brittleness index, total organic carbon (TOC), porosity, and gas content were utilized as evaluation indices. The entropy weight method and variation coefficient method were employed to calculate the combined weights, while fuzzy theory combined with the TOPSIS method and RSR method was used to evaluate the reservoir quality of the Wufeng Formation-Long1₁ subsection (Long 1₁¹, Long 1₁², Long 1₁³, Long 1₁⁴) of well F-2. Results The findings indicate that the shale mineral components of the Wufeng Formation-Long 1₁ subsection of well F-2 in the Wulong Area are primarily quartz and clay minerals, with significant vertical heterogeneity in material components and physical properties. The average quartz content in the Long 1₁¹ subsection is the highest, with an average TOC content exceeding 4% and porosity greater than 4%. A downward trend in these parameters is observed in the upward direction, reaching the lowest levels in the Long1₁⁴ subsection. The gas content is relatively high in the Long 1₁¹ subsection, but decreases to below 2% in the Long1₁⁴ subsection. The Long 1₁¹ subsection, characterized by relatively deep water and low energy during the sedimentation period, exhibits the best material composition ratio and the highest organic matter content. Its bedding is well developed and rich in biogenic silica, resulting in optimal reservoir quality. In contrast, the sedimentary environments of the Long 1₁² and Long 1₁³ subsections are shallower, with increased input of terrigenous detritus, leading to inferior reservoir quality. The reservoirs developed in a detention basin environment during the sedimentary period of the Wufeng Formation, with some intervals exhibiting relatively stronger heterogeneity due to terrigenous input, resulting in overall lower quality. The Long 1₁⁴ subsection displays the worst reservoir quality. Conclusions Therefore, it is recommended to prioritize the exploitation of the Long 1₁¹ subsection, with the Long 1₁² and Long 1₁³ subsections and other parts of the Wufeng Formation as secondary options.

Key words: shale gas; reservoir evaluation; Wufeng-Longmaxi Formation; fuzzy theory;fuzzy entropy weight  and coefficient variation method