A comprehensive evaluation index of gas-bearing property of shale reservoirs based on grey relation and its application: Case study of Jiaoshiba area, Sichuan Basin

Accurate evaluation of gas-bearing characteristics of shale reservoirs is an important prerequisite for scientific management of shale gas wells and improvement of shale gas exploration and development. Based on the grey correlation theory and geological conditions of Jiaoshiba area, the measured gas content, gas saturation, gas logging show (gas logging total hydrocarbon and methane), porosity, total organic carbon (TOC)and brittle mineral content (quartz+feldspar)were screened. Those indicators were used to analyze the gas bearing characteristics of 7 key wells in the study area. The results showed that: (1)According to the grey relational theory, the correlation and weight coefficient of each factor can be quantitatively calculated, and the gas-bearing comprehensive evaluation index can be obtained to realize the multi-factor geological and engineering factors to characterize the shale gas-bearing property; (2)Based on the comprehensive evaluation index difference, the shale reservoirs can be divided into three types. The evaluation index of typeⅠreservoir is more than 0. 8 and the shale gas bearing property is good, which is high-yield well (more than 20×104m3/d). TypeⅡ is 0. 6-0. 8, the shale gas bearing property is moderate, and it is medium-yield well (the yield is (5-20)×104m3/d). Type Ⅲ is less than 0. 6, and the shale gas bearing property is poor, which is low-yield well (less than 5×104m3/d). The comprehensive evaluation index was used to predict shale gas bearing and has a good correlation with actual production, which has a certain indication effect on the analysis and prediction of shale gas well productivity.