Study on Mineral Characteristics and Lithofacies Identification of Shallow Shale in the Taiyang Gas Field, Zhaotong Demonstration Zone

Shale lithofacies is a key geological factor controlling the hydrocarbon generation capacity and fracturing effectiveness of shale reservoirs. Current research on lithofacies remains insufficient for the exploration and evaluation of shallow shale gas in complex structural areas of southern China. This study focuses on the shale of the Wufeng-Longmaxi Formation in the Taiyang anticlinal structure within the Zhaotong National Shale Gas Demonstration Zone. By utilizing logging data to calculate mineral content characteristics in the study area and identifying lithofacies types based on the DEI (Dual-Energy Index) derived from dual-energy computed tomography scanning analysis of full-diameter core samples, this paper comprehensively analyzes the control of different lithofacies on key reservoir attributes. The results indicate that the target shale in the Taiyang area exhibits high brittle mineral content (averaging 66.07%), while the clay mineral content averages 30.89%, and the content of other minerals is only 3.04%, showing distinct regularity in both vertical and planar distribution. Based on the DEI method, lithofacies are classified into biogenic siliceous shale, argillaceous shale, calcareous shale, and limestone. Among these, biogenic siliceous shale, characterized by abundant brittle minerals and bioclast laminations, has the highest brittleness index and the richest organic matter content, making it the optimal lithofacies for reservoirs. Calcareous shale exhibits moderate brittleness and low organic matter content, while argillaceous shale, dominated by clay matrix, has the lowest brittleness index and moderate organic matter content. The findings highlight the critical influence of lithofacies on reservoir quality and provide important guidance for the preferential selection and exploration of favorable lithofacies in shallow shale gas reservoirs in similar complex structural regions in southern China.