SEDIMENTARY CHARACTERISTICS OF THE SHALE GAS RESERVOIR IN THE WUFENG FORMATION-LONGMAXI FORMATION, SOUTHEASTERN SICHUAN BASIN, CHINA

摘要

The Upper Ordovician Wufeng Formation (O_3w)-Lower Silurian Longmaxi Formation (S_1l) in the southeastern part of the Sichuan Basin is a key field of current shale gas exploration in China. However, there are few studies on "geological sweet spots" prediction based on quantitative characterization of shale gas sedimentary facies. In this paper, taking the Dingshan area in the southeastern Sichuan Basin as an example, the sedimentary facies of shale and its control on the distribution of geological sweet spots in this area were systematically analyzed using the method of point (sedimentary facies analysis using cores) to line (sedimentary facies analysis using single well) to plane (planar sedimentary facies analysis), combined with shale sedimentary background analysis, logging and seismic data. The results showed that, the Wufeng Formation-Longmaxi Formation in the Dingshan area mainly developed with carbonaceous siliceous shale, carbonaceous shale, calcareous shale, silty shale, argillaceous siltstone and calcareous siltstone. The Wufeng Formation and the I subsegment of the Long 1 member are the high- quality shale gas intervals. The high-quality shale section of the target layer in the Dingshan area has high TOC content, good gas content and shale thickness of more than 30 meters, which is conducive for shale gas development. Through the analysis of sedimentary environment recovery and sedimentary facies, it was confirmed that there was an underwater uplift in the Late Ordovician-Early Silurian near the Dingshan 1 well, which controlled the distribution of sedimentary facies and the development of high- quality shale, and finally plays a decisive role on the distribution of geological sweet spots.