Shale reservoir characteristics and exploration potential in the target: A case study in the Longmaxi Formation from the southern Sichuan Basin of China

The Lower Silurian Longmaxi shale Formation in southern China is experiencing a significant increase in gas exploration and development. The purpose of this paper focuses on the research of the reservoir characteristics and sweet spots inside the same local target. Based on the cores, field emission scanning electron microscopy (FE-SEM) observation, X-ray diffraction and organic geochemistry data, we determined that the organic-rich black shale in the Longmaxi Formation is deposited in the shelf. Organic geochemical characteristics (high TOC content, appropriate organic matter type, maturity and gas content) reveal that the Longmaxi shale has a good gas potential, especially at the bottom of the formation. There are four dominant reservoir space types, namely, organic matter pores, inter-particle pores, intra-particle pores and fractures. The medium pores are clearly dominant in the Longmaxi Formation. The Longmaxi Formation is dominated by quartz, calcite and clay, with a lesser amount of feldspar, dolomite and pyrite. The highly brittle mineral content indicates that the Longmaxi Formation is suitable for fracturing, especially at the bottom of the formation. By comprehensively analyzing gas potential generation, conservation and exploitation conditions, we divide the Changning gas demonstration zone into two subzones.