Gas-In-Place Content of Deep Shales and Its Main Controlling Factors: A Case Study on the Wufeng-Longmaxi Shales in the Middle Luzhou Block of the Southern Sichuan Basin, China

Abstract

Deep shale gas (>3500 m) is a promising fossil energy resource in the context of global efforts to achieve carbon neutrality. However, the accumulation, enrichment, and distribution of deep shale gas are complicated, which makes the gas-in-place (GIP) content and its main controlling factors of deep shales unclear. In this study, a group of deep shale samples with burial depths of 4200–4350 m were collected from the Wufeng-Longmaxi (WF-LMX) formations from the middle Luzhou block, southern Sichuan Basin, and the TOC contents, mineralogical compositions, porosities, pore water contents, water saturations, and GIP contents of the shales were systematically investigated. The results indicate that the TOC and brittle mineral contents, water-bearing characteristics, and effective porosities are the main factors controlling the GIP contents of deep shales. The deep WF-LMX shales in the middle Luzhou block have high TOC and brittle mineral contents, low pore water content (CPW), and water saturation (SW), and great effective porosity, which benefits the generation, storage, and development of shale gas. The GIP contents of the deep WF-LMX shales are in the range of 1.36–7.17 cm3/g and are higher for the shales located in the lower sublayer of the first member of the Longmaxi formation (LMX11–3). In general, the deep WF-LMX shales in the middle Luzhou block have advantageous reservoir properties and GIP contents, which indicate great shale gas potential, and the LMX11–3 shales are the most promising exploration and development targets.