关键词: 四川盆地, 永川页岩气田, 五峰组—龙马溪组, 成藏条件, 勘探开发关键技术

Abstract: The Yongchuan shale gas field, located in the low-steep structural belt in the central-southern Sichuan Basin, is another large-scale integrated deep shale gas field with proven reserves exceeding 100 billion cubic meters in complex tectonic area of China. The main production formation of the gas field is the marine organic-rich shale strata from the Ordovician Wufeng Formation to the Member 1 of Silurian Longmaxi Formation. Despite its substantial resource endowment, the gas field is strongly controlled by the complex tectonic setting and exhibits "dual complexity" in both surface and subsurface conditions, which is manifested as complicated preservation conditions, strong heterogeneity in the in-situ stress field, and great difficulty in fracturing stimulation. The efficient exploration and beneficial development of shale gas in the field face considerable challenges. By systematically reviewing the exploration and development practices of the gas field over more than ten years, the accumulation conditions, evolution stages, and accumulation models have been clarified, and a suite of key technologies applicable to deep shale gas exploration and development has been developed and integrated. The research results show as follows. (1) The accumulation process of the gas field can be subdivided into four stages, namely the immature stage of organic matter before Hercynian period, the main oil-generation stage during the Hercynian-Indosinian periods, the main gas-generation stage during the Late Yanshanian period, and the differential uplift stage of shale gas reservoirs during the Late Yanshanian to Himalayan periods. (2) The gas field is characterized by great burial depth, high TOC contents, high porosities and gas contents, as well as complex tectonic structures, fault systems, and geostress fields. The stable development and effective preservation of organic-rich shale in deep-water shelf facies constitute the primary controlling factors for shale gas enrichment and accumulation. (3) Key technologies for geological assessment and "sweet spot" prediction have been established, achieving the accurate prediction of critical "sweet spot" parameters, completing quantitative and fine-scale evaluation of fractures, in-situ stress, and "sweet spot" distribution, and providing a reliable basis for breakthrough in shale gas production. (4) A development strategy optimization approach centered on geological modeling and numerical simulation has been formulated, and a differentiated fracturing technology system tailored for complex structural zones has been innovatively proposed, providing effective support for achieving high and stable production in shale gas wells. These research achievements are expected to offer technical references and inspirations for the exploration and development of deep shale oil and gas in similar complex structural areas of China.

Key words: Sichuan Basin, Yongchuan shale gas field, Wufeng-Longmaxi formations, accumulation condition, key technologies for exploration and development