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

摘要： 位于四川盆地中南部低陡构造带的永川页岩气田,是中国复杂构造区内又一个成功探明储量超千亿立方米的大型整装深层页岩气田。该气田的主力产层为奥陶系五峰组—志留系龙马溪组一段海相富有机质页岩,其资源规模大,但受复杂构造背景控制,呈现地表与地下"双复杂"特征,表现为保存条件复杂、地应力场非均质性强、压裂改造难度大,页岩气的高效勘探与效益开发面临严峻挑战。通过系统总结该气田十余年的勘探开发实践,明确了成藏条件、演化阶段与成藏模式,研发并集成了适用于深层页岩气的勘探开发关键技术体系。研究结果表明:①气田的成藏过程可划分为海西期以前的有机质未成熟阶段、海西期—印支期的主生油阶段、燕山晚期的主生气阶段和燕山晚期—喜马拉雅期的页岩气藏差异抬升阶段;②气田整体具有埋深大、总有机碳含量高、孔隙度与含气量高,以及构造、断裂系统和地应力场复杂的特点,深水陆棚相富有机质页岩的稳定发育与有效保存是页岩气富集成藏的主控因素;③建立了地质评价与"甜点"预测关键技术,实现了"甜点"关键参数的精确预测,并完成断裂/裂缝、地应力和"甜点"的定量化精细评价,为页岩气的产量突破提供了可靠依据;④形成了以地质建模-数值模拟为核心的开发技术策略优化方法,创新提出了复杂构造区差异化压裂改造技术体系,为页岩气井的高产与稳产提供了有效支撑。该研究成果以期为中国同类复杂构造区深层页岩油气的勘探开发提供技术参考和借鉴。

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