Abstract: Since establishing the Da’an circulation block in western Chongqing in June 2021, Zhejiang oilfield has been making every effort to increase and accelerate the exploration and evaluation of deep shale gas, as well as implementation work, and constantly deepen geological understanding and improve engineering technology. Thus, industrial breakthroughs have been achieved in the production tests of multiple wells, and the Da’an deep shale gas field was discovered in western Chongqing. Through systematically introducing the exploration and discovery process of the Da’an block in western Chongqing in the past two years, the paper comprehensively analyzes the geological accumulation conditions in terms of regional geological characteristics, sedimentary lithofacies, organic geochemistry, pores and fractures, physical properties, gas-bearing properties, fracture characteristics, geological and mechanical properties of rock, as well as high-quality reservoir distribution characteristics, and also summarizes the key techniques for the exploration and development of deep shale gas in Da’an block, which have been formed through practice and innovation. Da’an block was the depocenter of the Upper Yangtze foreland basin at the northern foot of the Jiangnan-Xuefeng Caledonian orogenic belt during the sedimentary period of the submember 1 of Member 1 of Wufeng-Longmaxi formations. The high-quality shale layer in the lower section was of deep-water shelf facies, and the strong reduction and anaerobic environment provided good source and reservoir conditions. As a result, the organic carbon-rich siliceous shale was developed; this block possesses excellent organic geochemical indicators, well-developed micro-reservoir space, good physical properties, good self-sealing property of shale, and high gas-bearing properties, indicating an overpressure continuous shale gas reservoir with over-matured dry gas. Based on the good conditions of shale roof and floor and the deformation of comb-shaped fold structure, an enrichment and accumulation model has been built for the deep shale gas (burial depth of 3 500-4 500 m) in western Chongqing based on the characteristics of "narrow steep anticlinal faults as the barrier bed and contiguous widely-distributed gentle synclines, hydrocarbon enrichment and high production in tectonic transition belt and low-amplitude anticline structure", reflecting the theoretical connotation of enrichment, accumulation and occurrence of mountainous shale gas under the mode of "multi-field synergy, multi-element coupling, multi-factor superposition". Through practical exploration, five comprehensive evaluation methods and technologies have been developed for the exploration and development of deep shale gas in Da’an block, including the fine identification and stability evaluation technology of multi-scale natural fractures, the integrated evaluation and design technology for the full life cycle of well platforms, the matching technology of safe, excellent and fast drilling under high temperature, the segmented volume fracturing 2.0 technology for horizontal wells that focuses on increasing reserves and production under the control of dense crushed fractures while preventing casing deformation, and the fine pressure control and flowback technology for deep shale gas based on continuous monitoring of high-frequency pressure and dynamic evaluation optimization of artificial gas reservoirs. The exploration and discovery of Da’an deep shale gas field the western Chongqing has further promoted the rapid development of deep-ultra deep marine shale gas in China.

Key words: Da’an block in western Chongqing, deep shale gas, exploration and development process, accumulation geological condition, key technology, high-frequency pressure monitoring

摘要： 浙江油田自2021年6月获得渝西地区大安流转区块以来,全力加大、加快深层页岩气勘探评价及实施,地质认识和工程技术不断深化,多口井产量测试实现工业突破,发现了渝西地区大安深层页岩气田。通过系统介绍四川盆地渝西地区大安区块近两年的勘探发现历程,从区域地质特征、沉积岩相、有机地球化学、孔隙-裂缝、物性、含气性、断裂特征、地质岩石力学性质和优质储层分布特征等对地质成藏条件进行了综合分析,归纳了通过实践创新形成的大安深层页岩气勘探开发关键技术。大安区块五峰组-龙马溪组一段1亚段沉积期整体处于江南-雪峰加里东期造山带北麓上扬子前陆盆地沉积中心,下部优质页岩层为深水陆棚相,强还原缺氧环境为其提供了良好的源储条件,有机生物富碳硅质页岩相发育、有机地球化学指标优良、微观储集空间发育、物性好、页岩自封闭性好、含气性高,表现为过成熟度干气的超压连续型页岩气藏。基于良好的页岩顶、底板条件和隔档式褶皱构造形变的特点,建立了基于"窄陡背斜断层遮挡-宽缓向斜连续分布,构造转折带与低幅背斜构造富集高产"的渝西地区大安深层页岩气富集成藏模式(埋深为3 500~4 500 m),体现了"多场协同、多元耦合、多素叠置"的山地页岩气富集成藏赋存理论内涵。通过实践探索形成了适用于大安深层页岩气勘探开发的5项综合评价方法与技术,包括多尺度天然裂缝精细识别与稳定性评价技术、井平台全生命周期一体化评价与设计技术、高温安全优快钻井配套技术、密切压碎缝控增储提产兼顾套变防治的水平井分段体积压裂2.0工艺技术、基于高频压力连续监测和人造气藏动态评估优化的深层页岩气精细控压返排技术。渝西地区大安深层页岩气田的勘探发现,进一步推动了中国海相深层-超深层页岩气的快速发展。

关键词: 渝西地区大安区块, 深层页岩气, 勘探开发历程, 成藏地质条件, 关键技术, 高频压力监测