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

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