超深层页岩气立体缝网压裂技术进展与发展建议

Progress in Three-Dimensional Network Fracturing for Ultra-Deep Shale Gas and Suggestions for Further Improvements

  • 摘要: 为进一步明确我国超深层页岩气立体缝网压裂技术攻关方向,梳理了国内外垂深大于4 500 m页岩气区块的储层地质工程特征、压裂技术及压后排液试气动态,分析了伍德福德、曼科斯与四川盆地典型区块开发实践,归纳总结了不同储层条件下压裂工艺适应性及压后生产动态差异。伍德福德区块依托天然裂缝发育、应力差小、脆性较高等条件,形成了小簇间距、中等强度用液、高强度加砂、小粒径支撑剂和暂堵转向相结合的立体缝网压裂技术;我国超深层页岩气普遍具有高温、高应力、高应力差、高闭合压力和多夹层特征,压裂施工压力高、加砂窗口窄、缝网复杂化受限,部分井压后高返排率、高产液现象突出。分析认为,含气天然裂缝或微断裂和储层高含气性是复杂缝形成和高产气流的关键地质因素,高净压力和裂缝远支撑是高产稳产的工程保障。现有地质工程甜点评价标准、压裂工艺方法及监测技术等难以完全满足我国不同类型超深层页岩气高效改造需求。建议建立适用于超深层页岩气的双甜点评价标准,分类攻关适配性强的立体缝网压裂工艺、闷井排采制度和深远探缝监测技术等,构建适合国内不同区域超深层页岩气评−压−采一体化技术体系。

     

    Abstract: To identify the research direction of three-dimensional (3D) network fracturing for ultra-deep shale gas in China, a review was conducted on the geological and engineering characteristics, fracturing techniques, and post-fracturing flowback and gas testing performance of reservoirs in shale gas blocks with vertical depths exceeding 4500 m worldwide. The development practices of typical blocks, including the Woodford, Mancos, and Sichuan Basin, were analyzed. The adaptability of fracturing techniques under different reservoir conditions and the differences in post-fracturing production performance were summarized. Leveraging well-developed natural fractures, small stress differences, and high brittleness, a 3D network fracturing model is developed in the Woodford block, integrating small cluster spacing, medium-to-high fluid intensity, high-intensity of proppant, fine-grained proppants, and temporary plugging and divergence. In contrast, ultra-deep shale gas reservoirs in China generally exhibit high temperature, high stress, large stress differences, high closure pressure, and multiple interbeds. These result in high pumping pressure, narrow proppant-loading windows, and limited complexity of networks. In some wells, high flowback ratios and high liquid production are exhibited after fracturing. The analysis indicates that natural fractures or micro-faults are key geological factors for the formation of complex fractures and high gas productivity, while high net pressure and effective far-field fracture propping are engineering guarantees for high and stable production. The existing evaluation criteria for geological and engineering sweet spots, fracturing techniques, and monitoring methods are insufficient to fully meet the requirements for efficient stimulation of various types of ultra-deep shale gas reservoirs in China. It is recommended to establish dual sweet spot evaluation criteria suitable for ultra-deep shale gas, conduct classified research on differentiated 3D network fracturing technologies, soaking and flowback management strategies, and far-deep fracture monitoring and detecting technologies, and construct an integrated technology system of “evaluation-fracturing-production” suitable for ultra-deep shale gas in different regions of China.

     

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