煤层顶板水平井分段压裂卸压瓦斯排采技术研究进展、关键科学问题与展望

Research progress,key scientific issues,and prospects of segmented fracturing and pressure relief gas drainage technology for coal seam roof horizontal wells

  • 摘要: 煤层顶板水平井分段压裂卸压瓦斯排采技术是指导深部高瓦斯松软低渗煤层瓦斯高效抽采的关键手段。据此提出煤层顶板水平井分段压裂卸压瓦斯排采工程全生命周期开发思路,包括前期科学规划、中期工程施工和后期安全管理3个阶段。梳理了煤层顶板水平井分段压裂卸压瓦斯排采全生命周期开发研究进展,构建了煤层顶板水平井分段压裂卸压瓦斯排采关键科学问题的总体研究框架,并概述了其未来发展方向。结果表明:煤层顶板水平井分段压裂裂缝扩展受地质因素、施工参数和物性参数等影响变得极其复杂,综合评价裂缝扩展多因素影响下的主次关系,揭示多因素影响下的煤层顶板压裂裂缝扩展机理是亟待解决的问题。探寻应力、水、温度与煤体因素耦合对煤层瓦斯吸附、解吸与运移的促进与抑制作用的临界关系,建立多因素临界指标下的煤层瓦斯吸附与解吸最优模型,是实现煤层瓦斯高效排采的关键。目前,煤层顶板压裂遗留水在污染水源、抑制瓦斯排采和危险性聚集方面的研究不足,且缺乏“中国化”的管理经验和技术支撑。以煤层顶板压裂工程全生命周期开发思路为导向,分析了其高耗水性、压裂液选择及潜在污染、支撑剂合理选择、空气污染和地震风险等人文环境问题,提出了与之相对应的政策法规制定思路。实现复杂环境中多裂缝竞争扩展实时精准监测,揭示多因素影响下煤层顶板分段压裂与跨界面裂缝扩展机理,构建煤层顶板水平井分段压裂裂缝扩展有效影响半径评价模型,探究三向应力与煤体结构双重异性条件下水气运移规律,实现煤层顶板水平井压裂水气聚合潜在危险区超前探测,建立煤层顶板水平井分段压裂卸压瓦斯排采效果的精细化评价模型是目前亟待解决的关键科学问题。最后对煤层顶板水平井分段压裂卸压瓦斯排采技术的精准化、协调化、智能化、综合化和示范化发展方向进行了展望。

     

    Abstract: The segmented fracturing and pressure relief gas drainage technology in the horizontal well of the coal seam roof is a key means to guide the efficient gas extraction in deep, high gas, soft and low permeability coal seams.Based on this, a full lifecycle development concept for the segmented fracturing, pressure relief,and gas drainage engineering of the coal seam roof horizontal well is proposed, including three stages: early scientific planning, mid-term engineering construction, and later safety management.This paper summarizes the research progress on the full life cycle development of segmented fracturing and pressure relief gas drainage in coal seam roof horizontal wells, constructs an overall research framework for key scientific issues related to segmented fracturing and pressure relief gas drainage in coal seam roof horizontal wells, and looks forward to its future development direction.The results show that the expansion of segmented fracturing cracks in the horizontal well of the coal seam roof is extremely complex due to geological factors, construction parameters, and physical properties.It is urgent to comprehensively evaluate the primary and secondary relationships under the influence of multiple factors in crack expansion, and reveal the mechanism of coal seam roof fracturing crack expansion under the influence of multiple factors.Exploring the critical relationship between the coupling of stress, water, temperature, and coal factors on the promotion and inhibition of coalbed methane adsorption, desorption, and migration, and establishing an optimal model for coalbed methane adsorption and desorption under multiple critical indicators, is the key to achieving efficient coalbed methane extraction.At present, there is insufficient research on the residual water from coal seam roof fracturing in terms of polluting water sources, inhibiting gas drainage,and dangerous accumulation, and there is a lack of management experience and technical support in a "Chinese style" approach.Guided by the development concept of the entire life cycle of coal seam roof fracturing engineering, this paper analyzes its high water consumption, fracturing fluid selection and potential pollution, reasonable selection of proppants, air pollution and seismic risks, and puts forward corresponding policy and regulatory formulation ideas.Realizing real-time and accurate monitoring of multi crack competition expansion in complex environments, revealing the mechanism of segmented fracturing and cross interface crack expansion of coal seam roof under the influence of multiple factors, constructing an effective radius evaluation model for segmented fracturing crack expansion of coal seam roof horizontal wells, exploring the water and gas migration law under the dual anisotropy conditions of three-dimensional stress and coal body structure, achieving advanced detection of potential danger areas for water and gas aggregation during fracturing of coal seam roof horizontal wells,and establishing a refined evaluation model for the effect of segmented fracturing,pressure relief, and gas drainage in coal seam roof horizontal wells is currently a key scientific problem that urgently needs to be solved.Finally, the development direction of precision,coordination, intelligence, comprehensiveness, and demonstration of segmented fracturing and pressure relief gas drainage technology for coal seam roof horizontal wells was discussed.

     

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