近水力压裂孔区域瓦斯运移阻滞机制研究

    Study on gas migration blocking mechanism in near hydraulic fracturing hole area

    • 摘要: 水力压裂技术在压裂孔近场区域常出现瓦斯抽采浓度与流量阶段性“凹陷”或增长迟缓的阻滞现象。为揭示该现象的内在机制,本文基于流固耦合理论,建立了考虑气-水两相渗流与煤岩变形作用的耦合模型,采用COMSOL Multiphysics软件对近孔区域瓦斯运移过程进行数值模拟。结果表明,瓦斯运移阻滞主要由两大机制控制:一是“气-水两相流竞争机制”,压裂液侵入导致气液两相在裂隙-孔隙介质中竞争流动,形成局部水锁与气相滞留;二是“有效应力回弹与裂隙闭合效应”,即压裂后煤体应力重分布引起裂隙闭合,导致渗透率降低。模拟结果再现了瓦斯运移“阻滞区—竞争区—原状区”的三区分布特征。

       

      Abstract: Hydraulic fracturing technology often exhibits a stagnation phenomenon in the near-field zone of fracturing boreholes, characterized by a temporary "depression" or sluggish growth in gas extraction concentration and flow rate. To reveal the underlying mechanism of this phenomenon, this paper establishes a coupled model based on fluid-solid interaction theory, considering gas-water two-phase flow and coal-rock deformation. Using COMSOL Multiphysics software to numerically simulate gas migration processes in the near-hole region. Results indicate that gas migration stagnation is primarily governed by two mechanisms: First, the “gas-water two-phase flow competition mechanism,” where fracturing fluid intrusion induces competition between gas and liquid phases within fracture-pore media, leading to localized water lock and gas phase retention. Second, the “effective stress rebound and fracture closure effect,” wherein post-fracturing stress redistribution in coal causes fracture closure, resulting in reduced permeability. The simulation results reproduce the three-zone distribution pattern of gas migration (“blocked zone–competitive zone–intact zone”) and demonstrate good consistency with physical experimental data.

       

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