煤炭工程 ›› 2025, Vol. 57 ›› Issue (10): 132-138.doi: 10. 11799/ ce202510016

• 研究探讨 • 上一篇    下一篇

不同围压和应力差条件下水压裂缝细观扩展规律研究

张鹏飞,冯国瑞,王朋飞,樊一江,文晓泽   

  1. 1. 太原理工大学 矿业工程学院,山西 太原 030024

    2. 矿山岩层控制及灾害防控山西省重点实验室,山西 太原 030024

    3. 山西省煤基资源绿色高效开发工程中心,山西 太原 030024

    4. 山西浙大新材料与化工研究院,山西 太原 030024

  • 收稿日期:2024-10-17 修回日期:2025-03-11 出版日期:2025-10-10 发布日期:2025-11-12
  • 通讯作者: 冯国瑞 E-mail:fguorui@163.com

Research on the microscopic propagation of hydraulic fracture under different confining pressure and stress differences

  • Received:2024-10-17 Revised:2025-03-11 Online:2025-10-10 Published:2025-11-12

摘要:

水力压裂技术能有效改善煤炭开采的应力环境,研究应力对水压裂缝的细观起裂扩展规律是深化压裂控制理论,优化压裂位置选择的前提。利用MatDEM软件开展不同等围压和应力差两种条件下水力压裂模拟试验,结果表明:等围压时水压裂缝受到孔壁不均匀度以及单侧裂缝优先起裂的影响呈120°分布,应力差存在时主裂缝平直且单一。在裂缝两端分布的压应力集中区的范围与应力差呈负相关,尖端呈现拉应力断裂模式。泵注压力增速波动呈现出先增大又平稳的水压裂缝贯通表征,同步于微裂隙累积增速波动,依此将压裂过程划分为无微裂隙、微裂隙缓慢增长、稳定增长、急速增长4个阶段。高围压促进裂缝起裂,抑制断裂过程区发育,高应力差增强了对裂缝的控制作用,体现为分支裂缝的贯通与闭合现象。选择满足工况要求的最小水平主应力和应力差存在的压裂区域,实现对主裂缝、分支裂缝的控制,避免在高应力差的区域进行压裂施工时出现应力扰动的不良影响。

关键词:

水力压裂 , MatDEM , 裂隙 , 细观表征

Abstract:

The stress environment of coal mining can be effectively improved by hydraulic fracturing technology. Studying the stress-induced microscopic cracking and expansion patterns of hydraulic fracture is essential for advancing the theory of fracturing control and optimizing the selection of fracturing locations. Using MatDEM software, hydraulic fracturing simulation tests were conducted under two different conditions: constant confining stress and stress difference. The results indicate that: (1) Hydraulic fractures under constant confining pressure were distributed at 120° due to the uneven distribution of particles around the borehole wall and the priority expansion of unilateral fracture. In the presence of stress difference, the main fracture was straight and single. The compressive stress concentration area distributed at both ends of the fracture is negatively correlated with the stress difference, and a tensile stress fracture mode is visible at the tip. (2) The curve of pumping pressure growth rate initially sharply increases and then gradually stabilizes, indicating hydraulic fracture penetration. This pattern is consistent with the fluctuation characteristics of the cumulative increase velocity of micro-cracks. According to the above indexes, the fracturing process can be divided into four stages: no micro-cracks, slow growth of micro-cracks, steady growth of micro-cracks, and rapid growth of micro-cracks. (3) High confining pressure promotes the initiation of fractures and inhibits the development of the fracture process zone. A high stress difference enhances the control of fracture initiation and propagation, which is reflected in the connection and closure of branch cracks. (4) To ensure that the hydraulic fracture meets the requirements of the working conditions, the fracturing area is selected based on the minimum horizontal principal stress and stress difference. This approach allows for better control over both the main fracture and branch fractures, and helps to mitigate any potential adverse effects caused by stress disturbance during fracturing operations, particularly in areas with high stress differences.

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