水力压裂近井区裂缝转向扩展机理

针对水力压裂条件下煤层气井初始压裂缝转向问题,首先基于断裂力学原理与最大周向应力准则,分析了储层原始地应力场和压裂液渗透场时空演化规律,建立了裂缝转向起始模型,并考虑转向裂缝面复杂的应力边界条件,利用位移不连续法建立了裂缝转向扩展模型；其次着重考虑了射孔角度、地应力差及施工排量对压裂缝转向扩展的影响,结合焦作恩村矿区现场施工参数,分别计算了裂缝起偏角度和偏转距离。计算结果表明：水力压裂条件下,射孔角度与地应力差对近井区压裂缝转向影响较大,而压裂液排量则影响较小；当射孔角度或地应力差较小,压裂缝偏转距 离较大,形成的压裂缝曲率也较小；反之亦然。最后运用XFEM软件模拟裂缝转向扩展机制,经与计算结果对比,发现二者较为吻合,从而验证了理论模型的正确性,研究成果可为定向射孔水力压裂现场控制提供理论指导。

Research on the mechanism of fracture steering propagation in the near well area of hydraulic fracturing

In order to study deeply the initial pressure cracking problem of coalbed methane wells under hydraulic fracturing conditions. Firstly, based on the principle of fracture mechanics and the maximum circumferential stress criterion, the original geostress field and fracturing fluid permeability field of the reservoir are analyzed, the fracture steering control model is established. Secondly, considering the complex stress boundary conditions of the turning fracture surface, the crack propagation expansion model is established by displacement discontinuity method. Finally, the influence of perforation angle, geostress difference and construction displacement on pressure crack steering expansion are considered. Combined with the on-site construction parameters of encun mining area in Jiaozuo, the crack deflection angle and deflection distance were calculated separately. results show that the difference between the perforation angle and the ground stress has a great influence on the steering crack in the near-well area, while the influence of the fracturing fluid displacement is small. When the perforation angle or the ground stress difference is small, the pressure crack deflection distance is large, and the curvature of the formed crack is also small, the reverse is also true. Compared with the numerical simulation results using XFEM software to simulate the crack steering expansion mechanism, the simulation results are in good agreement with the theoretical values, which verifies the correctness of the model. Research results can provide theoretical guidance for field control of directional perforating hydraulic fracturing.