岩石定向水力压裂导控的数值分析

Numerical analysis of guide control of directional hydraulic fracturing of rock

水力压裂是改变岩体结构的一种人为手段,为控制压裂裂隙的扩展方向,需要研究定向水力压裂导控技术。根据裂隙产生及扩展机理,通过水力压裂力学分析,总结出轴向楔形槽导控、环形楔形槽导控及控制孔导控3种定向水力压裂导控方法。为对比分析3种导控方法的效果,运用数值模拟试验方法,对常规(非定向)压裂、轴向楔形槽导控压裂、环形楔形槽导控压裂及控制孔导控压裂进行了数值模拟,通过声发射及剪应力分布研究了4种压裂方式下压裂过程中裂隙扩展动态特征,对比分析了4种压裂方式的微裂压力及破裂压力。结果表明:3种导控方法均可起到控制裂隙发展方向的作用,且有效降低了水力压裂的微裂压力和破裂压力,3种导控方法中以轴向楔形槽导控为最优。

Hydraulic fracturing is a natural action and an artificial method to alter rock structure. In order to control the direction of fracture in the process of hydraulic fracturing, directional hydraulic fracturing is necessary. According to fracture initiation and extension mechanism, three methods for guide control fracture are proposed, including axial wedge-groove, annular wedge-groove and directional drilling. To study the effect of the three methods, a mathematical model is established. The dynamic characteristics of fracture initiation and propagation in the progress of hydraulic fracturing are gained based on the acoustic emission and distribution of shear stress by numerical simulation for four hydraulic fracturing modes, such as conventional fracturing, directional fracturing by axial wedge-groove guide control, directional fracturing by annular wedge-groove guide control and directional fracturing by directional drilling guide control. The initial and fracture pressures of the four hydraulic fracturing modes are compared and analyzed. The results show that the three methods for guide control have the function of controlling direction of fracture propagation and make the initial and fracture pressures decrease respectively, and axial wedge-groove guide control is optimal.