含瓦斯煤体定向水力压裂裂隙导控的数值分析

Numerical analysis of fracture guide&control of directional hydraulic fracturing in coal body containing gas

根据裂隙产生及扩展机理,总结出轴向楔形槽导控、环形楔形槽导控及控制孔导控3种裂隙导控方法.为对比分析3种导控方法的效果,以真实煤层为研究对象,运用数值试验方法,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,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.研究结果为指导煤(岩)体定向水力压裂提供了参考.

According to fracture initiation and extension mechanism,three methods for guide control fracture were proposed,including axial wedge-groove,annular wedge-groove and directional drilling.To study the effect of the three methods for guide control fracture,taking a real coal seam as an example,a related mathematic model was built,and the dynamic characteristics of fracture initiation and propagation were gained in the hydraulic fracturing progress based on an acoustic emission and the distribution of shear stress by numerical simulation of four hydraulic fracturing modes： conventional fracturing,directional fracturing by axial wedgegroove guide control,directional fracturing by annular wedge-groove guide control,and directional fracturing by directional drilling guide control.The initial pressure and fracture pressure of the four hydraulic fracturing modes were contrasted and analyzed.The results show that the three methods of guide control have the function of controlling the direction of fracture propagation and made initial pressure and fracture pressure decrease respectively,and that axial wedge-groove guide control were optimal.The results have some significant and referenced value to the corresponding practical field.