断层对煤层水力压裂裂缝扩展的影响

Effect of faults on hydraulic fracture propagation in coal seam

针对煤层中的次生断层或小型滑移断层会影响水力裂缝扩展方向的问题,通过建立压裂裂缝遇断层的二维模型,采用理论分析和数值模拟方法分析逼近角度、水平主应力差、煤岩体弹性模量差异等因素对水力裂缝扩展方向的影响规律,建立裂缝穿过断层形成有效压裂的判断准则,在给定煤岩体参数条件下,拟合出水力裂缝穿过断层形成上下盘煤层贯通裂缝的逼近角度-水平主应力差的临界曲线。结果表明:逼近角度、水平主应力差、煤岩体弹性模量是影响压裂裂缝走向的主要因素,在低主应力差、较小逼近角度、较高顶板弹性模量的情况下,断层面易产生张开型破坏;当逼近角度-应力差坐标点位于曲线上方时裂缝将穿过断层面进入顶板,当角度-应力差坐标点位于曲线下侧时断层面张开裂缝将扩展至下部煤层形成上下盘煤层贯通裂缝。

Considering the influence of sub-fault or slum fault in the coal seam on the fracture propagation of hydraulic fracturing,the effects of approximation angle,horizontal principal stress difference,and coal and rock elastic modulus difference on hydraulic fracture propagation direction were investigated using the theoretical analysis and numerical simulation in a two-dimensional physical model. The judgment criterion of forming effective fracture through the cracking passing the fracture was established. And the critical curve for the approaching angle-horizontal principal stress difference of the coal penetrating crack,which was formed by the hydraulic fracture passing the fault,was fitted out under given coal-rock mass parameters. It is found that the approximation angle,horizontal principal stress difference,and elastic modulus of coal-rock mass play the major roles on fracture direction. Under the circumstance of low principal stress difference,smaller approaching angle,and higher roof elastic modulus,the fault is easy to produce plane tensile failure. When the approaching angle-stress difference coordinate point is above the curve,the crack will pass through the fault plane into the roof. When the angle-stress difference coordinates of point is under the level curve,cracks will be extended to the lower coal seam forming upper and lower coal seam cracks.