诱导应力下天然裂缝的稳定性及破坏特征

STABILITY AND FAILURE FEATURES OF THE NATURAL FAULT UNDER THE INDUCED STRESS

为了探讨水力裂缝激活天然裂缝的力学机制,基于线弹性断裂力学理论,建立了水力裂缝扩展过程中天然裂缝面诱导应力场解析模型,分析了水力裂缝逼近条件下天然裂缝的稳定性行为及破坏特征。研究表明:天然裂缝的稳定性受到水平应力差、水平应力差异系数、孔隙压力、压裂液黏度及排量、逼近距离、天然裂缝空间展布及粗糙度等因素影响;逼近过程中天然裂缝可能同时出现张性和剪切滑移破坏,但更易发生剪切破坏,且剪切破坏区明显大于张性破坏区,破坏区也主要出现在倾斜天然裂缝的正半轴上,负半轴几乎没被激活;天然裂缝的失稳中心随着走向角的减小逐渐向正半轴移动,随着逼近距离减小逐渐向负半轴移动,其他因素对失稳中心影响很小。研究成果对体积改造复杂缝网形成机制的研究具有重要的参考价值。

In order to explore the mechanical mechanisms of activating the natural fracture by means of the hydraulic fracture,based on the linear elasticity fracture mechanics theory,an analytical induced-stress field model of the natural fracture surface was established during the hydraulic fracture extending,and the stability and failure features of the natural fracture were analyzed under the condition of the hydraulic fracture approaching. The study shows that the stability of the natural fracture is affected by the horizontal stress difference,horizontal stress difference coefficient,pore pressure,viscosity and flow rate of fracturing fluid,approaching distance and spatial distribution and roughness of the natural fracture etc.; in the process of the approach,the natural fracture maybe has the probability of the tensile and shear failure simultaneously,but the probability of the shear failure is rather higher,and moreover the zone of the shear failure is obviously bigger than that of the tensile failure,and furthermore the failure zone only appears in the positive axis of the inclined natural fracture,but the negative axis is barely activated; the stability failure center of the natural fracture gradually shifts towards the positive axis with the azimuth angle decreasing,and adversely step-by-step shifts towards the negative axis with the approaching distance decreasing,but the otherparameters have an insignificant effects on the center. The research achievements possess the significant references for the study of the generating mechanism of the complex fracture network of the reservoir volume stimulation.