受压脆性岩石Ⅰ-Ⅱ型复合裂纹水力压裂研究

The initiation of Ⅰ-Ⅱ mixed mode crack subjected to hydraulic pressure in brittle rock under compression

在线弹性断裂力学理论的基础上,运用最大周向拉应变理论,分析了受远场地应力作用及裂纹面受水压力作用下脆性岩石裂纹的起裂方向及起裂条件。论述了泊松比μ对开裂角θ0,θ0-β关系以及断裂包络线的影响,给出了满足最大周向拉应变理论的Ⅰ-Ⅱ复合型断裂包络线;定义水力压裂裂纹扩展影响因子D并分析其对水力压裂裂纹起裂及扩展的影响,D值逐渐增大时,KⅡ逐渐减小,KⅠ逐渐发挥主导作用,与数值计算结果一致;最后进行实例分析,并与现场水力压裂结果比较,二者结果比较接近。

The maximal circumferential strain criterion based on linear elastic fracture mechanics was employed for the analysis of the crack initiation. The effect of Poisson＇ s ratio on crack initiation angle θ0, the θ0-β relation and fracture envelope was conducted, and the I-II mixed mode fracture envelope that meets the maximal circumferential strain criterion was proposed. Crack propagation influencing factor D was defined as well as its effect on the crack initiation and propagation during hydraulic fracture was presented, mode I stress intensity factor K1 retains dominance while mode II stress intensity factor KⅡ plays a secondary role as D increases,the trend is in accordance with the numerical results. A practical case analysis was carried out in terms of the proposed method and the result was relatively closed to the field hydraulic fracture operation.