基于分形方法的水力压裂裂缝起裂扩展机理

Mechanism of hydraulically created fracture breakdown and propagation based on fractal method

利用分形几何模型描述岩石断裂裂纹的曲折形态,建立了裂纹分形模型下的岩石应力强度因子表达式。在此基础上,以裸眼井为例分析了井底岩石的起裂压力,并建立了考虑裂纹分形扩展的缝内压力计算模型和裂缝宽度方程。理论分析结果表明,岩石扩展路径的曲折程度对模型的计算结果影响较大,考虑裂纹分形扩展后的模型计算数值大于直线型扩展的计算结果,且考虑裂纹分形模型与直线型模型的裂缝宽度计算值之比随着断裂面分形维数的增大而增大。

The tortuosity shape of rock crack was described by using the fractal geometry model, and the expression of rock stress intensity factor was established. The fracture initiation pressure of bottom rock was analyzed as the example of bare well, and the computation model of crack internal pressure and the crack width equation considereing the crack ffactal extended were presented. The theoretical analysis results show that the calculation results were affected by tortuosity degree of extended way of rock. The results of model considering the crack fractal extended is bigger than the calculation result of right line extended model, and the crack width ratio of two models increases with the fractal dimension of fractured surface increasing.