裂缝性储层射孔井水力裂缝张性起裂特征分析

Tensile initiation characteristics analysis of hydraulic fracture in perforated well of fractured formations

基于弹性力学和岩石力学理论,考虑天然裂缝与射孔孔眼相交的空间关系,结合张性起裂准则,建立了裂缝性储层水力裂缝沿天然裂缝的张性起裂压力计算模型。计算结果表明:水力裂缝沿天然裂缝的张性起裂压力较岩石本体起裂压力显著降低,裂缝性储层水力裂缝倾向沿天然裂缝起裂。张性起裂压力大小对比分析表明,孔眼指端和孔眼顶部位置天然裂缝的张性起裂压力最小,为水力裂缝的最易起裂点;天然裂缝为低倾角时,水平最大和最小地应力方位的张性起裂压力差变小,水力裂缝将从井眼不同周向方位同时起裂延伸,扩展为径向缝网。实例计算分析证实了裂缝性储层水力裂缝的起裂特征。

Based on the theories of elastic mechanics and rock mechanics, taking account of the spatial relation of natural fractures and perforations with intersection, and integrating with the tensile initiation criterion, the calculation model of initiation pressure was established when hydraulic fracture is tensile initiation along natural fractures. The calculated results show that the tensile initiation pressure of hydraulic fracture along natural fractures is significantly smaller than the initiation pressure along rock body and the hydraulic fracture in fractured formations tends to initiate along natural fractures. Comparison analysis of the tensile initiation pressure states that the tensile initiation pressure is minimum at the finger tip and top of perforations where the hydraulic fracture is easist to initiate; when the dip of nature fractures is low, the difference of tensile initiation pressure become smaller between the azimuth of the maximum and the minimum horizontal geostress, the hydraulic fracture may simultaneously initiate and propagate from different circumferential orientations around wellbore and expand into radial fracture-network. Calculation and analysis of an example have confirmed the initiation characteristics of hydraulic fracture in perforated well of fractured formations.