油井水力压裂的三维数值模拟

为了研究油层岩石在水力载荷作用下的裂纹扩展及渗流行为,采用渗流应力耦合模型对水力压裂过程进行了三维有限元方法数值模拟研究.预设裂纹用粘结单元来模拟,裂纹的起裂和张开用单元的损伤因子表征.为了使得在裂纹扩展过程中,流体压力能随裂纹扩展动态地跟踪加载到裂纹面上,给出了流体压力在裂纹内传递的模型,并编写用户子程序予以实现.模拟结果得到了水力压裂过程中岩石中的应力分布、孔隙压力分布、压裂液的滤失以及裂缝的几何形态.分析了压力和隔层等因素对裂纹几何形态的影响.该研究结果对石油工程中压裂方案设计及故障诊断有一定的理论参考价值.

Three-dimensional numerical simulation of hydraulic fracture in oil wells

Three-dimensional finite element simulations were carried out to investigate the hydraulic fracturing and associated flow behavior in reservoir rock. A model of coupling pore fluid flow and stress was proposed. In this study cohesive elements were used to simulate the pre-defined crack path and its progressive damage. To update simultaneously the moving hydraulic loading on the crack surface,the redistribution of fluid pressure was computed and implemented with user-subroutine code. With the proposed coupling model,the stress distribution,the pore pressure,the fluid loss,and the geometry of the progressive damage are presented. The influence of pressure and interlayer was discussed. The obtained results are of significance to fracturing design and diagnosis.