基于离散元的注水作业水力裂缝扩展仿真研究

Numerical Simulation of Hydraulic Fracturing Based on Discrete Element Method during Water Injection Operation

为了掌握致密砂岩储层长期注水过程中水力裂缝的扩展形态,基于颗粒流离散元理论,利用颗粒流离散元流固耦合的计算方法,模拟并分析了在不同孔隙压力、水平应力差和天然裂缝产状情况下注水引起的水力裂缝的扩展延伸过程。仿真结果表明,随着地层注入水量的增加,孔隙压力升高,水力裂缝扩展速度加快,更能形成复杂裂缝网;水平应力差较小时,水力裂缝容易形成辐射状裂缝,低逼近角下水力裂缝易沿天然裂缝转向,高逼近角下水力裂缝易直接穿过天然裂缝;水平应力差较大时,水力裂缝沿着最大水平主应力方向迅速扩展,受天然裂缝的影响较小。

In order to grasp the propagation characteristics of hydraulic fractures in tight sandstone reservoirs dur-ing long-term water injection,the fluid-solid coupling model was proposed based on the discrete element method.Under different pore pressures,horizontal stress difference and occurrence of natural fractures,the initiation and propagation of hydraulic fractures caused by water injection were analyzed.The results show that the propagation speed of hydraulic fracturing is increased with the increase of injected water volume,then complex fracture network gradually forms.When the horizontal stress difference is smaller,the hydraulic fractures are prone to form radial frac-tures.At the low approach angle,the hydraulic fractures tend to turn along natural fractures,and at the high ap-proach angle,the hydraulic fractures tend to pass directly through natural fractures.When the horizontal stress differ-ence is bigger,the hydraulic fractures expand rapidly along the direction of maximum horizontal principal stress and are less affected by natural fractures.