水力压裂裂缝内支撑剂颗粒空隙率分布的形成机制

为了解水力压裂裂缝内支撑剂颗粒空隙率的演变,采用数值模拟方法模拟了裂缝内支撑剂颗粒在不同应力下的压缩过程,通过研究裂缝内支撑剂的接触力及配位数分布揭示了其空隙率分布的形成机制。结果表明:裂缝内支撑剂颗粒空隙率自下而上呈缓减小-急减小-缓减小-急增大-缓增大的分布趋势;将其分为底层、中层和顶层3个层位,相同应力状态下,底层支撑剂间接触力最弱为应力衰减区,平均配位数最小,空隙率最大;中层支撑剂间接触力最强为应力承受区,颗粒向下传递力的能力最弱,平均配位数最大,空隙率最小;顶层颗粒向下传递能力最强为应力传递区,支撑剂间接触力较弱,平均配位数和空隙率介于应力承受区和应力衰减区之间。

Formation mechanism of proppant particle voidage distribution in hydraulic fracturing fractures

In order to understand the proppant particle voidage evolution of the hydraulic propped fractures, the numerical simulation method was used to simulate the compression process of the proppant particle in fracture under different closed stresses.The formation mechanism of void distribution of the proppant particle in fracture was revealed by investigating the distributions of contact force and coordination number of the proppant particles in fracture. The results showed that the proppant particle voidage distribution from the bottom to top was as follows: decreasing slowly, decreasing sharply, decreasing slowly, increasing sharply,increasing slowly. The propped fractures were divided into three different layers: bottom, middle and top layers under the same stress state, the bottom proppants with the weakest contact force was the stress attenuation zone. In this zone, the average coordination number was the smallest and the void ratio was the largest. The middle proppant with the strongest contact force was the stress bearing zone. In the area, particles had the weakest ability to transmit force downwards, the average coordination number was the largest and the void ratio was the smallest. The top particles with the strongest ability to transmit force downwards were called the stress transfer zone. In this area, the contact force between the proppants was weak, and the average coordination number and void ratio were between those of the stress bearing zone and stress attenuation zone, respectively.