Numerical simulation study on formation mechanism of void distributions of proppant particles

Investigations of void distributions and formation mechanisms of proppant particles in closure fractures have extremely major significance for improving the production of coalbed methane. In this study, a numerical method was developed to simulate compaction processes of a proppant-filled fracture under different closure stresses. The particle trajectories, force chains and coordination numbers of proppants were extracted to analyze and investigate void ratio distributions and associated formation mechanisms. The results showed that during fracture closures from the top to bottom, some particles in the top layer of the proppant-filled fracture moved into the middle layer, which made the middle layer particles formed solid force-bearing structures. The greatest force was transmitted between particles in the middle layer. This was followed by particles in the top layer and finally, the bottom layer. In addition, the proportions of large coordination numbers, and average coordination numbers of the middle layer were the largest, followed by those of the top and bottom layers, which reflected that the particles of the middle layer were denser than those of the other two layers. The above factors caused the void ratios of the middle layer to be the lowest, followed by those of the top and bottom layer, respectively.