CFD-DEM investigation of blocking mechanism in pre-packed gravel screen

Sand production is one of the most challenging problems during the production of deepwater oil/gas, heavy oil, and gas hydrate. As an important mechanical sand control method, prepacked gravel screens (PPGS) have been used in the petroleum industry for many years. However, the blocking mechanisms of the PPGS during sand control have not been sufficiently understood. In this study, a CFD-DEM method was used to study the blocking mechanism of the PPGS. The results show that the blocking process of the PPGS can be divided into 4 stages: initial stage, bridging stage, accumulation stage, and equilibrium stage. During the blocking, the big particles first bridge in the gravel layer, and then the fine particles fill in the spaces among the big particles or accumulate on the surface of the blocking zone. However, the sand bridge could collapse as the pressure difference across the PPGS increases. Then, a new bridge is reformed. The phenomenon is regarded as a "bridging-collapse-bridging" process. This study demonstrates that the size and content of the big particles determine the position and the rate of the blocking, respectively, while the fine particles play a vital role in controlling the degree of the final blocking.