CFD-DEM study of particle-fluid flow and retention performance of sand screen

Sand screens are widely used to control sand production in unconsolidated reservoirs. Because of the lack of insightful understanding of this process, to date, reliably optimizing screen size is still a challenge. This paper presents a numerical study of the sand retention and production behaviors for widely used wire-wrapped screens by means of the combined approach of computational fluid dynamic (CFD) and discrete element method (DEM). The validity of the model has been verified by comparing the predicted critical slot sizes and sand production with published experimental results. On this basis, the effects of slot width-particle size ratios and wetting fluids, including gas and crude oil, are studied. The numerical results show that the increase in size ratio increases sand production, and the presence of fluid flow enhances sand production and causes unstable sand retention, which is more significant for crude oil compared to gas. Also, three mechanisms that allow the sand retention over a screen are identified, including stable bridging, bridging with intermittent collapse, and bridging with continuous collapse. Wetting fluids play an essential role in the sand production and bridging when the particle-fluid forces exerted on the particles near the slot are significant. Such forces induce strong localized particle-particle interactions in the nearby region over the slot, which accounts for the unstable bridging behavior.