Analysis of the migration patterns of sand particles below the screw pump in wells based on experiments and numerical simulations.

To enhance the sand particle migration capability in shale oil well progressive cavity pumps, it is essential to analyze the particle migration patterns in perforated well sections. A coupled Computational Fluid Dynamics and Discrete Element Method was employed to numerically simulate sand flow characteristics in wellbores, investigating the impacts of water content, flow rate, particle size, and pump tail pipe depth on particle migration. The study revealed sand migration patterns and established a full-scale experimental setup for sub-pump particle migration, conducting solid-liquid two-phase flow experiments to examine engineering impacts of pump tail pipe depth. Results indicate: After radial inflow into the wellbore from perforations, fluid converges with underlying flow causing intense collisions that force sand-liquid mixtures into lower velocity zones, inducing particle sedimentation. As water content increases, produced fluid viscosity decreases, resulting in a sedimentation ratio that initially grows slowly before sharply rising; As the production rate increases, the sedimentation ratio gradually decreases. When the production rate exceeds 50 m/d, the sedimentation ratio stabilizes. The study further clarifies the engineering implications of positioning the pump tail pipe below the perforation interval: when the water content exceeds 70% and production drops to 30 m/d, sand production reaches 16% with a sedimentation ratio of 44.2%. If the pump tail pipe is positioned at perforated layers 7-10, the risk of sand burial becomes extremely high. Based on sand production patterns in sand-prone wells, controlling the pump tail pipe depth within perforated layers 4-7 can effectively reduce sand particle deposition, thereby mitigating hazards such as reservoir sand burial and tubing sand blockage.