Abstract

In order to gain a better understanding on fluid and sand flow around and through a stand-alone-sand (SAS) screen, a scouting study on the flow-field and sand retention characteristics of a full-scale 5.5" OD sand screen was conducted. The velocity flow-field around a horizontal 1-metre long sand screen within a clear acrylic cylinder was investigated in air using state-of-the-art laser diagnostics experiments with complementary computational fluid dynamics (CFD) simulations. The flow-field in the annular space was interrogated by a 2D Particle Image Velocimetry (PIV) technique. CFD using standard solution techniques for dilute particle flows in air employed over 20 million elements to capture the fine details around the individual components in the screen shroud. The sand retention and pressure drop characteristics across the same sand screen were similarly conducted in the same flow loop. At the toe of the screen, some of the flow entering the base pipe also entered the annular space. The inflow from the base-pipe continues to contribute to the annular flow which builds up in magnitude towards the heel of the screen. As the flow approaches the heel of the screen, the annular flow is forced to re-enter the base-pipe via the screen. This phenomenon is observed in the PIV experiments and the CFD simulation results, albeit with minor differences. However, evaluation of the velocity range and span suggest that the CFD results are reasonably validated by the experimental data. Further tests on the sand retention and plugging characteristics of the screen demonstrated that the screen responds differently to low concentrations of coarse, medium and fine sands. Taken together, these provide field engineers some insight into the screen characteristics and behaviour when deploying such screens in the field. When validated with physical data, CFD is a reliable engineering tool to assess the complex single phase flow phenomena occurring in downhole completion equipment where it may not be economically viable to simulate in field conditions. The sand retention work on a 1-metre long full bore screen also provides a reality check for the screen when subject to low concentration of sand loading, which alters the pressure drop requirements and sand retention capability of that screen. For the first time, the annular flow in a full-sized sand screen has been measured in the laboratory using 2D Particle Image Velocimetry. The results provide supporting evidence to confirm the annular space flow features obtained in the CFD simulation results and provides some insight into the behaviour of annular flow around the sand screen.

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