Determining Gravel Pack Fluidization Velocity

Abstract In a gravel pack completion, non-uniform reservoir inflow with a very high velocity can fluidize the gravel and/or erode the sand screen. The gravel pack screen is equipped with a basepipe with a pattern of holes through which fluid must pass after flowing through the gravel pack and screen. In a cased hole completion, fluid reaches the pack through a pattern of perforation tunnels opening into the gravel pack. The result is a complex flow pattern inside the pack involving both vertical and annular flow in addition to the expected radial flow. Previous studies have addressed the risks of fluidizing the gravel pack in high flow rate deepwater wells and have quantified a critical velocity above which fluidization is at risk. However, no formal mathematical model has justified the value, and details of the failure mechanism are lacking. This paper presents a Computational Fluid Dynamics (CFD) model that captures the complex flow dynamics within a cased hole gravel pack completion. An ANSYS-FLUENT simulator was used to create a CFD model that simulated fluid flow through a gravel pack in conjunction with full particle motion phenomena. The Euler-Euler option treated each of two phases (flowing hydrocarbon and the gravel) as a continuum and enabled replication of gravel pack dynamics under producing conditions. Using well casing, screen, and basepipe geometries based on an actual field case from a conventional deepwater Gulf of Mexico well completion, the model provided visualizations of the nature of fluid flow through a gravel pack and captured destabilization (aka fluidizing) of gravel in a cased hole gravel pack completion. The CFD model replicated the velocity changes projected by Wong for cased hole gravel pack completions. Fluidization tendencies and estimation of the minimum fluidization velocity in a gravel pack cased hole completion were determined. Sensitivities to flow rate, perforation density, base pipe geometry, and packing efficiency were evaluated. The model illustrated that at sufficiently high flow rates for certain gravel pack configurations, alignment of a basepipe and perforation holes can produce a jetting effect that could cause screen erosion. The model also revealed how the jetting effect could be suppressed. This work underscores the importance of the gravel pack reserve height and packing efficiency. The fluidization velocity depends on gravel pack parameters that can guide the completion design. The model developed for this work enables testing whether a completion strategy is conservative enough to maintain the integrity of the pack. With aid of this model this study will be useful in designing gravel pack completions in ultra-high rate wells.