The selection of optimum screens for standalone screen (SAS)
applications has historically been based on experimental data, rules of thumb,
or correlations. Recent sand-retention tests conducted in various laboratories
offer empirical screen-selection criteria on the basis of different
sand-size-distribution parameters. Unfortunately, these experiments have their
own limitations. They provide substantially different results, depending on how
the tests are conducted and interpreted, leading to significant differences in
the recommended screen type and screen-opening size for any given sand sample.
To resolve these inconsistencies and to understand the physics of the problem
better, this paper presents 3D numerical simulations to evaluate the
performance of wire-wrapped sand screens and ultimately to develop systematic
In this paper, a new method is presented to estimate the mass and size
distribution of the solids produced through wire-wrap screens. The method uses
the entire particle size distribution of the formation sand and is validated
with experimental and numerical data. The new method allows us to evaluate the
performance of different screens without running expensive and sometimes
inconclusive experiments, enhances our understanding of screen performance, and
helps to design sand screens better to meet performance criteria under a wide
variety of conditions.
We first present results from 3D, discrete-element computer simulations
of sand screens placed in contact with granular sandpacks of approximately
100,000 particles. The numerical model computes the mass and the size
distribution of the solids produced. The effect of the most important
parameters, such as friction coefficient, fluid viscosity, pressure gradient,
and ratio of screen-opening size to sand size, on the mechanism of bridge
formation and amount of sand produced is studied using both monodispersed and
The results have helped resolve some key questions about the physics of
sand bridge formation. Numerous simulations are conducted to replicate the
experimental conditions over a wide range of screen-opening/sand-size ratios
for wire-wrap screens. Good agreement is observed between the laboratory
experiments and the simulations.
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