Summary Standalone screens (SASs) in open hole can provide highly reliable sand-control completions at a lower cost and with less operational complexity than other openhole sand-control completions and can provide long-term productivity performance comparable to other openhole completions when applied in the "right environment with the right procedures." Although many in the industry would agree with the preceding statement, there is no consensus on what the right environment is and what the right procedures are. Even when there is agreement on the applicability of SASs for a particular sand-size distribution, there are considerable differences in the recommended screen type and screen opening between various laboratories. In this paper, we critically review the various laboratory testing procedures used in the industry and the interpretations made to evaluate screen performance and screen selection for SAS applications. We demonstrate that the way some of the laboratory tests are performed makes them biased toward one type of screen (wire wrap) and that some are interpreted without sufficient information such that they almost always favor another type of screen (premium mesh). We show that severe screen plugging with clean formation sand is almost never an issue and that the probability of screen plugging because of other factors can be minimized when proper precautions are taken. We propose that candidates for SAS applications be initially selected on the basis of sand-retention performance, with the final selection confirmed on the basis of screen/sand pack permeability measurements. In addition, on the basis of approximately 185 laboratory tests performed on various types of wire-wrap (6 to 16 gauge) and premium mesh (60 to 600 μm) screens for unconsolidated sands and using a set criterion for sand retention, we conclude that many of the currently used criteria in the industry for selection between gravel packing and SAS are highly conservative and unduly limit the possible application of SASs.
There are two types of sand retention tests generally used in the industry to evaluate the performance of sand control screens for standalone screen applications: pre-pack tests and slurry tests. They represent complete hole collapse and gradual rock failure around the wellbore, respectively. In this paper, we present analytical results as well as Monte Carlo simulations to estimate sand production in slurry type sand retention tests with square mesh screens taking into account the full particle size distribution of the formation sand. We also compare the model results with experimental data and demonstrate that this approach can be used to predict sand production for different sand size distribution/screen size combinations without the need for physical tests. This work augments previously published slurry test models that were limited to wire-wrap screens, and enables comparison of the performance of square mesh screens to wire-wrap screens. The analytical model along with Monte Carlo simulations provide a direct and reliable way to estimate the amount of sand that will be produced for a given sand size distribution and a given screen size. Since the proposed methods are much more quantitative, they represent a significant improvement over current methods that rely on single design points or rules of thumb for screen selection.
Summary Woven-metal-mesh sand screens, commonly known as premium screens, have been used extensively by the industry. Sand-retention testing is often executed to evaluate the performance of these screens and to establish empirical guidelines for screen-size selection. These tests are tedious, however, and the results are prone to artifacts and have been used, at best, to correlate trends in sandretention performance with select sand-size-distribution parameters. A new method incorporating results from numerical modeling, in addition to experimental data, is presented to estimate the mass and size distribution of the produced solids in prepack sandretention tests (SRTs) through premium screens. This method provides a fast, reliable correlation to estimate sand production through premium mesh screens when the size distribution of the formation sand is known. This paper presents results from a wide range of pre-pack sand-retention experiments. In these tests, which represent complete hole collapse, the mass of sand produced and its size distribution over time are measured. Results of 3D, discrete- element computer simulations of woven-screen geometry placed in contact with granular sandpacks of approximately 100,000 particles are also presented. On the basis of both the simulations and the experiments, a new method for screen selection is presented. This method is based on a correlation that allows one to use the entire sand-size distribution of the formation sand and to estimate the mass and size distribution of the produced sand. The method is validated by comparisons with experimental data. A new method and new correlations for estimating the mass and size distribution of produced solids in prepack tests through premium screens are presented. Key differences in sand-retention mechanisms between premium screens and wire-wrapped screens (WWSs) have been identified. The method uses the entire-formation sand-size distribution (as opposed to a single design point), and has been validated with laboratory tests. The method also helps in screening anomalous test results.
The selection of optimum screens for standalone screen applications has historically been based on experimental data, rules of thumb and/or correlations. Recent sand retention tests conducted in various laboratories offer empirical screen selection criteria based on different sand size distribution parameters. Unfortunately, these experiments have their own limitations. They provide substantially different results based 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 better understand the physics of the problem, this paper presents three-dimensional numerical simulations to evaluate the performance of sand screens and ultimately to develop systematic screen selection criteria.In this paper, we present results from three-dimensional, discrete element computer simulations of sand screens placed in contact with granular sand packs of ~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 to sand size, on the mechanism of bridge formation and amount of sand produced are studied using both monodisperse and poly-disperse systems.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 to sand size ratios for wire-wrap screens. Good agreement is observed between the laboratory experiments and the simulations.The simulation tool 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 better design sand screens to meet performance criteria under a wide variety of conditions. In this paper, a new method is presented to estimate the mass and size distribution of the produced solids through wire-wrap screens. The method uses the entire particle size distribution of the formation sand and is validated with experimental and numerical data.
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