For decades the sand control industry has utilized Saucier's criteria to determine gravel sizes with a corresponding screen size for gravel pack operations, while many stand-alone (or non-conformance) screen proponents have utilized other criteria such as Rodgers. Other variations of sizing criteria have also been used with some success.
Recent advances in the expandable screen market have led to an increasing interest in these screens over gravel packing and non-conformable screens due to the perceived simplicity in screen-sizing criteria and increased productivity. With continually increasing sand control options available to the operator, it is fitting that screen-sizing criteria match the particular application and not be universally employed across all applications.
This paper will study the behavioral performance of conformable and non-conformable screens versus gravel packs, relative to plugging resistance and percent of formation solids in the effluent stream. A test matrix was developed using several simulated formation materials from sand prone areas around the world, along with sand control media that was chosen based on the uniformity of its pores. The results indicate that the plugging resistance and percentage of solids in the effluent that passes through the sand control media differs greatly depending on the method of sand control used. The authors outline specific sizing criteria that are necessary for conformable and non-conformable screen applications.
There are many sand control options available in today's market. Some are time-tested, others are relatively new to the marketplace. Whether it's using a gravel pack or an expandable screen, the desired result is optimum productivity with zero failure. Typical failure mechanisms in sand control include plugged gravel packs, plugged screens, or catastrophic failures due to screen erosion. These failures occur primarily because the sand control media was not properly designed or sized to the formation material with regards to the migration of formation fines.
In the case of gravel pack completions, the industry has utilized Saucier's criteria almost exclusively since the 1970's with varying degrees of success. Many of the failures associated with using Saucier's criteria can be attributed to such things as poor completion practices, poor quality gravel, poor carrier fluids, unclean perforations, and poor gravel pack efficiency (voids in the perforations and pack) rather than the criteria itself. Furthermore, it is difficult to size screens and gravel packs based on a "sand/formation ratio" due to the random nature of both the formation and gravel pack sand.
It has been well established that using more spherical particles (synthetic proppants) in a gravel pack combined with a tighter size range is beneficial at increasing permeability, thereby lowering pressure drop and increasing conductivity[3–4]. This principle can also be applied to other forms of sand control such as laminate wire meshes or any other media that contain uniform pore spaces. However, it is well known that the finer, rattier, more non-uniform sands present a greater sand control challenge than the larger, well sorted sands. It is also well known that these larger, cleaner reservoirs are becoming less prevalent. This would lead one to believe that a more appropriate sizing criteria should be based on the formation fines content and ultimately the percentage of fines allowed to be produced. It is the authors' contention that such a sizing criterion should be further investigated and a preliminary study is the subject of this paper.
Two modes of testing were performed: conformance and non-conformance. Conformance mode was meant to simulate a screen that was in conformance with the wellbore. Non-conformance mode was to simulate a stand alone screen that was not in conformance with the wellbore. The test procedures for both conformance and non-conformance can be found in the appendix.