Contribution of the Gravel Mesh Size in Screen Damage on a Gravel Pack System

摘要

mesh size, which is the key-parameter for designing efficient gravel pack systems. Indeed, the largest mesh size able to reduce solid production while keeping the head loss as minimal as possible, would always appear to be the logical choice. However, screen integrity should also be considered whenever choosing the gravel mesh size, and experimental results presented in this paper show that the larger the mesh size, higher is the chance of localized damage appearing on the screen of the gravel-pack system. Experimental tests with gravel pack prototypes were run in a large poliaxial frame, using two of the most common gravel sizes: 16/20 and 20/40 mesh. The system was set on artificial cubic rock samples of 11.8 in side, with a centered hole of 2.4 in diameter. The cubical samples were submitted to a triaxial stress field reaching the ratio SMAX/Smin equal to 1.6. Visible localized damage in the screen’s outer surface was observed when testing the larger gravel agent (16/20 mesh), as compared to the smaller 20/40 mesh. The experimental observation was explained by contact stress effect, indicating that larger particle sizes are more prone to damage the screen, while the stresses transferred by smaller particles are more uniform. On the long run, the contact stress effect can result in erosion and, in some cases, screen collapse. A simple, qualitative, analytical model is employed to corroborate the mechanical effects observed in the experimental test. Whenever designing gravel pack systems for deepwater wells, one should consider long term operation, avoiding complex and expensive workover operations. Thus, a more conservative design criterion is recommended to improve the gravel pack operational life, including the analysis of possible contact stress effects.