A New Computational Fluid Dynamics Model to Predict Flow Profiles and Erosion Rates in Downhole Completion Equipment

Abstract

Abstract Flow velocities and sand generation encountered in high-volume oil wells have exceeded the accuracy of current CFD modeling data. Advanced theoretical work and erosion modeling have been performed to address these high flow rates. The theory and models are compared and verified by testing several materials under an array of flow conditions. The models and test data provide a valuble design tool to ensure performance and reliability of critical completion hardware. Introduction Sand production is a major problem in oil and gas production operations. The presence of sand in produced fluid presents many challenges to equipment suppliers and production companies. Sand control has become increasingly important as high-rate wells with sand become more prominent. Sand erosion as a result of sand production is a major concern. It causes loss of pipe wall thickness that can lead to expensive failures and lost - production. Even when sand production is as low as a few pounds per day, it can cause erosive failure at high production velocities. Laboratory experience indicates that when the produced fluid is a liquid, exchange of momentum between sand particles and liquid reduces the impact velocity of sand particles, resulting in little or no erosion. However, current erosion data does not cover the range of materials and flow conditions experienced in high flow rate oil wells. American Petroleum Institute Recommended Practice 14E (API RP 14E) provides a criterion for sizing gas/liquid two-phase lines on the basis of flow velocity. The recommended practice states that (API RP 14E, 1991): "The following procedure for establishing an ‘erosional velocity’ can be used where no specific information as to the erosive/corrosive properties of the fluid is available. The velocity above which erosion may occur can be determined by the following empirical equation:Equation 1 where: Ve=fluid erosional velocity, ft/sec c=empirical constant ?m=gas/liquid mixture density at flowing pressure and temperature, lb/ft3 Industry experience to date indicates that for solids-free fluids, values of c=100 for continuous service and c=125 for intermittent service are conservative." The recommended practice adds: "If solids production is anticipated, fluid velocities should be significantly reduced. Different values of ‘c’ may be used where specific application studies have shown them to be appropriate." Eq. (1) is simple and easy to use, but it does not account for many factors contributing to erosion/corrosion. The only physical variable accounted for in Eq. (1) is the fluid density. The equation suggests that the limiting velocity could be higher when the fluid density is lower. This does not agree with experimental observations for sand erosion, because sand in gases with lower densities will cause higher erosion rates than liquids with higher densities. Therefore, the form of Eq. (1) does not seem to be appropriate for situations involving sand production.