Prediction Of Tool Erosion In Gravel-Pack and Frac-Pack Applications Using Computational Fluid Dynamics (CFD) Simulation

Abstract With the increasing slurry flowrate and sand concentration being seen in current frac-pack applications, erosion of crossover tools, casing extensions and other downhole tools has also drastically increased. In some cases, the velocity of the slurry entering the crossover tool is as high as 250 ft/sec. The ability to predict the degree of erosion on these downhole tools, and ultimately, the effect that it will have on tool life can improve the reliability of the completion/stimulation operations while maximizing the performance of these operations. For example, being able to reliably predict tool life allows one to maximize the amount of gravel or proppant that can be placed in an application. In the past, the downhole tools exposed to erosion had to be physically tested under simulated conditions to insure their performance. These surface tests are not only very costly but also time consuming. Computational Fluid Dynamics (CFD) has been used in the past to study the erosion characteristics of chokes and elbows used in oil and gas production. However, in that environment, the sand concentration in the flow stream is very low (less than 1%). For frac-pack applications, the conditions are very different, as the sand concentration in fracturing slurry can be as high as 15 lb/gal with the needed non-Newtonian fluid rheology. There were no CFD studies found in the literature involving high-solids concentration to address problems of this complexity for erosion modeling. This paper discusses a study in which a CFD model has been developed to analyze the flow field in the frac-pack tools when fracturing slurry is pumped through. Particle tracking studies are conducted to 1), determine where the tool surfaces are impacted by the proppant particles, and 2), what the impact speeds and angles are. Then, a material-specific erosion model is used to calculate the erosion patterns based on the flow field and particle trajectories obtained using CFD. Calculated erosion patterns are compared with results from large-scale flow tests in the lab testing. The CFD model developed in this study not only helps improve the flow field in the frac-pack tool, it also helps us better understand the mechanisms of the erosion so that changes can be made in the designs to reduce erosion severity. New frac-pack tool designs have resulted from this study, and significant erosion-life improvements have been achieved. This technique was used to make an erosion prediction for a field case, and the prediction results compared favorably with the actual field results. The data from the field application is compared with the model predictions later in this paper. Introduction Hydraulic fracturing was introduced in the early 1900's and is a technique wherein a fracture is created in the formation rock of a hydrocarbon reservoir to improve its effective permeability, and thus, to improve production1. In fracturing procedures, proppant-laden fluids are pumped from the surface into the reservoir through the perforations.