Reel-to-Injector Fluid-Flow Analysis Using CFD Software

Abstract

Abstract Until recently, fluid flow through coiled tubing (CT) was only discussed as a theory or an idea. With the aid of some sophisticated new software technology, Computational Fluid Dynamics (CFD), an understanding of the actual flow patterns of fluids in CT is now possible. This paper discusses a more complete study of multiple CT string components and their effect on fluid flow. Analysis of individual components or systems has been performed, but combining systems can change the outcome of the results. Previous analysis simulated a straight section of tubing running through a tubing guide. This analysis assumed fully developed flow entering the straight section of tubing. Based on results of an industry consortium, the flow into the straight tubing coming off the reel may not be fully developed. To expand the study of the actual full-scale model of a CT string, in this study, additional portions of the string will be included. The fluid-flow phenomenon from the reel and its effect on the flow path in the straight section of the tubing between the reel and tubing guide will be incorporated into the model. The results could affect the centrifugal forces and flow-path patterns previously thought to affect erosion. Results generated from these studies could help in understanding erosion principles, including sand particle migration and movement. Introduction CT is a more rapid deployment of well intervention than standard rig servicing. It has been used for many years in the areas of well cleanout, acidizing, fracturing, tool deployment, logging, fishing, and chemical placement.1–5 For many years, fluids or slurries were pumped through the CT with minimal knowledge of actual fluid dynamics. Because the CT industry has been expanding in recent years to greater depths, pressures, and applications, it has been essential that we understand the actual flow properties or fluid flow. This knowledge could help us examine the phenomenon of erosion, pressure loss or gradient, and fluid properties. What about the secondary flow regime and its effect, if any, on the fluid being pumped? This knowledge can increase the likelihood of a successful job, reduce down time, save money by optimizing resources and equipment, and improve service quality. All of these factors are important in assisting our customers in their goals of increasing profits. One tool that is more commonly being used to understand flow properties is the application of CFD software. This technology is being used in many other industries and has just recently become available in the oil industry. Using this type of product can eliminate many hours of full-scale testing, freeing up resources and saving money. Previous Work Previous work studied the fluid-flow phenomena between the reel and the injector using a homogenous flow pattern.6 Fig. 1 shows the velocity magnitude profile with water. Fig. 2 shows the velocity magnitude profile with gel. The velocity magnitude contours and the sand volume fraction contours for the straight section are shown in Figs. 3 and 4, respectively. The velocity magnitude contours and the sand volume fraction contours for the tubing guide section are shown in Figs. 5 and 6, respectively. This study was based on homogenous input patterns used by the CFD software and assumes a logical flow input. Because the outcome was speculative, the analysis started with a large amount of data input; in this case, more tubing and a large grid pattern. This generated a base of information for flow patterns over the tubing guide. Several parameters in this work paralleled previous work.7,8 This method enabled cross-comparisons of parameters between different applications. For example, the same size tubing and the same flow rate were used. Patterning work from previous applications can be helpful in establishing consistent methods of analysis, instead of, for example, having to extrapolate data for a different sized tubing. One conclusion from a previous study6 stated that "As knowledge in the fluid dynamics community is acquired, the model can be updated and compared to data collected in commercial operations." Therefore, to proceed with our analysis, we needed to review the actual flow pattern coming off the reel as the flow pattern headed to the tubing guide.