Abstract

Coiled tubing (CT) is widely used in well intervention as a practical and cost-effective means of servicing wells. Since CT's inception, the actual flow through CT has been a point of discussion and theory. Testing has been conducted to study what happens inside the CT. In recent years, the use of computational fluid dynamics (CFD) software has provided greater insight into actual CT flow patterns, including fluid-flow velocity profiles and secondary flow regimes. CFD helps to understand the fluid-flow phenomenon, which can lead to effective designs of friction-loss gradients. CFD has proven to be an effective alternative to full-scale testing.

The next development was modeling of actual field data from a fracturing service. This method compares predicted values, actual values, and computed values from the CFD solutions. CFD was used to provide correlations for the predictive model without full-scale testing, which greatly reduced the cost of development. Fluids investigated have included slurry pumped from an actual job.

Introduction

CT is becoming a standard mode of operation for well intervention. It is used in the areas of well cleanout, acidizing, fracturing, tool deployment, logging, fishing, and chemical placement.1–5 Many different types of fluids and slurries are pumped through the CT. Through field data, industry consortiums, and modeling, knowledge of actual fluid dynamics increases.

Understanding actual flow properties is essential in job design, tubing management, and safety. As the CT industry expands and need for energy increases, the impact of successful well intervention is vital. Job knowledge and proper design can increase the likihood of a successful job, reduce downtime, save money by optimizing resources and equipment, and improve service quality.

A tool being used more often is CFD software. Once limited, it has become a standard design product for most industries including well intervention. Any product that can eliminate hours of full-scale testing, free up resources, and save money is attractive to any company.

Past CFD Studies

Our previous work 6,7 studied the fluid-flow phenomena between the reel and the injector. We learned that the CFD input data was significant in the results of the fluid-flow patterns. Figs. 1 and 2 illustrate the difference in the sand-volume fraction between the two analyses. The maximum concentration of sand is lower for the analysis in the second paper than for the analysis in the first study. The change can be attributed to the difference in inlet conditions caused by the half-wrap inlet. In the second study, the velocity magnitude contours in both the straight section and the tubing guide section were similar to contour plots in the first study. The contours of sand-volume fraction for the straight section of tubing were drastically different in the second work than seen in the first paper. Figs. 3 and 4 illustrate the difference and Fig. 4 also illustrates that the center of the tubing is void of sand.

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