Study on Erosion Model Optimization and Damage Law of Coiled Tubing

Abstract

Coiled tubing (CT) is used as a velocity string to transport high-velocity gas in drainage gas recovery technology. Sand particles flowing at high speed can cause serious erosion of the pipe wall. Long-term erosion wear leads to the degradation of the string strength and can even cause local perforation. In order to study the erosion wear problem of CT, a gas–solid erosion experimental device was established for a full-size pipe with different radii of curvature. A 3D laser confocal technique was used to examine and characterize the microscopic erosion morphology of the inner wall of the CT. The CFD erosion model was selected based on the erosion test data of the inner wall of the CT, and the erosion results of the Finnie model show minimal error and good agreement compared with other models. The average value of the error of the maximum erosion rate at different radii of curvature is 8.3%. The effect of the radius of curvature, gas velocity and solid particle size on the maximum erosion rate of the inner wall of the CT was analyzed based on the Finnie model. The results reveal that erosion wear occurs on the inner wall of the CT’s outer bend. As the radius of curvature is reduced, the maximum erosion rate and area increase, and the position of the maximum erosion rate gradually shifts toward the inlet. The maximum erosion rate is positively correlated with the gas flow rate. However, as the particle size increases, the maximum erosion rate shows a trend of first increasing, then decreasing and finally stabilizing, with a critical particle size of 200 μm. This study can provide theoretical guidance and methods for improving the service life of CT. The erosion rate of the tubing in old wells can be reduced by controlling production and employing appropriate sand control methods, while the erosion rate of tubing in new wells can be reduced by adjusting the wellbore trajectory.