Friction and wear residual strength of coiled tubing under tripping conditions
When the coiled tubing is running in and out in a horizontal well, it only moves axially, but under the action of axial pressure, the coiled tubing will produce buckling deformation, which will inevitably make the coiled tubing and casing contact each other. Under the action of axial tension, when the coiled tubing is in the build-up section, its outer wall is easily in contact with the inner wall of the casing, resulting in friction.
This leads to mutual friction between coiled tubing and casing, and long-term friction and wear will reduce the remaining strength and service life of coiled tubing, resulting in failure, which will lead to a decrease in oil well production efficiency and an increase in the number of workover operations.
Therefore, it is of great practical significance to analyze the wear degree of coiled tubing and the remaining strength of worn coiled tubing during the friction between coiled tubing and casing, which can effectively reduce the production cost of the oil well and improve the operation efficiency.
At present, although relevant literature has gained some understanding on drill pipe-casing wear and the theory of residual strength of coiled tubing, few people have included friction factors in the research of residual strength of coiled tubing.
Considering that the current research on the degree of friction and wear of coiled tubing-casing and the remaining strength of worn coiled tubing is insufficient, this chapter uses the drill pipe-casing wear model to establish ideas, adopts the wear-efficiency model, and utilizes the theoretical knowledge of elastic mechanics to obtain the continuous
The calculation formula and method for the wear depth of the outer wall of the coiled tubing in the tubing-casing wear; and then use the ANSYS Workbench finite element software to simulate the internal pressure resistance and collapse strength of the unworn coiled tubing.
The numerical solution is in good agreement with the theoretical solution, which verifies the The correctness of the method; then use the same method to investigate the influence of outer diameter, wall thickness and wear rate on the remaining strength of coiled tubing, and calculate the sensitivity; then, use the theory of elastic mechanics to obtain the theoretical analysis of the remaining strength of coiled tubing Comparing the calculation method and comparing the results of three wear models under the same conditions, the calculation method of residual strength that is relatively close to the actual wear of coiled tubing is obtained; finally, combined with the above research, the wear condition of coiled tubing during lifting operation is predicted.
Coiled tubing-casing wear is similar to drill pipe-casing wear, both of which are metal-to-metal wear, and the wear shape is crescent-shaped.
The difference is that the drill pipe-casing friction is caused by the rotation of the drill pipe to form a crescent-shaped defect on the inner wall of the casing, and the radius of the crescent-shaped defect located on the inner surface of the casing is the outer radius of the drill pipe; while the coiled tubing-casing friction is Due to the reciprocating motion of the coiled tubing under running-in and pulling-out conditions, the outer surface of the coiled tubing forms crescent-shaped wear, and the radius of the crescent-shaped wear on the coiled tubing is the inner radius of the casing.
When the coiled tubing is running in and out of a horizontal well, it will cause friction and wear when it contacts the casing.
Among them, the volume of coiled tubing removed is proportional to the friction energy transmitted from the casing to the outer wall of the coiled tubing. In this section, a progressive approach is adopted to analyze the wear degree of coiled tubing starting from three parts: analysis of coiled tubing-casing contact force, establishment of wear analysis model and analysis of wear depth.
Coiled tubing-casing friction and wear will reduce the residual strength of coiled tubing. Through investigation, it is found that the residual internal pressure resistance strength of coiled tubing is related to many factors. This section studies the three factors of coiled tubing outer diameter, wall thickness and wear rate. Using ANSYS Workbench to analyze the influence of these three sensitive factors on the remaining internal pressure strength of worn coiled tubing and the sensitivity strength; using the knowledge of elastic mechanics, analyze the theoretical calculation method of the remaining internal pressure strength of worn coiled tubing, and compare three Based on the results of the wear model under the same conditions, the calculation method of the residual internal pressure strength that is relatively close to the actual wear of the coiled tubing can be obtained.
According to the wear analysis method between drill pipe and casing during drilling, the wear degree of the outer wall of coiled tubing in horizontal wells is analyzed by combining theory and numerical simulation; Sensitivity factors, influence rules and sensitivity strength of extrusion strength; applying elastic mechanics theory to obtain the residual strength calculation formulas of coiled tubing under uniform wear and eccentric cylinder wear models respectively; comparing eccentric cylinder wear, uniform wear and crescent The residual strength of the coiled tubing with the same specification and wear rate is obtained, so that the calculation method of the residual strength that is relatively close to the actual wear of the coiled tubing is obtained; the wear of the coiled tubing is predicted.
The remaining internal pressure strength and residual crushing strength of coiled tubing decrease linearly with the increase of wear rate and outer diameter, and increase linearly with the increase of wall thickness. The influence of sensitivity factors on the residual strength of coiled tubing is in the following order from strong to weak: wear rate>wall thickness>outer diameter.