Abstract
Abrasion between the Coiled Tubing and the well completion has been a significant failure cause over the last three years. In excess of twenty-eight of these specific failures have been observed, cataloged and investigated. These failures resulted in a series of experimental studies using a modified form of the ASTM G75 abrasion test. This test is performed with a test fixture that repeatedly slides test blocks over stationary test laps with a controlled normal force and in the presence of an intermediary fluid. In the tests reported in this investigation the blocks were made from 90 ksi yield Coiled Tubing material, the laps were made from 13Cr and L-80 tubing material, four different fluids and two different normal forces were used. The results are presented as a normalized wear rate to clearly demonstrate the high-risk conditions for abrasion. The risk associated with these failures is very high as catastrophic failures have been observed at pressures significantly below pre-job test pressures.
Well bore fluid is the most critical parameter for abrasion. Abrasion failures have occurred in both liquid and gas environments, while the gas environment severely worsens the problem. The abrasion in dry wells is almost 250 times worse than in liquid filled wells.
Based upon the experimental results, a methodology is proposed to determine the relative risk of incurring abrasion damage during Coiled Tubing operations. The methodology looks at Coiled Tubing and well parameters and results in an overall risk assessment. A table of critical running feet is given based on the overall risk assessment and minimum Coiled Tubing wall thickness. When the critical running footage is reached measures such as pressure tests or wall thickness inspection should be taken
