Localized Wear in Steel, Glass Fiber and Composite Casings Upon Drillstring Contact: A Full-Scale Experimental Comparison

Abstract

Abstract Localized dynamic casing wear due to drillstring contact (predominantly at the tooljoint) is a complex phenomenon to simulate due to the number of control variables influencing the non-linear wear behavior. Wear intensity is influenced by individual combinations of service loads (changing force-area distributions), metallurgical properties (material hardness and yield strength) and tribological parameters (surface roughness, friction factor and wear type). For wear simulations to be accurate, the required friction- and wear factors must be determined experimentally by full-scale wear tests to be used in model equations. This paper presents a comprehensive account of the experimental work carried out to reproduce friction- and wear factors via full-scale wear tests under variable conditions of casing material, side force, drillstring RPM, axial movement and circulation fluid. The design of the wear test frame, the test method and the application of determined friction- and wear factors to detect casing wear trends under downhole conditions is the core focus of this study. Full scale casing wear tests were carried out while incorporating different casing materials under a selected range of operational loads and lubrication conditions. The outcomes of the wear scenarios were then compared for steel, fibered glass and fibered carbon casings. Results of wear tests have been included and compared in the study for three casing materials under water-based mud lubrication environments. The test results show a trending wear pattern in terms of friction- and wear factors for all casing materials. After the initial peak values, the wear factor is observed to decline drastically to a steady range due to contact pressure reduction. For all tested materials, this steady range of values can provide a good estimate of field wear volume over time under particular service loads and drilling scenarios. In addition, the measured steady values of friction factors help determine close ranges on contact pressure threshold for the casings. It has been observed from the detected trends in the test results that repeated wear tests can make casing wear predictable. With the inclusion of more steel grades, casing diameters and casing types into the experimental scope, the wear frame can be used to develop a comprehensive record of wear performance of casings under different field scenarios. Attribution of wear factors and contact pressure thresholds to specific downhole conditions via a wear database, and its integration into a software solution can fill gaps to predict and reduce casing wear while retaining operational flexibility on downhole stresses.