Analysis and simulation of erosion in drilling tools

Erosion has been reported in the drilling tools used in the oil and gas industry. This paper focuses on the development of erosion modeling techniques and the application of the developed models to improve the design of drilling tools. Mechanisms of erosion have been formulated based on experimental and theoretical work done in the material science. The model adopted combines the two well known types of erosion (ductile and brittle) in a single model, in which the erosion is controlled primarily by the particle impact velocity and impact angle, as well as other secondary variables. Algorithms were developed for transient simulation of the erosion of any surface in 2D tool geometry. Because the erosion changes the geometry of the tool, which in turn changes the flow field, the algorithms must combine the moving boundary problem with the solution of the flow in the tool. Based on the theory developed, an “erosion simulator” has been written, which can use as a flow component any computational fluid dynamics (CFD) software. Actual data from TESCO Corporation casing drilling tools has been used to calibrate the physics of the process and validate the software. A general agreement between the two was obtained, but the validation process also identified areas of future laboratory and theoretical research needed. As an example of the ability of the software to identify “hot spots” in the tool design, the simulator has been used to modify the geometry of the “under-reamer casing-drilling tool”. This resulted in a substantial decrease in erosion rate and therefore increased life of the tool.