Prediction Model of Compound Wear Shape in Deep Well Drilling

As the objective conditions in drilling process become more complex, casing wear becomes more and more prominent, which poses a serious threat to safe and efficient drilling. Field measurement data shows that there are multiple wear areas on casing in some well sections, and wear areas present composed wear patterns. Thus, the wear problem is beyond the scope of conventional models due to the complexity of wear shape. Based on previous studies, the complex problem is divided into a combination of simple problems with spatial discretization of casing cross-section and time discretization of drilling process. The calculation model of wear depth and shape increment is established by introducing the independent control variable in casing wear process, and the specific steps to solve this problem are given. Finally, the model is applied to an extended-reach well, and the wear reduction measures are analyzed. The results show that the wear shapes are not always single crescents, but composed patterns of overlapping, crossing and separating of multiple crescents. Different reasons cause different wear patterns: overlapping is caused by the change of wear outer diameter, crossing is caused by small deviation of wear position and separating is caused by large deviation of wear position. There are multiple wear areas on the casing in build-up section, and meanwhile the wear depth is the largest. Reducing wear coefficient is a better way to reduce casing wear.