Casing Wear Prediction with Considering Initial Internal Casing Eccentricity

Casing components in drilling engineering possess problematic internal eccentricity due to mismachining and circumferential wear in the prophase. Said eccentricity markedly affects the accuracy of casing wear prediction. In this study, casing wear efficiency theory and a novel geometric description are used to establish a wear prediction model for the initial internal casing eccentricity in extended reach drilling (ERD). Composite casing wear analysis is conducted to explore wear in the same groove and across a series of different grooves; then, residual depth (RD) is used to evaluate wear in terms of risk. The model parameters are subjected to sensitivity analysis, and a case study is conducted to validate the model. The results show that slight eccentricity significantly affects the accuracy of casing wear prediction and that worn casing depth increases as drilling footage increases in a manner strongly dependent on composite wear. The RD percentage of the worn casing wall markedly decreased as initial internal casing eccentricity increased, particularly at the most dangerous angle; at footage of 6000 m, the RD of worn casing wall by drill string A and C combination was minimal. Initial internal casing eccentricity should be properly accounted for in ERD processes to ensure drilling safety.