Determination of Casing Wear Depth Limits for Multilateral Wells in the South China Sea

Casing wear is a major hidden danger affecting drilling safety and the long-term integrity of the wellbore. Excessive wear significantly reduces the casing’s residual collapse strength, internal pressure, and tensile strength, and in severe cases, can lead to wellbore failure or even well control accidents. Therefore, accurately predicting casing wear is of great significance for preventing casing failure and ensuring drilling safety. Based on the wellbore structure and casing data provided on site, this study calculates casing wear using the established casing wear prediction model, and systematically analyzes the development patterns and main controlling factors of casing wear across the entire well section and under different drilling conditions. Calculation results show that within the entire well, the build-up section and the bottom casing shoe are the two areas with the most severe wear, with predicted wear depths significantly higher than those in vertical and horizontal sections. At the same time, these two regions closely match the locations where dogleg severity is pronounced in the well trajectory, indicating that dogleg severity is a key geometric factor controlling the spatial distribution of wear. This research method focuses on the correlation patterns between engineering measurable parameters and prediction results, making it easier for field engineers to understand and apply. It can provide a basis for casing residual strength evaluation, drilling parameter optimization, and drill tool combination optimization.