Casing Wear Factors: How do They Improve Well Integrity Analyses?

Abstract

Abstract Casing wear factors form an integral part of casing wear estimation techniques. However, the values of experimental wear factors do not match field conditions when predicted casing wear is compared to measured values. Hence, adjustments and manipulations are made to wear factors to match field data so that these calibrated values can be effectively applied for more accurate predictions. These field calibrations, which often are extensive, have resulted in casing wear factors being mainly treated as just “fudge factors.” This has led to a lot of confusion regarding the fundamentals behind using wear factors for casing wear analyses. This paper aims to bridge this knowledge gap and provides a comprehensive treatise on casing wear factors and their underlying parameters. The paper describes the details, a clear definition, uncertainties involved, and concepts regarding the appropriate use of casing wear factors and their applications. The wear factors are inherently tied to the coefficient of friction or the friction factor, which in turn is also a proxy because of the larger uncertainties involved in the modeling process. Wear factor values are also dependent on the material properties and operation type and vary non-linearly with the wear groove shape. Additional variations in experimental values also arise resulting from downhole high-pressure/high-temperature (HP/HT) conditions, accuracy of well surveys, as well as wellbore tortuosity and torsion. Other operating parameters, such as rotational speed, rotating time, and normal contact force, can also influence wear factors. This paper investigates, in detail, the dependency of casing wear factors on these uncertainties through several example case analyses. It provides detailed explanations to help understand the fundamental concepts and apply appropriate wear factors for accurate downhole wear estimation. Accurate prediction of casing wear is essential to enhance well integrity and further the life of the well. Hence, this paper also presents a specific example for casing integrity analysis and provides insights to improve overall well integrity by performing a comprehensive casing wear analysis. In addition, the concept of casing wear maps is introduced. These can provide a new visualization and interpretation technique and help to minimize casing wear during drilling operations. Accurate casing wear prediction is crucial for helping to reduce the over-engineering of casing designs in increasingly complex drilling programs, as well as for helping to prevent catastrophic casing string failures caused by wear. This paper provides a sound engineering basis for future drilling engineers to effectively understand the challenges involved in selecting appropriate wear factors and the underlying uncertainties that govern casing wear estimation analyses.