Application of Casing Wear Theory to Top Tensioned Risers

During drilling and/or workover operations through a production top tensioned riser, the riser will experience contact with the rotating drill string, resulting in wall loss from the riser. This wall loss from the contact between the rotating drill string and riser is defined as riser wear.

Riser wear is primarily a function of riser curvature, which is dependent on riser stiffness, environmental loading, vessel offset, drilling operational parameters and drilling mud properties. Wear allowance and windows for conducting drilling operations can be defined prior to wear analysis. This paper discusses a complete methodology to determine riser wear, through application of casing wear theory, and thus confirm the wear allowance for the given drilling operating windows.

Environmental loading conditions are selected based on drilling windows and a global analysis is performed with FEA software to obtain riser curvatures. As casing wear theory and associated software are based on survey parameters, the riser curvatures obtained from FEA software are converted to survey parameters (i.e., total vertical depth (TVD), inclination, and azimuth) using the Minimum Curvature Method. Contact forces between the drill string and riser are determined based on torque and drag theory, and a cumulative wear volume is calculated considering drilling operational parameters. Various approaches for converting this cumulative wear volume to wall thickness loss are presented and compared.