Multistring Analysis of a Mudline Hanger System in High-Temperature Wells During Production

Summary We present a semi-analytical method to analyze the multistring response of tubulars in offshore wells with a mudline suspension system (MLS). Though the governing equations are linear, structural redundancies at the mudline hangers (MLH) require a one-step iterative solution. The iteration ensures that the final response of the MLS and the tubulars is consistent with restrictions at the wellhead and mudline. Our method is computationally simple and can be implemented in a spreadsheet. We apply the method to an offshore well with six strings, four of which are suspended at the mudline. The hangers at the mudline are arranged such that a suspended string transfers its weight to the next outer string. Furthermore, the MLS hardware is such that a lifted-off string raises its immediate inner neighbor. In the model, the tubulars are regarded as elastic springs, and the load transfer pathways at the MLH shoulders are represented by displacement constraints. The length changes created by pressure and temperature changes during well operations are combined with the installed conditions to determine the contact force at the MLH. The model shows that the net movement at the surface and the forces on the structural members depend on the installed condition, the preload in the casing strings, and annular pressures at the surface wellhead. Furthermore, the reduction of annular pressures significantly reduces the force on the conductor slip lock in the wellhead. Cold injection creates a net downward force at critical locations in the MLS. Finally, the model was used to show that the net downward force did not exceed the design capacity of the MLS hardware and to define annulus pressure management procedures to maintain well integrity.