Control of marine riser end angles by position mooring

For safe drilling and work-over operations on floating platform, one objective is to minimize the rigid riser angles at the well-head and at the top joint. One way to achieve this is to control the vessel’s position. For shallow water, drilling operations are normally carried out using a moored vessel. In this paper, a system consisting of a vessel, mooring lines and a drilling riser was mathematically modelled. The strategy was to control the vessel’s position by changing the tensions in the mooring lines to ensure that the riser end angles are within safe limits. Numerical simulations and experiments of a moored vessel were performed to illustrate the feasibility of the proposed control strategy.