Global Configuration Design of Umbilicals in Deepwater

Global configuration design of subsea umbilical risers in deep water is a major challenge due to extreme environmental and operational requirements. The critical issues considered in design are the interference between umbilicals in the presence of strong loop and submerged current, and the on-bottom stability along with the strength and fatigue requirements. The vessel motion primarily controls the selection of the configuration, catenary or lazy wave, and the latter is an obvious choice in the presence of significant heave motion. The length and routing on the seabed ensures the on-bottom umbilical stability by dissipating the axial load through soil friction. However, the interference with other subsea components as well as the space availability can also be a governing criterion in the routing. Finally, all these design requirements must be satisfied economically from the perspective of overall cost of the project without compromising quality of the product and safety of design. This paper presents a brief outline of the global configuration design of umbilicals accounting for various design considerations. The host is a semi submersible in a water depth of 6050-ft in the Gulf of Mexico. The lazy wave configurations of the chemical injection and control umbilicals are considered for the study presented herein. The methodology of design for the global configuration is discussed considering different environmental loadings such as the 100-yr and 10-yr loop current, and 100-yr submerged current. The stability of the umbilical on the seabed is discussed on the basis of analysis results for the environmental loadings with dominant vessel motions. The phenomenon of “walking” under the influence of dynamic loading is investigated and the necessary considerations in design to prevent the umbilicals from “walking” are also discussed.