Transportation Analysis of Dry Tree Semisubmersible

Abstract

With the advancement of oil & gas into ultra deepwater, the need for drilling and production platforms has becomes more acute. The dry tree semisubmersible can be used for direct vertical access into reservoirs from deepwater since it offers small in-place motions, large open deck areas, dockside commissioning and minimum offshore hookup. The direct access allows the operator to drill, complete and work over the well directly from the same platform. The drytree semisubmersible consists of a keel tank which can be telescoped up and down based on the requirement of the platform. The keel tank is fully telescoped down while in operating condition and telescoped up while in transportation condition. The transportation analysis of a drytree semisubmersible using the linear radiation, diffraction panel program WAMIT is presented in this paper. Parametric studies were carried out in WAMIT by varying the size of the keel tank by considering the keel tank size as 80X80m, 91.5X91.5m and 100X100m. The Case 2 in which the keel tank dimensions were 91.5×91.5 m was found to be most appropriate of all, as the response for it was lower compared to other cases and also the structure was good from stability point of view. It was found that the heave and response were high only beyond 15 seconds wave period thus making transportation operations safe, as transportation is carried out in sea states 5 and 6 which have wave periods less than 14 seconds. Also the pitch RAO was found to be very low thus posing no threat in transportation mode.