Two Dry Tree Semisubmersible Designs for Ultra Deep Water Post-Katrina Gulf of Mexico

Abstract

The increased interest in floater designs for ultra-deep water has produced a number of dry tree semisubmersible designs that allow the use of top tensioned risers (TTRs). The primary advantage of the TTRs is that they facilitate direct vertical access to production wells and thereby offer access for well completions and interventions. The principle behind several of the dry tree semisubmersible designs is to reduce the motions of a traditional shaped semisubmersible to a level that can accommodate TTRs. This is accomplished by using heave plates that are positioned beneath the semisubmersible hull and are supported by a lower structure, such as a truss. To a certain extent, the motion responses above and below the response amplitude operator (RAO) cancellation period can be manipulated by designing the relative sizes of the pontoons and columns as well as the size and depth of the heave plates such that the sum of the forces interacts to minimize the heave motion. The paper presents and discusses two semisubmersible designs that assume a common topsides and riser payload. The two designs are sized and analyzed for the new Gulf of Mexico metocean criteria. The comparison is based on hull dimensions, including heave plate and structural support construction. In both cases, results of the hull performance predicted by numerical simulations from fully coupled models are compared and discussed.

Numerical Investigation of a Tuned Heave Plate Energy-Harvesting System of a Semi-Submersible Platform

“…However, because of the small water plane area and the draft, the motions of semi-submersibles, especially heave motion, are much larger than other deep-water platforms such as Spars and the tension leg platforms (TLP). To improve the performance of semi-submersible platforms, many scholars have concentrated their efforts on inventing novel type semi-submersibles [6][7][8][9]. These concepts for improving the semi-submersible platform could be summarized as having a deeper draft, installing heave plates and using truss columns instead of conventional columns.…”

Recent structural design considerations related to floating production systems

“…Examples of application of the updated design criteria to new structural concepts are given by Murray et al (2008) and Yang et al (2008). In the former paper, two semisubmersible designs are presented that assume a common topside and riser payload.…”

A review of floating semisubmersible hull systems: Column stabilized unit

“…Hao et al (2013) described these concepts as a hybrid design, combining the advantages of a truss spar and a convention semisubmersible platform. Murray et al (2008) studied the dynamics of E-Semi and T-Semi (Figure 8). The investigation was carried out for 100-years wave return period for post Katrina sea state in the Gulf of Mexico.…”