Integrated Global Performance Analysis of Matterhorn SeaStar TLP
Authors: Leverette Steve , Rijken Oriol , Spillane Mike , Williams Neil 
Published: October 2008

Atlantia's global performance analysis of the Matterhorn SeaStar TLP is a unique integration of computational, analytical, and experimental techniques to design an optimal system for the development of the Matterhorn field. The key global performance issues addressed during the project are discussed. These include selection of metocean data, model test calibration, coupled analysis of hull tendon and riser systems, and mitigation of vortex induced vibration of tendons and risers.

Introduction

The Matterhorn SeaStar TLP was developed by Atlantia Offshore Limited for TOTAL E&P USA, INC. The project was sanctioned September of 2001, and was installed over the summer of 2003, with first oil in November of 2003. The Matterhorn structure is the 4th SeaStar TLP designed and built by Atlantia Offshore Ltd, and is the first to include a moonpool and surface completed wells. The global analysis methods and techniques have been developed by Atlantia beginning with the Morpeth SeaStar design in 1997, and have evolved through 4 designs, multiple model test programs, and evaluation of 5 years of field data of these platforms.

Platform Overview

The primary function of the Matterhorn SeaStar TLP is to serve as a production and workover platform utilizing both dry trees and remote subsea wells for extraction of oil and gas from the reserves identified in Mississippi Canyon Blocks 243 and 199. The platform design accommodates up to nine dry tree, vertical top tension production risers, and has future capacity for up to five remote subsea tiebacks with associated umbilicals. The platform supports facilities for controlling and workover of the wells, processing oil and gas production to pipeline quality, and exporting production into pipelines.

Figure 1 Matterhorn SeaStar TLP(Available in full paper)

The Matterhorn platform is a single-column TLP with a central moonpool for the dry tree risers. As shown Figure 1, the hull features a single surface-piercing column with three radiating pontoons extending from the bottom of the column. The TLP also includes an independent three-level deck supported above the column by a jacket-like structure; six tendons, with two tendons attached at the end of each of the three pontoons, and six foundation piles, mechanically connected to the bottom of each tendon. Particulars are as follows:Hull weight: 12279 KipsHull displacement: 52806 Kips (@104' draft)Main column diameter: 84 feetDraft: 104 feetPontoon radius: 179 feetPontoon height: 27-42 feetMain Column height: 125 feet

Figure 2 Matterhorn SeaStar TLP - Plan(Available in full paper)

Figure 3 Matterhorn SeaStar TLP - Elevation(Available in full paper)

The water depth is 2816 ft. The main tendon system is composed of 290 ft joints of nominally neutrally buoyant 32 inch pipe. The deepest sections are thicker wall (and therefore heavier) in order to resist hydrostatic collapse. The upper 1100 ft of each tendon is covered with fairings to reduce VIV response in currents.

Table 1 Tendon Pipe Properties(Available in full paper)

The payload carrying capacity of the Matterhorn SeaStar system is 26,196 Kips. The payload is comprised of the deck structure, topside facilities, drill rig, ballast and suspended risers.