Genesis Spar Hull and Mooring System: Project Execution
Authors: Krieger W.F. , Heslop J.C. , Lundvall B.E. , McDonald D.T. 
Published: October 2008

This paper provides an overview of the project execution phase for the Genesis hull and mooring system, beginning with project team scope, responsibilities, and organization. Safety, quality, cost and schedule are reviewed, with special attention given to the issue of safety. Selected technical challenges are discussed, including deck leg to hull connection, chain jack foundation, transportation, connector testing, riser guides, and strakes. Lessons learned are noted.

Introduction

The Genesis spar hull was successfully upended at Green Canyon block 205 on June 18, 1998, in 2590 feet of water. It will produce at a peak rate of about 55,000 barrels of oil and 72 million cubic feet of natural gas per day. Genesis is the first application of spar technology for both drilling and production.

The spar hull is a floating, vertical cylinder 122 feet in diameter and 705 feet in length, with buoyancy tanks in the upper part and a 58 foot square moonpool with slots for drilling up to 20 wells. It is held on location by a 14-line taut catenary spread mooring system. The mooring system is designed to position the spar over any of the seafloor wells for drilling operations.

The Genesis Spar Design and Construction contract between Chevron and Spars Intl. Inc. (SII) formally initiated project execution on July 1, 1996, following approximately one year of front-end engineering. Prior to contract award, the front-end engineering contract was expanded to include some material procurement and fabrication preliminaries.

Scope, Responsibilities, and Organization

Hull and Mooring System Scope.

Aker Rauma Offshore(ARO) was responsible for engineering, procurement, and fabrication of the Genesis spar hull and mooring system. The hull was fabricated at Aker Mäntyluoto (AMO), and has a lightweight of approximately 28,600 tons. The 14-line mooring system consists of on-vessel and off-vessel components.

The on-vessel components include chain jacks supplied by Bardex, fairleads supplied by Pusnes, and tail chain from Vicinay. The chain jacks are designed to pull in and let out chain at four feet per minute under a combined moderate storm/loop current condition, developed by Chevron for the GC205 location. The criterion was selected so that drilling operations would not be delayed due to an inability to reposition the spar in a timely manner during most anticipated environmental conditions.

The fairleads are located mid length of the spar hull, and change the direction of the chain from vertical (chain jack to fairlead) to 45 degrees downward (fairlead to piled foundation). The fairleads are retrievable from the surface with ROV support, using a tool designed for this purpose.

The tail chain, which is used for mooring line installation and to provide back tension on the chain after passing through the jack, remains permanently in the chain lockers and consists of 200 feet of 3 inch studded chain.

The off-vessel components include chain supplied by Vicinay, wire rope from Bridon, and connector plates and shackles from Forges LeBeon. Each mooring line consists of 1050 feet of 5 ¼ inch R4 studless chain at the top, 3000 feet of 5 ¼ inch spiral strand wire rope with HDPE jacketing, and another 250 feet of pile chain. Individual chain links are 31.5 × 18" × 5 ¼", and weigh 426 lbs. Breaking strength of the chain is approximately 1825 tons. The in-air weight of the wire rope is 62 lbs. per foot, and the wire rope has a breaking strength of approximately 1700 tons.