Abstract

This paper describes the fabrication, loadout and launching of the world's first cell spar hull. The hull was designed for fabrication by a Gulf Coast facility and represents a first for the industry, eliminating the time and cost of the traditional dry tow from a remote location. The fast-track schedule and first-of-a-kind design presented special challenges to hull fabrication. The paper will address basic design of the hull, capital improvements at the fabrication site, overall fabrication schedule, fabrication methods and construction sequence, including some special features in fabrication.

Introduction

The Red Hawk field is a deepwater gas field located in the Gulf of Mexico approximately 210 miles southeast of Sabine Pass, Texas in Garden Banks 877. The field development spans both the GB877 and GB876 blocks, as shown in Reference [1]. The field development consists of a cell spar moored in approximately 5300 feet water depth, and one or more subsea systems that are tied back to the spar. Kerr-McGee Oil and Gas Corporation (the Operator) is the operator and Devon Energy (Devon) is a 50% partner. The discovery well at Red Hawk was drilled in August 2001.

After a review of potential development options, including a number of novel proposed systems, the Operator opted to develop the field through the use of the cell spar, which is the third generation of spar technology. Conventional wisdom for a field of this type dictates the use of a subsea tieback to a host. Economic comparisons demonstrated clear value to development of a 'dry spot' in this area for the purposes of developing the Red Hawk field, as well as potential future production which may be located within the 'area-wide' development for Kerr-McGee. A more complete description of the selection process and rationale are provided in Reference [1].

Description of Cell Spar

The Red Hawk cell spar hull is composed of a bundle of cylindrical members called cells that are held together by a number of horizontal and vertical structural elements located in the interstitial space between the cells. The Red Hawk spar is a small hub-type facility designed to support a number of wet tree risers. Since the risers were all SCRs, no centerwell was needed for this application.

The upper portion of the Red Hawk cell spar is composed of six outer cells surrounding a central cell (see Figure 1). These upper cells provide the buoyancy required to float the vessel. Each cell is subdivided into four compartments using horizontal deck structures. These decks are constructed using ring beams that are closed off using elliptical heads. The ring beams are fitted with hatches to allow for routine inspection of the internal structure. The resulting 28 upper cell compartments provide even more redundancy in compartmentation than that of the truss spar, which already had significantly more redundancy than any other deepwater concept.

The lower portion of the spar is formed by extending three of the outer cells down to the keel.

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