Abstract

This paper covers the design and construction of the Diana/Hoover Topsides. A description of the facility covering capacity, major equipment, and environmental parameters is outlined. Design issues such as safety considerations on a floating platform, ABS certification, installation considerations, the impact of motion on process facilities, and methanol recovery are addressed. The Safety Management Philosophy is described. The paper concludes with an overview of the key success factors for the project.

Description of Production

The Diana field is composed of five subsea wells located in East Breaks 945, 946, and 989. The wells were drilled and completed with a Mobile Offshore Drilling Unit (MODU). The Hoover field is located in Alaminos Canyon Blocks 25 and 26, and the dry tree wells are being drilled and completed with an API Platform drilling rig installed on a Deep Draft Caisson Vessel (DDCV). The Hoover rig was refurbished and modified to withstand DDCV motions and perform operations not commonly performed by API platform rigs such as drilling and production riser installation and removal.

The Diana Subsea development is located fifteen miles west of the Hoover host facility in a water depth of approximately 4500 feet. The Subsea development consists of a northern drill center (NDC) and a central drill center (CDC).

The NDC is connected to the Hoover host facility via a single 10" production flowline and the CDC is connected to the Hoover host facility via one 10" and one 6" flowline. The manifolds are connected to each other by a three mile 10" infield flowline. The 10" flowlines serve as the primary production lines, while the 6" performs as a production line as well as a test line when required. Flowline and manifold configuration enables well testing capability of all subsea wells and loop pigging of all three of the flowlines.

Processing Facilities

The Hoover/Diana process facilities are represented in a simplified manner in Figure 1. General data for the topsides is given in Table 1. The design philosophy was to use the tried and true wherever possible and get operator input from the beginning. Mustang Engineering, Inc. was the primary topsides facility designer.

The initial process flow for Diana subsea production is heating, pressure reduction through a choke, and flow into the HP production manifolds at approximately 1100 psig. Local Hoover production flows into the IP or LP separator headers atapproximately 530 or 180 psig respectively.

Produced water dumping from the LP Separator flows through hydrocyclones and a vertical flotation unit prior to overboard discharge through a subsea diffusion pipe attachedexternally to the hull.

Each pressure system has a horizontal separator. Gas from each pressure system flows to the appropriate compression stage suction scrubber. Hydrocarbon liquids and water fromthe HP and IP separators flow through hydrocyclones, where the water dumps to a methanol recovery process. Oil then dumps to the next lower pressure separator stage.

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