P.3 ~ Feasibility study assesses two dry tree options for the Gulf of Mexico

Operators in the Gulf of Mexico (GoM) are increasingly looking to ultra-deepwater (>5,000-ft/1,524-m water depth) fields and more challenging reservoirs to deliver the hydrocarbons that the energy market demands and to satisfy their production growth objectives. DNV GL was granted an award by the Research Partnership to Secure Energy for America, partially funded by the US Department of Energy's National Energy Technology Laboratory, to manage a project to develop dry tree semi concepts for the ultra-deepwater fields in the GoM.

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HOE dry tree semi

The HOE PC Semi has two columns in each corner, which are connected by pontoons. The PC Semi configuration is different from a conventional deep draft semi in three aspects:

  • Eight versus four columns
  • Rectangular column versus square column
  • Larger column slenderness ratio.

KFD dry tree semi

The DWDTS hull is built on a conventional deepwater semisubmersible concept with four corner columns and a ring pontoon. The hull size is 308 ft by 308 ft (93 m) and the total height is 215 ft (66 m). The proposed draft is 145 ft (44 m). Freeboard is 70 ft (21 m) to the bottom of the deck box and 105 ft to the top of the deck box from mean waterline. The mooring system of the DWDTS consists of 16 mooring lines clustered in four groups (4x4) with chain-polyester rope-chain segments for each line.

The topside facilities are modularized and supported by a deck box structure with overall dimensions 254 ft (77 m) long (EW), 354 ft wide (108 m), and 35 ft (11 m) deep. The process module is on the north side of the deck and the living quarter is on the south end. The well-bay is arranged in the center of the deck to accommodate production and drilling systems.

Concept evaluation

This project engaged subject matter specialists to evaluate the concepts starting from establishing the design basis, to model tests and conceptual HAZID workshops. A WPG was established in the very beginning of the project to engage subject matter specialists from Chevron, ConocoPhillips, Statoil, Total, Marathon Oil, and RPSEA. WPG meetings were held on regular basis (every 1- 2 months) until the final workshop was conducted. The project participants (DNV GL, HOE, and KFD) also published several papers and held presentations at OTC Houston, OTC Brazil, and RPSEA conferences.

The objective of such industry participation and publication was to seek advice and feedback from the subject matter specialists and end users to ensure that concept development is in line with industry practice, and meets the requirements of a safe operation in the GoM.

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