Drilling semi conversion concept relaunched for marginal fields

As prospects for field development revive on the back of improved oil prices, GVA Consultants has relaunched the PROMS concept for converting semisubmersible drilling rigs into drilling and production platforms.

As prospects for field development revive on the back of improved oil prices, GVA Consultants has relaunched the PROMS concept for converting semisubmersible drilling rigs into drilling and production platforms.

The Gothenburg-based company, part of the BMT group, claims that PROMS - Process Mod-ule System - offers a cost-effective means of providing a floating production facility while retaining the benefit of drilling capability. By placing the process facilities on an extension to the rig, the concept involves a minimum of interfacing with the existing rig systems, thus significantly reducing the risk of conversion surprises which have often played havoc with the economics of conversions.

PROMS is aimed mainly at small and marginal fields with a typical production of around 30,000 b/d of oil. It is applicable to most rig designs with two pontoons, including the Pacesetter, Aker H3 and GVA 4500. Presentations to operators in the Gulf of Mexico and Europe have prompted substantial interest, and the concept has also been studied for use in Brazilian waters, according to marketing director Robert Ludwigson.

Short conversion time

The prefabricated extension consists of a grillage-type deck, two columns, and a pontoon arrangement. The pontoon arrangement involves extensions to the existing rig pontoons, and an additional transverse pontoon across the end of the extension. The extension brings the buoyancy needed to carry the additional topsides weight, the waterplane area needed for the stability of the converted unit, and space for the additional mooring required to take the increased environmental loads. The risers are connected at the end of the extension.

Both the process module and the deck and additional hull structures are prefabricated, so that the rig needs only to be brought to shore for the extension to be installed. The mating process takes place in a dry dock or while the rig is in floating condition in port. Hookup is minimized, as the extension facilities are mainly self-contained. The process is therefore expected to take two-three months, compared to traditional conversions requiring the rig to be in port for periods in excess of a year.

Buffer oil storage of up to 20,000 bbl can be provided in the PROMS columns, in the case where export by shuttle tanker was more attractive than by pipeline. The new layout is also satisfactory from a safety point of view, as the hazardous areas represented by the process and riser zones are located at the far end of the rig from the living quarters. The extension is segregated from the rest of the rig by a transverse firewall.

The addition of a 30,000 b/d process facility to a Pacesetter drilling rig is one of the cases studied. The PROMS would accommodate a two-level module weighing 1,600 tons with a footprint of approximately 46 meters in width and 22 meters in length.

For more information contact Robert Ludwigson, GVA Consultants. Tel: +46 31 106770, Fax: +46 31 106710, E-mail: robert.ludwigson@gvac.se

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