Dry-Tree Semi for Brazil and Gulf of Mexico

Abstract

A large number of dry tree concept's have been proposed to the offshore industry over the last few years for application in deepwater fields in the Gulf of Mexico, West Africa and Brazil. Looking into the details of these concepts, they all to a varying degree apply new and unproven technology that will increase project risk when brought to first use.PGS Offshore Technology has over the last 3 years developed the Dry Tree Semi or DTS, which limits the cost and risk aspects of unproven technology by using a standard semi-submersible hull with top-tensioned risers suspended by large volume buoyancy cans. A Norwegian patent has been awarded, and US and international patents are pending for the riser support system developed for the DTS, which comprises a light weight truss tower placed in the centre of the hull. Conventional sliding or roller bearings provide lateral support to the buoyancy cans inside the riser support tower. The DTS concept avoids the disadvantage of dry tree concepts with riser tensioners, which rapidly loose payload capacity in deep water because of the increasing weights of the riser system. Compared to SPAR alternatives, the DTS has a substantially better steel weight to payload ratio. Also, installation costs are considerably reduced since offshore lifting and mating operations are not required.At the OTC 2000 (ref. /1/), a DTS platform concept for West Africa was presented. This paper presents a DTS platform concept, primarily for use in the Gulf of Mexico, but also suitable for deepwater applications offshore Brazil.

VIM Model Testing and VIM Induced Mooring Fatigue of a Dry Paired-Column Semisubmersible Platform

“…For the first approach, TTRs supported by buoyancy cans have been proposed by Often et al (2000 and2001); Compliant Vertical Access Riser (CVAR) was presented by Mungall et al (2004); and Ram style tensioners with a nonconventional production riser stroke range of 11 m (35 ft) or even longer were considered by William and Leverette (2009) and Wang (2012). Development approaches can be categorized into two groups, 1) use a traditional semi hull form with an innovative dry tree riser design, and 2) utilize a traditional Ram style tensioner with a proven riser stroke range and extendable or adjustable base.…”