Morpeth SeaStar Mini-TLP

Abstract

The Morpeth project is the world's first application of a SeaStar®1 Mini-TLP and establishes that mono-column TLP's can be used to economically develop deepwater fields. This paper discusses the evolution and development of SeaStar technology and its niche in the deepwater platform market. Specifics of the Morpeth SeaStar platform are presented along with a discussion of some execution challenges that arose during the execution of this prototype project. Introduction The inventory of undeveloped deepwater discoveries is evidence that the offshore industry's ability to discover deepwater hydrocarbons exceeds its ability to economically exploit them. This inventory, which grew as deepwater wells were drilled, pointed out the need to develop more economic field development solutions for large and small deepwater fields. The Morpeth Field provides a specific example of discovery, deferral, and development of a deepwater discovery. Although discovered reserves were potentially substantial, proven reserves were not sufficient, or near enough to existing platform and pipeline infrastructure, to become a development priority in comparison to other opportunities in the operator's portfolio. Consequently, after the discovery was made, development was deferred. After a long offset subsea tie-back solution was deemed sub-optimal for this field, British-Borneo proposed a standalone SeaStar oil and gas production facility in the Morpeth Field to process oil and gas to pipeline specifications. This strategically located platform simplified the subsea system, improved flow assurance, increased recovery, and improved the economic attractiveness of future subsea developments in the area. The Morpeth Field development project was sanctioned in February 1997 and the SeaStar platform was fully installed by August 10, 1998. First production was achieved on October 11, 1998 despite interruptions in offshore hook-up operations by three named tropical storms, including a direct hit by Hurricane Earl in September 1998. Successful production operations at Morpeth prove that mono-column TLP's can be used to successfully develop fields in deepwater areas. Until Morpeth cost and schedule performance demonstrated otherwise, tension-leg mooring technology was widely believed to only be applicable to platforms that supported large numbers of dry trees. The Morpeth project demonstrates that tension-leg moorings provide reliable, cost-effective, stable, and expeditious means for mooring small deepwater platforms. The Morpeth project also achieved several other industry firsts including the first TLP hull fabricated in the USA, and the first TLP classed by a Classification Society.

The effects of coherent structures on the global response of floating offshore wind turbines

“…The TLP FWT design considered here corresponds to TLPWT #3 from Bachynski and Moan, 30 which is an approximately half-size version of the original Sea Star oil platform. 31 Compared with other published TLP designs (eg, Matha et al 32 and Stewart et al 33 ), this design has relatively stiff and highly pretensioned tendons. The tendons were modelled using axis-symmetric beam elements, with hydrodynamic loads according to Morison equation (with C a = 1 and C d = 1).…”

“…The pretension makes the platform stiff in heave, roll, and pitch, while still compliant in surge, sway, and yaw motions. The TLP FWT design considered here corresponds to TLPWT #3 from Bachynski and Moan, which is an approximately half‐size version of the original Sea Star oil platform . Compared with other published TLP designs (eg, Matha et al and Stewart et al), this design has relatively stiff and highly pretensioned tendons.…”

Design considerations for tension leg platform wind turbines

“…The hull, made of steel, consists of a main cylinder (diameter D 1 , length h 1 ) continued into a base node (diameter D 2 , length h 2 ), with overall draft T. Protruding from one of these cylinders at a vertical location z s are n p rectangular or circular pontoons that support the tension legs, as shown in Fig.1. For example, a TLPWT that resembles the Sea Star TLPs [24] with rectangular pontoons (height h p , width w p , and total radius from the cylinder center r p ) and n t tendons is depicted in Fig. 1b.…”

“…The hull of TLPWT 3 was an approximately half-scale version of the original Sea Star oil platform [24]. Somewhat higher initial tendon tension was required to satisfy the third criterion.…”

Coupled dynamic response of a three-column mini TLP

“…Several mini TLP designs have been discussed in the literature. These are: a downsized four column mini TLP for 1000 m water depth ; a family of concrete mini TLPs for generic applications (Logan 1996); a three column TLP for 800 m water depth, easily extendable to 1500 m under shorter development schedule with significant reduction in cost (Muren 1996); a mini TLP with vertical cylindrical hull connected to three radially tapered rectangular pontoons called SeaStar (Kibbee 1996 andKibbee et al 1999). …”