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.

Of the many deepwater platform concepts that were developed as deepwater platform technology matured, the TLP has been the most frequently selected for deepwater construction projects. Over the past two decades, TLP technology has proven to be a safe and reliable means for establishing deepwater real estate for supporting drilling, production, and transportation operations. As the deepwater exploration province evolves from a frontier area toward maturity, the commercial and technological environment of field development concept selection has changed and has opened opportunity for secondgeneration deepwater platform concepts, such as the SeaStar® Mono-column TLP. This concept has been used to successfully exploit deepwater opportunities in the Gulf of Mexico including AGIP's Morpeth Field, AGIP's Allegheny Field, Chevron's Typhoon Field, and now TotalFinaElf's Matterhorn Field. This paper briefly describes these four projects and then discusses the continuing evolution of this technology. Introduction In parallel with the beginning of exploration for oil and gas reserves in deep water, major oil companies began developing platform concepts to exploit deepwater discoveries. Tension-Leg Platform (TLP) technology emerged as a cost-effective means for providing stable deepwater real estate for drilling and production operations. Over three decades, the Offshore Industry invested enormous amounts of money and manpower to develop the design and analysis methods, software, specialized hardware, fabrication techniques, and installation equipment necessary to safely construct and operate TLP's. Early TLP's resembled semisubmersible Mobile Offshore Drilling Units (MODU's), in which the catenary mooring system had been replaced by a tension-leg mooring that eliminated vertical motions. Figure 1 presents a summary of TLP's installed to date. The structural reliability of a tendon, like the structural reliability of an airplane wing, is an essential safety issue, that receives focused attention throughout the project. Note that there has never been an operational tendon failure on any of these fifteen TLP's, three of which have been operating for a decade or more. The number of service years that tendon system components have delivered, with zero failures, is very impressive, measuring in the tens of thousands of service years. As exploration drilling proceeded in deepwater and a mix of large and small fields were found, it became apparent that there was a need for a new generation of less expensive TLP's, which would permit economic development of heretofore sub-marginal fields. In response to this need, Atlantia developed the SeaStar mono-column TLP, thanks to the help of funding from the U.S. Department of Energy. The primary geometric difference between a SeaStar TLP and a conventional TLP is the former's single column. The single column allows deck and hull to be separately optimized, resulting in a most versatile and cost-effective solution. The tension leg mooring was the key to allowing the platform size to be reduced while maintaining the favorable motion characteristics needed for the safe operation of facilities and risers. A freely floating platform, such as a spar, experiences relatively large angular motions that must be accommodated with respect to the earth-bound risers.

The Morpeth Field is located in the Ewing Bank area of the Gulf of Mexico in 1,670 feet of water. British-Borneo acquired the field in 1995 from Shell Offshore Inc (SOI) and now holds a 100% working interest in the field with SOI retaining a financial interest. The field has been developed utilizing a mono-column tension leg platform (TLP) known as SeaStar®, a proprietary design of Atlantia Offshore Limited. This paper describes British-Borneo's Morpeth Field development and entry into the deepwater Gulf of Mexico. In successfully undertaking this project, British-Borneo has demonstrated that an independent oil company can economically develop a marginal deepwater prospect using an innovative, "first of a kind" development concept. Introduction The Morpeth Field is an oil and gas development located in Ewing Bank Blocks 921, 964, and 965 in 1,670 feet of water in the Gulf of Mexico. Estimated reserves in the order of 70 mmboe make it a marginal development by typical deepwater Gulf of Mexico standards. A relatively low number of high productivity wells (each well having initial flow rates on the order of 15,000 bopd) is required for optimum reservoir development. The oil has an API gravity of 32 and a 1,000 GOR with a paraffin content of 0.77%. British-Borneo is an independent UK based oil and gas production company and has been active in the shallow waters of the Gulf of Mexico since 1989. The deepwater Gulf of Mexico was identified as a province that could offer substantial growth opportunities in terms of the excellent hydrocarbon potential and, interestingly, which also contained a number of undeveloped discoveries in various company portfolios. It was with these undeveloped discoveries in mind that in 1995, British-Borneo entered into a strategic alliance with Atlantia Offshore Limited to develop Atlantia's innovative and low cost deepwater development solution, the SeaStar® "mini" tension leg platform (TLP). The SeaStar®, which comprises a mono-column TLP, is ideally suitable for fields requiring a relatively low number of wells and little subsequent well intervention later in field life. This was seen as a key by the British-Borneo subsurface team to enable the meaningful pursuit of the undeveloped discoveries in the deepwater. One such opportunity was the Klamath Field discovered by SOI in 1991. This discovery presented an ideal opportunity for the mono-column TLP requiring a small (four) number of development wells. British-Borneo and Shell quickly consummated a deal utilizing this new technology. The field was then renamed Morpeth after the past chairman, Sir Douglas Morpeth. The field development plan was quickly agreed upon, based fundamentally upon tying back three subsea production wells and one subsea water injection well to the TLP. The wells are connected to the TLP by 4-inch ID flexible flowlines, where the TLP is host to a full processing production facility. The design capacity is for 35,000 barrels of oil per day, 42 mmscfd of gas, 28,000 barrels per day of water injection, and 10,000 barrels of produced water per day. Oil and gas are processed to trunkline specifications, then exported through steel catenary risers into the sales pipelines. Additional production can be tied into the export pipelines at a subsea tie-in sled located four miles from the platform in 1,200 feet of water. The Morpeth project was completed in 21 months from project sanction to first oil. This was 6 months earlier than first projected during conceptual engineering. Not surprisingly, some budget growth was experienced from the initial budget estimates generated early in the conceptual phase of this "first of a kind" project. While half of the cost increase was a result of signi