Garden Banks 388 Floating Production Vessel Selection & Conversion
Authors: Taylor M.J. , McBee H.E. , Edelblum L.S. , Henderson A.D. , Scovell D.C. 
Published: October 2008

This paper presents the key elements involved in the selection of the Ocean Victory Class semisubmersible drilling vessel by Enserch Exploration, Inc. for conversion to a Floating Production Facility (FPFJ. (t also presents an overview of the various facets of engineering required to specify and procure all mooring, production facilities and marine systems equipment, and all structural and naval architectural design work necessary to obtain ABS classification and provide a conversion specification bid package and detailed design.

INTRODUCTION

Prior to starting detailed conversion engineering of the FPF, Enserch undertook a vessel selection program resulting in the acquisition of the Ocean Victory Class vessel Glomar Biscay in December, 1992. The vessel was wet towed from Malta to the Gulf of Mexico, arriving in April, 1993, whereupon it was moored at Ham Industries yard in Pascagoula, Mississippi, and subsequently renamed the Enserch Garden Banks.

The detailed engineering for the conversion of theEnserch Garden Banks Floating Production Facility was awarded to Aker Omega, Inc. (AOI) with project start-up in March, 1993. The contract for the vessel conversion work was awarded in January, 1994 to Ham/PMB Joint Venture. On completion of the conversion yard activities, the vessel will be towed to the Garden Banks 388 site (approximately 160 miles south west of Grand Isle, Louisiana) and hooked up to the pre-set mooring system in 2,190 feet water depth.

This project provided a number of challenging design and interface aspects necessary to meet Enserch's goal of first production by mid-1995.

VESSEL SELECTION

During the preliminary engineering phase of the project, Enserch carried out an extensive search and evaluation of suitable candidate vessels for the service intended; "aFloating Production Facility with full drilling capability (FPF)". The candidate semisubmersible, mobile offshore drilling unit (MODU) had to be structurally sound and technically suitable for conversion in accordance withoperating requirements similar to those presented for the detailed design.

An industry standard data bank was used to delineate every existing semisubmersible and list the equipment installed on each rig. Important factors from this data included current geographical location, contract status (short or long term), or whether "warm" or "cold" stacked. Rigs under long term contract or newer than second generation were eliminated from further consideration. Those with a small deck area and/or a small operating air gap were also eliminated. Units that were considered to require an excessive life extension program and/or known to have a design fault or poor motion characteristics were also discounted.

To formulate a "short list" of rigs for detailed evaluation, a further review of the data bank was made. Rigs which would require expensive mobilization to the Gulf of Mexico or had other constraints that might affect their operation as an FPF were excluded. The preference was for units working under short term contracts or currently "warm" stacked.

After examination of data from over 200 rigs, it was possible to prepare a short list of seven candidates for further evaluation. A review of their suitability for operating as an FPF was made.