Development and Deployment of a Freestanding Production Riser in the Gulf of Mexico.
Authors: Fishe Ed , Hoolley Pat 
Published: October 2008

This paper describes the Freestanding Production Riser System that will be deployed by Enserch Exploration in the Gulf of Mexico (Garden Banks 388). The system will utilize many refurbished Components Of a FSPR system previously installed In the Gulf of Mexico (Green Canyon Block 29) in 1988.

The free standing production riser has been proven to be a viable and cost effective solution for many of the deep water development projects currently being considered. BY utilizing established technologies and fabrication methods, the system has proven to be a cost effective alternative to much larger installations with similar production rates.

An account of the refurbishment and redeployment of the FSPR is given in the paper. The information presented has direct application to the design and evaluation of deepwater freestanding risers.

PROJECT OVERVIEW

Enserch Expiration, inc. (ENSERCH) is developing oil/gas reserves discovered in Garden Banks Block 388 in the U.S. Guif of Mexico. The flied uses subsea Circled and completed well stied back to a floating production facility located directly above the subsea template/wells. water depth at the location is 2096 ft. The system is designed for a maximum production rate 40,000 bibs of oil per day and 120,000 maces of gas per day. The lightly processed oii and gas is piped to a shallow water facility for further processing before being exported to shore via separate oil and gas pipeline systems.

The subsea wells are tied back to a floating production facility through a free-standing production riser with integral production and control lines. The subsea wells are drilled through a 24 siot subsea template by use of the drilling facilities on the floating production vessel

DESIGN RATIONAL FOR GB388

Conceptual studies conducted by Enserch Expiration, inc. after the first discovery wei1 was drilled, determined a refurbished floating production facility (FPF) utilizing a freestanding production riser (FSPR) to be the most cost effective approach for developing this deepwater prospect. Other options that were studied included a complaint lower, tension platform or a new buiid FPF. The favorable characteristics of the FPF/FSPR system includedA short lead time to first production,low capital investment utilizing existing equipment, andminimized technological risk by using existing technology and equipment.

The ability to purchase an existing semi-submersible for conversion to an FPF and an existing production riser previously installed by Placid in Green Canyon 29, allowed Enserch to significantly cut the lead time to first production and thus increased the net present value of the project by accelerating the cash flow stream. A new build FPF would have required a longer time frame for engineering design, FPF construction and production riser fabrication.

A low initial capital investment was necessary to justify the development of GB388 after threshold reserves were confirmed. The ability to purchase the existing production riser joints and other riser components, and the candidate semi-submersible under favorable terms, assured initial costs would be much lower than would be expected for new build equipment. The additional water depth at GB388 required fabrication of 11 new riser joints.