Diana Subsea Production System: An Overview
Authors: Gist Gregory N. 
Published: October 2008

This paper presents an overview of the subsea systems for the ExxonMobil Diana Project located in the East Breaks Area of the Gulf of Mexico. The development is located 160 miles offshore in water depths ranging from 4,500 feet to 4,700 feet. The system features two, 4-well manifolds at remote drill centers connected via a looped flowline system, capable of producing 100,000 BOPD and 325,000 SCFD from the Hoover host facility located 16 miles away in 4,850 feet of water. The project was successfully installed and started up in May 2000, with a number of equipment designs utilized by ExxonMobil as an "ExxonMobil first" as well as the establishment of several industry records.

Introduction

The Diana field, located 160 miles offshore Texas (Fig. 1), consists of a four block unit in East Breaks (EB945, 946, 988 and 989). Equity is fixed at 66.67% ExxonMobil and 33.33% BP, with ExxonMobil serving as the designated operator. The discovery well (EB945 #1) was drilled in 1990, a gas appraisal well (EB945 #2) was drilled in 1996 and an oil rim appraisal well (EB946 #1) was also drilled in 1996 (Fig. 2). Diana is a gas and oil development. To develop this resource, the oil rim is being exploited first using five horizontal wells (Phase 1 of program). Following oil rim depletion in approximately 2005, some of the oil rim wells will be recompleted as horizontal gas completions and several new drill wells will make up the 6- well Diana Phase 2 program.

Diana features two 4-well manifolds located 2.3 miles apart and connected by a single 10" flowline. Each manifold is connected to the Hoover host facility, a deep draft caisson vessel (DDCV), via an un-insulated 10" flowline. A single uninsulated 6" flowline is also connected from the central drill center (CDC) to Hoover and functions as a test/production flowline. A steel tube umbilical between Hoover and the northern drill center (NDC) and an infield umbilical between the northern and central drill centers provide the combined electrical and hydraulic requirements to control the wells. Hydraulic and electrical flying leads are used to connect the umbilical termination assembly to each well and the manifolds. The wells are located around each manifold in a clustered arrangement and connected to the manifolds and flowlines using steel pipe inverted "U" jumpers (Fig. 3).

The installation operations of the Diana manifolds, trees and jumpers were all performed from the dynamically positioned Multi-Service Vessel (MSV) Uncle John. While some of these activities may have been on the threshold of the capabilities of the vessel under certain conditions, careful planning and execution by all parties enabled the project to achieve significant cost reductions and schedule flexibility over the traditional installation scenarios.

Development History

In January 1997, the Diana project kickoff meeting was held with ExxonMobil, BP and a number of outside engineering support teams to officially begin the execution of a Floating Production and Subsea Tieback System. By the end of the meeting the late breaking news of the oil discovery at nearby Hoover quickly turned the focus of the project from an execution mode to that of a concept screening. Since the team had been formed and was prepared to move ahead with preliminary engineering for the FPS, the same teams began a 4-month exercise of concept screening and selection. A number of concepts were evaluated (Fig. 4). These included:The development of the Hoover/Diana fields utilizing the Floating Production System (FPS) located between the two fields.