Troika Subsea Production System - An Overview

Abstract

Abstract The Troika Subsea Production System is located in the Green Canyon Area of the Gulf of Mexico, 150 miles offshore and in 2700 feet of water. Featuring an eight-well subsea manifold with five wells installed initially, Troika is designed to produce 80-100,000 barrels of oil per day to its host platform located 14 miles away in 1350 feet of water. Concern about paraffin and hydrates necessitated considerable analysis, which in turn pointed to the need to insulate the trees, manifold, jumpers, and flowlines. Key features of the Troika development are described in this paper. Introduction The Troika development is an oil field located 150 miles offshore Louisiana in the Green Canyon area of the Gulf of Mexico. Designated as the Green Canyon 244 Unit, which was formed in June, 1993, the development includes Green Canyon blocks 200, 201, 244, and 245 (Fig. 1). Troika is owned equally by BP, Shell, and Marathon, with BP serving as the designated operator. Water depth at the development site is 2700 feet. Troika features an eight slot subsea manifold with five wells installed initially (Fig. 2). The compact size of the subsea manifold permitted its installation in a novel manner using only a supply boat and the drilling rig. The Troika wells are non-TFL and have a 10,000 psi pressure rating. Production from Troika is processed at Shell's Bullwinkle platform located 14 miles away in 1350 feet of water on Green Canyon block 65. Concern about the potential to form hydrates and paraffin was a key factor in formulating the design and operating plan for the subsea production system. As a result, the trees, jumpers, manifold, and flowlines are all insulated to minimize heat loss during production, as well as to extend reaction time to manage hydrate formation potential following a shut-in. Methods used to insulate the trees, manifold, and jumpers were novel and innovative. Insulated tubing was installed in one well to facilitate start-up. Troika represents the longest multi-phase subsea tie-back system in the Gulf of Mexico. First production from Troika was successfully achieved approximately 39 months after discovery further demonstrating industry's ability to deliver fast-track development schedules in deepwater. While this paper is intended to provide an overview of the Troika project, further details may be found in the various companion papers listed in the Reference section. Development History Productive hydrocarbons were discovered at Troika in June 1994 when Marathon drilled the Green Canyon 244–1 well and found 250 feet of net oil pay in the primary S-10 reservoir. In the summer of 1995, Marathon further tested and defined the lateral and vertical continuity of the S-10 reservoir by drilling the Green Canyon 200-1 appraisal well. A second appraisal well, Green Canyon 245–1, was drilled in September, 1995 and discovered a separate, but much smaller, reservoir in a section of the Unit designated as Area 2. Both appraisal wells were temporarily abandoned. During 1995 tradeoff studies were conducted to determine a development approach for Troika, with the two leading candidate systems being a subsea tie-back and a floating production system, the latter featuring a converted drilling rig. The subsea tie-back to Shell's Bullwinkle platform was ultimately selected as it provided the most cost-effective solution based on NPV and capex utilization.