A Subsea Control System for Phase 1 Development of Garoupa Field
Authors: Carman R. Jan , McAdams J.P. , Vilarinho S.H. 
Published: December 2007

This paper discusses the development, design, and testing of an electrohydraulic control system for offshore subsea oil production. Both microprocessors and minicomputers are used in the subsea and surface equipment. Backup electronic and hydraulic subsystems will achieve long-term operation with minimum maintenance.

Background

The Phase 1 Garoupa Field development project has been described previously,* but the background is summarized briefly here.In 1975, Petroleo Brasileiro S.A. (Petrobras) formed a special engineering task force (ASCAM) within the Dept. of Exploration and Production to develop and produce the resources of Garoupa Field. This area is produce the resources of Garoupa Field. This area is located about 50 miles (81 km) offshore Rio de Janeiro state at a water depth of about 150 m.Field development was planned in three stages: Phase 1 would produce nine exploratory and field delineation wells as quickly as possible to help ease Brazil's energy shortage; Phase 2 would build a permanent production system; and Phase 3 would expand the facilities and lay pipelines to shore. pipelines to shore. An engineering review committee was created by ASCAM to write the control system specifications and to review periodically and modify the specifications as required during the engineering design and early manufacturing stages. This committee consisted of engineering representatives from Petrobras ASCAM, Cameron Control Systems, and Lockheed Petroleum Services Ltd. Lockheed was chosen to supply the subsea, dry, 1-atm (101-kPa) chambers. Cameron Iron Works Inc., Cameron Control Systems, based in Houston, was selected to supply the control system for operating the subsea production equipment.

System Description

The control system elements are located in three separate areas:process tanker,manifold center (MC), andin each of nine wellhead cellars (WHC).

Fig. 1 illustrates the system layout. The process tanker is moored permanently to an articulated tower by a swivel joint-and-yoke assembly located at the top of the tower. The tower and yoke provide support for two 10-in. (25.4-cm) flowlines, one 2 1/2-in. (6.4-cm) gas-lift line, one 4-in. (10.2-cm) test line, two 1-in. (2.54-cm) hydraulic control lines, and a composite electrical cable that connects the process tanker with the subsea MC. The MC is located about 800 m from the production tower. Nine subsea WHC's are spread throughout the production field at distances of about 1 to 7 km from the production field at distances of about 1 to 7 km from the MC. Each WHC is connected to the MC by one 4-in. (10.2-cm) flowline, one 2 1/2-in. (6.4-cm) gas-lift line, a 1-in. (2.54-cm) hydraulic control line, and a composite electrical cable. Each WHC contains a single completion Christmas tree with hydraulic fail-safe valve operators, manual master valves, and a scraper-launching system. The flowlines can be swept clean from the WHC to the tower by way of the MC. The cleaning sequence is operated by the subsea control system. Control equipment on the process tanker is located in two areas:a hydraulic pump-accumulator and control valve unit in the foredeck area, andthe control panels, computer console, and the uninterrupted electrical power supply system in the control room on the midship bridge.

JPT

P. 398