Dry Subsea Production Systems: Garoupa-a Case History

Abstract

Introduction Subsea one-atmosphere chambers for early petroleum production schemes or for wells beyond the reach of platforms have been in commercial use for several years. Such chambers are onstream in the Gulf of Mexico and offshore Brazil for Shell, Union Oil, Tenneco and Petrobras. This paper begins with a brief description of equipment experience with dry production system hardware supplied by Can Ocean Resources Ltd. (formerly Lockheed Petroleum Services) and installed in the Gulf of Mexico, and an outline of the impact on one-atmosphere technology for deepwater applications. The major and concluding part of the paper describes the Garoupa production system installed offshore Brazil for Petrobras. This system is one of the most ambitious undertakings of its kind and, therefore, a noteworthy case history of dry, subsea production technology. An over-all system description, key hardware descriptions and installation of the major subsea components are included in the paper. System commissioning and start-up progress to the end of February 1980 is described and some of the problems encountered, their solution and their impact on the project schedule are discussed. Introduction Every dry, one-atmosphere chamber has two basic functions in common: to isolate the equipment it contains from the subsea environment, and to allow trained oilfield technicians access to that equipment for installation and subsequent servicing. The first chamber (Fig. 1) was installed to produce oil from a subsea well in 114 m (375 ft) in the Gulf of Mexico by Shell Oil Company. At that time (mid 1972), it was the deepest producing subsea completion in the world. This single satellite well is still in production. A flow line carries well production to a nearby platform in shallower water. The one-atmosphere wellhead, called a wellhead cellar (WHC), encloses the Xmas tree, the hydraulic control package, and includes a flow-line connection port: A typical connector port is shown in Figure 2 during land tests for fitting the flow-line termination (bullnose) into it. A one-atmosphere servicing system (Fig. 3), consisting of a tethered diving bell, known as a service capsule, and surface support vessel (SSV), provided for personnel transfer to subsea chambers. The service capsule is rated for 365-m (1,200-ft) water depths and enabled work to be performed subsea on a 12-hour shift to set the Xmas tree, connect the flow line, and conduct final equipment preparation and checkout before well production start-up. Shell Manifold Center System In August 1975, Shell Oil Company successfully installed, in the Gulf of Mexico, an encapsulated subsea manifold center (MC) designed and developed by CanOcean. Figure 4, illustrates the part played by the MC in the subsea scheme. The 1-tonne MC (Fig. 5), with a chamber size 9.2 m (30 ft) long and 3.7 m (12 ft) in diameter, was designed to handle production from three wells in the Eugene Island Block 330 field. After installation in 74 m (240 ft) of water, and connections by flow line to satellite subsea wells and the adjacent platform, production commenced in August 1976.