Evolution of Subsea Production Systems: A Worldwide Overview

Abstract

This paper is SPE 29084. Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are notspecialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose:to inform the general readership of recent advances in various areas of petroleum engineering. A softbound anthology, SPE Distinguished Author Series:Dec. 1981-Dec. 1983, is available from SPE's Book Order Dept. Journal of Petroleum Technology, August 1995. Summary The evolution in the use of subsea technology has seen advancement from one well in the Gulf of Mexico in 1961 to more than 750 wells in a wide variety of locations by the end of 1993. Along with the growth in numbers, the industry has seen rapid advances in technology, increased distances from the host facility, and water depth records. This paper gives an overview of the evolutionary changes in subsea applications, with emphasis on the most active regions and on some of the milestone installations that shaped the technology advance. Introduction In the 33 years since the first subsea well was completed in the Gulf of Mexico in 1961, the use of subsea wells has spread to most offshore producing areas of the world (Fig. 1). By late 1993, a total of approximately 752 subseawells had been completed worldwide, with more than 440 of these wells still in service. This paper will provide an overview of subsea technology development by focusing on three areas that exemplify the technology used worldwide:the Gulf of Mexico and west coast of North America,the North Sea, andthe Campos basin of Brazil. Subsea Technology Overview Subsea wells have been used in a variety of configurations. Fig. 2 shows typical arrangements, including single satellite wells consisting of subseatrees on their individual guide bases; subsea trees on steel-template structures with production manifolds; and clustered well systems, which are single-satellite wells connected to a nearby subsea manifold. These various design layouts and their hybrid arrangements are usually produced back to platforms or to floating production vessels, although some have also been produced to shore. More than 50 floating production systems (FPS's) have been deployed worldwide, with more than 30 currently active. Maximum water depth of subsea wells has reached 3,369 ft in the Campos basin, 2,788 ft in the Mediterranean, and 2,245 ft in the Gulf of Mexico. Fig.3 shows the water-depth range for worldwide subsea wells. Maximum producing distance to the host facility is 30 miles for a gas reservoir and 12 miles for an oil reservoir, both in the North Sea. Most subsea wells have produced by natural flow, but more than 110 wells have been produced by gas lift. Pressure maintenance with subsea water injection wells is used where needed. Well servicing or workovers can be performed by use of re-entry from a floating drilling unit or jack up. Also, specialized techniques, such as through-flowline (TFL) operations, can be performed downhole by pumping tools from the surface host facility through the flowlines and down the tubing. Chemicals can be pumped into the formation through the flowlines, and chemical scan be injected into the subsea tree or downhole by pumping from the surface host facility through hydraulic hoses in the subsea control umbilical. Pressure and temperature can be monitored at the tree or even downhole. Subsea technology was first developed and used commercially in the Gulf of Mexico and offshore California in the early 1960's by various operators. Although subsea wells were installed only in shallow water accessible to divers for many years, shallow-water diver-assist technology evolved simultaneously with deepwater diverless technology from the very first applications