Subsea Production Systems - Trends in the Nineties

Abstract

ABSTRACT This paper describes recent subsea production system experience, with focus on cost reduction trends which are expected to continue throughout the remainder of the decade. First, the system configuration trend from large, heavy, multi- well integrated drilling template and production/injection manifold systems to small, lightweight, "minitemplate" systems or clustered well manifolds with individual satellite wells is addressed. Second, several equipment technology trends are addressed including towed flowline bundles with integral manifolds, development of improved reservoir management/data acquisition tools, subsea pressure boosting to extend the reach of subsea systems, emergence of the rental tool market and "tool pools", "horizontal" trees for certain applications, and standardization of subsea components and interfaces. This paper concludes that subsea production systems have successfully demonstrated their overall reliability, and have established a proven track record over the past thirty years of field experience. System configuration and equipment technology trends in the nineties are now improving the profitability and capability of subsea production systems. Subsea production system examples are cited along with generic costs to illustrate the effectiveness of these cost reduction trends. SYSTEM CONFIGURATION TREND Introduction The first "modern" subsea production systems, pioneered in the early 1960's, were developed with single satellite wells and trees tied back to host facilities with individual flowlines and control umbilicals. Many of these trees were extensions of existing land and platform tree designs, and were"marinized" for use underwater; however, several of these trees incorporated technology specifically designed for subsea applications. Flowlines and umbilicals were connected to the subsea trees with extensive use of air and saturation diving techniques. Although these pioneering subsea production systems were successful in their own right, their applicability was somewhat limited. Individual satellite well flowline and umbilical costs would be prohibitive for multi-well developments with relatively long distances back to the host facilities. In addition, technology at that time would not allow for deepwater subsea developments beyond diver depth limitations. In an effort to minimize the flowline and umbilical costs, a shift in system design philosophy emerged in the late sixties/eady seventies to commingle the produced fluids by way of subsea manifolding, as well as to distribute hydraulic and electric power/signals with subsea controls distribution trunking. In addition, designs were developed for diverless pull-in and connection of subsea flowlines and umbilicals, so that subsea production systems would be applicable for Potential deepwater developments. Figure 1 illustrates the flowline and umbilical cost difference between a generic satellite well system with individual flowlines and umbilicals, versus a manifolded subsea production system for a typical North Sea development 10 km from the host facility. Large, Heavy Integrated Template/Manifold Systems The very first integrated drilling template and production/injection manifold system was Exxon?s Submerged Production System (SPS), which was installed in the Gulf of Mexico in 1974. Because the SPS was a pilot test for future deepwater applications, all underwater operations were designed for diverless intervention, even though it was located in only 52m of water. Diverless operations included flowline and umbilical pull-in and connection, as well as insert valve.