Evolution of Subsea Production Systems: A Worldwide Overview
- R.L. Hansen (Exxon Production Research Co.) | W.P. Rickey (Exxon Production Research Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- August 1995
- Document Type
- Journal Paper
- 675 - 680
- 1995. Society of Petroleum Engineers
- 4.2.4 Risers, 4.5 Offshore Facilities and Subsea Systems, 2.4.3 Sand/Solids Control, 4.1.5 Processing Equipment, 4.5.10 Remotely Operated Vehicles, 4.2.3 Materials and Corrosion, 4.2 Pipelines, Flowlines and Risers, 4.5.7 Controls and Umbilicals, 6.5.2 Water use, produced water discharge and disposal, 3.3 Well & Reservoir Surveillance and Monitoring, 4.5.5 Installation Equipment and Techniques, 2 Well Completion, 4.5.3 Floating Production Systems, 4.1.2 Separation and Treating, 1.6.5 Drilling Time Analysis, 4.3.1 Hydrates, 2.2.2 Perforating, 5.3.2 Multiphase Flow, 3 Production and Well Operations, 1.6 Drilling Operations, 3.1.6 Gas Lift, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 2.4.5 Gravel pack design & evaluation, 4.3.4 Scale
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This paper is SPE 29084. Distinguished Author Series articles are general,descriptive representations that summarize the state of the art in an area oftechnology by describing recent developments for readers who are notspecialists in the topics discussed. Written by individuals recognized asexperts in the area, these articles provide key references to more definitivework and present specific details only to illustrate the technology. Purpose:to inform the general readership of recent advances in various areas ofpetroleum engineering. A softbound anthology, SPE Distinguished Author Series:Dec. 1981-Dec. 1983, is available from SPE's Book Order Dept. Journal ofPetroleum Technology, August 1995.
The evolution in the use of subsea technology has seen advancement from onewell in the Gulf of Mexico in 1961 to more than 750 wells in a wide variety oflocations by the end of 1993. Along with the growth in numbers, the industryhas seen rapid advances in technology, increased distances from the hostfacility, and water depth records. This paper gives an overview of theevolutionary changes in subsea applications, with emphasis on the most activeregions and on some of the milestone installations that shaped the technologyadvance.
In the 33 years since the first subsea well was completed in the Gulf ofMexico in 1961, the use of subsea wells has spread to most offshore producingareas 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 inservice. This paper will provide an overview of subsea technology developmentby focusing on three areas that exemplify the technology used worldwide: (1)the Gulf of Mexico and west coast of North America, (2) the North Sea, and (3)the Campos basin of Brazil.
Subsea Technology Overview
Subsea wells have been used in a variety of configurations. Fig. 2 showstypical arrangements, including single satellite wells consisting of subseatrees on their individual guide bases; subsea trees on steel-templatestructures with production manifolds; and clustered well systems, which aresingle-satellite wells connected to a nearby subsea manifold. These variousdesign layouts and their hybrid arrangements are usually produced back toplatforms or to floating production vessels, although some have also beenproduced to shore. More than 50 floating production systems (FPS's) have beendeployed worldwide, with more than 30 currently active.
Maximum water depth of subsea wells has reached 3,369 ft in the Camposbasin, 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 producingdistance to the host facility is 30 miles for a gas reservoir and 12 miles foran oil reservoir, both in the North Sea. Most subsea wells have produced bynatural flow, but more than 110 wells have been produced by gas lift. Pressuremaintenance with subsea water injection wells is used where needed.
Well servicing or workovers can be performed by use of re-entry from afloating drilling unit or jackup. Also, specialized techniques, such asthrough-flowline (TFL) operations, can be performed downhole by pumping toolsfrom the surface host facility through the flowlines and down the tubing.Chemicals can be pumped into the formation through the flowlines, and chemicalscan be injected into the subsea tree or downhole by pumping from the surfacehost facility through hydraulic hoses in the subsea control umbilical. Pressureand temperature can be monitored at the tree or even downhole.
Subsea technology was first developed and used commercially in the Gulf ofMexico and offshore California in the early 1960's by various operators.Although subsea wells were installed only in shallow water accessible to diversfor many years, shallow-water diver-assist technology evolved simultaneouslywith deepwater diverless technology from the very first applications of subseawells. Much early subsea technology focused on diverless technology inanticipation of future deepwater requirements, even thoughdeepwater-exploration success was yet unknown. However, operators wasted notime in using diver-assist technology for commercial development of shallowwater fields, even though subsea technology was in its infancy. By usingsurface hardware adapted to diver-assist underwater use, subsea fielddevelopments proceeded off North America in the decades 1960-70. Subseatechnology gradually evolved as refinements and improvements were made basedupon field experience.
The world's first subsea completion was installed in 1961 at West Cameron192 in 55 ft of water. This system was designed for remote installation andoperation to demonstrate deepwater capability. Numerous TFL operations wereperformed during the 4 years that the well was produced, establishing thefeasibility of TFL technology. When the well was later abandoned, the tree wasin good condition, with no significant corrosion damage after 17 years on theseafloor.
Subsea technology development continued in the 1960's with development oftwo wells in the Grand Isle Block 16 field. Although located in shallow water,these wells were designed to simulate remote, deepwater installation andoperation. Fig. 4 shows one of the trees used. TFL technology was used on onewell to perforate, consolidate sand, and bring the well on stream with no rigintervention.
The first full-field subsea development took place in the early 1960's with20 subsea satellite wells with gas lift and multiple-zone completions producingthe Conception field to a platform offshore California. At about the same time,the Molino gas field was developed off California with 10 subsea satellitewells producing through flowlines to shore. Evaluation of a Molino tree after20 years of subsea service found that it was still serviceable and in goodoverall condition with little deterioration. Although located in shallow wateraccessible to divers, Molino trees were designed for intervention by a specialrobot called MOBOT, which was another indication of future deepwaterexpectations.
In the Gulf of Mexico, eight multiple zone subsea wells were installed inthe mid-1960's at Eugene Island 175 to restore oil production lost when aplatform was destroyed by a hurricane. Numerous TFL operations were conducted,including washing of wellbore sand back to the platform from downhole,performing sand consolidation, and cutting paraffin. Subsea maintenance wasperformed by divers in the shallow water depth of 85 ft.
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