Subsea processing is the concept of gradually moving the entire topside processing facilities to the seabed. Many subsea fields would create better financial returns for their owners if subsea processing were installed due to increased recovery. In some cases, subsea processing is a prerequisite for making developments economically viable at all. By moving the processing of the well flow from the topside to the seabed, projects previously deemed non-commercial may become economically viable, and one may also increase the recovery rates on existing fields.
Currently, Petrobras, Statoil and the Majors are driving the developments behind subsea processing, together with the equipment manufacturers. These operators have the biggest potential and may sustain a market before smaller operators catch on. Subsea processing encompasses a large array of technologies and systems, but there are mainly four technologies that have been implemented by the industry so far; boosting, separation, water injection and compression.
Subsea boosting is the application of subsea pumps to “boost” the pressure in the well stream. The main advantages of subsea boosting is accelerated production, increased production & recovery, development of low energy reservoirs, heavy oil fields, long tiebacks and other fields where pressure differentials might be an issue.
The first subsea booster pump was a twin-screw multiphase pump developed by GE Oil & Gas, which was installed on Eni’s Prezioso field in Italy in 1994. Since this first installation in water depths of 50 meters, the technology has continuously been taken deeper. The Cascade oil field in the Gulf of Mexico is currently the deepest subsea boosting system installed, at a water depth close to 2,500 meters, and Shell is currently contemplating booster pumps at its Stones development in 2,900 meters. Although GE was first, it is OneSubsea (through Framo Engineering) that has become the market leader, capturing most of the market with their helico-axial pumps. Today, the booster technology is by far the most mature of the subsea processing technologies.
Booster pumps are mainly used on oil fields with low gas to oil ratios, both for heavier and lighter crudes. The key regions have been, and will continue to be, Brazil, the US Gulf of Mexico, the North Sea and West Africa due to the water depths, reservoir characteristics and tie back distances.
Subsea separation is the concept of separating gas/liquids or oil/water at the seabed. Such systems bring solutions to flow assurance challenges such as hydrates and slugging, enables viability of challenging reservoirs, prolongs economic lifetime of fields, debottlenecks flowlines, risers and topsides and handles water and sand at the seabed, thereby reducing the potential costs associated with a topside facility. Many of the installations have been in conjunction with booster pumps, and subsea separation is today a proven technology. Whilst OneSubsea has taken the lion’s share of the booster market, it is FMC Technologies that has become the market leader in the separation segment, being system provider on the majority of projects completed.
While there has been some experimentation on subsea separation systems prior to the 2000s (Zakum 1965, Highlander 1985 and Argyll 1986), most people regard the Statoil Troll C pilot on water separation and injection in 2001 as the first modern subsea separation unit. The Troll system was installed in 340 meters of water depth, 3.5 kilometer from the platform. Today, it is Shell’s Perdido field which is the deepest application of subsea separation at approximately 2,500 meters. Subsea separation systems have now been installed at 11 fields operated by Petrobras, Statoil, Shell and Total. All the fields lay in Brazil, Norway, US GoM or Angola, and going forward these areas, including the rest of the North Sea and West Africa, are seen as the primary markets for such systems.