Subsea separation to debottleneck Marlim production
The giant Marlim field in Brazil’s Campos Basin has received the world’s first deepwater subsea separation system for heavy oil that includes reinjection of the removed water to maintain reservoir pressure in a mature field. The system, supplied by FMC, is expected to increase oil production at Marlim by debottlenecking separation equipment aboard the host FPSO.
Typical mature field issues
Production began at Marlim in 1991. It is Petrobras’ largest field in the Campos Basin and was at one time considered the world’s most extensive subsea development. The challenge now for Petrobras is to extend Marlim’s productive life and maximize ultimate oil recovery. Two factors that reduce production at most aging fields are occurring at Marlim: declining reservoir pressure and increasing amounts of water in the production stream. The challenge at Marlim is complicated by growing sand production and the viscosity of the oil, a heavy API 19°.
Selecting the subsea solution
Petrobras could have addressed this problem in the traditional way by expanding Marlim’s existing separation capacity. Such an approach, however, would still have required lifting large volumes of unwanted water and damaging sand to the surface. Removing the water and sand at the seafloor eliminates this inefficiency and opens up large volumes of oil processing capacity aboard the FPSO. Reinjection of the separated water further benefits production by helping to maintain reservoir pressure.
The FMC subsea separation, pumping and reinjection system is installed at a water depth of 2,950 feet. The system receives the raw production stream -- a mixture of oil, gas, water and sand -- and first separates the gas from the liquids. The water is then removed from the heavy oil using an innovative pipe separator design that was licensed and developed in cooperation with Statoil. The separation module is retrievable to the surface, making its maintenance and replacement less costly and disruptive. The system also incorporates FMC’s proprietary InLine HydroCyclone and DeSander modules for water treatment and sand management. The separated gas is added back into the dewatered oil stream and sent to the platform, while the treated water flows through the pump module which boosts it for injection into the reservoir.
Large potential benefits
In addition to raising efficiency at Marlim and increasing production, subsea separation should also extend the life of the aging field, which in the case of Marlim is 20 years. With an estimated nine billion barrels of oil originally in place, even a relatively small percentage increase in Marlim’s ultimate recovery amounts to a large volume of oil. For example, a one percent increase would result in 90 million additional barrels, and a four percent increase would equate to 360 million additional barrels.