Subsea Technology. Hydrocarbon Extraction as a Key Factor in Developing Resources of the Arctic Shelf

October 10, 2011

   At the same time, the experience gained in developing the North Sea and the Beaufort Sea shows some active development of the subsea technology and tretment of the offshore downhole products.  The country’s scientific potential should be actively involved based on international expertise for the development of subsea technology in Russia.

   The technology of HC subsea conditioning significantly enhances the flexibility in the production of well fluids. Major private operators, such as Shell, Exxon, Total, BP, Woodside, Statoil and Petrobras, hold the leading positions in the promotion and application of new developments in subsea technologies for injection and well fluid treatment. Partially state-owned companies currently at the forefront worldwide, such as Statoil and Petrobras,  have been actively encouraging the development of the entire domain of submarine technology, despite the potentially high risk of investing into new developments. The interaction between the subsea technologies for fluids  treatment and injection, as well as their classification are shown in Fig. 1.
Having suceeded to create her national innovation system and make it simultaneously a part of the global one, Norway was able to ensure that the foreign corporations operating on the local market would localize their technologies inside the country and hand them over to the Norwegian research institutions.

   Subsea field development is regarded as the most promising trend to develop fields in both frozen and unfrozen seas, using the subsea versions of the equipment for treatment and injection of fluids which include multiphase pumps, separators, compressor units and drilling rigs.

Subsea Multiphase Pumps

   To date, the application of multiphase pumps (multiphase pumping – MPP) has become a real and viable solution for the efficient transfer of multiphase gas-liquid flows from the seabed wells across the flowlines and risers to the platform topsides or onshore facilities.

   Several types of pumps were developed that are used in the deepwater offshore oil fields in Alaska and in the fields of the Gulf of Mexico, South America and Australia.

   The spiral-axial multiphase pumps can handle large amounts of downhole products being superior to the rotary pumps in terms of gas-oil ratio, and the piston ones for performance.

   One of the latest developments is the High-Boost MPP made by Framo featuring the capacity of up to 1,600 cubic meters per hour at a discharge pressure up to 20 MPa that can operate at a gas ratio of up to 95 percent, which is a breaktrhough technology for potential development at the depths of 2-3 kilometers.

   The twin screw pumps manufactured by Bornemann, Flowserve, Nuovo Pignone, etc., became widely popular to be mainly used for pumping the wellstream with a high content of the gas phase. These pumps belong to the category of positive displacement and remain productive even under the volumetric content of the gas phase of up to 95 percent.

   Recently, Bornemann made a significant leap forward in the development of the subsea multiphase pumps. For example, in 2007, BP broke two world records simultaneously, in depth (1,700 meters) and the distance from the platform (29 kilometers), having installed two Bornemann MPC-335 deepwater subsea pump at the King field in the Gulf of Mexico.
The main drawbacks of today’s multiphase pumps include low (30 to 50 percent) efficiency of the plants. However, the ongoing improvements to the multiphase pumps, carried out since the 1990s, allows one to hope for substantial progress in the coming years given that the current efficiency of centrifugal pumps reaches 60-70 percent or 70-90 percent for compressor pumps.

Underwater Separartors

   Originally intended for use in the development of small coastal deposits in the North Sea, they then found application in the fields with existing platforms from which you control the work of underwater systems and provide them with energy.
The world’s first real operating plant for subsea separation of the formation’s products  and injection of separated water back into the formation is installed at the Troll field, 80 kilometers away from Bergen. The system includes a horizontal gravitational separator, where the hydrocarbon flow is separated into gas, oil and water.

   The subsea reservoir products separation plant, in addition to the multiphase pump and separator, includes the wellhead assembly for injection of stratal water into the reservoir and the manifold for the distribution of well flows.