A commercial version of a subsea booster designed to improve production of fluids containing both liquid and free gas is expected to be made available next year by Aker Solutions and its JIP partners. Jennifer Pallanich talks to Aker's Christian Abelsson about the enabling technologies that made the HybridBooster possible.
Fluids entering Aker Solutions' HybridBooster initially pass through newly developed mixed flow stages. Here, the mixed flow stages compress the gas to a reduced gas volume fraction (GVF). The fluids then move to the second stage type, based on Aker Solutions' LiquidBooster technology, which delivers the final boost.
Christian Abelsson, project manager at Aker Solutions, says the company's first step in 1Q 2008 was to design a gas-tolerant stage technology that could deliver a high differential pressure while handling a substantial amount of free gas.
Aker Solutions modeled and simulated several concepts before choosing two for testing.
The company tested the two competing concepts in a one-stage pump in early 2009. The winning concept from that trial moved into the third phase of development, which was to build a multistage full-scale pump and an extensive test program at the company's Tranby technology and manufacturing facility in Norway. In September 2010, Abelsson says, the pump delivered ‘some exciting results'.
The targeted results of a differential pressure of 200 bar and 20% GVF were exceeded. During testing, Aker Solutions says, the prototype delivered above 200 bar up to a GVF of 40%. All in all, the pump could handle up to 64% GVF, the company says. ‘We exceeded our target by far,' Abelsson says.
The semi-axial impellers are designed with a smooth pressure increase to reduce the tendency for phase separation as the fluids pass through the blades on the way to the diffuser; the impeller also has an internal mixing feature. ‘Internal mixing is the key to success of this impeller technology,' Abelsson says. ‘It prevents gas blockage' which can cause vibrations and lost prime. During testing, the pump was equipped with a number of sensors for measuring many aspects of the fluids and the unit itself, from suction and discharge properties to internal pump properties such as keeping track of the temperatures, pressures, and vibrations to recording torques and flow rates. ‘It was heavily instrumented,' Abelsson says.
The nine-stage pump design features two gas-tolerant semi-axial stages and seven LiquidBooster radial stages. The impellers are stacked in an opposed impeller arrangement for axial force balancing for stable pumping performance under varying gas and liquid conditions. The stackable design allows it to adapt to various field conditions, and Aker Solutions says it can arrange a pump individually to meet field-specific demands.
Field characteristics determine the stage count and number of mixed-flow stages in relation to radial stages.
Aker Solutions and the other Hybrid Pump JIP partners – ExxonMobil Upstream Research, Nexen Exploration Norway, Statoil, Total E&P Norway and Norway's Demo 2000 research initiative – are working to finalize the design for a commercial launch next year. Aker Solutions has been working on the final engineering that is required to fully qualify the pump, Abelsson says, and a subsea version of the HybridPump is next on the drawing board.
The subsea HybridBooster will be designed for use in water depths to 3000m. According to Abelsson, it makes sense to use the HybridBooster in developments with deeper waters and complex reservoirs, those with long subsea step outs, those where increased oil recovery is needed from mature fields, and those where costs must be kept low while the equipment used increases a field's economy.
Aker Solutions also plans to use the ‘promising' impeller technology with the company's ongoing MultiBooster technology development, he adds. OE
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