Page 95: of Offshore Engineer Magazine (May/Jun 2014)

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The gas pressure pump during proof of concept

Subsea testing. Photos from Aker Solutions.

is reduced in size and weight, we do not need the

VSD subsea, we don’t need the barrier fuid and related auxiliaries for the pump, and the cable cost can be reduced by using the RotoConverter unit. “The modular design with three small units means they will be easy to install, retrieve and change as necessary during feld life, as part of a building block strategy. We strongly believe these technologies unlock new possibilities for smaller gas accumulations and felds that currently cannot be exploited with existing technologies.” testing, to make sure there is no issue with sand accumulation.

RotoConverter

To address the issue with transmission of AC power over long distances Aker

Solutions has been developing a step-up device which is called the RotoConverter.

Gabelloni says, “typical loads in subsea is designed in the initial phase of the gas compression require quite high fre- project. quency to match the compressor rotating “On an active cooling system, we speed— up to more than 10,000rpm. But use forced convection cooling, with a transmitting power over long distances small subsea pump to push the seawa- with high frequency is limited due to ter through the cooler. The design is charging currents. Therefore we need similar to Åsgard, but with additional low frequency transmission, then locally, walls around the cooler and some baffes close to the compressor, we can have a inside, to increase the heat exchange. The frequency step-up device.” main beneft is the increase in the heat The RotoConverter consists of a motor transfer coeffcient, so we can reduce the and generator coupled together with a weight and the size of the module,” he different number of poles. “In this way explained. Aker Solutions is currently in we can increase the frequency to match the concept selection phase on the cooler. the requirements of the compressor,”

Gabelloni says.

Gas pressure pump “This is a proven concept and has “The challenge with current systems is been used in the industry for a number of that the subsea pumps needed for the years. Our program is to further develop liquid part of the well stream require the this for subsea use. We are planning to use of barrier fuid, with related tub- have an enclosure that will be oil-flled ing, and, in the case of a long step-out, with a pressure compensator, which a subsea variable speed drive. Also, in will allow the system to be installed some cases, when we have a small liquid in deep water. With this device, we content in the wellstream, we need to can remove the need for subsea VSDs, re-circulate most of the fow to allow the enable more power to be transmitted at pump to operate. longer distances and enable better cable “To overcome these issues, we are performance.”

Aker Solutions is moving to the developing a gas pressure pump. It uses proof-of-concept test phase, with plans pneumatic transport by leveraging the gas to test a small scale 50kW unit. coming out of the gas compressor outlet.

We use two vessels, and a set of axial

Simplifcation valves, which control the gas from the compressor. The two vessels are emptied “When targeting small gas felds, the alternately. The benefts are that we do need for a compact and simplifed sys- not need barrier fuids or any dedicated tem is quite clear,” Gabelloni says. “We www.mustangeng.com power supply.” are using fewer and smaller components

The company has completed concept with a long track record topside. That selection and is moving into a proof- helps to maximize the production and of-concept test phase, including sand provide a reliable solution. The system oedigital.com May 2014 | OE 97 094_OE0514_Subsea2_Aker_New.indd 97 4/19/14 8:39 AM