Subsea boosting is a valuable tool in the arsenal of reservoir engineers, and according to Marco Gabelloni, Aker Solutions global pump leader, the new MultiBooster multiphase unit can boost production significantly.

"The superior boosting performance means that we can produce more with one pump," Gabelloni explains. "A recent comparison with the other technologies in the market showed that we could provide additional revenues compared to the other technology that we calculated at $1 million per day of additional production.

"This also translates into a capex saving because for the same workload it would usually require two pumps. At the end of the day, it's a saving for the operator. In addition to that, it's an enabler to develop marginal fields that are located a long distance for other fields; by having such high capabilities, we can go to very long distance for subsea tiebacks."

Advantages Of Subsea Boosting
Subsea boosting systems are a very effective tool for maximizing hydrocarbon recovery. They can be utilized in a variety of applications for both brownfield and greenfield operations. For brownfield operations, they can help boost recovery where a mature field that has been producing for a long time is approaching end of life. Its production can be extended by installing subsea pumps; with these located as close as possible to the wellhead, recovery is maximized.

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They can also be used for greenfield applications, typically deepwater fields, where pumps allow operators to overcome the significant pressures in deep water. Then finally, subsea pumps can unlock new opportunities. "Think about marginal fields that are located far from other installations," Gabelloni said. "You cannot produce them simply with a tieback without any boosting because of the pressure drop over the long-distance tieback. Using a pump, you can tie those back to some existing infrastructure. Fields that otherwise would not be produced because they cannot justify the investment for a new platform or a new FPSO with subsea boosting can be developed."

Setting Ambitious Targets
Gabelloni explains that when the program was started back at the end of 2011, Aker had very ambitious goals. "The idea was to have the most powerful subsea pump in the industry, with the best pressure generation capability, and also, we were urged by our partners to implement an advanced condition monitoring system," he said. "Then we wanted to have a platform, a modular and scalable design that would cover the full range of duties from low, medium power up to the 6 MW flagship version.

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"Finally, we wanted to implement all the lessons learned over the years. We have more than 100,000 hours in our fleet of pumps. We want to make sure that all the experience from this fleet of units could be implemented in this program. We choose very robust technical solutions based on all these lessons learned.”

For condition monitoring, Aker made a step change in its sensor philosophy. The industry standard today is to measure the vibration of subsea pumps with sensors located on the outside of the pump casing. "For this pump, we decided to go one step further," Gabelloni said. "We have introduced proximity probes, which are located inside off the pump casing. Those probes can measure the position of the pump rotor very accurately with any radial displacement or axial displacement. In this way, we can incorporate all this data into the customer's monitoring platform to be able to judge the health of the unit more accurately."

Long Heritage In Subsea Pumps
Aker Solutions, in its various guises, has a long history of developing pumps at the Tranby facility. "We started manufacturing topside pumps in the middle of the '70s with more than 1,000 topside pumps delivered from what at the time was Kvaerner and then Aker Kvaerner, now Aker Solutions," Gabelloni said. "We were pioneers in the field of subsea boosting with the first Kvaerner booster station in the middle of '80s.

"We have been developing and building subsea pumps for commercial operations since the turn of the century. We have now delivered several projects for water injection, compensate boosting, and if you take all the systems, they have accumulated more than 100,000 of operating hours."

Three prime examples of that innovation are on display at Tyrihans, Ormen Lange and Asgard. For the 30-km tieback at Tyrihans, Aker supplied a subsea raw seawater injection system that included two 2.7-MW pumps. At the time it was the most powerful subsea pump installation in the world. For the Ormen Lange, it was a full-scale pilot system for subsea compression and boosting. Then in 2015, it installed the Asgard subsea compression and boosting system, which includes two condensate pumps.
 
Passing The Test
The latest landmark came last year when they finalized the qualification program for the MultiBooster. "This has been a long process," Gabelloni said. "We developed a completely new subsea motor and multi-phase hydraulics for this pump. We tested all those components separately, and then we did a system test including the pump, electric activator and vectors control system, which was completed at the end of last year.

"We achieved technology readiness level five last December. We achieved this with the support of several key companies in the oil industry who joined the program at different times, but their contributions were significant. They gave us input on the requirements for their field. They gave us input on the experience they have from the operation of a similar type of a system."

Gabelloni said to date the results have been excellent. The pump was on test for more than 1,660 hours last year. During that time, the company measured more than 2,500 operating points and ran the pump for more than 300 million rotations of the pump.

"The performance has been outstanding, we can say best in class because we were able to generate more than 250 bars increase in pressure at 60% of gas, oil, and water, which is unparalleled in the industry."

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