Rethinking subsea pumping

GE Oil & Gas is set to offer a new, compact take on multiphase subsea boosting. Elaine Maslin reports.

Image from GE Oil & Gas.

By the end of this year, GE Oil & Gas hopes to make great strides towards having a new weapon in its armory. The firm is developing a multiphase, modular contra-rotating pump (MCP) under a joint industry project (JIP) that includes majors Total, Shell, Chevron and Statoil.

The concept draws on expertise from across GE’s turbomachinery and aviation businesses, as well as making use of the GE Store concept, which leverages the firm’s global research teams’ combined knowledge. The MCP concept is also being pursued through GE’s FastWorks approach – a fail-fast mentality of technology development, designed to help accelerate innovation.

The MCP, as the name suggests, comprises of contra-rotating impellers, which are spun around a shaft on process lubricated bearings, with each impeller, or stage, driven independently by a shroud of permanent magnet motors.

One of the main benefits of the design is that it doesn’t need barrier fluid and is all-electric, which means it can be compact and doesn’t need hydraulic lines, so umbilicals can be simplified for power and communications, says Alisdair McDonald, business leader, Subsea Power & Processing, GE Oil & Gas. It also doesn’t need topside hydraulic power units or variable speed drives, etc. Rotor dynamic issues are avoided as a result of the static shaft and, because the impellers are contra-rotating, they’re more efficient than conventional systems that use diffusers. The set-up takes up less space, too.

Each stage is powered independently, which means there’s no limitation to the number of stages that can be added, although of course there would be a practical limit, McDonald says.

“For brownfields, where you want to pump late in life and don’t have topside space for variable speed drives, hydraulic power units, etc., the MCP is an enabler,” McDonald says. “Because of its compactness, its weight is much lower. We compared a conventional 15,000 psi multiphase pump with the MCP and it was 50% lighter, with the potential for up to a 50% reduction in topside footprint. We think it could be 20-30% cheaper than a conventional multiphase pump over life-of-field.”

Because of its modularity, the MCP could be used in different ways, McDonald says, either by having a number of units, each with its own variable speed drive, tied into a hub, as a distributed system, with one power and communications umbilical, or dedicated boosting systems on shore tied back to individual wells.

“I can imagine a 1.5MW MCP on an individual well,” he says, comparing the system to an electrical submersible pump (ESP). “Reliability is going to be much higher [than an ESP]. But, the system is really competing against conventional mudline multiphase pumps.”

The concept for the pump was first unveiled in February this year, at GE’s annual meeting in Florence, at which point Statoil and Total joined as initial phase partners. Since then, Chevron and Shell have also joined and an initial three phase demonstrator is being assembled at GE’s facility in Bari, Italy. It is due to be validated through a series of tests by the end of this year.

“It’s exciting because when we complete this project, the final product might not look exactly the same as it does now. Any learnings can be applied to the turbomachinery business, etc., and across other product companies within the GE portfolio,” says McDonald.

The idea was developed after discussion between engineers based at GE’s turbomachinery business, where work was underway on a conventional pump, and the aviation business. Inter-business unit collaboration is encouraged through the company’s GE Store concept, which seeks out cross-pollination to drive technology breakthroughs, supported by scientists, engineers and researchers from across eight GE Global Research Centers.

“It’s either a technology push or application pull that brings our teams together,” McDonald says, “leading to a scenario whereby ideas and innovation can be shared and capitalized on across GE’s different businesses.”

The FastWorks methodology should also help rapid prototyping. “The FastWorks methodology is fail-fast, spend the minimum amount of money to develop a minimum viable product and test leap of faith assumptions,” McDonald says. “If those assumptions are validated you go to the next stage. If it is not successful, you pivot and take a different approach or persevere. You’re running it like a small startup business. But, one of the key things is that the customer is involved in the development process. They (Total, Chevron, Statoil and Shell) have a lot of operational expertise and, as part of the JIP, are integral to the decision-making process. We’re not creating something in a vacuum, we’re creating something essentially approved by the operator.