Deep spill skimmer plan

Although there would be no chance of building such a leakage collection system in time to be of help at Macondo, Axel Jaeschke, head of Bornemann’s subsea research ­division, is promoting the idea of a joint industry project to evolve equipment that could be held on standby in readiness for any ­future spill.

“Of course, I hope it would never be used,” said Jaeschke, “but there has to be an industry back-up plan in case an accident like this happens again.”

He reckons that a concerted effort could produce a proven ­system in six to 12 months.

In an immediate emergency, he estimated it would take perhaps one or two months to pull something together that would work for a short period.

Bornemann claims to have extensive experience in supplying twin-screw pumps for boosting multi-phase mixtures of oil, gas and water, and has been involved in subsea applications of this technology since 2000.

The company’s concept for an oil leak collection system — which it has named “subsea skimmer” — centres on its existing SMPC series of twin-screw subsea booster pump and motor, with a lower collection cone added.

The whole assembly would be suspended from a surface vessel, or more likely manoeuvred into position, and clamped onto a structure sited at the leak with the assistance of remotely operated vehicles (ROVs), said Jaeschke. Also, if possible, a short lance or “snorkel” pipe would be inserted into the leaking pipe to draw off as much hydrocarbon as possible before it emerges from the pipe.

This is a principle already adopted in the Macondo oper­ations, where BP has used a so-called riser insertion tool.

The aim is to reduce the ­pressure of hydrocarbons flowing inside the leaking pipe to below ambient level, so that very little emerges. “A good compromise will be a combination of snorkelling from inside and collecting the remaining leakage outside,” said Jaeschke.

Because of the changes that ­occur in the emerging hydro­carbons as they meet and mingle with seawater, the nature of the fluid that has to be handled by the skimmer device could be extremely varied. In particular, deep cold water is highly likely to trigger formation of an ice-like mass of sticky hydrates that can quickly clog pipework. It was hydrates that thwarted an early attempt by BP to tame the Macondo spill.

Jaeschke is unperturbed by ­hydrates as far as the handling capabilities of Bornemann’s pumps are concerned. “We have long experience with twin-screw technology and we are not afraid of hydrates when they enter the rotors, The pumps can handle them perfectly,” he said.

“Also, emulsions are our daily business, and we are used to running with up to 95% gas fraction,” he added. “The pump/motor is virtually approved equipment already.”

However, hydrates could definitely disrupt operations if they build up and block an inlet funnel. So a study of how hydrates behave in free water in the inlet dome would form an important part of planned joint industry project work.

Although heat generated by the pump/motor is typically a problem to get rid of, here it could be a useful supplement to the injection of inhibitors in the fight to prevent build-up of hydrates.

Another major challenge for a joint industry project to tackle is the installation process, said ­Jaeschke. “To hang a pump from a vessel and place it by ROV above a leakage point — that has a lot of unknowns. We have to build up ideas about how to fix a pump there.”

Other areas of study involve aspects such as the flexible pipeline needed to take the pumped mix to the surface, and the power cable. “We need to have everything available on drums and installable on any supply boat to make sure we could be ready within three or four days.”

Jaeschke estimates the cost of such a joint industry project “in the range of $10 million, including building at least one prototype and some handling tests in really deep water”.

“The technology is available and all components are more or less approved,” he said. “Now the concept needs review by subsea experts in the industry.”