DPS Confronts Subsea Processing Complexities

19 October 2008 (Last Updated October 19th, 2008 18:30)

The development of processing technology for the subsea and deepwater sector could prove instrumental to the future shape of the industry. Alex Hawkes looks into the latest discoveries.

DPS Confronts Subsea Processing Complexities

As global demand continues to spiral, oil and gas exploration is being forced further down into deep and subsea reserves. For process engineering groups such as DPS, this has led to a period of vital innovation in subsea processing technology and applications.

With its headquarters in Bristol in the south-west of England – a city famed for its association with pioneering Victorian engineer Isambard Kingdom Brunel – DPS has accumulated upstream and downstream expertise covering many aspects of process, design and supply. Today the company operates globally, with offices in locations including Australia, the US, Nigeria, India and Malaysia.

The research and development of new and existing technologies encompasses subsea oil pressure boosting systems and bulk water separation, through to gas compression and flow assurance solutions. For DPS chairman David Parkinson, the field has proved fruitful.

"Our background lies in new, patented technologies. We have grown considerably in recent years and are now some 250 employees strong, with about 110 each in Bristol and Malaysia. We are now embarking on a period of consolidating, educating and innovating," says Parkinson.

"Oil and gas exploration is being forced further down into deep and subsea reserves."

In his opinion the UK needs to innovate if it is to remain an industry leader. "The UK market can no longer rely on manufacturing as it is becoming too expensive and the rest of the world is catching up in terms of engineering standards. If you look at our North Sea, there are about 100 wells or fields that are yet to be developed, which we now have the technology to address. A new heavy oil refinery is being constructed in Great Yarmouth, which is why our focus is also fixed on heavy oil and developing technology with our own oil before taking it around the world," says Parkinson.

Under pressure

Heavy oil production in deep water is not without its complexities. To address some of these, DPS aims to produce new-generation cyclonic centrifuges for water treatment and oil dehydration, desalting and desulphurisation.

This led DPS to confront the matter of subsea pressure. By boosting subsea oil pressure it is possible to carry out ultradeep light oil production and deep heavy oil production, and to increase recovery for deep light oil.

In all of these instances, the back pressure on the wells from the riser’s hydrostatic head can be reduced or eliminated.

Although most reservoirs can produce to the sea floor, ultradeep fields can become near to hydrostatic pressure and cannot produce to the sea surface under their own pressure. So subsea pressure boosting becomes a vital tool for oil recovery.

Subsea pressure can be induced by excessive produced water, which has been trapped in underground formations and is brought to the surface along with oil or gas. This leads to the need for bulk water knockout at the sea bed.

"Bulk subsea water can be used to de-bottleneck risers and water processing capacity where topside bottlenecking cannot be accomplished, enabling additional production at existing systems or an increase in producing wells. Bulk subsea water separation without solids handling is proven for relatively shallow water depths and easily separated oils," Parkinson says.

Consequently, DPS has designed a patent applied-for bulk water knockout separator. "The separator can pump the oil-rich stream to the driving port of a specially designed jet pump. This in turn inducts the free or evolved gas from the separator and boosts its pressure while reporting to the first-stage separator of the process plant, or reducing the hydrostatic end acting on the riser or the well," says Parkinson.

"Use of such a separator system will allow bulk water out to be retrofitted to process systems suffering high water cuts. It will also allow solids to be managed on the sea bed or at the process topsides with the ability to recover pressure burn while increasing apparent G-forces," he adds.

Strokes in motion

Complementing the bulk water separator, DPS has also recently revealed its Rotary Cyclone Unit (RCU) patent. The RCU is designed to utilise differential pressure control in order to meet the requirements of subsea separation phases. This includes separating solids from liquids including light, small and soft solids created by chemical or electrical flocculation methodology, oil from water, rag layers or emulsions and evolved gas.

Marketed as having the combined benefits of a cyclone and a centrifuge type separator, the RCU has recently entered its first pilot testing. Along with the bulk water knockout separator, the new British patents are being manufactured and tested in the US.

"DPS owns a manufacturing company in Louisiana and an office in Houston. So this is US technology that happens to be British patented," says Parkinson.

"We hope these patents will attract new business for DPS. The US is a good manufacturing base, although the industry there is more geared towards fixed and onshore structures then offshore," he adds.

The company also benefits from the twinning of its home city with the Chinese city Guangzhou. DPS believes the partnership offers the company a distinct opportunity to infiltrate the Chinese market and make use of its growing interest in offshore technology. "The twinning makes companies in China more aware of us then they would otherwise have been and allows for increased cooperation. It also allows us to apply a degree of political pressure as well," says Parkinson.

A game of Gulf

DPS also hopes to incorporate the new technologies in its future project management activities. As part of its involvement with the deepwater market, the company secured a significant Engineering Procurement Construction (EPC) for the crude stabilisation and flare modules on Petrobras’ potentially record-breaking Floating Production, Storage and Offloading (FSPO) facility at the Cascade and Chinook development in the Gulf of Mexico.

The FPSO is set to be installed in water depths of up to 2,600m. According to BW Offshore, which is contracted to convert, install and operate the ship, this puts it among the world’s deepest such facilities. The FPSO is set to begin production in the first quarter of 2010 and is specified to have 600,000 barrels of oil storage capacity, 80,000bpd processing capacity and 16mmcfpd of natural gas export capacity.

"It is an interesting job," says Parkinson. "There is a Brazilian oil company in American waters using a Norwegian ship with British engineers constructed in a Singapore shipyard through Chinese investment."

He adds: "We had to conduct studies to ensure that the gas going to shore and oil in the tanker was stabilised. The ship needs to be able to run from a tornado or hurricane, the likes of which have recently been seen in the middle of the Gulf of Mexico. The most recent hurricane would have gone straight through this job, so you can see how important it is for the FSPO to be able to run."

"The most recent hurricane would have gone straight through this job."

Although DPS will not introduce its new, patented technologies to the project at this stage, it believes the future potential is there. "When you start in a field of this nature, you may begin with 100% oil. Over a period of time, the water starts coming in. The problem comes when it is 50/50," says Parkinson.

"We can therefore bring those technologies into play later on in the ship’s life," he concludes.