The world's first full field subsea separator, developed as a result of the EUREKA E! 3040 SUBSEA SEPARATOR project, is a key component in a subsea processing system that will be installed in the Norwegian Statoil Tordis field in the North Sea in the 3rd quarter of 2007.  Carrying out part of the processing on the sea floor and re-injecting the separated water avoids the flow of water up from the subsea well to the production platform, leaving a much larger part of the system - pipelines and processing equipment - for the oil and gas content. This technology will enable higher recovery rates of already scarce oil reserves and increase production rates. Such highly innovative European equipment is already attracting worldwide interest.

"By installing a full field subsea separation facility, Statoil expects to improve the Tordis field's recovery factor from 49 to 55 per cent", explains Rune Mode Ramberg, Statoil's subsea processing discipline adviser. Along with other upgrades to the field, the separation system will allow Statoil to extract roughly 35 million extra barrels of oil from the Tordis field. This is achieved by reducing the back pressure towards the Tordis field by separating water and sand from the wellstream subsea, re-injecting the water and sand in a separate well subsea, boosting the wellstream with a subsea pump and reducing the receiving pressure at the topside production platform.

Separation equipment plays a crucial role in the oil and gas production process by splitting the wellstream, which may comprise of oil, gas, water and sand, into their individual constituents. Only through effective and efficient separation is it possible to carry out the subsequent processing steps - from gas dehydration and/or gas compression to oil treatment and water cleaning before disposal. Moreover, as oilfields age, the total production flow is often limited by the process system, outputs decrease and more water and/or gas mixes with the oil. This leads to a decrease in the amount of oil produced. Better equipment is necessary to debottleneck the existing separators. In this way, the decision to shut down an oilfield can be postponed and reserves can be more fully exploited. Oil companies therefore need more innovative, efficient and compact separators. The capital investment required to exploit a new field can be reduced and it is easier to economically exploit marginal fields with smaller separation equipment.

"CDS, now an FMC Technologies subsidiairy, was a small company and this was an expensive project. Without the EUREKA funding it would have been quite difficult."

Toine Hendriks,
CDS Engineering, the Netherlands

The EUREKA SUBSEA SEPARATOR project set out to qualify a compact subsea water separator with an integrated sand management system. The developed separation technology allows for a 40 to 50% size reduction compared to conventional separators. Subsea separation makes it possible to minimise the water flowrate to existing platforms and ensures that produced water can be directly re-injected with subsea pumps into water injection reservoirs. Oil production can be increased by reducing the back pressure towards the producing wells and flowlines to a topside platform are dedicated to only oil and gas.

There is also a reduced need for topside water cleaning. This is a strong ecological advantage, drastically reducing the load on platforms as produced water can be pumped back to where it came from.

"The consortium was very logical," explains Philip van Dessel, managing director of project leader CDS Engineering. "CDS provided the core separation technology, FMC Technologies - a company big in subsea oil production equipment - strongly cooperated in the subsea separator development, marinised and built the equipment and put it together with other key building blocks like subsea pumps for boosting into a complete subsea processing system. Norwegian oil company Statoil, as an end user closely involved in the development work, could tell us with what characteristics the equipment should comply and also provided important knowledge of field specific fluid characteristics. Moreover Statoil was keen to use the equipment which was particularly important because you can develop nice technology but in a sector such as the oil industry finding a first user is essential."

CDS designs and develops state-of-the-art separators for use in upstream and downstream activities of the oil and gas industry. Over the years, it has established a reputation for supplying highly-innovative separation solutions to the offshore industry. It modelled the gas/liquid and liquid/liquid flows inside the subsea separator using computational fluid dynamics (CFD) calculation tools.

"Reliability is crucial as you need to make sure that such equipment will continue to function for 20 years," says Steinar Eriksen, process lead Tordis for FMC Technologies. "Retrieving equipment from the seafloor is very costly; if you need to do that several times, you will kill the economics of the project. And compactness is crucial because everything that you install subsea is very expensive - and the bigger it is, the more expensive it becomes, both from a manufacturing and installation point of view."

Separation and sand handling performance was optimised using CFD simulations, followed by extensive small- and large-scale testing under both atmospheric and high-pressure conditions. The tests measured gas/liquid, liquid/liquid and sand separation performance. "CDS, now an FMC Technologies subsidiairy, was a small company and this was an expensive project: we literally had to build a 1:1 scale model in our test lab - and we had to extend the test lab for the project," explains Toine Hendriks, CDS Engineering's senior process engineer. "Without the EUREKA funding it would have been quite difficult."

"By using this technology, you can exploit an oilfield much deeper - so for instance you can recover five to 10% more from the original reserves, an enormous advantage"

Toine Hendriks,
CDS Engineering, the Netherlands

The initial result of this EUREKA project was a demonstration pilot separator installed in the CDS testlab in the Netherlands. The developed separation technology is currently being implemented in the Statoil Tordis Subsea Separation, Boosting and Injection (SSBI) project. Statoil is the largest operator on the Norwegian continental shelf. This application is a first but Statoil is an innovative company, highly motivated to improve oil recovery in its offshore fields. "By using this technology, you can exploit an oilfield much deeper - so for instance you can recover five to 10% more from the original reserves, an enormous advantage," insists Hendriks. "It is also expected that this technology will facilitate new oil field developments at deeper and more remote areas, an advantage for the future as most of the easy accessible oil has already been produced.

And, as only the relevant constituents run through the topside platform, the production rate can be increased, so that you can produce quicker, normally considered as a big advantage!"

The future for this EUREKA-developed technology is bright. "We are already looking at applying similar technology in several offshore fields", adds Hendriks. Oil companies realise that with oil reserves becoming scarcer it is important to exploit these reserves as efficiently as possible.

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