Cutting the umbilical

Eliminating the umbilical has been targeted as a way to help make the exploitation of small pools more viable. Elaine Maslin reports on a string of new technologies which aim to do just that.

An Exnics collar. Photo from Exnics.

According to a recent study by the UK’s Technology Leadership Board, there are 210 “small pools” of hydrocarbons (those containing less than 15 MMboe).

While recognized, these pools, containing 1.5 billion boe in total, remain undeveloped, due to their distance to existing infrastructure, their reservoir complexity or they are uneconomic because of their size.

An initiative in the UK is hoping to find technologies that will help unlock them – and most revolve around eradicating umbilicals.

The initiative is being pushed by Gordon Drummond, who leads of the UK’s National Subsea Research Initiative (NSRI), an organization which aims to connect the subsea industry and academia to find solutions to industry challenges.

Eliminating the umbilical, and even potentially the pipeline, could save significant costs – a key requirement in today’s market - and reducing infrastructure, installation time and assets, and maintenance concerns.

Gordon Drummond. Photo from NSRI.

A number of technologies that could help achieve this aim were presented at an NSRI event, supported by Subsea UK, in Aberdeen, late September.

Andrew Connelly, NASCoM product line manager at Aberdeen-based through-water wireless communications firm Nautronix, one of the presenters, says: “Cost is key at the moment, including the cost impact of umbilicals, the lead time to procure them, plus deployment and support requirements.”

For deepwater projects, the implications are even greater, he says, with deepwater umbilicals taking up significant deck space, and requiring more effort around connection and logistics, i.e. ROV or diver time, as well as suitable subsea construction vessels.

Start with control

Nautronix, recently acquired by Scotland-based Proserv, has offered to do away with the control and monitoring cable requirements in the umbilical with its NASCoM system, which has already been deployed on multiple oil and gas projects worldwide. The firm’s acoustic through water communications technology has even been used as the primary control for BOPs in deepwater.

Connelly says: “We can’t do much for wells products and chemicals, but we can look at control and monitoring. You don’t need a control and monitoring umbilical. Removing this can save time around deployment. You don’t need the work around the point to point connection. You can have one acoustic link on the vessel to multiple assets, which multiple vessels could also access. They could perform multiple control and logging functions for anything you want to do electrically subsea.”

What’s more, data processing, monitoring sensor data, and filtering data to give more relevant data back to the surface could all be done, to streamline operations.

Nautronix uses digital spread spectrum signaling, which is based on mobile phone technology, giving robust signaling, with data networks used to extend the range of the system. The range of Nautronix’s NASCoM system is 3-5km horizontally, depending on local topology, or 6-7km vertically and it has no interference with other acoustic systems, due to the coded signal.

A spool piece fitted with Exnics collars. Photo from Exnics.

Next, subsea power

Exnics has focused on how to power services at the well site, without using an umbilical. “We realized no one was looking at the geothermal energy a well produces,” says Stu Ellison, founder at Exnics. “There is a huge thermal potential at the mud line.”

An EC-OG subsea hub. Photo from EC-OG.

Exnics has studied using semiconductor material in a collar, which is installed around a subsea flowline in a two-part clamp and generates an electrical current which is then stored in lithium batteries from which the subsea power can be drawn down.

As an example, Exnics looked at the potential on the Devenick field, operated by TAQA. It is a 34km tie-back with two wells, with a wellhead temperature of about 140°C, according to their research. By assessing the production volume and phases, they worked out the thermal capacity and mass of each of the phases, the heat difference between the flow and the ambient temperature in the sea water around the pipeline was equivalent to 6.9MW of geothermal heat potential.

Ellison says each field is different so the Hot Rings power system is designed to be scalable to suit. Even if the geothermal heat potential at a certain field is relative low, the same power output can be achieved by ‘daisy chaining’ more Hot Rings in the train.

“There isn’t an upper temperature limit, but you do have certain flow assurance criteria, i.e. temperatures at which it is not worth doing, the cut-off point is estimated to be sub 50°C,” he says. “But there are not that many wells below 50°C. In the North Sea, most are in the high-60°C to 110°C range and HPHT wells can be much hotter”

From a flow assurance stand point, the amount of electrical power required and the heat needed to feed that generation needs to be considered so the production flow isn’t taken down to a temperature at which hydrates or wax could form downstream. “For very waxy or heavy crudes, this probably isn’t something you would consider,” Ellison says. “But for typical crudes, condensate, gas, HPHT or any well with a meaningful water cut there is an opportunity to harvest the produced heat.”

The technology itself – the Seebeck effect – has been around a long time. Thermoelectric generators or TEGs, are maintenance free and because of this they were used to power many space missions including Voyager, Ellison says. Since being developed for space TEG’s have been commercially developed and are now available as a relatively cheap component. “It is now at a point where there are industrial applications and they can be bought off the shelf,” Ellison says. The firm is now preparing to conduct demonstrations at their unit in Ellon.

Power alternatives

Stu Ellison. Photo from Exnics.

EC-OG, formed in 2013, has been developing a subsea power hub concept, an invention to use ocean currents to generate electrical power, and a full scale version of the concept is due to start trials next year.

The subsea power hub concept consists of three vertical axis turbines, each connected to direct drive DC power generators, and in turn batteries to store power, all housed in a no more than 7m-footprint over trawlable frame.

One unit can produce about 500w, according to EC-OG, with additional units to be daisy-chained if additional power is required.

The firm, which has been supported by a number of Scottish Enterprise “Smart Grants” to support trials of a scale subsea power hub. It is due to start full scale trials at the bottom of Loch Linnhe, at the Underwater Centre, Fort William, next year.

“Ocean current is predictable, and then there has been a massive leap in battery technology to store and deliver power when you want,” says Richard Knox, the inventor of the concept. “Then there is the research combining the two technologies. Our aim was to get as much energy out from as small a footprint as possible.”

EC-OG’s tidal turbines are each just 2m high, in a configuration which optimizes the flow and power generation, and can be removed individually from the frame. As each has its own DC generator, there is built in redundancy, and they can start producing electricity with a current flow as low as 0.4m/sec.

Key to the design has been to create a system that can sit in a compact, over trawlable structure, which meets road transport regulations, for ease of logistics, and a turbine configuration which gets the most from the ocean current, Knox says. The hub will also have an intelligent energy management system to get the maximum life out of the battery.

The firm started testing a model at Newcastle University two years ago, using a one third scale unit. The testing at Fort William is due to run for about 18 months and will also demonstrate the power hub’s ability to be remotely control and monitored subsea applications via a desk top, without the conventional umbilical.

While initially the concept was aimed at brownfield sites, where wells were being shut-in due to electrical failures, the firm is also looking at greenfield projects and even subsea surveillance. It could also be used as a power source for remote island communities.

“We are looking to offer a step change in electric current cost, and to use subsea power hub to extend life of subsea wells,” Knox says. “We are looking at a truly disruptive technology which will reduce the cost of supplying electric power.”

PowerBuoy

Ocean Power Technologies’ PowerBuoy off New Jersey.  Photo from Ocean Power Technologies.

While Ocean Power Technologies has not quite done away with the need for a cable to transport the power from the source to the user, its PowerBuoy solution does offer a way to reduce the need for manned surface facilities or long step-out umbilicals to provide power for the likes of AUVs or power for electric Xmas trees.

PowerBouy is a wave energy power generation device, one of which is currently being used offshore New Jersey to collect metocean data, the firm says could be used through the life of field, from environmental impact assessment to front end engineering studies, operations and decommissioning, with sensors mounted from the device through the water column as well as above the surface.

The firm’s first unit, APB-350, was built to produce 300w, but it has been producing 1000w offshore New Jersey. It was producing 25kW/hr late October. A larger unit, the PB10, is in the design phase.

“We have been looking at small units first, to prove the system, make sure it is reliable as a monitoring and data solution, and once it is proven reliable operationally, we can scale it up,” says Paul Watson, director of business development UK & Europe at the firm.

Earlier this year, the firm formed an advisory panel with operators, manufacturers, services companies and sensor companies, to involve the industry in the design phase of a unit that could supply power to seabed users. In October, it signed a memorandum of understanding the Gardline to jointly develop metocean monitoring and maritime security systems.

All in all, there are potential solutions out there to remove the umbilical. What was missing was a way to transport chemicals, such as MEG, for injection to the well site. But work is underway on this, too. For example, OceanWorks International, was awarded an engineering contract to help develop a deepwater permanent subsea pressure compensated chemical storage and injection system, as part of a project supported by the US Department of Energy, the Research Partnership for Securing Energy for America with support from the DeepStar program, as well as Baker Hughes and Fugro.

Oil major Total, working with French firm Doris Engineering, has also been exploring designs for subsea chemical injection systems, for both oil and gas subsea tiebacks, with a key benefit being reducing umbilical cost procurement and installation time. The longer-term goal would be to reduce the connections to an FPSO from the seabed to just the flowlines.

Drummond think’s there is potential, thanks to these technologies, to do away with the umbilical. The next challenge will be getting rid of the export pipeline. “If you can get a light-powered chemical injection skid, we have done away with the umbilical. The next step is to do away with the pipeline,” he says.