Resident ROVs 2: Oceaneering

While already at an advanced stage in the development of an innovative long-term resident ROV system, Oceaneering recently began work with Equinor on a pilot project to design a shorter-duration resident vehicle. Unsurprisingly, the two vehicles are completely different.

The tasks of inspection, repair, and maintenance (IRM) and underwater intervention are important parts of an effective field management programme. Normally routine or planned, this work is carried out using subsea vehicles deployed from large support vessels. These vessels can be expensive to contract and their operation is often weather sensitive, especially in the harsh environments of the North Sea. 

One theoretical solution is to remove the dependence on the support vessel and to relocate the remotely operated vehicle (ROV) on the seabed – a so-called resident ROV. For many years, subsea engineers have recognised the relative advantages that a resident ROV brings, but it has only been relatively recently that the technology has been sufficiently advanced to realise this aspiration.

A resident ROV would be typically garaged on the seabed, maybe for the life of the field or at least for extended periods in order to make the investment justifiable. When required, it would fly to the target, perform a function, and then return to the underwater garage – sometimes repeating this at planned intervals to build up a picture over time. The downside is that these permanently installed systems would be typically limited to a relatively small radius of operation governed by the length of the tether.

In 2017, Equinor put a low-budget, proof-of-concept contract out to tender, inviting partners to develop a self-contained resident ROV package in the form of an underwater vehicle/garage that could be lowered from a support vessel to a specific point on the seabed anywhere in the world and left to conduct a variety of subsea tasks once the surface vessel had departed. Importantly, however, its residency would be measured in days, not months.

The sort of work that this ROV would be called to do would include basic IRM work or well commissioning, such as operating valves for the production system. When completed, the garage/vehicle package would be collected and deployed elsewhere. By the end of five months, Oceaneering had fulfilled Equinor’s design brief with the development of the short-term resident E-ROV system.

“Perhaps surprisingly, the ‘E’ doesn’t stand for ‘electric’ but for ‘empowered’,” said Arve Iversen, ROV Operations Manager–Special Projects, Oceaneering. “It is basically a battery-powered work class ROV system that can be positioned on the seabed on a temporary basis. The sort of tasks that the ROV is designed to carry out would be subsea inspection and janitorial duties, as well as basic well commissioning such as operating valves on a Christmas tree.”

To make it fully independent, Equinor stipulated that this pilot design had to incorporate its own self-contained power storage facility. A major consideration in the E-ROV design, therefore, was the limited power budget. To overcome this, one might have reasonably thought that Oceaneering would have based the pilot project on a small, lightweight and less-power-hungry ROV. 

Far from it.

Conscious that a small ROV would not be able to perform the intervention tasks demanded without compromise, and coupled with the short development time available, Oceaneering needed to adapt an existing vehicle rather than design one from scratch. Therefore, Oceaneering based its new E-ROV design on its powerful top-end electrical vehicle, the eNovus ROV. 

“We knew that our large, high-performance eNovus vehicle would be able to carry out whatever tasks it was called upon to do,” Iversen said. “We just had to be mindful of the power consumption capacity of the ROV tooling. 

"All things being equal, electrical systems are far more power efficient than their hydraulic equivalents, and we wanted to maximise the use of these sort of devices whenever possible. 

"Of course, many tools and sensors, such as cathodic protection probes, were electronic/electric, and there is even electrical cleaning equipment on the market, so that wasn’t a problem. We also carried out successful tests with electric torque tools.”

When it came to electric manipulators, however, Oceaneering noted that, while they were considerably more power efficient than hydraulic manipulators, they did not have the performance capability. The designers conceded, therefore, that there was no real alternative but to use hydraulic manipulators – and this meant installing (or, to be more precise, retaining) the eNovus hydraulic power unit.

But how to control the E-ROV without a support vessel? The Tether Management System (TMS) on the garage can allow the E-ROV system to extend up to 600m (1969 ft) from the garage. The challenge to fly the vehicle in real time was met by means of a thin optical fibre within the tether extending from the garage up to a floating buoy piercing the surface. An antenna on the buoy would permit two-way data communications with land. 

“We have been controlling vehicles remotely from a remote land-based mission support centre for over for two years,” Iversen said. “Control/data signals from the E-ROV would be sent to and from the antenna on the buoy via 4G LTE broadband telemetry in the same way that mobile phones communicate. Its coverage in the Norwegian UK sectors is good, and, in the Gulf of Mexico, it is improving.”

While Equinor stipulated that the subsea package had to be totally reliant on self-contained subsea power as the base case, Oceaneering recognised that there was potential for incorporating a power conductor within the buoy mooring, and for using a wind sail, tidal energy converter, or some other electricity-generating device to trickle electricity down to recharge the batteries and extend the operational life. 

“While the Oceaneering team in Stavanger, Norway, were spearheading the E-ROV system,” Iversen said, “we were already working on a long-term resident ROV project called Freedom. This initiative has been developed in-house from offices around the world and fully financed internally.”

Iversen stated that, while both the E-ROV and Freedom projects share some technologies, they have different functions. Therefore, unsurprisingly, the eventually provided design solutions were quite different. Oceaneering also had time to finesse a much more purpose-designed vehicle for the long-term resident Freedom project.

“A typical function of the Freedom ROV would be to fly around the field, possibly inspecting miles of flow lines or remote wellheads,” Iversen said.

 “This encouraged a far more power-efficient hydrodynamic streamlined for minimal drag, while being dorso-ventrally flattened for roll stability. The long-term resident vehicle, however, had to be multifunctional and, to increase its versatility, the Oceaneering engineers envisaged a modular design with a central common core section onto which other various modules could be bolted depending upon the demands of each specific job.

“To increase endurance and thus power consumption, for example, the vehicle may benefit from a larger battery pack module. Conversely, if the operator wished to carry out inspection work, the vehicle could incorporate a module housing traditional survey equipment. For light intervention duties, the operators could select a module with the necessary tooling interfaces.”

Like the E-ROV, this vehicle would be steered in real time from an Oceaneering mission support centre while in tethered free-swimming mode. The Freedom ROV, however, is also capable of detaching the tether and operating autonomously. In addition, it can also take advantage in the latest underwater/through-water communications technology and be flown in real time without being tethered. 

“When the Freedom system – which is actually a hybrid ROV and autonomous underwater vehicle (AUV) – is in the garage, it can be recharged by inductive connectors,” Iversen said. “If the vehicle is flying in close proximity to the docking station, it will also be possible to receive data over a high-bandwidth optical system. It will be able to send back positional data over long distances, using its acoustic system, although this medium will not have the bandwidth capacity to transmit video.

“The maximum excursion distance that the Freedom ROV can venture from the subsea garage is dependent on the length of the tether, typically a maximum of 250 meters (820 feet). When in autonomous mode, however, this boundary is nearer to 50 kilometers (31 miles). It cannot be flown this distance, but it can certainly be programmed to move autonomously. 

“We are currently at the stage of specifying the tooling,” Iverson added. “Important selection criteria are power consumption, compactness, and, of course, price. We are planning sea trials for the Freedom ROV system next year.”