Remotely operated vehicles (ROVs) are synonymous with those underwater, umbilical-connected vehicles that perform a myriad of functions from visual inspection to intervention work to trenching operations… The list goes on. A mainstay of diver replacement, these have been the only widely used industrial marine remotely operated vehicle accepted within the oil and gas sector, until now.
Autonomous surface vehicles (ASVs) or unmanned surface vehicles (USVs) are vessels that can be set to perform pre-programmed tasks or can be remotely operated. Similar to ROVs, where the manned component – the diver – has been removed, ASVs function without a manned presence on board.
These types of vehicles have been around for a while and manufacturers have been focusing on different aspects of potential uses to produce vehicles of vastly different sizes and shapes, each tailored to a specific market segment. However, it is only in the past couple of years that, due to the drop in oil price and large reduction in work available, cost cutting measures and efficiency drivers have accelerated the use of ASVs in mainstream survey and inspection, repair and maintenance activities.
Why use a larger vessel consuming tons of fuel, crewed with a score of personnel? Removal of these high cost resources can be, and has been, achieved by utilising an ASV operated by a two to four personnel and consuming litres of fuel instead. The job is thus done at a fraction of the cost and risk.
Just as ROVs have not wholly replaced manned diving activity, ASVs will not replace vessels engaged in day to day activities – at least not in the near or medium future. ASVs come into their own when a specific task can be identified that an ASV can assist in accomplishing, where the economic and/or HSE risk benefit of using that ASV outweighs that of using the current manned vessel methodology.
Seabed lines, whether they’re pipelines, bundles or umbilicals, require inspection. Deeper laid lines are out of reach of ASV-based inspection equipment, but the shallower portions such as coastal or continental shelf areas with depths up to 300m are easily accessible to today’s ASVs, carrying inspection equipment such as side scan sonar and multi beam echo sounders, as well as inspection-class ROVs.
In-field subsea structures can also be inspected using ASV methods. Why mobilise a manned vessel at a port, steam to the worksite, perform the works then steam back to port for demobilisation when an ASV complete with ROV and crew of say four persons can be transported by already scheduled means (helicopter and supply vessel) onto the field’s platform from where the vehicle can be deployed and recovered and the personnel housed?
In the vein of ‘removal of high cost resources’ an ASV can also assist with the more efficient use of high value assets. When a large construction vessel is engaged in its namesake activity, it’s not particularly cost-effective for it to be performing tasks that a smaller vessel deployed from it could easily handle, such as: long baseline array calibrations, pre- and post-activity surveys, touch down monitoring, etc.
Regardless of manufacturer, the current trend is towards bigger and bigger autonomous surface vehicles. They are solely platforms for the carrying and use of third party equipment, and it is the need of the end user to have that equipment on-site at the lowest cost possible that is driving their use and development.
Current maximum payload for the larger of these vehicles is half a ton. Producing a vehicle that can accommodate 1, 2 or 3 tons is purely a matter of scaling up. The expectation is that these larger vehicles will be commissioned for build in the near future, especially when the non-revenue generating activity of decommissioning really starts to bite. ■
From Adjacent Oil & Gas 4, August 2016