Advances Needed to Untether AUVs From Support Vessels

Abstract

Autonomous Underwater Vehicles For years, the oil and gas industry has used autonomous underwater vehicles (AUVs) for simple tasks such as underwater surveys and inspection. However, because of their technical limitations, AUVs have not been able to compete with remotely operated vehicles (ROVs), which are already standard equipment for most offshore projects. While the market for AUVs remains modest, they are being used in deepwater oil and gas plays around the world. “AUVs are not a commodity yet, but they are getting there,” said Richard Mills, AUV sales manager at Kongsberg Maritime. He added that one Kongsberg customer has a long-term AUV contract with Petrobras for the use of two vehicles offshore Brazil. High-resolution Large-area seabed surveys are the oil and gas industry’s primary use for AUVs today, said Mills. Although shiptowed sonar arrays have been used for decades in ocean floor mapping, the sensors cannot reach the absolute bottom in many cases. On the other hand, AUVs can glide just a few meters above the ocean floor to create higher-quality images of the seabed and subsurface. Despite some unique advantages, the power, communications, and launch-and-recovery systems of AUVs will need improvements in order to make the leap from rig jewelry to a trusted tool. Extended Missions To fully take advantage of an AUV’s tetherless capabilities, users must be able to operate the vehicle for longer periods of time before needing to bring it to the surface for recharging or recovery. Without advances in this area, the nagging question will be, “Why not use an ROV instead?” Liquid Robotics’ Wave Glider is an extreme example of AUV endurance. Able to harness energy from the movement of water and from a floating solar panel on the surface, Wave Gliders can travel for months without human intervention. They have even crossed oceans by themselves. But these vehicles travel very slowly and do not operate more than 100 ft below the surface. Propeller-driven AUVs, the main class used for oil and gas operations, have more power-intensive propulsion methods and tend to be much heavier than gliders. The most common power sources for light workclass vehicles, such as Kongsberg’s torpedo-shaped Hugin line, are rechargeable lithium ion batteries. Each year, new variations of lithium- based batteries are developed and tested, each with slightly better chemistry, but so far, they have offered only incremental improvements. Daniel Gomez-Ibanez, an engineer at Woods Hole Oceanographic Institution (WHOI), said that most propeller-driven AUVs have functional battery lives of 1 to 2 days, even though the total battery life of some are listed as long as 60 hours.