Offshore oil and gas operations present a challenging environment. Operators incur substantial costs to maintain assets and verify compliance with regulations, and environmentally induced delays of infrastructure inspections cause loss of production revenue. In addition, inspection and monitoring ofdeepwater hardware is human and equipment intensive and increased operations strain resources.
As autonomous underwater vehicle (AUV) operations increase in scale and complexity, the need forsubsea persistence increases. Implementation of this resident AUV system will provide benefits for oil and gas operators and service companies in areas such as environmental baseline data, increased efficiency, improved safety, and reduced cost. The combination of Battelle and OceanWorks technologies to develop resident AUV interface infrastructure would make possible remote inspection and intervention without the need for surface support or complex umbilical handling systems.
|Distributed seafloor node network. (Image courtesy OceanWorks)|
Many of the challenges associated with offshore oil and gas operations, especially in deepwater, can be addressed by deploying subsea inspection and monitoring systems with increased persistence. The benefits of persistence include:
- The ability to conduct cost-effective long-term environmental monitoring to establish and track conditions before exploration, during exploration, and after exploration on through production
- The ability to conduct frequent, cost-effective inspections for pipeline and equipment integrity
- The ability to respond quickly to out-of-cycle inspection requirements
- The ability to tie-in with seafloor network instruments.
Battelle and OceanWorks International have demonstrated technologies to enable persistent AUV operations from a seafloor node network that incorporates a subsea docking, recharging, and communications.
Such a system would enable resident AUV presence on the seafloor, providing cost-effective support for a variety of oil and gas exploration and production activities.
Operators use AUVs for a variety of tasks, including bottom surveys, pipeline tracking and inspection, and infrastructure inspection. Current AUVs are supported from surface vessels. The equipment must be physically recovered aboard the ship to replenish batteries and download data. This means that the ship must remain on station while the AUV is working, and that safe AUV operations depend upon favorable weather and sea conditions.
|A Bluefin-12 AUV enters the Battelle-Bluefin AUV docking and recharging station (left) for recharging and data download (right) during a demonstration in Boston Harbor.|
In oil fields with assets spread over tens or even hundreds of square miles, a docking and recharging station would allow a vehicle to deploy from a central site, transit to an inspection area, perform the inspection, then return to the docking station to recharge batteries and offload inspection data. Once recharged, the vehicle would move to the next inspection area to repeat the operation. This would alleviate the need for a ship to tend the AUV while it works and would reduce potential for vehicle damage or loss during launch and recovery.
The persistence given by the AUV's independence from the surface enhances its efficiency in routine operations. In addition, a persistent, docking station-based AUV could deploy for out-of-cycle (e.g., post-hurricane) inspections more rapidly than transit-time-limited, surface-based system, reduce time required to complete inspections, and resume production faster after a natural event.
Recent developments, such as the 2011 demonstration of an AUV docking and recharging station in Boston Harbor performed by Battelle andBluefin Robotics, coupled with existing Seafloor Network infrastructures, such as the VENUS, NEPTUNE, and CSnet OCB subsea nodes, primarily developed and built by OceanWorks International, have established baseline capabilities to deploy a persistent seafloor-based AUV.
AUV docking station
In late 2011, an undersea system demonstration in Boston Harbor culminated several years of work by Battelle and Bluefin Robotics on an AUV docking and recharging station – the undersea equivalent of a filling station, where an AUV could "gas up" and "phone home." The system successfully demonstrated autonomous homing, docking, recharging, data exchange, and re-launch.
Work on the AUV docking and recharging station began in 2007 as an internally funded effort. A number of concepts were examined. The submarine-mounted version was the primary focus and came to fruition through sponsorship from the Office of Naval Research, and later supplemented by the Commander, Submarine Force.
In these programs, Bluefin outfitted one of its 12.75-in. diameter AUVs with a device that enabled it to home in and then dock for data exchange and recharging. Once docked, the vehicle used a Wi-Fi connection to download data and upload its next mission profile. Inductive coils on the vehicle and dock transferred energy from the dock to the vehicle – an approach not unlike a counter-top charger for an electric toothbrush – without the need for metal-to-metal contacts.
Building on this successful at-sea demonstration, Battelle has launched an internally funded research and development project to demonstrate an enhanced undersea electrical energy transfer system. The new project aims to improve the efficiency of an inductive power transfer subsystem. This would, in turn, enable increased persistence, higher reliability, and faster turnaround time for AUVs and other subsea systems.
The 2011 demonstration yielded undersea power transfer efficiency of 74% with a charge time of 12 to 16 hours for a 12-in. AUV. The new OceanHub system will be 85% to 90% efficient, reducing AUV charging time to four to six hours. Initial proof-of-concept tests were completed in early 2014, with additional development and demonstration to follow. Although initial development will focus on AUV replenishment, the system architecture supports a wide variety of subsea power transfer applications.