Page 654 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

flying leads, and perform other mechanical operations for maintaining the subsea field. And the brick wall is the power density of current battery technology to muscle the vehicle to the work site and perform the mechanical operations sufficiently to complete the assigned task. For the subsea oilfield of the future, the ability to combine logic-driven operations with sufficient power delivery will determine if the ROV will be replaced by fully autonomous operations. And the energy density of future batteries will only go so far, so the systems that require the energy, the manipulators and tools, need to become highly efficient electrically driven systems.
Again, by teaming robotic systems in a cooperative manner, time (and thus money) can be saved. Such teaming leads us to the next and most advanced combinations of technology, the hybrids, where the ROV and AUV become one.
23.3.3 Hybrids
If an AUV can provide the hands-off, long-range support described in the previous section, think about the possibilities if that AUV could also perform the IRM duties that require an ROV with a work system and tools. And what if such a system could remain underwater for months at a time performing the necessary tasks or on standby for when it is needed? Such a hybrid AUV/ROV could have a series of underwater garages or docking stations where it could recharge its batteries and communicate with an operator on shore or on the production platform. It could also have the capability of reaching a remote site where it can dock with a communication node and turn over control to an operator at a remote location who could launch and operate the integral ROV.
Well, this concept is being turned into reality by CYBERNETIX. The French company is develop- ing the Subsea Work, Inspection, and Maintenance with Minimum Environment ROV (SWIMMER). CYBERNETIX successfully demonstrated the SWIMMER prototype (Figure 23.11) with partners IFREMER and the University of Liverpool, in 2001 during full-scale sea trials. Since then, CYBERNETIX has worked with Statoil and Total to develop an operational system.
The concept of operation (Figures 23.12 and 23.13) is for the vehicle to be launched from an MSV or FPSO vessel (or from shore). The vehicle can then dock with the subsea docking station where power and data cables previously routed back to the operating consoles aboard the host ves- sel are embedded into the field control umbilical. This could resolve the power density question discussed previously! Further, the actual control of the vehicle can be via teleoperation performed from the host vessel or (alternatively) via satellite to an operations center ashore.
The ability to have hybrid systems such as the SWIMMER will be extremely valuable in harsh environments. In the North Sea, sea states can reach level 7 where MSVs, assuming they are even around, are not about to be launching an ROV. Having a hybrid system in place on the seafloor would eliminate that problem. One of the next hazardous frontiers is the Arctic. Within that envi- ronment complications exist from the sea ice that could form and prevent an MSV from reaching the area. With the hybrid already in place, it can be controlled remotely to perform necessary IRM operations. The system can also swim into the area below the ice to dock with the ice-covered sub- sea production system. The present SWIMMER vehicle with its lithium ion battery system has a projected range of 31 miles (50 km). With the use of fuel cells (which have been demonstrated on other AUVs) or auxiliary battery packs, this range can effectively be doubled.
SAAB Seaeye Ltd. (Fareham, Hampshire, UK) is also involved in advancing the AUV technol- ogy for offshore support. Their Sabertooth hybrid AUV (Figure 23.14(a)) will be capable of a
23.3 Autonomous ROVs 655