The Restoring of Dismissed Offshore Oil Plants by a Remotely Operated Robotic Platform

The paper gives an overview of the research project SBC (contract n° GIRD-CT-2000-03007), aimed at the environment protection and rehabilitation, by means of an innovative robotic equipment, purposely developed with active interaction between academia and industries, showing joint issues as for scientific, technological, economic, social and cultural aspects, along the challenging track to eco-consistency. The falls-off bring forth:- a new technology: the sub-bottom wire cutting; - a reliably tailored set-up: the robotic platform; - a low-impact duty-scheme: the dig-and-saw process; - a safe work-cycle: the remote monitoring and control. The Sub Bottom Cutter, SBC, approach grants highly conservative decommissioning operations of dismissed submerged offshore structures. Due to surrounding hostility (pressure, temperature, pollution, ...), the robot is remotely controlled from the surface, where a human operator monitors the task advance intervening if any snag occurs. The equipment uses the diamond wire technology (DWT) to cut the pile foundations beneath the sea bottom. The result is the full removal of the structure, which may be made by steel, concrete or a combination of the two, and the consequent restoration of the underwater environment, according to the enacted laws and regulations. The project originality relies on combining and improving known and co-operating technologies, namely: diamond wire cutting and sub-bottom operation; robot-based tools and remote monitoring and control. This leads to the never attempted task of shearing below sea bottom in a hostile environment by a low-impact duty-scheme (dig-and-saw), through reliable and safe process (unmanned work-cycles). The prospected technique allows the environmentally safe disposal of offshore installations (wellheads, platforms, terminals and sea-lines), as well as marine and harbour structures, limiting the volume of the seabed excavation to less than 10 m3 per each access to the structure to be cut, like, jacket piles or wellheads, etc.. The excavated volume of the solid materials per single dig is estimated to be 100–150 times less than the one removed by conventional dredge systems. Moreover, sub-bottom diamond wire cutting leaves mainly unaltered the surroundings, with most of metal discharges trapped at the operation site. The project was successfully fulfilled, and a prototypal equipment has been tested during July 2003, within a marine surroundings, properly accomplishing the cutting sequence. The paper presents an overall discussion of the technical background required by the case peculiarities, and summarises the main design incumbents faced for the ideation and the construction of the robotic platform. Emphasis equally focuses on the structural checks and on the work-cycle performance, with due account of the task specification, the prototype definition, the conditioning computational and experimental checks and the basic monitoring and overseeing environment asuuring reliable remote govern. The key benefits of the finally achieved prototype show the very relevant outcomes of the solution, such as: the use of a clean process, not interfering with the equilibrium of the marine habitat; the integrated design of mechanics, hydraulics and the underwater functional components; the unmanned operation, ruled by an intelligent remote control/drive station on surface; the guarantee of the completion of the cutting task, provided by remote monitoring; the previous assessment of life-cycle performance, by digital prototyping and virtual testing; the optimisation in terms of environmental impact, overall efficiency and system reliability for the use underwater, and the low energy consumption in relation to the total power applied (250/300 kW); the unaltered overall efficiency of removed structures and materials characteristics involved in the cutting process, thus allowing the re-use for the same or different work-scopes; the noteworthy efficiency of the dig-and-saw process, and the comparative low over-all costs. The presentation offers a noteworthy example where the integrated desing grants the successful merging of technologies, to efficiently and reliably fulfill demanding duties. The demand to restore uncontaminated conditions of marine sites modified by men activity and the global spreading of off-shore reclamation tasks require international concern, as, today, proper technologies are missing as for human and for environment safety. The urgency follows, in view of the European sustainability programmes and the North Sea case. In such a context, the prospected development could be winning reference.