Future Developments in Subsea Autonomous Control Systems

The need for life cycle cost reduction to increase or simply to allow the profitability of a subsea development does not permit the extended use of conventional control technologies in scenarios more and more characterised by deepwater and long distance. The future subsea scenarios will probably see the development of fields beyond 20 km from the host facilities. The economic advantages of the introduction of autonomous control systems has been demonstrated in several studies. Some technologies have been designed and successfully tested and can today be considered as the valid starting point for any other future initiative. The recent developments in the acoustic transmission techniques through seawater, in the autonomous subsea power generation and in the subsea closed loop hydraulic systems, make now possible to eliminate the control and power umbilical in many subsea development with step-out distances up to 40 kilometres. With respect to the acoustic through seawater, the research efforts in the last years have led to more sensitive and efficient acoustic transducers and to more capable detection algorithms based on coherent demodulation techniques. In this paper, an overview of these recent developments regarding the acoustic signal transfer is presented. Considering that the electrical power requirements increase with the number of functions and variables to be controlled and monitored, different solutions for subsea power generation are considered for different production scenarios. The progresses regarding the seawater batteries and the thermoelectric generators combined with the developments in the field of low power electronics allow now to satisfy the electrical power requirements in multi wells developments. In case of considerable amount of electric power, the feasibility of subsea turbines, powered by produced or injected fluids, was also demonstrated. Although autonomous solutions have been proven by means of prototypes their reliability is still to be demonstrated in order to gain the necessary acceptance by the oil industry. The next step will be the engineering of the existing prototypes in order to achieve devices suitable for real field scenarios.