ABSTRACT
The life and recovery factor of already existing subsea gas fields and infrastructure may be increased by installing boosting facilities to compensate for declining well pressures. The installation of such boosting facilities subsea has often been identified as more cost-efficient than installation topside. A recent example is the Åsgard Subsea Gas Compressor installed and started up in 2016 on the Norwegian Continental Shelf. The compressor system is highly complex, involving, beyond the compressor itself, numerous pipes, valves, sensors, a liquid removal facility and a liquid pump. The design of control and safety systems is based on requirements in regulations and key standards, many of which build on topside philosophies for process safety and protection. An ongoing research in the Centre on Subsea Production and Processing (SUBPRO) is to investigate if new requirement formulation methods can verify if the current subsea safety and control philosophy is adequate. A motivation is to investigate areas of improvement for future subsea installations or similar systems. One such method is the Systems-Theoretic Process Analysis (STPA), a method that has been developed specifically for hazard identification in system control architectures. The main advantage of STPA over other hazards identification techniques is its ability to capture system failures that may arise from the communication between equipment in the control architecture, and this insight can be used to build more robust and reliable systems. STPA has already been adopted in many different sectors and domains, but has not yet been tested for subsea processing systems. The main objectives of this paper are: (1) to apply STPA to a subsea processing system; a subsea compression system; (2) to discuss opportunities and challenges of applying STPA to subsea compression systems, and; (3) to extend the discussion to the general use of STPA and necessity to improve the method.
