Design of a Subsea Observatory to monitor the environmental impacts in a decommissioned area

When oil and gas fields end production, offshore installations need to be dismantled and disposed of. The set of processes used to do this could be summed up in the term Decommissioning. The Decommissioning of fixed offshore structures is one of the biggest technical and operational challenges in the O&G industry. Due to this complexity, also in term of HSE, in particular site Decommissioning could lead to potential environmental hazards which need to be monitored. The BP Miller platform is going to be completely decommissioned in the near future. Due to derogation to the OSPAR legislative framework for decommissioning in the North Sea, the Jacket footings of the platform and the contaminated drill cutting piles will remain in situ. The aim of this document is to examine the BP Miller site as a reference point to start an initial design for a subsea observatory which could be used to monitor the marine conditions around the BP Miller footings. The DELOS subsea observatory was chosen as a reference as it includes modularity in its design. This study was divided in two phases: the first phase consisted in a desktop study aimed to assess the state of art of the in-situ technology for marine environmental monitoring and the published reports about contaminated cutting piles characterization. At the end of the first phase a complete list of parameters to monitor was achieved. The second phase consisted in the conceptual design of the subsea observatory. Starting from each selected parameter, a subsea sensing technology was identified. Consequently, from the set of the chosen instruments a subsea observatory was conceived and designed following the DELOS logic which allowed adding modularity to the final project and offer the possibility to improve the design in time, following the necessary developments of the in-situ monitoring technique, which as highlighted in the first phase of the project, are steadily increasing but are far from being already effective.