PT Pertamina Hulu Energi Offshore North-West Java (PHE ONWJ) presently operates a fleet of more than 200 fixed offshore platforms and nearly three quarters of these platforms have been in operation for more than 30 years. Under newly implemented Gross Split Production Sharing Contract (PSC) scheme, PHE ONWJ is driven to seek an effective and efficient method for offshore platform decommissioning. Three offshore decommissioning options, i.e. Total Removal for Onshore Disposal, Total Removal for Rig-to-Reef, and Leave-in-Situ for Mariculture are examined closely. A qualitative evaluation, which involves comparing the total expected cost of each option against its total expected benefits, is conducted in view of decommissioning drivers, i.e. Safety, Environment, Technical, Cost, and Social Impact to other sea user and community. The evaluation of the expected cost of each decommissioning options is presented. The first two options are subjected to high cost activities e.g. platform removal; mobilization and demobilization of derrick barge; and material disposal onshore or reefing site. The Leave-in-Situ for Mariculture option, on the other hand, is not exposed to those activities as it leaves the retired platform on its existing location and turns the structure into the site for offshore cage system fish farming. This is significant because in the Gross Split PSC scheme, PHE ONWJ is expected to be more prudent and focus on cost efficiency. The social impact of the Mariculture method is potentially important considering the rapid growing of global per capita fish consumption and the fact that there are no offshore cage systems fish farming using retired offshore platform in Indonesian waters or even Southeast area yet. The suitability of the proposed mariculture site of Offshore North West Java waters is further evaluated against the guidelines from the Food and Agriculture Organization of the United Nations (FAO). The Mariculture method can be not only the most cost efficient solution for offshore platform decommissioning, but also providing alternative technique to increase marine fish production.

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