Comparative Assessment of Environmental Impacts Associated with the Decommissioning of Fixed Offshore Platforms

In the upcoming years, the number of offshore oil and gas installations, which have to be decommissioned, is going to increase around the world, as they approach the end of their productive lifetime. Decommissioning carries risks and safety problems beside ecological, economic as well as social effects. To assess the environmental impacts associated with the decommissioning process of offshore structures, life cycle assessment (LCA) is used. In accomplishing LCA, two main methods are applied to quantify those impacts which are process based method and Economic Input Output method (EIO). Both methods are studied and compared for their strength and limitations to obtain more reliable, representative and accurate results. The decommissioning options that are considered in the present study are complete removal and re-use as an artificial reef, whereas the environmental impacts of offshore decommissioning concerned in this paper are the total energy consumption and gaseous emissions such as carbon dioxide (CO2), nitrogen oxides (NOx) and sulphur dioxide (SO2). Using EIO method, the results of LCA show that the conversion to an artificial reef is the better decommissioning option in terms of energy consumption and gaseous emissions, whereas the process based LCA reveals the opposite results. The decommissioning activity which mostly contributes to energy consumption and gaseous emissions were identified, which is the marine vessel utilisation. The numerous results based on the decommissioning of Platform A, located in Malaysia, were compared with the quantified environmental impacts of decommissioning Heather Platform, installed in the North Sea, in order to find the relevant differences and coherences for further estimations of environmental impacts of future decommissioning projects. At the end of the present study, some suggestions of possible mitigation measures for environmental concerns in connection with the decommissioning of offshore platforms can be mentioned. Overall, the need to maintain the environment whether onshore or offshore is a global issue and affects the total humanity. To protect it for the future generations, the harm of the environment has to be reduced. In this case the environmental impacts could be less if the appropriate decommissioning option is found based on numerous results by using LCA tools.