Abstract
Since the commercial exploitation of marine oil and gas reserves began in the middle of the twentieth century, extensive networks of offshore infrastructure have been installed globally. Many of the structures are now nearing the end of their operational lives and will soon require decommissioning, generating renewed interest in their environmental impacts and in the ecological consequences of their removal. However, such work requires selection of a subsample of assets for surveying; censuses of the entire 'population' in any given jurisdiction are practically impossible due to their sheer number. It is important, therefore, that the selected sample is sufficiently representative of the population to draw generalized conclusions. Here, a formal clustering methodology, partitioning around medoids, was used to produce a typology of surface-piercing oil and gas platforms in the North Sea. The variables used for clustering were hydrocarbon product, operational state, platform design and material, and substructure weight. Assessing intra-cluster variability identified 13 clusters as the optimum number. The most important distinguishing variable was platform type, isolating floating platforms first, then concrete gravity-based and then fixed steel. Following clustering, a geographic trend was evident, with oil production more prevalent in the north and gas in the south. The typology allows a representative subset of North Sea oil and gas platforms to be selected when designing a survey, or an assessment of the representativeness of a previously selected subset of platforms. This will facilitate the efficient use of the limited funding available for such studies.