Cost-Effective Design Criteria for Australian Monopod Platforms

Abstract

Assessments of structural reliability under storm overload have been performed on various monopod configurations located on Australia’s North West Shelf (NWS). The results have shown that these monopods have lower reliabilities than typical platforms in other petroleum provinces, due to a number of factors. In itself, this may not be a concern, as it may be argued that minimum facilities platforms have relatively low consequences of failure. Reasons for this could center around these monopods being satellites with small production throughput, having short service lives, being not-normally-manned, and having environmental protection features which minimize the possibility of a hydrocarbon spill resulting from a structural failure. A suitable target probability of failure for monopod platforms may be computed using a cost-benefit approach, where the total platform cost, including the cost of failure, is minimized. This analysis is developed for four distinct monopod configurations involving single pile, pile cluster and outrigger foundations in water depths ranging between 9-52m LAT. The relationship between platform CAPEX and probability of failure is derived from first principles for cases of appurtenances located within and external to the main caisson.