Potential of repurposing decommissioned subsea flowlines to dynamically installed anchors

Abstract

Subsea flowlines are flexible or rigid pipelines that are used in oil and gas fields commonly for transporting production fluids from wells. The majority of the flowlines operating in basins across the world (including e.g. Australia's 1700 km infield flowlines) are approaching the end of their productive life, and will need to be decommissioned over the next 5 decades. This paper, for the first time, investigates the potential of repurposing decommissioned flowlines to dynamically installed anchors for mooring floating facilities. Five shapes of anchor have been developed using segments of flowline. Two series of tests were subsequently carried out on models of those shapes. The first series of tests involved releasing the models in still water to assess free-fall trajectory (i.e. verticality), terminal velocity, and anchor drag coefficient. The second series of tests were carried out at 50 g in clay to investigate the performance of the anchors in terms of tip embedment depth during dynamic installation and capacity under vertical loading. The results confirmed performance similar to conventional dynamically installed anchors, suggesting that there is potential to fabricate offshore anchors using segments of flowline.