400350 A New Quantitative Approach to Assess the Risk of Hydrate Blockage Formation in Subsea Flowlines

Monday, April 27, 2015
Exhibit Hall 5 (Austin Convention Center)
Bruce W.E. Norris, Zachary M. Aman, Michael L. Johns and Eric F. May, School of Mechanical and Chemical Engineering, University of Western Australia, Crawley, Australia

As production systems move toward deeper water, high operating pressures and longer thermal exposure times will significantly increase the risk of gas hydrate formation and potential flowline blockage. Over the past two decades, thermal and chemical hydrate management strategies have been developed with a goal of decreasing capital and operating costs while minimising the risk of hydrate blockage formation. The successful adoption and refinement of these management technologies hinges on accurate predictive capabilities for hydrate formation and transportability. Current simulations of hydrate blockage formation rely on a set of deterministic calculations, which do not account for distributed phenomena such as hydrate nucleation. In this presentation, we introduce a new risk engine that is designed to couple probabilistic phenomena – such as hydrate nucleation, deposit sloughing, and jamming – with existing deterministic models. The current incarnation of this engine utilises the Hydrate Flow Assurance Simulation Tool (HyFAST) to describe deterministic phenomena, where the severity of hydrate blockage formation is quantified through the increase to hydrate slurry viscosity for water- and oil-continuous systems. The first deployment of this risk engine incorporates a new probability distribution to describe hydrate nucleation as a function of system temperature; thousands of hydrate nucleation events were observed in an Automated Lag Time Apparatus (ALTA) to inform this distribution. The results of this pairing demonstrate a new ability to quantify the risk of observing hydrate blockage formation in a subsea flowline. In this presentation, we will apply this risk engine to a hypothetical long-distance tieback. The results demonstrate how flow assurance engineers can decide upon an acceptable risk tolerance (e.g. 90% of observations) and deploy this simple calculation strategy to optimise subsea design decisions, such as insulation thickness, flowline diameter, and choke opening.

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