This work provides a new method to directly predict the effect of hydrate formation on transient flow in oil & gas flowlines. The method couples established models for transient flow, fluid properties, and hydrate formation to allow for prediction of the severity of hydrate formation in transient operations and rapid exploration of a large parameter space for design considerations.
As subsea oil and gas production moves to deeper water, the increasing reservoir and transit pressure and lower seafloor temperature increase the driving force for gas hydrate formation. Overcoming such large driving forces using the conventional strategy of thermodynamic hydrate inhibitor (THI) injection may be economically limiting because the volumes of THI required become prohibitively expensive . This reality has motivated a paradigm shift toward hydrate management, wherein the ability for hydrate particles to cause a blockage is limited as a result of the operating strategy or the injection of low dosage hydrate inhibitors (LDHIs) . The successful application of this new approach requires the application of rigorous multiphase flow models that are capable of coupling hydrodynamic flow descriptions with fundamental descriptions of hydrate growth rate and particle transportability. Traditional simulation strategies have isolated hydrodynamic predictions from hydrate-specific calculations, precluding a direct coupling of both phenomena when describing the pipeline pressure network. Instead, heuristics for hydrate modules such as CSM-HyK OLGA have been developed that allow coarse estimation of hydrate blockage severity in oil-continuous flowlines, based primarily around the maximum apparent viscosity of the hydrate-in-oil slurry . While such approaches have provided an ability to even attempt the modelling of hydrate blockage formation in pipelines, the next generation of these predictive tools must directly integrate hydrate-specific formation and transportability models within a transient multiphase flow algorithm. In this manuscript, we present the first attempt at such a direct coupling, and illustrate the application of this approach to an example case study.