A New Transient Framework for Assessing Hydrate Formation

As the production of oil and gas moves toward deeper water, the problem of hydrate formation in flowlines becomes more prominent. Traditionally, a strategy of avoidance requiring the addition of large volumes of thermodynamic inhibitors has been pursued. The fiscal constraints of deepwater production may be overcome if hydrates are allowed to form, and the risk of blockage can be successfully managed. This evolving view posits that the flowline may be allowed to operate within the hydrate equilibrium region, while employing both unique operating strategies and novel technologies to avoid blockages. For such methods to be applied with confidence, a robust understanding of both hydrate formation and multiphase transport behaviour are required. The current engineering approach models both concepts independently, where the effect of hydrate growth on slurry transportability is typically isolated from transient flow simulations. In this work, we introduce a new approach to bridge this gap by incorporating the effect of pressure loss due to slurry viscosification and stenosis, or a narrowing of the flow channel, on the driving force for multiphase flow. We present the results of a deepwater flowline case study, in which established hydrate formation and transportability calculations are coupled to a fully transient multiphase flow engine; this unique approach enables flow assurance engineers to evaluate the severity of hydrate formation on a physical basis. For the first time, the quantitative effects of operating within the hydrate stability region can be estimated with respect to hydrate growth, production rate, and fluid properties.