One-dimensional modelling of hydrate formation in pipelines

Abstract

Hydrate formation in oil and gas pipelines can be troublesome and often, without a proper remediation, the formation of hydrates can lead to a pipe blockage. As hydrate formation is a non-isothermal process, the modelling of the thermodynamic behaviour of the phases within the flow is proposed. A single energy equation has been formulated and verified with parametric analyses. A new hydrate kinetics routine, based on a two-step hydrate formation mechanism, in an oil-dominated flow is proposed. The first step involves the mass transfer of gas from the free gas phase into the oil (gas dissolution rate) and the second step is the mass transfer of the dissolved gas into the water (gas consumption rate). Suitable models in the form of transport equations for each mechanism, together with appropriate closure relations to account for the agglomeration of hydrate particles and hydrate slurry viscosity, are formulated. Both the energy equation and the hydrate kinetics routine were integrated into an existing in-house research code, TRIOMPH (Transient Implicit One-Dimensional Multiphase). The model was tested and validated against two flow loop experiments, and has shown good agreement. Advancement over the only other existing model in predicting hydrate formation in the heavily slugged hypothetical pipe, has also been shown, giving the current model versatility in simulating both slug and non-slug cases.