EVENTS ANALYSIS OF UNILATERAL DEPRESSURIZATION OF PIPELINES IN THE PRESENCE OF CONDENSATE
Subsea pipelines are responsible for draining all the gas production from offshore fields that, simultaneously, produce gas and oil. Subsea pipelines operate under conditions of low temperatures (4°C) and high pressures (above 100 bar), favoring the formation of condensate (liquid phase) and hydrate plugs (solid phase) that can completely block the production flow, causing substantial economic losses due to production deferment and operational expenditures to clean out the pipeline. In practice, the bilateral depressurization is the most common option for removing the hydrate plug and restart the production, yet, in some situations, it is not possible, and the unilateral depressurization ends up being performed. However, problems may arise during this procedure due to
the ballistic velocity that the plug can reach after the dissociation process. The goal of the present work is to
simulate the hydrate plug displacement in unilateral depressurization operations in the presence of condensate.
The plug velocity is obtained by the coupled solution of fluid conservation equations of mass, momentum and energy, with the momentum balance at the plug. The fluid properties are determined based on a compositional model of phase equilibrium. A typical operation situation is investigated, with an estimation of the amount of condensate formed, and composition of each phase. The dynamic behavior of the plug displacement, in the presence of condensate, is discussed.