Hydrates in high MEG concentration systems

Currently the most common flow assurance strategy is to rely upon injection of organic inhibitors, e.g. methanol, monoethylene glycol (MEG) in order to inhibit hydrate formation and to ensure unimpeded flow of hydrocarbons. The current trend for the gas industry is to favour the use of MEG over methanol for new developments. MEG loss to the vapour phase is very small and it has also the advantage that it can be effectively recovered, regenerated and recycled.

As exploration and production activities have moved into colder and deeper regions in recent years, higher concentrations of inhibitors are required. The majority of existing data are for inhibitor concentration at or below 50 wt%. Therefore, the industry is demanding data for the conventional inhibitors at higher concentrations.

In this communication, we report new experimental dissociation data for various systems consisting of methane and a natural gas at MEG concentration up to 70 wt%. The hydrate dissociation measurements were conducted using standard constant volume (isochoric) technique together with step-heating for achieving equilibrium conditions. A statistical thermodynamic approach, with the Cubic-Plus-Association equation of state, is employed to model the phase equilibria. The hydrate-forming conditions are modelled by the solid solution theory of van der Waals and Platteeuw. A good agreement between predictions and experimental data is observed, supporting the reliability of the developed model.