Question

When preventing methane hydrate formation, why is Monoethylene Glycol (MEG) preferred over Methanol for long-term subsea flow assurance in closed-loop systems?

Accepted Answer

Monoethylene glycol, known as MEG, is preferred over methanol in closed-loop subsea systems primarily because it is recyclable and has a significantly lower vapor pressure. Methane hydrates are ice-like structures that form when water molecules trap methane gas under high pressure and low temperature, which can block subsea pipelines. To prevent this, thermodynamic inhibitors are injected to disrupt hydrate formation. Methanol is a volatile alcohol that evaporates easily, meaning it is lost into the gas stream and cannot be recovered from the production fluid. This makes methanol prohibitively expensive and environmentally hazardous for continuous, long-term use in large volumes. In contrast, MEG is a liquid with a high boiling point and low vapor pressure, which prevents it from evaporating into the gas phase. Because MEG remains in the liquid water phase, it can be collected at the receiving facility, processed to remove water and impurities through a process called reclamation, and pumped back to the subsea wellhead for reuse. This closed-loop cycle significantly reduces operational costs and the environmental footprint of the project. Furthermore, MEG is less toxic and has a higher flash point than methanol, which improves the safety profile of the facility. While methanol is still used for infrequent, short-term maintenance or emergency inhibition where recycling is not required, MEG is the industry standard for continuous flow assurance in permanent subsea infrastructure.

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When preventing methane hydrate formation, why is Monoethylene Glycol (MEG) preferred over Methanol for long-term subsea flow assurance in closed-loop systems?