Economic evaluation of MEG injection and regeneration process for oil FPSO

Abstract

Injection and regeneration of MEG for an offshore oil field to prevent the risk of hydrate formation was compared to those of conventional hydrate inhibitor, MEOH (methanol). It was presumed that the injected MEG was regenerated in FPSO to 90 wt% concentration while the MeOH was simply treated without re-use. A multiphase simulation tool was employed to determine the temperature and pressure profile in subsea flowline, which provided the required concentration of hydrate inhibitors for hydrate prevention. While the required concentration of MeOH was around 18 to 30 wt% depending on the water depth, the concentration of MEG was varied from 28 to 46 wt%. NPC (net present cost) for MeOH and MEG injection was estimated as a function of injection count per year with economic assessment. The resulting NPC of MEG injection system for single injection event per year was expensive than that of MeOH injection system due to the higher total capital costs for MEG injection and regeneration system. However, the economic benefit of MeOH systems was decreased with increasing the injection event frequency because the injected MeOH cannot be recovered, and increasing storage tank and purchased MeOH cost were directly added to the total cost. When varying the water depth, i.e. ambient sea water temperature of the offshore oil field, the minimum number of injections per year was different for the MEG injection system to be economically favorable than the MeOH injection system. It became economically favorable when injected more than 2.2 times per year for the case of water depth 1250 m, while it required more than 3.3 times per year for the case of water depth of 600 m. The results showed that the MEG injection and regeneration system can be a feasible option for remote oil fields depending on the average number of hydrate inhibitor injection per year.