Chemical-assisted minimum miscibility pressure reduction between oil and methane

Abstract

Miscible gas injection is an important enhanced oil recovery technique due to favourable displacement efficiency by eliminating interfacial tension (IFT) between the injected gas and oil phases. Miscible displacement often results in far higher recovery compared to immiscible displacement. However, miscibility can be difficult to achieve in high temperature reservoirs due to high minimum miscibility pressure (MMP) with increasing reservoir temperature and in shallow reservoirs where MMP would be higher than fracture pressure. Limited studies have been performed to explore the potential of reducing MMP in CO2-oil system using chemical additives. These additives work by collecting at the boundary between the two phases thereby reducing the interfacial tension. Specifically, none have investigated potential chemical additives to reduce the MMP in methane-oil systems, which limits the potential of methane injection. We thus investigated the effect of promising chemicals (surfactant based & alcohol based) for reducing the MMP in the methane-oil system at different temperatures (333 & 373 K) for an oil with a high acidity (4.0 mg KOH/g). Results using the vanishing interfacial tension (VIT) technique show that the tested surfactant-based chemicals reduce the MMP (methane-crude oil) by up to 9% at 373 K, whereas the tested alcohol-based chemicals have little effect on the MMP. Moreover, the results show that increasing temperature improves chemical performance and yields a higher MMP reduction, suggesting that these additives are more effective in high temperature reservoirs. The outlined research likely expands the application envelop of miscible natural gas injection in shallow and high-temperature reservoirs, in addition to the environmental benefits of reducing the associated gas flaring.