A New EOR Application in a Gas-Oil System

Abstract

Abstract Gravity drainage in a gas-oil system can be an efficient natural recovery process and may give rise to high unit recovery efficiencies. However, as the Gas-Oil Contact descends during drainage, there is a large, effectively immobile, oil target remaining. Detailed mechanistic studies have been performed where a miscible injectant (MI) hydrocarbon gas has been injected into the expanded gas region to recover additional oil and to accelerate production compared with continued gravity drainage. The studies were performed with finely gridded fully compositional models in both 2 & 3 dimensions. This work has built upon the significant EOR experience of three phase water-dominated systems and begins to explore two phase gas-dominated EOR processes. There are a number unique features of the two-phase Gravity Drainage Miscible Injection (GDMI) EOR process including: –The importance of vapourisation for "oil" transport;–A condensation imbibition mechanism;–The MI having greater density than the carrier fluid;–Utilisation of gravity and reservoir flux as drive for the MI;–Some dilution of MI by mobile free gas;–Low MI trapping. The results of the study indicate that GDMI is a viable recovery process that can be used to selectively target immobile oil at high gas saturations and, under certain conditions, achieve recovery efficiencies comparable to conventional EOR processes such as Water Alternating Gas (WAG).