Search

Abstract A range of techniques have been developed to improve the recovery efficiency of oil reservoirs. Of these, gas injection is currently the second most common EOR process after thermal methods that is practiced on a material scale with some 250 mbd directly attributable. Initial exploration of gas injection focused on use of a hydrocarbon injectant. However, competitive sales markets for hydrocarbon gas led to the identification of CO2 as a potential injectant. There is now over thirty years experience with the injection of CO2 for Enhanced Oil Recovery. Although initially developed as a means to improve oil recovery, there is renewed interest in the potential for CO2 EOR as an option to reduce global emissions of Greenhouse Gases. This may lead both to a significant expansion in the level of application as well as to some significant changes in the way in which CO2 EOR is applied. Introduction Many areas of the world are actively implementing gas injection to maximise the potential of extensive oil reserves. A successful gas flood requires two key criteria be satisfied. Firstly, the injected gas must be able to mobilise additional oil. Secondly, the flood must be able to sweep the mobilised oil to producers. Additional oil may be mobilized in two ways. Firstly, gas may be able to access parts of the reservoir that have been bypassed by water. Second, gas may enable some incremental recovery from those parts of the reservoir already swept by water by virtue of the fact that the residual oil saturation to gas is usually somewhat lower than for water. Many of the current gas injection schemes operate near to miscibility conditions to mobilise the maximum amount of incremental oil. The injected gas is often used in combination with water in order to get the joint benefits of mobilising oil with the miscible gas while using water to sweep mobilized oil to producing wells.