This paper summarizes the results of reservoir simulations performed to investigate steam-air injection and its potential as a thermal recovery process. The steam-air injection process is considered to be any process that involves both steam and air injection whether they are injected together or at different times. The objective of the simulations was to develop steam-air injection based on its ability to divert steam from more to less oil depleted regions thereby improving reservoir contact (conformance) and increasing oil production. This diversion is caused by the deposition of coke and/or asphaltene in depleted regions or high permeability channels or thief zones. It primarily results from low temperature oxidation (LTO) of the oil. Air injection is most effective when used to divert injected steam when significant channeling/over-riding is occurring prior to air injection.
Air should be injected at a relatively low rate and temperature in order that coke/asphaltene deposition occurs and facilitates steam diversion. Simulations showed that in a field application of the steam-air injection process, it is important to stop injecting air with/without steam once diversion has been obtained. Otherwise, oil will unnecessarily be consumed or degraded by LTO reactions and steam diversion may be reduced due to consumption of deposited coke/asphaltenes by high temperature oxidation (HTO) reactions. Continued injection of air could even increase channeling as it removes the coke and any residual oil by oxidation reactions thereby reducing the flow resistance in channels/thief zones. Air injection in a steam process is complex and it is not simply a case of injecting air with steam without careful consideration of the process.