Carbon Dioxide Emission Intensity: Steam versus Air Injection EOR
This article is intended to address a pervasive inaccuracy concerning the relative amounts of carbon dioxide generated by steam versus air injection projects. The prevailing perception is that air injection EOR has a significantly higher CO2 emission intensity than steam injection. Let us examine typical operating conditions of both types of processes.
Approximately 75 standard m3 of natural gas is required to generate 1 m3 of 100% quality steam (cold water equivalent). If we assume that the natural gas is essentially methane, then burning 1 m3 of gas will produce 1 m3 of CO2.
Assuming different steam-oil ratios (SOR) allows us to calculate the amount of CO2 generated per m3 of oil produced, the CO2 intensity.
The table shows CO2 intensities for SOR’s from 2 to 6. The best SAGD projects have SOR’s from 2.0-2.5 and average projects are in the 4.0-6.0 range. For typical projects we can therefore expect a CO2 intensity of around 400 ST m3 / m3 oil.
If we assume that during underground combustion there is equimolar replacement of the oxygen in the injected air to form CO2, then 1 m3 of oxygen will burn hydrocarbons to produce 1 m3 of CO2.
The most efficient air injection projects make use of gravity and have lower air-oil ratios (AOR), in the range 800 to 1,000 standard m3 per m3 of oil. On average, however, the AOR’s are around 2,000. For typical projects we can therefore expect a CO2 intensity of around 400 ST m3 / m3 oil.
While individual projects may have superior or inferior performance, on average, air and steam injection projects will have essentially the same CO2 emission intensity.