Preprint A32/2013
Recovery of light oil by medium temperature oxidation
Mailybaev, Alexei | Bruining, Hans
Keywords: in-situ combustion; light oil recovery; air injection; traveling wave; porous media
We study one aspect of combustion in porous media for the recovery of light oil. We assume that there is a temperature range above low temperature combustion where oxygen is added to the aliphatic oils to form oxygenated compounds and below the temperature where cracking and coke formation occurs. In the intermediate range oil is combusted to form small combustion products like water, CO$_2$, or CO. We call this medium temperature oxidation (MTO). Our simplified model considers light oil recovery when it is displaced by air at medium pressures in linear geometry, for the case when water is absent. The resulting MTO combustion displaces all the oil. There are adjacent vaporization and combustion zones, traveling with the same speed. The MTO reaction is assumed to be slow, so that vaporization is much faster. The solution of the model equations leads to a thermal wave upstream, a MTO wave in the middle and a cold isothermal Buckley-Leverett gas displacement process downstream. One of the unexpected result is that vaporization occurs upstream of the combustion zone. In the initial period the recovery curve is similar to gas displacement, but after a critical amount of air has been injected the cumulative oil recovery increases linearly until all oil has been recovered. In our model, the oil recovery is independent of reaction rate parameters, but the recovery is much faster than for gas displacement. Finally the recovery is slower for higher boiling point and higher oil viscosity, but faster at higher injection pressure. We give a simple engineering procedure to compute recovery curves for a variety of different conditions.