Primarily as a result of low temperature oxidation (LTG) reactions, the utilization of air as a steam additive results in an increase in the rate at which oil is recovered. The individual mechanisms of the steam-air injection process are complicated and difficult to isolate. This paper presents results which were obtained from an ongoing mechanistic investigation into the LTG process.
In particular, the experiments were designed to determine the effect of air on residual oil saturation, pressure drop (i.e. ability of air to divert steam), bitumen properties (asphaltene content, viscosity, and acid number), produced aqueous phase properties (pH, sulfate, acetate, and total inorganic carbon). and coke formation during both steam and water injection experiments.
In physical simulator experiments at the Alberta Research Council the addition of air or O2 to a saturated steam injection stream markedly increased the bitumen recovery rate. The experiments were performed at 216 °C and the higher recovery was primarily due To the effects of LTD reactions on the horizontal high permeability communication path between the injection and production wells. Air also increased the final bitumen recovery When it was co-injected with water 12.
Air increases the bitumen recovery rate as a result of one or all of the following factors:
Steam diversion due to increased flow resistance in the communication path. The increased resistance is caused by (a) rapid movement of cold bitumen into the communication path, (b) reduced absolute permeability of the communication path due to coke formation and asphaltene precipitation, (c) change in sand wettability (from water-wet to oil-wet) due to the low pH conditions produced by low temperature oxidation (LTD) reactions, and (d) increase in the volumetric flow rate due to the presence of incompressible gases (N2, O2, CO, CO2, H2S).
Heat produced by oxidation reactions.
I n-situ production of CO and CO2.
The purpose of the present study was to isolate some of the above mechanisms and determine their relative importance. This was accomplished by performing core size experiments in which different mechanisms were eliminated.
A number of studies were performed to determine kinetic data for LTO reactions. They all resulted in rate equations of The form: Equation (Available in full paper)
Table (Available in full paper)