Reaction Kinetics of In-Situ Combustion: Part 2—Modeling

A model is proposed to analyze and differentiate between crude oil/oxygen reactions at different temperatures. The results of this analysis along with correlations of apparent hydrogen/carbon (H/C) ratio and molar carbon dioxide/carbon monoxide (CO2/CO) ratio indicated three major reactions at different temperatures. Low-temperature oxidation (LTO) appears to occur between the gas and liquid phases. Middle-temperature fuel deposition reactions appear to be homogeneous. The latter was found to be the rate-determining step in clean sands. Natural cores from the reservoirs were found to have different kinetic behavior than the clean sand matrices for these reasons: (1) metallic additives lower the activation energy of the combustion reaction and hence shift the rate-determining steps, and (2) clay and finer sands adsorb more fuel. The proposed kinetic model was found to be applicable to the five oils tested and hence may be generalized for application to any oil.