Oxidation of crude oil in porous media

Abstract

In recent years, results of laboratory and field experiments have been reported in the literature describing the forward combustion process. But as yet, no qualitative or quantitative study of the kinetics of fuel combustion involved in this process has been reported. The main purpose of this work was to study the oxidation reaction kinetics in the forward combustion oil recovery process. A total of 48 runs were made wherein a stationary thin layer of coked unconsolidated sand was burned isothermally in a combustion cell. Individual runs were made at various temperature levels to permit determination of the effect of temperature upon the reaction. The method was reasonably fast and can be used to measure the oxidation and deposition of fuel for a given crude oil and porous media. An expression was obtained for the burning rate of carbon as a function of carbon concentration, combustion temperature, and oxygen partial pressure. The carbon burning rate for two types of crude oil indicated a first order reaction with respect to both carbon concentration and oxygen partial pressure. The results have shown that the effect of combustion temperature on the reaction rate constant matched the Arrhenius equation. The activation energy was not affected by the gravity of the few crude oils examined. The activation energy decreased for a porous media containing clays. The rate of oxidation of crude oil at reservoir temperature was found to be significant. A reaction rate expression for this low-temperature oxidation was also determined. The fuel deposited on sand decreased as coking temperature increased, and larger amounts of fuel were deposited on the system containing clays. The atomic hydrogen-carbon ratio for the fuel decreased with increase in temperature. A higher weight percentage of hydrogen than weight percentage of carbon was burned at the beginning of the combustion run. The reaction rate constants computed for two combustion tube runs compared reasonably well with values obtained from the isothermal combustion cell runs. An increase in the gas flux at the higher oxidation temperatures investigated resulted in a slight decrease in the reaction rate constant. At about 900??F, the gas flux was found to have a negligible effect on the reaction rate constant.