New Findings in Low-Temperature Oxidation of Crude Oil

Abstract

ABSTRACT Clay and sand fines reduced the permeability of sand packs in combustion tube experiments and also provided a large reaction surface area. Consequently, residual oil saturation and hence fuel concentration increased, resulting in high-temperature oxidation (HTO). In contrast, low-temperature oxidation (LTO) resulted from low fuel concentration. A combustion front temperature of 500°C (932°F) was obtained for HTO runs, compared to only 350°C (662°F) for the LTO run. During HTO, practically all injected oxygen was consumed, whereas during LTO, oxygen moved through the combustion front resulting in the formation of an oxygenated hydrocarbon fuel (atomic oxygen-carbon ratio of 0.3 was measured). As a result of distillation, the viscosity and specific gravity of the produced oil in HTO runs were reduced significantly. In contrast, LTO resulted in an increase in viscosity and specific gravity of the produced oil. A new method was developed to estimate the heat of reaction of oxygenated hydrocarbon fuels. Kinetic tube experiments showed oxidation of crude oil to consist of two stages: low-temperature oxidation followed by high-temperature oxidation, with reaction peaks at about 250°C (482°F) and 400°C (725°F) respectively. Kinetic and combustion tube experimental results indicated that an oxygenated hydrocarbon fuel was formed during low-temperature oxidation. A new oxidation model for kinetic tube experiments was developed. Oxygen consumption based on the new model agreed well with experimental data. Before implementing an in-situ combustion project, it is critical to carry out combustion tube experiments using actual crude oil, oil saturation and matrix found in the field to ascertain the type of oxidation reaction. Further, standard kinetic tube experiments may not yield the correct kinetic parameters, since fuel oxygenation is unavoidable in kinetic tube experiments. An alternative approach needs to be found to estimate the heat generated at the combustion front.