Combustion Kinetics of Heavy Oils in Porous Media

Abstract

In this study, the kinetics of heavy crude-oil combustion in porous media are reported. Ramped temperature oxidation (RTO) tests with effluent gas analysis are conducted to probe in situ combustion (ISC) reaction kinetics along with isothermal coke formation experiments. The role of oxygen on coke formation reactions (i.e., fuel formation for ISC) is investigated using X-ray photoelectron spectroscopy (XPS) of intermediate reaction products. The XPS data is analyzed along with companion RTO experiments to obtain a simplified multistep reaction scheme. Synthetic cases illustrate the connection between a proposed reaction scheme for oil/matrix pairs and one-dimensional combustion front propagation. Analysis of experimental results illustrate that the reaction scheme is capable of reproducing experimental results including the basic trends in oxygen consumption and carbon oxides production for RTO experiments as a function of heating rate for both good and poor ISC candidates. The combination of XPS and RTO studies indicates that the quality (or reactivity) of coke formed during the process is a function of oxygen presence/absence. Coke formed in the presence of oxygen is significantly more reactive due to additional oxygen functional groups on the coke surface in comparison to coke formed under an inert atmosphere. Additionally, this work extends relatively easy to perform RTO tests as a screening tool for ISC performance.