An experimental investigation in the formation damage mechanism of deposited coke in in-situ combustion process using nuclear magnetic resonance

The success of an in situ combustion process is dependent on the stability and movement of the combustion front. During an in situ combustion process, coke is an important product for maintaining the stability of the combustion front. However, before being consumed by the combustion reaction, coke is deposited in the porous media; thus, it may cause the blockage of the pore throat and affect the subsequent air injection. In this study, the low-field nuclear magnetic resonance technique was applied to examine the influence of oxidized coke and pyrolyzed coke on the porous media. The results revealed that the coke deposition phenomenon was considerable in porous media and affected porosity. The formation damage was considerably severe in oxidized coke because of the drastic low-temperature oxidation. In case of the pyrolyzed core, the influence of coke on porosity is limited because of the low amount of coke generation. The average reduction in porosity was 21.90%, while that of the pyrolyzed coke is only 9.09%. Montmorillonite had the greatest catalytic effect on coke deposition for both oxidation and pyrolysis processes. Illite, kaolinite, and chlorite have an impact on coke deposition; however, because the change in porosity is attribute to a combination of multiple factors, the result is a lack of regularity. Heat causes the pore to reform and the fracture to form. The change in porous media can reduce the impact of coke deposition phenomenon on total porosity. Because of the high-temperature environment, this influence is more pronounced in the pyrolyzed core.