Mass transfer between CO2 and heavy hydrocarbon components in shale – Insights from the effect on flow

Physicochemical interactions between CO₂ and crude oil induce the deposition or blockage of heavy components. The integration of nuclear magnetic resonance (NMR) and theoretical calculations was employed to elucidate the pore-scale mass transfer mechanisms of CO₂-heavy component interactions and quantify their impacts on flow. The results indicate that the interaction between CO₂ and heavy components exhibits a pressure threshold that exceeds the miscible pressure of CO₂ and heavy components. Thermal effect makes the impact of heavy components on flow approximately 1.8–2.5 times lower than low temperatures. When injection pressure is below the miscibility, low temperature and nano-confinement effect cause heavy components in micropores to gasify after CO₂ injection, leading their migration towards macropores for liquefaction and then adsorption or blockage. Conversely, macropores' heavy components migrate towards micropores with thermal effect, resulting in endothermic adsorption. When injection pressure exceeds the miscible pressure, heavy components extracted by CO₂ adsorb and form a boundary layer away from the pore wall. As injection pressure increases to the threshold, CO₂ repeatedly contacts and extracts this fluid phase, eventually migrating out with the gas flow. This process can increase the maximum flow capacity by 70.09 % and pore volume by 8.12 %.