Adsorptive behaviors of supercritical CO2 in tight porous media and triggered chemical reactions with rock minerals during CO2-EOR and -sequestration

Abstract CO2 injection has been recognized as a promising method to improve oil recovery while reducing CO2 emission through geo-sequestration especially in tight reservoir due to significant capillarity. The injection of CO2 into reservoir breaks the initial equilibrium of subterranean environment, and thus triggers chemical reactions between CO2 and rock minerals in the presence of water. There is however a lack of understanding of the interaction dynamics under realistic reservoir conditions. Herein, the adsorptive behaviors of supercritical CO2 in tight porous media (Lucaogou, Jimsar sag, Junggar Basin) and reactions triggered were investigated experimentally. Special attention was placed on pore-scale alterations of the rock petrophysical properties caused by these reactions. Our results indicate that the adsorption capacity of CO2 species in tight porous media gradually increases with the imposed pressure before finally reaching equilibrium at roughly 11.0 MPa. Extended-Langmuir and Langmuir-Freundlich models show improved fitting than the commonly applied Langmuir and Freundlich models, but the increase in temperature affects the fitting of these models. CO2-triggered reactions increase the permeability of tight core leading to the consumption of injected CO2. For CO2 huff-n-puff, the generated differential pressure (ΔP) across the core declines with cycle numbers and hardly changes after the third cycle. The NMR T2 spectrums conclusively evidence that the chemical reactions mainly occur in large pores of tight rock during either flooding or huff-n-puff processes.