Supercritical Carbon Dioxide Enhanced Natural Gas Recovery from Kerogen Micropores

The increasing global energy demand necessitates the development of sustainable methods for methane (CH4) extraction that align with environmental goals. Supercritical carbon dioxide (CO2) has recently gained attention as a promising agent for enhanced gas recovery (EGR) from CH4-rich source rocks, offering the dual benefit of methane extraction and carbon sequestration. Yet, the intricacies of how supercritical CO2 facilitates EGR at the molecular level remain elusive. In this investigation, we utilized constant chemical potential molecular dynamics (C
MD) to examine the dynamics of CH4 recovery when supercritical CO2 is injected into both immature (Type I-A) and overmature (Type II-D) kerogens under typical reservoir conditions (365 K and 275 bar).

Our results underscored the marked differences in adsorption and desorption kinetics between the two kerogen types. Immature kerogen, with its more interconnected pore structure, allowed faster fluid diffusion, translating to quicker simultaneous adsorption of CO2 and desorption of CH4. In contrast, the structural complexity of overmature kerogen inhibited fluid movement, making both processes slower. The kinetic coefficients we obtained reveal CO2 adsorption and CH4 desorption in Type I-A to be considerably faster than in Type II-D. Moreover, overmature Type II-D kerogen's inaccessible micropores mean not all CH4 can be extracted. Our data indicates that for each CH4 molecule displaced, Type-II-D and Type I-A kerogens adsorb at least two and six CO2 molecules, respectively. Ultimately, CO2 injection can lead to CH4 recovery rates of 90% in Type I-A kerogens and 65% in Type II-D kerogens, emphasizing the potential of this method in different reservoir conditions.