Hydrocarbon Mixture and CO2 Adsorptions in A Nanopore-Bulk Multiscale System in Relation to CO2 Enhanced Shale Gas Recovery

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  • Thanks to the continuous depletion of conventional gas reservoirs, shale gas plays an important role to meet the global natural gas demand. The CO2 'huff-n-puff' process has been proven to be an effective method to enhance shale gas recovery and sequestrate CO2. Unlike conventional reservoirs, shale media can contain a significant number of nano-scaled pores and their pore volume can be comparable to that of macropores and fractures in which fluids behave as bulk. While previous works studied the mechanisms of CO2 ‘huff-n-puff’ process in shale gas exploitation, the volume partitioning between nanopores and macropores/fractures is not fully taken into account. In this work, we built a nanopore-bulk multiscale model with varying pore size distributions (PSDs) to study the CO2 'huff-n-puff' process in a constant volume depletion (CVD) setting by using density functional theory (DFT). We found that the volume partitioning effect on adsorption, fluid compositions, hydrocarbon mixture (C1, C2, and C3) recovery is significant in the CO2 'huff-n-puff' process. The majority of hydrocarbon mixtures can be released from micropores and smaller mesopores during the CO2 ‘huff’ and ‘soak’ process, while the average hydrocarbon densities in larger mesopores might increase. During the CO2 ‘huff’ and ‘soak’ process, due to a stronger confinement effect in smaller pores, the PSD case with a higher volume ratio of smaller pores releases fewer hydrocarbons, while stores more CO2 per unit pore volume. Overall, the volume partitioning has a significant effect on hydrocarbon adsorption, compositions, and recovery as well as CO2 storage during the CO2 ‘huff-n-puff’ process in shale gas exploitation and geological CO2 sequestration.

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    Attribution-NonCommercial 4.0 International