Optimal Separation of CO2/CH4/Brine with Amorphous Kerogen: A Thermodynamics and Kinetics Study

H Lee and FA Shakib and M Shokouhimehr and B Bubach and LY Kong and M Ostadhassan, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 20877-20883 (2019).

DOI: 10.1021/acs.jpcc.9b04432

Carbon dioxide (CO2)-enhanced oil recovery and sequestration are both processes that are associated with the separation and storage of gas in organic-rich shale formations. The current study investigates the applicability of kerogen, an amorphous and insoluble organic matter abundant in unconventional shale formations, for the separation of the mixture of gases (CO2 and CH4) in dry and wet (brine) conditions for an effective storage and injection operation. Here, through molecular dynamics, thermodynamics, and kinetics, we investigate the CO2 transportation and adsorption behavior on three-dimensional kerogen molecular models from the Bakken, which contains nonperiodically arrayed functional groups. The diffusion/separation of CO2 and CH4 is probed subject to a varying range of concentrations as well as pressure from atmospheric to high (30 bar) and realistic temperatures (333-393 K) to represent an unconventional reservoir system. It is found that kerogen models from the Bakken would demonstrate an unprecedented CO2 sorption selectivity over methane in the presence of brine (formation or interstitial water, a mixture of water and salt). Moreover, the concentration of brine shows a positive effect for CO2/CH4 selectivity that supports our goals of sequestration and enhanced production. Based on the quantitative results, the developed kerogen model is suggested as an appropriate framework for CO2 sequestration and injection to further facilitate hydrocarbon-improved recovery in organic-rich shale reservoirs and promote sequestration in a major shale formation.

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