Kerogen Differential Swelling during CO₂-CH₄ Adsorption: Mechanism and Significance

Abstract

There exists differential swelling during the pure and competitive adsorption of CO2-CH4, whose mechanism was of broad interest to CO2-ESGR (CO2 enhanced shale gas recovery) and CCUS (carbon capture, utilization, and storage) engineering. However, the kerogen differential swelling during CO2-CH4 adsorption has been rarely reported, and so is its mechanism and significance. Here, the differential swelling mechanism of kerogen atomic representation was investigated using molecular simulation and the poromechanical model. Results indicated that swelling ratios for the systems of pure CO2, pure CH4, and a binary mixture of CO2 + CH4 (mole ratio = 1:1) gradually increase with the increasing temperature, pressure, and bulk mole of CO2. The activation energy of swelling deformation can be calculated via the Arrhenius formula, where they were 1.58 and 1.33 kJ/mol for CO2 and CH4, respectively, at 0.1 MPa, indicating that the swelling deformation of CO2 adsorption requires more energy to trigger than CH4. CO2 plays a dominant role in triggering the swelling deformation of competitive adsorption system. The swelling activation energy of pressure dependence firstly increases and then decreases with the increasing pressure. The outcomes of this paper have a higher fidelity than many previous efforts and were expected to be of broad interest to CCUS and CO2-ESGR.

Matrix Compressibility and Multifractal Nature of Nanoporous Shale

“…Generally, in shale or coal reservoirs, matrix deformation can be attributed to two common effects: (i) deformation caused by adsorption/desorption with matrix swelling/shrinkage , and (ii) pressure-induced deformation characterized by geomechanical matrix compression. , Extensive research has been conducted on adsorption swelling and desorption shrinkage. ,, However, there is limited research on geomechanical matrix compressibility for shale reservoirs. , Compared to nonporous materials, the compression behavior of nanoporous shale is more intricate. Mercury injection capillary pressure (MICP) measurements with the combination of low-pressure N 2 adsorption (LPN 2 A) were employed to evaluate compression deformations in porous materials. − Liquid mercury can penetrate the nanopores in dense rock samples due to its extremely low compressibility, making it more resistant to compression compared to the solid matrix. , With the increasing intrusion pressure, the matrix skeleton would be compressed by high-pressure mercury, , and the volumetric deformation from matrix compression would provide noticeable intrusion volumes .…”