Effect of Kerogen Type and Maturity on Performance of Carbon Dioxide Storage in Shale

Abstract

Abstract Potential for sequestration of carbon dioxide in organic rich shale is investigated in this work. Adsorption isotherms and Onsager diffusion coefficients are determined using molecular dynamics simulations for atomistic kerogen models. The kerogen unit models prepared by (Ungerer et al., 2014) are used in this study. To build representative solid state models for kerogen, eight kerogen molecules are placed in a periodic cubic cell. Once the initial configuration of kerogen molecules is prepared, constant-temperature constant- volume simulations and then constant-temperature constant-pressure simulations are performed to obtain the final structures. For the final structure, computed density and adsorption isotherms are within the reported experimental values. Grand Canonical Monte Carlo (GCMC) simulations are performed for CH4-CO2 mixtures to investigate binary adsorption isotherms in kerogen models with different maturities. Equilibrium molecular dynamics (EMD) simulations are used to determine Onsager diffusion coefficients. As pressure for each species in the binary mixtures increases, its adsorbed amount increases and adsorbed amount of the other species decreases. Adsorbed amount of CO2 is higher than that of CH4 for all kerogen types at all pressures tested due to the strong permanent quadrapole moment of CO2. Due to higher adsorption affinity of CO2 to kerogen pore surfaces compared to CH4, its Onsager diffusion coefficients are smaller than those for CH4 for all kerogen types.