Molecular Investigation of CO2/CH4 Competitive Adsorption and Confinement in Realistic Shale Kerogen

Abstract

The adsorption behavior and the mechanism of a CO2/CH4 mixture in shale organic matter play significant roles to predict the carbon dioxide sequestration with enhanced gas recovery (CS-EGR) in shale reservoirs. In the present work, the adsorption performance and the mechanism of a CO2/CH4 binary mixture in realistic shale kerogen were explored by employing grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. Specifically, the effects of shale organic type and maturity, temperature, pressure, and moisture content on pure CH4 and the competitive adsorption performance of a CO2/CH4 mixture were investigated. It was found that pressure and temperature have a significant influence on both the adsorption capacity and the selectivity of CO2/CH4. The simulated results also show that the adsorption capacities of CO2/CH4 increase with the maturity level of kerogen. Type II-D kerogen exhibits an obvious superiority in the adsorption capacity of CH4 and CO2 compared with other type II kerogen. In addition, the adsorption capacities of CO2 and CH4 are significantly suppressed in moist kerogen due to the strong adsorption strength of H2O molecules on the kerogen surface. Furthermore, to characterize realistic kerogen pore structure, a slit-like kerogen nanopore was constructed. It was observed that the kerogen nanopore plays an important role in determining the potential of CO2 subsurface sequestration in shale reservoirs. With the increase in nanopore size, a transition of the dominated gas adsorption mechanism from micropore filling to monolayer adsorption on the surface due to confinement effects was found. The results obtained in this study could be helpful to estimate original gas-in-place and evaluate carbon dioxide sequestration capacity in a shale matrix.

Enhanced Recovery From Organic-Rich Shales through Carbon Dioxide Injection: Molecular-Level Investigation

“…The rate at which the ultimate recovery can be reached, however, was determined by the connectivity of reservoir pores and the extent of the induced hydraulic fractures. The adsorption results of CH 4 –CO 2 presented in this study shared a similar trend to some others reported in the literature. ,,,, …”

“…The results also showed that in the case of the CO 2 /CH 4 binary mixture, increasing the pressure resulted in a slight increase in carbon dioxide adsorption and a slight decrease in methane adsorption. They also examined the impact of thermal maturity on adsorption; the simulation results showed that a mature type II kerogen had a larger adsorption capacity than other type II kerogen molecules …”

“…They also examined the impact of thermal maturity on adsorption; the simulation results showed that a mature type II kerogen had a larger adsorption capacity than other type II kerogen molecules. 21 In addition, Gu et al discussed the effect of shale pore structure and composition on the selectivity of carbon dioxide over methane. The authors showed that a higher carbon dioxide adsorption in comparison to that of methane does not necessarily mean more CO 2 −shale interactions.…”

Confinement Effects and CO2/CH4 Competitive Adsorption in Realistic Shale Kerogen Nanopores

“…The in-depth adsorption mechanism and confinement effect in realistic kerogen nanopores are still not fully understood. Based on our previous molecular studies on competitive adsorption of CO 2 /CH 4 in kaolinite clay and graphene slit-like nanopores in shale reservoirs, ,, we focused on the molecular investigation of gas adsorption mechanism and confinement effect in realistic kerogen nanopores in the present work. Type III-A kerogen proposed by Ungerer et al was employed to develop the inkbottle-shaped and slit nanopores with surface roughness.…”

The estimation of CO2 storage potential of a gas-bearing shale succession at the early stage of reservoir characterization: a case study from the Baltic Basin (Poland)

“…Due to its phys i cal prop er ties, CO 2 is a per fect agent for stim u la tion of meth ane (CH 4 ) pro duc tion from ul tra-tight shale res er voirs, as well as from con ven tional res er voirs. Firstly, a higher CO 2 (than CH 4 ) ad sorp tion af fin ity to or ganic mat ter and clay min er als leads to CH 4 re place ment by CO 2 in or ganic matter and other min eral pore sur faces (Heller and Zoback, 2014;Zhou et al, 2019). This mech a nism pro duces an ac tive push of gas off the res er voir and en sures per ma nent bond ing of CO 2 in the shale vol ume.…”