Study of displacement behavior and dispersion characteristics based on low-field NMR in the context of CO2 geological sequestration and enhanced methane recovery

Abstract

Visual characterization of the spatial and temporal distribution patterns of displacing fluids and CH₄ within the pore space and exploration of the differences in sweep effect on CH₄ are key to predicting the scale of CO₂ geological sequestration and production capacity within the reservoir. There are large differences in the displacement efficiency of CH₄ in the pore space by different components of the displacing fluid. In this study, the more cost-effective displacing fluid injection scheme is explored on the basis of CO₂ sequestration and enhanced gas recovery. Thus, the displacement behavior and dispersion characteristics of CO₂, gas mixture (50 % CO₂ + 50 % N₂) and N₂ at the pore scale are investigated. N₂ has the highest overall sweep efficiency during displacement, but it also causes the greatest degree of mixing. In contrast, liquid and supercritical CO₂ has the weakest diffusion ability and the lowest overall sweep efficiency on CH₄, but cause the least mixing. In addition, it is found that the dispersion coefficients of all three displacing fluids become smaller with increasing pressure, with the entrance/exit effect causing the CO₂ dispersion coefficients to increase by 11.3 % to 23.4 %.