Impact of Pore Structure and Hydrate Distribution on CO 2 -CH 4 Replacement in CH 4 Hydrate: A Pore-Scale Numerical Analysis

The mining of CH 4 hydrate through the CO 2 -CH 4 replacement method mostly occurs within CH 4 hydrate-bearing sediments. Therefore, it is crucial to investigate the replacement process on the pore scale. This study aims to explore the impacts of pore microstructure and the CH 4 hydrate non-uniform distribution on the replacement of CO 2 for CH 4 . A two-dimensional numerical model has been adopted to investigate this issue. A pore-scale numerical simulation is conducted in a physical model of real porous media. Then, the replacement process in a comparative model, in which the pore microstructure and the non-uniform distribution of the CH 4 hydrate are not considered, is simulated. The findings indicate that the CH 4 hydrate dissociation and the CO 2 -CH 4 mixed hydrate generation are affected by the effective throat length of pores. When the pore microstructure and CH 4 hydrate heterogeneous distribution are ignored, the replacement rate and CO 2 storage rate are underestimated. However, the effective throat length does not exert a significant impact on the pure CO 2 hydrate generation, which is produced by the reaction of water with dissolved CO 2 . In addition, in terms of gas migration, ignoring the heterogeneous distribution of CH 4 hydrate will underestimate the impact of initial water on the relative permeability of gas.