Abstract: CO₂ enhanced shale gas recovery (CO₂-ESGR) can not only increase CH4 production, but also store CO₂. In order to investigate the effects of physical parameters of shale on CO2 sequestration mechanisms, a dual-porosity, dual-permeability homogeneous model was established using CMG-GEM based on the shale of Yanchang Formation in Ordos Basin. This study analyzed the effects of vertical permeability to horizontal permeability ratio (Kv/Kh), water saturation and porosity of shale on CO₂ storage capacity with different mechanisms in CO₂-ESGR. Moreover, 27 sets of orthogonal tests were designed to investigate the extent of influence of these three factors by range analysis. The results showed that Kv/Kh increase in the range of 0.1 to 1 leads to enhanced CO₂ storage capacity with different mechanisms, and the maximum storage capacity can increase by 69.96%, of which the adsorption storage capacity can increase by 97.96%. Water saturation increase in the range of 0-0.9 induces the total CO₂ storage to show an increase first and then a decrease. The maximum storage capacity can reduce by 67.12%, of which the dissolved storage capacity can reduce by 83.35%, with the largest range fluctuation. Shale porosity increase in the range of 0.1- 0.99 leads to the reduction of total CO₂ storage capacity, and the maximum storage capacity can reduce by 95.38%, of which the adsorption storage capacity can reduce by 99.99%. Range analysis showed that water saturation has the largest impact on the amount of structural trapping, residual trapping and solubility trapping, porosity has the largest impact on total CO₂ storage capacity and adsorption storage capacity, and Kv/Kh has the least effect on CO₂ storage capacity with different mechanisms. For CO₂ storage in shale reservoirs, shale with low water saturation, low-porosity and high Ky/Kh ratio is suggested to obtain the maximum storage capacity.

Key words: CO₂ geological storage, shale, physical parameter, sequestration mechanism, numerical simulation