Pore-scale investigation on dissolution and precipitation considering secondary reaction in porous media by LBM

Secondary reaction happens during dissolution and precipitation when developing shale oil resources by CO2 injection. The reactive transport process considering secondary reaction based on two-dimensional porous media is numerically researched by the lattice Boltzmann method (LBM) with the multiple-reaction boundary condition in this study. The velocity is obtained with the multiple relaxation time (MRT) operator, while the temperature and concentration are obtained with the BGK operator. The qualitative impacts of the Peclet number, pore morphology and the equilibrium constant for the secondary reaction are investigated respectively and the cases with and without the secondary reaction are compared. It is found that high Peclet number, porosity and equilibrium constant for the secondary reaction have positive impacts on quick thorough solid dissolution. The time for thorough dissolution with the secondary reaction is 3.33 times as long as that without the secondary reaction. A low Peclet number and the existence of secondary reaction lead to a small horizontal range where the dissolution happens. The equilibrium constant for the secondary reaction does not affect the dissolution pattern. The generated secondary precipitation is ununiformly distributed on the solid-fluid interface and the maximum percentage of its volume to the total solid volume is only 0.84%. Both the maximum volume of the secondary precipitation and its corresponding time increase with decreasing Peclet number or the equilibrium constant. The position corresponding to the maximum temperature coincides with the reaction zone. The maximum raised temperature without the secondary reaction is 2.9 times higher than that with the secondary reaction.