Carbon dioxide (CO 2 ) injections in geological formations are usually performed for enhanced hydrocarbon recovery in oil and gas reservoirs and storage and sequestration in saline aquifers. Once CO 2 is injected into the formation, it propagates in the porous rock by dispersion and convection. Chemical reactions between brine ions and CO 2 molecules and consequent reactions with mineral grains are also important processes. The dynamics of CO 2 molecules in random porous media are modeled with a set of differential equations corresponding to pore scale and continuum macroscale. On the pore scale, convectivedispersive equation is solved considering reactions on the inner boundaries in a unit cell. A unit cell is the smallest portion of a porous media that can reproduce the porous media by repetition. Inner boundaries in a unit cell are the surfaces of the mineral grains. Dispersion process at the pore scale is transformed into continuum macroscale by adopting periodic boundary conditions for contiguous unit cells and applying Taylor-Aris dispersion theory known as macrotransport theory. Using this theory, the discrete porous system changes into a continuum system within which the propagation and interaction of CO 2 molecules with fluid and solid matrix of the porous media are characterized by three position-independent macroscopic coefficients: the mean velocity vectorŪ * , dispersivity dyadicD * , and mean volumetric CO 2 depletion coefficientK * . 123 88 F. Javadpour Nomenclature A A-function (cf. Eq. 19) B B-field (cf. Eq. 23) C Concentration, mol m −3 D Dispersivity dyadic, m 2 s −1 DMolecular diffusion coefficient, m 2 s −1 D g Diameter of a mineral grain, m D x Macrotransport dispersivity coefficient in x-direction, m 2 s −1 D * Macrotransport dispersivity dyadic coefficient, m 2 s −1 J ∞ 0 Asymptotic probability flux density, m −2 s −1 K Permeability tensor, m 2 K * Macroscale depletion rate, or mean volumetric CO 2 sequestration coefficient, s −1 K x Macrotransport depletion rate coefficient in x-direction, s −1 lBasic lattice vectors, m l Unit cell length, m L Length of porous bed, m p Pressure, kPa P ∞ 0 Steady state conditional probability density, fraction r Radial vector, m R Macroscale position vector, m R n Discrete position vector specifying the location of the nth unit cell, m s Ratio of reactive surface to the interstitial space volume, m −1 (m 2 m −3 ) s g