Saline aquifers are chosen for geological storage of greenhouse gas CO

2

because of their storage potential. In almost all cases of practical interest

CO

2

is present on top of the liquid and CO

2

dissolution leads to a small increase in the density of the aqueous phase. This situation results in the creation of negative buoyancy force for downward density-driven natural convection and consequently enhances CO

2

sequestration. In order to study CO

2

injection at pore-level

an isothermal Lattice Boltzmann Model (LBM)with two distribution functions is adopted to simulate density-driven natural convection in porous media with irregular geometry obtained by image treatment. The present analysis showed that after the onset of natural convection instability

the brine with a high CO

2

concentration infringed into the underlying unaffected brine

in favor of the migration of CO

2

into the pore structure. With low Rayleigh numbers

the instantaneous mass flux and total dissolved CO

2

mass are very close to that derived from penetration theory (diffusion only)

but the fluxes are significantly enhanced with high Ra number. The simulated re

sults show that as the time increases

some chaotic and recirculation zones in the flow appear obviously

which promotes the renewal of interfacial liquid

and hence enhances dissolution of CO

2

into brine. This study is focused on the scale of a few pores

but shows implications in enhanced oil/gas recovery with CO

2

sequestration in aquifers.