Computer simulation of the structure and dynamics of methane in hydrated Na-smectite clay

Monte Carlo and molecular dynamics computer simulation has been used to stu dy the microscopic properties of aqueous fluids and methane in smectite cla ys, at the elevated temperatures and pressures that are encountered in sedi mentary basins. Methane particles are solvated by approximately 12-13 water molecules, with six oxygen atoms from the clay surface completing the coor dination shell. The tendency for hydrophobic methane-methane contacts reach es a maximum at 1 km (310 K and 150 bar), in close agreement with the behav iour observed in the bulk solutions. The self-diffusion coefficients are in excellent agreement with the experimental values for methane diffusion thr ough near-surface shales. (C) 2000 Elsevier Science B.V. All rights reserve d.