Published online by Cambridge University Press: 10 February 2011
We propose a Monte Carlo method to simulate the magnetization decay for NMR in porous media. In this method, the diffusive spins in the fluid phase are modeled by 3-d random walkers, whose absorption at the solid surface simulates surface-mediated decay. Our method is 20 times faster than direct relaxation of the diffusion equation when a variable-step size implementation is used. We demonstrate our method by computing the surface relaxivity ρ for a Fontainebleau sandstone, whose structure was determined by X-ray tomography.