Pore-scale network simulation of NMR response in two-phase flow

Wettability controls fluid saturation and distribution in reservoir rocks, that in turn affects two-phase properties such as Nuclear Magnetic Resonance (NMR) response. We simulated the NMR response of two-phase systems during drainage and waterflooding in pore-scale networks representing sand packs and sandstones using a random walk method. Different wettabilities were studied and the simulation results were compared with previously published experimental measurements. In oil-wet media, we predict a slow decay with a broad T2 distribution because water in the center of the pores has a low bulk relaxivity; there is little surface relaxivity since the grain surfaces are covered by oil layers. This suggests a straightforward technique to indicate oil wettability in core samples.