Saturation gradients in drainage of porous media: NMR imaging measurements

A steady‐state method recently proposed for measuring two‐phase flow properties of a porous medium is supplemented by NMR imaging for measuring the saturation gradients which are allowed to persist in the specimen. The method relies on a strong capillary end effect which is assumed to be enforced by an outlet capillary pressure boundary condition, but direct verification of this has not hitherto been available. For constant flow rates, incremented stepwise, steady‐state profiles of hydrocarbon saturation S o are obtained which agree with predictions that they be monotonic, nonintersecting, and convex. Using D 2 O for the aqueous phase allows unambiguous detection of hydrocarbon by NMR, and imaging measurements of transverse relaxation time T 2 were included in the protocol. T 2 shows a dependence on S o which is mild but not negligible for quantitative NMR imaging.