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Simplified Green-Ampt model, imbibition-based estimates of permeability, and implications for leak-off in shale reservoirs

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Jul 14, 2020 version files 124.09 KB

Abstract

Predicting water imbibition into porous materials is important in a wide variety of fields, yet is often challenging because of uncertainties in both the permeability and capillary pressure driving force. Here, this uncertainty is reduced through evaluating correlations between the permeability and the effective capillary pressure associated with the wetting front, Pc,f. These correlations allow elimination of Pc,f from the Green and Ampt equation, and concentrates all uncertainties in fluxes on the effective permeability k. Over a wide range of k and n, imbibition scales approximately with k1/3. Although Leverett k1/4 scaling for predicting Pc,f is shown to be inferior when tested with data spanning a wide range of porosities n, it nevertheless predicted imbibition fairly well. From simple imbibition measurements, both the empirical and Leverett scaling approaches allow estimates of k that have root mean-square deviations of about 1 order of magnitude relative to measurements that ranged over 10 orders of magnitude in k.