Pore-throat characterization in highly porous and permeable sandstones

Several methods have been developed to characterize the pore spaces in sandstone reservoirs using data on the pore-throat-size distribution obtained from mercury injection tests. The Winland equation, the threshold pressure, the displacement pressure, and Pittman's equation are mostly used for this purpose to delineate the stratigraphic traps and seals. This study examines the reliability of these methods applied to the highly permeable Nubia sandstones in their type section in southern Egypt. These sandstones are composed mainly of siliceous sandstones and constitute the main Paleozoic-Cretaceous aquifers and reservoirs in Egypt. Routine core analysis and mercury injection tests were conducted to delineate the pore network characteristics for these rocks. The relationships between helium porosity and the uncorrected air permeability from the routine core analysis, and the various parameters derived from mercury injection-capillary pressure curves were established using multiple regressions. This study indicates the high reliability of the displacement pressure at 10% mercury saturation and also reveals the apex of Pittman's hyperbole at 45% mercury saturation as a complexity apex at which the pore network becomes highly chaotic. Despite the great benefits of such types of measurements, they are not commonly used because of their high cost. This study introduces a series of empirical equations for constructing a partial pore-aperture-size distribution curve from routine core analysis for the highly permeable rocks.