Porosity and Permeability of Mesaverde Sandstone Core from the U.S. DOE Multiwell Experiment, Garfield County, Colorado

Abstract

Abstract As received water saturation was measured and several dry core analyses were performed on 32 Mesa Verde sandstone core samples from depths between 1496 m (4910 ft) and 2475 m (8118 ft) in Garfield County, Colorado. Eight of the higher permeability samples were then selected for determination of the effect of fractional water saturation upon permeability. The samples were from 13 sandstone intervals covering four depositional environments (fluvial, coastal, paludal and marine). The dry core analyses measured porosity, Klinkenberg permeability, Klinkenberg slope, and pore volume compressibility at net stress representative of the midpoint of reservoir drawdown. In addition, pressure was measured using a conventional mercury injection porosimeter. Klinkenberg permeabilities for the samples dried to constant weight at 60°C and 45% relative humidity at 1 atmosphere pressure averaged 1.9 μ darcy at net stress representative of the midpoint of reservoir drawdown. Porosities under these same stress conditions varied between extremes of 4.4 and 11.4% with an average of 7.2 %. The decline in permeability to gas with increasing fractional water saturation was found to be surprisingly sharp. For net confining stress representative of the midpoint of reservoir drawdown, water saturations required to reduce relative permeability to 0.01 were in the range of 40% to 55% with an average of 46%. Of the 8 samples, only two exhibited Klinkenberg permeability in excess of 0.1μ darcy for water content equal to the as received" value. Measurement of the variation in permeability to gas as functions of net stress and water content revealed a dramatic difference between fluvial samples with high pore volume compressibility and paludal samples with lower pore volume compressibility.