Effect of Fluid, Confining Pressure, and Temperature on Absolute Permeabilities of Low- Permeability Sandstones

Abstract

Summary The combined effect of temperature, confining pressure, and test fluid on absolute permeabilities of low-permeability sandstones has been investigated. Absolute permeabilities to liquids were dependent on polarity but were always significantly less than Klinkenberg permeabilities for gases. Differences are ascribed to swelling and dispersion of fine particles. Changes in state of dispersion caused by ultrasonication were investigated by measurement of resulting changes in permeabilities. Nitrogen, brine, and distilled water were used as test fluids in a main series of tests for which temperatures ranged from 0 to 93°C [32 to 199°F] and confining pressures from 3.45 to 34.47 MPa [500 to 5,000 psi]. Absolute permeabilities of five formation samples of various origins differed by up to three orders of magnitude, with the highest permeability being a few millidarcies. All specimens showed marked reduction in permeability with increase in confining pressure. For all cores, however, absolute permeabilities to gas were essentially independent of temperature at all levels of confining pressure. Comparable measurements of brine permeability were made for two core samples and, as with gas flow results, no significant temperature effect was found. Klinkenberg slip factors, B, were found to vary linearly with absolute temperature, but gave positive intercepts on the temperature axis of B vs. T plots. The intercepts were larger for gases of higher boiling point. This deviation is shown to be mainly a result of the nonideal effect of temperature on gas viscosities.