An improved technique for determination of the Swanson Petrophysical parameter, (Sb/Pc)A for correlating permeability with capillary pressure data has been developed. (Pc/Sb)1/2 as a function of Sb, yields a well defined minimum which corresponds to the values of Pc and Sb from the Swanson graphical method. The improved technique leads to ease of computer determination of the parameter. The relationships developed by Swanson for correlating permeability with capillary pressure work well for samples with permeabilities greater than 10 microdarcies. A new relationship between the Swanson parameter and permeability has been developed for tight gas sands which leads to a more accurate permeability prediction below 10 microdarcies.

Mercury capillary pressure data at wetting phase saturations higher than 50% are approximately a factor of 10 greater than centrifuge air-brine capillary pressure for tight gas sands. This contrasts with the more commonly assumed value of 5. Consequently gas-water relative permeabilities computed from mercury injection capillary pressure data will result in predictions of higher water-gas ratios than the air-brine data. Optimistic cleanup times for tight gas wells completed in water-base fluids would, therefore, be deduced from the mercury injection data.

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