Apparent cementation factor concept for water saturation determination from well logs

Abstract EN

A method for calculating water saturations from well log resistivity/porosity data that does not require use of the Archie saturation exponent was developed.

The method uses empirically determined variations of the cementation exponent with respect to water saturation.

Resistivity and porosity data were measured for 71 clean carbonate reservoir cores.

Statistical regression analysis was then used to obtain the relationship between the apparent cementation factor, ma, and water saturation, Sw.

The regression equation is then used to determine all water saturations for the specific reservoir.

Comparisons to water saturations using Archie’s equation were excellent.

At high porosities, however, the apparent cementation concept yields lower water saturations than does Archie’s equation; and at lower porosities higher saturations are obtained.

The method simplifies the evaluation of Sw because three variables in Archie’s equation (a, m, and ri) are incorporated into the variations of ma with respect to Sw.