ABSTRACT: A Relationship Between Critical and Irreducible Water Saturations

HARRIS, O. A., JR., Texaco USA, New Orleans, LA

Irreducible water saturation is the minimum interstitial water saturation existing above the water transition zone. Critical water saturation is the upper limit for formation water saturation above which a specific sample will produce a significant percentage of water with hydrocarbons. For many years, critical water saturation has been estimated from routine porosity and permeability data. However, there are no published data to estimate irreducible water saturation from critical water saturation.

In general, the critical water saturation increases linearly with irreducible water saturation. The proposed relationship is used to estimate either water saturation if the other one is known. With the two water saturations estimated, one can make improved water saturation analyses, as well as make better watercut predictions.

Other applications include resistivity reconstruction from core porosity and formation water resistivity. Formation resistivity can be reconstructed from irreducible water saturation for verification of assumed cementation and saturation exponents used in the Archie equation for evaluating high-resistivity formations. Reconstructed resistivity provides a valuable tool for analyzing thin-bedded or low-resistivity formations.

AAPG Search and Discovery Article #91014©1992 AAPG GCAGS and GC-SEPM Meeting, Jackson, Mississippi, October 21-23, 1992 (2009)