--> Abstract: Critical Water Estimates for Gulf Coast Sandstones, by Raymond J. Granberry, Dare K. Keelan; #90967 (1977).

Datapages, Inc.Print this page

Abstract: Critical Water Estimates for Gulf Coast Sandstones

Raymond J. Granberry, Dare K. Keelan

Hydrocarbon-productive sandstones in the Gulf Coast area exhibit wide variances in formation-water saturation. Values ranging from 10 to 70% pore space are not uncommon. These variances are related to the capillary properties of the sandstone, height above the water level, fluid interfacial tensions, and density difference of the entrained fluids. This formation water may, or may not, flow in appreciable quantities, depending on the water-retentive characteristics of the rock, the relative permeability of the formation, and fluid viscosities. The combined influence of these variables results in a critical upper limit for formation-water saturation, above which a significant percentage of water will be produced. This limiting water saturation exceeds the irreducible satura ion value and has been called the "critical interstitial water saturation" (Sciw). It can be correlated with the basic rock properties of permeability and porosity.

A generalized correlation of critical interstitial water saturations for Gulf Coast sandstones allows a critical saturation to be estimated from permeability and porosity data given in a routine core-analysis report. Critical water saturations are higher as porosity increases in samples of constant permeability and as permeability decreases in samples of constant porosity.

The range of critical interstitial water saturation also influences the interpretation of the quick-look computer-calculated Rwa ratio curve used to predict hydrocarbon-productive zones. The Rwa multiple of three, commonly used to indicate hydrocarbon production, corresponds to water saturation of 58% of pore space. Low-permeability zones will yield hydrocarbons with a Rwa ratio of two, which corresponds to a water saturation of 70%. High-permeability sandstones may require Rwa multiples of six or more to be hydrocarbon productive. The required multiple for a sample of any given permeability and porosity also can be estimated from the generalized correlation of critical water values presented.

AAPG Search and Discovery Article #90967©1977 GCAGS and GC Section SEPM 27th Annual Meeting, Austin, Texas