Geologists exploring for oil and gas need quantitative field criteria for estimating the reservoir potential of rocks. Such criteria are presented in this paper. They were derived by correlating visual rock characteristics with measured reservoir properties. The criteria are based on approximately 2,000 samples of various lithologic types from several areas.

The rocks were first examined in polished section with the binocular microscope and classified according to surface texture. They then were analyzed for reservoir properties of porosity, permeability, and pore-size distribution. An empirical correlation was found between these rock textures and reservoir properties. A classification was developed in which both sandstone and carbonates were divided into four major surface-textural types. Using the empirical correlation that was found, one can estimate reservoir properties from surface texture alone.