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Summary The permeability, capillary properties. and m values of carbonate rocks are related to the particle size, amount of interparticle porosity, amount of separate vug porosity, and the presence or absence of touching vugs. Particle size. percent separate vug porosity, and the presence or absence of touching vugs usually can be determined visually. The amount of interparticle porosity is more difficult to determine visually and is done best by subtracting the visual estimate of separate vug porosity from the measure of total porosity obtained from wireline porosity logs or laboratory measurements. In the absence of touching vugs, the permeability, in values, and capillary properties can be estimated if the particle size, percent separate vug porosity, and total porosity are known. No acceptable method has been developed to estimate visually the permeability of touching vugs. A classification of carbonate porosity is proposed based on the data presented. This classification is intended to be used in the field or for routine laboratory description. Interparticle porosity is classified according to particle size and the dense or porous appearance of the interparticle area. Vuggy porosity is classified according to type of interconnection. Separate vugs are connected through the interparticle pore space and classified by percent porosity. Touching vugs are connected to each other and classified by presence or absence. Introduction The role played by the visual description of pore space in carbonate rocks in the field evaluation of a well has changed dramatically over the past 25 to 30 years. The change has been brought about by the development of new and improved logging techniques. The Archie classification, developed in 1952, was the only method at that time to estimate the amount of porosity in uncored wells. The development of porosity wireline tools (neutron, sonic, and density) has provided us with effective ways to measure wellbore porosity. The permeability of a carbonate rock, however, can not be measured directly by wireline tools and it is not directly related to total porosity. Visual descriptions of the pore geometry, therefore, still are needed to estimate permeability. While the Archie classification provides some insight into permeability relationships, new data presented here allow more accurate estimates. In addition, the relationship between pore types and Archie's m value and capillarity can be described. The role that the visual description of pore space can play in the evaluation is to describe factors that cannot be obtained from logging techniques but that are needed together with the logs to calculate saturations and productive capacities of the reservoir rock. This paper describes the basic geologic parameters that control the petrophysical parameters and shows how they are related. JPT P. 629^