Publications

Carbonate classification schemes usually focus in the visual analysis of core, sidewall core, cuttings and outcrop data. In situ classification based on electrical images provides another dimension. Due to the introduction of high resolution imaging techniques, many of the meso scale features of carbonates are identifiable in place. Most carbonates exhibit a pronounced response to resistivity and hence conductivity. Fragments and diagentic features, are usually resistive and the intervening ",matrix", is usually conductive.Interactive computer techniques are used to quantify the shape, size, frequency of occurrence, interconnectivity and coverage, of resistive and conductive features on images. In this way, the electrical images are reduced to logs which can be zoned into facies when displayed versus depth. The most indicative curves are the size curves. These are plotted on the same scale in square millimeters and a shading is applied. Whenever the resistive size log approaches a minimum, close to zero and the conductive size log approaches a maximum, then the facies are matrix supported and classed as micrites. Grainstones show a resistive and conductive size fraction that is virtually the same allowing the logs to overlie. Packstones show a median resistivity size fraction and a slightly higher conductive size fraction. Wackestones show more conductive than resistive fractions and packstones are dominated by resistive (carbonate fragments or grains) fractions. Floatstones and diagenetic cementation facies are essentially completely resistive dominated, with occasional conductive fractions from moulds, vugs and minor inter fragmental matrix.