Porosity and Lithology from Logs in Carbonate Reservoirs
Authors: Bertrand M.A. , Prikel K. , Kyte J.R. 
Published: December 2007

American Institute of Mining, Metallurgical and Petroleum Engineers, Inc.
This paper was prepared for the 42nd Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Houston, Tex., Oct. 1–4, 1967. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.
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Abstract
Measures of vuggy and matrix porosity, together with an identification of gross lithology, enable better engineering of carbonate reservoir operations. Multiple regression methods applied to a suitable set of well logs and core analyses can give equations that predict these rock properties from log data. These techniques have been applied to a particular carbonate reservoir to differentiate predominantly limestone and dolomite sections, respectively, as well as to measure matrix and vuggy porosity. Neutron, acoustic velocity, density, and natural gammaray logs were used in the application. Comparisons of predictions and core data are given.

Introduction
Adequate reservoir description is needed for sound evaluation, development, and operation of an oil field and for application of additional recovery methods. The need is particularly great in carbonate reservoirs comprised of some sections that have only intergranular porosity and others that have vuggy and fracture porosity as well. In these reservoirs, the oil recovery mechanism, optimum development pattern, and optimum field operation differ from section to section according to the type of porosity present Identification of the type of porosity, in addition to a measure of the amount, enhances engineering capabilities.
Well logging programs using several tools in combination help to satisfy reservoir description requirements. An appropriate set of logs can compensate for the fact that no single one measures simply and directly either porosity or lithology. The desired set includes tools that respond differently to a combination of rock properties. This group of measurements provides some mutual compensation among the logs, and permits interpretations giving values for individual properties. Practical application of these interpretations rests in the use of high speed computers to relieve formation evaluation personnel from the tedious arithmetic associated with interpreting combinations of well logs.
Two general approaches are available that isolate a measurement of a single rock property from responses of several logging devices.