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GC9304D. Comparison of Empirical Models for Calculating the Vuggy Porosity and Cementation Component of Carbonates from Log Responses, by F. P. Wang and F. J. Lucia. 27 p., 17 figs., 1 table, 1 appendix, 1993. doi.org/10.23867/gc9304D. Downloadable PDF
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Formation evaluation in heterogeneous carbonate reservoirs is complicated by the presence of multiple pore types. Acoustic properties, Archie cementation exponents, and permeability transforms differ according to pore type. This study evaluates the various models for estimating vuggy porosity and the Archie cementation exponent from wireline logs, illustrates the difficulty of log interpretation applied to complex pore types, and presents generalized models developed to resolve some discrepancies within various models. A comparison of the four existing models for calculating vuggy porosity from acoustic logs shows that vuggy porosities calculated by each model do not match. The quadratic and power-law models estimate separate-vug porosity more accurately than does either the Nurmi or the Secondary Porosity Index model. The Lucia model, based on the point-count-derived vuggy porosity and the response of acoustic logs, differs significantly from other models that are based solely on the response of acoustic logs. Six models for calculating the cementation exponent from acoustic and resistivity data are reviewed, and the Lucia and Myers models are tested against core data. A generalized dual-porosity model for estimating cementation exponents is developed from a review of the six models. This generalized dualporosity model can be used for calculating cementation exponents of carbonate rocks containing both separate and touching vugs.
Keywords: acoustic log, carbonate, cementation exponent, formation evaluation, log interpretation, touching vug, vuggy porosity
Wang, F. P., and Lucia, F. J., 1993, Comparison of Empirical Models for Calculating the Vuggy Porosity and Cementation Component of Carbonates from Log Responses: The University of Texas at Austin, Bureau of Economic Geology, Geological Circular 93-4, 27 p. doi.org/10.23867/gc9304D.