American Institute of Mining, Metallurgical and Petroleum Engineers Inc.

Abstract

Because fundamental reservoir information is frequently lacking in complex carbonate formations,, sound interpretive methods cannot be applied. This report presents the results of numerous laboratory tests of core samples from 20 wells in the Ratcliffe interval of the Madison limestone in the Flat Lake field in northeastern Montana.

Correlations between porosity, permeability, saturation characteristics, mineral permeability, saturation characteristics, mineral constituency and pore geometry inferred from mercury injection measurements are discussed. The heterogeneity of the matrix and its influence on fluid flow, saturation and wettability characteristics of the reservoir are considered.

The matrix permeability is preponderantly related to a relatively small fraction of the pore volume having pore entry radii larger than pore volume having pore entry radii larger than about 0.5 microns, while the porosity is mainly attributable to smaller pores. Pore geometry determined by mercury injection measurements may be correlated with permeability but not with porosity. Although a favorable water-oil mobility ratio for the matrix is inferred from the laboratory data, the very low effective permeability to water indicates that injection permeability to water indicates that injection rates will be low.

Background

In general there is less fundamental knowledge about the physical properties and performance characteristics of carbonate performance characteristics of carbonate [limestone and dolomite] reservoir rocks than of sandstones, because of the usually more complex depositional environment and post depositional processes that affect carbonates. In many processes that affect carbonates. In many fields these factors result in frequent vertical and lateral changes in lithology that make meaningful correlations very difficult. When basic reservoir information is lacking, fundamental engineering principles and sound interpretive procedures cannot be applied, and more or less intuitive procedures become accepted practice. practice. The petroleum industry has recognized for some time the need for greater emphasis on carbonate reservoir research and in recent years has supported a much greater research effort in this area.

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