--> ABSTRACT: Limitations and Pitfalls of Using Quantitative Image Analysis for Reservoir Assessment, by Kenneth Ruzyla; #91030 (2010)

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Limitations and Pitfalls of Using Quantitative Image Analysis for Reservoir Assessment

Kenneth Ruzyla

Automatic image analysis is a potentially powerful technique for reservoir evaluation. The technique has been applied to analysis of porosity in thin sections for direct measurement of pore volume fraction, size, shape, and surface area. Estimates of porosity and permeability, mercury injection curves, and other reservoir parameters can be derived from pore image data. Since the technique is relatively rapid and applicable to drill cuttings, many samples can be economically analyzed, thus improving the chances of properly evaluating reservoir performance. Despite recent advances in hardware and software, many pitfalls are concealed in the process of image digitization, processing, and data interpretation. Important pitfalls include: (1) choice of magnification or scale, ( ) the Holmes effect, (3) edge effects, (4) sample anisotropy and heterogeneity, and (5) choice of parameter measured.

The main limitations of automatic image analysis arise from the problem of correct feature detection. Detection involves setting the gray-level threshold in order to define accurately the boundaries of the features to be measured. Detection is a function of sample preparation, the optical system and scanner employed, system resolution, shading, and noise. Pore measurements are strictly valid only when made on true 2-D planar sections, a condition not satisfied when using transmitted light. Sample preparation methods must insure sufficient contrast for accurate feature detection. Back-scattered electron images and incident fluorescent light images provide both adequate contrast of pores and true 2-D image data. Most reservoir pore systems are complex and many high-magnification images ust be analyzed to obtain reasonable statistical accuracy. Speed of analysis is therefore an essential consideration.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.