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Abstract: Using Borehole Images to Quantify Reservoir Quality and Stratigraphic Distribution

Jon W. Roestenburg

Understanding the distribution of good-quality reservoir rock in a prospective formation is essential to improved reserves computation and maximized production.

High-resolution borehole images provide a rapid and efficient method to evaluate reservoir quality over extended sequences. Microconductivity curves from images are evaluated using modal analysis on histograms to establish specific populations. These populations are assigned to electrofacies, which are discriminated using other logs and core data to generate a lithofacies column. Net pay, or sand counts, are computed based on the distribution of log-derived lithofacies. Reservoir distribution is based on the integration of structural and stratigraphic image analyses.

This method is applied to two different reservoirs, the first example is of a well developed, valley-fill sequence comprising thick, stacked fluvial-deltaic channel sands. These sands are over 100 feet thick, have >20% porosity, and over 200 md permeability. The distribution and thickness of optimum quality reservoir is random, however. The second example is of multiple, small scale, depositional units between 3 in. and 24 in., which have 15% porosity with >500 md permeability. The net thickness and exact position of high-quality reservoir intervals is not apparent from standard logs, but becomes clear after image analysis.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994