--> ABSTRACT: Core-Log Integration: Importance of Depth Control, by Thomas L. Knode and Keith V. Vickers; #91022 (1989)

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Core-Log Integration: Importance of Depth Control

Thomas L. Knode, Keith V. Vickers

The key to any successful exploration or development program lies in proper data acquisition and assimilation. Integration of the disciplines of geology and geophysics will be complementary only if the underlying principles of both are understood and, more important, if data acquisition and correlation are proper.

A fundamental basis for correlation between geology, petrophysics (cores), and geophysics (wireline and seismic) is the proper depth match of the information. Depth correlation of cores has evolved since its inception. The potentially least accurate method of correcting the depth of a core is marking the cores with driller's depths at the time of coring, then later correcting the depths by the difference between bottom depths of the drilling company and the logging company. This method is sometimes accurate and will work only if the driller is on or off depth consistently.

Laboratory gamma-ray logging of the core to correlate with the open-hole logs is another way of correlation. If the laboratory logging is done well, then theoretically the core can be put on depth and missing intervals can be identified. The problem in this method lies in the vertical resolution of the open-hole logging tool, which is approximately 2 ft. Therefore, the core can be placed with confidence within 2 ft of its open-hole log depth.

For further refining of the depth correlation, it can be shown that tools with increasingly smaller vertical resolutions (such as dipmeters and borehole televiewers) will be of great value. The small vertical resolution of these tools should allow depth correlation based upon visible natural markers within the core that correspond to geophysical responses on the logs.

When comparing the results from petrophysical analysis to wireline responses, if the method used to integrate the two sets has a poor resolution, then the results will have a poor correlation. A successful core-to-log integration package relies first upon the integration methods (depth control), then on the understanding of the relationships between results of the open-hole tools and the laboratory measurements.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.