Abstract

While the dip of structural features on recovered rotary-drilled core can be accurately measured, the azimuth of such features in a geographical reference frame is not known. Scribing techniques and analysis of magnetic signatures have been used in attempts to solve this problem, but scribing has so far failed in deep-sea drilling operations and magnetic signatures cannot always be easily resolved. Here, we demonstrate a method for core reorientation and accurate location within a borehole using a comparison between borehole electrical images and whole-core digital images.

ODP Hole 735B penetrates a 1500 m section of lower oceanic crustal (gabbroic) rocks with an average core recovery of 86.6%. The absence of orientated core pieces severely restricts the interpretation of these data. In this study, the entire outer surface of individual core pieces was scanned using the DMT Digital Colour CoreScan™ system. Structural features on these unrolled digital images are correlated with images of the same features on Formation Microscanner logs obtained during the wireline-logging programme. Using this approach it is possible to reorientate and accurately locate core pieces within the drilled section.

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