Relocating and orientating cores by the integration of electrical and optical images: a case study from Ocean Drilling Program Hole 735B

While the dip of structural features on recovered rotary-drilled core can b e accurately measured, the azimuth of such features in a geographical refer ence frame is not known. Scribing techniques and analysis of magnetic signa tures 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 reorienta tion and accurate location within a borehole using a comparison between bor ehole electrical images and whole-core digital images. ODP Hole 735B penetrates a 1500 m section of lower oceanic crustal (gabbroi c) rocks with an average core recovery of 86.6%. The absence of orientated core pieces severely restricts the interpretation of these data. In this st udy, the entire outer surface of individual core pieces was scanned using t he DMT Digital Colour CoreScan (TM) system. Structural features on these un rolled digital images are correlated with images of the same features on Fo rmation Microscanner logs obtained during the wireline-logging programme. U sing this approach it is possible to reorientate and accurately locate core pieces within the drilled section.