Orienting drill core using borehole-wall image correlation analysis

•A method for orienting drill core is presented.•Rotational parameters for coordinate transformations are defined using Euler angles.•Planar structures in drill core are correlated with those in borehole wall images.•The method is simple, rapid and has uncertainty of <5°.

A method for orienting drill core is proposed that correlates measurements of planar structures in drill core with those observed in spatially referenced images of borehole walls. The drill core orientation is expressed in terms of a transformation between the geographic coordinate system and the drill core coordinate system, using the Euler angles θ, Φ, and φ. The angles θ and Φ are the azimuth (trend) and the plunge of the inclined borehole, respectively. The angle φ is the rotation angle about the drill core axis and is determined through correlation analyses of planar structures in the drill core with those observed in the borehole wall images. Orientations of planar structures in the drill core are measured in terms of a reference line that is drawn along the length of the drill core in an arbitrary position. The proposed method is applied to drill core samples recovered from a borehole that penetrates the Median Tectonic Line (MTL) at Matsusaka-Iitaka (ITA), eastern Kii Peninsula, Japan. The results suggest that the accuracy of the determination of φ is about ±5°.