High-resolution core-log integration techniques: examples from the ocean drilling program

Cores offer the ability to describe lithological, physical, and chemical properties of rocks at the millimetre and smaller scale. However, continuous coring is expensive and only occasionally recovers 100% of the drilled interval. Microresistivity images of the borehole wall depict features down to the centimetre and smaller scale and can complement, or in some cases substitute for, core description as a means of geologic interpretation. This paper describes two techniques of integrating core data with borehole image and log data. Two case studies in carbonate rocks recovered during Ocean Drilling Program Legs 160 and 166 are presented. Microresistivity log images, grey-scale reflectivity from core photographs, and gamma ray logs are correlated at the centimetre scale over up to 300-metre cored intervals. Direct visual correlation of core photographs with borehole images and correlation of gamma ray measurements on core with downhole logs are shown to be complementary techniques. High-resolution core-log depth matching may be best achieved by correlating multiple datasets to reduce the error inherent in each and more precisely constrain depth matching. Depth matching of individual features allows a more accurate and consistent depth scale for use in quantitative stratigraphic analysis.