Abstract

Borehole image logs provide high-resolution directional data sets, in addition to a wealth of information concerning sedimentary fabric and texture. The data derived from these images are typically used for lithofacies characterization, palaeotransport analyses, and fault and unconformity recognition. These data are ideal input variables to the development of correlative models, particularly within a sequence stratigraphical context. However, in field settings characterized by low structural dip (less than 15°), unconformity recognition can be very difficult within shallow marine sediments, which would have had very low depositional or sedimentary dip. In the study described, integration of borehole image data with core sedimentological and ichnofabric analyses has enabled calibration of images for lithofacies recognition, identification of bioturbation fabrics, and the degree of bioturbation present. In particular, comparison of the results of dip trend analyses with the results of ichnofabric analyses has indicated that subtle, though consistent variations in shale bed dip azimuth correspond closely with the locations of sequence boundaries. This has provided increased confidence in unconformity recognition in un-cored well sections, and enabled correlations to be developed. Lessons learned from interpretation and calibration of high sample density borehole image logs (FMI) within cored well sections has enabled interpretive methodologies to be transferred to lower density FMS and SHDT data sets. Similarly, examination of core-photographs as a continuous ‘photographic image log’ in the workstation environment has revealed that when displayed at appropriate scales, even vintage core photographic plates contain a phenomenal amount of data. This is obviously useful for calibration of dipmeter data where, due to climate etc., cores are poorly if at all preserved. Perhaps more surprisingly, comparison of core-photographic data with existing cores has revealed that when displayed on a workstation, core photographs are suitable for detailed ichnofabric analysis. This has allowed reinterpretation of effectively ‘lost’ data within the context of recent advances in sedimentology. The procedures described constitute an innovative approach to the integration of different data types gathered using existing, proven techniques.