Abstract

This study makes use of the qualitative (facies distribution) and quantitative (bed/channel dimensions) information incorporated in three-dimensional virtual outcrops and together with other techniques such as ground-based remote sensing and analysis of terrain surfaces of outcrops, provides new tools for geologic mapping and interpretation. The deepwater deposits that crop out at Big Rock Quarry, Arkansas are used as a test site to illustrate the potential of this approach.

Three-dimensional photo real mapping techniques have been recently developed as effective tools for detailed outcrop studies, but their potential has not been fully exploited. Examination of the virtual outcrop allows the extraction of three-dimensional information, as well as geometries and orientations, which allow the accurate analysis of geology. The photo real model of the outcrop at Big Rock with assigned lithologies is used to reconstruct the bedding surfaces by interpolation between differently oriented exposures. The three-dimensional model of sedimentary bodies allowed capturing the three-dimensional spatial distribution of lithological units, which is fundamentally important for understanding the internal architecture of erosional and depositional features, in this case channelized features.

Multi-spectral analysis has been successfully used from space and airborne platforms, but in this study it is used to remotely sense lithology at outcrop scale, obliquely at close range with an increased spatial and spectral resolution. Analyses of the spectral characteristics of sandstone and shale samples from the outcrop at Big Rock over the visible and thermal infrared regions has identified spectral responses of these sedimentary rocks. Multi-spectral images of the outcrop were acquired using a thermal camera for the infrared part of the spectrum and a conventional camera for the visible range. Spectral images are co-registered and displayed in Red-Green-Blue color space to create false color images that are useful for highlighting lithologic variation.

By developing a surface classification algorithm for fracture identification and orientation it was possible to evaluate the fracture geometry, which is helpful in interpretation of reservoir quality. High-density, high-accuracy terrestrial laser scanners have been used to capture the surface morphology of the outcrop at Big Rock. Visualization and analysis of the centimeter-resolution terrain data provided a characterization of this fracture system.

Conventional outcrop information combined with new techniques, such as three-dimensional detailed geologic mapping, ground-based multi-spectral imaging, and 3-D analysis of terrain surfaces of the outcrop can add valuable information for a better description and interpretation of deepwater sedimentary successions in particular, but geology in general.