Digital Outcrop Models

Jerome A. Bellian¹, Charles Kerans¹, Xavier Janson¹, and Ted Playton²
¹Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, The University of Texas at Austin,
²Department of Geological Sciences, John A. and Katherine G. Jackson School of Geosciences, The University of Texas at Austin

Geologists have been trained to recognize patterns on flat media as representations of three-dimensional geologically significant objects and geological associations. The standard procedure in outcrop characterization is to acquire photographic panoramas for use in correlation and mapping of 3-D relationships that we have collapsed to 2-D planes. As a result, however, a systematic loss of important spatial relationships occurs. It is desirable to have numerous side canyons and irregularities in outcrop to provide a better 3-D context for the study area, but because of a paucity of suitable methodology to capture these geometries, we have been reluctant to move away from the pseudo-2-D photo pan. Laser technology has been honed to meet the needs of modern field geologists, and the Digital Outcrop Model (DOM) has shown great utility in quantitatively capturing spatially complex geology observed in outcrop.

Here we describe the process of constructing and utilizing a DOM for the purpose of modeling flow-unit-scale reservoir heterogeneity in outcrop as an analog of production from mixed siliciclastic and carbonate reservoirs. Examples from three outcrop settings are presented. The first is from Cretaceous rudist reefs near Pipe Creek, Texas, which captures surface exposures along Red Bluff Creek. The second data set, from the Permian of West Texas, uses 3-D exposures in the Victorio Canyon to display the architecture of a toe of slope channel and fan system. Upper Pennsylvanian exposures along U.S. Highway 82 in Dry and Yucca Canyons near Cloudcroft, New Mexico, provide an excellent example of mixed siliciclastic and carbonate shelf-edge stratigraphy. Field acquisition, data processing, photographic co-registration, surface construction, interpretation technique, and importation into modeling software are discussed for each outcrop.
Modern commercial terrestrial laser scanners are capable of acquiring data from up to 1 kilometer away at rates as fast as 2,000 points per second at sub-centimeter sampling intervals. Lidar (light detection and ranging) is forming the cornerstone of DOM technology, with its speed of acquisition and accuracy. Once digital capture of an outcrop is complete, unlimited numbers of observers can interrogate previous observations with the ability to fly around and even through the outcrop, discuss interpretations, and locate critical zones for further interrogation. Will lasers remove the need to conduct fieldwork? No. In fact, this technology may underscore the need for additional fieldwork for accurate 3-D geometries to be more fully understood.

Figure 1: Field-acquired laser scans are combined into a single, continuous data set. The laser-intensity data are used to calibrate the photograph to the surface mesh with minimal distortion.