James M. Borer1
(1) Colorado School of Mines, Golden, CO
A study of Eocene lacustrine Green River strata along the northeast margin of the Uinta Basin is used illustrate three fundamental ways outcrop studies are applied to subsurface problems. These are 1) the rare direct application to exploration and development in the same stratigraphic interval in the near subsurface, 2) the application of outcrop-derived facies and element statistics as an analog for a similar subsurface setting, and 3) the important utility of an outcrop to demonstrate the essential processes, concepts and techniques required to adequately characterize a particular (e.g., high-gradient, high-energy lacustrine shoreface) depositional setting. The direct application of outcrop information to nearby production provides insight on how to package outcrop data for use as a subsurface analog. The subsurface data also enhances the outcrop study by providing a dip-oriented regional subsurface cross-section to help hang a regional outcrop section. Geometric artifacts can be generated in regional outcrop cross-sections if incomplete measured sections are hung using multiple datums.
To increase the utility of an outcrop analog, it is important that any statistical summary of outcrop data is organized to reflect key stratigraphic and sedimentologic controls on nonstationarity. Subsurface data types and resolution issues require that statistics are gathered for facies, as well as facies tracts grouped to a level recognized in the subsurface. Outcrop gammaray logs enhance outcrop-subsurface correlation and allow for a complete assessment of log motifs. Stochastic techniques, including spatial cumulative histograms, net-to-gross trends and proportion curves are used to quantify facies variation both along the depositional profile and by stratigraphic hierarchy.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado