Abstract

Structural and/or stratigraphic traps may be located on aerial photographs using photogeologic-geomorphic methods. Once “normal” drainage and landform patterns are established, abnormal drainage patterns, erosional patterns, alignments of streams, vegetation, color and/or topography, fracture and fault patterns, and color and tonal characteristics may be determined and their significance interpreted. This interpretation may then be used a guide to locating more expensive subsurface studies (i.e., seismic, gravity, magnetic, and/or geochemical programs).

Examples of structural traps delineated on aerial photographs include the Broadview dome in Stillwater County, Montana (annular drainage pattern); the Runamuck Viola oil field in the Forest City basin, Atchison County, Missouri (barbed drainage pattern); a tonal anomaly near the Frederick field, Tillman County, Oklahoma; and prominent northeast-trending drainage alignments in northwest Colorado.

A stratigraphic-structural trap in the Sorrento field, Cheyenne County, southeast Colorado, is marked at the surface by prominent drainage and erosional anomalies and by drainage and topographic alignments. Although the trap is primarily stratigraphic in nature, paleostructural and paleotopographic control on deposition of the sandstone reservoir rock resulted in surface expression of the hydrocarbon trap.