Surface mapping can be used to evaluate reservoirs where fractures influence the flow of fluids. Fracture zones mapped at the surface appear to reflect structures at depth that act as impermeable barriers to flow across the zone and as conduits for fluid flow along the zone.

Airphotos were used to evaluate a fractured carbonate reservoir at Cottonwood Creek field, Bighorn basin, Wyoming. Cottonwood Creek produces from a Stratigraphie trap in the Permian Phosphoria Formation at depths from 1538-3077 meters. Surface lineaments were interpreted on color-infrared stereo airphotos (1:58,000) and then digitized. Contour maps were generated of total surface fracture density and fracture density within various trends. These maps were compared to subsurface data to determine if they had any relationship to reservoir properties.

The principal (northwest) fracture set is unrelated to production. A map of northeast fracture density shows intense fracturing that corresponds to zones of increased total porosity-feet and high cumulative production. Enhanced recovery programs must account for these fracture zones.

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