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Abstract: Reservoir Characterization Using Surface Geochemistry, Sorrento Field, Cheyenne County, Colorado

James M. Fausnaugh

The survey was performed in July of 1994 as part of the Colorado School of Mines Reservoir Characterization Project. In addition to the geochemical survey, the study included a complete geologic and engineering evaluation, a 3-D seismic survey, an Previous HitelectricalNext Hit resistivity survey, and a radiometric survey. Geochemical Previous HitmethodsNext Hit included soil gas hydrocarbons, pH, Eh, and soil Previous HitelectricalTop conductivity measurements.

The data were analyzed and interpreted for concentration and compositional anomalies. Field analog comparisons provided additional support for the compositional characterization. With the exception of local lineaments, defining anomalies based on direct hydrocarbon concentration proved difficult due to field depletion. The indirect parameters of pH, Eh, and conductivity exhibited a greater degree of anomaly definition by identifying areas of varying reservoir potential and exposing a complex system of faults and fractures. Compositional analysis of the data yielded information regarding reservoir lithology and hydrocarbon type. Surface hydrocarbon ratios were compared to gas compositions from known Pennsylvanian and Mississippian wells within Cheyenne County. Discrimination of these r servoirs, by analog comparison, was possible within the Sorrento Field limits.

The final report, released by CSM in August of 1995, asserted that the hydrocarbons and pH parameters reliably detected the major trends. The conclusion stated that the geochemical anomalies were consistent with the geologic and geophysical interpretations.

AAPG Search and Discovery Article #90952©1996 AAPG Rocky Mountain Section Meeting, Billings, Montana