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Abstract: Characterization of Shallow Hydrocarbon Reservoirs Using Surface Geochemical Methods


Multiple shallow reservoirs have been characterized using surface geochemical techniques over the Teapot Dome Field in Natrona County, Wyoming. The study is located in Sections 14 and 15, T 38 N - R 78 W, where the Upper Cretaceous reservoirs can be easily identified and separated. Reservoir fluid characteristics can be estimated though compositional analysis of surface hydrocarbon measurements while some structural aspects, such as faults and fractures, can be determined using indirect surface exploration methods. Geochemical techniques used in the study include surface hydrocarbons, Eh, pH, soil electrical conductivity, iodine, and bacteria.

The raw hydrocarbon data exhibits a positive anomaly over the anticlinal axis at the southern end of the Teapot Dome structure. The Shannon sandstone, the Steele and Niobrara shales, and the 2nd Wall Creek sandstone, all of which produce in the study area, are easily differentiated by surface hydrocarbon ratios. Average values for GOR and API, using surface hydrocarbon measurements, were calculated to be 673 cu. ft/bbl, with a range of 184 to 2030 cu. ft/bbl, and 36.6 degrees, with a range of 17 to 54 degrees, respectively. Actual values for the Steele Niobrara shales are 1000 cu. ft/bbl and 35 to 42 degrees API. Actual GOR values for the Shannon and 2nd Wall Creek are variable. Actual oil gravity for the Shannon and 2nd Wall Creek ranges from 29 to 38 degrees. The reservoir lithology determined through surface hydrocarbon measurements is primarily sandstone.

The indirect geochemical methods indicate the primary strike of the faults in the study area is NE / SW which is consistent with the available geologic data. Several trends normal to the NE / SW orientation were also detected which may be fault related or due to the stratigraphic relationships of the overlapping reservoirs.

AAPG Search and Discovery Article #90946©1997 AAPG Rocky Mountain Section Meeting, Denver, Colorado