Detection of hydrocarbons and hydrocarbon microseepage in the Bighorn Basin, Wyoming using isotopic, biogeochemical, and spectral reflectance techniques

A stable isotope, biogeochemical, and geobotanical reflectance study was conducted at five areas in the Bighorn Basin of Wyoming. Three of the areas are active hydrocarbon producing fields, including Little Buffalo Basin, Bonanza, and Enigma oil fields. One area contains no surface or subsurface hydrocarbons, the Cody Base area. The fifth area, Trapper Canyon, is a surface tar sand deposit. In each area numerous reflectance spectra were measured and leaf samples collected from sagebrush (Artemisia tridentata) over and surrounding the fields. At two areas, Bonanza and Trapper Canyon, sagebrush plants were also sampled growing directly in hydrocarbon impregnated formations.;Unusually low ;Significant distinctions between the surface hydrocarbon occurrences at Trapper Canyon and Bonanza Seeps are highlighted by chemical differences in sagebrush leaves. At Trapper Canyon relatively high concentrations of aluminum and iron are found. Sagebrush leaves at the Bonanza Seeps are relatively high in phosphorus, magnesium, and sodium. Sagebrush leaves at both Trapper Canyon and the Bonanza Seeps contain relatively low concentrations of calcium and potassium, and a relatively high amount of organic material.;Analyses from sagebrush growing over subsurface commercial hydrocarbon deposits tend to be relatively low in magnesium and relatively high in sodium. This tends to confirm a model forwarded by Klusman et al. (1992). The increase in sodium tends to agree with Malhotra (1988), and may indicate subsurface reservoirs without regard to their hydrocarbon content.;The results of the geobotanical reflectance study shows that a consistent and significant blue shift of the green peak and red trough positions is the most reliable indicator of hydrocarbon-induced stress in sagebrush plants, and can only be detected where the sage is actually growing in visible surface or near-surface hydrocarbons. Spectral reflectance intensity data have no significant correlation with the presence or absence of surface or subsurface hydrocarbons.