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Dept. of Geosciences, Southeast Missouri State University, Cape Girardeau, Missouri

Abstract: Examination of Soil and Vegetation for Microseepage Effects at a Gas Production Site in Wyoming

In areas overlying oil and gas deposits, hydrocarbons migrating upwards into the near-surface environment can induce unique conditions, that if detected, may serve in the exploration for productive wellsites. One result of microseepage can be the anomalous concentration of certain trace elements in the soil or plant tissue which might cause discernible alterations in their physical properties.

A newly developed site in the eastern portion of the Wind River Basin was chosen to determine if microseepage effects were present and to what extent they could be used to indicate whether planned drillsites, would be successful in producing natural gas. Geochemical analyses of soil and sagebrush samples were made using ICP and AAS methods to determine their trace metal content. XRD analysis was performed on soils for clay mineral identification. Sage leaves were further analyzed using a field spectroradiometer to measure spectral reflectance response in the visible and near-infrared regions. Multivariate statistical analysis assisted in identifying spectral differences with biogeochemical attributes.

Preliminary results show higher than normal concentrations of pathfinder elements, like chromium in the soil and nickel in the sage, over the production site. Significant relationships between spectral reflectance and the relative magnitude of some trace metals in leaves exist, and examination of first derivative spectra indicated curve deviations in specific wavelength regions that differ between sampled onsite and offsite vegetation. Comparison of findings with post-drill outcome reveals that evaluation of this kind had some success in identifying where well production was more likely to occur.

AAPG Search and Discovery Article #90919©1999 AAPG Rocky Mountain Section Meeting, Bozeman, Montana