The Geosat test site at Patrick Draw, Wyoming, was resampled during the summer field season of 1983, to conduct a more detailed soil-gas survey on and around the area's producing fields. The results of this study agree with the 1980 Geosat assessment that the faults and fractures visible as linear features on satellite and aircraft imagery provide paths for active microseepage of hydrocarbons from depth to the near surface. This association is particularly true near the earlier described "blighted sage zone," where extensive resampling reveals a much wider area of anomalously high free soil-gas values and fluorescence than was previously reported.

Discriminant analysis suggests that the geochemical seepage signature found over the fields differs statistically from that present for adjacent areas of no known production. This observation was found to be true for all three soil-gas techniques used in this study.

Anomaly patterns appear to be related to the type of soil-gas sample studied. Data obtained from shallow free soil-gas samples reveal that direct anomalies, controlled by faults and fractures, formed over production, whereas data obtained from samples treated by acid-extraction or thermal/mechanical disaggregation techniques exhibit magnitude lows over the producing areas. Such patterns indicate halo features around the composite producing areas. At present, this conflicting behavior cannot be explained.