Soil gases were recovered with hand-held probes in a survey pattern over the Rose Hill oil field in Lee County, Virginia. The gases were analyzed for lighter hydrocarbon gases (C₁-C₄) plus hydrogen and helium, using a custom-built, dual-column chromatograph. Methane and propane

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concentrations were separated into regional and anomalous values and contoured along with values of C₃/C₁. Analytical techniques developed to discriminate gas-prone areas from oil-prone areas confirmed the oil-prone nature of this field.

Geochemical anomalies were interpreted in the context of surface fracture distributions and areas of good production. Geochemical anomalies correspond with areas of optimal production from fractured reservoirs having mostly a north-northeast orientation. For this area a predominantly vertical leakage path from reservoir to surface is inferred. Geochemical prospecting using probes can identify oil versus gas-prone areas and can suggest which among many fracture directions are most likely to contain petroleum concentrations.

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