Page 230 - Geochemical Remote Sensing of The Sub-Surface

Light hydrocarbons for petroleum and gas prospecting 205

Fig. 5-40. a) Ethane colour compositional dot map for 1985 Currant detailed soil-gas data,
Railroad Valley, Nevada; b) Pixler-type diagram characterisation of anomalous soil-gas
hydrocarbons associated with known oil fields in Railroad Valley, Nevada; c) methane/ethane
scatter plot for 1985 Currant detailed soil-gas data, Railroad Valley, Nevada.

The distinct compositional change associated with this regional lineament suggests
that subsurface hydrodynamic processes related to the lineament may control not only
the sources at depth but also the light-hydrocarbon seepage compositions associated with
these sources. The lineament may form a barrier to subsurface water flow and divert
fluid flow to the east of the lineament. Oil accumulations east of the lineament could,
therefore, be water-washed, resulting in the non-commercial heavy oil observed in the
Currant No. i well. Potential petroleum reservoirs west of the lineament may be
protected from water-washing, retaining their volatile constituents, and providing a
gassier soil-gas signature at the surface. If this interpretation is correct, it proves the

Fig. 5-39. Railroad Valley, Nevada: a) methane contour map of 1985 Currant detailed soil-gas
data; b) propane contour map of 1985 Currant detailed soil-gas data.