Page 255 - Geochemical Remote Sensing of The Sub-Surface

228 T. Ruan and Q. Fei

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Fig. 6-8. Contour map of C~ in soils, Jingbian gas field, Ordos Basin.

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Fig. 6-9. Contour map of Hg in soils, Jingbian gas field, Ordos Basin.

field and the surface is 0.04 atm/m. This pressure gradient could be the main driving
force for vertical gas migration.
The Pinqiao oil field occurs in sandstone lenses of Triassic age, at a depth of less
than 1000 m. A gas geochemical survey was carried out over a 1500 km 2 area in order to
test for microseepage from the known oil field and detect any neighbouring fields. Soil
samples were collected on a 1 x 1 km grid and analysed by the acid treatment method for
CI.
The surface material in the region is loess that is quite homogeneous and possesses
high concentrations of syngenetic hydrocarbons (450 ~tl/kg of C!). This has the effect of