Page 238 - Geochemical Remote Sensing of The Sub-Surface

Light hydrocarbons for petroleum and gas prospecting 211

Fig. 5-44. Composite cell map in which the Monte Carlo simulations have been applied to
methane, ethane and'propane anomalies in the Overthrust Belt, Wyoming-Utah, highlighting the
regions where all three of these gases are above their respective medians.

CONCLUSIONS

Surface and near-surface hydrocarbon occurrences arise as a result of a complex
series of events and interrelationships. Except in rare instances, surface prospecting
cannot reveal the outline of subsurface accumulations, nor indicate the potential
commercial worth of a prospect. It can allow the explorationist a means to high-grade
prospects, but should never be used as the sole criteria for delineating drilling locations.
Surface soil-gas anomalies exist for many understandable reasons, although some do
appear rather random. The interpretation of such data is derived from the general ability
to extrapolate from macroseepage to microseepage, and the fact that often the surface