This study considers the significance of geochemical exploration for hydrocarbons as used by Geochemical Surveys of Dallas, Texas, for over 40 years.

The search for petroleum has evolved into a highly sophisticated technology where today practically every scientific discipline known is being employed with many attendant new tricks. However, with geochemical hydrocarbon exploration, we have an "old dog that employs no new tricks."

Very simply, all geochemical hydrocarbon exploration methods are based on the much debated premise that the lighter hydrocarbon components flow vertically from a trap through the overlying sedimentary pile by differences in concentration (diffusion) or partly by differences in pressure (effusion). Upon reaching the near-surface sediments, they leave their signatures in one form or another that can be detected by physicochemical methods. These two mechanisms--diffusion and effusion--are aided by the discharge of waters in a vertical direction through reservoir seals that function as membranes much as a wick would do in a kerosene lamp. These chemically imprinted leaking waters create what is called the "geochemical halo" as the lighter hydrocarbon components become oxidized in the near surface environment in accordance with CH₄ + CO₂ ^rarr H₂O + CO₂ to create the ^DgrC anomaly.

Four case histories of producing fields, from California, Texas, North Dakota, and Kentucky, illustrate the significance of the ^DgrC geochemical method as a hydrocarbon exploration tool.

The theoretical basis for hydrocarbon geochemistry is complex and, as with all exploration tools, the problems and difficulties of interpretating the data will never be completely eliminated.

Is it too much to ask of explorationists to view geochemical hydrocarbon exploration from an "aposteriori" viewpoint as the many unheralded geochemical discoveries warrant? If so, then this method has to be reckoned with.

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