Geochemistry is widely used in field operations, and represents about 25 per cent of the petroleum exploration research in the U.S.S.R. Three approaches are used: (1) subsurface prospecting which included mudlogging,

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hydrocarbon distributions in sediments, and geochemical criteria for indicating oil such as the presence of organic compounds in waters; (2) surface prospecting which is concerned with rates of diffusion and filtration of hydrocarbons through sedimentary rocks, micro-biological detection of hydrocarbons, and the evaluation of radiometric, organic, and inorganic anomalies of the surface; (3) studies on the origin of petroleum and the recognition of favorable oil forming environments.

About 90 per cent of the 300 geochemical field parties are doing subsurface prospecting. The other 10 per cent are engaged in surface surveys, and these are on a research basis. They are limited to arid areas of shallow young sediments such as around Volgograd, Baku, and Turkmenia. In contrast, about half of the geochemical research at 30 institutes or more in the U.S.S.R. involves surface prospecting techniques. The Soviets hope to develop a practical surface method that can be combined with geology for use in stratigraphic prospecting.

In general, the Soviet scientists seem to be using more manpower and developing more geochemical parameters for field use than U. S. oil companies. The established facts of petroleum geochemistry, such as the organic nature of source beds and the detection of hydrocarbons in sediments and subsurface waters, are understood and taken into account in exploration programs. Thus the practical application of geochemistry in exploration is more widespread than in the U. S.

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