760 Subsurface Geologic Methods 



have been disappointing. It is believed that the porous zones are probably 

 too soft to be artifically fractured."*^ 



GEOCHEMICAL METHODS 

 R. MAURICE TRIPP 



The use of geochemical techniques and methods to aid in determining 

 subsurface conditions as a means of exploration for petroleum depends 

 upon acceptance of the following philosophy: The occurrence of any sub- 

 stance in the earth's crust in unusual concentrations tends to shift the equi- 

 librium value of the various chemical, physical, and biological factors in 

 the immediate environment to an abnormal position. The problem of the 

 prospector, then, becomes one of recognizing deviations from normal condi- 

 tions. 



It is not practical or possible to detect these deviations from normality 

 in all properties. Some lend themselves to more precise measurement be- 

 cause of more highly refined analytical techniques or instruments now 

 available or because the variations are on a grander scale. A surprising 

 number of the early oil-field discoveries are credited to the recognition of 

 macro-seeps of oil and gas. It is a natural consequence of logic, then, to 

 look for micro-seeps of oil and gas which are not normally detectable to 

 the eye or nose, but require highly specialized instrumentation and analy- 

 tical techniques. 



It is important that one does not lose sight of the fact that petroleum 

 exploration is first, last, and always a geological problem. The accumula- 

 tion of data, whether it be chemical, physical, or biological, has little or no 

 usefulness until a method has been defined for expressing its geological 

 significance. This does not mean that an exploration aid can not be use- 

 fully employed if there is a difference in opinion regarding the underlying 

 theory any more than one cannot drive a car because the origin of oil is not 

 fully understood. 



Historical Development 



In 1930, V. A. Sokolov, a young Russian nuclear physicist, and his 

 co-worker, M. G. Gurevitch, devised an apparatus for measuring the minute 

 quantities of gas liberated during the radioactive disintegration of certain 

 elements. It occurred to Sokolov that there was a possibility that micro-gas 

 seeps might exist over oil reservoirs, and they made micro-tests for such 

 gases at Grozny and Baku with the appartus designed for nuclear studies. 



At about the same time the same idea occurred to G. L. Hassler in 

 this country and to G. Laubmeyer in Germany. These investigators were 

 all concerned with analyzing the free-soil gas for hydrocarbon constituents. 



About 1937, E. E. Rossaire and L. Horvitz introduced the technique 

 of taking soil samples in the field rather than gas samples and then, re- 

 moving the intrained occluded and adsorbed gas in the laboratory. 



^'Mackenzie, W. D. C, Paleozoic Limestone of Turner Valley, Alberta, Canada: Am. Assoc. Petro- 

 leum Geologists Bull., vol. 29, no. 9, pp. 1620-1640, 1940. 



