CHEMICAL METHODS 955 



The closed portion is then exhausted through a vacuum pump, and the 

 collector at the end of a small hose placed on the bottom of the sampling 

 hole. When the hole has reached a condition of equilibrium, as indicated 

 by a gauge on the suction line, the sample is collected, the packer removed, 

 and the next station sampled in like manner. The radon concentrations are 

 determined by means of an electroscope and, after plotting the values, the 

 crest of the curve of emanation is determined. It is along this crest that 

 the most favorable wells are expected. Successful extension work has 

 been reported for Hunton lime areas in Oklahoma and many areas in the 

 Texas Gulf Coast. 



Based on the escape of hydrocarbons from a petroleum accumulation, 

 Trippf suggests another approach to the search for oil. The technique 

 involves the determination of the concentration of radioactive minerals in 

 the zone of maximum colloidicity and simultaneous determination of the 

 mineral wax content. Tripp states that the concurrence of anomalies in 

 both properties has been experimentally demonstrated to be related to the 

 occurrence of petroleum at depth. The experience background has been 

 obtained in areas believed to be ideal with respect to soil and climate 

 conditions. 



Costs. — The expense of conducting a geochemical survey depends 

 upon the type of method employed. In general, the surveys which involve 

 the collection of samples from about eight to twelve feet and report deter- 

 minations for the volatile hydrocarbons cost approximately fifteen cents 

 per acre in the case of reconnaissance and twenty-five to fifty cents per 

 acre for detail surveys. On an individual sample basis, the analysis charge 

 is about $15 and the cost of collection averages about $7.50 per sample. 

 In employing the methods which involve the analysis of near-surface 

 samples, the costs range from about $5 to $10 per sample for collection 

 and analysis. 



The average cost of a geochemical survey is usually less than one-half 

 the cost of a seismic survey and approaches the cost of a gravity meter 

 survey. 



Application of Geochemical Prospecting Methods. — The direct 

 approach afforded by the use of geochemical methods in prospecting for 

 oil and gas and their relatively low cost suggest reconnaissance surveying 

 as an important application. Localized areas which show favorable indi- 

 cations may then be detailed by the more expensive seismograph to deter- 

 mine if structure is associated with the geochemical anomalies. Although 

 used to a limited extent in reconnaissance work, geochemical methods are 

 more frequently employed to obtain data for correlation with information 

 already available from the use of other methods such as the seismograph, 

 gravity meter, or subsurface geology. 



t R. Maurice Tripp, "Geophysical Principles for Determining Subsurface Conditions," The Oil 

 Weekly, June 9, 1947. 



