before the drill reached the reservoir sands. The details of this operation are 

 similar to geochemical logging. 



SOIL METHOD It was not until the late 1930's that Rosaire 



and Horvitz (1939) investigated the possibil- 

 ities of extracting hydrocarbons from soil material, a process that differs from 

 the soil-gas method in which the gas is drawn from the interstices of the soil. 

 Rosaire and Horvitz learned that hydrocarbons were adsorbed or occluded by 

 soils in amounts far greater than those that are detected by the gas technique, 

 a fact which means that analytical techniques could be used whose sensitivities 

 were considerably less than those used in soil-gas studies. In the soil method, 

 sample collection was expedited, since water-logged terranes, and compact 

 clays did not affect the quality of the sample. This new technique showed that 

 ethane, propane, and higher hydrocarbons yielded more significant information 

 than methane, because ethane, propane, and the higher hydrocarbons were 

 derived more generally from petroleum, whereas methane could originate from 

 decaying organic matter in soils. 



Figure 28-2. The laboratory set-up used by Horvitz to determine methane, ethane, and 

 higher hydrocarbons entrained by soils. 



625 



