890 



MISCELLANEOUS GEOPHYSICAL METHODS 



[Chap. 12 



which incidentally corresponds approximately to the temperature range 

 at the depths where most of these oils are found, and (h) for the 250°-300° 

 fraction. 



In natural gases, methane predominates, then follow ethane, propane, 

 butane, and pcntanc. Contents generally decrease with molecular weight 

 (Table 85). Other gases present may include oxygen, hydrogen, helium, 

 nitrogen, and carbon dioxide. According to this table, therefore, the most 

 significant hydrocarbons of the crudes and natural gases are the paraffins, 



Table 84 

 COMPOSITION OF SOME CRUDE OILS" 



Type 



Grozny, high paraffin 



Grozny, paraffin free 



Texas (Mexia) 



Oklahoma (Davenport) j 73 



California (Huntington Beach) 65 



Aro- 

 matics 



17% 



28 



12 



17 



29 



'9 From G. Egloff, Reactions of Pure Hydrocarbons (Reinhold, 1937). 



Table 85 

 SOME U. S. GAS ANALYSES'" 



Field 



Oklahoma City . 

 Oklahoma City 

 Kettleman Hills 

 Kettleman Hills 



Source 



Separator gas 

 Oil gas 

 Free gas 

 Gas in solution 



" A. R. Bowen, Science of Petroleum, op. cit., Vol. II, p. 1504. 



naphthenes, and aromatics. Of these, the aromatics take last place, are 

 not present in all crudes, and would probably not be a unique indicator 

 at the surface. Of the naphthenes and paraffins, the latter are unquestion- 

 ably the more important for gas detection and soil analysis, since at least 

 the first members of the series are more readily isolated and determined 

 quantitatively. 



It must be remembered that the determination of the constituents in a 

 hydrocarbon mixture is a very difficult and sometimes impossible pro- 

 cedure. Bowen*' refers to an analysis of one oil by eight Bureau of 

 Standards investigators who isolated in one fraction twenty-three par- 

 affinic, eighteen naphthenic, and six benzenoid hydrocarbons. This work 



" Ihid. 



