NOTES ON PRINCIPLES OF OIL ACCUMULATION^ 



ALEX. W. McCOY 

 Empire Gas and Fuel Company, Bartlesville, Oklahoma 



Petroleum deposits of commercial importance occur in sedi- 

 mentary rocks. The great majority of such deposits "in the 

 mid-continent field are found in sands or in thin-bedded porous 

 limestones with intervening shales. These shales are generally 

 dark colored, often black, and carry bands of highly bituminous 

 material. Paying amounts of oil have not been found in very 

 thick sandstones or limestones without notable shale "breaks,"^ 

 or without being closely associated with shale horizons. Even 

 the Bartlesville, the thickest pay sand of the region, shows many 

 black shale partings when the cuttings of each screw are examined 

 carefully. 



The examination of a number of such cuttings in the prox- 

 imity of many different oil sands throughout the mid-continent 

 field reveals the fact that black bituminous shales are invariably 

 present.^ These beds are often described by the drillers as coal, 

 asphalt, or black lime, according to the hardness and appearance of 

 the material. The shales are typical oil shales, quite similar 

 in character to those of Colorado and Utah. The bituminous 

 material occurs in solid form as none of the ordinary solvents 

 show coloration after solution tests. Upon distillation, such shales 

 have given off petroleum-hydrocarbons. The sands are entirely 

 barren of such compounds. 



Before concentrations of petroleum can take place, it is neces- 

 sary that this solid organic gum called kerogen be changed so 

 that liquid hydrocarbons are formed. Such a change has com- 



^ Published through courtesy of the Empire Gas and Fuel Company. 



* Drillers are accustomed to speak of thin changes in a thick formation as 

 "breaks." ' 



3 In cuttings examined to date the one exception to this statement is the Hoy 

 (i,ioo feet) sand of the Garber, Oklahoma, field. 



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