Notes on Principles of Oil Accumulation

Alex. W. McCoy
1919 The Journal of geology  
Petroleum deposits of commercial importance occur in sedimentary 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,"2 or without being closely associated with shale horizons. Even the
more » ... izons. 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 proximity of many different oil sands throughout the mid-continent field reveals the fact that black bituminous shales are invariably present.3 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 necessary 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. 2 Drillers are accustomed to speak of thin changes in a thick formation as "breaks." a'In cuttings examined to date the one exception to this statement is the Hoy (1,ioo feet) sand of the Garber, Oklahoma, field. 252
doi:10.1086/622659 fatcat:7eatlcjpuzakjgkbcruzurtrka