The Conditions of Accumulation of Petroleum in the Earth

Abstract

In 1897 I published a proposed explanation for the variation in color andspecific gravity of Pennsylvania oils. A resume of this subject was alsopresented at the First International Petroleum Congress, in Paris, in 1990.Since that time much experimental work bearing upon this explanation has beencarried on by me, in the United States Geological Survey, and under mydirection, by Dr. J. Elliott Gilpin, Marshall P. Cram, and O. E. Bransky, atthe Johns Hopkins University. The experimental results thus accumulated seem tothrow considerable additional light upon the variations in color and specificgravity of petroleum, as found in different parts of the world, and also uponthe variations in chemical composition. Therefore, it seems as if a summary ofthe evidence thus obtained might be of value to those members of the Institutewho are interested in the examination of oil- fields. The summary is herepresented for that purpose. The phenomenon has often been observed in many oil-fields that oils of different color, specific gravity, and chemical composition may be foundwithin short distances of each other. A conspicuous example of this is the occurrence at Jennings, Welsh, and Anse la Butte, La., of petroleum chemicallysomewhat similar to Russian petroleum; that is, characterized by the presenceof naphthenes. Another characteristic is the presence of considerablepercentages of asphaltic compounds, sufficient in quantity to disguise the presence of' solid paraffin wax, and perhaps also to render that paraffin waxmore soluble in the oil than it would be were not these asphaltic compoundspresent. At Belle Isle, La., only 40 miles from Anse la Butte, petroleum isfound unusually light in color, about that of sauterne wine. This petroleum ispractically free from sulphur, very much lighter in specific gravity than theother oils, free from asphalt, and shows abundantly the presence of paraffinwax in solution. At first glance the oils seem to be entirely different, butchemical examination shows them to be as closely related to Russian oils as arethose from Texas, and markedly different from the oils of theparaffin-hydrocarbon series found in Pennsylvania. Other instances are noted of similar variations in oils within short distances, especially in Mexico, as well as in California, Wyoming, Oklahoma, Texas, andelsewhere. The oils usually, however, contain some characteristics in common, which would indicate that one oil has been derived from the other. Inendeavoring to express such a genetic relationship, it has been supposed thatthe dark oils have been derived from the lighter ones by evaporation andoxidation. AIME 041–24