6'0'8 R. ARNOLD GENERAL CONDITIONS OF PETROLEUM INDUSTRY 



at ordinary temperature; in its wider sense the term is made to include 

 natural gas and the solids, such as asphaltum and paraffin. It is usuall_y 

 lighter than water, its specific gravity varying from about 1.000 to 0.750. 

 Its color in reflected light ranges from light amber through green to 

 black; in transmitted light, amber through deep red to black. Tlie 

 lieavier oils are very viscous, the lighter ones much less so. The calorific 

 value of oil ranges from 18,000 to 20,000 B. T. U.'s, or about one and one- 

 half times that of good bituminous coal. The flash point and fire point 

 of crude petroleums vary greatly, the lighter oils, containing much gas, 

 usually being dangerous to handle on account of low flash point, while 

 the heavier oils are hard to kindle. 



CONDITIONS NECESSARY FOR COMMERCIAL DEPOSITS OF OIL 



Without going into details, it may be said that to have a commercial 

 deposit of oil three things are essential: First, an adequate source of 

 supply in the form of organic sediments, such as shales or limestones; 

 second, a suitable reservoir in the shape of porous beds or zones covered 

 by or inclosed in impervious formations ; and, third, the occurrence of the 

 reservoir near enough to the surface to permit of the recovery of the oil 

 on a paying basis. In nature it is not at all unusual to have two of the 

 conditions fulfilled, such, for instance, as the presence of organic shales 

 near the surface — this is common throughout practically all of the areas 

 of sedimentary rocks — but to find reservoir conditions in proper associa- 

 tion with an adequate supply near the surface is a rare coincidence. 



WORLD'S SUPPLY LIMITED 



Because petroleum is a natural product and is sometimes produced in 

 prodigal quantities in certain fields, people commonly have the notion 

 that there is an unlimited supply of oil in the earth's crust. It is true 

 that petroleum or associated hydrocarbons occur almost universally, espe- 

 cially in regions of sedimentary rocks; but it is likewise true that petro- 

 leum in commercial quantities is confined to a limited number of re- 

 stricted areas throughout the world. As indicative of the relatively small 

 area yielding commercial quantities of petroleum, it might be mentioned 

 that the total area of the United States is 3,025,640 square miles; the 

 proven oil-producing area 4,109 square miles, or 13 one-hundredths of 

 one per cent of the entire area. When it is considered that the United 

 ■States is the most extensively developed of the important oil-producing 

 countries, it can be readily understood that commercial deposits of oil 

 are rare. 



