236 ANNTJAL REPORT SMITHSONIAN INSTITUTION, 1940 



ample of the soda-water syphon can be quoted as an illustration of 

 the process. When the well is drilled the oil may flow at the surface 

 under great pressure or it may flow gently under low pressure, or it 

 may rise to a certain level in the hole and no higher, from which level 

 it must be pumped to the surface — all depending on local pressure 

 conditions and gas saturation pressure. The life history of an oil 

 field after discovery is first exuberant youth, then, as initial vitality 

 declines, sober middle age, followed by a long period of tired old 

 age with ever-decreasing productivity. The best results are obtained 

 under conditions of controlled production whereby the initial flow is 

 throttled down and both the gas and the water pressures, which are 

 the motive forces of the oil production, are carefully controlled. A 

 carefully managed oil field may be made to produce several times as 

 much oil as it would under wasteful conditions of control. 



After complete exhaustion, what is the corpse of an oil field like? 

 The porous rock skeleton remains unaffected, as the oil has been 

 drained only from the interstices between the sand grains of a sand- 

 stone or from between the grains or fissures of a limestone, and a 

 large amount of oil still remains wetting the surfaces of these grains. 

 •Only about 20 or 30 percent, on an average, of the total oil of a 

 reservoir can be produced by ordinary means, but more is possible 

 where a competent natural or artificial water flush or drive is opera- 

 tive. In some cases, particularly where the reservoir rock is a lime- 

 stone, too rapid oil production may draw water up the fissure system 

 and cause premature and unnecessary ruin of an oil field ; this hap- 

 pened in Mexico in 1922, as some investors may remember to their 

 cost. Eventually it may be economically possible to mine the oil 

 sands of exhausted oil fields to recover the residual oil, a process 

 which, aided by high protection, is now in operation at Wietze in 

 Germany. 



Oil fields vary within wide limits both in size and in productivity. 

 The world's record for size is the oil field of east Texas, which, in its 

 9 years of life to date, has produced 205,200,000 tons of oil and is 

 credited with an ultimate possible total of 650 million tons. It has a 

 length of about 40 miles, an average breadth of about 7 miles, and 

 25,800 wells have been drilled. The world's depth record is a well in 

 California which reached 15,004 feet. Such spectacular figures how- 

 ever are the journalistic scoops of the oil world and give a distorted 

 impression of the average condition. Oil fields may be classified as 

 giants, major fields, and average fields. In the first category, and 

 not more than about a dozen oil fields in the world belong here, are 

 fields which will give an eventual total of 100 million tons or more. 

 Major oil fields, and even these are not too plentiful, are from 5 to 

 100 million tons, and average fields are under the 5-million mark. 



