786 Subsurface Geologic Methods 



siderable amount of redrilling will be required will, of course, be subtan- 

 tially higher. 



Some of the results obtained from secondary-recovery operations are 

 most impressive. Certain of them are cited briefly as follows: 



Water flooding has increased the production of oil in New York by 

 500 percent over what it was in 1920, and the ultimate recovery of oil in 

 the state will at least be doubled. 



In Pennsylvania about 80 percent of the current oil production comes 

 from secondary-recovery operations, and the recovery from the great 

 Bradford field has been more than doubled by the application of water 

 flooding. Elsewhere in Pennsylvania it has been shown that an average 

 increased recovery of 42 barrels per acre-foot can be obtained by sys- 

 tematic injection of air and gas into the Venango sand series. The reserve 

 of oil which may be produced in Pennsylvania by secondary methods is 

 believed to be adequate to maintain the current rate of production for 

 about 50 years. 



In Illinois information obtained on the results from 128 secondary 

 projects indicates that oil recovery can be increased by about 370 million 

 barrels, which is somewhat more than the present proved primary re- 

 serve of the state. 



Approximately 140 million barrels of oil have been produced by the 

 application of secondary methods in Oklahoma, and the proved secondary 

 reserve is estimated to be at least 1 billion barrels of oil. 



In Texas, it has been estimated that the water-injection program in 

 the East Texas field will result in an increased recovery of more than 600 

 million barrels of oil. This project cannot be classified strictly as a sec- 

 ondary-recovery operation, in accordance with the definition proposed 

 previously, but it does represent an outstanding example of the application 

 of secondary techniques. 



Recent studies by the Arkansas Oil and Gas Commission ^ have shown 

 that the secondary reserves of Arkansas, which include all additional oil 

 that may be obtained by the injection of gas or water, are almost equal to 

 the existing proved primary reserve. This determination is of significant 

 importance on account of the low current rate of discovery of new fields 

 in the state. 



Secondary-Recovery Operations in Rocky Mountain States 



The Rocky Mountain region, which embraces the Rocky Mountain 

 system and subordinate folded areas, the Colorado Plateau, and the west- 

 ern part of the Great Plains, extends from central New Mexico to the 

 Canadian border. Oil of highly different physical and chemical charac- 

 teristics is produced from rocks ranging in age from the Cambrian to the 



* Fancher, G. H., and Mackay, D. K., Secondary Recovery of Petroleum in Arkansas, El Dorado, 

 Ark., Arkansas Oil and Cas Comm., 1944. 



