Secondary Recovery of Petroleum 781 



has been practiced successfully on a few properties in Pennsylvania and on 

 several properties in Oklahoma and Kansas where permeability and vis- 

 cosity relations are favorable for the injection of substantial quantities of 

 water. The advantages of flowing over conventional production by pump- 

 ing are found in the economy of cost and in the economy and simplicity of 

 operation. Experience with flowing projects indicates that there is no loss 

 in ultimate recovery under comparable conditions. 



Mining 



Except for the operation at Rocky Grove, Pennsylvania, attempts at 

 oil mining in the United States have been on such a small scale that no 

 standard technique has been developed similar to some of the foreign 

 operations. The information that has been obtained from the United States 

 mines, therefore, has not been adequate to determine whether mining op- 

 erations might be economically feasible in this country. Data on the 

 Rocky Grove operation have not been released, but it may be assumed 

 that it was a failure because of cessation of the development program. 



No attempt was made at Rocky Grove to excavate the oil-bearing rock 

 as has been done in various European operations, where a recovery of 40 

 percent of the original oil content of the reservoir has been reported. Such 

 recovery is definitely superior to most of the secondary-recovery operations 

 in the United States, and encourages the beUef that the feasibility of min- 

 ing for petroleum in this country clearly justifies further investigation. 



Secondary Oil Reserves 



The estimation of secondary oil reserves in the United States that can 

 be made at the present time can be regarded only as a first approximation, 

 and, undoubtedly, will be revised from time to time just as estimates of 

 the total proved primary reserves are revised. In the aggregate, figures 

 which can be developed currently on secondary reserves are probably con- 

 servative, but, specifically, they may be somewhat in error, because it is 

 not yet possible to break down and classify all estimations of secondary 

 reserves as proved, probable, and possible. The secondary oil reserves of 

 the United States are estimated currently to be in excess of 7 billion bar- 

 rels, but the author is willing to venture the guess that the physically re- 

 coverable secondary oil reserve of the nation may be as much as twice 

 this figure. 



Undoubtedly, important secondary reserves exist in other oil-produc- 

 ing countries. So far as the author has been able to determine, no sys- 

 tematic effort has been made to evaluate the magnitude of foreign sec- 

 ondary reserves. 



Susceptibility of Oil Fields to Secondary Methods 



From the time of the earlier secondary operations in the Eastern states 

 it has been recognized that all oil fields are not adapted to the application 



