Secondary Recovery of Petroleum 785 



Capillary forces, undoubtedly, affect the permeability of the oil-bear- 

 ing formation to a fluid phase and, as such, are important in determining 

 the most advantageous rate of advance of the injection medium. 



Artificial control of interfacial tension betw^een water and oil by use 

 of surface-tension depressants in the water has so far failed in practical 

 application, because the surface-active compounds tend to be absorbed 

 on the solid surfaces. The advancing water front, therefore, is depleted 

 of these agents before any beneficial effects can be observed. 



Many of the factors which will control the success or failure of sec- 

 ondary-recovery projects can be determined in advance by laboratory 

 analysis of cores and from studies of reservoir conditions. Indicated re- 

 coveries, as obtained from laboratory flooding tests, have proved to be 

 remarkably accurate if reliable relative permeability data are available. 

 Gas and water saturations are particularly important in ascertaining the 

 ratio of injected fluid to oil produced. If the initial mobility of the water is 

 greater than that of oil, water flooding will probably not be economically 

 feasible on account of excessive water-oil ratios. 



Information of great value in the formulation of plans for the de- 

 velopment and operation of secondary-recovery projects can be obtained 

 from small-scale pilot-plant tests of gas- or water-injection capacities and 

 pressures. Such tests can be made usually at moderate expense with port- 

 able compressors and pumps and using the existing production facilities. 

 The information so gained provides a useful check on laboratory deter- 

 minations. 



Some Costs and Results of Secondary-Recovery Operations 



Development and operating costs in secondary-recovery operations 

 are so variable that any figures presented must be specific in order to avoid 

 misinterpretation. 



Present-day costs (1949) for the complete development of water- 

 flooding projects in the Bradford field of northern Pennsylvania will range 

 from $4,000 to $5,000 an acre, depending on the drilling depth. 



The two earliest water floods in north Texas have had an over-all de- 

 velopment and operating expense, adjusted to prices prevailing during the 

 early part of 1948, of $1.40 and $1.47 a barrel respectively. Similarly 

 adjusted average costs, which include land cost or over-riding royalty, 

 on 17 water-flooding operations in Oklahoma are $1.55 a barrel, and on 

 16 water-flooding operations in Kansas are $1.32 a barrel. These figures 

 do not include any allowance for interest on the investment or for federal 

 taxes. They were compiled from records of the earlier secondary opera- 

 tions in both states, all of which are now depleted or are in the final stages 

 of depletion and where drilling depths have ranged from 700 to 1,500 feet. 

 The cost of development and operation in deeper fields, where any con- 



