ELECTRICAL METHODS 



439 



approaches the conductivity of the absorbed electrolyte (moisture), while 

 for very low values of moisture content the resistivity values are high 

 and are governed by the properties of the rock materials, t 



The decrease in resistivity with increased moisture content is of special 

 significance with regard to the possible use of electrical methods in the 



Fig. 264. — Resistivities plotted against moisture percentages for various 

 rocks. (Jakosky and Hopper, Geophysics.) 



direct location of petroliferous rocks. Crude oil is an almost perfect 

 insulator against electrical current; hence, it might be expected that a 

 porous rock containing oil would have a very high resistivity. However, 

 practically all oil reservoir rocks contain both oil and water in their pores, $ 

 and the presence of dissolved salts in this water tends to lower the re- 

 sistivity of the rock. 



t J. J. Jakosky and R. H. Hopper, "The Effect of Moisture on the Direct Current Resistivities 

 of Oil Sands and Rocks," Geophysics. Vol. 2, No. 1, pp. 33-35, 1937. 



t H. C. Pyle and T. H. Jones, "Quantitive Determination of the Connate- Water Content of 

 Oil Sands," Oil and Gas Journal, Nov. 12, 1936. Paper delivered at 17th annual meeting, American 

 Petroleum Institute, Los Angeles. 



