Subsurface Logging Methods 



381 



Figure 164. Log illustrating behavior of lateral curve with resistive beds of different 

 thicknesses. Comments on curves to right of depth column: dashed line repre- 

 sents the lateral A0 = 15'; solid line represents the normal AM = 16"; solid 

 line curve at extreme right represents the normal AM = 63". 



It has been proved experimentally that the resistivity of a water-satu- 

 rated permeable formation is related to the resistivity of the water, to the 

 amount of void space, and to the size, shape, and distribution of this space. 

 This relationship may be expressed as:^^ 



Ro=FR^ (1) 



where Ro = resistivity of formation 100-percent water-saturated. 

 F = formation-resistivity factor. 

 Ry, = resistivity of water saturating the formation. 



The factor F has been shown, in general, to be equal to : 



F = 



(2) 



where p = fractional porosity. 



m = proportionality factor. 



The factor m is related to size, shape, and distribution of the void 

 space. Experimental data have shown that it varies from 1.3 to somewhat 

 over 2.0. The lower values are generally found in unconsolidated sands, 

 the higher in consolidated sands. 



A knowledge of the value of Ro, the resistivity of a formation 100- 

 percent water-saturated, is fundamental to any interpretation for fluid 



" Archi. 

 istics: Am. 



, G. E., The Electrical Resistivity Log as an Aid in Determining Same Reservoir Character- 

 Inst. Min. Met. Eng. Tech. Pub. 1422, Jan. 1942. 



