836 



GEOPHYSICAL WELL TESTING 



[Chap. 11 



J i 



PesisftV/f/fs in ohm-m 



10 iO 100 5 



so m 



leled by the permeabilities and porosities measured on cores. Likewise, 

 the resistivity and water-analysis curves are quite similar. 



The main value of electrical logs lies in the possibility of well correlation 

 by the "character" of the indication. A structural correlation can be 



made, regardless of whether 

 the geologic significance of 

 an indication is known or 

 not. Small changes in 

 moisture and lithologic 

 character are detected much 

 more readily and with more 

 continuity in an electrical 

 log than is possible by any 

 mechanical coring process. 

 Even if formations do not 

 appear to be differentiated 

 in respect to lithologic and 

 paleontologic characteris- 

 tics, the electrical log can 

 usually be depended on to 

 segregate them. 



Fig. 11-11 shows corre- 

 lation on the basis of resis- 

 tivity logs between two 

 wells three-quarters of a 

 mile apart in the Oklahoma 

 City field . The water sands 

 there are quite readily dis- 

 tinguished by their low 

 resistivities. The jagged 

 peaks indicate limestones 

 (Tonka wa lime at II) or 

 sandy shales; the smooth 

 portions (I and III) repre- 

 sent fairly homogeneous 

 shales and clays. In some 

 oil fields, such as in Ru- 

 mania, correlations have been possible over considerable distances. Fig. 

 11-12 shows well logs taken in the Gorgoteni field. The wavy appearance 

 of both porosity and resistivity logs in the Dacian formation (composed 

 of alternating sands and marls) is in striking contrast to their smooth 

 character in the Pontian, which consists of argillaceous marls. The sandy 



Fig. 11-11. Electrical log correlation between 

 two wells in Oklahoma City field (after Schlum- 

 berger). 



