852 



GEOPHYSICAL WELL TESTING 



[Chap. 11 



6.6 given on page 848, the conductivity should be about 2.8 units for the 

 overlying sediments, which agrees with the values for sands and clays 

 given on page 849. An increase in the reciprocal gradient in salt is also 

 evident in Fig. 11-22. from the arrangement of the isogeothermal surfaces. 

 Usually the contrast on the contact of two media is not so sharp as that 

 indicated in Fig. 11-21 but is more gradual because of the crowding of the 

 lines near a medium of better heat conductivity. 



Where formations are definitely anisotropic in respect to heat conduc- 

 tivity,^^ the reciprocal gradient changes with dip. If b is the (normal) 



500 



750 



Salt Dome 



-£:.T.J-\ 



V V 



Fig. 11-22. ^Isothermal lines through Grand Saline salt dome, showing increased 

 interval in the salt and a decrease in interval above it (after Hawtof). 



vertical gradient, Ci the conductivity in the bedding planes, C2 the con- 

 ductivity normal thereto, and r? the thermal anisotropy that is equal to Ci/c2 , 

 then the normal gradient is reduced in the ratio 



1 



r = 



• 2 , 2 1 



7j sm (p -f- cos (j5 



(11-9) 



2« Mathematically, the problem is similar to the calculation of electrical potential 

 distribution about a conductive body. See, for instance, J. Koenigsberger, Gerl. 

 Beitr., 18(1/2), 115-126 (1927). 



" Van Orstrand, Amer. J. Sci., 16, 507 (June, 1928). 



