OPTICAL METHODS OF BORE-HOLE LNVESTIGATION 



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The value of the transiuiLtancc T falls sharply as the specific gravity of 

 the drilling fluid increases, and becomes a little lower as the wavelength 

 is reduced. 



For not very large thicknesses of the layer of fluid the connection between 

 the transmittance T and the thickness of the layer h of the <la\ suspension 

 can be expressed approximatelv by the formula 



T = 100 



-Ml 



(1) 



where k is a certain coefficient., called the attenuation coetficient, rejnesenting 

 the rate of reduction of light transmission wdth increase in layer thickness. 

 For monochromatic light the attenuation coefficient (see Fig. 2) is: 



A=.(y^l) 



(2) 



200 



150 



lOO 



50 



lO 



1-05 



MO 



■y 



1-20 



Fig. 2. Dependence of attenuation coefficient K. on the specific gravity y of the 

 suspension and the wavelength }. of the hght. 



For the dark-coloured clay suspensions investigated a = 1.4 and n — 1.5. 



A suspeitsion prepared from the light clay transmits light better than 

 a suspension from the dark clay, the average difference being 50 per cent 

 (see Fig. 3). The difference in the transmission of light by suspensions 



