Chapter 14 

 OPTICAL METHODS OF BORE-HOLE INVESTIGATION 



T. V. Shcherbakova 



In order to determine the sequence of stratification and the nature of beds 

 penetrated by a well use is currently made of geophysical methods, of bore 

 hole investigation, the chief of which are electric and radioactivity logging. 

 However, in many cases the data from electric and radioactivity logging 

 do not give a sufficiently complete representation of the rocks penetrated by 

 the well, either because of unfavourable conditions of logging (for example, 

 strongly saline clay suspensions) or because certain lithological and petro- 

 graphical features of the beds, important for geologists, are not indicated 

 by electric and radioactivity logging. In this connection it is necessary to 

 work out new methods for studying the geological sections of wells. 



The so-called optical methods of photographing the rocks along the well 

 walls, and possibly also direct examination by means of television deserve 

 much attention as possible methods of studying the lithological and petro- 

 graphical nature of beds penetrated by a bore-hole. 



Some problems connected with the photography of rocks along the wall 

 of a well are reviewed below, and the results of Avork carried out along these 

 lines are presented. 



OPTICAL PROPERTIES OF DRILLING FLUID 



The bore -hole is filled with a liquid (the drilling fluid), which may be 

 clay suspension, very muddy water or, in extremely rare cases, clear water. 

 When the wall of a well is being photographed there will be between it and 

 the objective lens of the camera a layer of drilling fluid which impairs visi- 

 bility. Therefore in examining the problem of photography in a well it is 

 first of all necessary to find tlie effects of the layer of clay suspension or 

 muddy water on the image of the well wall. For this it is necessary to know 

 certain optical properties of clay suspensions. 



Clay suspensions used in drilling consist of solid mineral particles sus- 

 pended in water. According to the degree of division of the particles, clay 

 suspensions can be referred to as polydisperse solutions containing particles 



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