OPTICAL METHODS OF BORE-HOLE LNVESTIGATION 



347 



CONCLUSION 



In a well with a sand- clay section (or in part of a well penetrating sand- 

 'clay deposits), from photographs of the well walls it is possible to disting- 

 uish approximately between clays and sand beds and for the latter to iden- 

 tify medium and coarse-grained sands and sandstones. However, generally 

 speaking, this is not of particular interest. These problems are mpre suc- 

 cessfully solved by other geophysical methods of investigation or by sam- 

 pling ground by a lateral core -lifter. At the same time the drilling fluid is 



Fig. 11. Photographs of well walls (Donbass region). 1-2 — coals; 3 — clay rock; 



4 — sand rock. 



cloudy in sand-clay deposits, and on the walls of the well there is a thick clay 

 crust which is difficult to remove. Therefore at the present time optical 

 methods of surveying wells can be recommended for application in those 

 wells where the section consists of dense, finely grained rock; dense sand- 

 stones, carbonate rocks and hydrochemical sediments. In such wells the 

 drilling fluid is often transparent; if necessary, it can easily be made trans- 

 parent. From the photographs in such wells it is possible to identify fissured 

 reservoir rock and to determine the nature and structure of various beds. 

 To solve these problems by geophysical means is difficult and sometimes 

 even impossible. 



