YIELD OF WELLS. 189 



probably have decreased, as will be seen by the examination of the 

 other figures, because notwithstanding the enormous rise of over 

 roo°/ in the production of this class of wells the increase of the 

 total production has only been 3,163 viss or about 18%. 



If we assume that the wells of the first two classes in the older 

 part of the field yielded the same quantity in 1895 as in 1893, we 

 find that the increase in this class is 4,842 viss, which represents 

 very nearly the output of the 107 new wells. 



(b) III class wells. — The wells of this class chiefly drain the 



3rd oil sand, and since regular observations were made, they have 



proved to be the chief supporters of the petroleum production. Their 



shares were, in 



1S88 58-3°/" 



1891 58'S7. 



1893 497% 



1895 39'5 7. 



We see therefore that, notwithstanding the preponderance of the 

 III class wells as regards the absolute number, their share in the pro- 

 duction has been slowly but steadily on the decrease since 1888, and 

 the balance has shifted more in favour of the other wells. In 1893 

 the deeper wells had to supply the deficit, in 1895 the difference 

 was nearly equally divided by the shallower and deeper wells. Now 

 if we keep in mind that with the exception of a few, the III class 

 wells are situated in the older part of the oil fields, this is by no means 

 a favourable indication for the future. In fact we may assume that 

 within the area of the native reserve the 3rd oil sand begins to show 

 signs of exhaustion, and the wells draining it begin to fall off in 

 production. 



(c) IV and V class -wells. — Much remains to be said about these 

 wells : in formeryears up to 1891 their contribution towards the total 

 production was small, being 196% in 1888 and 14% in 1891 ; after 

 1891, for reasons already explained, their share suddenly rose to the 

 extent of 34'3%> bu t since that time it has again slightly fallen off to 

 2 9'7 % chiefly on account of the recently constructed shallow wells 

 which fully supplied the production without the necessity of deepen- 



( 235 ) 



