436 R. ARNOLD OIL GEOLOGY IN RELATION TO VALUATION 



salt domes of Texas, where the presumptive recoverable oil is 50,000 

 barrels per acre, and a similar area in the Kern Eiver field in California, 

 where the same production per acre may be expected. Assume the oil to 

 be the same grade and value per barrel, which, in reality, it may be. In 

 the first case, the great bulk of the oil could be recovered in the first two 

 years of operation; in the second, twenty years would elapse before the 

 oil would become even approximately exhausted. 



Of course, there are artificial factors governing the rate of production, 

 such as the depth of the well (which in reality is a natural factor, as it is 

 dependent on the structure), size of hole, character of pump and other 

 production equipment used, efficiency of management, etcetera ; but these 

 may be considered as secondary, as compared with the factors with which 

 the geologist has to deal. 



WATER ASSOCIATED WITH OIL 



The influence of the water situation in any field on the values in the 

 field may be said to be of equal rank with that of the quantity of recov- 

 erable oil and rate of production; for, in a measure, the two latter are 

 often directly dependent on the former. In nearly all producing areas 

 water exists above and below the oil reservoir and underlying or adjacent 

 to the oil in the reservoir. The first is known as "top" water, the second 

 as "bottom" water, and the third as "edge" water. Besides these simple 

 cases, there are many special ones in various fields. As long as these 

 waters remain isolated from the oil, no harm is done, but as soon as the 

 water begins to show in the well, either through faulty shutting off above 

 or below the producing horizon or through infiltration on account of the 

 exhaustion of the oil and the resultant "following up" of the water, pro- 

 duction and likewise values are affected. Often the effect is almost in- 

 stantaneous ; in others gradual. The harmful effects of top or bottom 

 water may be remedied through manipulation, but when edge water shows 

 it means the beginning of the end of that well and eventually of the pool. 

 In some cases water may act advantageously for the production, and 

 therefore for values, but these cases are rare. Innumerable cases of the 

 harmful effect of water on production and values might be cited. As 

 illustrating the few exceptions, there are some parts of the Kern River 

 field, California, and the Bradford pool, Pennsylvania. In the former, 

 natural waters have helped flux the heavy oil into the wells, while in the 

 latter water has been artificially forced into certain wells to drive the oil 

 along to other wells, higher up on the dip of the formation. 



As illustrating the importance of the water problem, it may be stated 

 that the most effective and usually the first practical work undertaken 



