10 
BULLETIN 102, UNITED STATES NATIONAL MUSEUM. 
notable quantities of natural gas, yield only under the inducement of 
pumping. All wells, however, soon reach a maximum production, 
after which they pass into a period of decline, and eventually become 
extinct . 1 So inexorable is this procedure that a curve may be plotted 
in advance depicting the future behavior of a given group of wells. 
When an oil well becomes extinct, its nonproductiveness does not 
signify that all the oil is exhausted. On the contrary, current prac- 
tice in general leaves over half of the oil underground still clinging 
to the pores and capillary spaces in the rock. To obtain a greater yield 
from productive ground constitutes a problem of the first magnitude, 
and promising results have been obtained by forcing compressed air 
into some of the exhausted wells of a group, with the result that the 
laggard oil is swept to the neighborhood of other wells from which it 
may be pumped . 2 
When a gusher is struck, adequate facilities are often lacking for 
catching and storing the product, so that veritable lakes of oil gather 
between quickly thrown-up earthen embankments. Quantities, in 
such instances, are dissipated through seepage and evaporation, 
while disastrous fires of spectacular nature are not uncommon. With 
more careful development, however, field storage tanks shaped like 
huge cheese boxes are in readiness to receive the oil and prevent the 
glaring waste inherent in more hasty operations . 3 
Turning attention from the single well to the oil field, we observe 
that in petroleum mining sustained production depends upon an un- 
broken campaign of drilling operations. Thus the producers must 
not only draw oil from existing wells, but at the same time must 
persist in the drilling of an increasing 4 number of new wells and in 
the location of promising territory in advance of drilling. Any 
factor that retards any one of these three related activities quickly 
reacts to cause a falling off in production . 5 
Output, development, and exploration, therefore, must go hand in 
hand. In a general way, this threefold activity of production is 
carried on either as a large-scale engineering procedure or as a com- 
posite of small, individual operations. Large oil companies engaged 
in production naturally adopt what might be called the engineering 
1 Wells during decadence are spurred into temporary renewals of activity by the 
explosion of charges of nitroglycerine at their bottoms. The life of an oil well varies 
from a few months to twenty years or more. The average life of Pennsylvania wells is 
estimated to be seven years. 
2 See J. O. Lewis, Methods for increasing the recovery from oil sands : Bulletin 148, 
U. S. Bureau of Mines, 1917. 
3 Only the most carefully constructed tanks prevent the escape of the volatile con- 
stituents of petroleum. 
4 As an oil field ages, new wells yield less than the initial yields of the earlier wells, 
hence a growing number of active -wells is necessary to maintain production. 
5 For example there has recently been a strike in one of the Gulf fields, of such a 
nature as to affect not the current production, but the drilling campaign upon which 
the production of coming months is dependent. Thus a wave is started which will not 
be felt until the future ; and like all waves, once started, nothing can stop the reaction. 
