160 E. W. Evans on the Action of Oil- Wells. 
wells strike oil at the same depth, whether the strata be hori 
zontal or dipping. It is one chance out of many to strike oil at 
all, even in neighborhoods where it exists in abundance. ) 
drill, as it enters the cavity, sinks variously from four or five 
inches to as ma y feet, sometimes sticking fast, as if between 
the oblique sides ‘of a narrow fissure. But there are facts con- 
nected with the history of oil- als ‘particularly their intermit- 
tent action and their interference with one anot er, ‘ae serve 
to show the existence, in many cases, of systems ese cavi- 
ks connected together by channels of noah anin ce more or 
$8 
sy gdamandt 
us Besin with the most simple case, that of a single or iso- 
lated om -cavity ; of which a cross section is represented by gw, 
-1. Every collection of oil is accompanied with varying 
quantities of gas and water, the gas occupying of course the top of 
the cavity and the water the bottom, according to the order of 
their specific gravities. First suppose that a well is bored at 
so as to enter the gas. Being in a high state of tension the gas 
escapes, sometimes with explosive violence, mpetee out with 2 
Slnetee water there may be collected in the ing. If wat 
enters the cavity freely, as is usually the case, the oil, floating 6 
its surface, is soon driven upward to the mouth (i.e., lower end) 
of the tube ; it may then be pumped out till the line of division 
between it and the water rises to the mouth of the tube; after 
which, mixed oil and water will be drawn. But it often hap- 
pens that the water rises faster than it can be thus exhausted, 
and the oil, driven into the top of the cavity, is lost, until the 
water is reduce y ma- 1 
chinery of greater work- ; 
ing power. But as it can- c 
not be reduced below the a 
mixed oil cannot again 
be obtained So the well. 
In all wells from which 
the gas has escaped, there 
is ultimately a saving of 
work if the oil is pumped 
out as rapidly as possible 
before the intrusion of LY 
_ water. Secondly, aap ¢ 
| poe Be the pre is at B 
enters the oil. In this case, the oil rises in the tube toa 
epending on the tension of the gas above it; a mode of 
is illustrated by the familiar apparatus called 
