156 OIL FIELDS OF TEXAS-LOUISIANA COASTAL PLAIN, [bull. 212. 
the depth to which the well is drilled into the oil rock; and their 
rapidity, and consequently the yield of the well, is generally increased 
by deeper boring. It is also probably influenced by the character of 
the oil rock, the more porous rock yielding its contained oil more 
rapidly than that which is relatively compact. In addition to this 
longer period, the stream of oil generally shows a very rapid pulsation, 
similar to that observed in a jet of mingled water and steam when 
a boiler is blown off. 
A common method of raising oil in wells which do not flow is to 
carry air under high pressure to the bottom of the well by means of 
a small pipe within the casing. When the air is turned on and 
accumulates sufficient pressure to lift the column of oil in the casing, 
the oil is expelled in a pulsating stream exactly similar to a natural 
gusher. In one case, however, the expansive force of artificially com- 
pressed air is the expelling force, and in the other case it is the expan- 
sive force of the naturally compressed gas which is associated with 
the oil in the rock reservoir. 
In addition to the expansive force of the gas, there is also probably 
some hydrostatic pressure in this field, but its influence in producing 
the phenomena of a gusher must be relatively insignificant. Quite 
generally throughout the Coastal Plain region an artesian water flow 
is obtained at depths ranging from GOO to 1,500 feet, but this has only 
a very moderate head. This is seen in the 1,400-foot artesian well at 
the Beaumont court-house, where the head is only a few inches above 
the surface. The existence of a slight hydrostatic pressure in the 
Spindletop pool is shown in the invasion of some wells by salt water 
as the overlying gas and oil are removed. This will doubtless con- 
tinue until the pool is exhausted, although the head may not be suffi- 
cient to bring the salt water to the surface. 
If the pressure to which the gushing in the Spindletop and other 
Coastal Plain pools is due is chiefly the expansive force of gas, it fol- 
lows that this force will expel only a part of the oil, and the remainder 
will necessarily be won by pumping or by supplying the place of the 
natural gas by compressed air. If the oil and gas were arranged in 
the order of their specific gravities and sharply separated by a plane 
surface, the gas, being at the top, would naturally be first tapped and 
would escape without lifting the oil. It would force the oil out only 
from such wells as did not tap the reservoir in its higher portions, 
but lower down where the oil reached entirely to the cover, by exert- 
ing a downward pressure on the oil. The conditions theoretically 
existing in an oil pool are shown in the accompanying sketch (fig. 9). 
The well A taps the top of the reservoir and yields only gas; the well 
B, on the side of the reservoir, penetrates only oil-bearing rock and 
the oil is forced out by the downward pressure of the overlying gas; 
the well C penetrates the reservoir rock below the lower limit of the 
