HAYKS 
KENN 
^y D ] WELL PRESSURE. 155 
approximately measured. Some closed pressures of 500 pounds and 
over per square inch have been reported, but these are not well 
vouched for. The reliable measurements vary from 70 to 350 pounds. 
The following are the most trustworthy measurements which have 
been made of closed pressure: 
Measurements of closed pressure of oil wells in Gulf Coastal Plain field. 
Pounds. 
American Oil and Refining Company _ 79 
Texas Oil and Pipe Line 112 
Trans-Mississippi . 300 
Yellow Pine 340 
San Jacinto No. 1 350 
The Hooks well at Saratoga showed a steady closed pressure of 127 
pounds. 
Cause of pressure. — Two theories have been employed in explain- 
ing the pressure which causes oil and gas to gush, namely, the hydro- 
static theory and the gas-expansion theory. 
In accordance with the first of these theories, the gas, oil, and water 
are arranged in the subterranean reservoir in the order of their specific 
gravities, the gas being on top and the Avater at the bottom. The 
waler is assumed to saturate the porous stratum continuously from 
beneath the oil reservoir to the outcrop and to transmit the pressure 
due to the greater elevation of the outcrop to the overling oil. A 
close correspondence was found by Orton between the closed pressure 
of wells in the Trenton field of Ohio and Indiana and the weight of a 
column of water equal to the difference in elevation between the well 
head and the Trenton outcrop. Even in this region, however, which 
is the one commonly cited in support of this theory, it does not explain 
certain cases of exceptionally high and low pressures. In the Texas- 
Louisiana field the theory fails to explain the extreme range in pres- 
sure observed in different parts of the same pool, and, further, it is 
inconsistent with the behavior of the wells when flowing. 
It appears highly probable that the pressure in the oil reservoir is 
due largely to the expansive force of the associated gas. When the 
oil rock is penetrated by the drill it is usually, though not alwa} T s, 
necessary to remove the water from the casing by bailing. When the 
pressure is thus relieved there is first a rush of gas, followed by a 
stream of oil, which is expelled with great violence. The oil, however, 
never flows in a steadj^ stream, like the water from an artesian well, 
but by a series of jets or pulsations. These may be relatively slow, 
each flow of oil lasting for several minutes, followed by an equal or 
longer period of quiescence, in which only gas escapes; or they may 
be rapid, several pulsations occurring within a single minute. The 
rapidity of the pulsations appears to depend, among other things, upon 
