16 NEW YORK STATE MUSEUM 
advance of the water, is called flood oil and is obtained by drilling 
wells in advance of the oil flood. These oil wells continue to produce 
oil until the oil flood has passed and they are reached by the water 
flood after which, unless they are subjected to cross and reversed 
flooding, they serve only as additional pressure wells forcing the oil 
beyond into an ever increasing area where new wells are drilled to 
obtain the flood oil. 
The number of floods which now exist in southwestern New York 
is not known with a certainty. Perhaps as much as 5 or 10 per cent 
of the sand has been flooded out. This percentage, however, does 
not apply to the acreage which is somewhat less, since many of the 
floods have been in areas where the sand is the thickest. During the 
field season of 1922, eighteen floods were studied and mapped. The 
floods mapped include some of the old and largest as well as the 
more recent ones which are, of course, smaller. Most of the floods 
mapped started from a single flood well and as some of the adjacent 
wells went to water these were changed to pressure wells thus grad- 
ually enlarging the area that is watered out, and at the same time 
increasing the area of flood oil into which new wells are drilled. The 
shape of many of the flooded areas is roughly a circle, but on account 
of loose streaks in the oil sand and other influencing factors, the 
shape often becomes irregularly oval. Instead of using a sin le 
water well in starting a flood, the present tendency is to start by 
using two or three wells along a straight line as original flood wells, 
thus producing what is termed a line flood. Floods of this type 
are more easily controlled and the progress of the flood more easily 
determined. | | 
The construction of flood maps gives a reliable basis for estimat- 
ing the percentage of the field that has been flooded out, especially 
the area of the flooded parts, the velocity of the flood and erratic 
movement of the water. The maps are also an aid in determining 
what the effect of cross flooding will be. One of the largest floods 
mapped covers an area of about 150 acres of which about one-third 
was actually flooded out and two-thirds affected by the flood. The 
flood maps also show that the velocity of the flood water varies in 
the same pool and even in what is considered the same sand. This 
is due to changes in the character, thickness, depth of the rock and 
perhaps other factors. Failure to allow for the factors involved, 
sometimes leads to unsuccessful results at flooding. It is necessary 
for the producer to study carefully the sands on his own lease, 
determining as much as he can from his well logs the various changes 
