Page 13 - Geochemistry of Oil Field Waters

2 INTRODUCTION

suspected flood, the existence of which was not known when the location
for the test well had been selected. The upper part of the sand was not
cored. Toward the end of the cutting of the first core with a Baker cable tool
core barrel, oil began to come into the hole so fast that it was not necessary
to add water for the cutting of the second section of the sand. The lower 1 m
of the Bradford Sand therefore was cut with oil in a hole free from water.
Two samples from this section were preserved in sealed containers for satura-
tion tests, and both of them, when analyzed, had a water content of ap-
proximately 20% of pore volume. This well made about 10 barrels of oil per
day and no water after being shot with nitroglycerine. Thus, the evidence
developed by the core analysis and the productivity test after completion
provided a satisfactory indication of the existence of immobile water, in-
digenous to the Bradford Sand oil reservoir, which was held in its pore
system and which could not be produced by conventional pumping methods
(Torrey, 1966).
Fettke (1938) was the first to report the presence of water in an oil-
producing sand. However, he thought that it might have been introduced by
the drilling process.
It was recognized by Munn (1920) that moving underground water might
be the primary cause of migration and accumulation of oil and gas. However,
this theory had little experimental data to back it until Mills (1920) con-
ducted several laboratory experiments on the effect of moving water and gas
on water-oil-as-sand and water-oil-sand systems. Mills concluded that
“the up-dip migration of oil and gas under the propulsive force of their
buoyancy in water, as well as the migration of oil, either up or down dip,
caused by hydraulic currents, are among the primary factors influencing
both the accumulation and the recovery of oil and gas.” This theory was
seriously questioned and completely rejected by many of his con-
temporaries.
Rich (1923) postulated that “hydraulic currents, rather than buoyancy,
are effective in causing accumulation of oil or its retention.” He did not
believe that the hydraulic accumulation and flushing of oil required a rapid
movement of water, but rather that the oil was an integral constituent of the
rock fluids and that it could be carried along with them whether the move-
ment was very slow or relatively rapid.
The effect of water displacing oil during production was not recognized in

the early days of the petroleum industry in Pennsylvania. Laws were passed, a
however, to prevent operators from injecting water into the oil reservoir
sands through unplugged wells. In spite of these laws, some operators at
Bradford surreptitiously opened the well casing opposite shallow ground-
water sands in order to start a waterflood in the oil sands. Effects of artificial
waterfloods were noted in the Bradford field, McKean County, Pennsylvania,
in 1907, and became evident about 5 years later in the nearby oilfields of
New York (Torrey, 1950). Volumetric calculations of the oil-reservoir
volume which were made for engineering studies of these waterflood opera-