Capillary
Pressures--Their Interpretation and Use
Jeffrey B. Jennings
Capillary
pressure techniques have been available to the petroleum industry
for over 40 years, but have been used primarily in engineering applications.
With the search for petroleum becoming more difficult, exploration and
development geologists should take a closer look at
capillary
pressures as
another tool with which to improve the odds.
A capillary
pressure curve is obtained by injecting mercury into a rock
sample plug to produce a plot of injection pressure vs. mercury saturation. The
resulting
capillary
pressure curve is a valuable piece of data for exploration
and development. In exploration, the data can be used to "high-grade" prospects,
define areas to concentrate further exploratory efforts, study oil migration,
and make regional studies that can be used in much the same fashion as
stratigraphic studies. All of these can be integrated into geological,
geophysical, and engineering programs. In development,
capillary
pressure data
can locate oil-water contacts, calculate oil columns, give relative
permeabilities, define multiple reservoir systems, and explain some reservoir
tilting. Stratigraphic traps result fr m
capillary
pressure differences, and
understanding the concept of a "
capillary
pressure release valve" can help
exploit this type of trap. For enhanced recovery programs,
capillary
pressures
can provide a relatively inexpensive source of essential data.
By understanding how
capillary
pressures work within a reservoir and
how
they
affect migration and entrapment, valuable insight can be gained and applied to
the search for petroleum deposits.
Capillary
pressure data are neither difficult
nor expensive to acquire and may yield answers unobtainable by any other method.
AAPG Search and Discovery Article #91033©1988 AAPG Rocky Mountain Section, Bismarck, North Dakota, 21-24 August 1988