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XI-25
The production histories of the Indian Draw and Paduca pools were plotted
with annual oil production as a function of time (Figs. 38, 39). The production
history curves show two distinct peaks. The first peak on each plot occurs a few years
after pool discovery and reflects maximum production from primary recovery
techniques. The second peak occurs several years later. It reflects maximum production
from the waterflood. Production begins to increase within two years of onset of
waterflooding and peak production due to waterflooding occurs within three to four
years.
Two distinct production trends can be seen on each of the plots. The first trend
is for production by primary methods. The second trend is for production resulting
from the waterflood. Each trend was extrapolated into the furure with an exponential
decline curve (FfgS.38, 39). The area:Under each curve was calculated to give
estimated ultimate recovery for primary production and for waterflood production.
Waterflooding is expected to increase ultimate recovery at the Paduca pool by 61 %
and at the Indian Draw pool by 81 %. This is a significant increase in recoverable oil.
Worthington (1994) studied the Shugart East Delaware oil pool. located 21
miles north of WIPP. Production in this pool is from multiple stacked sandstones in
the upper part of the Brushy Canyon Formation. Ultimate primary recovery was
estimated to exceed 5 million BO and 10 BCF gas. Worthington estimated that an
additional 5 million BO could be recovered through secondary recovery (waterflooding).
This is approximately equal to a 100% increase in ultimate recovery.
These analyses can be applied with caution to estimate ultimate secondary
recovery for pools projected to extend underneath the WIPP land withdrawal area. A
60% increase in ultimate recovery was selected for calculations because it represents
the lesser (more conservative) value of the two analogous pools that were analyzed.
Values of estimated ultimate secondary recovery and estimated total (primary plus
secondary) recovery are given in Tables 11-13.
The low permeability and the presence of clays (variably illite, mixed layer
illite/smectite. and chlorite) in Brushy Canyon sandstones may pose problems for
secondary recovery that do not exist with many other oil reservoirs. These factors
may act to increase costs associated with water flood operations; such increased costs
have been incorporated into the economic analyses of Anselmo (this report). The
relatively low permeability of the Brushy Canyon sandstones will require that
injection and production wells be located on 2G-acre spacing. in contrast to the
existing 4O-acre spacing that is allowed for primary production. One new injection
well will need to be drilled for each existing production well. The production and
injection wells will almost certainly be located on five-spot patterns. This need to
double the number of wells will cause waterflood costs to significantly exceed primary
recovery costs.
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