Beauheim 1987 - Waste Isolation Pilot Plant - U.S. Department of ...

Two type-curve matches are shown with the test data
on Figure 5-71. The early-time data were best fit by a
type curve characteristic of damaged (i.e., having a
positive skin) wells, whereas the late-time data were
best fit by a type curve characteristic of undamaged
(i.e., having a neutral or no skin) wells. The two typecurve
matches also provide contrasting
transmissivity estimates. The transmissivity derived
from the early-time match is about 4 x 10-3 ftz/day,
while that from the late-time match is about 7 x
10-5 ftzfday (Table 5-3). These observations indicate
that the P-18 wellbore may be poorly connected
hydraulically to a small portion of the Culebra having
a higher transmissivity than more-distant portions.
The contrast between the transmissivity of the
Culebra and that of the well "skin" may decrease as
the transmissivity of the Culebra decreases with
distance from P-18, resulting in the neutral skin
shown by the late-time data. The fact that the slope
of the data on Figure 5-71 changes abruptly as
opposed to smoothly appears to indicate that the
change in transmissivity is discrete rather than
gradational. Drilling of the borehole may have
caused minor fracturing of the formation around the
hole, which may have led to a slightly enhanced
transmissivity in the immediate vicinity of the hole.
Casing, cementing, and perforation may have
resulted in a poor connection between the wellbore
and the surrounding formation, resulting in the
positive skin observed.
Given the peculiarities in the response to the P-18
slug test and the uncertainties as to their cause, the
transmissivity of the Culebra at P-18 remains poorly
defined. The estimate provided by the early-time
type-curve match does not appear to be valid beyond
the immediate vicinity (a few feet?) of the well. The
transmissivity estimate provided by the late-time
type-curve match may not be quantitatively reliable
because the time match between the data and the
type curve, which defines the transmissivity, would
probably be greater, thus indicating a lower
transmissivity, if the hydraulic response of the
Culebra had been more consistent (i.e-,
homogeneous). In summary, the transmissivity
estimate from the early-time data, 4 x 10-3 ftz/day, is
probably unrealistically high, but is reliably a
maximum value. The estimate from the late-time
data, 7 x 10-5 ft*/day, is probably more representative
of the Culebra in the vicinity of P-18, but cannot be
interpreted as a minimum value.
5.2.2.19 ERDA-9. Two falling-head slug tests
were performed in November 1986 to evaluate the
transmissivity of the Culebra at ERDA-9. The first
was initiated on November 20, 1986. The test lasted
about 18 hr, by which time over 99% of the induced
pressure differential had dissipated. Figure 5-72 is a
semilog plot of the slug-test data, along with the
best-fit type curve. This fit provides a transmissivity
estimate of 0.45 ftZ/day for the Culebra at ERDA-9
(Table 5-3). The second test began on November
24, 1986, and lasted about 16 hr. A semilog plot of
the data from this test is presented in Figure 5-73,
along with the best-fit type-curve match. This match
is very similar to that used to fit the data from the first
test, and provides a similar transmissivity estimate of
0.47 ft2/day (Table 5-3). The data from these tests
are reported in Stensrud et al. (1987).
5.2.2.20 Cabin Baby-1. Two falling-head slug
tests were performed at Cabin Baby-1 to evaluate the
transmissivity of the Culebra at that location. The first
test was initiated on March 10, 1987 and the second
was initiated on March 12, 1987. Complete
dissipation of the induced pressure differential was
achieved during the first test, and about 99%
dissipation during the second. The data from these
tests are presented in Stensrud et al. (1987).
Figure 5-74 is a semilog plot of the data from the first
test, along with the best-fit type curve. This fit
provides a transmissivity estimate of 0.28 ftzjday for
the Culebra at Cabin Baby-1 (Table 5-3). The
semilog plot of the data from the second test
(Figure 5-75) shows an identical type-curve match
with a slightly better overall fit, leading to a second
transmissivity estimate of 0.28 ft*/day (Table 5-3).
5.2.2.21 DOE-1. After an 8-hr step-drawdown test
of the Culebra conducted at DOE-1 on May 3, 1983
indicated that the productivity of the well was much
higher than previously believed, a 440-hr pumping
test was conducted beginning on May 6, 1983. The
average pumping rate during the test was 9.93 gpm.
After the pump was turned off, pressure recovery in
the well was monitored for nearly 422 hr. The fluid-
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