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

Just before the minipacker was deflated on
November 6,1987, the transducer, located at a depth
of 778.22 ft, measured a pressure of 110.9 psig. After
the packer was deflated and just before it was
removed from the tubing, the pressure was
43.15 psig. If the water above the transducer had a
specific gravity of 1.05, a pressure of 43.15 psig
would correspond to a water level about 683.4 ft
deep. The first water-level measurement made after
the minipacker was removed, however, showed a
depth to water of 690.2 ft. Extrapolation of the first
few water-level measurements back to the time when
the minipacker was deflated indicate that the initial
water level was probably about 690.9 ft deep. This
extrapolation indicates that either the water in the
tubing had a specific gravity of 1.14, or that the
transducer was actually about 7.5 ft deeper than was
thought. Because greater confidence was placed in
the specific-gravity measurements made when the
tubing was last bailed than in the transducer-depth
measurement, the recorded transducer depth was
assumed to be incorrect. With the transducer 7.5 ft
deeper, the pre-test "static" pressure of 110.9 psig
would correspond to a depth to water of about
542.0 ft. Accordingly, an initial depth to water of
(DTW,) 690.9 ft and a static depth to water (DTW*) of
542.0 ft were used in interpreting the P-18 slug test.
Figure 5-71 shows a semilog plot of the P-18 slugtest
data. The most notable feature of the plot is a
change in the slope of the data beginning about
600 hr after the test was initiated. Initially, the water
level was rising relatively rapidly, as shown by the
steep slope of the data in Figure 5-71. After 600 hr,
however, recovery slowed and the slope of the data
changed abruptly. The reason for the change in
slope is unclear. This type of change would not
occur if the Culebra were behaving hydraulically as
an infinite, homogeneous medium on the scale of
the test. The fact that the change did occur may
indicate that the transmissivity of the Culebra near P-
18 is not constant even over the small volume
stressed by the slug test.
0.2
0.1
lo = 310103200
[I DATA
- TYPE CURVE
\\
V."
107 100 103 102 103 IO'
ELAPSED TIME, hours
Figure 5-71, P-l8/Culebra Slug-Test Plot
99