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

Considering that all other pumping tests at wells
where the Culebra has a transmissivity greater than
about 1 ftZ/day have shown double-porosity effects
and negative skins caused by fracturing (e.g.. DOE-1,
DOE-2, H-3, H-8, H-11 , WIPP-13), the relatively high
transmissivity, positive skin, and single-porosity
behavior indicated for the Engle well appear
anomalous. One possible explanation for this
apparent anomaly is that although the well has been
pumped for years by a windmill, the low-volume
windmill pump may never have stressed the aquifer
enough to develop the well properly, Le., to clean out
the fractures. The positive skin factor obtained from
this test provides an indication of wellbore damage
consistent with this argument. DOE-2 provides an
example, albeit extreme, of this phenomenon. Until it
was acidized and developed, hydraulic responses to
testing at DOE-2 showed only single-porosity
behavior with a positive skin (Beauheim, 1986).
While Engle does not display the extreme conditions
shown by DOE-2 before acidization, its apparent
single-porosity behavior and positive skin may,
nevertheless, be related more to wellbore and nearwellbore
conditions than to the true nature of the
Culebra at this location.
5.2.3 Tamarisk Member. The Tamarisk Member of
the Rustler Formation was tested in wells H-14 and
H-16. The purposes of the Tamarisk testing were to:
1) define the hydraulic head of the unit; and 2)
measure the transmissivity of the unit. Information
on the hydraulic head of the Tamarisk is needed to
evaluate potential directions of vertical movement of
groundwater between the Rustler members. The
transmissivity of the Tamarisk is a parameter needed
for vertical cross-sectional or three-dimensional
modeling of groundwater flow in the Rustler. The
claystone/mudstone/siltstone portion of the Tamarisk
(referred to hereafter simply as the claystone) is
believed to be more permeable than the
anhydrite/gypsum sections, and therefore easier to
test. Consequently, tests were attempted only on
the claystone portion of the Tamarisk at H-14 and
H-16.
5.2.3.1 H-14. At H-14, the Tamarisk claystone
extends from about 517 to 525 ft deep (Figure 3-6).
The initial test was performed over an interval from
the base of a packer at a depth of 494.5 ft to the then-
bottom of the hole 533 ft deep. Thus, the test interval
included the 8-ftthickness of claystone, and 30.5 ft of
overlying and underlying anhydrite and gypsum.
Descriptions of the test instrumentation and the test
data are contained in Stensrud et al. (1 987).
Testing began on October 7, 1986, by setting the
packer, swabbing the tubing to decrease the
pressure in the test interval, and closing the shut-in
tool to isolate the test interval and allow the testinterval
pressure to recover and equilibrate at the
existing static formation pressure. The pressure
response observed during the testing is shown in
Figure 5-82. After being shut in for nearly 37 hr, the
fluid pressure in the Tamarisk claystone test interval
had still not stabilized, but was rising at an everdecreasing
rate. The pressure in the wellbore above
the packer, in contrast, was dropping as fluid was
apparently entering the exposed Magenta and Fortyniner
Members. Because the Tamarisk pressure had
not stabilized, and did not appear likely to stabilize
for several days or weeks, no drillstem tests were
performed.
To verify that the observed response during the shutin
period was representative of the Tamarisk
claystone and not caused by a tool malfunction, the
packer was deflated and the DST tool was reset 8 ft
deeper in the hole on October 9, 1986. After
swabbing and shutting in the new test interval, a
pressure buildup similar to that observed at the
previous depth was measured for 4.5 hr
(Figure 5-82). At this point, we concluded that the
permeability of the Tamarisk at H-14 is too low to
allow testing on the time scale of a few days, and
abandoned the effort.
No conclusions about the static formation pressure of
the Tamarisk can be drawn from the observed
pressure buildups, because we have no way of
evaluating the role played by the overpressure skin
that was probably created during drilling.
Subsequent testing of the Magenta and Forty-niner
Members, discussed below, revealed fluid-pressure
buildups to be significantly affected by overpressure
skins.
5.2.3.2 H-16. At H-16, the Tamarisk claystone
extends from 677.5 to 690.1 ft deep (Figure 3-8). The
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