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

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\ PRESSURE BELOW TEST INTERVAL
TION ON
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SWABBING TUBING
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PEAK AT 134 2 psia
:- -
PRESSURE ABOVE TEST INTERVAL
PEAK AT 123 2 psia
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PEAK AT 115 4 psia
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E -. 5 15 2. 5 3: 3*. 5 45 52.5 SC 6’. 5 “5
Sto-t Jots: iC :E. ;986
Start 7ime: C8:CO:OD
E.opsec Time in t‘ours
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LinearLinear Sequence Plot
H-14, MGEKTP DST‘e
Figure 5-84. H-l4/Tamarisk Claystone Shut-In Linear-Linear Sequence Plot
the remainder of the buildup period. After 13.5 hr of
the SBU, the pressure peaked at 115.4 psia and then
began to decline. At the end of the TBU, the
pressure was essentially constant at 110.3 psia. This
successive decrease in the magnitude of the
pressure peaks provides a clear indication of the
dissipation of an overpressure skin.
Figure 5-85 shows a log-log plot of the FBU data up
to the time of the pressure peak, along with an
INTERPRET-generated simulation. The simulation is
representative of a single-porosity medium with a
transmissivity of 5.6 x 10-3 ftz/day (Table 5-2).
Assuming a porosity of 20%, a total-system
compressibility of 1.0 x 10-5 psi-’, and a fluid viscosity
of 1.0 cp, the skin factor for this simulation is about
0.5, indicating a well with very little wellbore damage.
The simulation does not fit the observed early-time
data very well, but it does fit the middle- and latetime
pressure data adequately. The sharp decline of
the pressure derivative at late time clearly shows the
effects of overpressure skin.
Figure 5-86 shows a log-log plot of the SBU data up
to the time of the pressure peak, along with a
simulation generated by INTERPRET. This
simulation, like that of the FBU data (Figure 5-85), is
representative of a single-porosity medium with a
transmissivity of 5.6 x 10-3 ftz/day, but the skin factor
is slightly lower at about 0.4 (Table 5-2). The
expected sharp decline in the pressure derivative at
late time due to the overpressure skin is evident on
the plot, but an unexpected preceding rise in the
derivative is also seen. The cause of this rise is not
clearly understood. One possibility is that the
pressure-derivative data show a superposition of
pressure-skin effects resulting from episodes of
significantly different hydraulic loading, such as the
drilling of the Magenta and the later testing of the
Tamarisk Member, with the residual effects of
different episodes dominating at different times
during the buildup.
The dimensionless Horner plot of the pre-peak SBU
data also shows this superposition of pressure-skin
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