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Dynamic Data Analysis – v5.12.01 - © KAPPA 1988-2017
Chapter
3 – P ressure Transient Analysis (PTA)- p64/743
After transformation, we get the equation of the Horner plot straight line in terms of pressure:
t
t
t
kh
qB
p p
p
i
BU
log
6. 162
Permeability-thickness product and the skin are then calculated.
Permeability-thickness product:
mh
qB
k
6. 162
Skin factor if t
p
is large enough:
23.3
log
1
log
151 .1
2
1
wt
p
p
wf
hr
rc
k
t
t
m
p p
S
Note that the time function is such that the data plots ‘backwards’, as when ∆t is small, at the
start of the build-up, the Horner function (log (tp+∆t)/∆t) will be large, and when ∆t tends to
infinite shut-in time the Horner time tends to 1, the log of which is 0.
Fig. 3.B.3 – Horner plot
If the reservoir were truly infinite, the pressure would continue to build-up in infinite-acting
radial flow and eventually intercept the y-axis at pi, the initial pressure. However, as no
reservoir is infinite, the extrapolation of the radial flow line at infinite shut-in time is called p*,
which is simply an extrapolated pressure.
If the reservoir is infinite:
*
p p
i
It is important to notice that the calculation of the permeability is valid even in the case of a
short production before the shut-in, while the validity of the calculation of skin is conditioned
to a producing time long enough, so IARF was reached before t
p
.