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Dynamic Data Analysis – v5.12.01 - © KAPPA 1988-2017
Chapter
3 – P ressure Transient Analysis (PTA)- p66/743
3.B.5
Complex productions and rate normalized superposition plot
In some cases the engineer will want to interpret producing periods when the rate is not
stabilized, or the rates data will be sandface rate, and therefore the value of the rate will not
instantaneously go down to zero during the shut-in period. These cases are a little more
complex than the cases above. However the principle of the semi-log analyses will be kept
with the following modifications:
For a multi-rate production or injection (whether rates are measured at surface or downhole),
the adequate semi-log plot will still have the same superposition time as the X axis, but the
pressure will be replaced by:
tp p
tq
Q
i
Where Q is a reference value for normalization, that will be generally chosen to be the last
stabilized rate of the interpreted period so that the function tends to ∆p at late time.
For a multi-rate build-up or fall-off using sandface rates, the Y axis will still be
wf
p tp
but the calculation of the superposition time will allow rates to be changed during the period.
Furthermore the reference rate will not be the difference of rates before N and N-1 (this has no
meaning when dealing with continuous downhole rate measurements), but the last stabilized
rate before shut-in.
3.B.6
Using type-curves
Loglog type-curvesType-curve matching originally consisted in plotting a loglog plot of the
pressure response versus time on tracing paper that could then be slid over a set of pre-
printed type-curves, the log cycles being square and of the same size in both plots. The
selection of the type-curve matching the data can provide one or several parameters, and the
relative positions of the two plots in the X and Y direction, also called the match point, will give
two other interpretation results.
Fig. 3.B.5 – Type-curve matching
The type-curve used for wellbore storage and skin in an infinite homogeneous reservoir (in the
following Figure), the pressure match (relative positions in the Y direction) will give the
permeability. The time match (relative positions in the X direction) will give the wellbore
storage, and the selection of the curve will give the skin factor.