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Dynamic Data Analysis – v5.12.01 - © KAPPA 1988-2017
Chapter
3 – P ressure Transient Analysis (PTA)- p61/743
3.B
The old stuff
Twenty years ago, the core of well test interpretation was the dual use of specialized plots and
type-curve matching:
Specialized plots correspond to a selected scale where some flow regime of interest such as
infinite acting radial flow, linear flow, bilinear flow, spherical flow or pseudo-steady state
are characterized by a straight line. The slope and the intercept of this straight line will
generally give two parameters of the system.
Type-curve matching consists in sliding a plot of the data, generally on a loglog scale, on
pre-printed type-curves. The relative position between the data and the type-curve, also
called the time match and pressure match, provides two quantitative parameters. The
choice of type-curve will give additional information.
We will start with the semilog plots, the main specialized plots used to quantify the main flow
regime in PTA: Infinite Acting Radial Flow, or IARF.
3.B.1
IARF and Semilog plots
We have seen in Chapter ‘Theory’ that IARF is the main regime of interest in Pressure
Transient Analysis. In the case of a production at a constant rate, IARF is characterized by
linearity between the pressure change and the logarithm of time. We will see that such
linearity is also found for more complex production history, provided that the right time
function is used.
3.B.2
Drawdown response and MDH plot
In the case of a constant production from time 0 to infinity, the IARF is characterized, for a
finite radius well in a homogeneous reservoir, by the equation:
S
rc
k
t
kh
q
p
wt
8686 .0 228 .3
log
log
6. 162
2
In the case of more complex well geometries and reservoir heterogeneities, the constant term
may be more complicated, as it will integrate the cumulative effect of these geometries and
heterogeneities. Still the response will have the same shape. The value of skin S calculated
from the equation above may not be the right value in terms of well damage according to
Darcy’s law, but it will have some meaning. It is called the ‘equivalent skin’.
The Miller-Dyes-Hutchinson (MDH) plot is a graph of the pressure or the pressure change as a
function of the logarithm of time. IARF is characterized by a linearity of the response.
Drawing a straight line through these points gives a slope and an intercept:
IARF straight line:
b t
mb t
kh
qB
Y
log
log
6. 162
Where:
hr t
p
t
p b
LINE
LINE
1
0 )
log(