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Ecrin v4.20 - Doc v4.20.01 - © KAPPA 1988-2011
Topaze Guided Session #1
•
TopGS01 - 17/24
Blasingame plot
The x-axis of the Blasingame plot is an equivalent time defined as:
t
Q t
q t
e
( )
( )
The plotted channels are:
With triangles in green (gauge color), an instantaneous productivity index:
PI =
q t
p p t
i
With plus signs in green (gauge color), the integral of the previous function divided by the
time:
PI Int. =
1
t
q d
p p
e
i
O
t
e
.
With plus signs in red, the derivative of 'PI Int' with respect to the log of equivalent time.
The essential feature of this presentation is that even in the case of changing pressure, the
boundary dominated flow period will exhibit a –1 slope on all three channels. In addition, PI Int
and its derivative will merge together during that period. By plotting a given model on the
same scale and with adequate drag options, this plot will allow refining the model parameters.
Loglog plot
The loglog plot is almost an inverted Blasingame plot. The x-axis is the equivalent time, and
channels plotted by default are:
With plus signs in green (gauge color), the integral of a rate normalized pressure, divided
by the time:
Normalized pressure integral =
1
t
p p
q
d
e
i
o
t
e
( )
( )
.
With plus signs in red, the derivative of the previous function with respect to the log of
equivalent time.
It is also possible to plot the rate normalized pressure, rather than its integral, but this
function is usually too noisy hence the default usage of the integral.
Normalized pressure =
p p t
q t
i
( )
( )
During boundary-dominated flow, both the pressure integral and its derivative exhibit a
straight line of unit slope, similar to a pseudo-steady state regime in a pressure transient
interpretation. The similarity goes further and one can check that other flow regimes appear –
at least on test designs – with the same signature as for constant rate solutions.
The methods traditionally used in Pressure Transient Interpretation can thus be applied on the
loglog plot. In particular, a stabilization of the derivative can provide an estimate of kh and the
late time unit slope, when seen, can readily provide an estimate of Re.
Normalized rate cumulative plot
Another plot that can be created is the 'Normalized rate cumulative' plot. In oil, this option
creates a plot of normalized rate versus normalized cumulative:
w i
p p
q
versus
w i
t
p pc
Q
