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Dynamic Data Analysis – v5.12.01 - © KAPPA 1988-2017
Chapte
r 4 – R ate Transient Analysis (RTA)- p145/743
In the PSS oil flow rate equation
t m b p
q
pss o
pss o
o
,
,
1
, the slope
pss o
m
,
is a function of the fluid
compressibility, which is highly pressure dependent in gas cases.
The objective is to keep the linearity and the PSS flow rate equation for gas in the same shape
as for oil:
egas
pss g
pss g
p
g
t m b p
q
,
,
1
with a constant slope
pss g
m
,
We take the varying viscosity and compressibility into account by introducing the ‘pseudo’
pressure and ‘pseudo’ normalized time:
p
p
g
i
i gi
p
base
dp
z
p
p
z
p
t
t
g
g
g
ti
gi
egas
dt
pcp
t q
t q
c
t
0
) ( ) (
)(
)(
The slope is then:
t
pss g
Gc
m
1
,
The intersect becomes:
s
r
A
Ce
kh
B
b
wA
gi
gi
pss g
2
,
14
ln
2
1
141.2
The consequence of not using this time function is that the linearities expected during the
various flow regimes may be distorted.
It is not necessary in the Blasingame plot since this plot only provides a basis for comparing
the data and a model response calculated for the particular case. Handling the non linearities
is the model responsibility, not that of the plot. If the model is representative, the model and
the data will be consistent. So it does not matter whether such or such period exhibits a
linearity or not.
This is different when using a type curve as the type curve embeds modelling assumptions.
That is why this time function is used in Topaze in the match with the Blasingame type curve.
4.D.3.b
Loglog plot
The linearities expected during the various flow regimes may be distorted when the diffusion
does not follow a linear equation, with gas or in multiphase cases, it is important to realize
that the loglog plot, like the Blasingame plot, only provides a basis for comparing the data and
a model response. Handling the non-linearities is the model responsibility, not that of the plot.
If the model is representative, the model and the data will be consistent. It does not really
matter whether such or such period exhibits linearity or not. When using a type-curve this is
different as the type-curve embeds modelling assumptions.