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Dynamic Data Analysis – v5.12.01 - © KAPPA 1988-2017
Chapte
r 4 – R ate Transient Analysis (RTA)- p133/743
4.C
The right stuff
4.C.1
Blasingame plot
Previous sections have described the conventional Decline Curve Analysis methods, and their
extension using Fetkovich type-curves. We recall that the latter were obtained by combining a
theoretical model response and the empirical decline stems of Arps.
Broadly speaking, one could say that the introduction of type-curve matching techniques in
production analysis has opened the way to applying methods developed for well test
interpretation to the analysis of production data. The main limitation in the Fetkovich type-
curve is the assumption of constant flowing pressure. Blasingame and McCray noted that using
a pressure normalized flow rate when the bottom-hole pressure varies significantly did not
remedy the problem. They sought functions that would transform the variable
pressures/variable rates solution into an equivalent constant pressure or constant rate
solution. They introduced two specific time functions, t
cr
the constant rate time analogy, and t
cp
for constant pressure. For the liquid case, the constant rate analogy time function is defined as
the ratio of the cumulative and the flow rate:
t
Q t
q t
cr
When the normalized rate
q t
p p t
i
w
is plotted versus this function on a loglog scale, the
boundary dominated flow period follows a negative unit slope line:
The Black Oil Pseudo Steady State flow rate equation is:
t m b p
q
pss o
pss o
o
,
,
1
With:
oi
o
t
pss o
B
B
Nc
m
1
,
;
s
r
A
Ce
kh
B
b
wA
o o
pss o
2
,
14
ln
2
1
141.2
;
and
o
p
q
N
t
When the Pseudo Steady States dominates
p
q
o
is function of
t
at exponent (-1).
Therefore a loglog plot of
p
q
o
vs
t
will show a negative unit slope straight line.