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Dynamic Data Analysis – v5.12.01 - © KAPPA 1988-2017 Chapte - p146/743
4.D.3.c Material balance (Normalized rate-cumulative) plot
The boundary dominated flow obeys the same equation:
DA D Q q  
 2
1
Provided that the dimensionless rate and cumulative production be defined as:
 
) ( ) (
. . 1422
w i
D pm pmkh
qT
q

 and
 
 
) ( ) ( . .
)( ) ( . . . .50.4
w i i
i i i
DA pm pmphA
pm pmGzT
Q




All equations are in Oil Field units.
Unlike the oil case, we cannot find a simple expression of a normalized cumulative that is
independent of the fluid in place. This is because the gas in place is involved in a non-linear
fashion in the expression of the dimensionless cumulative. However by extension with the
previous method for oil we can choose to plot:
) ( ) (
w i pm pm
q

versus
 
 
) ( ) (
)( ) ( .
w i
i i
DA pm pm
pm pmG
Q



The value of ‘X’ at the intercept is:
 
 
Intercept
pm pm
pm pmG
w i
i i @
) ( ) (
)( ) ( .


Gi
B
PV
p Tsc BT
TppPV
zT
pPV
zT
pAh
gi i gi
sc i
i
i
i
i     
. . . .2.50.4
. . .
. .2.50.4
.
. . .2.50.4
. .. .
  

Note: the X-axis value  
 
) ( ) (
)( ) ( .
w i
i i
DA pm pm
pm pmG
Q


 depends on the gas in place Gi value, therefore
a change in the straight line coefficients changes the intersect therefore the abscissa of the
data, in other word moving the straight line will move the data points through which we draw
it, it becomes an iterative process that converges easily.