Beauheim 1987 - Waste Isolation Pilot Plant - U.S. Department of ...

A positive value of s indicates wellbore damage, or a wellbore with a lower permeability than the formation as a
whole as a result of drilling effects. Conversely, a negative value of s indicates a wellbore with enhanced
permeability, usually caused by one or more fractures intersecting the wellbore.
The type curves begin with an initial segment having a unit slope, corresponding to early-time dominance of
the pressure response by wellbore storage and skin effects. The duration of this unit slope segment is
proportional to the amount of wellbore storage and skin that are present. At late time, the curves flatten as
infinite-acting radial flow dominates.
Bourdet et al. (1 984) added the pressure derivative to the analytical procedure by constructing a family of type
curves of the semilog slope of thedimensionless pressure responseversus thesame dimensionless time group,
tD/CD. The semilog slope of the dimensionless pressure response is defined as:
(A-5)
where: pfD = dimensionless pressure derivative
These curves are plotted on the same log-log graphs as the type curves of Gringarten et al. (1979), with the
vertical axis now also labeled (tD/CD)p'D (Figure A-2). Again, each individual type curve is characterized by a
-n
P
n
Y
-
6 s n
-
nL
w3
5 g lo',
$0
w w
Z E
cna
102 - 1 I Ill,, I I 1 1 1 1 1 1 I I l 1 1 l I 1 I 1 1 1 1
- - SINGLE-POROSITY TYPE CURVES
--- PRESSURE-DERIVATIVE TYPE CURVES
h
- 3
K - -
n.
n
2
a
-
-
- -
-
-
3
10-1
I 1 1 1 I l 1 1 l I L 1 L L , , , I I 1 I I , #Ill I I I O 1 1 1 1 1 I I, I , ,
IO-' I00 10' 102 103 104
Figure A-2.
DIMENSIONLESS TIME GROUP, 1,
CD
Single-Porosity Type Curves and Pressure-Derivative Type Curves for Wells
with Wellbore Storage and Skin
147