Page 294 - Fundamentals of Reservoir Engineering

OILWELL TESTING 230

1000

McKinley type
(curve (T/F = 5000)
100
X match point
∆t
(mins) ∆ p = 800 psi
buildup plot X
X
X
10 X X
X
X ∆ p F
X = .05
q
1
10 -4 10 -3 10 -2
∆ p F
q

Fig. 7.41 Buildup plot superimposed on a particular McKinley type curve for
T/F = 5000

The transmissibility obtained in this manner is for the damaged or stimulated
region close to the wellbore, T w.

f) If, for large values of ∆t on the buildup plot, the pressure points trend away from
the McKinley type curve, this indicates the presence of a mechanical skin factor,
as shown in fig. 7.42.

S (positive)
S (negative)

∆ t
(mins)

∆ p F
q

Fig. 7.42 Deviation of observed buildup from a McKinley type curve, indicating the
presence of skin

Since the latter part of the buildup, for large ∆t, is not influenced by the skin it should
reflect the actual transmissibility of the formation beyond the damaged or stimulated
zone near the well.

Therefore, to obtain the formation transmissibility, T f, the late part of the buildup plot is
re-aligned with another of the type curves, for which the value of T/F is again noted.