Page 211 - Petrophysics 2E

184 PETROPHYSICS: RESERVOIR ROCK PROPERTIES

Where (t*Ap’)R is obtained from the horizontal straight line, which
corresponds to the infinite acting radial flow regime. On the semilog
plot this flow regime corresponds to the straight line of slope m.

EXAMPLE

A new well in a small bounded reservoir, North of Hobbs, New Mexico,
was produced at a constant rate of 250 STB/D. The initial reservoir
pressure is 4,620 psia. Other relevant data is as follows:

Calculate the permeability from:

(a) The semilog plot of Pwf versus time, and
(b) The pressure derivative, using Tz’ub’s Direct Syntbesis technique

SOLUTION

Figure 3.57 is a semi-log plot of the flowing bottom-hole pressure versus
time in Table 3.14. Figure 3.57 shows a log-log plot of AP = Pi - Pd
and the pressure derivative (t*AP’) versus test time.

(a) The absolute value of the slope of the straight line corresponding to
the infinite acting line, i.e. radial flow regime, is 18.5 psflogcycle.

I

0.1 1 10 100
The, t, hrs
Figure 3.57. Semi-log plot of pressure drawdown versus test time.