Page 196 - Petrophysics

PERMEABILITY-POROSITY RELATIONSHIPS 169

and 0: is the variance of the natural log of the permeability estimates:

(3.126)

where:

- Chki
Ink=--- (3.127)
n

The effective permeability obtained from Equation 3.124 should be
expected to be in the same range as the effective permeability obtained
from the interpretation of a pressure transient test, if VK < 0.25.
Corederived permeability is an accurate representation of a particular
core sample. Using this permeability value to represent reservoir
formation permeability can however lead to erroneous predictions
of well productivity, as core samples represent a small portion of
the interval in a particular well and an even smaller portion of a
reservoir [62]. The average effective permeability obtained from pressure
transient test should be considered as an accurate representation of the
reservoir, but only within the drainage area of the test. Beyond this
drainage area, the average permeability could be different if the radial
variation in permeability is significant. As long as the measurements
are consistent, the core derived permeability can be very useful in
completion design, particularly in choosing the phasing and vertical
spacing of perforation [ 581.

EXAMPLE

Given the permeability data in Table 3.7 1581 for well HBK5, calculate:

1. The arithmetic, geometric and harmonic averages of the corederived
permeability values.
2. The effective permeability, and
3. The Dykstra-Parsons coefficient.

SOLUTION

(1) Average values of permeability