Page 573 - Petrophysics

540 PETROPHYSICS: RESERVOIR ROCK PROPERTIES

Equation 8.78 becomes:

k = Jkfkm (8.79)

The fracture permeability (plus connected vugs) can therefore be
estimated from:
k2
kf = - (8.80)
km

Where km is the matrix permeability, which is measured from
representative cores, and k is the mean permeability obtained from
pressure transient tests. Combining equations 8.77 and 8.78 yields:

1 - (k/ki)1’3
Cf = (8.81)
AP
Where

ki = average permeability obtained from a transient test run when the
reservoir pressure was at or near initial conditions pi and
k = average permeability obtained from a transient test at the
current average reservoir pressure, p
Ap=pi-r)

Matrix permeability is assumed to remain constant between the two tests.
Note that equations 8.77 and 8.81 are valid for any two consecutive
pressure transient tests, and therefore Ap = p1 - p2. The time between
the two tests must be long enough for the fractures to deform significantly
in order to determine an accurate value of cf.
The fracture permeability can also be estimated from the following
correlation [3 11, if the fracture width (or aperture) wf is known from
logs or core measurements:

kf = 33wtwf (8.82)

where wf is in microns (1 micron = lop6 m), the storativity ratio o and
total pososity t$t are expressed as a fraction and kf in mD.
The effective permeability of a naturally fractured reservoir may also
be approximated from the following equation:

This equation should preferably be used for verification purposes, i.e.
once kf is calculated from equations 8.80 or 8.82 and +f from Eq. 8.76,