Page 142 - Petrophysics

PERMEABILITY-POROSITY RELATIONSHIPS 115

T = tortuosity of the flow path, and
KT = Kpsz = effective zoning factor.

Equation 3.27 may be written as:

(3.28)

where +R is:

The parameter KT, called here the pore-level effective zoning factor,
is a function of pore size and shape, grain size and shape, pore and
grain distribution, tortuosity, cementation, and type of pore system, e.g.
intergranular, intercrystalline, vuggy, or fractured. This parameter varies
between flow units, but is constant within a given unit.
The parameter KT for a homogeneous sandstone formation can be
estimated from [25]:

1
KT = - (3.30)
J:

The lithology index J1 is determined from capillary pressure data.
Experimental data show that the plot of the Leverett J-function, J(SG),
against the normalized water saturation S& on a log-log graph yields a
straight line according to the following equation:

where J1 is the intercept of the straight line (extrapolated IF necessary)
at S& = 1, as shown in Figure 3.16. The normalized water saturation is
defined as:

The pore size distribution index h is the slope of the line. The lithology
index J1 ranges from 0.44 for an unconsolidated spherical grain to
0.20 for a consolidated clean sandstone formation with homogeneous
pore size distribution. Table 3.2 shows typical values of J1 and KT
for different formations. High values of J1 are usually found in high
permeability reservoirs, while low values of J1 correspond to low
permeability reservoirs.