Page 149 - Petrophysics 2E

122 PETROPHYSICS: RESERVOIR ROCK PROPERTIES

Taking the logarithm of Equation 3.45 on both sides yields:

Equation 3.47 yields a straight line on a log-log plot of RQI versus
& with a unit slope. The intercept of this straight line at Qz = 1 is
the flow zone indicator. Samples with different FZI values will lie on
other parallel lines. Samples that lie on the same straight line have
similar pore throat characteristics and, therefore, constitute a flow unit.
Straight lines of slopes equal to unity should be expected primarily in
clean sandstone formations. Slopes greater than one indicate a shaly
formation.
The flow zone indicator (FZl) is a unique parameter that includes the
geological attributes of the texture and mineralogy in the structure of
distinct pore geometrical facies. In general, rocks containing authogenic
pore lining, pore filling, and pore bridging clay as well as fine grained,
poorly sorted sands tend to exhibit high surface area and high tortuosity,
hence low FZI. In contrast, less shaly, coarse-grained, and welI-sorted
sand exhibit a lower surface area, low shape factor, lower tortuosity, and
higher FZI. Different depositional environments and diagenetic processes
control the geometry of the reservoir and consequently the flow zone
index.

(c) Tiab flow unit characterization factor (Ht). Sneider and King
showed that most of the petrophysical properties of sandstones and
conglomerates can be related to grain size and sorting, degree of
rock consolidation, cementation, sizes of pores, and pore intercon-
nections [29]. They also showed that there are a finite number of rock
types and corresponding pore geometries that characterize geologic
units. However, geologic units may or may not coincide with hydraulic
flow units. It is also possible that a geologic unit may contain several flow
units. Equation 3.27 can be written as:

(3.48)

HT is called the Tiab flow unit characterization factor. Substituting for
KT = zKps and svg (Equation 3-34), HT becomes:

(3.49)