Page 145 - Petrophysics 2E

1 18 PETROPHYSICS: RESERVOIR ROCK PROPERTIES
+.

8.)
‘E
P n
m

- 1 -
* 0

Roundness
Figure 3.18. Roundness and sphericity of different shapes.

roundness 30.5. The general form of Equation 3.33 is:

(3.34)

Note that, as sphericity and roundness approach unity, Kgs approaches 6
(which is valid only for perfectly spherical sand grains). The petrographic
image analysis or PIA method may be used to characterize the porous
rock if well-prepared samples are available, i.e. samples with good optical
contrast between the pores and grains, and the thin sections are obtained
at overburden conditions. The specific pore surface can be determined
from

4LP
spv = - (3.35)
ZAP

where Lp and Ap are the pore perimeter and the pore cross-section,
respectively. Using PIA, a planar pore shape factor fps can be
determined as:

G
fps = - (3.36)
&Ap

The factor fps, shown in Table 3.3, indicates what the perimeter Lp
would be if the planar or 2D feature were a circle. The range of fps
is 3.75 (sphericity of 0.5 or less and roundness of 0.3 or less) to 5.84
(sphericity of 0.5 or less and roundness greater than 0.5). There is no