Page 45 - Petrophysics

PROPERTIES OF SEDIMENTARY PARTICLES 19

30-- -
- -

20--
-

lo--
-
0. lI r

SILT I SAND
MEDIUM 1 COARSE I V. FINE I FINE I MEDIUM I COARSE

PHI SCALE
6 5 4 3 2 1 0

1 /64 1 I32 1/16 1 /8 114 112 1
Grain Size, rnm
Figure 1.4. Histogram and cumulative size curves showing textural parameters
for the Elgin sandstone, Cleveland, Oklahoma. Porosity = 0.240; permeability =
3,484 mD.

Sphericity is a measure of how closely a particle approximates the
shape of a sphere. It is a measure of how nearly equal are the three
mutually perpendicular diameters of the particle, and is expressed as the
ratio of the surface area of the particle to the surface area of a sphere of
equal volume 117, 181.
Roundness is a measure of the curvature, or sharpness, of the particle.
The accepted method for computing the roundness of a particle is to
view the particle as a two-dimensional object and obtain the ratio of the
average radius of all the edges to the radius of the maximum inscribed
circle.