Page 180 - Petrophysics 2E

PERMEABILITY-POROSITY RELATIONSHIPS 153

Field Example
TAGI (Trias Argileux Greseux Inferior) sandstone is a fluvial formation
located in Algeria. The Triassic depositional environment involves facies
changes as well as reservoir extension. Sandstone units of TAGI formation
are multi-layered producing zones, isolated by clay intercalation from
flood plain deposition. TAGI has long been producing in Algeria in various
basins with porosities ranging from 10 to 2 1 % and often exceeding these
values. Horizontal permeability ranges from 10 to 100 mD.
On the basis of a radiocrystallography study of the clay fraction, TAGI
may be subdivided into two parts:

(a) The first part is characterized by the presence of relatively equal
Kaolinite-Illite content; and
(b) The second part is characterized by a high content of Illite (80% to
90%) and only traces of Kaolinite.

Figure 3.38 shows the results of a mineralogical study of TAGI. It is
clear that TAGI is composed of very fine sandstone and has three types
of porosity: inter-granular, dissolution, and fissured. A log-log plot of
vertical permeability versus horizontal permeability values measured
on cores obtained from the TAGI formation yielded the following
correlations (Figure 3.39):

(a) Equal Kaolinite-Illite content:

0 9707
kv = 0.598 kH' (3.104)

I000

2 loo
0 -

! lo
k 1

0.1
0 0.1 0.2 0.3
d,, mm
+ Kv Kv(High % of iIllite)
0 Kh(Kao1inite-Iillite) WKh(High %of Illite)
Figure 3.38. Permeability-mean grain size relationship in TAGI formation
(Kaolinite-Illite).