Page 33 - Reservoir Formation Damage

Mineralogy and Mineral Sensitivity of Petroleum-Bearing Formations 17

SILICON-OXYGEN
TETRAHEORA
SHEET ~T~
I
o
SILICON-OXY6EN
TETRAHEDRA
SHEET

8I88SITE OR
BRUCITE SHEET

SILICON-OXYGEN
TETRAHEORA
SHEET
O

AI 4 -Ft 4 -Ms 4 -Mg,)(SI,. y -Aly) 0 2O
Figure 2-5. Schematic description of the crystal structure of illite (after Grim,
Bray, and Bradley-Grim, 1942, and Hughes, 1951; reprinted courtesy of the
American Petroleum Institute, 1220 L St., NW, Washington, DC 20005,
Hughes, R. V., "The Application of Modern Clay Concepts to Oil Field
Development," pp. 151-167, in Drilling and Production Practice 1950, Ameri-
can Petroleum Institute, New York, NY, 1951, 344 p.).

media, calcium-montmorillonite platelets remain practically intact, close
to each other, while the sodium-montmorillonite aggregates readily swells
and the platelets separate widely. Therefore, water can easily invade the
gaps between the platelets and form thicker water envelopes around the
sodium-montmorillonite platelets than the calcium-montmorillonite plate-
lets (Chilangarian and Vorabutr, 1981) as depicted in Figure 2-6.
Clay damage can be prevented by maintaining high concentrations of
+
+
K cation in aqueous solutions. At high concentrations of K cation, clay
+
platelets remain intact, because the small size K cation can penetrate the
interlayers of the clay easily and hold the clay platelets together
(Mondshine, 1973 and Chiligarian and Vorabutr, 1981) as depicted in
Figure 2-7.
Many investigators, including Mungan (1965), Reed (1977), Khilar and
Fogler (1983), and Kia et al. (1987), have determined that some degree
of permeability impairment occurs in clay containing cores when aque-
ous solutions are flown through them. This phenomenon is referred to
as the "water sensitivity."
Reed (1977) observed that young sediments are mostly friable mica-
ceous sands and proposed a mechanism for damage. To justify his theory,