Page 35 - Reservoir Formation Damage

Mineralogy and Mineral Sensitivity of Petroleum-Bearing Formations 19

he also conducted laboratory core tests by flowing various aqueous
solutions through cores extracted from micaceous sand formations. The
data shown by Figure 2-8 of Reed (1977) indicates permeability reduc-
tion. Based on the severeness of formation damage indicated by Figure
2-8, he concluded that mica alteration is a result of the exchange of K +
cations with cations of larger sizes. Figure 2-8 shows that the deionized
water caused the most damage, CaCl 2 solution made the least damage
and damage by the NaCl solution is in between. Thus, the cations in-
volved can be ordered with respect to the most to least damaging as
+
+
++
H >Na >Ca . Whereas, Grim (1942) determined the order of re-
placeability of the common cations in clays from most to least easy cat-
++
+
++
+
++
+
+
+
++
+
ions as Li >Na >K >Rb >Cs >Mg > Ca >Sr >Ba >H . Hughes (1951)
states: "hydrogen will normally replace calcium, which in turn will re-
place sodium. With the exception of potassium in illites, the firmness with
which cations are held in the clay structure increases with the valence
of the cation."
Reed (1977) postulated that formation damage in micaceous sands is
a result of mica alteration and fines generation according to the process
depicted in Figure 2-9 by Reed (1977) and later deposition in porous
rock. As depicted in Figure 2-10, when clays are exposed to aqueous so-
+
lutions containing no or small amounts of K cation or larger cations such
+
+
as H , Ca +2 and Na , the K + cation diffuses out of the clay platelets ac-
cording to Pick's law, because there are more K + than the solution. In
100<
3% CaCI 2
WELL 4290 CORE
Kls1188md
O ID
DEIONIZED WATER
WELL 1030 CORE
Kl = 1247md

VOLUME THROUGHPUT (liters)
Figure 2-8. Comparison of the permeability damages by the deionized
water, and calcium chloride and sodium chloride brines in field cores
(after Reed, ©1977 SPE; reprinted by permission of the Society of Petro-
leum Engineers).