Page 371 - Reservoir Formation Damage

Inorganic Scaling and Geochemical Formation Damage 351

Saturation Index Charts for Clay Minerals

Schneider (1997) constructed the illite saturation index curves for
mixing the Mule Shoe water with the JMU connate water as a function
of the volume percent Mule Shoe water in the mixture. For this purpose,
he considered the following dissolution/precipitation reaction for the
Rotliegendes illite formula:

+
Illite+ IOH 2O<^ K + 0.15Mg +2 +2AAl(OH)~
(13-46)

He explains that the Mule Shoe Ranch water is usually treated with lime
and therefore its pH is above 10. A comparison of Figures 13-8A and B
reveals that injecting a high pH Mule Shoe Ranch water into the reservoir
reduces the illite stability of the JMU connate water upon mixing. The
saturation index curves shown in Figures 13-9A and B by Schneider
(1997) indicate that adding KCl into the Mule Shoe Ranch water improves
the illite stability.
In Figures 13-10A and B, the illite stability curves obtained by Schneider
(1997) are given for the Santa Rosa and Canyon Reef waters, respectively.
Figure 13-10A indicates that injecting large volumes of the Mule Shoe
Ranch water into the JMU reservoir reduces the illite stability. In contrast,
the Canyon Reef water is compatible with the JMU connate water
and should not create any illite unstability problems as indicated by
Figure 13-1 OB.
Schneider (1997) constructed the chlorite saturation index curves shown
in Figures 13-11A and B based on the following dissolution/precipitation
reaction for the North Sea chlorite formula:

+2
Chlorite + 4H 2O + 6H + <-> 2.15Mg + 2.25Mg +2
(13-47)
+2.8Al(OH)-+2.1H 4Si0 4
Figure 13-11A reveals that the Mule Shoe Ranch water becomes incom-
patible with the JMU Connate water with respect to the chlorite stability
upon large volumes of water injection. Whereas, the Canyon Reef water
is compatible, as indicated by Figure 13-1 IB.
Schneider (1997) constructed the kaolinite saturation index curves
shown in Figures 13-12A and B based on the following dissolution/
precipitation reaction:

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