Chapter 4
with naphthenate and form ion pairs. If naphthenate and C8TAB are added in
stoichiometric amounts, adsorbed naphthenate and C8TAB are minimized. If
C8TAB is overdosed, the excess C8TAB will adsorb on the negative surfaces of
kaolinite and make them more oil-wet. Hence as C8TAB concentration increases,
water-wet fraction of kaolinite increases to maximum and then decreases.
4.2.4.2. Effect of betaine
Figure 4.8 shows water-wet fraction of 1.0 w.% kaolinite in toluene-brine
mixture (1:1, v∕v) with 100 ppm naphthenate adding 1000 ppm betaine (based on
activity of betaine and total volume of the mixture) at pH 8.3 24 hours after
preparation. The red and black dashed lines show water-wet fraction of kaolinite
with/ without naphthenate as control, without betaine added. Comparison of all the
results reveals that sample adding 1000 ppm betaine 13 has largest water-wet
fraction of kaolinite (90%). Hence betaine 13 was used as optimal surfactant in
the following wettability test to study the effect of dosage.
Figure 4.9 shows water-wet fraction of 1.0 w.% kaolinite in toluene-brine
mixture (1:1, v∕v) with 100 ppm naphthenate adding different amounts of betaine
13 at pH 8.3 24 hours after preparation. The two black dashed lines show
water-wet fractions of kaolinite with or without naphthenate as control, without
betaine added. The red dashed line shows 1:1 stoichiometry value of betaine 13
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