Caustic Consumption by Kaolinite and Quartz and Their Mixtures at Temperatures up to 120°C

Hot caustic waterflooding has been shown to improve oil recovery by a number of different mechanisms. To design properly a hot caustic waterflood the consumption of caustic by reservoir minerals at high temperatures must be considered. This study presents the results of a series of batch experiments in which the interaction of quartz, kaolinite and caustic was examined at temperatures expected during hot alkaline waterfloods. The reaction of quartz, kaolinite, and a mixture of the two minerals with 0.1 N NaOH at 120°C was examined. Also, the dissolution of kaolinite at 70°C and 100°C was studied. The results show that at 120°C a mixture of 80% quartz/20% kaolinite by weight appears to consume as much or more caustic than either of those minerals alone. The major difference between pure quartz dissolution and that of the mixture was the mechanism of caustic consumption. In quartz dissolution, the hydroxide ion was consumed by silica speciation reactions. When pure kaolinite or a mixture of quartz and kaolinite was reacted, the bulk of the caustic was irreversibly consumed through the formation of new aluminosilicate minerals. The new mineral was identified as the synthetic zeolite Na-Pc, a structural relative of the zeolite phillipsite. In the case of kaolinite dissolution, increasing temperature from 100°C to 120°C caused a five-fold increase in the rate of caustic consumption. The initial rates of Si and Al dissolution from kaolinite was found assuming first-order kinetics. An Arrhenius plot of the data gave psuedo-activation energies of 8.5 and 1.1 Kcal/mole for the dissolution of Si and Al from kaolinite.