A Study of Caustic Consumption by Clays

The reactions of alkaline with clay minerals in reservoir rocks have been investigated under static conditions. With the help of the titration, the determinations of the irreversible chemical kinetics of the reaction of alkaline with 3 kinds of clay minerals and quartz were carried out at 60°C. High concentration sodium hydroxide and orthosilicate were used in these treatments for a time period as long as 1000 hours. The supernatants were analyzed for hydroxide, (Si), (Al) etc. and precipitated solid parts at different time periods were analyzed by X-ray differaction and other methods. The results show that the irreversible consumption of sodium hydroxide is the highest on montmorillonite and it is not a simple reaction. The consumption is very fast at first and slow down gradually. The alkali consumption can not be described by a single first-order reaction. The reaction is associated with the formation of new minerals which are mostly zeolites and the consumption of dissolved (Al) in later reaction, other than (Si), was observed. On the other hand, fast reversible alkaline consumption by ion exchange was observed at room temperature accompanied with the reaction controlled by chemical kinetics. H/Na exchange adsorption isotherms are Langmuir type in shape. The reversible alkali consumption is also the highest on montmorillonite. The test results show that it can be decreased by using a high salinity preflush and a subsequent low salinity caustic solution injection.