Wettability studies of reduced-charge montmorillonites modified by quaternary ammonium salts using capillary rise test

A series of montmorillonites with systematically reduced layer charge were prepared by a standard method of different fractions of Li+-fixation in montmorillonite, which could be used to mimic an oil reservoir. Three kinds of quaternary ammonium salts (QASs) with different cationic charges and structure sizes were used singularly or in compound form to modify the reduced-charge montmorillonites (RCMs). The wettability alterations of the organo-RCMs for deionized water and cyclohexane were studied based on capillary rise method and were compared using the Lipophilic to Hydrophilic Ratio (LHR). The results indicate that RCMs singularly modified by three kinds of QASs show different wettability characteristics, whereas compound modified by QASs have a synergistic effect on the wettability. Moreover, the compound type of the QASs plays a more important role on LHR values than the mix proportion. The results of this work also indicate that it is possible to regulate the wettability of the organo-RCMs by simultaneous control of the type, the compound ratio of QASs and the layer charge characteristics, which is helpful in providing theoretical guidance for the oil production.