This study reports the applicability of quillaja saponin (QS) as a vigorous and environmentally friendly shale swelling inhibitor. QS is a natural surfactant, which is extracted from herbal sources. The inhibition strength of this surfactant was assessed through various experiments, such as sedimentation, inhibition, filtration, particle size, Scanning Electron Microscope (SEM) images, and cutting recovery. Data obtained from these tests illustrated that QS greatly inhibits clays from swelling. The optimal concentration for QS in this intend was 10 g/L. Compatibility of this surfactant with other common additives was also investigated, which showed that it is totally compatible. Finally, the potential inhibition mechanism was assessed through thermal gravimetric analysis (TGA), zeta potential, and contact angle measurement experiments. Surface coating, and wettability alteration of clay particles to the oil-wet state was recognized as the most probable mechanism.
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