The effect of compaction parameters on the swelling kinetics of compacted Na-bentonite/quartz sand tablets

Abstract

Short-term shale swelling during initial fluid contact remains poorly constrained despite its importance for wellbore stability during geotechnical drilling. Conventional linear swelling measurements provide limited insight into early-time swelling kinetics. We present data from a novel, high-resolution non-contact linear displacement apparatus to evaluate the effects of artificial shale tablet preparation variables. Bentonite and bentonite–quartz mixtures, representative of the major constituents of many shales, were tested using NaCl brine (0.5 and 2 M) and deionized water to induce clay swelling. Tablets varied in quartz content (0–30%) and grain size (125–250, 250–300 and >300 µm), compaction pressure (4 and 8 tonnes) and duration (5, 8 and 10 min). The results show that quartz content and salinity strongly influence short-term swelling kinetics. Notably, 2 M NaCl induced the highest initial swelling rate, further amplified by higher quartz content. These findings highlight the importance of considering both swelling and non-swelling components when evaluating short-term shale swelling behaviour.