Shale Swelling/Shrinkage, Suction and Osmosis

Abstract

Samples were cut from nine different preserved shales, representing in situ states from 11% to 29% porosity and native water contents from 5% to 15%. In an air environment, each shale shows well-defined relationships among suction, water content, bulk volume and saturation. The native state for some shales corresponds to RH<0.8, even though the samples are fully-saturated. The shales will always shrink if placed into RH lower than native state. In contrast, when placed in direct contact with brines, the shales nearly always swell even when the brine water activity is less than the shale activity. The shales are confirmed to be unable to exclude ions; however, the swelling is correlated with the amount of water gain. Brine contact results in water gain that is difficult to explain through osmotic theory. However, some osmotic-type effects are observed.