Osmotic flow through a Cretaceous clay in southern Saskatchewan, Canada

Clays and shales can act as semipermeable membranes, causing osmotic flow a nd (or) osmotically induced fluid pressures. Despite laboratory proof of th e osmotic behaviour of clay-rich geologic material, the influence of this o smotic behaviour on in situ groundwater flow and solute transport is inconc lusive. This is due in part to the lack of laboratory experimental work inv olving undisturbed core samples, and to the lack of field-scale research. T he ability of undisturbed clay samples to conduct flow hydraulically and os motically was investigated using dilute salt solutions. Undisturbed Cretace ous clay samples from southern Saskatchewan were used in a laboratory exper imental program. The experiments included constant-head hydraulic conductiv ity (K-h) tests and osmotic flow tests conducted over a range of pore-fluid concentrations of 0.054-1.12 equiv./L. The clay samples exhibited semiperm eable membrane behaviour by conducting flow osmotically. The hydraulic cond uctivity of the clay increased by a factor of two as the pore-fluid concent ration increased from 0.070 to 0.56 equiv./L. Osmotic efficiencies ranged f rom 0.0028 to 0.42 for concentrations from 0.84 to 0.096 equiv./L. Both the osmotic compressibility and osmotic efficiency decreased with increasing p ore-fluid concentration. The behaviour of the clay was consistent with diff use double-layer theory.