EXPERIMENTAL CHARACTERIZATION OF THE SEMIPERMEABLE MEMBRANE BEHAVIOUR OF PIERRE SHALE AT SOUTHERN SASKATCHEWAN

Abstract

Chemical osmosis is a process in which fluid movement occurs through a porous media in response to a chemical concentration gradient within the pore fluid. The porous media acts as a semipermeable membrane that restricts solute transport while allowing pore fluid flow in response to osmotic gradients. Knowledge of the semipermeability character and the factors governing the semipermeability of a membrane is required to fully assess the impact of chemical osmosis. In this study the semipermeable membrane was a sample of Cretaceous-aged Pierre Shale collected at a depth of 121 m from Mosaic Company’s K2 mine, located approximately 15 km east of the town of Esterhazy, Saskatchewan within the Williston Basin. Two approaches were used to characterize the semipermeability of the samples. The main approach was through direct measurements of osmotic pressure which could then be used to calculate the osmotic efficiency. The value of osmotic efficiency ranges from zero (indicating no restriction to pore fluid flow) to one (indicating a perfect membrane that inhibits pore fluid flow). The second approach was through back analyses of the observed solute transport. The observed solutes were cations and anions transported in and out of the sample as a result of advection, diffusion as well as partitioning with the solid phase.