Hydraulic and chemical pulse-tests in shut-in chamber imbedded in an argillaceous formation :Numerical and Experimental approaches

International audienceHydraulic and chemical pulse tests were performed in four shut-in chambers to obtain hydraulic and chemical parameters of the Callovo-Oxfordian shale. The osmotic tests, i.e., chemical pulses, were carried out by exchange of the formation water for a different solution either more or less concentrated. Two sets of two osmotic tests were done in March and October 2006. These osmotic tests are superimposed on a purely hydraulic response because of the drilling of the well causing a pressure drop. The pressure records (hydraulic and osmotic responses) were interpreted using a 2-D model to obtain the hydraulic and chemical parameters. The osmotic efficiency inferred for the Callovo-Oxfordian shale is on the order of 0.012 for a concentration of 0.43 mol L-1 and 0.12 for a concentration of 0.086 mol L-1. These results suggest that the Callovo-Oxfordian shale behaves as a weakly semipermeable membrane and only 0.1-0.15 MPa of the 0.2-0.5 MPa can be explained by these osmotic efficiency values

Layer charge and electrophoretic mobility of smectites

International audienceThe aim of this study is to determine the effect of the layer charge of smectites on their electrophoretic mobility (EM), using electrophoresis measurements. In order to cover the charge domain from 0 to 2 charges per unit structural cell, two clay series were used: thermally treated Cu-montmorillonite (0-0.7) and synthetic saponites (0.7-2). All the studied samples are negatively charged in a pH range from 2 to 12. Neither layer charge nor ionic strength influences the EM of smectites at neutral to alkaline pH. At acidic pH, the EM of smectites ranges from −3 to −0.4 10−8 m2 s−1 V−1 when the layer charge ranges from 0.8 to 2. High charge and low charge smectites, which are not expandable, tend to aggregate in aqueous suspension, and the measured EM corresponds then to the amphoteric sites of the edge faces of the layer stacks. These sites are negatively charged at pH values above 3