The effect of double layer overlap on measured streaming currents for toluene flowing through sandstone cores

Streaming current measurements have been made on toluene flowing through sandstone rock cores, whose pore size was estimated by mercury porosimetry. The streaming current method, though requiring pico–amp measurements, was preferred over streaming potential as the latter is subject to surface conductivity errors. Having estimated pore area/length ratios an (apparent) electrokinetic potential was obtained which, as expected, increased numerically with pore size as a result of double layer overlap effects. After a measurement using a 1 mm internal diameter silica capillary, to represent effective infinite pore size, the data were fitted to a theoretical expression for double layer overlap in slit-like pores.