Measurements of the Relationship Between Microstructure, pH, and the Streaming and Zeta Potentials of Sandstones

A large number (1253) of high-quality streaming potential coefficient ([Formula: see text] measurements have been carried out on Berea, Boise, Fontainebleau, and Lochaline sandstones (the latter two including both detrital and authigenic overgrowth forms), as a function of pore fluid salinity ([Formula: see text] and rock microstructure. All samples were saturated with fully equilibrated aqueous solutions of NaCl (10[Formula: see text] and 4.5 mol/dm[Formula: see text] upon which accurate measurements of their electrical conductivity and pH were taken. These [Formula: see text] measurements represent about a fivefold increase in streaming potential data available in the literature, are consistent with the pre-existing 266 measurements, and have lower experimental uncertainties. The [Formula: see text] measurements follow a pH-sensitive power law behaviour with respect to [Formula: see text] at medium salinities ([Formula: see text] , units: V/Pa and mol/dm[Formula: see text] and show the effect of rock microstructure on the low salinity [Formula: see text] clearly, producing a smaller decrease in [Formula: see text] per decade reduction in [Formula: see text] for samples with (i) lower porosity, (ii) larger cementation exponents, (iii) smaller grain sizes (and hence pore and pore throat sizes), and (iv) larger surface conduction. The [Formula: see text] measurements include 313 made at [Formula: see text] mol/dm[Formula: see text] , which confirm the limiting high salinity [Formula: see text] behaviour noted by Vinogradov et al., which has been ascribed to the attainment of maximum charge density in the electrical double layer occurring when the Debye length approximates to the size of the hydrated metal ion. The zeta potential ([Formula: see text] ) was calculated from each [Formula: see text] measurement. It was found that [Formula: see text] is highly sensitive to pH but not sensitive to rock microstructure. It exhibits a pH-dependent logarithmic behaviour with respect to [Formula: see text] at low to medium salinities ([Formula: see text] , units: V and mol/dm[Formula: see text] and a limiting zeta potential (zeta potential offset) at high salinities of [Formula: see text] mV in the pH range 6–8, which is also pH dependent. The sensitivity of both [Formula: see text] and [Formula: see text] to pH and of [Formula: see text] to rock microstructure indicates that [Formula: see text] and [Formula: see text] measurements can only be interpreted together with accurate and equilibrated measurements of pore fluid conductivity and pH and supporting microstructural and surface conduction measurements for each sample. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s11242-017-0954-5) contains supplementary material, which is available to authorized users.