Measurements of spontaneous potential in chalk with application to aquifer characterization in the southern UK

Abstract

We report the first measured values of the streaming potential coupling coefficient in chalk samples saturated with natural groundwater, and preliminary field measurements of the spontaneous potential (SP), at both ambient and pumped conditions, at a test site in the Berkshire Chalk aquifer in the southern UK. The ultimate aim of the work is to use measurements of SP, in conjunction with borehole data, to characterize groundwater flow and aquifer properties. Laboratory measurements yield a value of the streaming potential coupling coefficient of -60 ± 4 mV MPa −1 and a corresponding zeta potential of -13 ± 1 mV. A negative zeta potential contrasts with previous published open-system measurements on artificial calcite, and may reflect the presence of organic material in the natural chalk samples or HCO 3 and SO 4 ions in the groundwater. Field measurements at ambient conditions show temporal variations in SP consistent with flow processes within the aquifer, but no coherent spatial variations. Measurements during water abstraction demonstrate that voltages at the ground surface and in monitoring boreholes become more positive during pressure drawdown and more negative during pressure buildup, consistent with the negative values of streaming potential coupling coefficient and zeta potential observed in the laboratory. Moreover, the magnitude of the change in voltage is similar to that estimated using the laboratory value of the coupling coefficient. Our results suggest that measurements of SP may make a valuable contribution to characterizing groundwater flow in the UK Chalk aquifer. 2011-021r esearch-articleResearch Article45X10.1144/qjegh2011-021JacksonSpontaneous potential in chalk 2012 at

Tidal influence on self‐potential measurements

“…However, further analysis of the trend is beyond the scope of this paper (see Jackson et al . [] for further discussion of SP monitoring at the inland site).…”

“…Figure shows coastal SP, head, and conductivity in July and August 2013. The SP, here smoothed with a 2 h window, is anticorrelated with head, which is consistent with a negative EK coupling coefficient as measured in chalk [ Jackson et al ., ].…”

“…The head fluctuations observed in the coastal borehole are ~0.5 m (Figure a), and the maximum EK contribution is estimated using the coupling coefficient (−0.575 ± 0.080 mV/mH 2 O in Jackson et al . []) resulting in a ~290 μV EK contribution, around half the ~600 μV fluctuation observed in the borehole‐referenced SP data. This estimate is consistent with observations made by Jackson et al .…”

“…In coastal aquifers, tides alter the pressure and concentration gradients [ Kuan et al ., ] and are expected to give rise to SP signals with a tidal signature. An electrokinetic response to pumping has previously been detected in the UK Chalk aquifer [ Jackson et al ., ]. Furthermore, modeling suggests that SP may indicate the movement of a saline front some distance from a monitoring borehole [ Gulamali et al ., ; Bolève et al ., ; Jackson et al ., ; Jougnot et al ., ].…”

A study on the variation of zeta potential with mineral composition of rocks and types of electrolyte

“…Therefore, the experimental data can be analyzed and compared to a theoretical model developed for silica surfaces. The electrolyte concentration of 10 -3 M is used in this work because that value is comparable to the groundwater as stated by Jackson et al (2012). From streaming potential coefficients, the zeta potential is obtained for different systems of electrolyte and rock.…”