Experimental Study of Electrokinetics in Porous Media

Abstract

In brine-saturated porous media the existence of a space-charge layer at the solid/liquid interface leads to a coupling between fluid and electric currents. This coupling is seen as a streaming potential (STP) across a porous plug when the fluid flows through it, or conversely, as electroosmosis (ELO) of the fluid when an electric field is applied. The magnitude of these electrokinetic effects depends on the thickness of the space-charge layer relative to the pore size, which in turn depends upon the salinity of the brine. From electrokinetic measurements one can obtain an effective hydraulic radius Reff and an effective zeta-potential at the slipplane ζeff. We have developed a high-sensitivity AC technique that can detect these small coupling effects, and have measured them in a suite of natural and artificial rock samples. We find that Reff and ζeff depend on salinity in ways which may be attributed to the roughness of the pore surfaces.

Frequency-Dependent Streaming Potentials

“…extrapolate the frequency-dependent streaming potential value to the dc limit. This is done for the purposes of determining the zeta or surface potentials (7,8). Low-frequency measurements are also used to determine the effective pore size and hydraulic permeability (9).…”

Streaming Potential Collection and Data Processing Techniques

“…Equation [9] is the ac Helmholtz-Smoluchowski equation. The frequency at which inertial terms start to dominate over viscous terms is often called the transition frequency and for a capillary model is given by…”

“…Therefore, low frequencies should be avoided in fitting the frequency-dependent coupling coefficient theory, Eq. [9], to the transient data. It is also useful to look at the streaming potential and pressure spectra individually to see at what frequency the signal-to-noise ratio starts to skew the coupling coefficient data.…”

“…They also reported discrepancies between their transient results and their dc results. In 1995, Pengra et al (9) developed an apparatus and data acquisition technique for measuring low-frequency streaming potentials. They used a phase lock loop amplifier and digital signal analyzer to process the signals.…”

Peristaltic pumping through porous medium in presence of electric double layer

“…enhanced. Electro-osmotic flows in porous media are also of significance and arise in both biological systems and industrial systems and have been shown to markedly influence transport rates [12]. The classical approach to simulating transport in porous media is the Darcy model which is valid for viscousdominated, low Reynolds number flows.…”