Frequency-dependent streaming potentials: a review

The interpretation of seismoelectric observations involves the dynamic electrokinetic coupling, which is related to the streaming potential coefficient. We describe the different models of the frequency-dependent streaming potential, mainly the Packard's and the Pride's model. We compare the transition frequency separating low-frequency viscous flow and high-frequency inertial flow, for dynamic permeability and dynamic streaming potential. We show that the transition frequency, on a various collection of samples for which both formation factor and permeability are measured, is predicted to depend on the permeability as inversely proportional to the permeability. We review the experimental setups built to be able to perform dynamic measurements. And we present some measurements and calculations of the dynamic streaming potential

Electrokinetic techniques for the determination of hydraulic conductivity

International audienceIn a porous medium the fluid flux and the electric current density are coupled, so that the streaming potentials are generated by fluids moving through porous media and fractures. These electrokinetic phenomena are induced by the relative motion between the fluid and the rock because of the presence of ions within water. Both steady-state and transient fluid flow can induce electrokinetics phenomena. It has been proposed to use this electrokinetic coupling to detect preferential flow paths, to detect faults and contrast in permeabilities within the crust, and to deduce hydraulic conductivity. This chapter proposes a comprehensive review of the electrokinetic coupling in rocks and sediments and a comprehensive review of the different approaches to deduce hydraulic properties in various contexts

Reply to comment by A. Revil on "Seismo-electrics, electro-seismics, and seismo-magnetics for earth sciences" by L.Jouniaux and F.Zyserman

International audienceThe relation between the volumetric charge density Q_V expressed as a function of permeability has not been validated using inde-pendent measurements of permeability and charge density.This equation has been used to calculate Q_V , using permeability values, to deduce that Q_V is inversely related to the permeability. Therefore this approach is considered not appropriate and should not be used. We advice thereader to use the electric current density as a function of the pressure, rather than as a function of the velocity and Q_V

Changes In The Permeability, Streaming Potential And Resistivity Of A Claystone From The Nankai Prism Under Stress.

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Lattice Boltzmann modelling of streaming potentials: variations with salinity in monophasic conditions

International audienceS U M M A R Y The streaming potential phenomenon is produced by the flow of an electrolyte in a porous medium and is used for geophysical prospecting. It is quantified through an electrokinetic (EK) coefficient. The dependence of the EK coefficient on the conductivity of the electrolyte is described by the Helmholtz–Smoluchowski (HS) equation. This equation provides successful forecasts of the EK coefficient in the standard range of concentration. However, experimental measurements show deviations to this equation at extreme low and extreme high salinities. The aim of this study is to model the EK coefficient using Lattice Boltzmann simulations in a 2-D capillary channel, with a view to understanding these deviations. The effect of the constitutive parameters of the HS equation such as the permittivity and the viscosity is discussed. The validity of the HS equation using strong ζ potentials is assessed. Finally, a model of bulk fluid conductivity is derived. This model allows to take into account the change of local ionic distribution in the vicinity of the mineral. It appears to have a significant impact on the derivation of ζ potentials at low salinities and in the presence of polyvalent counterions

Streaming potential dependence on water-content in Fontainebleau sand

The final version is available on www.blackwell-synergy.comInternational audienceThe electrokinetic potential results from the coupling between the water flow and the electrical current because of the presence of ions within water. The electrokinetic coupling is well described in fluid-saturated media, however its behaviour under unsaturated flow conditions is still discussed. We propose here an experimental approach to investigate streaming potential variations in sand at unsaturated conditions. We present for the first time continuous records of the electrokinetic coefficient as a function of water content. Two drainage experiments have been performed within a column filled with a clean sand. Streaming potential measurements are combined with water pressure and water content measurements every 10 centimeters along the column. In order to model hydrodymanics during the experiments, we solve Richards equation coupled with an inverse problem to estimate the hydraulic parameters of the constitutive relations between hydraulic conductivity, water pressure and water content. The electrokinetic coefficient $C$ shows a more complex behaviour for unsaturated conditions than it was previously reported and cannot be fitted by the existing models. The electrokinetic coefficient increases first when water saturation decreases from 100\% to about 65\% - 80\%, and then decreases as the water saturation decreases, whereas all previous works described a monotone decrease of the normalized electrokinetic coupling as water saturation decreases. We delimited two water saturation domains, and deduced two different empirical laws describing the evolution of the electrokinetic coupling for unsaturated conditions. Moreover we introduce the concept of the electrokinetic residual saturation $S_w^{r,ek}$, which allows us to propose a new model derived from the approach of the relative permeability used in hydrodynamics

Reply to comment by A. Revil and N. Linde on 'Streaming potential dependence on water-content in Fontainebleau sand'

International audienceRevil and Linde recently commented our paper concerning streaming potential (SP) measurements in unsaturated sand during drainage experiments. This comment suggests that the approach used to infer SP coefficients was inappropriate for unsaturated conditions, and therefore yielded wrong conclusions and 'unphysical' results regarding the behaviour of the relative SP coefficient. This reply argues that even if in Allègre et al. we neglected some secondary electrokinetic sources, the resulting conclusions are still representative of the behaviour of the true SP coefficient, and that the remarks of Revil & Linde arose from a misunderstanding of the drainage experiment conditions. We also find support for our results from a comparison between our observations and previous experimental studies

Borehole seismoelectric logging using a shear-wave source: Possible application to CO2 disposal?

International audienceThe behaviour of CO2 deposition sites-and their surroundings-during and after carbon dioxide injection has been matter of study for several years, and several geophysical prospection techniques like surface and crosshole seismics, geoelectrics, controlled source electromagnetics among others, have been applied to characterize the behaviour of the gas in the reservoirs. Until now, Seismolectromagnetic wave conversions occuring in poroelastic media via electrokinetic coupling have not been tested for this purpose. In this work, by means of numerical experiments using Pride's equations-extended to deal with partial saturations-we show that the seismoelectric and seismomagnetic interface responses (IR) generated at boundaries of a layer containing carbon dioxide are sensitive to its CO2 content. Further, modeling shear wave sources in surface to borehole seismoelectric layouts and employing two different models for the saturation dependence of the electrokinetic coefficient, we observe that the IR are sensitive to CO2 saturations ranging between 10% and 90%, and that the CO2 saturation at which the IR maxima are reached depends on the aforementioned models. Moreover, the IR are still sensitive to different CO2 saturations for a sealed CO2 reservoir covered by a clay layer. These results, which should be complemented by the analysis of the IR absolute amplitude, could lead, once confirmed on the field, to a new monitoring tool complementing existing ones