Self-potential and induced polarization: Geophysical tools to map flowpaths and monitor

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1 Self-potential and induced polarization: Geophysical tools to map flowpaths and monitor contaminant plumes André Revil (1) and Susan S. Hubbard (2) (1) Colorado School of Mines (2) L. Berkeley National Laboratory

2 Rocks have a complex texture and chemistry, Geophysics is sensitive to both New science: Mechanistic understanding of the geophysical signals

3 Medical Science (electro-encephalography) Self-potential Network of non-polarizing electrodes connected to a voltmeter Geophysics (self-potential)

4 Generalized constitutive equations Take-home message: any king of non-equilibrum disturbance generate an EM signal Chemical potential

5 Self-potential associated with a salt plume Multichannel system (256 ch., 7 khz) Ag/AgCl smart electrodes

6 Time-lapse self-potential signals Snap shots of the electrical potential distribution over time

7 Modeling Buoyancy driven saline plume Darcy equation Generalized Fick law Continuity equation for the mass of the fluid Continuity equation for the mass of the solute State equations Mass density Viscosity Hydrodynamic dispersion tensor (Fickian model) Fickian model (change with scale?)

8 Finite element simulation of the forward problem (comsol multiphysics) Self-potential field Salinity Constitutive equation Source term Continuity equation

9 Self-potential time lapse tomography (deterministic) Data misfit Regularization over time Martinez-Pagan, Revil et al., in press in Geophysics

10 Stochastic inversion (AMA) of the permeability and dispersivities (15,000 realizations) (the vertical bar represents the measured horizontal permeability)

11 Spectral induced polarization (complex conductivity) Can be used as a geophysical tomographic technique (see Williams et al. Work at Rifle)

12 Excess Surface (in Siemens) Similar values for clays and silica

13 The spectral polarization of a granular material Complex conductivity Magnitude Phase

14 Polarization of a single grain

15 Polarization of a single grain Upscaling using DEM theory for instance

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17 Application to the data of Tong et al. (2006) Sanstones

18 Presence of a second fluid phase (immiscible, non wetting)

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20 Comparison with the prediction from the model Experimental data Model prediction

21 Influence of a change in the composition of the aqueous phase

22 Change in the composition of the aqueous phase over time

23 Change in the phase No change in resistivity Modeling with PHREEQC

24 Complexation model (with electrostatics) Induced polarization is truly a geophysical spectroscopic tool sensitive to chemistry

25 The effects of biofilms Pictures: courtesy of Yuri Gorbi Pili = 100 S/m (electron tranfer possibly by tunneling effect between the hemes packed in the pili)

26 Electronic contribution to EC through biofilms At the interface between sharp redox gradient

27 Self-potential anomaly associated with an oil spill

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29 From Atekwana et al. (2004) Responsible for a conductivity increase at the water table

30 In few weeks: Application to Oak Ridge Cooperation with David Watson Imaging the preferential flow-paths Model the transport of contaminants (effect of recharge )

31 Conclusions Get a catalog of the effect of contaminants/bacteria upon induced polarization Develop the inverse problem (speciation using SIP) Developing joint inversion tools for map permeability change / chemistry amendments Use of chemical tracers to follow them using geophysical techniques Use of electromigration / electroosmosis to bring specific chemical components (redox active) to specific targets non-intrusively Can we act non-intrusivey on bacteria with electrical field? Doing all the couplings in TOUGHREACT (Nic Spycher & Magnus Skold) We thank the DOE for Financial support Scientific papers can be downloaded at