No abstract

[1] Electrokinetic effects of water flow during pumping tests have been shown to generate surface Streaming Potential (SP) anomalies of several tens of mV that are well correlated with the geometry of the water table. It follows that SP measurements can be used to estimate aquifer hydraulic properties. We have developed an inversion scheme for surface SP data generated by flow pumping and found that we are able to estimate the hydraulic conductivity and the depth and the thickness of the aquifer. We applied our inversion scheme to the data from Bogoslovsky and Ogilvy [1973] and found a hydraulic conductivity of 10 À5 m.s À1, an aquifer thickness of roughly 28 m and an electrokinetic coupling coefficient of À1 mV.m

[1] Stimulated fluid flow in geothermal reservoirs can produce surface Self-Potential (SP) anomalies of several mV. A commonly accepted interpretation involves the activation of electrokinetic processes. However we can not rule out electrochemical or electrothermal processes generated by the differences in chemical composition and temperature between the in-situ and injected fluids. We analyzed the relative contribution of electrokinetic, electrochemical and electrothermal potentials to the SP anomalies observed above the Soultz-sous-Forêts geothermal reservoir while injecting cold fresh water. We found that electrokinetic effects were dominant during the stimulation phase (injection rates larger than 30 kg s À1) and that electrochemical and electrothermal effects became significant at small injection rates (less than 10 kg s À1 ) and after shut-in.