Correction to “On the origins of self-potential (SP) anomalies induced by water injections into geothermal reservoirs”

Authors

Errata

This article corrects:

  1. On the origins of self-potential (SP) anomalies induced by water injections into geothermal reservoirs Volume 31, Issue 19, Article first published online: 14 October 2004

[1] In the paper “On the origins of self-potential (SP) anomalies induced by water injections into geothermal reservoirs” by Mathieu Darnet, Alexis Maineult, and Guy Marquis (Geophysical Research Letters, 31, L19609, doi:10.1029/2004GL020922, 2004), which focused on the electrokinetic, electrothermal, and electrochemical contributions to self-potential (SP) anomalies recorded above geothermal reservoirs during injections at depth, the electrochemical contribution was overestimated. The electrical difference potential ΔVEC generated by the diffusion of a NaCl concentration gradient ΔC must be written [e.g., Maineult et al., 2005]:

equation image

where C is the salt concentration (mol L−1), R the molar gas constant (J mol−1 K−1), N Avogadro's number (mol−1), e the absolute unit charge (C), T the absolute temperature (K), uCl and uNa the ionic mobilities of Cl and Na+ (m2 s−1 V−1) respectively, and ϕ the porosity (we used a value of 0.1 % for granite).

[2] Therefore, the electrochemical SP anomaly induced by the Soultz-sous-Forêts stimulation experiment is roughly one thousand times smaller than previously estimated (Figure 1, to be compared with our original Figure 3b). The corrected relative contributions of electrokinetic, electrothermal, and electrochemical processes to the total SP anomaly are shown in Figure 2. We can observe that whatever the injection rate, the electrochemical contribution is almost negligible. Therefore, the Soultz SP anomaly is mainly related to the temperature contrast between the in-situ brine and the injected fresh water only at the earliest stage of injection, and is essentially related to water-flow afterwards.

Figure 1.

Electric potential anomaly induced by chemical diffusion (correction of Figure 3b).

Figure 2.

Relative contribution of electrokinetic (EK), electrochemical (EC), and electrothermal (ET) potentials as a function of (a) injection rate and (b) electrokinetic coupling coefficient CHS (correction of Figure 5).

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