[HSC05-P01] Changes in self-potential observed around gas injection wells and their interpretations based upon “geobattery” numerical simulations
Keywords:self-potential monitoring, geobattery, CO2 injection
We will report the results of SP measurements during gas (CO2 or air) injections at test sites in Japan and their interpretations based upon numerical simulations carried out using the extended SP postprocessor, which incorporates the above “geobattery” mechanism in addition to electrokinetic coupling. When air was injected into a 100-meter well in the Sumikawa geothermal field, a clear simultaneous increase in SP centered on the wellhead was observed. A small but unmistakable SP increase also took place near the wellhead when CO2 was injected slowly, which we believe was caused by local pH reduction at depth resulting from dissolution of the injected CO2 in the subsurface liquid water.
SP changes were also observed around a deep well at the Yubari test site in Japan (Tosha et al., 2008), where CO2 was injected into a coal bed and the CO2 content of the fluid produced from a nearby well was monitored. SP increased substantially around the injection wellhead during about six months of CO2 injection, but no significant SP changes attributable to the injection were observed near the production wellhead. This is consistent with the observation that CO2 did not break through into the production well during the experiment.