Geothermal Well Casings Used as Electrodes in a Resistivity Study at Reykjanes Reservoir in Iceland

Direct current resistivity measurements are performed at Reykjanes geothermal reservoir in southwest Iceland to investigate the possibility of using steel casings as electrodes to transfer electric current deep into the ground during cross-well resistivity surveys. Various wells are studied including well IDDP-2 that has been deepened by the Iceland Deep Drilling Project (IDDP) to a depth of 4.7 km. Electrical resistance measured between two well casings is compared to the resistance between a well casing and an electrode on the surface. The results indicate that the current travels deeper into the ground and through water channels from one casing to another when using the well casings as electrodes instead of traveling closer to the surface as when surface electrodes are used. Steel casings provide good conduction into the ground in resistivity studies and cross-well resistivity measurements can be used to gain information about the subsurface such as the fracture connectivity between wells.