Casing-to-casing resistance study performed at Reykjanes geothermal field in Iceland to estimate fracture connectivity.

• Steel well casings used as electrodes in a resistance study. • Low resistance measured at Reykjanes due to high salinity of geothermal fluid. • Electric current travels between casings through brine-filled fractures. • Casings transfer electric current deeper into the ground than surface electrodes. Successful drilling of geothermal wells into fractured hot rock through which geothermal fluid flows is critical to ensure efficient operation of geothermal power plants. This study focuses on investigating a casing-to-casing resistance method for estimating fracture connectivity between wells at Reykjanes geothermal reservoir in Iceland to better understand the fluid-flow in the reservoir. Conductive well casings were successfully used as electrodes to transfer the electric current deeper into the fractured reservoir in an electrical resistance survey. The low resistance measured between wells implies that the wells are connected to the main production zone at Reykjanes and that the current is travelling through fractures filled with conductive geothermal brine from one well casing to another rather than going through a less conductive rock. The measured resistance is compared to an analytical study showing the promising potential the casing-to-casing resistance method has for gaining valuable information about the fracture connectivity in geothermal reservoirs. [ABSTRACT FROM AUTHOR]