Preliminary Magnetotelluric monitoring results at Rittershoffen

Abstract

Changes in fluid pathways in the subsurface of a geothermal project during stimulation and operation are typically inferred from micro-seismic monitoring. Micro-seismicity can provide information about where fractures shear and open, but neither on fracture connectivity nor on the fluid content. Electromagnetic methods are sensitive to conductivity contrasts and are typically employed as a supplementary tool to delineate reservoir boundaries (e.g. Geiermann et al., 2010). In this respect, in July, 2011, an injection test for a 3.6~km deep EGS at Paralana, South Australia, was continuously monitored by both micro-seismic and magnetotellurics (Peacock et al., 2012). First results from continuous magnetotelluric (MT) measurements suggesting transient variations in subsurface conductivity structure generated from the introduction of fluids at depth. Furthermore, phase tensor representation of the time dependent MT response suggests fluids migrated in a NE direction from the injection well. Results from this experiment support the extension of MT to a monitoring tool for not only EGS but other hydraulic stimulations.