oa Monitoring Fluid Reservoir in an Enhanced Geothermal System Using Magnetotellurics

Geothermal exploration plays an increasing role worldwide and in Australia in order to meet carbon emission targets and to provide green and renewable energy alternatives to coal. In Australia, EGS systems are widely used to extract geothermal energy from the subsurface. Initially, the stimulation process involves pumping large amount of fluids into the subsurface at depths of reasonable temperature to ensure a maximum energy output. The high-pressured fluids penetrate from the borehole into the surrounding sedimentary rocks and increase the permeability of the system until the stimulation is finished. Subsequently, a second borehole is put in place to extract the heated fluids.

Magnetotelluric (MT) measurements will be undertaken at the Paralana drill site in 2010, where the stimulation is conducted by Petratherm. The measurements take place in three stages in order to image the extent of the fluid body at depths of 3.5-4 km. To improve the outcome of the deployments, about 50 stations measure the MT response between periods of 100-0.01s prior to the stimulation to provide an initial model of the area. This is then used to compare and constrain the responses collected during and after the stimulation of the fluids into the reservoir. The aim of the survey is to delineate the extent of the water-filled reservoir.

During the stimulation, time-series of magnetic and electric field changes will also be recorded for comparison with events from the Micro Earthquake Array. These studies will look into the seismoelectric effect associated with the seismic events during the stimulation.