Realization of enhanced geothermal systems (EGS) prescribes the need for
novel technology to monitor the created reservoir. Conventionally,
micro-earthquake arrays are used to monitor seismic events associated
with the postulated pressure front of the injected fluid. We propose the
additional use of the magnetotelluric (MT) technique which is directly
sensitive to elevated electrical conductivity
... [Show full abstract] allowing mapping the
conductive injected fluid in the subsurface. MT is a passive
electromagnetic method that characterizes geoelectric structure by
measuring the Earth's response to natural magnetic fields. Measuring the
MT response before, during and after fluids are injected into the
reservoir provides a tool to delineate reservoir boundaries at depth.
This is important as electrical conductivity can change by a few orders
of magnitude making a conductive fluid in resistive host rock a viable
MT target at depth. Three-dimensional MT forward modelling illustrates
the dependence of reservoir size and depth as well as the dampening
effect of a conductive overburden, such as a sedimentary basin. Forward
modelling suggests changes in the MT response of a proposed reservoir at
3.5km depth will be on the order of a few percent, advising an accurate
and precise prior data set is collected. A test case from Paralana,
South Australia will be presented illustrating results of MT responses
before and after fluids are injected as well as time-lapse transfer
function variability during the injection.