Nodal Ambient Noise Tomography (NANT)
A fluid-sensitive and cost-effective method to track geo-fluids at depth
Background
The geothermal industry has been heavily relying on exploration methods imported from the hydrocarbon sector. This includes geophysical tools that are not tailored to identify a geothermal target. The most established of such methods are the costly seismic reflection methods that capture lithostratigraphic horizons, dip-slip faults and hydrocarbon traps. It however does not provide a direct indication of the presence of fluids, an essential ingredient to the success of hydrothermal projects, and performs poorly in regions of high lateral geological contrasts and seismic scattering and at depths beyond the top of the crystalline basement. So far seismic reflection surveys have not guaranteed the success of geothermal projects despite costly investments. Invert changes the way geothermal exploration (and fluid-related prospection in general) is conceived by using geophysical methods directly sensitive to fluid-bearing structures at a low financial and logistical cost and a fast acquisition-to-delivery time. In particular, NANT is an emerging technology that is revolutionising the upper crust prospection market.
Advantages of NANT
NANT is an Innovative, non-invasive and cost-effective passive seismic method using hundreds of wireless geophones to investigate in ideal conditions up to 5 km depth. Some of its advantages are:
The source of signal is the seismic ambient noise. No vibrotrucks or any other invasive man-made source of energy;
Ambient noise tomography is a well-established method. We improve its current resolution by using dense networks of hundreds of geophones. This allows us reaching a high degree of lateral resolution on a local scale;
NANT provides images of the subsurface that can be interpreted in terms of presence of fluids. The method is tailored to identify geothermal reservoirs;
NANT acquisition campaigns often go unnoticed by locals, helping with a high social acceptance.
