Detection and delineation of geothermal resources using 1D joint inversion of MT and TEM data with practical applications from Reykjanes geothermal field, SW-Iceland

Abstract

Geophysical exploration is a vital part of geothermal prospecting, particularly during the initial stages of development. When conducted alongside geological and geochemical work, a better understanding of the subsurface of the geothermal resource and its characteristics can be obtained. The resistivity methods in geophysical exploration are considered the most powerful geophysical tool in prospecting for high-temperature geothermal resources. This is because the subsurface distribution of resistivity can tell about the parameters that directly influence the geothermal system. A typical alteration distribution in a hightemperature geothermal field is expected but it is subject to the elevation of the area and its distance to the coast. Systems close to the coast do not tend to have as sharp a correlation between alteration and subsurface resistivity (e.g. Reykjanes, SWIceland) as systems further away from the coast; this is due to the high salinity in the geothermal fluids. 1D joint inversion of TEM and MT data was done to remove the static shift of the MT data from the Reykjanes geothermal field. Results from the 1D joint inversion revealed a homogeneous low resistivity at shallow depths as was discovered by past studies in the area. An iso–resistivity map at a depth of 10,000 m revealed two heat sources, one to the southwest and another to the northeast. They are associated with deep seated intersecting fractures and faults.