Deriving Microstructure and Fluid State within a Geothermal Reservoir, Reykjanes Peninsula (Iceland)

In this presentation, we refer to a mechanical framework and develop an effective medium model for estimating velocities in porous media. It makes it possible to derive the distribution of crack density beneath the Reykjanes Peninsula from accurate tomography data. Outside the active hydrothermal areas, crack density is shown to decrease with depth. This can be explained mainly by two reasons: the closure of cracks because of the increasing overburden and the secondary filling of cracks because of hydrothermal flows. However, locally beneath the southwestern part of the Kleifarvatn lake, crack density increases with depth. This is consistent with the presence of a deep reservoir with supercritical fluids under pressure, which would trigger off hydrofracturing processes. This study stresses that capturing the link between seismic data and the physical properties of crust is very difficult. The combination of mechanical concepts and effective medium theory contributes to improve our understanding of the phenomena occurring within the Icelandic crust.