Few methods give direct insights on reservoir permeability. The induced micro‐seismicity from hydro‐fracturing experiments provides indirect information on reservoir permeability. Several existing S.B.R.C.‐based inversion methods have been proposed to estimate the diffusivity of reservoir before fracturing. In this paper, we extend this approach to estimate the heterogeneous diffusivity of an anisotropic 3D medium and its time evolution during the stimulation. This approach is applied on the HDR geothermal reservoir at Soultz‐Lès‐Forêts, France.