Multi-physics Imaging of a High Enthalpy Geothermal Field: the Darajat Case

Magnetotelluric (MT) measurements are of particular value in volcanic-hosted, high-enthalpy geothermal exploration, since electrical resistivity depends dramatically on the mineral composition of the hydrothermally altered rock, which is in turn a function of temperature. We present an integrated study from the Darajat geothermal field in West Java – a vapor-dominated field associated with an eroded andesitic stratovolcano, currently producing at 271MW capacity. Besides MT data, also gravity and micro-earthquake event data from seismic monitoring were incorporated in the workflow. A cross-gradient approach was followed in the joint inversions to structurally link the different domains. An additional cross-gradient link to porosity from a geological model was further used to promote structural similarity. The 3D joint inversion modeling resulted in mutually consistent resistivity, density and velocity models, in agreement with the current understanding of the field. We expect that similar joint inversion workflows employed both early in and during the lifetime of the field would strengthen the building of a concept model for exploration, and later updates guiding development drilling programs.