Geologically consistent multiphysics imaging of the Darajat geothermal steam field

Abstract

Darajat is a vapor-dominated, producing geothermal field in West Java, Indonesia. Located along a range of Quaternary volcanic centres, it is associated with an eroded andesitic stratovolcano, and its reservoir is predominantly comprised of thick lava flows and intrusions in a stratovolcano central facies (Rejeki et al., 2010). First production from the field was started in 1994 with the installation of a 55 MW plant, and capacity was added in 2000 and 2007 to bring the total to 271 MW. Several ground geophysics data sets have been acquired during successive surveys – including gravity and magnetotelluric (MT) surveys, and continuing micro-earthquake (MEQ) monitoring (Soyer et al., 2017). While each survey was independently modelled and interpreted, a quantitatively integrated 3D inversion modelling study had not been undertaken. We present a joint 3D inversion workflow, incorporating the production field model as a structural reference in order to derive mutually consistent subsurface resistivity, density and velocity distributions, as well as relocated MEQ events.