The 3D Seismic Velocity Model and Hypocenter Relocation Results of Patuha Geothermal Field

Abstract

Geothermal reservoir monitoring using micro seismic survey has been implemented recently in several geothermal fields in Indonesia. Micro seismic survey has been conducted from January 1st until later April 1st 2018 in Patuha Geothermal Field using 9 seismometers that are placed near well locations and fault distribution. 654 micro seismic events (ts-tp less than 3 second) and 640 regional (ts-tp more than 5 second) was identified in this period, but only 491 micro seismic events have clear onset of P and S waves arrival time. Initial location is determined using NonLinLoc algorithm and will be used as input for Velest program to obtain 1D velocity model. Double difference seismic tomography is applied to jointly determine relocation hypocenter and 3D seismic velocity model (Vp, Vs, & Vp/Vs). The aim 3D seismic velocity model determination is to infer reservoir condition, because Vp/Vs ratio is sensitive with sub-surface variations in rock and fluid properties. The results show hypocenter location (depth 0-500 masl) is correlated with existing production zone with high permeability and main fault direction. It is expected to support well targeting for the next development stage of Patuha geothermal field.