Karakterisasi Reservoir Panas Bumi Berdasarkan Analisis Lokasi Hiposenter dan Struktur Kecepatan 3D dari Implementasi Seismik Tomografi (Studi Kasus: Lapangan Panas Bumi Wayang Windu)
Fluid injection process for hydraulic fracturing has been conducted for two months from May 19-July 20 2005 and had been observed using Micro-earthquake (MEQ) method. MEQ is a powerful method to assess the effectiveness of hydraulic fracturing treatments and to image the subsurface by delineating fluid in reservoir for geothermal reservoir characterization.
357 events of MEQ waveform data had been used for this research from at least 17 installed stations. Initial MEQ locations were determined using Geiger's method with Adaptive Damping (GAD) and two-layer 1D velocity models as input. Next processing data was using VELESTs software for updating travel time event and 1D velocity model. VELESTs output was used for input of travel time tomography application using SIMULPS12s software. Total data used including 1.173 P-wave and 1.068 S-wave travel time. Tomographic method was applied to generate image of 3-D velocity structure and relocate hypocenter simultaneously.
Our results:hypocenter distribution formed some clustering, scattered at geological structures closed to MBD-2, indicated as high permeability area;  very low Vp anomaly, low Vs anomaly, and low Vp/Vs ratio at elevation of 500 m above mean sea level (asl) was interpreted as related to the steam zone in the reservoir;  an underlying zone below the lower steam reservoir zone with low Vp, very low Vs and high Vp/Vs may be related to pore fluid pressure zone or brine fluid zone;
Based on the results, we can conclude that tomographic method can give good information of hypocenter relocation and 3D velocity model for geothermal reservoir characterization. Steam zone at elevation of 500 m above mean sea level (asl) and brine zone below, can be predicted from travel time tomography