Rachmat Sule

3-D seismic velocity and attenuation structures in the geothermal field

We conducted delay time tomography to determine 3-D seismic velocity structures (Vp, Vs, and Vp/Vs ratio) using micro-seismic events in the geothermal field. The P-and S-wave arrival times of these micro-seismic events have been used as input for the tomographic inversion. Our preliminary seismic velocity results show that the subsurface condition of geothermal field can be fairly delineated the characteristic of reservoir. We then extended our understanding of the subsurface physical properties through determining of attenuation structures (Qp, Qs, and Qs/Qp ratio) using micro-seismic waveform. We combined seismic velocities and attenuation structures to get much better interpretation of the reservoir characteristic. Our preliminary attanuation structures results show reservoir characterization can be more clearly by using the 3-D attenuation model of Qp, Qs, and Qs/Qp ratio combined with 3-D seismic velocity model of Vp, Vs, and Vp/Vs ratio.

Crosshole Tomographic Imaging of Velocity and Attenuation Structure

Crosshole tomographic can be used for geotechnical purposes. We conducted data in the ITB campus. We used two boreholes with a distance of 19.8 m. The first one have a depth of 39 m and the second one have a depth of 19 m. Seismic wave sources were generated by impulse generator and sparker and then they were recorded by borehole hydrophone with 12 channels. Recorded first arrival time is reconstructed by using pseudo bending ray tracing method. For the tomographic inversion procedure, we started from 1-D model as initial velocity model and set up block size of 1 x 1 km2 for model parameterization. LSQR method is applied to solve the tomographic inversion solution. First, we determine velocity structure among two boreholes and then we used waveform data to invert for attenuation structure (1/Q). The input for attenuation tomographic inversion is t*. This parameter is obtained using spectral-fitting curve method. As results, velocity structure show three layers of soil including unconsolidated layer (down to 8 meters), consolidated layer (from 8 m down to 20 m), and bedrock (>20 m). High attenuation layers are observed at depths of 14 m to 24 m that may relate to water saturated condition.

Development of Hard- and Software of Microseismic for Geothermal Exploration and Monitoring: First Results

The Ministry of Research and Technology (RISTEK) of Republic Indonesia launched a so called “Riset Insentif RISTEK” since 2005. This allows Indonesian researchers to be active in research activities, which its funding is higher than other research funding available in Indonesia for small group of researchers. We received this kind of funding for the year of 2010 with its theme is development of hard- and software of microseismic for geothermal exploration and monitoring. This paper describes the first achievements after the funding is granted to us 8 (eight) months ago. This research theme is grouped into 3 main activities, namely development of borehole seismometer by using MEMS, development of precise microseismic relocation technique, and development of first arrival travel time tomography software. The overall current achievements are beyond the target of first year, so that the funding will be extended for the 2nd year.