3D SEISMIC VELOCITY OF RANTAU DEDAP GEOTHERMAL FIELD USING DOUBLE-DIFFERENCE TOMOGRAPHY

• Main Author: HIJRIANI, ARIFA
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/21229
• Institution: Institut Teknologi Bandung

Geothermal surface exploration entails a multi-geoscientific process, which is aimed to define the geometry and characteristics of the geothermal reservoir prior to drilling. Lately, microseismic event monitoring is becoming a standard procedure in inferring the structure of the potential geothermal reservoir. However, a good coverage of seismic station and abundant seismic events must be fulfilled in order to map the subsurface structure. Taking advantage of the well-designed seismic station deployed at the Rantau Dedap geothermal field prior its first drilling, a study of microearthquake tomography for 3D reservoir structure delineation is performed in this field. A seismic network of 26 stations was set up for more than eight months from August 2011 within 20 km radius from the center of the expected-reservoir. There are 637 local events were detected and located, which is very high number of seismicity for a region that is not yet under geothermal development. The purpose of this study is to construct 3D seismic velocity structure using double-difference tomography and to infer fluid properties, i.e. steam and brine, from the ratio of the P- and S-wave velocity. An advance waveform cross-correlation technique is applied to improve the quality of the arrival time picking. Double-difference tomography is used due to its ability to reduce uncertainties of the model associated with picking and velocity structure. Low velocity anomaly is observed in velocity structure Vp and Vs perturbation, and also low ratio of Vp/Vs that correlate to steam zone. Below the steam zone, there is a high velocity anomaly in structure velocity Vp and Vs and high ratio of Vp/Vs that correlate to non-permeable zone.