[en] Partial CRS-Stack method is proved as an alternative method that can produce excellent subsurface image, especially if this method is applied to a seismic data that is acquired from complex subsurface structure areas. The application of this method will give a new hope in determining subsurface structures in a better way, especially if it is implemented to seismic data obtained from Indonesian region, which is dominated by complex geological structures. The Partial CRS-stack method is tested by using a seismic dataset, which is acquired from eastern part of Indonesia. Here, the continuity of reflectors cannot be seen clearly. To prove the ability of Partial CRS-stack method, its result will be compared with the result obtained from the conventional sequences. The stacked section resulted from Partial CRS-stack is much better than the result of conventional one. This could be understood, since the Partial CRS-stack method uses the information of reflectors along fresnel zone, instead conventional method that only uses information in a CDP. During its processing sequence, CRS kinematic wavefield attributes, e.g. emergence angle (α), radius curvature of normal ray (R_N) and radius curvature of normal incident point ray (R_NIP) must be determined previously, which indicates the location and behaviour of reflectors. As a conclusion, the Partial CRS-stack method is proved as a good alternative method to give better seismic sections. Because of this, the interpretation of unclear events that are seen in the conventional stack section can be avoided. (paper)

[en] In geothermal exploration, magnetotelluric method (MT) has the capability to resolve conductive body which then can be interpreted as cap rock. A reliable representation of the Earth’s resistivity dimensionality can be achieved by incorporating the direction of geoelectrical strike and geological condition in the geothermal area. In this study, the magnetotelluric method was applied in Tangkuban Parahu volcanic area to reveal the subsurface structure of the area. Due to the uncertainty of MT modelling result, dimensionality analysis (polar diagram) is performed to find out MT data characteristic prior to MT inversion modelling. After that, lineament is mapped based on elevation map to estimate geological strike. Both methods are validated by geological condition in Tangkuban Parahu. The result of polar diagram analysis shows that the direction of geoelectrical strike is dominated NE-SW in mostly frequency and the result of lineament shows similar direction with polar diagram analysis as plotted in rose diagram yields about N45°E. (paper)

[en] The development of a user-friendly Common Reflection Surface (CRS) Stack software that has been built by implementing Graphical User Interface (GUI) is described in this paper. The original CRS-Stack software developed by WIT Consortium is compiled in the unix/linux environment, which is not a user-friendly software, so that a user must write the commands and parameters manually in a script file. Due to this limitation, the CRS-Stack become a non popular method, although applying this method is actually a promising way in order to obtain better seismic sections, which have better reflector continuity and S/N ratio. After obtaining successful results that have been tested by using several seismic data belong to oil companies in Indonesia, it comes to an idea to develop a user-friendly software in our own laboratory. Graphical User Interface (GUI) is a type of user interface that allows people to interact with computer programs in a better way. Rather than typing commands and module parameters, GUI allows the users to use computer programs in much simple and easy. Thus, GUI can transform the text-based interface into graphical icons and visual indicators. The use of complicated seismic unix shell script can be avoided. The Java Swing GUI library is used to develop this CRS-Stack GUI. Every shell script that represents each seismic process is invoked from Java environment. Besides developing interactive GUI to perform CRS-Stack processing, this CRS-Stack GUI is design to help geophysicists to manage a project with complex seismic processing procedures. The CRS-Stack GUI software is composed by input directory, operators, and output directory, which are defined as a seismic data processing workflow. The CRS-Stack processing workflow involves four steps; i.e. automatic CMP stack, initial CRS-Stack, optimized CRS-Stack, and CRS-Stack Supergather. Those operations are visualized in an informative flowchart with self explanatory system to guide the user inputting the parameter values for each operation. The knowledge of CRS-Stack processing procedure is still preserved in the software, which is easy and efficient to be learned. The software will still be developed in the future. Any new innovative seismic processing workflow will also be added into this GUI software. (paper)

[en] We observed 754 microearthquake data by at least 15 stations for six months as a tool to monitor and characterize the subsurface condition in two-phase geothermal field in Southern Bandung. The data were reduced to 417 events having azimuthal gap less than 180°. We determine the initial earthquake locations in this study by using Geiger method and we update the hypocenter locations by performing simultaneous inversion for hypocenters and 1D velocity structure followed by 3D tomographic inversion. We obtained the velocity structure by utilizing TomoDD to perform 3D tomographic inversion. There are four clusters of seismicity observed in this study which we suspected related to the injection, production, and tectonic activity of the study area. The southern cluster is consistent with the location of injection wells and spread from 1 km depth to 8 km depth, indicating that MEQ events were triggered by injection activity. The production area is characterized by a denser population of events and the events were distributed closely ranging from 1 to 3 km depth. We suspect that the third cluster is caused by development activity of steam dominated geothermal field omit in the east of our main field. The fourth cluster is located in the southernmost of our area and suspected caused by tectonic activity. Low Vp/Vs values near to the surface are observed in the north direction and coincide with the location of the first cluster. The location of anomaly is highly corresponded with the production area and the low value of Vp/Vs anomaly is interpreted as the steam zone. (paper)

[en] 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

[en] Enhanced Geothermal system assessment conducted to have a better understanding of characteristics of fracture caused by a fluid injection in the geothermal reservoir. Fluid injection may cause microseismic occur. These events allow us to map and characterize fractures in the geothermal system. Fractures play important role at the geothermal system due to its ability to increase permeability for fluid movement within the reservoir. In this study, we combined tomographic inversion method and fuzzy clustering to identify fracture characteristics at the EIF Geothermal Field. Tomography helped in delineating fluid-filled fractures with high permeability area which shown by lower velocity Vs anomaly than Vp and higher Vp/Vs ratio. Fuzzy clustering allowed us to map microseismic movement and estimate suitable locations for the future well injections or productions. (paper)