SUBSURFACE RESISTIVITY IMAGING OF “X” GEOTHERMAL FIELD IN WEST JAVA PROVINCE USING 2D LONG-OFFSET RESISTIVITY TOMOGRAPHY

• Main Author: Ridho Nurul Ihsan, Muhammad
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/68485
• Institution: Institut Teknologi Bandung

Exploration and development of geothermal fields require good subsurface characterization. This characterization is needed to identify the subsurface structure, alteration zone, and optimal geothermal field play system. One of the geophysical methods that can map the subsurface of the earth with the good lateral and vertical resolution is the geoelectric method or resistivity tomography. This method was then developed by adding a stretch for current injection and voltage measurement so that it became the Long-Offset Resistivity Tomography method which is expected to produce a subsurface model with a deeper penetration depth. Measurements were carried out with a stretch of ±2760 meters with 24 electrodes having a distance of ±120 meters. The measurement configuration used is the Wenner-Alpha and Wenner-Schlumberger configurations. This configuration is used because it has the best lateral resolution and depth range compared to other configurations. The data obtained from field measurements are then processed through an inversion process using the RES2DINV software. The inversion process aims to determine the actual resistivity value based on the apparent resistivity obtained. Based on the 2D inversion modeling results that have been obtained, for the Wenner-Alpha configuration, the penetration depth obtained is about 470 meters, and the model has a fairly good lateral cross-section. As for the WennerSchlumberger configuration, the penetration depth obtained is about 570 meters, but the lateral section has a contour that tends to be evenly distributed at a depth of ±300 meters. The results of the interpretation of the two configurations indicate that there are hydrothermal alteration zones and cap rock, which have low resistivity, igneous magma intrusion which has high resistivity at a fairly shallow depth, and fault zones which are zone with significant displacement of low resistivity rock to high resistivity rock in that geothermal field. The modeling results already correspond with the geological conditions and the presence of geothermal wells in the field. Thus, this method can be used as a geophysical method for the exploration and development of geothermal fields.