| Abstract |
Pertamina has conducted geothermal exploration in Sibayak, showing that the depths to the top of most geothermal reservoir area about 1000-2000m. Previous geophysical exploration work by Pertamina emphasized the use of DCresistivity (Schlumberger) methods. However, these techniques can typically only penetrate to a depth of less than 1000m and are too shallow to map the geothermal system in this area. The area covered by very low resistivity of 10Wm gave a false geothermal prospect at the southwestern part of the area. This anomaly indicates the area of outflow of geothermal fluids from the nearby Mt. Sibayak. By using the magnetotelluric (MT) method to investigate to a depth of greater than 1000m (e.g. f=0.33Hz for resistivity > 3Wm), it may help the explorationist get a better picture of the deep resistivity structure. The pattern of the resistivity contours may depict the flow of geothermal fluids; the tongue-like structures show the area where the outflow of geothermal fluids is. Pertamina has been tapping the hot fluids by drilling into the selected prospect area. Eight wells have penetrated a region of high temperatures (250-275?C). The highest temperatures were found in SBY-5, in the area near the Mt. Sibayak. The sub-surface temperature then decreased southward to 200?C. An important part of the interpretation process is to integrate the results with other available data. This is necessary because low resistivity anomalies are not always suitable as geothermal targets. For this reason, integration with other geologic and drilling data can help to eliminate undesirable low-resistivity targets from consideration. |