Abstract

The geothermal field of Kamojang, the first developed in Indonesia is located about 60 km South of Bandung (West Java).

The surface geology of Kamojang and the first sub-surface studies have been described by GENZL and VSI. PERTAMINA has recently carried out a new interpretation of the geological setting which is presented herein.

Kamojang is located in the centre of a volcanic chain which has progressively grown from WSW to ENE. In the Kamojang concession, prominent tectonic features are described as follows: firstly, the circular collapse of Pangkalan, 2 km in diameter occupies the central part of the Kamojang field; secondly, NE faults of tensional and lateral origin, are parallel to the magmatic axis; thirdly, 5 km wide graben is a major expression of NW-SE tensional faults.

The occurrence, origin and relative chronology of those tectonic features are being considered in this paper, particuarly in their role for the localization of favourable geothermal areas.

The lithological type section, compiled from surface and well data, reveals a volcanic rock formation. Geological correlations between the 18 wells drilled up to date show evidence that the structures correspond to the surface features described above.

It is further observed that a convection flow of small amplitude has been detected when considering the temperature correlations between wells. Thermal anomalies are strictly related to the geological features.

Hydrothermal alteration, the role of the self-sealing and di-self sealing processed are mentioned in this paper.

The combination of all those parameters paves the way to the elaboration of a geothermal model. This will provide leads for the determination of areas with greater potential, therefore, assist in the planning of the development necessary to reach the target of 140 MW.