An upsurge of interest in the indigenous geothermal potential of Indonesia has followed the Governments encouragement to develop other energy resources as alternatives to oil for the generation of electricity. Accordingly fresh estimates for the geothermal potential of known prospects is proposed.

Only the major fields in Java, Bali, Sulawesi and Sumatra, and which are expected to be developed rapidly, are considered. A brief description of each field is included in the paper and the basis on which the estimates are made is given. Using a modification of the concept, estimation and terminology used in defining mineral reserves, these estimates are quantified. Other factors, expected to influence either way the actual rate of development, are included.

The geothermal potential that is conservatively estimated can be developed in the next 10 – 15 years, is predicted as totalling 1500 MW (e) for the whole of Indonesia. Of this some 900 MW (e) is confined to Java which has the main demand for power.

As well as these major fields, numerous other good prospects are known. Together they may increase the ultimate potential of Indonesia many times what is here suggested. As they are thought unlikely to be rapidly exploited they are not included in these estimates which have been kept deliberately conservative.

A method by which these and future prospects can be ranked in priority is suggested. Based on crude statistical probabilities, the method allows for the combination of factors, other than geothermal, to be taken into account. The resultant quantitative combination, which gives an overall and relative priority, can be of assistance in future planning.

1.0 Introduction

Worldwide concern for future energy supplies, coupled with escalating prices for liquid fuels, has led many countries to reassess their indigenous energy resources. These include hydro, oil, natural gas, coal, and more recently nuclear, solar and geothermal. Only when such an inventory is complete can planning of a future energy policy be contemplated.

Indonesia is particularly fortunate in having an abundance of indigenous resources which allow a choice to be made as to the way the country's future energy demands are to be met. Once an optimum energy mix is formulated it should be recognised that it can never remain static but must remain sensitive to changes that develop both internally as well as externally. How quickly such changes occur was demonstrated in 1977 at an Energy Workshop held in Jakarta when fresh estimates for proven oil resources in Indonesia were calculated as being sufficient for only 19 years at the then current rates of production.

While further discoveries are anticipated, the use to which these reserves can be put is expected to change dramatically. With the growing rate of domestic consumption and assuming constant output the whole of the domestic production is predicted to be absorbed internally before 1995. The comparative decline in revenue that must result from this smaller amount of oil available for sale and its effect on the total economy has encouraged the Indonesian Government to support the substitution of other forms of energy and restrict where possible the domestic consumption of oil.

While coal is expected to be the major replacement of oil in new electrical generation developments, geothermal energy has also been recognised as an alternative in the total energy scene. It is this potential, which can be exploited in the near future, that is potential, which can be exploited in the near future, that is accordingly examined.

The exploration and development, on which the following estimates are based, is part of a bilateral agreement between the Indonesian and New Zealand Governments. Our good friends and counterparts have been provided by PERTAMINA, Perusahan Umum Listrik Negara (PLN) and what is now the Volcanological Survey of Indonesia (VSL). In conjunction with these agencies, GENZL, as the executing agency for the New Zealand Government, has enjoyed participating in this assessment of the geothermal resources of Indonesia.

2.0 Previous Work

Van Dijk (1) was the first to propose the utilisation of geothermal energy for electric power generation in Indonesia. Despite opposition it was supported by Taverne (2) who instigated detailed geological investigations in a number of volcanic areas. Exploration drilling followed these studies at Kamojang in West Java where five shallow wells were sunk, one of which continues to discharge to this day. Results from these early investigations were summarised by Stehn (3) but the experiment to utilise the steam was not pursued. After the war a report by Kusumadinata (4) renewed interest in possible geothermal development which led to reconnaissance possible geothermal development which led to reconnaissance surveys being undertaken by Indonesian teams drawn from the Power Research Institute, the Bandung Institute of Technology Power Research Institute, the Bandung Institute of Technology and the Geological Survey of Indonesia. These surveys were followed by others which included experts drawn from UNESCO, UNDP, France, United States of America and New Zealand; recent participants have been drawn from Japan and Italy.

Reports and recommendations from these surveys are summarised by Sigit (5) Zen and Radja (6) and Radja (7) but significantly all groups fully supported further geothermal investigations in Indonesia. What none could claim, without more data, was to quantify on a rational basis, the potentials for the individual prospects they supported.

The first open publication which attempted to allocate values for the potentials of given prospects was by Djajadi et al (8). By then considerable detailed exploration had taken place and a better understanding gained with some types of Indonesian fields. In a prudent appraisal Djajadi proposed values that, while conservative, prudent appraisal Djajadi proposed values that, while conservative, were the first realistic estimates suitable for planning purposes. Since then further exploration and production drilling at a number of different locations has led to a better appreciation of their underground reservoirs.

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