Elsevier

Geothermics

Volume 37, Issue 3, June 2008, Pages 220-266
Geothermics

History of geothermal exploration in Indonesia from 1970 to 2000

https://doi.org/10.1016/j.geothermics.2008.01.001Get rights and content

Abstract

Reconnaissance surveys undertaken since the 1960s show that more than 200 geothermal prospects with significant active surface manifestations occur throughout Indonesia. Some 70 of these were identified by the mid-1980s as potential high-temperature systems using geochemical criteria of discharged thermal fluids. Between 1970 and 1995, about 40 of these were explored using geological mapping, geochemical and detailed geophysical surveys. Almost half of the surveyed prospects were tested by deep (0.5–3 km) exploratory drilling, which led to the discovery of 15 productive high-temperature reservoirs. Several types of reservoirs were encountered: liquid-dominated, vapour-dominated, and a vapour layer/liquid-saturated substratum type. All three may be modified by upflows (plumes) containing magmatic fluid components (volcanic geothermal systems). Large, concealed outflows are a common feature of liquid-dominated systems in mountainous terrain. All explored prospects are hosted by Quaternary volcanic rocks, associated with arc volcanism, and half occur beneath the slopes of active or dormant stratovolcanoes. By 1995, five fields had been developed by drilling of production wells; three of them supplied steam to plants with a total installed capacity of 305 MWe. By 2000, with input from foreign investors, the installed capacity had reached 800 MWe in six fields, but geothermal developments had stalled because of the 1997–1998 financial crisis.

Introduction

Geothermal exploration in Indonesia began in 1970 with the aim of finding and developing high-temperature geothermal systems. The developments between 1970 and 1990 (in many cases until 1995) are not well documented. An attempt is made here to summarize the early surveys, referring to information in publications and reports written in English, mainly by Indonesian scientists and engineers, which are accessible in the public domain. Thus, the exploration of prospects is discussed where detailed geological, geochemical, and geophysical methods were combined to assess field characteristics of importance when siting exploration wells over inferred high-temperature reservoirs. Results of early geophysical surveys are discussed in more detail where they led to proper estimates of reservoir areas and, combined with important geochemical and geological findings, allowed a prediction of reservoir characteristics. Since most of the earlier exploration efforts are not listed in the scientific literature, theses and diploma reports of Indonesian geothermal graduate students attending the University of Auckland between 1979 and 2003 became an important source of information and were used for this paper. The geothermal terminology employed here is that adopted in Hochstein and Browne (2000). The description of a few prospects not covered by published work is based on observations and field notes collected by the authors.

Descriptions of Indonesian geothermal resources probably started with the reconnaissance surveys described by Junghuhn over 150 years ago (Junghuhn, 1854), whose studies covered mainly active volcanoes and large thermal areas on Java. From around 1900 until the beginning of World War II, most of the Indonesian Quaternary volcanoes and their fumarole and solfatara fields were mapped by the Dutch colonial Geological Survey; the results were later published in the first volume of the Catalogue of the Active Volcanoes of the World (Neumann van Padang, 1951). A summary of documented thermal springs on Java, the Molucca Islands, and Sumatra can be found in the lists of global thermal springs by Waring (1965). After Indonesia gained independence, the Volcanological Survey of Indonesia (VSI) started work in the 1960s with reconnaissance-type surveys that led to the compilation of an inventory of sites with thermal manifestations. A map showing the location of these sites on Java and Bali was compiled by VSI in 1968 (Purbo-Hadiwidjojo, 1970). The studies were supported by the State Electricity Company (PLN) and the Bandung Institute of Technology (ITB). International and foreign missions (UNESCO, EURAFREP) visited several geothermal prospects at that time and, with reference to the size and type of manifestations, drew attention to prospects associated with hot spring discharges. A revised catalogue of volcanoes and fumarole fields in Indonesia published by VSI (Kusamadinata, 1979) provided important information now incorporated in a world-wide catalogue of volcanoes that can be accessed through the Smithsonian volcano website (see bottom of Table 1).

All Indonesian geothermal systems associated with surface manifestations discharging fluids at boiling temperature occur in areas with Quaternary volcanism and active volcanoes along well-defined volcanic arcs. There are five active arc segments in Indonesia that define regions of interest for geothermal exploration (Fig. 1). Using plate tectonic concepts, all active Indonesian arcs can be interpreted as the result of sub-crustal melting induced by subducted lithosphere plates (Katili, 1975). The major plate tectonic structures shown in Fig. 1 had already been recognised during the 1970s (Hamilton, 1979). All young Quaternary volcanoes can be associated with cooling magma and igneous intrusions, which, in turn, are heat sources for active arc-type geothermal systems.

The first inventory (in English) of Indonesian thermal areas and prospects, compiled by VSI as part of a New Zealand (NZ) Aid project in 1987 (NZMFA, 1987, Mahon, 1987), listed 215 sites. The inventory has been upgraded and about 245 thermal prospects are listed in its 1998 version, which is accessible through a VSI website (see bottom of Table 1). We have used the same names, numbering system, and coordinates of the geothermal sites shown in the 1998 VSI catalogue (with the exception of a few not yet given there). A list of 87 Indonesian geothermal prospects already covered by inventory/reconnaissance surveys was also presented by Manalu (1988). Another important registry of Indonesian geothermal prospects is that contained in an unpublished report by Kingston and Morrison (1997), which lists 204 sites and describes their state of exploration.

The selection of Indonesian geothermal prospects for exploration studies was based on earlier reconnaissance surveys. The characteristics of the discharged thermal fluids, types of manifestation, and extent of thermal alteration at the surface, together with geothermometer data derived from chemical analyses, were taken into consideration for the selection. Initially, empirical (liquid and gas) geothermometers were used (Henley et al., 1984); later, theoretical based geothermometers (for example, Giggenbach, 1980, Giggenbach, 1981) were often applied, using selected fluid samples. Between 1970 and 1995, about 70 sites were tentatively classified as high-temperature prospects where geothermometer data indicate deep fluid equilibrium temperatures of >220 °C. Reconnaissance and more detailed exploration studies of most of the 70 prospects are discussed below. Geothermal exploration increased in 1994 when foreign and private investors were encouraged by the Indonesian Government to develop and to run so-called independent power projects (IPPs), which had to sell geothermal power under Energy Sales Contracts to the state electricity company PLN. This resulted in accelerated exploration and production drilling, which came to a halt as a result of a financial crisis in 1997–1998. The history of geothermal exploration in Indonesia between 1970 and 2000 has therefore been divided into three stages: (1) the ‘starting period’, covering 1970–1980; (2) a ‘diverse period’ from 1980 to 1995, and (3) an ‘accelerated development period’ from 1995 to 2000.

Section snippets

The first attempts (1918–1970)

Exploration of geothermal resources associated with active fumarole and solfatara fields with the objective of generating electricity was first proposed in 1918. Initial exploration drilling was undertaken by the Volcanological Section (later to become the Volcanological Survey of Indonesia, or VSI) of the colonial Geological Survey of Indonesia (GSI), at Kawah1 Kamojang, on Java, in 1926.

Geothermal exploration (1970–1980)

During the first PELITA (first 5-year development plan, 1969–1974), the Volcanological Survey group (VSI) completed a geothermal inventory of Sumatra, Sulawesi, and the Halmahera Islands (Radja, 1985, Soetantri, 1986). Geothermal exploration was supported by foreign aid projects. The Indonesian State Oil Company (Pertamina) entered geothermal exploration from 1974 onwards and became responsible for all geothermal exploration in Java and Bali, in line with Presidential Decree PD 16/1974.

The second period (1980–1994): exploration and development on Java

The second period saw a rapid expansion of new and follow-up exploration activities (Ganda et al., 1992). Most of the activity occurred on Java, involving the exploration of roughly 20 prospects (see Fig. 2). For the first time, outflow structures of two prospects were explored by deep drilling. Deep wells were also drilled in six other areas, and four discovered and tested fields were developed by further drilling. Geothermal prospects with significant acid surface manifestations and

Geothermal exploration of Sumatra prospects (1980–1995)

Exploration studies of a few Sumatra prospects conducted during the first half of the 1980s are mentioned by Radja (1985). These led, in 1983, to the drilling of the first deep geothermal exploratory well on Sumatra by VSI in the Lempur–Kerinci prospect, which was sponsored by JICA. The activities of the Pertamina geothermal group began in 1987 with the reconnaissance and exploration of Sumatra prospects. In 1989–1990, a subsidiary of Unocal undertook a follow-up geochemical survey of most

Bali

Exploration of the Bratan Caldera prospect during the 1980s was restricted since parts of the caldera had been given National Park status. However, some additional resistivity surveys (MT) were undertaken by Pertamina in 1987. These were disturbed in part by topographic effects, but allowed penetration of the thick, low-resistivity layer on top. At the beginning of 1994 the fate of the prospect was still uncertain.

High-temperature prospects on Banda Arc Islands (Nusa Tenggara)

Seventeen prospects with significant thermal manifestations occur on Banda Arc

Exploration and development of prospects from 1995 until 2000

The industrial development of explored Indonesian geothermal resources was rather slow prior to 1995. Power plants with a total generating capacity of about 305 MWe had been constructed at Kamojang, Awibengkok, and Darajat. A complex local energy market and inflation made it difficult to secure overseas funding for partial developments. Fixed contracts were introduced from 1994 onwards to allow for development of IPP where steam field development, steam production, and electricity generation

Summary and discussion

About 70 out of more than 200 geothermal prospects throughout Indonesia were identified as potential high-temperature systems before 1995 (Sudarman et al., 2000a) and 42 of these were explored in some detail between 1970 and 2000 using geological mapping as well as geochemical and geophysical surveys (see summary in Table 1, Table 2, Table 3). Another 30 or so areas have only been subject to reconnaissance studies; only half of the sites are mentioned in the literature. Almost all explored

Acknowledgements

During the search of old records and events, important information was provided by Mr. B. Budiardjo, Mr. S. Ganda, Mr. F. Hendrasto, Mr. R. Mulyadi, Ms. P. Utami (the Indonesian team) and Mr. E. Anderson, Mr. I. Bogie, Mr. H. Hole, Mr. E. Layman, Dr. A. Reyes, and Mr. K. Seal. A/Prof. P.R.L. Browne and Dr. J. Moore provided constructive comments to earlier versions of the paper. Ms. L. Cotterall drafted the figures.

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