Past, Recent and Future of Indonesia Geothermal Play Target

Geothermal play is quite different with petroleum play that consists of source, fluid migration, reservoir, trap, and seal. According to Moeck (2014), geothermal play is a setof geological conditions that may host accumulations of potential recoverable heat. Based on its thermal transfer, the geothermal systems are divided into two main categories, namely convective and conductive (Rybach, 1981 in IGA, 2014; Moeck, 2014). The understanding of geothermal play type is important on exploration phase to constrain regional-scale assessment of conceptual mode of the geothermal system that is strongly influenced by plate tectonic setting (IGA, 2014).

Convective geothermal play has circulating fluid and heat from the heat source to the shallower part of the system. This play generally shows on active volcanism, tectonism, young plutonic and extensional setting such as Indonesia, Philippines, and Japan (Moeck,2014). Geothermal field exploration and development in Indonesia at the past and present has focused on this geothermal play especially in the volcanic play. All producing geothermal field such as Muara Laboh, Kamojang, Lahendong, Ulumbu, etc and developed field such as Rajabasa, Rantau Dedap, Sekincau, Hululais, etc are in this volcanic geothermal play type associate with Quaternary volcanoes. Convective-volcanic play that is considered ‘low-hanging fruit’ has been explored well and may not remain significant discovery for new field in the future.

Conductive geothermal play refers to the condition where thermal transfer occurs without any fluid flow from the heat source. It is important to note that the conductive system with respect to the porosity-permeability ratio of the reservoir rock and the absence or presence of producible fluids in the reservoir should be complemented with advanced technology (Moeck,2014). This play occurs on intra cratonic, orogenic belt, and basement. Based on Moeck (2014), on a global scale, the conductive geothermal play research and development are still ongoing (i.e Soultz, FRN and Fenton Hill, USA) and commercially proved (i.e Cooper Basin, AUS). Indonesia is not really familiar with this play type, due to some factors such as the lack of expertise, high-cost research, unclear regulation standing, etc. Furthermore, the geologic setting of Indonesia causes volcanic geothermal play more favourable. Several systems that include on conductive geothermal play, such as:

1. Hot dry rock is hot fractured rock because of either the need to fracture the virtually impermeable formations or the presence of natural fractures in the hot reservoir (Wyborn, et al., 2005; Goldstein, et al., 2011). Temperatures may vary from 150°C to 500°C at depths in the order of 5 to 6 km (Potter, et al., 1974 on Breede, et al., 2013).
2. Hot sedimentary aquifer is heat energy source from high temperature gradients or hot rocks which the reservoir zone is located in sedimentary formation with high porosity and permeability with temperature (Adelina, et al., 2009, Soldo, et al., 2015, Corbel, et al., 2012; Bu, et al., 2011; Mijnlieff, 2020)
3. Geopressured, geothermal system that occurs in a sedimentary basin within a confined sedimentary reservoir with pressures much higher than local hydrostatic pressures (Sanyal, 2010). Such systems are found at depths 3-7 km (Nicholson, 1993); 2-4 km (Saemundsson et al, 2009). The fluids are tightly confined by surrounding impermeable sedimentary rocks and heated in normal/enhanced geothermal gradients by their greater burial (Lund, 2007).
4. Super hot is defined as heat energy mined in excess of the critical point of water (Hill, et al., 2021).

At present, the term of unconventional geothermal system began to gain popularity. However, the definition of the term is still unclear and lead to uncertainty of future development (Breede, et al., 2013). The systems in conduction play are often included in this kind of unconventional system. However, in our opinion, a geothermal system is said to be unconventional because they need advanced technology to tap the energy. This kind of system requires high technological approach both for exploration and extraction methods. For the hot dry rock exploration, it requires advanced in-situ stress study and fracture modelling to determine the distribution of area that uncommon practice on geothermal exploration in Indonesia since require high-cost data and research. The drilling operation also needs some adjustment to tap deeper and higher temperature target. The application of advanced technology includes Enhanced Geothermal System (EGS) and Closed Loop Geothermal System (CLGS) may also require to adapt so the project would be more efficient and beneficial. For example, the hot dry rock and superhot rock have the condition with sufficient high temperature (heat source) with little or no permeability (reservoir) and fluid presence (fluid flow). They need to engineer using fracturing to enhance the permeability and provide fluid injection from surface to the system using injection well so the heat could be extracted through production well.

The understanding of the geothermal play may help us to redefine this kind of the system, because each type of the play would need certain exploration and/or extraction techniques for proper evaluation. Subject to this understanding, we try to develop the schematic mind map of the geothermal system based on its exploration and extraction method to provide a basis for distinguishing conventional and unconventional systems. The geothermal system type was adapted following to previous studies include Wohletz & Heiken (1992), Hochstein (2000), Goff & Janik (2000), Lund (2007), Saemundsson (2009), Sanyal (2010), and Moeck (2014) as shown on Figure 1.

Figure 1 Schematic mind map of geothermal play adapted from previous study.

The future of Indonesia’s geothermal development should accommodate the potential of these kind of resources which are still green and may support the geothermal needs in the future. There are several published studies that assess the unconventional geothermal potential in Indonesia, such as:

1. Hendrawan and Draniswari (2016) studied that North Sumatra Basin basement is the highest potential for hot dry rock using enhanced geothermal system with ~313.7 Mw, while the South Sumatra basin is the largest potential area (928.4 m2).
2. Syarifudin, Octavius, and Maurice (2016) studied the potential of hot sedimentary aquifer that extracted using abandoned oil/gas well in Arun field. The study reveal it could produce 2.65 kg/s of 170°C fluid for 2900 kW electricity. While the direct utilization also could be applied for drying, heating, and refrigeration on industry around Arun field.
3. Suryantini (2021) also state about the potential of utilization oil/gas well to extract geothermal fluid from hot sedimentary system on Northwest Java Basin.

Finally, the integrated support from technical, regulation, and economic perspectives is strongly recommended to unlock the unconventional potential in Indonesia. The understanding of geothermal play also holds an important role to gain a better understanding of this potential. Dobson (2016) states, this method as Play Fairway Analysis which involves identification of key resource attributes, including a heat source, permeability, seal/cap, and the fluids through the use of regionally extensive geologic, geochemical, and geophysical indicators. The collaboration with petroleum industry also should be developed since several unconventional systems overlaid with oil and gas industry. For instance, hot dry rock on basement may collaborate with an oil and gas company that has development plan to tap the fractured basement petroleum system in South Sumatra Basin, so the data exchange and joint study could lead to comprehensive result for both sides.

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References

Breede, K., Dzebisashvili, K., Liu, X., & Falcone, G. (2013). A systematic review of enhanced (or engineered) A systematic review of enhanced (or engineered). Geothermal Energy : A Springer Open Journal.

Bu, X., Ma, W., & Li, H. (2012). Geothermal energy production utilizing abandoned oil and gas wells. Renewable Energy, (pp. 80-85).

Corbel, S., Griffiths, C., Dyt, C., & Ricard, L. P. (2012). Hot sedimentary aquifer characterization using stratigraphic forward modelling, Perth Basin, Australia. Stanford Geothermal Workshop. California.

Dobson, P. (2016). A Review of Exploration Methods for Discovering Hidden Geothermal Systems. GRC. GRC.

Garg, S. K., Pritchett, J. W., & Combs, J. (2010). Exploring for Hidden Geothermal System. World Geothermal Congress. Bali: World Geothermal Congress.

Goldstein B, H. G.-N. (2011). IPCC special report on renewable energy sources and. (p. 406). Cambridge University Press.

Hendrawan, R., & Draniswari, W. (2016). Assessing the Possibility of Enhanced Geothermal System in Western Indonesia. IOP Conference Series: Earth and Environmental Science.

Hochstein, M., & Browne, P. (2000). Surface Manifestation of Geothermal System with Volcanic Heat Source. San Diego.

International Geothermal Association (IGA). (2014). Best Practice Guide for Geothermal Exploration.

Lund, H. (2007). Renewable Energy Strategies for Sustainable Development. Elsevier.

Mijnlieff, H. (2020). Introduction to The Geothermal Play and Reservoir Geology of the Netherlands. Geothermal Energy.

Moeck, I. S. (2014). Catalog of geothermal play types based on geologic controls. Renewable and Sustainable Energy Reviews, 867 - 882.

Nicholson, K. (1993). Geothermal Fluids.

Reinsch, T., Dobson, P., Asanuma, H., Huenges, E., Poletto, F., & Sanjuan, B. (2017). Uttilizing Supercritical Geothermal System: A Review of Past Ventures and Ongoing Research Activities. Geothermal Energy.

Saemundsson. (2009). Geothermal System in Global Perspective. Exploration for Geothermal Resources. Kenya: United Nation University.

Sanyal, S. K. (2010). Future of Geothermal Energy. Stanford Geothermal Workshop. California: Stanford.

Syarifuddin, M., Octavius, F., & Maurice, K. (2016). Feasibility of Geothermal Energy Extraction from Non-Activated Petroleum Wells in Arun Field. IOP Conference Series Earth and Environmental Science.

Wohletz, K., & Heiken, G. (1992). Volcanology and Geothermal Energy. Los Angeles: Oxford.

Wyborn, D., Graaf, L., Davidson, S., & Hann, S. (2005). Development of Australia's first hot fractured rock (HFR) underground heat exchanger, Cooper Basin, South Australia. World Geothermal Congress. Antalya: WGC.

Ferdino R. Fadhillah. (2021). Past, Recent and Future of Indonesia Geothermal Play Target. SMI Institute, PT Sarana Multi Infrastruktur (Persero). Diakses , dari