Pancen amenangi jaman edan, sing ora edan ora kaduman. Sing waras padha nggragas, sing tani padha ditaleni. Wong dora padha ura-ura. Begjane sing eling lan waspada. Ratu ora netepi janji, musna prabawane lan kuwandane. Akeh omah ing ndhuwur kuda. Wong mangan wong, kayu gilingan wesi padha doyan rinasa enak kaya roti bolu.
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Indonesia which comprise of more than 200 volcanoes located along Sumatra, Java, Bali and the islands of eastern Indonesia – known as The Ring of Fire – has given rise to large concentration of high temperature geothermal fields. A research from the Ministry of Energy & Mineral Resources mentioned that there are 253 geothermal-potential locations in the country.
With the combined high and low enthalpy geothermal resources, the potential estimated by Directorate General of Geology and Mineral Resources is more than 27,000 MW which makes Indonesia the country with the highest geothermal potential in the world. Indonesia has however, developed only less than a thousand MW of geothermal power. The Indonesian government is planning to utilize the big geothermal energy resource as a leading alternative energy to substitute fossils that may be fulfilling Indonesia’s growing demand for electric power during the 21st century.
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Surface Geology
The Patuha Geothermal field is located in West Java approximately 45 kilometers southwest of the city of Bandung. The nearest sizable town to the project area is Ciwidey, located about 15 kilometer to the north.
The field occurs within a Quaternary volcanic highland with several volcanic centers including Gunung Urug (+2201 masl), Gunung Patuha (+2414 masl) and Patuha Selatan (+2390 masl). The surface rocks in the project area is primarily covered andesitic lavas and pyroclastic rocks, the dacitic lavas dome is distinctly observed at Gunung Urug and Patuha Selatan. Most of drillsites are located at the elevation of 1800-2200 masl.
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The Dieng geothermal field is located in central Java Island approximately about 80 kilometers northwest of the city of Yogjakarta surrounded by mountainous terrain. The geothermal area at Dieng is heavily farmed (rice and vegetables) and highly populated. The nearest sizable town to the project area is Wonosobo, located about 25 kilometers to the south.
The mountain range in central Java has an east-west trend, extending from Gunung Slamet on the west to Gunung Ungaran on the east. These volcanic centers are considered as high in their geothermal prospects. The Dieng mountain complex is located between the two mountain ranges and is part of this E-W trend with its highest top at Gunung Prau (2555 masl). Another major structural feature is defined by the NW-SE volcanic alignments of Gunungs Mangunan-Dieng (NW), Sundoro, Sumbing and Merbabu-Merapi (SE).
After the last eruption, erosion of the caldera wall and the soft pyroclastic and sedimentary deposits continued within the caldera to the present day. Some group considered the Dieng Mountain complex as the remnants of a large caldera structure. Gunawan (1968) and others, however disagree with the caldera theory and suggests that the escarpment exposed at G. Prau and G. Patakbanteng to be an older eroded volcano. The SE-trending young volcanic centers are also considered to be genetically related to a major fault zone.
Historic eruptions have been reported in the Pakuwaja area in 1826 and 1847. But it has not been confirmed whether the eruptions were from Pakuwaja or nearby volcanic centers. A number of historic phreatic or hydrothermal eruptions have occurred in Sikidang and Sileri areas. Similar activities have also been reported in the Candradimuka area, NW of Dieng project area.
The nearest exposure of older sedimentary rocks are in the ? western part of the Dieng field, near Rataamba. The sedimentary outcrop are Pliocene limestone underlain by marine clays.
The field has three main active hydrothermal surface thermal features, Pakuwaja, Sikidang and Sileri areas. The features are active fumaroles, mud pools, steaming ground and are surrounded by extensively altered ground. Thermal features also include neutral pH chloride hot springs located below 1700 masl. The Sikidang and Sileri thermal features cover significant steaming and extensively altered grounds. The Bitingan and Siglagah hot springs have temperatures ranging from 45 to 58°C and neutral pH. Pulosari hot spring (48°C) and the Jojogan warm spring (25°C) are located about 3.7 km WSW and 2 km NE of Sikidang fumaroles. The field has several small lakes of volcanic or hydrothermal origin. The presence of active thermal features and very young volcanism made the field one of the attractive target for commercial development.
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Sokoria Geothermal Field is situated about 37 km northeastern part of Ende city, belong to the administrative region of Sokoria village, district of East Ndona, Ende regency, East Nusa Tenggara. The thermal gradient well of the Sokoria geothermal field consists of 2 wells, those are SK-1 and SK-2. Geographically, SK-1 and SK-2 are respectively located at 121° 45’ 58” East – 08° 47’ 25” South and 121° 45’ 59” East – 08° 47’ 10” South.
Rock unit of SK-1 from top to bottom consists of Top Soil, Tuff Breccia, Andesite, Altered Andesite, Altered Andesite Breccia and Altered Andesite Basaltic, whereas SK-2 composes of Altered Andesite, Altered Andesite Breccia and Altered Andesite Basaltic. An interbedding occurred among Altered Andesite, Altered Andesite Breccia and Altered Andesite Basaltic characterize the rock originating from several times of eruption periods of the Mutubasa Volcano in the Mutubasa’s old caldera.
The entirely rock have undergone a hydrothermal alteration with a varied alteration intensity from weak to intense (SM/TM = 10-85%). The hydrothermal alteration is generally characterized by processes of argilitization, oxidation with/without piritization, silicification, carbonatization, anhydritization and chloritization. The type of alteration is included into “Argillic” functioning as caprock in the geothermal field of Sokoria. The environment setting of alteration mineral indicates a netral to acid fluid condition characterizing its formation on a high-temperature of hot water and vapour system.
From the result of temperature logging measurement it has been obtained an anomaly of average temperature at SK-1 by 13 times normal thermal gradient, that is about 40 deg C/100 m, whereas SK-2 has an anomaly of average temperature by 12,6 times normal thermal gradient, that is about 37,8 deg C/100 m. Based on the result of geological analysis and temperature logging measurement show subsurface heat flow at the field of Sokoria and it has a prospect to be developed further.
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Lesugolo geothermal prospect area is located 5 km southern part of Mboto village. It is administratively in the districts of Maurole and Kotabaru, Ende regency, East Nusa Tenggara province. The study area covers an area of about 144 km2 (12 x 12 km2) which is bounded by the following longitudes and latitudes : 121°50’30″ – 121°56’30″ E and 08°32’00″ – 08°38’00″ S.
Stratigraphically, it comprises of two main rocks, i.e., quartemary volcanic rocks located unconformity on the neritic fasies volcanoclastic sedimentary rocks of tertiary age. The geological structure represents the lineament which are interpreted as a fault directed to northeast-southwest, northwest-southeast and west-east. The appearance of the geothermal discharges consists of hot spring of Lesugolo and Ae Dhara and warn spring of Lowo Geru dan Ae Petu with the presence of travertine sinter.
The interpretation of resistivity data combined with the interpretation of geological and geochemical data has proved to be able to delineate the prospect area of Lesugolo geothermal field and its vicinity more clearly. The prospect area is located in the northwest of the southeast side of Gunung Keli Watuapi, with an area of about 6,2 km2. Hot water system reservoir lies at an average depth under 500 m with a temperature of about 160-190°C. The rocks of the reservoir and caprock is on bedrock made of tertiary volcanoclastic sedimentary rocks in the form of tuffs and tuff breccias. The rain catching area is around Gunung Keli Watuapi with the outflow runs moving up to southeastward of the hot spring of Lesugolo. The presents of the three paths of fault in the study area is expected to be the permeability area that has the very potential of trapping system of Lesugolo geothermal.
The results of geothermal potential calculation recognized the prospect area with potential up to 50 MWe. The geothermal area of Lesugolo has a significant prospect necessary to develop both for the purpuse of indirect use as a small-scale geothermal power plant and various direct used of it.
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With the combined high and low enthalpy geothermal resources, the potential estimated by Directorate General of Geology and Mineral Resources is more than 27,000 MW which makes Indonesia the country with the highest geothermal potential in the world. Indonesia has however, developed only less than a thousand MW of geothermal power. The Indonesian government is planning to utilize the big geothermal energy resource as a leading alternative energy to substitute fossils that may be fulfilling Indonesia’s growing demand for electric power during the 21st century.
The field occurs within a Quaternary volcanic highland with several volcanic centers including Gunung Urug (+2201 masl), Gunung Patuha (+2414 masl) and Patuha Selatan (+2390 masl). The surface rocks in the project area is primarily covered andesitic lavas and pyroclastic rocks, the dacitic lavas dome is distinctly observed at Gunung Urug and Patuha Selatan. Most of drillsites are located at the elevation of 1800-2200 masl.