| Title | The Preliminary Conceptual Model of Tolehu Geothermal Resource, Based on Geology, Water Geochemistry, MT and Drilling |
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| Authors | Asnawir NASUTION, Miman AVIFF, Sigid NUGROHO, Yudistian YUNIS, Mitshuru HONDA |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | Tolehu Ambon, alteration minerals of volcanic rocks, MT-TDEM, gradient thermal and exploration wells |
| Abstract | The low topography Tolehu geothermal area, about 70 m above sea level is located in an Ambon volcanic island, Indonesia and has long been studied. The re-surveyed by additional MT-TDEM methods, continued by shallow gradient thermal drillings and an exploration well, which is 930 m is to constrain a preliminary conceptual model for the prospect. The integrated 1D and 2D MT inversion images with data from geochemical thermometry and wells had indicated a temperature resource having over 200ºC. Shallow cores of about 150 m depth and deeper drill cuttings until 930 m depth were analyzed by using petrography and x-ray methods. At the shallow level, they had confirmed that the low resistivity detected by MT-TDEM surveys closely correlated with the distribution of low and high temperature smectite-illite and chlorite clay alteration. The extreme temperature of a thermal gradient well at the shallow hole represents 123oC at the depth of 150 m. The deeper level of overlying volcanic rocks assumed as a clay cap, due to the greater tendency of clay minerals, eq. illite, smectite, phyrophlite, chlorite clay to inhibit the formation of fracture permeability relative to more brittle clays. The top of the permeable reservoir generally conformed to the geometry of the base of the low resistivity clay alteration. The rough correlation of geothermometry with the 5 and 10 ohm-m contours below the transition from smectite-illite - illite to chlorite clay were used to predict the depth of the cap rocks, with a maximum 800 m depth. The water dominated reservoir has shown the Chloride’s concentration lower than 5000 ppm at the 930 m depth, which indicates sea water un-involved to the geothermal system. The extended wells will be drilled to the south an old volcanic complex to confirm the elements of the model and to proven geothermal reservoir until 1.5 to 2 km depth. |