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HIDROGEOKIMIA FLUIDA GEOTERMAL ARJUNOWELIRANG DAN SONGGORITI, JAWA TIMUR

Hydrogeochemistry of Geothermal Fluid in Arjuno-Welirang and Songgoriti, East Java

Master Theses from JBPTITBPP / 2018-07-13 15:33:27
Oleh : MOCHAMAD IQBAL (NIM : 22015021), S2 - Geological Engineering-FITB
Dibuat : 2017-08-15, dengan 9 file

Keyword : daerah resapan geotermal, geokimia, isotop, parent fluid, tritium.

Daerah penelitian memiliki dua sistem geotermal yaitu sistem geotermal Arjuno-Welirang yang terletak di Kabupaten Mojokerto dan sistem geotermal Songgoriti yang terletak di Kota Batu. Tujuan dari penelitian ini yaitu untuk mengetahui parent fluid dari masing-masing reservoir serta mencari elevasi daerah



resapannya. Penelitian ini dilakukan dengan menggunakan data kimia air, isotop stabil (δ18O dan δD), dan tritium dari mataair panas dan air dingin. Perhitungan parent fluid reservoir menggunakan asumsi heat balance dan mass balance. Berdasarkan perhitungan, parent fluid sistem geotermal Arjuno-Welirang memiliki temperatur sekitar 300°C dengan kandungan Cl: 400-550 mg/kg. Parent fluid kemudian boiling di temperatur 160°C dan mengalami conductive cooling ke temperatur 80°C. Temperatur boiling ditandai oleh kemunculan solfatara/fumarol di permukaan dengan temperatur 160°C. Fluida geotermal (t: 80°C) mixing dengan airtanah (t: 25°C) di dekat permukaan dengan proporsi 0,4 fluida geotermal dan 0,6 airtanah yang menghasilkan mataair hangat Padusan dan Coban bertipe Cl-HCO3 (t: 39-46°C, pH: 6,22-6,44). Mataair hangat Cangar (t:50-55°C, pH: 6,52) bertipe bikarbonat juga muncul sebagai manifestasi akibat kondensasi uap geotermal di dekat permukaan (steam condensates/steam heated waters). Parent fluid sistem geotermal Songgoriti memiliki temperatur sekitar 190°C dengan kandungan Cl: 3.200-3.300 mg/kg. Parent fluid kemudian mengalami conductive cooling ke temperatur 80°C. Fluida geotermal (t: 80°C) kemudian mixing dengan airtanah (t: 23°C) di dekat permukaan dengan proporsi 0,4 fluida geotermal dan 0,6 airtanah yang menghasilkan mataair hangat Songgoriti bertipe klorida (t: 46°C, pH: 6,11) dan Kasinan bertipe Cl-HCO3 (t: 32°C, pH:6,5). Hasil analisis isotop δ18O dan δD menunjukkan sistem geotermal Arjuno-Welirang memiliki elevasi daerah resapan sekitar 1.000-1.300 mdpl. Pada sistem geotermal Songgoriti, elevasi daerah resapan sekitar 1.000-1.200 mdpl. Nilai tritium air panas (3,12 TU) lebih kecil dari air dingin (3,74 TU) yang mengindikasikan bahwa air panas memiliki waktu tinggal/interaksi di bawah permukaan yang lebih lama (tua) yaitu sekitar 65 tahun.

Deskripsi Alternatif :

The research area has two geothermal systems that is Arjuno-Welirang geothermal system which is located in Mojokerto Regency and Songgoriti geothermal system which is located in Batu City. The purposes of this research is to know the parent fluid of each reservoir and to obtain the elevation of the recharge area. The study was conducted using water chemistry data, stable isotopes (δ18O and δD), and tritium from hot and cold springs. Parent fluid reservoir calculation is done by using heat and mass balance assumption. Based on the calculations, the parent fluid of the Arjuno-Welirang geothermal system has temperature of about 300°C with Cl content: 400-550 mg/kg. The parent fluid then boiling at 160°C and conductively cooling to 80°C. Temperature boiling is characterized by the appearance of solfatar/fumarole on the surface with temperature of 160°C. The geothermal fluid (t: 80°C) then mixing with groundwater (t: 25°C) near surface with the proportion of 0,4 geothermal fluid and 0,6 groundwater producing dilute Cl-HCO3 hot springs Padusan and Coban (t: 39- 46°C, pH: 6.22-6.44). Cangar bicarbonate hot spring (t: 50-55°C, pH: 6.52) also appear as a steam heated water/steam condensates near the surface. The parent fluid of Songgoriti geothermal system has temperature about 190°C with Cl content: 3.200-3.300 mg/kg. The parent fluid then cooling conductively to 80°C. The geothermal fluid (t: 80 ° C) then mixing with groundwater (t: 23°C) near the surface with a proportion of 0,4 geothermal fluid and 0,6 groundwater producing chloride warm spring Songgoriti (t: 46 ° C, pH : 6,11) and Cl-HCO3 Kasinan water (t: 32 ° C, pH: 6.5). The results of the isotope analysis δ18O and δD show that the Arjuno-Welirang geothermal system having elevation of the recharge area about 1.000-1.300 masl. In the Songgoriti geothermal system, the elevation of the recharge area is about 1.000-1.200 masl. The value of tritium hot water (3.12 TU) is smaller than cold water (3.74 TU) which indicates that hot water has longer residence time (old) and interaction beneath the surface (~65 years).


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  • Pembimbing : Ir. Niniek Rina Herdianita, M.Sc., Ph.D., Editor: PKL-UIN-Raden Fatah

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