Geochemistry of the surface and deep fluids of the Miravalles volcano geothermal system (Costa Rica) |
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| Authors: | Fabrizio Gherardi Costanzo Panichi Antonio Yock Jane Gerardo-Abaya |
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| Affiliation: | 1. International Institute for Geothermal Research, via G. Moruzzi 1, Pisa 56124, Italy;2. Instituto Costarricense de Electricidad, Departamento de Récursos Geotérmicos, San José, Costa Rica;3. International Atomic Energy Agency, Wagramerstrasse 5, PO Box 100, Vienna 1220, Austria;1. Department of Mechanical and Industrial Engineering, Universitas Gadjah Mada, Yogyakarta, Indonesia;2. Faculty of International Resource Sciences, Akita University, Akita, Japan;3. Department of Earth Resources Engineering, Kyushu University, Fukuoka, Japan;1. Dept. of Mechanical Engineering, Anna University, Chennai 600 025, India;2. Dept. of Management Studies, Anna University, Chennai 600 025, India;3. School of Mechanical Engineering, Tel Aviv University, Tel Aviv 6997801, Israel;1. Faculty of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka-shi, Fukuoka, 819-0395, Japan;2. Tohoku Sustainable & Renewable Energy Co. Inc., 3-7-1 Ichiban-cho, Aoba-ku, Sendai-shi, Miyagi, 980-0811, Japan;1. Postdoctoral Scholar, Department of Prosthodontics, Faculty of Dentistry, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Brazil;2. Associate Professor, Department of Prosthodontics, Faculty of Dentistry, Cukurova University, Adana, Turkey;3. Assistant Professor, Department of Prosthodontics, Faculty of Dentistry, Cukurova University, Adana, Turkey;4. Professor, Department of Prosthodontics, Faculty of Dentistry, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Brazil;5. Professor, Department of Prosthodontics, Faculty of Dentistry, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Brazil |
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| Abstract: | The Miravalles high-temperature geothermal reservoir, located in the northwestern part of Costa Rica, is liquid-dominated. Reservoir temperatures generally range between 230 and 240 °C. The highest measured value is 255 °C. Bottom-hole measurements and solute geothermometry indicate that thermal conditions within the reservoir are very stable over time. The waters discharged from the wells have a neutral or slightly alkaline pH and are of the sodium-chloride type. Based on isotope data, the main recharge zone appears to be located on the northeastern side of the Guanacaste Cordillera. Several mixing trends have been identified between reservoir fluids and regional groundwaters. Gas discharges are dominated by CO2, with minor amounts of H2S and N2. Relative N2, Ar and He contents reveal a typical arc-type signature and significant inflow of meteoric-derived gases. Cl–SiO2-enthalpy and δ18O–δ2H–Cl relationships suggest the existence of a maturation trend that is the result of both natural (i.e. direct drainage of deeper fluids) and anthropogenic causes (reinjection of Cl-rich waste waters). Acid fluids with SO4-acidity (pH ranging between 2.4 and 3.7) have been encountered in three wells at the eastern border of the well field. Preliminary data assessment indicates two possible sources, either superficial H2S oxidation or inflow of “immature” volcanic waters. |
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| Keywords: | Geothermal Miravalles Fluid geochemistry Stable isotopes Reinjection Acid fluids Costa Rica |
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