Geochemical monitoring of the Aluto-Langano geothermal field, Ethiopia

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Conference Proceedings: Geochemical monitoring of the Aluto-Langano geothermal field, Ethiopia

Abstract

The Aluto-Langano pilot power plant is the first geothermal power plant producing electricity in the country. It has been operational since July 1998, and the commissioning work by Ethiopian Electric Power Corporation (EEPCO) was completed on June 16, 1999. The designed power output of the pilot power plant was 8.52 MWe (Gross) and 7.28 MWe (net). However, due to various problems, the power output is currently restricted to less than 2 MWe. The Aluto-Langano geothermal power plant is the binary type, which consists of Geothermal combined cycle unit (GCCU) and Ormat energy converter (OEC). The pilot power plant is supplied with steam and brine from the four production wells (LA-3, LA- 4, LA-6 and LA- 8) of around 2000-2500m depth. There is one re-injection well (LA-7), which is an original field exploration well. Evaluation of change of concentrations of elements (e.g. chloride and silica) through time has demonstrated the absence of dilution or cooling effects in the deep wells of LA-3 and LA-6 due to invasion of cold water. The chemical data collected in the year 1999-2000 has indicated substantial increment of Cl, Si, Na, and K. Evidence for the occurrence of stable thermal regime or slight heating of the upflow zone of the system (wells LA-3 and LA-6) has been documented by a comparison of chemical and gas geothermometric temperatures ( Na-K-Ca = 355- 362°C ; CO2 = 337- 347 °C ) with the measured in hole temperatures ( 320-335 °C). The Na-K-Mg diagram is also supported this evidence where the recently collected discharge fluids (1999-2000) of wells LA-3 and LA-6 are found to be in full equilibrium with the reservoir rock at a temperature > 300°C. The discharge fluids collected during the year 1985-86 has fallen along the broad dilution/mixing line between the ground water and the deep reservoir fluid that is in equilibrium with the reservoir rock. Evaluation of solution-mineral equilibria based on saturation indices has demonstrated the presence of likelihood of calcite and silica scaling problems in the productive wells of the Aluto-Langano geothermal field. Quartz could possibly precipitate within the boreholes, at the separator and in the brine transmission line of all four productive wells (LA-3, LA-4, LA-6 and LA-8). The scaling problem of calcite within the borehole, at the separator and in the brine transmission line is recognized only in well LA-4. There is a possibility of precipitation of amorphous silica in the brine transmission line of all

four productive wells.

Author 
Meseret Teklemariam and Kibret Beyence






Conference 
26th Workshop On Geothermal Reservoir Engineering; Stanford University; 2001/01/29


Published 
26th Workshop On Geothermal Reservoir Engineering, 2001





DOI 
Not Provided
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Citation

Meseret Teklemariam and Kibret Beyence. 2001. Geochemical monitoring of the Aluto-Langano geothermal field, Ethiopia. Proceedings of 26th Workshop On Geothermal Reservoir Engineering; Stanford University: 26th Workshop On Geothermal Reservoir Engineering.

Related Files
ETH1.pdf