Well data analysis and volumetric assessment of The Sol de Mañana geothermal field, Bolivia

Abstract

Bolivia is located in South America, where the subduction of the Nazca Plate under the South American Plate generates the Andes volcanic chain that crosses Bolivia. In 1976, ENDE and the Ministry of Energy and Hydrocarbons, with funds from the United Nations Development Programme (UNDP), began evaluating the geothermal potential of 42 hydrothermal manifestations, and the Laguna Colorada area was considered the most prospective. Geo-volcanological mapping indicates the existence of an extensive ignimbrite unit that almost completely covers the area, and overlies an andesitic-dacitic lava sequence and possibly ignimbrites of Neogene origin. The structural geology shows two orthogonal tectonic systems, NNW-SSE and NNE-SSW, and this structural system has caused secondary deep fracturing that allows hot water to rise up through faults and fractures to reach the surface in hydrothermal alteration zones. The temperature obtained from geothermometers are in agreement with the measured reservoir temperature of around 250°C. Geophysical studies carried out in the exploration stage identified important gravimetric and resistive anomalies. When correlated with MT data, this information allows the identification of the possible reservoir extension.

Six wells were drilled between 1989 and 1994 in the Sol de Mañana geothermal field, confirming high temperature (250-260°C). Temperature cross-section allows better understanding of the reservoir characteristics. Results of well testing show similar characteristics for wells SM-01 and SM-02 and better connection between these two wells than other wells in the field. These results correlated with the structural geology, indicate that wells SM-01 and SM-02 could intersect the same fault. Based on temperature measurements and well test analysis, an initial resource assessment is done using the volumetric method considering two scenarios. The most likely value obtained for the production capacity of the Sol de Mañana geothermal field, is 75 MWe for 25 years.