Háskóli Íslands

Selamawit Worku Sisay will give a lecture about her masters thesis in geology. The thesis is titled Subsurface geology, hydrothermal alteration and 3D modeling of wells LA-9D and LA-10D in the Aluto Langano geothermal field, Ethiopia.

Abstract

Aluto Langano geothermal field is located in the Aluto Volcanic Complex (AVC), within the Central Main Ethiopian Rift System (CMERS). The Aluto Volcanic area is a silicic peralkaline complex, which is affected by the Wonji Fault Belt (WFB), trending NNE-SSW. Ten exploratory wells (LA-1 to LA-10D) have been drilled in Aluto Langano geothermal field with a maximum depth of 2500m and maximum measured temperature of 335°C. This study is focused on subsurface geology and hydrothermal alteration of wells LA-9D and LA-10D. The wells were drilled directionally on the top of AVC. Data from neighboring wells (LA-3 to LA-8) are used for comparison purpose. Lithologies, which are found in the study wells, were identified with the aid of binocular microscopy and petrography microscopy, and consist of pyroclastics, silicic tuff and breccia, sediment, rhyolite, trachyte, basalt and ignimbrite, while ICP-OES analysis led to the identification of very scarce and thin layers of trachyandesite, basaltic trachyandesite, trachydacite, basaltic andesite and andesite units. Hydrothermal alteration minerals were found as replacement of primary minerals and as fillings of veins and vesicles. Four alteration zones are recognized in both study wells; unaltered zone, smectite zone, illite/chlorite zone and illite/chlorite/epidote zone. Eight feed zones (one major and seven minor) are in well LA-9D and seven (one major and six minor) in LA-10D. Most of the feed zones are located in fractured basaltic units. The highest temperature recorded is more than 300°C, in well LA-9D below 1560m depth and in LA-10D below 1600m, indicating that they are located in the up-flow zone of the system.

Advisors:Anette K. Mortensen, Björn S. Harðarson and Guðmundur H. Guðfinnsson

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