Sub-Surface Geology, Hydrothermal Alteration and 3d Modeling of Wells La-9d and La-10d in the Aluto Langano Geothermal Field, Ethiopia

Worku Sisay, Selamawit. Sub-Surface Geology, Hydrothermal Alteration and 3d Modeling of Wells La-9d and La-10d in the Aluto Langano Geothermal Field, Ethiopia. University of Iceland, 2016.

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  • Sub-type Master's thesis
    Author Worku Sisay, Selamawit
    Title Sub-Surface Geology, Hydrothermal Alteration and 3d Modeling of Wells La-9d and La-10d in the Aluto Langano Geothermal Field, Ethiopia
    Year 2016
    University University of Iceland
    Department Faculty of Earth Sciences
    Place of Publication Reykjavik
    Publisher United Nations University Geothermal Training Programme
    Pages 95
    Language eng
    Abstract Aluto Langano geothermal field is located in the Aluto volcanic complex (AVC), within the Central Main Ethiopian Rift System (CMERS). AVC is a silicic peralkaline complex, which is affected by 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 2500 m and maximum measured temperature of 335°C. This study focused on sub-surface geology and hydrothermal alteration of wells LA-9D and LA-10D. The wells were drilled directionally on the top of AVC. Data form neighbouring wells (wells LA-3 to LA-8) are used for comparison purposes. Lithologies that are found in the study wells, identified with the aid of binocular microscopy and petrographic microscopy, are pyroclastics, silicic tuff and breccia, sediments, rhyolite, trachyte, basalt and ignimbrite, while ICP-OES analyses also led to the identification of very scarce and thin layers of trachyandesite, basaltic trachyandesite, trachydacite, basaltic andesite and andesite units. Hydrothermal alteration minerals are found as replacement of primary minerals and as fillings of veins and vesicles. Four alteration zones are recognized in both study wells, and include an unaltered zone, smectite zone, illite/chlorite zone and illite/chlorite/epidote zone. Eight feed zones (with one major and seven minor) were identified in well LA-9D and seven (one major with six minor) feed zones in LA-10D are observed. Most of the feed zones are located in fractured basaltic units. The highest temperature recorded was more than 300°C in well LA-9D below 1560 m depth, and below 1600 m in LA-10D, the recorded temperature indicated is more than 300°C. Both wells appear to be in the upflow zone of the system.
    UNBIS Thesaurus ETHIOPIA
    Keyword Sub-surface geology
    Hydrothermal alteration
    3D Modeling
    Wells LA-9D and LA-10D
    Aluto Langano Geothermal Field
    Copyright Holder United Nations University Geothermal Training Programme
    Copyright Year 2016
    Copyright type Fair use permitted
    ISBN 9789979684107
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    Created: Tue, 17 Jan 2017, 22:58:47 JST by Malfridur Omarsdottir on behalf of UNU Iceland