| Title | Evaluating the Thermal Evolution History of a Geothermal System Through Correlation of Alteration Mineralogy and Down-Hole Temperature Isotherms. A Case Study of the Olkaria Northeast Field, Kenya |
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| Authors | Victor OTIENO, Xavier MUSONYE |
| Year | 2017 |
| Conference | Stanford Geothermal Workshop |
| Keywords | geothermal system, thermal evolution, hydrothermal alteration, mineral assemblages, mineral zones. |
| Abstract | Thermal evolution history of geothermal fields has been of keen interest for the purpose of drilling successful production wells. This paper aims to combine the data from down-hole temperature gradients, alteration mineral assemblages and hydrothermal mineral zones from Olkaria Northeast field to unravel the historical evolution of the thermal system. A systematic study of hydrothermal mineral assemblages found in six wells (with a total depth of 3000 m) of the Olkaria Northeast geothermal field exhibit a complex water-rock interaction processes. The region considered as the upflow zone is characterized by high formation temperatures (up to 280˚C) and the presence of green schist facies alteration mineral assemblages (chlorite, epidote, prehnite, actinolite) as the major phases. On the other hand, the region considered as the zone of lateral outflow, largely demarcated by wells drilled close to and intersecting, as well as those outside the proposed ring structure is characterized by relatively low formation temperatures (about 180-200˚C) and, low temperature minerals that overprints the high temperature ones. In the uplow zone, it is observed that the calculated formation temperatures corroborates with the alteration products. We infer the temperature changes in the geothermal system to be indicative of different thermal regimes. The tectonic structure of the studied area is caused predominantly by NW-SE and ENE-WSW directional forces. |