3D shear wave velocity structure of the southeastern segment of the Olkaria geothermal field using ambient noise tomography technique

Abstract:

Kenya is targeting 100% transition to renewable energy by the year 2030. Geothermal energy is identified as a critical driver to the energy transition with a resource potential of about 10000MWe occurring in the Kenya Rift Valley System(KRVS). The Olkaria geothermal field (OGF) is Kenya’s most prominent and productive field located in the central segment of the KRVS producing about 862Mwe. Plans are underway to increase its production to achieve the country’s target of 5000Mwe by 2030. However, limited information exists on the 3D structure and the intricacy of the geothermal motor driving the OGF leading to uncertainties in defining the impacts of ongoing development and exploitation of the field. Previous geoscientific studies and drilled wells are the basis for our understanding of the OGF. The studies identified a high-temperature geothermal system having a localised heat source of magmatic origin, a porous and permeable reservoir of trachytic composition, a clay cap of hydrothermally altered rocks on top of the reservoir and a recharge system dominated by faults and fracture networks. Nonetheless, these studies do not sufficiently delineate the subsurface structures characterising the OGF. In this work, we apply the ambient noise tomography technique to retrieve the 3D shear wave velocity structure of the OGF. The study will analyse continuous seismic data acquired with 15-broadband seismometers installed in the southeastern segment of the OGF installed before the operationalisation of the new power plant (Olkaria-V). We expect to retrieve baseline information of the geothermal system from the velocity structure before operation of Olkaria-V, which will be instrumental in the characterisation of the OGF. Expected results include information on the distribution of lithological units and their boundaries, fluid flow through the shallow crust, evidence of the influence of faults and fractures on flow, and possible imaging of the magmatic body hypothesised as the heat source driving the geothermal system in the OGF. Thereby improving our understanding of the geothermal system and help minimise the uncertainties in defining the impacts of ongoing development and exploitation of the field and enable the development of suitable filed monitoring and sustainable development plans for resource utilisation.