Analysis and interpretation of magnetotelluric data in characterization of geothermal resource in Eburru geothermal field, Kenya

Abstract

The magnetotelluric method (MT) is an essential geophysical method for the exploration of geothermal systems. In this study, the MT method was used to assess the extent of the geothermal resource in Eburru geothermal field, Kenya, with the aim of delineating the electrical conductivity structure of the area. Dimensionality analyses demonstrated that the MT data could be interpreted using two-dimensional approaches, but some localized 3-D effects were detected. A 2-D MT inversion was performed to generate resistivity models of Eburru geothermal field. Given its ability to recover complex resistivity models for the ground, three dimensional (3-D) MT inversion was also carried out, and a joint interpretation made from the 2-D and 3-D models. Both inversion approaches gave similar results and revealed a low resistivity layer (<10 Ωm) interpreted as clay cap, and an intermediate resistivity beneath interpreted as a geothermal reservoir immediately below the low resistivity. The sequence here infers the presence of geological structures controlling the geothermal system. The resistivity profiles analyzed revealed a structure of low resistivity (<10 Ωm) interpreted as the fluid pathway. This structure trend an S-N direction which is consistent with the faults orientation in the field and serves as a conducting channel for transporting heat from the heat source to the shallow region approximately 2 km above sea level.