A Case Study Of Three-Dimensional Inversions Of Electrical Resistivity To Image Geothermal System In Korosi Geothermal Prospect-Kenya

Abstract

In real situation the physical earth is in three Dimension (3D), a two dimension (2D) and one dimension (1D) earth models may not therefore explicitly explain or characterize the 3-D Earth in all situations. This is a simple and apparent reason why one needs a higher dimensional interpretation of Magnetotelluric (MT) resistivity data in modelling geothermal reservoirs. 2D MT interpretation is frequently applied in geothermal assessment and in many cases has effectively provided accurate information of geothermal reservoirs. Conversely, due to intricate geological environments, 2D interpretation sometimes fails to produce representative models, especially for deeper parts of reservoir. It is also the case in other natural resource assessment and geo-scientific research, such as oil exploration or underground water resources, volcanological studies etc. In this regard, 3D interpretation techniques are now in high demanded for understanding of true resistivity structures in various geological applications. This research describes (3D) MT inversion for 147 MT data sets obtained from Korosi geothermal prospect. The inversion scheme was based on the linearized least-squares method with smoothness regularization. Forward modelling was done by the finite difference method, and the sensitivity matrix was calculated using the adjoint equation method at each iteration. The research has helped to recover deeper resistivity structures in Korosi geothermal prospect. The results further infer two geothermal reservoirs below Korosi - Chepchuk massif. A close correlation between major surface structures, fumaroles, and the 3D model is observed. Consequently, the extent of geothermal resource at Korosi - Chepchok prospect, the depth of the inferred geothermal reservoirs. This research will in future assist in future prospecting of Korosi Geothermal area.