Three Dimensional Inversions of Mt Resistivity Data to Image Geothermal Systems: Case Study, Korosi Geothermal Prospect

摘要

In real situation, the physical Earth is in three Dimension (3-D), a 2-D and 1-D Earth models may not therefore explicitly explain or represent the 3-D Earth in all situations. This is a simple and obvious reason why one needs a higher dimensional interpretation of MT resistivity data in modelling geothermal reservoirs. 2-D MT interpretation is commonly applied in geothermal exploration and in many cases, has successfully provided accurate information of geothermal reservoirs. However, due to complex geological environments, 2-D interpretation sometimes fails to produce realistic models, especially for deeper parts of reservoir. It is also the case in other natural resource exploration and geo-scientific research, such as oil exploration or underground water resources, volcanological studies etc. In this regard, 3-D interpretation techniques are now in high demanded for understanding of true resistivity structures in various geological applications. This paper describes (3-D) magneto telluric (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 modeling was done by the finite difference method, and the sensitivity matrix was calculated using the adjoint equation method in each iteration. The research has proved the practicality of 3D inversion with real field data to recover deeper resistivity structures in Korosi prospect. The results 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 and possible recharge zones for the system have been inferred.