Data Transform for EM Sounding Direct Interpretation

The Magneto-Telluric method (MT) uses natural electromagnetic fields to investigate the conductivity structure of the Earth, however, as in any geophysical method, usually, an inversion process is required in order to generate a view of the structure which causes the data that has been retrieved, this process might be computationally expensive and very time consuming. The main goal of this work is to determine if it is possible to determine a polynomial function to relate MT measurements to a specific point in depth using several constraints. To do it a first depth approximation is obtained using theoretical relationships proposed previously and the difference between real and theoretical depths is studied. A polynomial regression is performed with several representations of the data to retrieve a mathematical expression that describes the difference between real and theoretical behavior as a function of the electrical properties in the subsurface. The applicability of the method was tested in two scenarios synthetic scenarios aiming to simulate the characterization phase of a field of interest in which only one exploratory well was drilled. The method was also tested in a real scenario in which the goal was to monitor the difference in the resistivity of the target layer due to water injection on a geothermal field. Based on all the tests that were performed, the proposed rescaling process should work for tracking resistivity changes in shallow targets. The proposed methodology should be studied in more detail with different approaches for the modeling phase. also trying to combine different sets of data might improve the overall capabilities of the proposed method. Overall further research is needed to determine the actual limits of the proposed rescaling process, as a first step, the method seems promising especially for identifying resistivity variations in shallow targets.