GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 3.3 ______ ___ GNGTS 2023 Direct Data Transform for EM Sounding Interpretation O. Calderón Hernández 1 , L. Socco 1 , E. Slob 2 1 Dipartimento di Ingegneria dell'Ambiente, del Territorio e delle Infrastrutture, Politecnico di Torino, Italy. 2 Faculty of Civil Engineering and Geosciences, Delft University of Technology, Netherlands Introduction Electromagnetic methods (EM) for the exploration of the subsurface have been widely used since the early 20th century to map the electromagnetic properties of the materials in the subsurface (Nabighian, 1988). In general, electromagnetic methods rely on inversion processes using 1D, 2D or 3D reference models. The inversion process is highly non-linear and is affected by solution non-uniqueness. Global search methods used to mitigate this issue are characterized by high computational costs. Over the last years, new techniques are being implemented for other geophysical data to directly estimate the geophysical model of the subsurface without using an inversion process. This can be achieved by obtaining relationships between the data obtained by geophysical surveys and the local physical properties measured in a location of interest. This approach has proved to be useful to retrieve geophysical models for self-potential (Florio 2018), for seismic surface wave dispersion data (Socco et al. 2017). The relationships between the model and the data can be applied as a rescaling tool to generate geophysical models in areas in which only surface measurements have been acquired by transforming the data into models. Based on these results we explore if the same approach could work for other data from geophysical prospecting techniques such as apparent resistivity obtained from EM measurements. Using the apparent resistivity measurements from an MT survey and the resistivity measured in an exploratory well, we want to assess if it is possible to obtain a transforming function that can be used to correct the misfit between the depth-apparent resistivity model obtained by MT surveys and the depth-resistivity ground truth model obtained from wells. In addition, we want to assess if the expression obtained can be used to retrieve an accurate resistivity model in nearby areas where only apparent resistivity measurements have been acquired. The applicability of the proposed methodology was assessed in different scenarios. The testing phase aims to retrieve an electrical model using apparent resistivity data measured in the vicinity of where the data from the exploratory well was acquired.