Profile Transient Electromagnetic Soundings over 3D Structures: Methodology, Modeling, and Experiment

Abstract

In this paper, the possibilities of reconstructing 2D cross sections based on the data of the profile soundings by the transient electromagnetic method with a single ungrounded loop are illustrated on 3D models. It is demonstrated that the data processing of field measurements and recovery of the geoelectrical profile to consist of three main stages: (i) transformation of the measured profile responses into resistivity pseudoprofiles as a function of time and then stitching of the pseudoprofiles as a function of depth, (ii) 1D inversion of responses into a layered 1D profile taking into account the number of layers and their positions determined by the pseudoprofile, and (iii) refinement of the pseudoprofile using 3D inversion with the initial parameters of blocks determined by 1D pseudoprofiles. Transient electromagnetic soundings make it possible to study geological media within a local area at the sounding depth. The structure of the medium outside this area has a little effect on the measurement results. Such localization allows reconstruction of the electrical structure of a 3D medium using 2D profiles with minimal distortion due to the lack of information on the medium outside the profile when measuring transient responses.