Study on 3D forward modeling & inversion of surface-borehole electromagnetic data.

Liu, Chong (2021). Study on 3D forward modeling & inversion of surface-borehole electromagnetic data. (Thèse de doctorat). Université du Québec en Abitibi-Témiscamingue. Repéré dans Depositum à https://depositum.uqat.ca/id/eprint/1294

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Résumé

The purpose of this research is to develop an interpretive tool to meet the requirements of deep mineral exploration. Therefore, we carried out a series of research work as part of a doctoral training program and achieved the relevant objectives below.

The core of this doctoral thesis is the development of 3D modeling tools to interpret the electromagnetic data collected in boreholes. First, a 3D model creation tool is designed, with which we can easily build a 3D geological model from sections and quickly discretize it. The sections could be true geological cross-sections or from a conceptual geological model. The utility of this tool is to facilitate the tests of the algorithms developed within the framework of this thesis, in order to model the electromagnetic responses in various geological situations and allow to easily change the parameters of the geophysical measurement system.

Two parallelization algorithms, MPI-based and hybrid MPI/OpenMP-based methods, are designed for surface borehole time domain electromagnetic (BHTEM) forward modeling. The BHTEM responses are calculated from anomalous regions distributed in a 3D model (discretized into cells). The forward modeling additionally uses multiple meshes, fine meshes are used for the anomalous region in the high-frequency range and coarser meshes for geological background in the low-frequency range. Based on varying meshes for different frequency ranges, the parallel computation greatly reduces the computation time of the TEM forward modeling.

An optimal survey design benefits from quick forward modeling. We found that the target BHTEM response depends upon the transmitting pulse width, target time constant, and the duration of measurement time. We proposed the formula with respect to the three variables to design optimal pulse widths in advance for different off-times in order to maximize the efficiency of TEM measurement in the field.

Finally, a 3D BHTEM inversion algorithm is developed based on the Gauss-Newton method with high spatial resolution. By introducing the isosurface, neighborhood anomalies search, 3D trace envelope, and false targets elimination into the inversion process, the predicted model is improved through iterations and interactions between the computation and the user intervention.

Type de document:	Thèse ou mémoires (Thèse de doctorat)
Directeur de mémoire/thèse:	Cheng, Li Zhen
Codirecteurs de mémoire/thèse:	Erchiqui, Fouad et Chouteau, Michel
Mots-clés libres:	Surface-borehole TEM ; Inversion ; Forward modeling
Divisions:	Génie > Doctorat en ingénierie
Date de dépôt:	01 sept. 2021 14:51
Dernière modification:	17 sept. 2021 13:12
URI:	https://depositum.uqat.ca/id/eprint/1294

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