3D electromagnetic modeling of graphitic faults in the Athabasca Basin using a finite-volume time-domain approach with unstructured grids

Abstract

Uranium exploration in the Athabasca Basin, Canada, relies heavily on ground-based transient electromagnetic (TEM) surveys to target thin, steeply dipping graphitic conductors that are often closely related to the uranium ore deposits. The interpretation of TEM data is important in identifying the locations and trends of conductors in order to guide subsequent drilling campaigns. We present a trial-and-error modeling approach and its application to the interpretation of a data set acquired at Close Lake in the Athabasca Basin. The modeling process has two key tasks: building geo-electric models and computing their TEM responses. The modeling process is repeated with the geo-electric model being iteratively refined based on the match between three-component calculated and measured data from early to late times. To create geo-electric models, we first build a realistic geological model and discretize it using an unstructured tetrahedral mesh, with each mesh cell populated with appropriate resistivities. To calculate the TEM responses of the geo-electric model, we use a 3D finite-volume time-domain (FVTD) algorithm. We construct our initial model based on existing geologic information and drilling data. We show that this modeling process is flexible and can easily handle thin, steeply dipping conductive graphitic fault models with variable resistivities in the fault and background, and with topography. Our interpretation of the Close Lake data matches well with the trend and location of the main conductor as revealed by drilling data, and also confirms the existence of a smaller conductor which only caused noticeable anomalous responses in early-time horizontal-component data. The smaller conductor was suggested by previous electromagnetic data but was missed in a recent interpretation based on the modeling of only late-time vertical component data with plate-based approximate modeling methods.

Development and Consideration of 3D Transient Electromagnetic Forward Modelling for the Hydraulic Fracturing Monitoring

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Grounded source transient electromagnetic 3D forward modeling with the spectral-element method and its application in hydraulic fracturing monitoring

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Characteristic Research on Electromagnetic Response of Two‐Dimensional Complex Structure Targets Based on Meshless Method

“…There are mainly two kinds of models, one is the actual geological target, and the other is composed of several geological targets with regular shape. In general, the model is established based on unstructured grids or discrete nodes, and the high‐precision numerical simulation is realized by using the finite element method (FEM) (Cao et al., 2022; Key & Weiss, 2006; Li et al., 2017; Ye et al., 2018; Zhu et al., 2020), finite volume method (Ismagilov, 2015; Jahandari & Farquharson, 2015; Liu et al., 2019; Lu et al., 2021; Wang et al., 2016) or meshless method (Ji et al., 2018; Long & Farquharson, 2019; Nicomedes et al., 2021; Ortiz et al., 2021; Shams et al., 2022; Wittke & Tezkan, 2014). In these methods, the meshless method has been widely used in the modeling of complex structures in recent years due to its advantages such as no mesh generation and strong adaptability.…”