Benchmarking multiphysics software for mantle convection

NSERCPeer ReviewedNumerical simulations are a highly valuable tool for improving our understanding of mantle dynamics. COMSOL Multiphysics® is a commercial software suite designed to numerically model experiments featuring multiple branches of physics. This modeling approach applies to mantle convection, which can be viewed as a combination of fluid dynamics and thermodynamics. COMSOL® is of interest to the geoscience community due to its ease of use compared to other available codes, and it has been used in previous mantle convection studies. However, COMSOL® has not been extensively benchmarked for mantle convection. In this study, we confirm the accuracy of COMSOL® against several established benchmarks pertaining to a variety mantle convection features and geometries. Overall, we find reasonable agreement between the results from COMSOL® and reported benchmark data. This study may also serve the geoscience community as a guide for using COMSOL® to model mantle convection

Forward modeling of magnetotellurics using Comsol Multiphysics

NSERCPeer ReviewedMagnetotellurics is an electromagnetic geophysical method that has been widely used to study structures in Earth's subsurface. Numerical modeling of magnetotellurics is important for survey design, inversion, geological interpretation and many other aspects of geophysical studies. For example, modeling a subsurface conductive body in terms of its conductivity, geometry and dipping angle would yield substantial information on the phase response and sensitivity in an MT survey. While there are many different modeling techniques, the finite element method is most commonly used. In this effort, we present magnetotelluric models of layered Earth, uplift structures, auroral electrojets, and geomagnetically induced currents in power-line skywires using the commercial finite-element package Comsol Multiphysics. The AC/DC module in Comsol can be used to solve Maxwell's equations in the quasi-static limit for modeling the magnetotelluric response. One of the advantages of Comsol modeling is its Graphical User Interface (GUI), which allows users to solve complex single or multi-physics problems in a meshed domain. The use of Comsol also reduces the need for sophisticated computer coding when solving partial differential equations such as Maxwell's equations. In the effort presented here, we first discuss model validation for layered Earth geometries. We then present two examples of magnetotellurics modeling in impact crater and geomagnetically induced current studies. Numerical results were compared with analytical solutions or benchmark results whenever possible

Computer Modelling of Electromagnetics for Brine Layer Detection near Potash Mines

Safe mine expansion has been a reoccurring issue for potash mines in Saskatchewan over the years. One of the key issues facing mining operations is the potential for water inflow; this concern is even more serious specifically for potash mines due to the solubility of halite and sylvite minerals of which potash mines are largely comprised. The source of water in-flows are porous sedimentary formations above the mine. In this project we are proposing, through computer modelling, the possibility of remotely detecting the presence of these zones of water bearing strata, specifically water bearing carbonates, specifically using geophysical electromagnetic methods. Normally the sedimentary layers near potash mines in Saskatchewan are considered low-hazard for having porous water-bearing characteristics. However, under certain conditions there is the potential for unsaturated water to have been introduced both into the carbonates above the mine, and even into the salt of the prairie evaporate formation itself, enhancing and even creating porosity in the lithology. Areas of higher porosity have been identified in core samples and have been spatially tied to areas of absent overlying salt layers. Historically, several different geophysical techniques have been proposed to determine the presence of water-bearing anomalies near mine. The techniques that have been tested for this purpose include 3D resistivity, frequency-domain electromagnetics, and time-domain electromagnetics. In many cases these efforts have produced effective results. This project sought to investigate the potential of using time-domain electromagnetics to determine the presence of water-bearing anomalies within the carbonates of the Dawson Bay Formation which lie above the Prairie Evaporite Formation. This project consisted of two principal components. One is computer modelling of time-domain electromagnetics in a full-space or mine environment performed in COMSOL Multiphysics, the other, as part of a Mitacs Accelerate internship that the student author participated in concert with Nutrien, under the joint supervision of Dr. Samuel Butler of the University of Saskatchewan and Randy Brehm of Nutrien, is an in-mine time-domain electromagnetics survey conducted in an area of suspected Dawson Bay water-bearing anomalies. The survey found a decisive conductive zone in the vicinity of the suspected carbonate anomaly. Subsequent computer modelling, both forward and inverse, has been performed to attempt to constrain the location of this anomaly relative to the Prairie Evaporite salt