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Robust conductance estimates from spatial and temporal derivatives of borehole electromagnetic data
Get PDFThis paper is © 2019 Society of Exploration Geophysicists. The posting is available free of charge and its use is subject to the SEG terms and conditions: https://seg.org/Terms-of-UseThe conductance of an infinite uniformly conductive thin sheet can be calculated using the ratio of the temporal gradient and the spatial gradient in the normal direction of any component (or combination of components) of the secondary magnetic field. With standard borehole electromagnetic (BHEM) systems, the temporal gradient can either be measured or readily calculated from transient-magnetic-field data, and the spatial gradient in the normal direction can be estimated using adjacent stations. Synthetic modeling demonstrates that, for a finite thin sheet, the magnitude of the field provides a robust and reliable apparent conductance in typical three-component BHEM survey configurations. The accuracy in which the apparent conductance can be calculated is hindered by low spatial gradient signal values and can only be reliably estimated where the fields are large (i.e., in close proximity to the target). In a field example of BHEM data collected over a massive sulfide deposit in Sudbury, Ontario, Canada, the spatial gradient could be calculated over a roughly 100-m-wide zone, and a consistent apparent conductance could be calculated at each delay time using the magnitude of the field. Increases in the apparent conductance with increasing delay time are likely due to currents migrating into more conductive parts of the body. The apparent conductance values were also consistent with Maxwell models and time constant derived conductance estimates. This simple and robust apparent conductance is ideal as a first-pass estimate for target discrimination, grade estimation, and starting values for forward and/or inversion modeling.NSERC, Vale, Sudbury Integrated Nickel Operations, a Glencore Company, Wallbridge Mining, KGHM International, and the Centre for Excellence in Mining Innovation (CEMI)
New computational approaches for the transportation models
Get PDFThe Transportation model (TP) is one of the oldest practical problems in mathematical programing.
This model and its relevant extensions play important roles in Operations Research for finding the
optimal solutions for several planning problems in Business and Industry. Several methods have
been developed to solve these models, the most known is Vogels Approximation Method (VAM).
A modified version of VAM is proposed to obtain near optimal solutions or the optimum in some
defined cases. Modified Vogel Method (MVM) consists iteratively in constructing a reduced cost
matrix before applying VAM. Beside to MVM, another approach has been developed, namely the
Zero Case Penalty, which represents different penalty computational aspects. Through the research,
the results of methods-comparison studies and comparative analysis are presented. Furthermore,
special classes, the Unbalanced TP and the Transshipment models, were studied and solved with
different approaches. Additionally, we provide an application of MVM to Traveling Salesman
Problem
