Fracture Network and Fluid Flow Imaging for Enhanced Geothermal Systems Applications from Multi-Dimensional Electrical Resistivity Structure
We have developed an algorithm for the inversion of magnetotelluric (MT) data to a 3D earth resistivity model based upon the finite element method. Hexahedral edge finite elements are implemented to accommodate discontinuities in the electric field across resistivity boundaries, and to accurately simulate topographic variations. All matrices are reduced and solved using direct solution modules which avoids ill-conditioning endemic to iterative solvers such as conjugate gradients, principally PARDISO for the finite element system and PLASMA for the parameter step estimate. Large model parameterizations can be handled by transforming the Gauss-Newton estimator to data-space form. Accuracy of the forward problem and jacobians has been checked by comparison to integral equations results and by limiting asymptotes. Inverse accuracy and performance has been verified against the public Dublin Secret Test Model 2 and the well-known Mount St Helens 3D MT data set. This algorithm we believe is the most capable yet for forming 3D images of earth resistivity structure and their implications for geothermal fluids and pathways.
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- Technical Report
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- Related Information: Kordy, M. A., P. E. Wannamaker, V. Maris, E. Cherkaev, and G. J. Hill, Three-dimensional magnetotelluric inversion using deformed hexahedral edge finite elements and direct solvers parallelized on SMP computers, Part I: forward problem and parameter jacobians: Geophysical Journal International, 204, 74-93, 2016.Kordy, M. A., P. E. Wannamaker, V. Maris, E. Cherkaev, and G. J. Hill, Three-dimensional magnetotelluric inversion using deformed hexahedral edge finite elements and direct solvers parallelized on SMP computers, Part II: direct data-space inverse solution: Geophysical Journal International, 204, 94-110, 2016.Kordy, M. A., E. Cherkaev, and P. E. Wannamaker, Variational formulation for Maxwell’s equations with Lorenz gauge: existence and uniqueness of solution: International Journal of Numerical Analysis and Modeling, 12, 731-749, 2015.Kordy, M., V. Maris, P. Wannamaker, and E. Cherkaev, 3D edge finite element solution for scattered electric field using a direct solver parallelized on an SMP workstation, Proc. 5th International Symposium on Three-Dimensional Electromagnetics, Sapporo, May 7-9, 4 pp., 2013.Maris, V., and P. E. Wannamaker, Parallelizing a 3D Finite Difference MT Inversion Algorithm on a Multicore PC using OpenMP: Computers & Geosciences, doi: 10.1016/j.cageo.2010. 03.001, 5 pp., 2010.
- Research Org:
- University of Utah, Salt Lake City, UT (United States)
- Sponsoring Org:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Geothermal Technologies Office (EE-4G)
- Country of Publication:
- United States
- 15 GEOTHERMAL ENERGY magnetotellurics; finite elements; topography; forward modeling; inversion
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