Application of MT Forward Modeling Responses for Time-Lapse Monitoring of the Subsurface Electrical Resistivity Changes

Document Type : Research Article

Authors

1 M.Sc. Student, Department of Earth Physics, Institute of Geophysics, University of Tehran, Tehran, Iran

2 Assistant Professor, Department of Earth Physics, Institute of Geophysics, University of Tehran, Tehran, Iran

Abstract

Monitoring fracture developments in the rupture area of an earthquake or unconventional energy reservoirs (ex: enhanced geothermal systems (EGS), coal seam gas (CGS) or shale- gas reservoirs, where massive fluid injection enhances ground permeability) are crucial to determine the stress field direction and optimize well placement and energy production. In addition to microseismic tomography, magnetotelluric (MT) monitoring method provides an independent verification tool to determine more constraints on fluid distribution and migration in target lithologies.
MT phase tensors (PT) and apparent resistivity tensors (RT) are calculated from impedance tensor. Assuming that geological and geo-engineering processes leave an electrically anisotropic volume in their corresponding damage zones, we investigate the time variation of RT and PT residuals for time-lapse MT monitoring purposes. First, we see how the PT and RT are influenced by layered models containing dipping and azimuthal anisotropy and then two synthetic models, representative of real earth situations including general 2D anisotropic features are studied.
The results of our numerical experiments show that despite the phase tensor ellipses, the real part of apparent resistivity tensor could discriminate between isotropic, azimuthally and generally anisotropic half spaces. Furthermore, the PT and RT residuals provide complementary tools for MT monitoring of the variations in the subsurface electrical resistivity structure. Although PT residuals could confine the anomalous region more accurately, the RT residuals determine whether a conductive or resistive variation has been occurred in the anomalous region.

Keywords

Main Subjects

References

Aizawa, K., Kanda, W., Ogawa, Y., Iguchi, M., Yokoo, A., Yakiware, H. and Sugano, T., 2011, Temporal changes in electrical resistivity at Sakurajima volcano from continuous magnetotelluric observations. Journal of volcanology and Geothermal Research, 199, 165-175.
Booker, J.R., 2014, The magnetotelluric phase tensor: A critical review. Surv. Geophys., 35, 7–40, doi:10.1007/s10712-013-9234-2.
Brown, C., 2016, Magnetotelluric tensors, electromagnetic field scattering and distortion in three-dimensional environments. Journal of Geophysical Research: Solid Earth, 121(10), 7040-7053.
Cagniard, L., 1953, Basic theory of the magnetotelluric method of geophysical prospecting. Geophysics, 18, 605–645.
Caldwell, T.G., Bibby, H.M. and Brown, C., 2004, The magnetotelluric phase tensor. Geophysical Journal International, 158, 457–469.
Eberhart‐Phillips, D., Stanley, W.D., Rodriguez, B.D. and Lutter, W.J., 1995, Surface seismic and electrical methods to detect fluids related to faulting. Journal of Geophysical Research: Solid Earth, 100(B7), 12919-12936.
Heise, W., Caldwell, T.G., Bibby, H.M. and Brown, C., 2006, Anisotropy and phase splits 625 in magnetotellurics. Phys. Earth Planet. Inter., 158, 107-121.
Heise, W., Caldwell, T.G., Bibby, H.M. and Bannister, S.C., 2008, Three-dimensional modelling of magnetotelluric data from the Rotokawa geothermal field, Taupo Volcanic Zone, New Zealand. Geophys J. Int., 173, 740–750.
Honkura, Y., Oshima, N., Matsushima, M., Serif, B., Tuncer, M.K., Tank, S.B., Celic, C. and Ciftci, E. T., 2013, Rapid changes in the electrical state of the 1999 Izmit earthquake rupture zone. Nat. Commun., 4, 2116, doi: 10.1038/ncomms3116.
Martí, A., 2013, The role of electrical anisotropy in magnetotelluric responses: from modelling and dimensionality analysis to inversion and interpretation. Surv. Geophys., 35(1), 179–218.
McFarlane, J., Thiel, S., Pek, J., Peacock, J. and Heinson, G., 2014, Characterisation of induced fracture networks within an enhanced geothermal system using anisotropic electromagnetic modelling. J. Volcanol. Geotherm. Res., 288, 1–7.
Ogaya, X., Ledo, J., Queralt, P., Jones, A.G. and Marcuello, A., 2016, A layer stripping approach for monitoring resistivity variations using surface magnetotelluric responses. J. Appl. Geophys., 132, 100–115.
Pek, J. and Verner, T., 1997, Finite-difference modelling of magnetotelluric fields in two-dimensional anisotropic media. Geophysical Journal International, 128, 505–521.
Pek, J. and Santos, F.A.M., 2002, Magnetotelluric impedances and parametric sensitivities for 1-D anisotropic media. Comp. Geosci., 28, 939–950.
Peacock, J.R., Thiel, S., Reid, P. and Heinson, G., 2012, Magnetotelluric monitoring of a fluid injection: example from an enhanced geothermal system. Geophys. Res. Lett., 39, L18403, https://doi.org/10.1029/2012GL053080.
Peacock, J.R., Thiel, S., Heinson, G.S. and Reid, P., 2013, Time-lapse magnetotelluric monitoring of an enhanced geothermal system. Geophysics, 78, B121–B130.
Thiel, S., 2017, Electromagnetic monitoring of hydraulic fracturing: relationship to permeability, seismicity and stress. Surveys in Geophysics, 38(5), 1133-1169.
Wannamaker, P., 2005, Anisotropy versus heterogeneity in continental solid Earth electromagnetic studies: fundamental response characteristics and implications for physicochemical state. Surveys in Geophysics, 26, 733–765.
Weckmann, U., Ritter, O. and Haak, V., 2003, Images of the magnetotelluric apparent resistivity tensor. Geophys. J. Int., 155, 456–468.
Yin, C., 2003, Inherent non-uniqueness in magnetotelluric inversion for 1D anisotropic models. Geophysics, 68, 138–146.
Journal of the Earth and Space Physics
Volume 46, Issue 4
February 2021
Pages 1-12

Files

Share

How to cite

Statistics