Changes

''Magnetotellurics'' (''MT'') is an electrical method of geophysical exploration that makes use of naturally occurring electromagnetic energy propagating into the earth to determine the electrical resistivity of the subsurface.<ref name=pt07r42>Orange, A. S., 1989, Magnetotelluric exploration of hydrocarbons: Proceedings of the IEEE, v. 77, n. 2, p. 287–317., 10., 1109/5., 18627</ref><ref name=pt07r61>Vozoff, K., ed., 1986, Magnetotelluric methods: Tulsa, OK, Society of Exploration Geophysicists, Geophysics Reprint Series, 763 p.</ref> The low frequency electromagnetic field is measured, and the wave impedance is calculated and expressed in terms of the resistivity of the subsurface. The depth of investigation is a function of the frequency of the electromagnetic wave, taking advantage of the fundamental principle that the lower the frequency of a wave, the deeper the penetration into the crust. MT surveys generally involve applications that range in depth from a few hundred meters to [[length::10 km]] or more.

''Magnetotellurics'' (''MT'') is an electrical method of geophysical exploration that makes use of naturally occurring electromagnetic energy propagating into the earth to determine the electrical resistivity of the subsurface.<ref name=pt07r42>Orange, A. S., 1989, Magnetotelluric exploration of hydrocarbons: Proceedings of the IEEE, v. 77, n. 2, p. 287–317., 10., 1109/5., 18627</ref><ref name=pt07r61>Vozoff, K., ed., 1986, Magnetotelluric methods: Tulsa, OK, Society of Exploration Geophysicists, Geophysics Reprint Series, 763 p.</ref> The low frequency electromagnetic field is measured, and the wave impedance is calculated and expressed in terms of the resistivity of the subsurface. The depth of investigation is a function of the frequency of the electromagnetic wave, taking advantage of the fundamental principle that the lower the frequency of a wave, the deeper the penetration into the crust. MT surveys generally involve applications that range in depth from a few hundred meters to [[length::10 km]] or more.

The resistivity versus depth cross section developed from MT data can be interpreted in terms of rock type. Spatial variations in the resistivity-depth relationship observed at closely spaced locations on the surface can be interpreted in terms of subsurface geological structure. While MT cannot be used to detect oil directly, the identification of favorable rock types and the presence of geological structure capable of trapping hydrocarbons is critical to successful exploration. MT data are interpreted using forward and inverse modeling techniques. Resolution is considered low when compared with exploration or exploitation seismology, but may be adequate in certain instances to provide valuable information concerning reservoir geometry, rock characteristics, and a regional geological framework. For the larger deep reservoirs, MT may be considered as a possible candidate for EOR monitoring if model studies indicate that the resistivity changes over time associated with the operation are within the resolving power of the method.

The resistivity versus depth [[cross section]] developed from MT data can be interpreted in terms of rock type. Spatial variations in the resistivity-depth relationship observed at closely spaced locations on the surface can be interpreted in terms of subsurface geological structure. While MT cannot be used to detect oil directly, the identification of favorable rock types and the presence of geological structure capable of trapping hydrocarbons is critical to successful exploration. MT data are interpreted using forward and inverse modeling techniques. Resolution is considered low when compared with exploration or exploitation seismology, but may be adequate in certain instances to provide valuable information concerning reservoir geometry, rock characteristics, and a regional geological framework. For the larger deep reservoirs, MT may be considered as a possible candidate for EOR monitoring if model studies indicate that the resistivity changes over time associated with the operation are within the resolving power of the method.

==Applications for development geology==

==Applications for development geology==