Estimation of the Sub-Surface Temperature by Means of Magnetotelluric Sounding

Abstract

Estimation of temperature in the Earth's interior is usually based on the ground heat flow data and assumptions on the vertical temperature gradient. Meanwhile, in geothermal areas characterized by significant fluid migration this approach may fail. We have developed an alternative way based on incontact temperature estimations using the measurements of magnetotelluric (MT) field on the Earth's surface. Basing on the neuronet analysis of MT and temperature data measured at the Bishkek geodynamical testing ground in the northern Tien Shan, a feasibility of indirect electromagnetic geothermometer is substantiated. An optimal technique for MT measurements and involvement of temperature logs available is developed. This technique provides a reduction of the remote temperature estimation errors down to their minimum level. It is shown that the use of 6-8 temperature logs for calibration of electromagnetic data results in 12% relative error of the temperature estimation, whereas availability of prior geological information about the region under study makes it possible to decrease this error furthermore. Practical application of this method will enable one, first, to refine the temperature estimates in cases when the amount of temperature logs available is insufficient; second, to perform more precise temperature prediction in extrapolation mode; third, to monitor the well temperature basing on surface observations of MT field and, at last, to carry out contactless remote estimation of temperature in wells in the regions with extreme conditions unsuitable for traditional geothermometers.