Magnetotelluric Studies Of The Caldas Novas Geothermal Reservoir, Brazil

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Journal Article: Magnetotelluric Studies Of The Caldas Novas Geothermal Reservoir, Brazil

A magnetotelluric (MT) survey was conducted on the Caldas Novas geothermal reservoir located in the state of Goias, Central Brazil. The region of Caldas Novas is a popular tourist spot because of the occurrence of hot water springs. The purpose of the first MT survey in this area is to provide more information on the geoelectrical structure of this important geothermal reservoir. The MT method is a frequency domain technique that utilizes naturally occurring magnetic and electric signals as source to obtain a resistivity map of the subsurface. Since temperature and permeability are some of the factors controlling electrical resistivity, MT is widely utilized for surveying geothermal areas such as Caldas Novas. Data were acquired along two profiles crossing the Serra de Caldas (Caldas Mountains) with a total of 25 MT stations. Frequencies of acquisition were in the range from 0.008 to 176 Hz. Spacing between stations were usually around 5 kin. Apparent resistivity and phase data from the transverse electric (TE) and transverse magnetic (TM) modes were computed for both profiles. Very high (100,000 Q m) apparent resistivity values in the TM mode indicate distortion, possibly caused by 3-D resistive structures. In this work, we focus on Profile 2, which was acquired aligned at N40degreesE, approximately following the direction of weakness N50degreesE. Two-dimensional (2-D) inversion suggests a basin-like model with very high-resistivity block structures associated with concentric faulting below the Caldas Mountains inside a resistive basin that extends to depths of approximately 25-30 km. This model is in good agreement with gravity data and the available geological information in the area and can help delineate areas of new geothermal reservoirs. The high resistivity associated with the depression in the MT model can be interpreted as caused by the low-permeability quartzites that form the Caldas Mountains. Although the survey configuration does not allow for a full three-dimensional (3-D) interpretation, a 3-D resistivity model was constructed and the MT responses computed. The 3-D synthetic data explains the behavior of both the TE and TM modes in this faulted resistive environment. (C) 2002 Elsevier Science B.V. All rights reserved.

Patricia Pastana de Lugao, Emanuele Francesco LaTerra, Berthold Kriegshauser and Sergio L. Fontes

Published Journal 
Journal of Applied Geophysics, 2002




Patricia Pastana de Lugao,Emanuele Francesco LaTerra,Berthold Kriegshauser,Sergio L. Fontes. 2002. Magnetotelluric Studies Of The Caldas Novas Geothermal Reservoir, Brazil. Journal of Applied Geophysics. (!) .