Summary
A magnetotelluric research was carried out in the Xiongjing geothermal area, China, to clarify the geothermal structure underground. The CSAMT (CSAMT - Controlled Source Audiofrequency Magnetotellurics) survey was conducted. Based on an initial model of Bostick transformation, two-dimensional (2D) resistivity inversion was performed using the nonlinear conjugate gradient method. The inversion has revealed a low-resistivity zone beneath the compact slabstone, which indicated the location and depth of the geothermal reservoir. Temperature and porosity are considered as the main causes of this low-resistivity zone. As Yala fault went through the low-resistivity zone, a part of heat from deeper in the earth can be taken directly to the shallow formation through the groundwater circulation system.
Utilizing temperature log,further studies were carried out for the CSAMT section. High temperature response in the shallow formation indicated that there must be much more favorable reservoirs exit underground. Another low-resistivity zone in the west of the well was proposed for the next exploration target.
Introduction
Expanding our energy supply portfolio to include more indigenous and renewable resources is a sound approach that will increase energy security in a manner that parallels the diversification of ideals. Geothermal energy provides a robust, long-lasting option with attributes that would complement other important contributions from clean coal, nuclear, solar, wind, hydropower, and biomass (Tester et al., 1999). Geothermal resources are ideal targets for electromagnetic (EM) methods since they produce strong variations in underground electrical resistivity. In geothermal areas, the electrical resistivity is substantially different from, and generally lower than in areas with colder subsurface temperature (Oskooi et al., 2005).
Xiongjing geothermal field is located at the eastern margin of the Tibetan Plateau (Figure 1). Crustal deformation of the eastern Tibetan Plateau caused major strike-slip faults. Active faults in a region would be flow channels for geothermal energy (Bai et al., 2010). Geothermal systems have complex structures that control the flow of the fluids within the system. In order to further understand the properties of the system, it is important to investigate the subsurface structure thoroughly.
