Application of Electromagnetic Methods in Recognizing of Hydrogeothermal Conditions Inside Crystalline Massifs

Abstract

Geophysical methods are widely applied in geothermal water reservoirs prospection as well as in recognition of its resources and geological conditions of occurrence. There could be distinguished in Poland three areas of radically different geological characteristics that demand separate methodology of geological surveys with use of geophysical methods. These are: Polish Lowlands with predominant sedimentary formations of relatively simple geological structure, Flysch Carpathians with intensive fold and thrust type tectonics and Sudetes region with predominant role of crystalline rocks in geological structure. Hydrogeothermal reservoirs usually occur inside crystalline massifs in Sudetes area, the most frequently as fractured zones accompanying faults. The Sudetes Region is characterized by diverse and highly complex geological structure. High level of geological structure complexity causes strong difficulties in prospection works. Recently, magnetotelluric surveys were made in the Sudetic area in small scale but with good results. Four basic methodological variants of the method were applied: deep magnetotelluric soundings (MT/AMT), audiofrequency magnetotelluric soundings (AMT), continuous MT and AMT profilings as well as soundings and profilings with use of artificial source of primary field (CSAMT). Results of survey with use of magnetotelluric methods in recognizing of thermal and mineral water illustrate works made in Cieplice Śląskie-Zdroj, Polanica-Zdroj, Lądek Zdroj and Nysa areas. The mentioned above investigations as well as other surveys made on the commission of individual private investors confirm effectivity of MT methods in recognition of relatively deep (up to 3–4 km) fault zones as prospective for thermal and/or mineral water occurrence.