Geophysical research: article

Аnnotation: Studies of sedimentary basins using the magnetotelluric (MT) sounding method have been carried out for more than 50 years. Over the past fifteen years the number of MT surveys increased manifold, which prompted the development of MT data acquisition technology, inversion and interpretation methods and the efficiency of the method achieved a new level. MT sounding method have become in high demand in the market of geophysical services. The application of MT sounding is especially effective in the regions with basalt traps, salt tectonics and folded belts, i.e. in the areas where seismic methods are confronted with certain difficulties. The paper deals with special features of sedimentary rocks electrical conductivity and its dependency on petrophysical and hydrophysical parameters: clay content, porosity, fluid salinity and temperature. Specific requirements to MT studies technology in sedimentary basins are formulated: wider period range in use and significantly smaller distances between acquisition sites to compare with deep academic studies. MT analysis and interpretation technology includes: dimensionality analysis, static shift correction, multistage data inversion and geological interpretation of resistivity structure. The use of a priori geological and geophysical information is essential. The results of a geological interpretation of MT sounding data obtained in the Parana Basin and in the Eastern Siberia (the biggest inland areas of basalt traps) are given as examples. MT data interpretation enables to study structure of sedimentary basins in details and to identify main geological formations. Also the results of MT investigations in the Taimyr, where several new objects with good prospect for oil and gas were revealed and resistivity anomalies probably related to gashydrates were singled out, are presented. The basic directions of the further development of the MT method to enhance the efficiency of studying sedimentary basins were formulated.