The Nord-Wets Ltd. Has been carrying out regional MT surveys at the Eastern European Craton since 1997. The surveying is a part of a governmental project and is funded by the Ministry of natural resources. The largest volume of the MT data has been collected in Volga region (over 5000 sites; see the map).

Seismics, geochemichal methods and gravity are applied along with MT for regional studies. The main goal of the investigations is to obtain information on the sedimentary cover structure and to locate the prospective areas in order to conduct detailed oil and gas exploration surveying within them.

The sedimentary cover in the Volga region consists of three main horizons. The middle (containing terrigenous sediments and reefs in Permian, Carboniferous and Upper Devonian) and lower (terrigenous Devonian and Riphaean) horizons are of key interest in the context of hydrocarbons prospects.

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The seismic and electrical logging data are taken into account when the MT data are interpreted. In this case main geoelectric (which are also seismic) boundaries are locked while the resisitivity values are the subject for optimization. Such an approach provides the possibility o obtain more detailed and reliable information on geoelectric structure along the profile.

Some results of MT investigations in Volga region are shown in figures below.

The CD and EF lines are crossing eastern and southern flanks of Tokmov Arch of the Volga-Urals Antelise. Zones of the appearance of the terrigenous alternations in Carboniferous along with pinch of the terrigenous Middle Devonian and changes in the resistivity of Riphaean have been revealed as the result of MT-data interpretation. This could be an evidence for reservoir properties changes.

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The GH line is located in the axial part of the Ryazan-Saratov trough. The geoelectric section clearly shows it’s block pattern. Deep troughs filled with Riphaean, which could significantly differ in it’s properties, are changing each other. Rather large thickness of the terrigenous strata in the mainly carbonate Carboniferous are imaged within the southern part of the profile.

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