Specific features of the deep structure of the Novo-Elkhov and Romashkin hydrocarbon fields based on geoelectric data

Abstract

In recent decades, problems of the active role of fluid factor in the structural transformations of lithosphere matter and its influence on the genesis of oil and ore deposits have been discussed in several publications [1‐3]. In our work, we present experimental results of electromagnetic studies, which allow us to analyze the structural‐tectonic links between the location of large (Romashkin and Novo-Elkhov) oil fields with trends in the distribution of electrical conductivity σ of rocks at depths from 10 m to 100‐120 km. Along with the mineral composition of rocks, conductivity σ is an important physical parameter that characterizes the rheological properties of the medium, such as convective heat and mass transport, filtration of melts in the asthenosphere, viscous and brittle deformations in the crust, hydrothermal circulation, and others. This new information about the composition and state of the Earth’s interior significantly complements the data on seismometry, deep seismic profiling, gravimetry, and other geophysical methods. Choice of the study region was not accidental. Both oil fields are located in the sedimentary cover of the South Tatarstan Dome (STD) in the East European Platform, where crystalline rocks of the basement are located comparatively not very deep (1750‐1850 m) below the surface. This territory has been studied well in the geological and geophysical aspects. Numerous wells drilled in this region include two superdeep ones (Fig. 1, wells 20000 and 20009). Borehole 20000 recovered soft and fissured basement rocks in the depth interval 4700‐5099 m, characterized by the circulation of highly mineralized solutions saturated with gases and hydrocarbons [2]. High level of low-temperature hydrothermal processing of the basement with the indications of hydrocarbon-containing fluids was found in Borehole 20009 at great depths [1]. Thus, geostructural factors of the STD indicate that geoelectric prospecting can be successfully used for solving the problem formulated in our work. Before the beginning of the work, we had some data concerning the electrical resistivity ( ρ ) of the sedimentary cover based on the borehole logging data [2] and the transient field sounding method [4]. However, they do not allow us to find the relation between the fluid saturation of the medium with specific features of the geotectonic structure in the consolidated part of the section. Such problems can be solved by applying the methods of deep geoelectric prospecting, including magnetotelluric methods.