Study of magnetic anomalies of the southeastern part of the Russian Platform and their connection with the radial-concentric structures of the foundation

Abstract

Relevance. Many magnetic anomalies of the southeastern part of the Russian Platform have an arc-shaped structure and coincide with the contours of radially concentric structures in the foundation that are promising in terms of oil and gas potential. Oil and gas deposits are equally confined to magnetic extremes of different signs. The configuration of some hydrocarbon deposits repeats the shape of magnetic field anomalies. The maximum values of the anomalous magnetic field are associated with the centers of the Orenburg and Middle Volga radial-concentric structures. The aim of the work was to study the nature of magnetic anomalies in the southeastern part of the Russian Platform and their connection with radial-concentric structures. Methods. The analysis of geological and geophysical information of the south-west of the Orenburg region, including data from seismic exploration, gravity exploration, monitoring of modern geotectonic processes, gas-geochemical, remote, geomorphological studies, well drilling results, was carried out. Magnetometric measurements were performed in a parametric well drilled on the slope of a magnetic anomaly within the Sverdlovsk radial-concentric structure us- ing a complex borehole magnetometer-inclinometer MI-3803M (Bulashevich Institute of Geophysics, Ural Branch of the Russian Academy of Sciences, Russia). Results. Analysis of geological and geophysical information and drilling data in the southwestern part of the Orenburg region showed that magnetic anomalies are associated with the deep structure of the foundation. The coincidence of neotectonic disturbances of the Orenburg radial- concentric structure and the contours of magnetic anomalies indicates their deep origin. Modern seismic events are often associated with zones of sharp change in the values of magnetic anomalies. Magnetic anomalies do not illustrate the structure of the foundation surface, while on temporary seismic sections, high-amplitude deep faults correspond to a change in the values of magnetic field anomalies. The results of drilling and magnetometric stud- ies of a parametric well that uncovered the foundation in the Pre-Ural regional deflection on the slope of a local magnetic anomaly show that the well is located in the oil and gas prospective zone of a deep fault and, possibly, a flower structure. According to the results of magnetometric studies, a powerful magnetic object is located below the bottom of the well, which causes an increase in the level of the vertical component of the magnetic field. It is concluded that a sharp change in the values of magnetic anomalies and their configuration can be attributed to new criteria for identifying hydrocarbon deposits. According to the map of magnetic anomalies, a new promising Samara radial-concentric structure has been identified, recommended for further study.