Orenburg Radial-Concentric Structure at Great Depth: Experimental Modeling under Fluid Dynamic Loads and Comparative Analysis of Sandstone Samples from Oil Fields in Western Siberia

Abstract

The study of the deep structure of the Orenburg radial-concentric structure in the basement of the Russian Platform based on seismotectonic and geomorphological data has been carried out. Interpretation of temporal regional seismic profiles crossing the structure was performed, identifying the main deep faults and measuring their dip angles. It was revealed that the radial-concentric structure is a large flower structure. Its structure involves the main multidirectional deep faults dipping at angles of \(\perp \)60°–85° and limiting horst or reverse fault zones in the basement. The hierarchy of faults structure has been established. Oil and gas fields are confined to the main deep dislocations of the Orenburg structure and represent flower structures of minor sizes. An experimental modeling of the formation of “flower” structures was performed based on the analysis of the results of studies using data from the acoustic emission activity of rocks and under the action of fluid dynamic loads performed at the “UIK-AE” unit (Institute of Geophysics, Ural Branch of RAS, Russia) on sandstone core samples from reservoir rocks of oil fields in Western Siberia. The developed model showed that the formation of flower structures can occur without horizontal shear due to lateral compression and deep pressure. With the help of the seismo-acoustic emission method, characteristic noise was recorded during the formation of cracks in core samples, sound attenuation before splitting, and then its sharp explosive increase from a break in the continuity of the rock. Analysis of the core of wells drilled within the Orenburg radial-concentric structure revealed signs of hydrothermal fluid discharge in the sedimentary cover rocks, such as wavy (or flat) layering, bizarre textures and intervals of breccias, shell-shaped inclusions, stillotite seams, fluid textures. It is concluded that the genesis of the Orenburg radial-concentric structure is associated with the impact of deep heat flows, fluids, high pressure and has a commonality with the explosive ring structures of shields and platforms.