One of the promising areas of exploration is entering new territories. One of the examples of poorly studied, but promising areas of Eastern Siberia is the Pre-Patom regional trough. At the moment, only a few hydrocarbon oilfields have been discovered within the Nyuya-Dzherba depression of the Pre-Patom regional trough, the productivity of which is established in the deposits of the Vendian-Lower Cambrian oil and gas complex, although the high prospects of this area are not in doubt.
Using the example of the Otradninskoye oilfield, located in the junction zone of the Nyuya-Dzherba depression and the Vilyuchanskaya saddle, complex overthrust nappe structures are shown, the formation of which took place under the influence of multidirectional tectonic movements. Their geological structure was influenced not only by subhorizontal movements, but also by subvertical ones overlaid on them. On the one hand, they contributed to overthrust the large blocks of the sedimentary cover, and on the other hand, they limited their distribution. Seismic survey data can reveal only large thrust dislocations. As a rule, the results of drilling in the zones of thrust dislocations show that the errors in the picks of reflecting horizons traced from seismic data are greater than the calculated accuracy of structural constructions, and reach 70-100 m. The section of subsalt deposits of the Cambrian within the dislocated part is characterized by a complex wave pattern, the interpretation of which is significantly difficult due to the presence in the section of many subhorizontal thrust dislocations with subvertical faults overlaid on them. To clarify the geological structure of this thrust zone, successive paleoprofiling was performed based on detailed well-log correlation, which confirms the presence of three or more repetitions of the section or its parts in individual wells. As a result, a consedimentary subvertical fault of the Vendian terrigenous complex was revealed in the underlying deposits, which subsequently manifested itself as a postsedimentary one. It is noted that the modern overthrust nappe structures in the Otradninskaya zone was formed in several stages. Initially, the Vilyuchanskaya saddle and the Nyuya-Dzherba depression experienced differently directed subvertical tectonic movements. The subhorizontal movements of the blocks that occurred later formed a complex multilevel thrust structure, the distribution boundary of which was a vertical fault formed in the Vendian time. The last stage was the vertical downward movement of the central part of the Otradninskaya structure.
References
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