Identification of faults and geodynamic conditions of their formation for the detection of oil and gas prospects (case study from a local area of the south of the Siberian platform)

Introduction. One of the key problems in the search and exploration of oil and gas fields of the Siberian platform is a lack of substantiated fault maps that clarify the models of the geological structure of objects. Important factors are the geodynamic conditions of the formation of tectonic faults that affect the hydrocarbon accumulation.

Aim of this work was to map the fault-block structure of a local area of the Southern Siberian platform and reconstruct stages of its formation to identify discontinuities favorable for localization of oil and gas along them. The area is located 50 km southwest of the city of Ust-Kut.

Materials and methods. Tectonophysical analysis of data on faults and fracturing, river and relief lineaments derived from interpretation of topographic maps, satellite images and digital elevation models (from https:// search.earthdata.nasa.gov/search?q=SRTM); work materials of 2D seismic exploration, electrical exploration (ZSB method, volume — 1038 points), magnetic exploration (measurement step 250 m) and gravity exploration (measurement step 500 m).

Results. As a result of the research, we identifi ed six main stages of tectogenesis, which are associated with tectonic events in the Sayan-Baikal and Baikal-Patom folded regions of the Central Asian mobile belt. For each main stage, faults that could have formed or become active in a certain geodynamic setting were identified, and the slip type along them was reconstructed. According to the obtained tectonophysical model, the steeply dipping and inclined fault zones trending north-west, north-north-west, submeridional, north-north-east and north-east were favorable for saturation with hydrocarbons in the studied area at different times. The north-easttrending faults were synsedimentary and, at the stage of formation of hydrocarbon deposits, could increase the permeability of the strata. Migration of fl uids with their possible accumulation along the NW faults could have occurred in the fourth stage of shear deformation with the north-west compression axis and the north-east extension axis.

Conclusions. The studies carried out to map faults and study the stressed state of the earth’s crust for different time stages of the development of territories make it possible to more effectively search for oil and gas deposits, and the results may be useful for other adjacent territories that are promising for hydrocarbon exploration. 

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