Role of the tectonomagmatic factor in formation of giant hydrocarbon accumulations in the East Barents basin

Abstract

In terms of tectonics, the East Barents basin(megabasin) represents an extended (~1400 km)wedgeshaped ~500 to 300kmwide structure thatcrosses the West Arctic continental–marginal platform in the meridional direction and is truncated by asystem of pericratonic depressions of the East European Platform on the beam of the Kola Peninsula.According to geological–geophysical data, the Paleozoic–Mesozoic sedimentary cover of the basin is presumably >20 km thick [11, 13], although its exactthickness is unknown so far. Approximately 14 km ofthe sedimentary section are represented by Upper Permian–Mesozoic terrigenous sediments, 11 km ofwhich correspond to the Upper Permian–Triassicsequence. The underlying Paleozoic complex is composed of terrigenous–carbonate and carbonate facies.In the opinion of many researchers, such a giantsize of the basin and its sedimentary prism implydevelopment of significant hydrocarbon accumulations in the latter. These assumptions are confirmed bythe discovery of five hydrocarbon fields in the southernhalf of the megabasin (Fig. 1); they are representedonly by gas and gas condensate accumulations confined to Mesozoic sedimentary complexes [2–4, 8, 9,12, 13, 15, and others].Two gas fields (large Murmanskoe and mediumSeveroKil’dinskoe) are located in the southwesternperipheral part of the South Barents Basin in its slopeand nearslope zones, where productive formationsare represented by Triassic sediments.Another group of accumulations associate with thesocalled Shtokman–Lunin Sill (Uplift) [2–4], whichseparates the South and North Barents basins. Withrespect to hydrocarbon reserves, the Shtokman andLedovoe gas condensate and Ludlovskoe gas fieldswith Jurassic productive formations are classed withunique and large categories, respectively.For hydrocarbon accumulations of both groups,source formations are considered to be represented byPermian–Triassic sediments; in the last case, theyprobably also include Lower Jurassic sediments withhumic and sapropelic organic matter.With respect to the economic potential and geological prerequisites for further searches for analogs andspecifying the factors responsible for their formation,of particular interest is the second group of hydrocarbon accumulations confined to the elevated boundaryzone between the two basins (Fig. 1). These problemsare considered in several publications [1–4, 9, 15],where factors responsible for the formation of suchgiant hydrocarbon accumulations are characterized bya different degree of substantiation and from differentstandpoints.In this connection the following question arises:what are the peculiar features that determine the geological structure of hydrocarbon fields in the Shtokman–Lunin Uplift?It should primarily be noted that all the local anticlinal trap structures hosting hydrocarbon accumulations are distinctly reflected in Triassic and Cretaceoussediments as well as in the surface topography of Jurassic sequences with an amplitude of approximately100–200 m (seismic reflector B, Fig. 1). They are isometric in plan and from 500 to 1500 km