Geochemistry of organic matter in between-the-salt deposits: northern block of Pripyatsky petroleum basin

The results of studies of core material taken from between-the-salt deposits of three wells drilled in the oilfield situated in the northern flank zone of the Pripyatsky trough are presented in the paper. Laboratory studies included pyrolysis before and after extraction, chromatography-mass spectrometry of chloroform extracts, petrographic studies of thin sections, determination of mineral composition and hydrocarbon-saturated porosity. Integrated interpretation of pyrolysis data before and after extraction, as well as molecular characterisation of extracts, allowed making the conclusion on marine origin of the Organic Matter of the studies wells and high oil generation potential of kerogen in the Petrikovsky-Yeletsky deposits of the Pripyatsky trough. In the case of the wells 1, 2, syngenetic Organic Matter is at the early stages of oil window (МК1 and МК1-2). In the well 3, the matter is more mature (МК2-3), and the oil generation potential is gone up to about 70 %. According to lithological (variations of carbonate, siliceous, and clay material content in the rocks) and geochemical characteristics of the Organic Matter (II and II-III type kerogen), high facies variability is typical of the deposits, which allows identifying a migration bitumoid according to its distinct molecular characteristics and degree of bitumoid maturity. Despite the approximately equal depth of occurrence, deposits from the wells 1, 2 contain different amount of migration bitumoid. This is first of all responds to different porosity and permeability and, evidently, to isolation of the accumulation because of tectonic processes. Porous reservoir in the well 1 contains an authigenic bitumoid from the same layer, but from the deeper horizons and having the higher degree of catagenetic transformation of the deposits