Petroleum source rocks and hydrocarbon potential of Lower Palaeozoic deposits in Laisky swell of Denisovsky trough, Timan-Pechora petroleum province (based on Kerlaiskaya-1 well data)

Deposits of the Upper Ordovician-Lower Devonian carbonate play in the Denisovsky trough territory are regarded as exploration targets promising for hydrocarbon accumulations. Their productivity was determined in the West Komandirshorsky-II field and in the Kerlaisky area, where light oil inflow was obtained in exploratory Well 1 from the Upper Silurian deposits. To assess hydrocarbon potential of the Lower Palaeozoic deposits and possibility of the formation of indigenous accumulation, core and oil samples from Kerlaiskaya-1 well were studied using coal petrography, organic, and isotope geochemistry methods. In the well column studied, petroleum source rocks were identified in the Upper Silurian and Upper Frasnian formations. They are initially classified as medium to highly productive. Organic petrology (RVeq, %) and organic geochemistry (Tmax, 20S/(20S + R), αββ/(αββ + ααα), 22S/(22S + R), Ts/Tm, MPI-1) data are altogether indicative of that fact that the organic matter of source rocks has reached the high degree of catagenetic transformation (МC3 end to МC4 end), which corresponds to the final stages of main oil generation phase. Organic matter composition represented only by bituminite and its transformation products, as well as n-alkanes distribution with predominance of odd homologues (n-С15, n-С17) and light isotope composition of organic carbon (δ13С = -32…-28 ‰) in bitumoids of rock and oil are indicative of the same-type algae and plankton source. It is found that in accordance with n-alkanes and n-alkylcyclohexanes distribution, especially predominance of odd С15 and С17 in hydrocarbons, as well as lighter isotope composition of saturated fraction, oil correlates with the organic matter of the Upper Silurian petroleum source rocks. The known high generation potential of the Upper Silurian deposits as well as possibility of indigenous hydrocarbon accumulations, together with the determined oil and gas content in different areas of the Denisovsky trough (Kerlaisky, West Komandirshorsky-II fields) give grounds for considering the Lower Palaeozoic deposits as an promising target for geological exploration and discovery of new accumulations