MOLECULAR FEATURES OF OILS FROM THE EMBA REGION (PRECASPIAN BASIN): ORIGIN, THERMAL MATURITY, AND GENETIC CORRELATION

The Precaspian Basin, including its southeastern part, represents a unique oil and gas province with giant fields such as Tengiz and Kashagan, whose reserves are estimated in billions of tons. Despite extensive research in the region, questions regarding the genetic affiliation of oils and their paleoformation conditions require additional geochemical analyses of oil samples. To conduct a comprehensive geochemical characterization and genetic correlation of oils from the Emba region, with a focus on molecular marker analysis to reconstruct oil formation conditions seven oil samples were taken from various stratigraphic horizons. The study employed advanced analytical techniques gas chromatography (Agilent 7890B) for detailed analysis of n-alkanes and isoprenoids (pristane and phytane) and gas chromatography-mass spectrometry in selected ion monitoring mode m/z 191, 217 for terpane and sterane identification, respectively. Particular emphasis was placed on the computation of essential geochemical indices isoprenoid, hopane, and sterane isomerization ratios along with the generation of diagnostic plots. The results indicate a marine origin of the studied oils with dominant carbonate source rocks (C₂₇ steranes > 30%, C₂₉/C₃₀ hopanes > 1). Pr/Ph ratios (0.79–1.07) and elevated C₃₅ homohopanes suggest formation under reducing conditions. Thermal maturity parameters (Ts/(Ts+Tm) = 0.15–0.64; C₂₉ ββ/(αα+ββ) = 0.55–0.71) confirm that the samples were generated during the oil window. Genetic correlation grouped all samples into a single oil family of marine carbonate origin. The findings are practically significant for predicting analogous accumulations in the region.