Enrichment characteristics and major controlling factors of hydrocarbons in the Neogene of Raoyang Depression,Bohai Bay Basin

Based on accumulations and distributional characteristics of hydrocarbons in the Neogene of the Raoyang Depression,Bohai Bay Basin,we discussed accumulation characteristics and major controlling factors of Neogene hydrocarbons.Oil and gas in the Neogene of the study area are mainly derived from the lower Es1 and upper Es3 source rocks of the Paleogene.Laterally,hydrocarbons are accumulated in zones either adjacent to the center of primary hydrocarbon-generative sub-depressions or with stronger Neogene fault activities and an appropriate sand-to-shale ratio,where hydrocarbons are distributed in a banded pattern.Vertically,hydrocarbons are mainly accumulated in the Neogene Guantao Formation,showing a complementary correlation with hydrocarbon distributions in underlying Paleogene and pre-Tertiary strata.Major controlling factors of hydrocarbon accumulations include: the oil and gas distribution in general is controlled by primary hydrocarbon-generative sub-depressions;the vertical transport capacity and concentrated blocks of hydrocarbons are dominated by the time span and intensity of Neogene fault activities;the accumulation extent of Neogene hydrocarbons is affected by the development of Paleogene clasolite and pre-Paleogene carbonate buried-hill traps;and the height of oil columns in Neogene reservoirs is dependent on the thickness and quality of cap rocks.