Lithology and formation conditions of paleogene rocks in the Dongying Depression (Bohai Bay Basin, China)

Abstract

The Dongying Depression is one of the largest depressions in terms of hydrocarbon reserves not only within the Bohai Basin, but also in the whole Pacific region. This is related to the inherited pattern of geological evolution, as well as the optimal combination of oil source rocks, reservoirs, and caprocks, which alternate in both lateral and vertical directions. Diversity of the lithofacies composition of Eocene and Oligocene sediments in thick (proluvial, deltaic, fan deltaic, and deep-water) hemipelagic and gravitational deposits in the composition of various fans, predetermined the wide distribution of sandstone and gritstone beds with good filtration-capacity properties. The beds were filled with hydrocarbons that migrated from the adjacent layers of oil shales and clays. The role of the principal reservoirs was played by sandstones, which were deposited in distributary channels of Eocene deep-water fans. The detailed study of these underwater fans will make it possible to expand the reserves of hydrocarbons explored now in the Dongying Basin.