The genetic mechanism and hydrocarbon accumulation of quality reservoirs in the deep complex Paleogene re-servoir rocks of Dongying Sag are studied by core observation

thin section analysis

petrophysical testing

isotope testing and well testing.The studies show that the secondary porosity resulted from alternative dissolution of acid-alkaline fluids improved the local physical properties of deep reservoirs to some extent and is the key to the formation of the deep quality reservoirs.The reservoirs in different deep sequences have different genetic mechanisms

reflecting the differences in ori-ginal components

fluid environment

source-reservoir combination and other conditions.The quality reservoirs of red beds in fulvial-alluvial fans of the initial rifting sequences were formed in alkaline environment and contacted laterally with source rocks

featuring in not only the dissolution of large amount of feldspar and carbonate

but also the intensive dissolution of quartz.The quality coarse clastic reservoirs of steep slope fan delta and underwater fan in the expanded rifting sequences are in interfingered contact with source rocks

and connected with deep alkaline fluids through basin-controlling faults

featuring in the erosion of large amount of feldspar and carbonate but just a small amount of partial quartz.The quality reservoirs of beach bar sands and turbidite in the expanded rifting sequences mostly occur in the source rocks

featuring in the erosion of feldspar and carbonate.The fault terrace zones on ramp are on the major migration pathway

thus the quality red reservoirs juxtaposing with the source rocks are favorable for hydrocarbon accumulation.The quality coarse clastic reservoirs in middle-fan that are screened by root-fan of steep slope are favorable for hydrocarbon accumulation.The quality beach bar sands and turbidite reservoirs that are in source rocks with high pressure are favorable for hydrocarbon accumulation.