Through integration of geological and geochemical data

this paper comprehensively analyzed the conditions

main controlling factors and characteristics of oil accumulation in the Chang 7 tight oil reservoir from such aspects as the tight oil distribution

physical properties

geochemical features of the oil source

reservoir characteristics and heterogeneity

trap conditions

and oil and water distribution.The following results were obtained.The Chang 7 tight oil reservoirs own the geological conditions and characteristics for the formation of quasi-continuous oil and gas accumulation.The Chang 7 reservoir interval contains high-quality source rocks

of which the Zhangjiatan shale in the Chang 7

3

layer is the best one.The outer boundary of the tight oil reservoirs is controlled by the distribution of the source rocks.The favorable area of hydrocarbon accumulation occur in where the thickness of hydrocarbon source rocks is over 20 m.The Chang 7 tight oil accumulation has favorable source-reservoir-seal assemblages and the gravity flow sandbodies occur in the mudstone or source rocks mainly in lenticular or stripped shapes

thus are advantageous in trapping oil and gas.The importance of trapping conditions is relatively low for the accumulation of oil in the Chang 7 tight reservoir

as the main seals are lithological

physical property and diagenesis boundaries.Dynamic trap is also an important trap type.Oil enrichment in the Chang 7 tight reservoir has no direct relationship with the local tectonic background

instead is mainly controlled by reservoir distribution and their physical properties.The high intensity of hydrocarbon generation

expulsion and charging results in the relatively high original oil saturation in the Chang 7 reservoir.Due to the influences of the origin material composition and diagenetic intensity

the Chang 7 reservoir is of strong heterogeneity

resulting in the poor differentiation of oil

gas and water

and a complicated oil-water contact in the tight reservoir.