In order to better understand the characteristics and main controlling factors of hydrocarbon accumulation in low-permeability lithological reservoirs of Member 8 of Yanchang Formation(Chang-8)in Zhenjing area

Ordos Basin

we performed dynamic analysis of the Chang-8 lithological reservoirs based on study of burial history

thermal history

hydrocarbon generation history and diagenetic process.The evolution features of various hydrocarbon accumulation factors were clarified such as porosity

timing of traps

formation pressure of source rocks and the window of hydrocarbon charging kinetics.Finally

a comprehensive analysis of the dynamic process of hydrocarbon accumulation was performed.The results indicate that porosity of Chang-8 reservoir was of 20% during hydrocarbon accumulation in the middle Early Cretaceous and lowered progressively to current 12% due to reservoir tightening of the later evolution stage.The lithological traps of the Chang-8 were formed at the Late Jurassic and kept on developing till now

thus they are characterized by early formation and long process of development.The formation pressure of Chang-7 source rocks was 22 MPa during the period of hydrocarbon accumulation.It increased up to 35 MPa with a pressure coefficient of 1.5 at the end of Early Cretaceous and later lower progressively to normal pressure in the Neogene.The charging pressure of oil was 15 MPa higher than the pressure of resistance

and the window of hydrocarbon accumulation lasted for a long time from the Early Cretaceous to the end of Neogene.The formation of the low-permeability lithological reservoirs in the Chang-8 is controlled by the favorable temporal and spatial matching of between the factors and process of hydrocarbon accumulation.Physical properties of sandstone and charging kinetics are the main factors controlling hydrocarbon accumulation.