Research On The Hydrocarbon Accumulation Process And Mechanism Of Tight Oil Of Lower Cretaceous In The Qingxi Sag Of Jiuquan Basin

The Qingxi sag,locating in the western of the Jiuquan Basin,has large exploration potential of tight oil with good forming conditions of tight oil.But the exploration of tight oil in Qingxi sag is still in infancy stage with low degree of understanding and unclear exploration targets.Therefore,it is of great significance for exploring and predicting the dessert spot of tight oil in Qingxi sag to research on Qingxi sag accumulation conditions and study further in tight oil accumulation process and mechanism.The division standard of source reservoir assemblage is established based on the study of the characteristics of source rocks and reservoirs,and a total of 8 types of source reservoir assemblage in 3 categories has been divided in view of the study area.The characteristics of distribution of tight oil including distributing Along the fracture,large area spreading and no unify oil-water interface are found based on the statistics and analysis of the oil testing data of 12 target layers in the study area.Balanced section technique is applied to recover the tectonic evolution history of the study area and the hydrocarbon accumulation process of tight oil has been recreated by IES basin modeling software.The physical modeling experiment for hydrocarbon accumulation shows that according to oil-bearing and hydrocarbon-charging efficiency,the“sandwich” type of source reservoir assemblage is better than the “source below reservoir” type and the “source above reservoir” type.And with the analysis of accumulation conditions and accumulation process in the study area,the experimental results help illustrating the accumulation mechanism and accumulation mode: source and reservoirs are closed or united,hydrocarbons are propelled by pressure difference,transported through microfractures and micropores,and accumulated inhomogeneously and differentially.Synthesized all the research above,it is indicated that the main controlling factors influencing tight oil accumulation include lithological association,fracture development degree and source reservoir assemblage type.And according to those factors,the dessert spot has been predicted.The prediction results show that the main dessert area located in the heart of the depression and its south.