Organic matter composition characteristics and geological significance of Chang 8 oil layers,Yanchang formation in Longdong area

Under the geological conditions,density,viscosity,freezing point of crude oil are important indicator to measure oil flow performance and capacity,as well as the key to influence formation pressure,and they are closely related with the organic composition of reservoir.By integrated application of thermal evaporation hydrocarbon,rock pyrolysis gas chromatograph,nuclear magnetic resonance(NMR),fluorescent micro-image and various reservoir laminar liquid discriminant methods,organic matter composition characteristics of Chang 8 oil layer from Yanchang formation of Longdong area in Ordos basin and its effect on the performance of fluid and formation pressure have been analyzed.The results show that the reservoir of organic matter containing high colloid asphalt and other heavy components,which are the reasons for low movable oil content and testing not accord with expectation under the geological conditions.Including dissolved gas formation in the reservoir under the conditions of the composition,abundance and vertical distribution characteristics of organic matter are one of the important reasons for leading to abnormal low pressure of formation.