Laboratory simulation experiments of air injection with low temperature (65°C, 17 MPa) for a low permeability (4.5 mD) reservoir was conducted by using crude oil from the Dagang Oilfield, Northern China. The initial oil density and viscosity are 12 API and 74.5 mPa.s, respectively. The physical properties of the crude oil such as viscosity, density in the oxidation zone before and after air injection were measured. Changes of both the saturated hydrocarbons and aromatic fractions were analyzed using GC X GC-FID. The changes of resin, asphaltene and oxygenated products were analyzed using a Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS).
The results indicate that the produced CO, CO2 and the gasified low molecular weight hydrocarbons drive the oil out from the tight reservoir core with an oil recovery of 45 %. The viscosity of the produced oil is reduced slightly by 2.6 %. The in situ viscosity, although not measured directly, should have been reduced significantly due to the thermal effect. The physical properties of the oil in the oxidation zone are deteriorated significantly, with the viscosity being increased by 30 % and the content of Oxygen by 7 %.The oxidization pathways from molecular alterations based the static oxidization of light oil at low temperature are also explored in accordance with the molecular heterogeneities.