Low-temperature oxidation of light crude oil in oxygen-reduced air flooding

Light crude oil from the lower member of the Paleogene Xiaganchaigou Formation of Gaskule in Qinghai Oilfield was selected to carry out thermal kinetic analysis experiments and calculate the activation energy during the oil oxidation process. The oxidation process of crude oil in porous medium was modeled by crude oil static oxidation experiment, and the component changes of crude oil before and after low-temperature oxidation were compared through Fourier transform ion cyclotron resonance mass spectrometry and gas chromatography; the dynamic displacement experiment of oxygen-reduced air was combined with NMR technology to analyze the oil recovery degree of oxygen-reduced air flooding. The whole process of crude oil oxidation can be divided into four stages: light hydrocarbon volatilization, low-temperature oxidation, fuel deposition,and high temperature oxidation; the high temperature oxidation stage needs the highest activation energy, followed by the fuel deposition stage, and the low-temperature oxidation stage needs the lowest activation energy; the concentration of oxygen in the reaction is negatively correlated with the activation energy required for the reaction; the higher the oxygen concentration,the lower the average activation energy required for oxidation reaction is; the low-temperature oxidation reaction between crude oil and air generates a large amount of heat and CO, CO2and CH4, forming flue gas drive in the reservoir, which has certain effects of mixing phases, reducing viscosity, lowering interfacial tension and promoting expansion of crude oil, and thus helps enhance the oil recovery rate. Under suitable reservoir temperature condition, the degree of recovery of oxygen-reduced air flooding is higher than that of nitrogen flooding for all scales of pore throat, and the air/oxygen-reduced air flooding development should be preferred.