New insights on low temperature oxidation characteristics and possibility of auto-ignition in light oil reservoir

High pressure air injection (HPAI) can improve oil recovery by 10%-20% due to its unique oxidation heat effect. The high temperature and pressure thermostatic device is used to study the low temperature oxidation char-acteristics and oxidation kinetic parameters of light oil. Then a numerical model based on the oxidation kinetic parameters is established to study the possibility of auto-ignition of low temperature oxidation of light oil. Temperature rises due to the heat release of low temperature oxidation. Higher temperature makes low tem-perature oxidation more intense, so the reaction rate increases. When temperature is relatively low, the oxygen addition reaction dominant, the content of oxygen-containing functional groups increases continuously, and aromatic hydrocarbon is converted into resin. With the progress of oxidation, resin is further oxidized into asphaltene. When temperature rises, carbon bond stripping reaction begins to occur, which makes macromo-lecular oxygenated hydrocarbons in oil decompose into small molecules of hydrocarbons and CO2. After considering gas (mainly CO2 generated by oxidation and natural gas) dissolution into oil, the viscosity of un-derground oil after low temperature oxidation is lower than that of original oil, which improves the mobility of oil. The activation energy of oxygen addition reaction is 49.0 kJ/mol and pre-exponential factor is 8.72 x 103s-1. The activation energy of carbon bond stripping reaction is 68.9 kJ/mol and pre-exponential factor 1.6 x 106s-1. The static low temperature oxidation experiments are simulated by CMG-STARS module based on experimental results. The simulation results show that decreasing the heat loss of experiments makes the temperature rise rapidly, which indicates that the light oil with little asphaltene also has high oxidation activity, and auto-ignition can occur in the light oil reservoir for HAPI. The conclusions of the research can provide references for field applications of HPAI in light oil reservoir.