Influence factors of coking amount during recovery of heavy oil by air injection

Through building the experimental apparatus for reservoir HTHP reaction simulation and physically simulating the coke generation process during recovery of heavy oil by air injection, a study was conducted on the influences of reaction atmosphere, temperature, pressure and air ventilation intensity on the coking amount with certain Xinjiang heavy oil. The research indicated that in the air atmosphere, the low temperature oxidization (LTO) of crude oil can significantly promoted coke generation. with the reaction pressure 5 MPa, each gram of heavy oil can generate the maximum coking amount of 0.375 g, 2.5 times over that in N₂ atmosphere. Influenced by LTO, the initial coke generation temperature is lower than that in N₂ atmosphere by nearly 200℃. With the pressure rising, the aggravated LTO can increase the coking amount; when the pressure exceeds 5 MPa, its effect is not significant. With the increase of air ventilation intensity, the coking amount is not continuously increased, and a peak will appear at around 33.4 N·m³/(m²·h). A comparative analysis was carried out on the influences of coke high-temperature oxidization consumption as well as crude-oil component distillation and weightloss on coking amount. The results indicated that coke oxidization was the major cause of the reduction in net coking amount with the temperature ranging from 225℃ to 300℃ in air atmosphere. When the temperature reaches 450℃ in N₂ atmosphere, the aggregated crude-oil pyrolysis condensation reaction can increase the coking amount, but the further rising of temperature will lead to coke pyrolysis and weightloss, resulting in a decline in coking amount. Additionally, the experiments revealed that when the temperature exceeds 200℃, the oil sand center temperature in the reaction tube was higher than the outer-wall heating control temperature. The analysis results showed that the temperature exceeding phenomenon was caused by the LTO of crude oil component and the high temperature oxidation of certain coke with high activity; This heavy oil has the spontaneous ignition potential.