Abstract: There are major operational safety problems in the high-pressure air injection huff and puff process, which can easily lead to explosion accidents in injection or production wells. Taking the wellbore explosion accident during the air injection huff and puff process in a certain oilfield as an example and combining with the accident process and the situation of on-site investigation, this paper determined the process risks from such aspects as explosion type, explosion limit, safe oxygen content, and ignition source and then gave the proposal of explosion-proof measures. The results show that the explosion energy is between 61.5 and 205.2 MJ and the chemical explosion energy is consistent with the actual explosion energy. Under normal temperature and pressure, the explosion limit of flammable gas in the wellbore is 3.94% - 13.65%, and the critical oxygen content is 10.36%. It is recommended to reduce the probability of explosion accidents during the high-pressure gas injection process in terms of continuous gas injection of multiple compressors, design of packers, control of the oxygen content of the oxygen-reducing air and injection of inert protective gas.

Key words: high pressure, air injection, explosion accident, explosion limit, critical oxygen content