Explosion Risk Analysis And Prevention Measures Of Air Injection Process In Heavy Oil Reservoirs

The oil and gas components in the oil reservoir may form mixture of explosive gas with oxygen in the wellbore and pipeline in the process of exploiting oil reservoirs by air injection,so that there is a danger of combustible explosion in all links,which seriously prevents promotion and application of air injection.The application of air injection in heavy oil reservoirs mainly includes combustion oil in-situ and air injection assisted steam stimulation.This paper studies the explosion characteristics of combustible gas and heavy oil in the wellbore and oil reservoir,analyzes the explosion risk sources and risk locations in the air injection process,and provides effective prevention measures and safe prevention oxygen content warning values for air injection.The main research content of this paper includes: Through explosion experimental results of natural gas components under simulated oilfield air injection conditions,make sure the explosion limit of combustible gas,analysis of the influence of temperature,pressure and gas types on the explosion limit and critical oxygen content required for explosion;Analyze the explosion possibility of mixture gas of methane and air in the porous media of the oil reservior;Conduct heavy oil ignition explosion experiments and spontaneous explosion experiments under high temperature and high pressure with typical heavy oil samples,and analyze the impact of pressure on the ignition point and spontaneous ignition point of heavy oil;According to the results of heavy oil explosion experiments and theory,analyze the explosion causes of the two heavy oil air injection assisted steam stimulation accidents;Analyze the explosion risk of each process of air injection based on the results of the oil and gas explosion experiment and the explosion theory,make sure the location of the explosion and the cause of the explosion,and establish an accident tree model of the explosion;Formulate corresponding prevention measures according to the risk of the air injection process,and propose the critical oxygen content value for explosion warning and monitoring.The research results show that with the increase of temperature and pressure,the lower flamability limit of combustible gas explosion decreases,the critical oxygen content required for explosion decreases and the explosion risk increases.The porous medium of the oil reservior has a significant inhibitory effect on methane explosion,and there will be no violent explosion in the porous media of oil reservior.However,the oxidation reaction of crude oil will occur in the oil reservior.As the pressure increases,the spontaneous combustion and explosion temperature of the heavy oil components decrease,and the explosion risk increase.The analysis of many heavy oil wellbore explosion accidents at the site shows that the spontaneous explosion of the adherent heavy oil in the wellbore is the main reason for the explosion during the air injection assisted steam stimulation;The explosion in air injection includes air compressors,surface gas injection pipelines,air injection wellbore and production wellbore,and there is no risk of explosion in the reservior due to the explosive barrier properties of porous media.Therefore,oilfields need to strengthen the control and monitoring content of combustibles and oxygen,so that the combustible gas concentration in the wellbore and pipelines is lower than the lower flamability limit,or the oxygen concentration is lower than the safe oxygen content,meanwhile,avoid mixing heavy oil and air in the wellbore at high temperatures to prevent spontaneous explosion of heavy oil as much as possible.For the explosion prevention of the natural gas and heavy oil mixture in the air injection in heavy oil reservoirs,the reduced oxygen air index is generally 6% above 20 MPa and 100℃.