Explosive Behavior of CH4/C2H6/C3H8 Mixtures in the SAGD Process with CO2 Fusion Gases in Extra-Heavy Oil Reservoirs

In the crude oil recovery industries, explosion accidents involving associated gases can often result in fatal damage. The main purpose of this study is to provide theoretical support and engineering background for the SAGD operations in the extra-heavy oil reservoirs. To investigate the explosive behavior of CH4/C2H6/C3H8 gases and the inhibition mechanism of CO2 gas, the authors have experimentally studied the factors influencing the explosion behavior of the associated gas in a standard-designed 20 L spherical explosion vessel at ambient temperature and pressure. Based on experimental data, they analyzed the explosive parameters of the combustible gas mixtures, including the explosive peak pressure, time to reach the maximum pressure, the velocity of flame propagation, upper explosive limit (UEL), and lower explosive limit (LEL). The results show that a small amount of C2H6/C3H8 could promote the explosive characteristics of CH4. The addition of CO2 gas has a different inhibitory effect on the explosive behavior of CH4/C2H6/C3H8. The explosive overpressure strength of the CH4/C2H6/C3H8 gas mixture decreases with increase in the CO2 concentration. When the CO2 gas is added to the extra-heavy-oil associated gas, the flame propagation velocity of the CH4/C2H6/C3H8 mixture explosion decreases accordingly. Due to the inert effect of the CO2 gas, with the continuous addition of CO2 to the mixture, the UEL parameter of CH4/C2H6/C3H8 decreases linearly and the LEL parameter increases exponentially. The results of the study are important for eliminating potential risks and providing safety management of the SAGD operations at the extra-heavy oil reservoirs.