Study on the sensitivity and hazard of combustion and explosion in 175 MPa ultra-high pressure blowout gas mixtures

At present, the underground pressure of ultra-deep wells can reach up to 175 MPa, making blowouts under such conditions significantly more hazardous. However, the safety distance for the control system of the Christmas tree has not yet been effectively determined, primarily due to the lack of accurate assessment of the gas ignition conditions. To scientifically evaluate the blowout-induced combustion and explosion risks of ultra-high-pressure gas mixtures in ultra-deep wells, this study conducted ignition experiments and developed a theoretical prediction model to comprehensively analyze the ignition sensitivity parameters and explosion hazards of gas mixtures at 175 MPa. The results show that increasing the ignition energy from 20 mJ to 1000 mJ lowers the lower explosion limit (LEL) by 13.77 %, while raising the hot surface ignition temperature from 820 °C to 1600 °C reduces the LEL by 11.92 %. Under blowout conditions, the explosion overpressure decreases from 1.90 bar to 0.94 bar—cut nearly in half—and the flame temperature drops from 754.21 °C to 621.34 °C, indicating a substantial reduction in explosion severity. With increasing initial pressure, fewer cracks appear on the surface of spherical flames of the same radius, suggesting enhanced flame stability. Based on thermodynamic and heat transfer theory, a theoretical prediction model for the minimum ignition energy (MIE) of blowout gas mixtures was proposed, incorporating analysis of energy loss mechanisms. The model's prediction error remains within 30 %. This study provides a scientific foundation for the prevention and control of combustion and explosion risks associated with blowouts in ultra-high-pressure, deep oil and gas reservoirs.