Study on emergency plugging mechanism after BOP seal failure under UHP blowout conditions in natural gas wells

Once a natural gas well blowout occurs, the liquid fluid in the well will be drained in a short time, and the wellhead will rapidly transform into an ultra-high pressure and large displacement blowout environment dominated by natural gas. However, the suspension capacity and motion state of particles in the blowout fluids of natural gas wells and oil wells vary greatly. Therefore, it is of great significance to study whether the particle bridging method can be used for emergency plugging in the case of blowout preventer (BOP) sealing failure in ultra-high pressure (70 MPa) natural gas well blowout conditions. Based on an analysis of the common failure modes of BOPs, this paper establishes a plugging model for BOP. The reliability of the model is verified through a large-scale BOP plugging experimental system, and the mechanism of emergency plugging under gas well blowout conditions is studied using this model. The results show that the plugging efficiency is lower than that of oil wells but remains effective. The "1/3 bridging rule" is not applicable to particle bridging plugging under ultra-high pressure and large displacement conditions. Plugging efficiency is negatively correlated with particle size and positively correlated with particle concentration. There is no significant effect of pumping displacement or particle injection volume on plugging efficiency.