Study on Plugging Process Parameters and Mechanism of Large- Scale Plugging Experimental Device for Blowout Preventer Stack

The blowout preventer (BOP) stack is the last line of defense for well control (pressure control of the wellbore), and the failure of its sealing components will cause serious well control accidents. At present, there is a lack of suitable experimental device to verify the feasibility of the emergency rescue method proposed for the early seal failure of the BOP stack by pumping plugging particles. However, it is costly, risky, and time- consuming to build and implement a large- scale plugging experimental model for BOP stack with ultrahigh pressure (70 MPa) and large displacement. Therefore, based on this device, this paper establishes a large- scale plugging experimental model of BOP stack by using computational fluid dynamics- discrete element method (CFD- DEM). The volume flow rate is used as the evaluation index to analyze the influence of the shape, size, concentration, and pump displacement of the plugging particle on the plugging efficiency, and the plugging parameters of the experimental device are researched and selected. The results show that the plugging particles can be divided into four stages-particle pumping, particle diffusion, particle bridging, and particle accumulation. The 5- mm spherical particle has the best plugging efficiency for the largest dimension of flange connection seal failure. The particle concentration and pump displacement affect the bridging time of particles but have no obvious effect on the plugging efficiency. A pump displacement of 2.4 m(3)/min and 5- mm spherical particles with 25% concentration were selected for emergency plugging of the experimental device. This study not only reduces the cost and risk of large- scale plugging experimental device for BOP stack but also further promotes the feasibility study of emergency rescue of BOP seal failure.