For ultra-deepwater wells, the ability to control and plug the blowout well is more and more important as regulatory agency has more strict rules to issue a drill permit. After the blowout well is killed, cement plugs need to be placed in the borehole to prevent migration of fluids between the different formations. Because of the mixing and contamination process of the cement slurry pumping through relief well, to ensure required cement height and good quality for blowout well, is more challenging than the topside intervention well plugging operations.
In this study, dynamic simulations are carried out to assess the difficulties faced during blowout well control and abandonment. In the selected scenarios, the capping stack system is installed on the wellhead of the blowout well and three vessels are used to capture the oil with risers connected to each vessel separately. Through the relief well, sea water is pumped to the blowout well, increasing the hydrostatic pressure and reducing the rate of production. The injection of sea water together with the manipulation of choke outlet pressures on the vessels provides proper conditions for controlling the blowout well, keeping the liquid flow rates within the limits imposed by the processing capacity at surface. As sea water accumulates in the blowout well, reducing oil production rate, each vessel is shut down accordingly. Once the blowout well is completely filled up with sea water, kill mud is used to replace sea water to ensure static kill. Cement slurry is then pumped to blowout well to set the cement plug. The displacement is specially studied when the cement slurry is flowing into the blowout well. In the sensitivity analysis, borehole enlargement, cement slurry rheology, and flow rate are considered to investigate the contamination of the cement slurry.
The presented outcomes allow engineers to better understand the operation procedures for blowout well control with capping, containment and zero discharge to the environment under capping and containment scenario after worst case discharge, and the methods to mitigate cement slurry contamination and ensure good cement plug for well abandonment.