Experimental evaluation of control fluid fallback during off-bottom well control in vertical and deviated wells

This study measured the liquid fallback during simulated blowout conditions. The purpose of the study was to establish a basis for developing a procedure for controlling blowouts that relies on the accumulation of liquid kill fluid injected while the well continues to flow. The results from experiments performed with air, water, 10.5 ppg and 12.0 ppg mud in an experimental 48 ft flow loop at 0°, 20°, 40°, 60° and 75° deviation angles from the vertical, as well as results from full-scale experiments performed with natural gas and water based drilling fluid in a vertical 2787-foot deep research well, are presented. The results show that the critical velocity that prevents control fluid accumulation can be predicted by Turner's model of terminal velocity based on the liquid droplet theory by also considering the flow regime of the continuous phase when evaluating the drag coefficient, and the angle of deviation from the vertical. Similarly, the amount of liquid that flows countercurrent into and accumulates in the well can be predicted based on the concept of zero net liquid flow (ZNLF) holdup. Finally all these concepts are integrated in the dynamic kill procedure, which is based on system performance analysis to better predict the feasibility of an off-bottom dynamic kill.