Abstract The "Dynamic Kill" technique has been used to perform off-bottom kills of both, surface and underground blowouts. Usually these kills are designed under the assumption that no kill fluid falls below the injection depth into the upward flow of the formation fluid. If this conservative assumption indicates that the kill is possible to achieve, the operator can confidently proceed with the field operations. However in some cases, calculations under this assumption will indicate that the kill is not possible, discarding a valuable potential solution to the problem. Recently completed research on counter-current flow of kill fluid falling through formation fluid that is flowing upward is applied here to off-bottom blowout wells. This study presents a procedure for controlling off-bottom blowout wells. It relies on the accumulation of liquid kill fluid injected while the well continues to flow to increase bottom hole pressure and assist in killing the well. The method is based on:The critical velocity that prevents control fluid accumulation which can be predicted by a new adaptation of Turner's model of terminal velocity (based on the liquid droplet theory.) This new model considers the flow regime of the continuous phase when evaluating the drag coefficient and the angle of deviation from the vertical.
The amount of liquid that flows countercurrent into and accumulates within the well, which can be predicted based on the concept of Zero Net Liquid Flow (ZNLF) holdup.
These two 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. These concepts were validated with full-scale experiments in a 2787-foot deep research well.
Introduction Considering the counter-current flow of liquid kill fluid in an off-bottom blowout scenario can provide a realistic basis for determining the conditions needed for a successful dynamic kill. In contrast, some practical kill alternatives would otherwise be overlooked if this phenomena is not taken into consideration. In this paper, the general principles of the dynamic kill technique are applied to off bottom conditions, and a step by step procedure is proposed herein to be applied in an off bottom dynamic kill. As mentioned before, this dynamic kill procedure relies on the application of two concepts, the critical velocity that prevents control fluid accumulation, and the Zero Net Liquid Flow (ZNLF) holdup, and it is divided in three sections. First, calculations of the critical gas velocity required to completely remove a liquid droplet in a high velocity gas core is determined as proposed by Flores-Avila et al.. Second, a method for calculating ZNLF holdup based on the procedure originally proposed by Duncan is presented, and third, a general step by step procedure to apply all these concepts to an off-bottom dynamic kill is defined. Finally the results of the full-scale experiments in a 2787-foot deep research well by Flores-Avila et al. that validate the procedure are discussed, as well as an application example based on a case presented by Gillespie et al..
Off-Bottom Dynamic Kill Principle Applying a steady state system performance analysis to a blowout well in an off bottom condition, Fig. 1 can be constructed. Considering an injection rate of kill fluid of QL3 BPM, this kill rate will not be enough to establish a dynamic kill condition, given by the continuous line, as its outflow curve, intercepts the IPR curve, this means that there are steady state conditions of combined formation and kill fluid flows that can be achieved, such that the formation is not overbalanced and the blowout continues.
It is possible that at the new steady state conditions, the velocity of the formation fluid would not be enough to prevent some of the injected kill fluid falling back into the well countercurrent to the gas. This kill fluid would then generate an additional hydrostatic head that would be acting against the formation pressure, increasing the flowing bottom hole pressure, and therefore, reducing the formation flow rate. This condition will generate the dotted lines in Fig. 2, with a higher bottom hole pressure, which in this case for QL3 BPM, will be enough to achieve a dynamic kill.