A dynamic unified well-killing model for synergistic regulation of multiple well-killing methods

Ultra-deep and complex formations are characterized by narrow safety density windows and challenging well control. The combined use of multiple well-killing methods or temporary adjustments to well-killing strategies is becoming common. However, conventional well-killing models often struggle to calculate the parameters required for these special cases. In this paper, a boundary matrix for well-killing fluid density and volume is proposed to unify the driller’s method, the engineer’s method, and the weight-while-circulating method. Furthermore, a dynamic unified well-killing model is developed to enable the synergistic regulation of multiple well-killing methods. The model also can be applied with or without accounting for gas dissolution. Using this model, it is able to dynamically track key parameters during well killing and shut in the well at any time to determine the standpipe and casing pressures. The results indicate that the casing pressure drops to zero before the well-killing fluid returns to the annulus wellhead, and continued injection of the fluid leads to a gradual increase in standpipe pressure, a phenomenon not previously accounted for. The discrepancy between the actual and calculated standpipe/casing pressures after shut-in can be utilized to assess whether the downhole gas kick is effectively controlled. Through real-time adjustments to the boundary matrix, updated well-killing parameters can be derived for conventional method, multi-method combination, temporary strategy modification, and other well-killing scenarios. The model was applied to two field wells under water- and oil-based drilling fluids. No secondary downhole complications occurred during well killing, and the calculated pressure curves closely matched the measured construction pressure curves, confirming the model’s reliability and applicability. This study provides valuable theoretical guidance for enhancing well control safety in ultra-deep and complex formations.