Predicting pressure behavior during dynamic kill drilling with a two-phase flow

• A variable flow rate proportion scenario for dynamic kill drilling is presented.
• Annular density varies with time and depth in the model described in this paper.
• Wellbore pressure is mainly determined by annular hydrostatic fluid pressure.
• Bottom hole pressure should be monitored to optimize flow rate proportion.

Dynamic kill drilling technology can effectively handle well kick, loss of circulation and wellbore collapse during surface drilling in deepwater. To ensure a safe and successful dynamic kill drilling operation, accurately predicting wellbore pressure is highly important. Based on dynamic kill drilling characteristics in deepwater, this paper develops a wellbore pressure prediction model with variable flow rate proportions. The complexity of the gas–liquid two-phase flow inside the annulus is included in the model. An analysis of the liquid holdup, annular density, annular pressure, annular pressure loss and bottom hole pressure during dynamic kill drilling is performed for a deepwater well using the wellbore pressure prediction model described in this paper. The results suggest that the key issue for dynamic kill drilling technology is controlling the mixture density by regulating the flow rates of the seawater and weighted drilling fluid. To demonstrate the model's validity, it was used to predict the wellbore pressure of two deepwater wells that had been constructed using dynamic kill drilling in the Gulf of Mexico (GOM). The wellbore pressure prediction model presented in this paper is valuable for guiding field operations involving dynamic kill drilling.