Study on multiphase flow modeling and parameter optimization design for bullheading

Abstract

Deepwater and deepwell oil and gas drilling face complex environmental challenges. The limitations of conventional well control methods make it difficult to ensure the safety of wellbore pressure control. Bullheading is an efficient and simple well control technique for resolving complex kick problems, but the success rate of a single bullheading operation is low due to the inadequacy of well control parameter design. In this study, we first address critical challenges in designing critical bullheading displacement, calculating loss pressure, and characterizing reverse flow characteristics. We then propose a transient multiphase flow model and solution method for bullheading that comprehensively considers gas-liquid counterflow, formation loss, energy transfer, and PVT characteristics. By comparing simulation results with full-scale test wells and field construction parameters, the simulation errors were found to be less than 5% and 10%, respectively, verifying the accuracy of the model and method. Sensitivity analysis of bullheading parameters was conducted using the model, revealing that wellbore pressure is extremely sensitive to bullheading displacement and formation parameters. The combination of bullheading parameters within a safe range is constrained by the downward gas flow, the pressure limit of the blowout preventer, and the formation fracture pressure conditions. Based on the simulation results, we propose a bullheading parameter optimization design process. This work provides a comprehensive description of the response characteristics of wellbore flow parameters during bullheading and offers a theoretical basis for the optimization and control of bullheading parameters, helping to improve the safety of wellbore pressure control.