An experimental and numerical study of gas-liquid two-phase flow moving upward vertically in larger annulus

During drilling in ultra-deep wells of petroleum engineering, the challenges associated with the dynamics of gas and drilling fluid in large annular spaces with diameters exceeding 190 mm, which significantly impacts pressure variations, flow stability, and operational safety. To explore these complex flow behaviors, numerical simulations were conducted based on Computational Fluid Dynamics. A total of 105 simulations were performed to analyze flow behavior under various combinations of air and water velocities. Superficial liquid velocities ranged from 0.001-1 m<middle dot>s-1, while superficial gas velocities varied from 0.01-30 m<middle dot>s-1. The simulations identified four distinct flow regimes, bubble flow, cap-slug flow, churn flow, and annular flow. Notably, slug flow was absent in the large annulus. The findings highlighted the critical influence of annular diameter on flow regime transitions. The larger diameter resulted in a reduced cross-sectional void fraction, diminished surface tension effects, and an increased gravitational impact, which inhibited the formation of a stable gas-liquid interface. A flow pattern transition chart was developed based on the drift flux model, identifying critical void fractions for flow pattern transitions, a void fraction of 0.3 indicated the transition from bubble flow to cap-slug flow, while a value of 0.51 marked the transition from cap-slug flow to churn flow. The insights gained from this research enhance the understanding of gas-liquid flow dynamics in large annuli, contributing to the development of more accurate predictive models for flow behavior. This knowledge is essential for optimizing wellbore design and management, ultimately improving well control strategies during ultra-deep drilling operations.