Study on the Migration Patterns of Intruding Gas in Wellbores with Different Inclinations

Although offshore horizontal wells offer high production efficiency, the gas invasion behavior in these wells differs markedly from that in vertical wells. Therefore, a systematic study is required to better understand the gas migration mechanism under inclined wellbore conditions. This study analyzes the influence of wellbore inclination on bubble migration paths and velocities, and establishes a mathematical model of bubble migration that accounts for wellbore inclination. The forces acting on the bubbles were decomposed, and a dimensionless expression of the drag coefficient was introduced, providing a theoretical basis for subsequent simulations and fittings. Three-dimensional annular wellbore geometries with different inclination angles were constructed, and the migration process of bubbles under various wellbore inclinations was investigated using numerical simulation. The results indicate that the migration velocity of invading gas decreases as the wellbore inclination increases. When the initial gas injection velocity is increased to 5.65 m3/h (5 m/s), the migration velocity rises, ranging from 0.16 m/s to 1.28 m/s, and reaches 0.31 m/s at equilibrium. Increasing the drilling fluid flow rate to 407 m3/h also increases the gas migration velocity, ranging from 0.25 m/s to 1.10 m/s, and reaches 0.42 m/s at equilibrium. With a constant annulus inner diameter, increasing the outer diameter to 1 m leads to an increase in gas migration velocity, ranging from 0.22 m/s to 1.18 m/s, and reaches 0.38 m/s at equilibrium.