Study Of The Impacts Of Bubbles Fusion Behavior To Annular Fluid Flow

When the gas cut occurs in underbalanced drilling, an accurate determination of the annular bubble's generated size and migration regularity is the key to design and maintain safety drilling. At present, the research on impacts of annular bubble migration velocity based on the bubble fusion characteristics is not enough depth. In this study, truly reflection the bubble ascend and the influence of bubble fusion to ascending velocity in annual, and therefore accurate scientific basis for the design of reasonable underbalance pressure in air cushioning were provided.First, according to unstable filtration theory, model of bubble formation were established, bubble formation was divided into two phases of inflation and departure during bubble formation on force analysis. The calculating model of critical gas were established by bubble coalescence conditions, the geological conditions and drilling parameters were considered.At the same time, the fusion mechanism of bubbles from bubble dynamics were analysed, bubbles in the ring together with the condition and fusion rate, which reflected in the air bubbles during migration, and therefore accurate scientific basis for fluid type of compartmentalizing were provided. Finally, according gas bubble fusion velocity to establish calculation model of bottom hole pressure. An example of calculation for a well under balanced drilling process was carried out in Daqing area. The gas quantity and well backpressure variation by the present model were well agreed with the actual defects, the model of gas bubble fusion and the model of bubbles formation, migration and deformation could be provides necessary basis for the rational design of underbalance pressure in gas underbalance stage, also has great theoretical and practical value.