Development and application of transient gas‐liquid two‐phase flow model considering sudden density change.

In deepwater drilling, accurate prediction of wellbore gas‐liquid two‐phase flow behavior is significant for gas kick detection and well‐control treatment. In this study, a new transient gas‐liquid two‐phase flow model was developed to simulate the wellbore gas‐liquid two‐phase flow during gas kick in deepwater dual‐gradient drilling based on downhole separation. This model accounts for the impact of a sudden change in density on gas‐liquid flow behavior. The transient model was solved using the finite‐difference method. The accuracy and stability of the model were verified using data measured from a full‐scale experimental well. Using this model, the differences in the apparent liquid velocity and the flow rate at the annular outlet during gas kick were compared between deepwater dual‐gradient drilling and conventional single‐gradient drilling. Additionally, the influences of numerous factors on variations in flow rate at the annular outlet were also studied. A new method of early gas kick detection was proposed for deepwater dual‐gradient drilling based on downhole separation. [ABSTRACT FROM AUTHOR]