Volumetric Well Control Method For Gas Kicks
The volumetric method is mostly used in workover and production well control operations. It is a means of allowing the gas to migrate (gas kick behaviour) to the surface under control. The gas needs to migrate at over (approx.) 1000' per hour.

To allow the bubble to expand the casing pressure is held constant for a given volume of mud bled off. This operation is repeated, holding an ever-increasing casing pressure until the gas reaches the surface (Holding Bottom Hole Pressure constant).
https://www.drillingmanual.com/volumetric-well-control/