Petro Shine The Place for Oil and Gas Professionals.
Related Articles
U-Tube Effect
The pump rate may be unable to keep the casing full of cement during the early part of the job. The falling cement will push fluid down the casing and up the annulus, creating a situation where efflux from the annulus is greater than the slurry volume being pumped into the casing. Eventually the situation will correct itself as hydrostatic pressure equilibrium is approached. But the problem may occur several times as, for example, a lighter density wash is displaced around the casing shoe and fills the annulus at the bottom of the well.
These events can be misinterpreted as a loss of circulation or a loss of well control and the potential for U-tubing must be considered in the job design. Algorithms exist for accurately simulating U-tube effects.
The check-valve assembly fixed within the float shoe or float collar prevents flow back of the cement slurry when pumping is stopped (for example when the second wiper plug is dropped). Without the check valve, the cement slurry placed in the annulus could U-tube, or reverse flow back into the casing.
