velocity strings new v depleted reservoirs

[ttuengr]

Throughout one field study in particular, I have noticed that in reference to velocity string applications, depleted reservoirs are typically better candidates than new wells. Why is this?

 

[DrillerNic]

Beacause velocity strings are a solution used when the reservoir pressure has dropped and the tubing has become too large.

As reservoir pressure drops, the PI curve (or inflow curve) drops down and may not intersect the tubing performance curve (or outflow curve) or may intersect in the tubing curves unstable portion. Changing to a smaller tubing size results in a new tubing performance curve, which may intersect with the new, lower PI curve.

The 'ideal' solution would be to recomplete a well in a depleted reservoir with smaller size tubing, but it's often cheaper to hang a velocity string in the tubing, achieving much the same thing.

You would hope that a new well would have the correct size of tubing installed anyway....