Definition of Casing and Tubing Pressure 1

[KatherineT]

A civil engineer new to the world of petroleum engineering, I have a basic question.

What is the difference between casing and tubing pressure? Where are they measured?

 

[zdas04]

You know what a wellhead is, right? Somewhere close to the bottom of the wellhead there is something called a "tubing hanger" that, oddly enough, you hang the tubing from. The tubing hanger seals the tubing/casing annulus from the tubing. At the bottom of the tubing you have both the annulus and the tubing open to the same pressure. If you are flowing the tubing and not flowing the casing, then the casing pressure is bottom hole pressure minus fluid hydrostatic pressure. The tubing pressure is bottom hole pressure minus fluid friction and fluid hydrostatic pressure. For a gas well, you can generally ignore the gas gradient so if you can verify whether there is a liquid column in the annulus (and its height) or not then you can determine bottom hole pressure from casing pressure which lets you determine the friction drop in the tubing.

Both are measured on the wellhead piping connected to the appropriate space.

David Simpson, PE
MuleShoe Engineering

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