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Tubing Checks - Leak To Annulus

This page shows a few examples you could expect to see while looking for a tubing leak into the tubing annulus. Please keep in mind that these are "ideal" reactions but should give you a good understanding of the sensor responses we are looking for in such a test.

The tubing has been shut-in and the well has been allowed to flow up the tubing annulus in these examples. See Tubing Check Strategies for information on proper configuration and test management.

The first example shows a typical response where the tubing has been shut-in for a sufficient amount of time to allow all the fluids in the tubing to be purged down to the highest leak. The building gas head has displaced this fluid and will remain trapped until the tubing is opened.

The temperature log shows a cooling anomaly across the leak due to a pressure falloff and gas expansion. This is very helpful in finding leaks of small volumes.

This example is exactly the same, but with no, or little gas expansion, at the leak. This can be caused by a large diameter leak, numerous small (pinhole) leaks, or just the lack of any free gas at the leak point. Great care must be taken while interpreting these types of surveys.

The temperature log shows only a gradient change at the leak. It can be easy to assume the fluid level in the tubing is the indicator for a leak. It rarely is, but it is usually close to the leak.

Take a look at the next example.

More Realistic

This plot is like those we actually see in the field. It is rare for the customer to have configured and allowed the well to stabilize for a tubing leak test. Allowing the well to stabilize for a tubing check

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could take weeks and for economic concerns is not reasonable. That is why there is usually a fluid level above the leak, unless the leak moves a lot of fluid.

The Delta PSI, Temperature, Spinner, and Capacitance logs all indicate a fluid level (gas/oil) interface. Notice how similar the fluid level appears to a tubing leak.

How do we know the fluid level is not at the leak? Can you determine why with the data at hand?

We have two very good indicators as to why the fluid level is not the leak. They are the Temperature and Capacitance logs. The temperature is the most obvious. See the cooling anomaly at the exit point? The capacitance is a bit more subtle but very useful. The fluids above the leak are in a trap and are static. They quickly separate and show as columns of homogeneous fluids. All fluid from the leak and down is dynamic and represents the fluid ratio being produced at that time. The Delta PSI also reflects that, but can be harder to interpret.