Test Objectives
The primary purpose of performing a build-up test is to determine the wellbore damage (skin) and the reservoir permeability. However, during the course of a build-up, it is possible to encounter reservoir boundaries. If all the reservoir's boundaries are contacted during the build-up, the size of the reservoir can also be determined. If the well has been pressure tested before, subsequent testing allows relative material balance calculations (decline curve analysis), as well as the determination of the drive mechanism for the reservoir.
Procedure
Install the SPIDR on a well that has been flowing steadily for several days. Check for leaks in the system after installation. The SPIDR must be recording for at least 15 minutes prior to shut in (check the box for the SPIDR wake-up time). Shut the well in manually at the wing. Do not shut in using the automatic chokeÖit has a tendency to leak. After the well has been shut in, check for leaks again. When the build-up is over, the SPIDR may be rigged down and returned, or it may be left on the well for further testing while the well is flowing.
Advantages
A build-up test is one of the simplest tests to perform. The biggest advantage in performing a build-up is that it is a constant rate test: Q = 0. Simply install the equipment while the well is flowing, then shut the well in upstream of the choke.
Disadvantages
The drawback to performing a build-up test is that you lose cash flow. (Some people might think that you are actually losing gas, but it's still down there.) Nevertheless, if the test objectives are to determine skin and perm, and the rock has a permeability greater than 2 milliDarcies, most build-up tests can be limited to 2 days.
Commentary
It has been our experience that it is easier to obtain management approval for a build-up test when it is done in conjunction with a planned shut in due to facilities scheduled maintenance. After a build-up it is advisable to perform a single rate drawdown, or a Modified Isochronal test.
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