DST Applications

Drill Stem Testing (DST)

Drill stem testing or DST has been the industry standard for testing new and especially exploration wells for almost a century.  These tests are one of the primary methods used to evaluate a new formation to determine its commercial feasibility.  These tests are typically performed using a special DST tool that has downhole pressure gauges installed.  Pressure is then recorded during a series of flowing and shut-in tests to measure reservoir characteristics via pressure transient analysis.  These tests are done using downhole pressure gauges, but there may still be a need for DRC’s SPIDR system.  

Using the SPIDR During DST Testing

In new formations operators have very limited information about their reservoir.  This lack of information will make it difficult to plan a well test.  If the permeability of the formation is unknown, there is no way to determine the length of time required to perform your well test.  In this situation the SPIDR can be used as a surface read-out during the test.  The operators will be able to watch the test as it happens and begin their analysis of the early portion of the test before the test is even completed.  This will give the added benefit of possibly ending your test sooner once you decide you have all the data needed.  Because DSTs are performed with a rig on location, saving even an hour of testing time will be an immense benefit.

The SPIDR can also be used as a back-up during these tests.  The worst case scenario on any DST is to have downhole equipment fail during the test.  If this failure occurs you will have no choice but to retest the well, because the information obtained from a DST is crucial to future planning.  By using the SPIDR at surface you will ensure that at a minimum you will be able to use the DRC converted bottomhole pressure to perform your analysis.

Downhole Shut-in Tool During DST Testing

A key consideration to take into account if you plan to use the SPIDR during a DST is the use of a downhole shut-in tool.  Many operators plan to use a downhole shut-in tool during their DST to minimize afterflow or wellbore storage affects.  This downhole shut-in tool is used to isolate the bottom of the wellbore, to obtain the best test results possible.  While there is definitely some value in this method, especially if you are concerned about near wellbore limits, using a downhole shut-in tool will make it impossible to get any information at surface.  A tradeoff decision must be made between data quality and the security of having a surface read-out/backup at surface.  This decision will be made on a case by case basis and depends on the type of well that you are drilling.

In certain cases it may be possible to use the SPIDR even if a downhole shut-in tool will be used.  Many well test plans contain an initial surface shut-in, that is followed by a multi-rate flow test and downhole shut-in.  The SPIDR can be used during the initial surface shut-in and multi-rate flow test to determine initial calculations of reservoir characteristics.  These calculations can then be used to determine the shut-in time required during the downhole shut-in.  This method also give the added value of having the SPIDR data as a backup should anything go wrong during the downhole shut-in.