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The Drill Stem Test
In the old days before the use of drilling mud, the drilling
crew immediately knew when they had hit a good oil reservoir
because the well would blow out. This would be an event of great
excitement as well as great danger. Fortunately, things are done
differently today. The excitement and tension of finally
determining if the well is a discovery are still present, but much of
the danger has been removed.
After the geologist has analyzed the logs and identified a
formation that appears (from the log ana lysis) to be porous,
permeable and contain hydrocarbons, the excitement begins to
build. This is the time of reckoning for the well. It is time to do a
drill stem test (DST). The DST involves the lowering of
specialized equipment into the well bore that isolates the formation
of interest from the pressure exerted by the drilling mud so as to
allow the fluids within the formation to flow to surface. This
determines the flow capability and the type of fluids (oil, natural
gas or water) present in the formation. The DST also records
valuable information on the formation pressure, which is critical to
determining whether the well can produce at a high enough rate
and for a long enough time to be profitable. For example, if a well
flowed oil at a rate of 100 barrels an hour for 24 hours and showed
very little decrease in reservoir pressure, one could conclude that
this was a pretty good well and should produce for a long time. If,
however, at the end of the test the pressure had dropped off by
50%, it would mean that this oil reservoir was small and could not
produce for a long enough time to be profitable. A well that cannot
produce hydrocarbons in commercial quantities is called a dry
hole.

The Blowout Preventor
It should be evident, from our discussion thus far, that a
drilling rig is a very complex piece of machinery containing a
broad range of specialized equipment. Although we won’t go into
a detailed discussion on the workings of every part of a drilling rig
here, there is one special piece of equipment that is critical to the
safe operation of the rig and warrants special mention. Have you

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