Page 67 - Drilling Technology in Nontechnical Language

58 Drilling Technology in Nontechnical Language Second Edition

If a shallow gas pocket is penetrated, the chances of recognizing and
controlling it are much better if a smaller size hole is drilled. If the gas
pressure is high enough to push all the mud out of the well, this uncontrolled

flow is called a blowout, as explained previously. If the well does blow out,

the gas will flow through a smaller hole, and so the initial flow will be
much less. This allows a few vital moments to get the diverter closed and

to start pumping fluid down the drill string as fast as possible, to try to

slow or stop the flow. The intensity of a shallow gas blowout is such that

large volumes of rock will be removed from the well as the gas flows,
rapidly making the hole much larger.

The first drill bit will be 12¼" (311 mm) diameter (fig. 3–12). The hole

it drills is termed a pilot hole because the hole will be redrilled later with
a larger bit. The start of drilling the well is called spudding the well. The
time that the well is spudded, by convention, is taken to be the time that the
drill bit exits the bottom of the conductor pipe.

Fig. 3–12. Drillbit cutters

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