Page 371 - Air and Gas Drilling Manual
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8-54 Air and Gas Drilling Manual
volumetric flow rate, detailed calculations to determine the pressures in the annulus
and inside the drill string can be carried out in the same manner as those in
Illustrative Example 8.3b (for a drilling depth of 10,000 ft). Figure 8-10 shows the
air flow pressures in the annulus and inside the drill string as a function of depth for
this illustrative example. The figure shows an injection pressure of 294 psia and a
pressure at the bottom of the annulus of approximately 269 psia. Comparing these
pressures to those shown in Figure 8.7 (for q g = 2,400 acfm) it is clear that the
general pressure increases through the circulation system for this example are due to
the higher volumetric flow rate used for this illustrative example (i.e., q g = 2,400
acfm).
Figure 8-10: Pressure profile in the inside the drill string and the annulus for Illustrative
Example 8.4 (q g = 3,396 acfm and a drilling depth of 10,000 ft).
