Page 465 - Air and Gas Drilling Manual

Chapter 9: Aerated Fluid Drilling 9-69
injection pressure. And while drilling at 7,000 ft of depth, the lowest air volumetric
flow rate and highest injection pressure will be required.
The anticipated drilling rate of penetration is estimated to be 60 ft/hr. The
vertical interval section to be drilled is from a depth of 7,000 ft to a depth of 10,000
ft, or a 3,000 ft length of borehole. Therefore, the estimated actual drilling time to
drill this interval is approximately 50 hours. Using similar calculations as those
given above, the injection pressures as a function of drilling depth and, thus, drilling
time can be obtained. Figure 9-6 shows the injection pressure as a function of
drilling time for the interval from 7,000 ft to 10,000 ft. Figure 9-7 shows the
injection air volumetric flow rate as a function of drilling time for the interval from
7,000 ft to 10,000 ft.

Figure 9-5: Pressure profile in the inside of the drill string and in the annulus for
Illustrative Example 9.3 (q g = 1,168 acfm and a drilling depth of 10,000 ft).