Page 251 - Air and gas Drilling Field Guide 3rd Edition

242 CHAPTER 9 Aerated Fluids Drilling

Pressure (psia)
0 500 1000 1500 2000 2500 3000 3500
–7000
–2200
–7500
Injection Pressure
–2400
–8000
Depth (ft) –8500 Bottom Hole Pressure –2600 Depth (m)

–9000
–2800
–9500

–3000
–10000
0 400 800 1200 1600 2000 2400
Pressure (N/cm 2 abs)

FIGURE 9-11. Drilling ahead, bottom hole annulus, and injection pressures versus depth.

shows that the injection changes very little as the open hole is drilled. The injec-
2
tion pressure is 87.4 psia (60.4 N/cm abs) at the casing shoe and 62.4 psia (43.0
2
N/cm abs) at the bottom of the section at 10,000 ft (3048 m). The bottom
hole annulus pressure variation is much larger, changing from 2151.2 psia
2
2
(1483.7 N/Cm abs) at the casing shoe to 3372.2 psia (2326.2 N/cm abs)at
the bottom of the open hole section.

9.5 CONCLUSIONS
The discussions in this chapter have concentrated on direct circulation perfor-
mance drilling operations. The Mathcad illustrative examples in Appendix D
utilized lumped geometry approximations for the drill pipe body and drill pipe
tool joints. These approximations appear to quite adequately model the overall
friction resistance along the circulation system and give reasonable results, par-
ticularly for the bottom hole annulus pressures. The large variations in pres-
sure versus depth in the annulus and inside the drill string are masked in the
aeratedfluid model(duetolarge pressure magnitudes)ascomparedtothe simi-
lar air drilling model plots in Chapter 8 (small pressure magnitudes). Field