Page 233 - Air and gas Drilling Field Guide 3rd Edition

224 CHAPTER 9 Aerated Fluids Drilling

1
API 4 2 = -in (114 mm), 16.60-lb/ft (7.52 kg/m) nominal, IEU-S135, NC46 drill pipe
1
to the surface. The tool joints of this drill pipe have an outside diameter of 6 4 = in
3
(154.8 mm) and an inner diameter of 2 4 = in (69.9 mm). The drilling is carried
out at a surface location of 4000 ft (2129 m) above sea level (see Table 5-1 and
Appendix B). The regional geothermal gradient is approximately 0.01 F/ft

(0.018 C/m).
The incompressible drilling fluid has a specific weight of 10 lb/gal (1200.0
3
kg/m ) and a viscosity of 30 cp. The drill pipe injection technique is used, and
the drilling operation is carried out to maintain a bottom hole pressure of 3360
2
psig (2414 N/cm gauge) at the bottom of the open hole interval at 10,000 ft
(3048 m). A horizontal section of API line pipe that runs 100 ft (30.5 m) from just
above the BOP stack to the mud tank is used as the return flow line. The surface
5
return line is an API 6 8 = -in (168 mm) line pipe, 32.71 lb/ft (49.0 kg/m) nominal,
Grade B. The inside diameter of this line pipe is 5.625 in (143 mm). Two gate
valves are installed in the return flow line at the end of the line that is attached
=
9
to the BOP stack. These valves have an inside diameter of 5 16 in (141 mm).
An average drilling cuttings particle diameter of 0.36 in (9.14 mm) and a spheric-
ity coefficient of 1.0 are used to determine the approximate minimum volumetric
flow rate of the incompressible drilling fluid that is required for this aerated
drilling operation.

Minimum Incompressible Fluid Volumetric Flow Rate (USCS Units)
The incompressible fluid used in this illustrative example is a water-based drilling
mud with plastic properties. Therefore, the minimum volumetric flow rate of
the incompressible drilling fluid is determined using Equations (9-1) through
(9-5) above.
The anticipated drilling rate is 60 ft/hr. The critical concentration velocity is
60
V c ¼
ð
3; 600 0:04Þ
V c ¼ 0:417 ft=sec:
The specific weight of the sedimentary rock to be drilled is approximately
g ¼ 2:7Þ 62:4Þ
ð
ð
s
3
g ¼ 168:5lb=ft ;
s
where the specific gravity of sedimentary rock is assumed to be approximately
2.7 (see Chapter 6).
The specific weight of the 10-lb/gal incompressible drilling fluid in consistent
units is
3
ð
10 12Þ
g ¼
f
231
3
g ¼ 75:0lb=ft :
f