Page 239 - Air and gas Drilling Field Guide 3rd Edition

230 CHAPTER 9 Aerated Fluids Drilling

and the compressible gas (air) can be used as initial values for the complicated
trial and error solution required for the full friction solution.
Illustrative Example 9.2 Using the nonfriction method and the given data and
results obtained in Illustrative Example 9.1, determine the approximate volumetric
flow rate of air required for the incompressible drilling fluid (drilling mud) volumetric
flow rate of approximately 191 gpm (723 lpm) while drilling at 10,000 ft (3048 m).

USCS Units
Table 5-1 gives an average atmospheric pressure of 12.685 psia for a surface loca-
tion of 4000 ft above sea level (also see Appendix B). The actual atmospheric pres-
sure for the air at the drilling location (that will be used by the compressor) is
p at ¼ 12:685 psia
P at ¼ p at 144
2
P at ¼ 1826:6lb=ft abs:
The actual atmospheric temperature of the air at the drilling location (used by the
compressor), T at ,is

t at ¼ 44:74 F
T at ¼ t at þ 459:67
T at ¼ 504:41 R:

Thus, P g and T g become
2
P g ¼ P at ¼ 1826:6lb=ft abs

T g ¼ T at ¼ 504:41 R:
Using Equation (4-11), the specific weight of the gas entering the compressor is
ð
ð 1826:6Þ 1:0Þ
g ¼
g
ð 53:36Þ 504:41Þ
ð
3
g ¼ 0:0679 lb=ft :
g
The bottom hole pressure in absolute pressure is
p bh ¼ 3360 þ 12:685
p bh ¼ 3372:685 psia
P bh ¼ p bh 144
2
P bh ¼ 485666:6lb=ft abs:
The temperature of the rock formations near the surface (geothermal surface
temperature) is estimated to be the approximate average year-round temperature

at that location on the earth’s surface. Table 5-1 gives 44.74 F for the average year-
round temperature for a surface elevation location of 4000 ft above sea level (see