Page 203 - Air and gas Drilling Field Guide 3rd Edition

194 CHAPTER 8 Air, Gas, and Unstable Foam Drilling

The weight rate of flow is

st at Q minat:
_ w min ¼ g Q minat ¼ g
This becomes
_ w min ¼ð0:0763Þð26:48Þ¼ ð0:0679Þ Q minat
ð 0:0763Þ
Q minat ¼ ð 26:48Þ
ð 0:0679Þ
3
Q minat ¼ 29:76 actual ft =sec
ð
q minat ¼ 60ð Þ 29:76Þ
q minat ¼ 1765:6 acfm:

Number of Primary Compressors Units Required
The primary compressor of choice is the four-stage reciprocating piston Dresser
Clark CFB-4 compressor described in Chapter 5, Section 5.7.2. This compressor
has a rated input of 1200 acfm. The minimum flow rate required to clean the well
is 1785.6 acfm. Therefore, to drill this example section of well at the 4000-ft
surface location, two Dresser Clark CFB-4 primary compressors will be required.
The factor of safety for the example drilling operations is

ð
2 ðÞ 1200Þ
FS ¼
ð 1785:6Þ
FS ¼ 1:34:
This exceeds the required minimum factor of safety for volumetric flow rate of 1.2.

SI Units
Specific Weight of Air at API Standard Conditions
At API standard conditions the atmospheric pressure is
2
p st ¼ 10:134 N=cm abs
P st ¼ p st 10000:0
2
P st ¼ 101340:0N=m abs;
2
where p st is atmospheric pressure (N/cm abs) and P st is atmospheric pressure
2
(N/m abs).
At API standard conditions the atmospheric temperature is
o
t st ¼ 15:6 C
T st ¼ t st þ 273:15
T st ¼ 288:76 K;
where t st is atmospheric temperature ( C) and T st is absolute atmospheric tem-

perature (K). Using Equation (5-11), the specific weight of the air at standard
conditions is