Page 337 - Air and Gas Drilling Manual

8-20 Air and Gas Drilling Manual
7 7/8 inch diameter, 10,000 ft deep borehole was approximately 1,840 acfm (for a
surface drilling location of 4,000 ft above sea level).
There are several possible candidate compressor units that could be used to
provide the compressed air supply for this example drilling operation. Two of these
candidates are discussed below.
Figures 4-22 and 4-23 show skid mounted Gardner Denver Model WEN, two-
stage, reciprocating piston primary unit and the Gardner Denver Model MDY, two-
stage, reciprocating piston booster compressor unit. The primary compressor has a
volumetric flow rate capability of 700 acfm at the 4,000 ft surface elevation location.
Thus, four primary compressor units would be needed for this operation (or 2,800
acfm) and would give a volumetric flow rate factor of safety of 1.52.
Figure 4-24 shows a semi-trailer mounted unit which has a MAN Model GHH-
CF2466, two-stage, rotary screw primary compressor and an Ariel Model JGJ/2, two
stage, reciprocating piston booster compressor integrated so that both compressors
can be driven by one large prime mover. The primary compressor has an
approximate volumetric flow rate capability of 1,727 acfm at the 4,000 ft of surface
elevation location. This compressor system is rated at ASME standard atmospheric
conditions. The specific weight of air at ASME standard conditions (i.e., 14.7 psia,
3
68˚F, and 36 percent relative humidity) is 0.0750 lb/ft (see Chapter 4). Therefore,
the volumetric flow rate output of this compressor unit adjusted to the reference API
standard conditions is
.
q =  0 0750  (1 727 )
,
 0 0763 
.
q = 1 698 scfm
,
or the above can be read as
,
q = 1 698 acfm
Thus, two of these compressor units would be required for the drilling operation (or
3,396 acfm) and would give a volumetric flow rate factor of safety of 1.85.
Figure 4-25 shows a semi-trailer mounted unit that has a Dresser Clark Model
CFB-4, four stage, reciprocating piston primary compressor. This four stage
compressor system is operated as a combined primary-booster system with a
continuous maximum output pressure of 1,000 psig. This compressor has a
volumetric flow rate capability of 1,200 acfm at the 4,000 ft of surface elevation
location. Thus, two compressor units would be required for the drilling operation
(or 2,400 acfm) and would give a volumetric flow rate factor of safety of 1.30.
Of these three candidate compressor systems, the semi-trailer mounted unit with
the Dresser Clark Model CFB-4, four stage, reciprocating piston compressor system
is selected for follow-on example calculations. This system should be more
economic than the other candidates since it is a single unit four stage reciprocating
piston compressor and two of these units have an overall factor of safety nearest to
the required 1.2. Also, this compressor system is capable of continuous operation at