Page 356 - Air and Gas Drilling Manual

14 .

04 .
2

2 635 
.

0 00802 

 .
+
P i5 = (,     Chapter 8: Air, Gas, and Unstable Foam Drilling 8-39
1
29 454)

14 
 232 2 . )  . (, 0 913) 
(
29 454) ( .
04 
   .  
2
,
P i5 = 31 330 lb/ft abs
P i5
p i5 =
144
.
p i5 = 217 6 psia
where for air k = 1.4 [12].
The open orifice diameters considered in this example yield only a slight
increase in the pressure (from approximately 205 psia at the bottom of the annulus to
a pressure of approximately 218 psia inside the drill bit above the orifices).
If jetting nozzles are inserted in the drill bit orifice openings they will create
sonic flow at the nozzle throats. This will result in higher pressures inside the drill
bit above the nozzles. Higher pressures above the nozzles will affect the pressures
inside the drill string. When nozzles are used, the pressure inside the drill string
will be higher and the injection pressure will be higher than where open orifices are
used. In general, jetting nozzles are only used in air and gas drill operations when
downhole motors or downhole air hammers are used. This will be demonstrated in
Chapter 11 where a downhole motor and an air hammer will be employed in the drill
string.
Geometry Inside the Drill String
Starting at the bottom of the drill string, the total length of the drill collars
length increment, H 5, in the openhole section is
H 5 = 500 ft
The inside diameter of the drill collars length in this openhole section is
d = 2 8125 inches
.
5
d
D = 5
5
12
D = 0 234 ft
.
5
The total length of the drill pipe tool joints lumped geometry increment, H 4, in
the openhole section is