Page 334 - Air and Gas Drilling Manual

Chapter 8: Air, Gas, and Unstable Foam Drilling 8-17
V
= 21 8 ft/sec
.
bh
In Chapter 1 an analytic comparison was made between an air drilling example
and a mud drilling example. Using Equations 1-1 and 1-2 from that discussion, the
kinetic energy per unit volume at the bottom of the borehole in the annulus, KE bh, is
.
ρ = 0 407
bh
.
32 2
ρ = 0 0126 lb − sec 2
.
bh
ft 4
.
) 21 8 . )
KE bh = 1 (0 0126 ( 2
2
ft − lb
.
KE bh = 3 003
ft 3
The trial and error process for the above requires an iterative selection of the
value of q g until the kinetic energy at the bottom of the borehole in the annulus is
3
equal to 3.0 ft-lb/ft . In this example the value of q g that will give a kinetic energy
3
value equal to 3.0 ft-lb/ft is 1,588.8 scfm. Figure E-13 in Appendix E gives the air
minimum volumetric flow rates for a 4 1/2 inch drill pipe in a 7 7/8 inch borehole.
Figure E-13 shows the approximate minimum volumetric flow rate of 1,588.8 scfm
for the drilling rate of 30 ft/hr and depth of 10,000 ft. This example demonstrates
how these figures Appendix E were developed.
Illustrative Example 8.2 As in Illustrative Example 8.1, a 7 7/8 inch diameter
borehole (drill bit diameter) is to be drilled out of the bottom of API 8 5/8 inch
diameter, 28.00 lb/ft nominal, Grade H-40, casing set to 7,000 ft (see Figure 8-4 for
well casing and openhole geometric configuration). The openhole interval below the
casing shoe is to be drilled from 7,000 ft to 10,000 ft. The drill string is made up
of 500 ft of 6 3/4 inch by 2 13/16 inch drill collars above the drill bit and API 4 1/2
inch, 16.60 lb/ft nominal, EU-S135, NC50 (IF) to the surface. The drilling is to be
carried out at a surface elevation location of 4,000 ft above sea level where the actual
atmospheric temperature is 60˚F. The regional geothermal gradient is approximately
0.01˚F/ft. The anticipated drilling rate of penetrations in the sedimentary rock
formations is 60 ft/hr. The blooey line for this drilling operation is a single
horizontal section of casing that runs 200 ft from just above the BOP stack to the
burn pit. The casing used for the blooey line is API 8 5/8 inch, 24.00 lb/ft
nominal, Grade J-55, casing. Two gate valves are in the blooey line at the end of
the line that is attached to the BOP stack. These valves have an inside diameter of 7
9/16 inch. Determine the direct circulation approximate minimum volumetric flow
rate for this drilling operation.
It is only necessary to obtain the approximate minimum volumetric flow rate for
a drilling operation. The borehole is never drilled with only the minimum