Page 408 - Air and Gas Drilling Manual

9-12 Air and Gas Drilling Manual
tri-cone roller cutter insert type (nozzles 11/32 inches). The anticipated drilling rate
in a sandstone and limestone sequence in the interval is approximate 60 ft/hr. The
average rounded diameter of the rock cutting particles generated by this drill bit is
estimated to be 0.198 inch. The openhole interval below the casing shoe is to be
from 7,000 ft to 10,000 ft.

Figure 9-4: Illustrative Example 9.1 casing and openhole well geometric configuration.
The drill string for this illustrative example 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 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 borehole
is to be drilled with an aerated fluid composed of a fresh water base drilling mud and
compressed air. The drilling mud is to have a specific weight of 10 lb/gal drilling
2
mud with a plastic viscosity of 30 cps and a plastic yield stress of 5 lb/100 ft .
Drill pipe injection technique will be used and the drilling operation will be carried
out to maintain a bottomhole pressure of 3,500 psig while drilling the interval from
the 7,000 ft to 10,000 ft. A horizontal section of API line pipe that runs 100 ft
from just above the BOP stack to the mud tank is to be used as the return flow line.
The surface return flow line is API 6 5/8 inch line pipe, 32.71 lb/ft nominal, Grade
B. The inside diameter of this line pipe is 5.625 inches. Two gate valves are