Page 431 - Air and Gas Drilling Manual

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D
3
The total length of the drill collar increment (fifth), H 5, in the openhole section
of the borehole is 0 552 ft Chapter 9: Aerated Fluid Drilling 9-35
H 500 ft
5
The inside diameter of the openhole along this length of the openhole section of the
borehole is
.
D h 0 656 ft
and the outside diameter of the drill collars along this length is
d 4 675 inches
.
d 4
D 4
12
D 4 0 563 ft
.
Using the description of the annulus geometry given above each of the five
increment changes in cross-sectional area can be analyzed starting with the gas flow
exiting at the top of the annulus.
Cased Section of the Annulus (Surface to 7,000 ft)
The first annulus section increment is denoted by the length H 1. The
temperature at the bottom of the length H 1 in the cased annulus section of the
borehole (bottom of the drill pipe body lumped geometry), T 1, is
.
T 1 T r 001 H 1
,
T 1 T r 0 01 6 650)
.
(
T 1 570 91.˚R
The average temperature of this cased annulus section H 1 is
T r T 1
T av1
2
T av1 537 66.˚R

In order to obtain the approximate value of the Fanning friction factor for
Equation 6-74, it is necessary to estimate the Reynolds number and, thus, the flow