Page 347 - Air and Gas Drilling Manual

8-30 Air and Gas Drilling Manual
The total length of the drill collars increment (fifth), H 5, in the openhole section
of the annulus is
H 5 = 500 ft
The inside diameter of the openhole along this length of the openhole section of the
annulus is
D = 0 656. ft
h
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 arean 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 seciton increment is denoted by the length H 1. The
temperature at the bottom of the length H 1 in the cased annulus section (bottom of
the drill pipe body lumped geometry), T 1, is
T = T + 001 H
.
1 r 1
T = T + 0 01 6 650)
,
(
.
1
r
T = 570 91 R
o
.
1
The average temperature of this cased section length H 1 is
T + T
T av1 = r 1
2
o
T av1 = 537 66 R
.
Since both surfaces in this annulus section are commercial steel, then the surface
roughness is
e p = 0 00015 ft
.