Page 527 - Air and Gas Drilling Manual

10-52 Air and Gas Drilling Manual
The inner surface of this annulus section is the outer surface of the drill collar
geometry has the surface roughness of commercial steel pipe, e p. The surface
roughness of commercial steel pipe is
e p 0 00015 ft
.
Thus, using Equation 8-2, the average absolute surface roughness of this annulus
section, e av5, is
0 656)
(. (. 2 (. (. 2
0 563)
0 00015)
001)
4 4
e av5
0 563)
0 656)
(. 2 (. 2
4 4
e 0 0058 ft
.
av5
Therefore, Equation 6-92 becomes
2
1
f a5
.
0 656 0 563
.
2 log 114
.
.
0 0058
f a5 0 079
.
Equation 6-88 for the fifth increment in the annulus can be solved for the
pressure at bottom of the increment, P a5. This involves selecting this upper limit of
the intergral by a trial and error procedure. The magnitude of the upper limit
pressure on the left side of the equation is selected to allow the left side integral to
equal the right side integral. The integration can be carried out on the computer
using one of the commercial analytic software programs. The trial and error
magnitude of the upper limit pressure that satisfies Equation 6-88 for this annulus
section is
.
p a5 1 116 2 psia
,
P p 144
a5 a5
2
P a5 160 728 lb/ft abs
,
Substituting the values of ˙ w , Q g, Q w, P g, P a4, P a5, T g, T av5, D h, D 4, f a5, and g
t
into the left side of Equation 6-88 gives