Page 423 - Air and Gas Drilling Manual

surface return flow line will be at nearly the surface geothermal temperature at steady
state flow conditions). Equation 6-74 can be altered to allow its application to
horizontal flow in the surface return flow line. This altered equation is
P s dP L s Chapter 9: Aerated Fluid Drilling 9-27
dl (9-11)
B () 0
P
P g s
where
2
P g T r
Q g Q m
w ˙ t f sr P T g
P
B ()
s P g T 2 gD 2
r
Q g Q m sr 4 D sr
P T g

2
and P is the pressure at the entrance of the surface return flow line (lb/ft , abs),
sr
f is the Fanning friction factor for flow in the surface return flow line,
sr
D is the inside diameter of the surface return flow line (ft),
sr
L is the length of the surface return flow line (ft).
sr
In order to obtain the approximate value of the Fanning friction factor for
Equation 9-11, it is necessary to estimate the Reynolds number and, thus, the flow
conditions inside the surface return flow line. This is accomplished by determining
the Reynolds number at the exit end of the surface return flow line and assuming
this Reynolds number approximates the flow conditions throughout the flow line.
The inside diameter of the surface return flow line, D , is
sr
.
d sr 5 625 inches
.
5 625
D sr
12
.
D sr 0 469 ft
The length of the surface return flow line, L , is
sr
L 100 0.ft
sr
The absolute viscosity of the gas (air) at atmospheric conditions, g , is
.
0 012 cps
g
(.012 ) (.001 ) (.02089 )
0
0
0
g