Page 500 - Air and Gas Drilling Manual

From Equation 9-7, the kinematic viscosity of the foam just upstream of the back
, is
pressure valve,
sfbp
.
0 00009459 Chapter 10: Stable Foam drilling 10-25
sfbp
.
0 0461
ft 2
.
0 00205
sfbp
sec
The average velocity of the foam just upstream of the back pressure valve, V ,
sfbp
is
Q gbp Q w
V sfbp
D sr 2
4
(.46 . 0 234 )
11
V sfbp
. 0 469 2
4
V 67 8 ft/sec
.
sfbp
Equation 6-103 can be altered to allow its application to the horizontal flow in
the surface flow line. Thus, the Reynolds number of the foam flow just upsteam of
the back pressure valve, N , is
Rsfbp
V sfbp D sr
N Rsfbp
sfbp
8
0
(67 . ) ( .469 )
N Rsfbp
. 0 00205
N 15 489
,
Rsfbp
The Reynolds number calculation above is greater than 4,000. This indicates that
the flow condition is turbulent. Therefore, the empirical von Karman equation (i.e.,
Equation 6-106) must be used to determine the Fanning friction factor for the aerated
fluid flow inside the return flow line. Equation 6-106 can be modified for
application to the surface return flow line situation.
The surface roughness of the inside of the steel surface return flow line is the
absolute surface roughness of commercial steel pipe, e . This is
p