Page 502 - Air and Gas Drilling Manual

Chapter 10: Stable Foam drilling 10-27
The stable foam flows from the top of the annulus into the entrance of the
surface return flow line. The friction flow loss of the turn and of the two valves at
the entrance of the surface return flow line must be included. The approximate
specific weight of the foam just after it passes through the Tee and the valves at the
top of the annulus is determined using the above value for P . The approximate
sr
specific weight at the Tee, Tee, is
w ˙
t
Tee P g T
r
Q g Q w
P sr T g
Substituting the values of ˙ w , P g, P , T g, T r, Q g, and Q w into the above equation
t
sr
gives the specific weight just downstream of the Tee and valves. This is
17 37
.
Tee
1 826 6 . 504 41
.
,
( 27 64) 0 234
.
.
,
.
4 604 4 . 519 67
.
1 597 lb/ft 3
Tee
The approximate velocity of the foam flow just downstream of the Tee and valves is
P
g T r
Q g Q m
P T
sr g
V Tee
D sr 2
4
Substituting the values of Q g, Q m, P g, P , T g, T r, and D into the above equation
sr sr
gives
,
1 826 6 . 504 41
.
.
.
( 27 64) 0 234
,
4 604 4 . 519 67
.
V Tee
(. 2
0 469)
4
.
V 63 02 ft/sec
Tee
The approximate pressure change, ∋ P Tee , through the two valves and Tee is