Page 448 - Air and Gas Drilling Manual

9-52 Air and Gas Drilling Manual
From Equation 6-80, the equivalent single diameter for this drill bit, D e, is
D
.
e 3 0 02865 2
D e 0 0496 ft
.
The approximate specific weight of the aerated fluid at the bottom of the
annulus, mixbh, is
w ˙ g w ˙ m
mixbh
P g T 5
Q g Q m
P a5 T g
Substituting the values of ˙ w , ˙ w , P g, P a5, T g, T 6, Q g, and Q m into the above
m
g
equation gives, the specific weight of the aerated fluid mixture at the bottom of the
annulus is
.
.
1 282 31 92
mixbh
,
.
1 826 6 . 604 41
.
(. 0 426
19 47)
,
.
505 858 519 67
65 4 lb/ft 3
.
mixbh
Using Equation 6-79, the pressure change in the aerated fluid through the drill bit,
∃ P b, can be approximated by
2
.
.
1 282 31 92
∃ P b 2
.
2 32 2) ( 65 4) ( 0 81) 2 0 0496 4
.
(
.
.
4
∃ P b 106 782 lb/ft 2
,
where the nozzle loss coefficient is taken to be 0.81 (see Chapter 6, Section 6.4).
Using Equation 6-81, the pressure in the aerated fluid just above the drill bit
inside the drill string, P i5, is
P P ∃ P
i5 a5 b
Using the above equation, the pressure in the aerated fluid just above the drill bit
inside the drill string is