Page 528 - Air and Gas Drilling Manual

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∃
&
&
& 160 728 dP Chapter 10: Stable Foam drilling 10-53
500
!
2
& 58 477 0 . 0 234
,
.
& 17 37 0 079 P
.
.
% 137 281 1 ∀
,
58 477 0 .
,
.
.
.
.
0 234 599 0 656 2 0 563 2
P 4
#
Substituting the value of H 1, H 2, H 3, H 4 and H 5 into the right side of Equation 6-88
gives
,
,
6 650 350 2 375 125 500
1 dh 500
,
6 650 350 2 375 125
,
As can be seen in the above, the right and left hand sides of Equation 6-88 yield the
same answer. This shows that the upper limit pressure is correct.
At this point in the calculation process it is necessary check the two controlling
criteria. These are the foam quality at the bottom of the annulus and the kinetic
energy per unit volume of the flowing foam at a position just above the drill collars.
Using Equation 4-11, the approximate specific weight of the gas at the bottom
of the annulus is determined from P a5. This is
,
1
(160 728 ) ( . )
0
gbh
(53 .36 ) (604 . )
41
4 984 lb/ft 3
.
gbh
The volumetric flowrate of the gas at the bottom of the annulus is
w ˙ g
Q gbh
gbh
1 821
.
Q gbh
.
4 984
3
Q gbh 0 365 ft /sec
.
The foam quality at the bottom of the annulus is
Q gbh
sfbh
Q gbh Q w