Page 511 - Air and Gas Drilling Manual

10-36 Air and Gas Drilling Manual
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.
The second annulus section increment is denoted by the length H 2. The
temperature at the bottom of the length H 2 in the cased annulus section (bottom of
the drill pipe tool joints lumped geometry), T 2, is
T 2 T r 001 ( H 1 H )
.
2
.
T T 0 01 6 650 350)
,
(
2 r
T 2 574 41˚R
.
The average temperature of this cased annulus section H 2 is
T 1 T 2
T
av2
2
.
T av2 572 66˚R
In order to obtain the approximate value of the Fanning friction factor for
Equation 6-91, it is necessary to estimate the Reynolds number and, thus, the flow
conditions in the cased annulus section along H 2. This is accomplished by
determining the Reynolds number at the exit end of this annulus section and
assuming this Reynolds number approximates the flow conditions throughout the
annulus section.
Using Equation 4-11, the approximate specific weight of the gas as it exits this
cased annulus section is determined from P a1. This is
.
,
( 70 504) ( 1 0)
a2
.
( 53 36) ( 572 66)
.
.
2 307 lb/ft 3
a2
The volumetric flowrate of the gas as it exits this cased annulus section is
w ˙ g
Q ga2
ga2

1 821
.
Q ga2
.
2 307
3
.
Q ga2 0 789 ft /sec