Page 545 - Air and Gas Drilling Manual

10-70 Air and Gas Drilling Manual
P
p 144
i1
i1
2
P
,
i1 179 196 lb/ft abs
Substituting the values of ˙ w , ˙ w , Q g, Q m, P g, P i1, P i2, T g, T av2, D 6, f i2, and g
g
w
into the left side of Equation 6-102 gives
,
∃ 190 555
&
& dP
& 2 ! 350
,
& 55 635 3 .
.
& 16 42 0 017 P 0 234
.
.
% 179 196 55 635 3 . 1 ∀
,
,
.
.
.
0 234 18 80 0 292 2
P 4
#
Substituting the values of H 1, and H 2 into the right side of Equation 6-102 gives
6 650 350
,
1 dh 350
6 650
,
As can be seen in the above, the right and left hand sides of Equation 6-102 yield
the same answer. This shows that the lower limit pressure is correct.
The first drill string section increment is denoted by the length H 1. The
temperature at the bottom of the drill pipe body lumped geometry in the cased
section is
T 1 570 91˚R
.
The average temperature of the drill pipe body lumped geometry along H 1 and, thus,
the temperature of the aerated fluid flow inside the this drill string length is
T av1 537 66˚R
.
In order to obtain the approximate value of the Fanning friction factor for
Equation 6-102, it is necessary to estimate the Reynolds number and, thus, the flow
conditions inside the drill pipe body lumped geometry along H 1. This is
accomplished by determining the Reynolds number at the entrance end of the inside
of this drill string section and assuming this Reynolds number approximates the
flow conditions throughout the inside this drill string section.
Using Equation 4-11, the approximate specific weight of the gas as it enters this
drill string section is determined from P in. This is