Page 441 - Air and Gas Drilling Manual

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# 445 579 dP Chapter 9: Aerated Fluid Drilling 9-45
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2 375
2
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# 40 123 1 . 0 426
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# 34 15 0 065 P
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∀ 291 298 1
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40 123 1 .
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0 426 18 10 % 0 656 2 0 375 2 &
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P 4

Substituting the values of H 1, H 2 and H 3 into the right side of Equation 6-74 gives
6 650 350 2 375
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,
1 dh 2 375
,
6 650 350
As can be seen in the above, the right and left hand sides of Equation 6-74 yield the
same answer. This shows that the upper limit pressure is correct.
The fourth annulus section increment is denoted by length H 4. The temperature
at the bottom of the length H 4 in the openhole annulus section of the borehole
(bottom of the drill pipe tool joints lumped geometry), T 4, is
T 4 T r 001 ( H 1 H 2 H 3 H )
.
4
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,
(
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T 4 T r 0 01 6 650 350 2 375 125)
T 599 41.˚R
4
The average temperature of this openhole annulus section H 4 is
T 3 T 4
T av4
2
T av4 598 79.˚R
In order to obtain the approximate value of the Fanning friction factor for
Equation 6-74, it is necessary to estimate the Reynolds number and, thus, the flow
conditions in the openhole annulus section along H 4. 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
openhole annulus section is determined from P a3. This is
( 445 579) ( 1 0)
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ga4
( 53 36) ( 598 78)
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