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8/13/2019 Lesson 14 Air, Gas, Mist Cont
1/19
ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Lesson 14
Air, Gas, and Mist Drilling
Read: UDM Chapter 2.1 - 2.4
pages 2.1-2.74
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Circulating Pressures
Calculating
standpipe pressure
starts withpredicting the
pressure just below
the bit, and workingyour way back to
the surface
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Bit Pressure Drop
As air flows through the jets, it expands in
response to the decrease in pressure and its
velocity increases
Once the pressure drop exceeds a certain
level, the air velocity reaches the prevailing
speed of sound.
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Bit Pressure Drop
At this point, the air cannot expand any
faster and the upstream pressure becomes
independent of the downstream pressure.
This implies that under sonic discharge
conditions the standpipe pressure is
independent of the annular pressure
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Bit Pressure Drop
b
k
k
b
a
P
kP
P
89.1Pand
1.4kair,For
olumeconstant vatthattopressure
constantatheatspecificofratiok
pressuredownstreamP
psiaflow,sonicofonsetat thepressureupstreamP
1
2
:isgasesidealinflowsonicofonsetfor theconditionThe
a
b
a
1
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Bit Pressure Drop
If the upstream pressure is more than 1.89
times the annulus pressure beneath the bit,
flow through the bit will be sonic.
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Upstream bit pressure - sonic
flow
2
a
n
5.0
1
1
ft/s32.17constant,nalgravitatiog
air)for(1gravitygasS
airforRlbf/lbm-ft53.3constant,gasuniversaltheR
Rbit,theaboveatureair temperT
sq.in.nozzles,bittheofareatotalA
lbm/sinairofrateflowmassG
1
2
k
k
a
n
akSgk
RT
A
GP
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Upstream bit pressure
sub-sonic flow
1
22
2
a2
11P
:bybitebeneath thpressureannulus
theandrateflowmassthetorelatedisbit
theabovepressurethesonic,-subremains
jetsethrough thvelocityflowairtheIf
k
k
bn
bb
PgkSATGkRP
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Upstream bit pressure
sub-sonic flow
lbm/cu.ft.STP,at0.0764
lbm/cu.ftSTP,atdensitygas
Rbit,thebelowretemperatu
60
236.01P
:becomesair thisfor
air
g
5.3
22
2
a
b
g
bn
bb
T
QG
PA
TGP
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Upstream bit pressure
sub-sonic flow
sonicisjetsthe
throughflowifbittheabovethatlower than
17%elyapproximatbebit willthebenow
atureair temperabsolutethat theIndicating
T
:fromestimatedbecandecrease
retemperatuthebehavior,idealAssumingbit.the
throughexpandsitascoolsairgcirculatinThe
1
b
k
k
a
baP
PT
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Standpipe pressure
ft.g,drillstrintheofdiameterinternal
10625.1
3.53
1
333.5
26
/2
/222
i
i
Th
Th
avas
D
D
Q
S
e
eTPP
av
av
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Steps to predicting standpipe
pressure Assess whether flow through bit is sonic or
sub-sonic
If sonic, the pressure above the bit is
determined with equation 2.21
This value is used in equation 2.25 to
predict standpipe pressure
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Steps to predicting standpipe
pressure If flow is sub-sonic, the annulus pressure
below the bit must be first predicted
(Angels analysis, etc) using equation 2.12. The pressure above the bit is determined by
equation 2.23
This value is used in Equation 2.25 todetermine standpipe pressure
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Important point
When air drilling, large changes in annulus
pressure may result in smaller changes in
standpipe pressure, or in the case of sonicflow through the bit, no change in standpipe
pressure at all.
Hole problems that lead to an increase inannulus pressure may be indicated by small
changes in standpipe pressure.
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Important point
It is very important to monitor the standpipe
pressure closely and react promptly to
unanticipated changes.It is important to know if flow through the bit
is sonic or not.
If flow is sonic, standpipe pressure will notchange with changes in annulus pressure
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering
Example
8.1/2 hole at 6000 drilled with 4 1/2
drillpipe air rate is 1400 scfm. Penetration
rate ranges up to 300 ft/hr. Bit has nonozzles in one example and 3- 14s in the
other.
TPETE 625T
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ATMPETE 625ATM
ATM ATMHarold Vance Department of
Petroleum Engineering