8/13/2019 Lesson 14 Air, Gas, Mist Cont

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ATM ATMHarold Vance Department of

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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