Lesson 4 Air, Gas, Mist Drilling

8/3/2019 Lesson 4 Air, Gas, Mist Drilling

1/82

PETE 689Underbalanced Drilling (UBD)

Harold Vance Department of Petroleum Engineering

Read: UDM - Chapter 2.1 - 2.4

Lesson 4Air, Gas and Mist Drilling.


2/82

Air, Gas, and Mist DrillingGases used in UBD.

Dry air drilling. Nitrogen drilling.

Natural gas drilling.

Mist drilling.

Optimized hole cleaning.



3/82

Gases for UB Drilling

Air.

Cryogenic Nitrogen.Membrane Nitrogen.

Engine Exhaust.Natural gas.



4/82

Gases for UB Drilling

79% N2, 21% O

2.

Corrosion.

Fire.

US$3,000 Day.

Mod and Demob.


Compressed Air


5/82

Cryogenic Nitrogen40 year old technology.

Made as a by product of liquid

oxygen manufacture.

Air replacement.

No corrosion.

No downhole fires.

99.9% pure N27K-40K US$/day.



6/82

Delivery

Bottled gas.

Truck.

Storage tank ona ship.


Cryogenic Nitrogen


7/82

Stainless Steel

Liquid Nitrogen

(-320O

F)

Carbon Steel

Gaseous Nitrogento well

80OF, 0-10,000 psi

Pump

Vaporizer

Cryogen Nitrogen-PumpingEquipment



8/82

ProcedureDetermine Gas Volume Required.

Convert from Liquid Volume.

1 gallon liquid nitrogen produces93.12 ft3 of N2

at SCP.

1 m3 of N2

liquid produces 698 m3

of gas at SCP.



9/82

Nitrogen

Conversion Factors

1 gal of liquid nitrogen is

93.12 ft3 at STC.

1 gal of liquid nitrogen is0.1333 ft3.

1 liter of liquid nitrogen is698 litres of gas at STC.



10/82

Cryogenic Nitrogen CostWorld-wide

1-3 US $/gal. 0.10 US $/scf.

Canada

0.02 US $/scf.South America

1.00 US $/m3.Harold Vance Department of Petroleum Engineering


11/82

UB Drilling Gas AlternativesNitrogen Membranes

95% N2, 3-5% O2.

Corrosion considerations.

Combustion considerations.

Approximately 15,000 US $/day.Mob/demob costs.



12/82

Membrane NitrogenOn site manufacture.

Dependent on concentration.

Directly proportional topressure and rate.

Inversely proportional to gaspartial pressure.

Driven by dissolution anddiffusion.



13/82

Individual Hollow

Polmeric Gas Separation Fiber



14/82

Individual Hollow

Polmeric Gas Separation Fiber


Oxygen and Water Vapor are Fast Gaseswhich quickly permeate the membrane,allowing Nitrogen to flow through thefiber bores as the product stream.

Nitrogen

Oxygen

Water VaporNitrogen


15/82

HOLLOW FIBERMEMBRANE

FEED AIR

OXYGEN- ENRICHED AIR

NITROGEN

ENRICHEDGAS

N2 Generating

Unit A Bundle Of Fibers



16/82

Equipment RequiredCompressor.

Filters-fibers will plug ifthe air is not filtered.

NPU or NGU.

Controller.Booster(s).



17/82

Drilling

Rig

Optional BoosterCompressor

Filter andAir Separation

Membrane System

Feed Air

Compressor

Membrane

Nitrogen Production Unit



18/82

1997 Nitrogen Unit.

N2 units with

coolers.8x30x8 high

23,000 psi

1200 scfm N2 at5% 02



19/82

Skid-Mounted Nitrogen

Producing Unit (NPU)1998



20/82

Weatherford 2000

Nitrogen Generation Unit.

1. N2 500-600 scfm.

2. 2000 psi comp.

3. 27 gph diesel.

4. 8x20x16 high.

Nominal O2 5%

1.

2.3.

4.



21/82

Nitrogen Membrane System

1999

1

2 35



22/82

ProcedureDetermine volume requirement.

Determine maximum oxygenconcentration.

Determine effective volume fromunits.

Determine pressure requirement.



23/82

Oxygen Concentration

% Oxygen is only partially a

valid concept for fire. Ignition temperatures and

water content play a big part.

% Oxygen is important forcorrosion.



24/82

Recent Combustion Work

Testing:

Alberta Research Council.

Counter claims of increasedcorrosion and combustion with

membrane generated N2


Mi i


25/82

MinimumOxygen for Combustion

(with Methane)


%OxygenR

equiredforCom

bustion

Pressure (psia)

12.00

11.50

11.00

10.50

10.00

9.50

9.00

8.50

8.00

0 500 1000 1500 2000 2500 3000


26/82

Nitrogen Source SelectionCryogenic vs. Membrane

Location.

Job duration.

Volume requirement.

Pressure requirement.Purity requirement.



27/82

Operating Cost

Canada

USA Crossover between cryogenic costs

and membrane costs is generallyabout three days of operation.

Transportation and mobilization arebig items.



28/82

Cryogenic

Nitrogen Operating Cost

Canada

10,000 US $/day minimum. 40,000 US $/day maximum.

(500-1800 scfm for 20 hrs/day).



29/82


Flow Path


30/82

Exhaust Gas

Generating Unit 1980



31/82

ExhaustGas System



32/82

Natural Gas for UB Drilling

Available.

No downhole fires.

No corrosion.

Low cost, long termcontracts.



33/82

Pressure

Determine requirement

as for air, but allow forlesser specific gravity.

Delivery pressure set atsource.



34/82

Fuel Gas & Group Gas Pipeline



35/82

Natural Gas Pipeline Hook Up(Lyons, 1984)

~500Psig

Pipeline

Flow

Choke/Controller

Flow to rig.

Auxiliary line

to rig.

Main Pipeline.



36/82

Natural Gas Concerns

May be pressure limited.

Heavier hydrocarbonsrepress foam so be surethat they are stripped out.



37/82

Amoco Crossfield

Gas Recovery Project



38/82

177.8 mm Casing @ 2403 m

155.6 mm Openhole

778 m

2350m

Target TMD = 3181 m

88.9 mm Drill Pipe

KOP = 2250 m

120.6mm PDM

Elkton: GasBHP = 7.0 MPaBHT = 80oC

Drilling FluidWater = 1000 kg/m3

Viscosity = 1cP

Amoco Crossfield 9-12 Well



39/82

Crossfield

Gas Recovery ProjectWhy it was done:

Increasing public concernsover flaring.

Increasing EUB requirements

for public consultation andnotification.



40/82

Perfect fit with Amocos goal of

reducing greenhouse gasemissions.

Try out new idea and technology.Great plumbing setup.

Crossfield




41/82


Gas Flare System

Horizontal Separator

Choke Manifold

RBOPTM

Produced GasCompressors

Feed Gas Line

Gas Gathering Line

Drilling Rig

Feed Gas Compressors

Gas Processing Unit

Flare KnockoutVessel



42/82

Compression

& Scrubber/Filter Units

Recovery Gas CompressorsScrubber/Filter Unit

Feed Gas Compressors



43/82

Flow Control Manifold



44/82

Gas Scrubber & Filter Unit



45/82

Gas Recovery Summary


0

2

4

6

8

10

12

14

16

MMCFD

Gas Conserved Gas Flared


46/82

Gas Recovery SummaryConserved 92%.

Inc. Cost 170k US $.

No need to optimizeGLRs.

75 MMCFD well.


0

2

4

6

8

10

12

14

16

Gas Conserved Gas Flared


47/82

Crossfield

Gas Recovery ProjectResults

Estimated costs were 250kUS $,actual cost was 170kUS $.

Conserved 92% of flow from thewell.

Eliminated need to optimize thegas/liquid ratios.

75 MMCFD storage well.



48/82

Hole CleaningOptimizing hydraulics with gasses is

primarily concerned with holecleaning - getting the cuttings that

are generated by the bit out of thehole.

With gas, rheological properties have

very little to do with hole cleaning.Hole cleaning with gasses is almost

entirely dependent on the annularvelocity.



49/82

Drag and Gravitational ForcesFlowing air exerts a drag force on

cuttings.

Gravitational force on the cuttings

Therefore there is a thresholdvelocity in which the cuttings will

be lifted from the wellbore.

Threshold velocity increases withsize of cuttings.



50/82

Hole CleaningCompressibility of air (or gas)

complicates matters.

Frictional pressure increasesdownhole pressure - decreasesvelocity downhole.

Suspended cuttings increase thedensity of the air, increasingdownhole pressure.



51/82

Hole Cleaning


Temperature has an effect on

volumetric flow rate.

We must pump at a velocity

high enough to remove the

cuttings, but not too highwhere we waste energy.


52/82

Hole Cleaning Criteria

Terminal Velocity Criteria.

Minimum Energy Criteria.

Minimum BHP Criteria.



53/82

Terminal Velocity CriteriaGray determined that the

minimum velocity of the gas

must be at least as high as theterminal velocity of the cuttingin order to lift the cutting from

the wellbore.

Vc = Vf- Vt



54/82

g gravitational acceleration, 32.17 ft/sec2

dc characteristic particle diameter, ft.

Cd drag coefficient.

c density of cuttings, lbm / ft3

f density of fluid, lbm/ ft3

Terminal Velocity


=Vt 4gdccf

3Cd f


55/82

Terminal Velocity


Vt = 3.369dcTc

P

For flat cuttings

Vt = 4.164dcTc

P

For sub-round cuttings, T and P are atbottom hole conditions in 0R and psia.


56/82

Terminal Velocity

Terminal velocity in air drilling

is determined mainly by: cutting diameter, shape, and

density.

bottom hole temperature andpressure.



57/82

Factors Effecting Vt

Shape (roundness).

Increased Size.Increased Temperature.

Increased Density.

Increased Pressure.

Increases.

Increases. Increases.

Increases.

Decreases.



58/82

Terminal VelocityAs pressure increases Vt decreases.

As pressure increases Air velocity

decreases.

If the mass flow rate of gas remainsconstant the local air velocity

decreases with increasing pressure.The air flow rate required to lift the

cuttings increases with increasing BHP.Harold Vance Department of Petroleum Engineering


59/82

=m +dP fm mV

2m

dL 2g (Dh Dp)Eq. 2.5

fm Friction factor of the mixture

of air and cuttings.

m Mixture density, lbm/cu.ft.

Vm Mixture velocity, ft/s.g Acceleration due to gravity.

Dh Hole diameter, ft.

Dp Pipe diameter, ft.

Friction Pressure



60/82

Friction Pressure


fm= a + c

a =

0.14

( Dh Dp)0.333

Weymouth quation.

Gou argued that Nikuradse is more correct.

1a

= 1.14 0.86ln 2

Dh - Dp

= absolute roughness of the pipe.


61/82

Friction Pressure

Mixture density of air and cuttings inthe annulus is determined by the massof the cuttings and the density of theair.

Air density is a function of the pressure.

Mass of the cuttings in the wellbore is afunction of:

ROP Hole cleaning efficiency.



62/82

Friction Pressure

Pressure drops down the drillstringand through the bit play a part inBHP due to temperature effects.

Temperature is also effected by:

Formation temperature.

Influx of formation fluid (expansionof gas into the wellbore).

Mechanical friction.

Pressure.Harold Vance Department of Petroleum Engineering


63/82

Required injection rates?Relating downhole air velocities to

surface injection rates is quite

complex.We need cuttings shape and size

to determine terminal velocity.

Methods required knowledge ofthe cutting shape and size.



64/82

Minimum Energy CriteriaProbably the most widely used criteria

was developed by Angel in 1957.

Angel assumed that, for efficientcuttings transport downhole, thekinetic energy of the air striking each

cutting should be the same as that ofair giving efficient cuttings transportat standard pressure andtemperature.



65/82

Minimum Energy Criteria


1

2minV

2min= stpV

2stp

1

2

Pmin Density of air (or gas) at the minimumrequired downhole injection rate, lbm/cuft.

Vmin Air (or gas) velocity downhole, ft/min.

Pstp Density of air (or gas) at standard temp andpressure, lbm/cuft.

Vstp Air (or gas) velocity at standard Temp andpressure, ft/min.


66/82



Vmin= Vstp

Pstp

Pmin


67/82


Experience from shallow blast holes,drilled in limestone quarryingoperations, indicated that cuttings were

transported efficiently if the air velocityequaled or exceeded 3,000 feet perminute.

This is equivalent to Grays terminalvelocity for flat cuttings with a diameterof 0.46 in. and for sub-rounded particlesof 0.26 in.




68/82



dP

dL= m+

mmV2

m

2g (Dh Dp)

m = a 1+Wc

Wa

Wc Mass of cuttings generated in a given time;the mass flow rate of cuttings, lbm/min.

Wa Mass of air flowing past any point in the well ingiven time; the mass flow rate of air, lbm/min.

Angel computed the downhole air pressure

with eq. 2.5


69/82



Pb = P2

s-abTs

2 T abT2

G a Ts G - a+

2aG

Ps Surface air pressure, lbf/sq.ft, absolute.

Ts Surface temperature,0F.

G Annular temperature gradient,0

F/100.T Downhole temperature = Ts+Gh

h Hole depth.


70/82



SQ + 28.8.

ROP.

Dh2

53.3Qa =

S Gas specific gravity (air=1)

Q Gas flow rate, scf/mROP Penetration rate, ft/hr

1.625 x 10-6Q2

(Dh Dp) 1.333 (Dh2 Dp2)2b=

Dh Hole diameter, ft.

D2 Drillpipe diameter, ft.


71/82

Minimum Energy CriteriaThis was combined with the cuttingstransport criterion defined in Eq 2.10to deduce the minimum air flow rate

as a function of hole depth, annulargeometry, and penetration rate.

Eq. 2.10


Vmin = Vstp stpmin


72/82


To simplify, the average downholetemperature can be used to

calculate BHP.


6.61S(Ts + Gh) Q2

(D2

h D2

p)2

V2

stp

= (P2s + bT2

av) e2ah/Tav bT2av


73/82

This was solved numerically for the gasinjection rate required to give anannular velocity equivalent in cuttingslifting power to air with a velocity of3000 ft/min.

A series of charts was generated fordifferent combinations of hole size,drillpipe diameter and penetration rates




74/82

Qmin can be approximated by:

Qmin = Qo + NH

Qo Injection rate (scfm) at zerodepth that corresponds to anannular velocity of 3000 ft/min

N Factor dependent on thepenetration rate (Appendix C)

H Hole depth, (thousands of feet).




75/82

Data for calculating approximate circulation rates required toproduce a minimum annular air velocity which is equivalent in

lifting power to standard air velocity of 3.000 ft/min.

(Angel, 1957).

Appendix C



76/82


BottomholePress

ure(psia)

250

200

150

100

50

0

0 2000 4000 6000 8000 10000 12000

Depth (feet)


77/82


BottomholePress

ure(psia)

0 2000 4000 6000 8000 10000 12000

Depth (feet)

80

70

50

40

30

20

10

0

60


78/82

7-7/8 hole 3-1/2 drillpipe

6 drill collars 3800 hole depth


Annular Bottomhole Pressuresin An Air Drilled Hole-comparison OfPredictions And Measurements Made While Circulating Off-bottom


79/82


BottomholePressure(psia)

45

40

25

20

30

35

500 600 700 800 900 1000 1100 1200 1300

Flow Rate (scfm)


80/82


BottomholePress

ure(psia)

500 600 700 800 900 1000 1100 1200 1300

Flow Rate (scfm)

34

32

30

28

26

24

22

20


81/82


Comparison of air rates recommended by several different cuttingstransport analyses (after Guo et al, 199412).

RequiredRateo

fAir(scfm)

3.5

3

2.5

2

1.5

1

0.5

00 2000 4000 6000 8000 10000 12000 14000 16000 18000

Depth ( feet)

Minimum BHP Criteria


82/82

Minimum BHP Criteria

Angel analysisdoes not predict aminimum BHP, butgives a pressure

that decreasesmonotonicallywith decreasingair flow rate.

The influence of air flow rate onannular pressure drop (after Supon

and Adewumi 19915)

Annulus Air Velocity

AnnulusPressureDrop

AnnulusPressureDrop

Documents

Lesson 4 Air, Gas, Mist Drilling