PETE 689 Underbalanced Drilling UBD

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PETE 689 Underbalanced Drilling (UBD)
Lesson 4 Air, Gas and Mist Drilling.

• Read UDM - Chapter 2.1 - 2.4

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Air, Gas, and Mist Drilling

• Gases used in UBD.
• Dry air drilling.
• Nitrogen drilling.
• Natural gas drilling.
• Mist drilling.
• Optimized hole cleaning.

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Gases for UB Drilling

• Air.
• Cryogenic Nitrogen.
• Membrane Nitrogen.
• Engine Exhaust.
• Natural gas.

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Gases for UB Drilling
Compressed Air

• 79 N2 , 21 O2.
• Corrosion.
• Fire.
• US3,000 Day.
• Mod and Demob.

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Cryogenic Nitrogen

• 40 year old technology.
• Made as a by product of liquid oxygen
  manufacture.
• Air replacement.
• No corrosion.
• No downhole fires.
• 99.9 pure N2
• 7K-40K US/day.

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Delivery
Cryogenic Nitrogen

• Bottled gas.
• Truck.
• Storage tank on
• a ship.

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Cryogen Nitrogen-Pumping Equipment
Stainless Steel
Carbon Steel
Vaporizer
Liquid Nitrogen (-320OF)
Pump
Gaseous Nitrogen to well 80OF, 0-10,000 psi
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Procedure

• Determine Gas Volume Required.
• Convert from Liquid Volume.
• 1 gallon liquid nitrogen produces 93.12 ft3 of N2
  at SCP.
• 1 m3 of N2 liquid produces 698 m3 of gas at SCP.

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Nitrogen Conversion Factors

• 1 gal of liquid nitrogen is93.12 ft3 at STC.
• 1 gal of liquid nitrogen is0.1333 ft3.
• 1 liter of liquid nitrogen is698 litres of gas
  at STC.

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Cryogenic Nitrogen Cost

• World-wide
• 1-3 US /gal.
• 0.10 US /scf.
• Canada
• 0.02 US /scf.
• South America
• 1.00 US /m3.

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UB Drilling Gas Alternatives

• Nitrogen Membranes
• 95 N2 , 3-5 O2.
• Corrosion considerations.
• Combustion considerations.
• Approximately 15,000 US /day.
• Mob/demob costs.

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Membrane Nitrogen

• On site manufacture.
• Dependent on concentration.
• Directly proportional to pressure and rate.
• Inversely proportional to gas partial pressure.
• Driven by dissolution and diffusion.

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Individual Hollow Polmeric Gas Separation Fiber
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Individual Hollow Polmeric Gas Separation Fiber
Nitrogen Oxygen Water Vapor
Nitrogen
Oxygen and Water Vapor are Fast Gases which
quickly permeate the membrane, allowing Nitrogen
to flow through the fiber bores as the product
stream.
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N2 Generating Unit A Bundle Of Fibers
OXYGEN- ENRICHED AIR
FEED AIR
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Equipment Required

• Compressor.
• Filters-fibers will plug if the air is not
  filtered.
• NPU or NGU.
• Controller.
• Booster(s).

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Membrane Nitrogen Production Unit
Filter and Air Separation Membrane System
Optional Booster Compressor
Feed Air Compressor
Drilling Rig
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1997 Nitrogen Unit.

• N2 units with coolers.
• 8x30x8 high
• 23,000 psi
• 1200 scfm N2 at 5 02

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Skid-Mounted Nitrogen Producing Unit (NPU)1998
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Weatherford 2000Nitrogen Generation Unit.

• 1. N2 500-600 scfm.
• 2. 2000 psi comp.
• 3. 27 gph diesel.
• 4. 8x20x16 high.
• Nominal O2 5

1.
3.
2.
4.
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Nitrogen Membrane System 1999
2
3
5
1
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Procedure

• Determine volume requirement.
• Determine maximum oxygen concentration.
• Determine effective volume from units.
• Determine pressure requirement.

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Oxygen Concentration

• Oxygen is only partially a valid concept for
  fire.
• Ignition temperatures and water content play a
  big part.
• Oxygen is important for corrosion.

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Recent Combustion Work

• Testing
• Alberta Research Council.
• Counter claims of increased corrosion and
  combustion with membrane generated N2

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Minimum Oxygen for Combustion (with Methane)
Oxygen Required for Combustion
0 500 1000 1500
2000 2500 3000
Pressure (psia)
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Nitrogen Source SelectionCryogenic vs. Membrane

• Location.
• Job duration.
• Volume requirement.
• Pressure requirement.
• Purity requirement.

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Operating Cost

• Canada
• USA
• Crossover between cryogenic costs and membrane
  costs is generally about three days of operation.
  
• Transportation and mobilization are big items.

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Cryogenic Nitrogen Operating Cost

• Canada
• 10,000 US /day minimum.
• 40,000 US /day maximum.
• (500-1800 scfm for 20 hrs/day).

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Flow Path
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Exhaust Gas Generating Unit 1980
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Exhaust Gas System
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Natural Gas for UB Drilling

• Available.
• No downhole fires.
• No corrosion.
• Low cost, long term contracts.

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Pressure

• Determine requirement as for air, but allow for
  lesser specific gravity.
• Delivery pressure set at source.

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Fuel Gas Group Gas Pipeline
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Natural Gas Pipeline Hook Up(Lyons, 1984)
Main Pipeline.
Auxiliary line to rig.
500 Psig
Flow to rig.
Choke/Controller
Pipeline Flow
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Natural Gas Concerns

• May be pressure limited.
• Heavier hydrocarbons repress foam so be sure that
  they are stripped out.

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• Amoco Crossfield
• Gas Recovery Project

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Amoco Crossfield 9-12 Well
88.9 mm Drill Pipe
Drilling Fluid Water 1000 kg/m3 Viscosity 1cP
KOP 2250 m
2350 m
177.8 mm Casing _at_ 2403 m
155.6 mm Openhole
120.6mm PDM
Elkton Gas BHP 7.0 MPa BHT 80oC
778 m
Target TMD 3181 m
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CrossfieldGas Recovery Project

• Why it was done
• Increasing public concerns over flaring.
• Increasing EUB requirements for public
  consultation and notification.

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CrossfieldGas Recovery Project

• Perfect fit with Amocos goal of
• reducing greenhouse gas
• emissions.
• Try out new idea and technology.
• Great plumbing setup.

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Gas Recovery Project
RBOPTM
Gas Flare System
Drilling Rig
Choke Manifold
Flare Knockout Vessel
Horizontal Separator
Feed Gas Compressors
Produced Gas Compressors
Gas Processing Unit
Feed Gas Line
Gas Gathering Line
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Compression Scrubber/Filter Units
Recovery Gas Compressors
Feed Gas Compressors
Scrubber/Filter Unit
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Flow Control Manifold
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Gas Scrubber Filter Unit
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Gas Recovery Summary
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Gas Recovery Summary
Gas Conserved
Gas Flared
16

• Conserved 92.
• Inc. Cost 170k US .
• No need to optimize GLRs.
• 75 MMCFD well.

14
12
10
8
6
4
2
0
10-Jul
12-Jul
14-Jul
16-Jul
18-Jul
20-Jul
22-Jul
24-Jul
26-Jul
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Crossfield Gas Recovery Project

• Results
• Estimated costs were 250k US , actual cost was
  170k US .
• Conserved 92 of flow from the well.
• Eliminated need to optimize the gas/liquid
  ratios.
• 75 MMCFD storage well.

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Hole Cleaning

• Optimizing hydraulics with gasses is primarily
  concerned with hole cleaning - getting the
  cuttings that are generated by the bit out of the
  hole.
• With gas, rheological properties have very little
  to do with hole cleaning.
• Hole cleaning with gasses is almost entirely
  dependent on the annular velocity.

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Drag and Gravitational Forces

• Flowing air exerts a drag force on cuttings.
• Gravitational force on the cuttings
• Therefore there is a threshold velocity in which
  the cuttings will be lifted from the wellbore.
• Threshold velocity increases with size of
  cuttings.

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Hole Cleaning

• Compressibility of air (or gas) complicates
  matters.
• Frictional pressure increases downhole pressure -
  decreases velocity downhole.
• Suspended cuttings increase the density of the
  air, increasing downhole pressure.

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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 high
• where we waste energy.

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Hole Cleaning Criteria

• Terminal Velocity Criteria.
• Minimum Energy Criteria.
• Minimum BHP Criteria.

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Terminal Velocity Criteria

• Gray determined that the minimum velocity of the
  gas must be at least as high as the terminal
  velocity of the cutting in order to lift the
  cutting from the wellbore.
• Vc Vf - Vt

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Terminal Velocity
?c ?f 3Cd ?f
Vt
4gdc

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
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Terminal Velocity
dcT?c P
Vt 3.369
For flat cuttings
dcT?c P
Vt 4.164
For sub-round cuttings, T and P are at bottom
hole conditions in 0R and psia.
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Terminal Velocity

• Terminal velocity in air drilling is determined
  mainly by
• cutting diameter, shape, and density.
• bottom hole temperature and pressure.

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Factors Effecting Vt

• Shape (roundness).
• Increased Size.
• Increased Temperature.
• Increased Density.
• Increased Pressure.

• Increases.
• Increases.
• Increases.
• Increases.
• Decreases.

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Terminal Velocity

• As pressure increases Vt decreases.
• As pressure increases Air velocity decreases.
• If the mass flow rate of gas remains constant the
  local air velocity decreases with increasing
  pressure.
• The air flow rate required to lift the cuttings
  increases with increasing BHP.

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Friction Pressure
?m
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.
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Friction Pressure
fm a c
Weymouth quation.
0.14 ( Dh Dp) 0.333
a




Gou argued that Nikuradse is more correct.
1 a
2? Dh - Dp
1.14 0.86ln
? absolute roughness of the pipe.
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Friction Pressure

• Mixture density of air and cuttings in the
  annulus is determined by the mass of the cuttings
  and the density of the air.
• Air density is a function of the pressure.
• Mass of the cuttings in the wellbore is a
  function of
• ROP
• Hole cleaning efficiency.

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Friction Pressure

• Pressure drops down the drillstring and through
  the bit play a part in BHP due to temperature
  effects.
• Temperature is also effected by
• Formation temperature.
• Influx of formation fluid (expansion of gas into
  the wellbore).
• Mechanical friction.
• Pressure.

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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 of the cutting shape
  and size.

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Minimum Energy Criteria

• Probably the most widely used criteria was
  developed by Angel in 1957.
• Angel assumed that, for efficient cuttings
  transport downhole, the kinetic energy of the air
  striking each cutting should be the same as that
  of air giving efficient cuttings transport at
  standard pressure and temperature.

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Minimum Energy Criteria
1 2
1 2
?min V 2min
? stp V 2stp
Pmin Density of air (or gas) at the minimum
required downhole injection rate,
lbm/cuft. Vmin Air (or gas) velocity downhole,
ft/min. Pstp Density of air (or gas) at
standard temp and pressure, lbm/cuft. Vstp
Air (or gas) velocity at standard Temp and
pressure, ft/min.
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Minimum Energy Criteria
Pstp Pmin
Vmin Vstp
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Minimum Energy Criteria

• Experience from shallow blast holes, drilled in
  limestone quarrying operations, indicated that
  cuttings were transported efficiently if the air
  velocity equaled or exceeded 3,000 feet per
  minute.
• This is equivalent to Grays terminal velocity
  for flat cuttings with a diameter of 0.46 in. and
  for sub-rounded particles of 0.26 in.

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Minimum Energy Criteria
Angel computed the downhole air pressure with eq.
2.5
m ? m V 2m 2g (Dh Dp)
dP dL
?m
Wc Wa
?m ?a
1
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 in given time the mass flow
rate of air, lbm/min.
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Minimum Energy Criteria

2aG
abTs2 T abT2 G a Ts
G - a

Pb P2s-
Ps Surface air pressure, lbf/sq.ft,
absolute. Ts Surface temperature, 0F. G
Annular temperature gradient, 0F/100. T
Downhole temperature TsGh h Hole depth.
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Minimum Energy Criteria
SQ 28.8 . ROP . Dh2 53.3Q
a
S Gas specific gravity (air1) Q
Gas flow rate, scf/m ROP Penetration rate,
ft/hr
1.625 x 10-6Q2 (Dh Dp) 1.333 (Dh2
Dp2)2
b
Dh Hole diameter, ft. D2 Drillpipe
diameter, ft.
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Minimum Energy Criteria
This was combined with the cuttings transport
criterion defined in Eq 2.10 to deduce the
minimum air flow rate as a function of hole
depth, annular geometry, and penetration rate.
? stp ? min
Vmin Vstp
Eq. 2.10
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Minimum Energy Criteria
To simplify, the average downhole temperature can
be used to calculate BHP.
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Minimum Energy Criteria
This was solved numerically for the gas injection
rate required to give an annular velocity
equivalent in cuttings lifting power to air with
a velocity of 3000 ft/min. A series of charts was
generated for different combinations of hole
size, drillpipe diameter and penetration rates
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Minimum Energy Criteria

• Qmin can be approximated by
• Qmin Qo NH
• Qo Injection rate (scfm) at zero
  depth that corresponds to an annular
  velocity of 3000 ft/min
• N Factor dependent on the
  penetration rate (Appendix C)
• H Hole depth, (thousands of feet).

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Appendix C
Data for calculating approximate circulation
rates required to produce a minimum annular air
velocity which is equivalent in lifting power to
standard air velocity of 3.000 ft/min. (Angel,
1957).
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250
200
150
Bottomhole Pressure (psia)
100
50
0
0 2000 4000 6000
8000 10000 12000
Depth (feet)
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80
70
60
50
Bottomhole Pressure (psia)
40
30
20
10
0
0 2000 4000 6000
8000 10000 12000
Depth
(feet)
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7-7/8 hole 3-1/2 drillpipe 6 drill
collars 3800 hole depth
Annular Bottomhole Pressuresin An Air Drilled
Hole-comparison Of Predictions And Measurements
Made While Circulating Off-bottom
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45
40
35
Bottomhole Pressure (psia)
30
25
20

• 600 700 800 900
  1000 1100 1200 1300
• 
  Flow Rate (scfm)

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34
32
30
28
Bottomhole Pressure (psia)
26
24
22
20

• 600 700 800 900
  1000 1100 1200 1300
• 
  Flow Rate (scfm)

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3.5
3
2.5
2
Required Rate of Air (scfm)
1.5
1
0.5
0
0 2000 4000 6000 8000 10000
12000 14000 16000 18000
Depth ( feet)
Comparison of air rates recommended by several
different cuttings transport analyses (after Guo
et al, 199412).
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Minimum BHP Criteria
Angel analysis does not predict a minimum BHP,
but gives a pressure that decreases monotonically
with decreasing air flow rate.
Annulus Pressure Drop
Annulus Pressure Drop
Annulus Air Velocity
The influence of air flow rate on annular
pressure drop (after Supon and Adewumi, 19915).
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