Harold Vance Department of Petroleum Engineering

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PETE 689 - Underbalanced Drilling, UBD
Lesson 6 Foam Drilling Read UDM Chapter
2.5-2.6, Pages 2.75-2.130
Harold Vance Department of Petroleum Engineering
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(No Transcript)
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The Pattern Of Foam
1/2 inch
1 cm

• Classic static foam pattern on the left.
• Foam in flow probably looks more like the one on
  the right.

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Types of Flow Regimes(Lorenz, 1980)
MIST
GAS
AERATED
FOAM
LIQUID
LIQUID
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Fluid Phase Continuity
Air/Gas
Water
Mist
Foam or Gaseated
(97-100 Gas)
(50-97 Gas)
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Mist Aerated Foam
50/1
Foam Quality
Injection Ratio
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Foam and Gaseation

• FOAM
• Emulsion.
• Hard to Separate.
• NO Pressure Surges.
• Huge lifting capacity.
• Plugs lost circulation and reduces head.

• GASEATION
• Mixture.
• Separates easily.
• Heading and pressure surges.
• Normal lifting capacity.
• Reduces lost circulation by reducing head.

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Reasons for UB Drilling with Foam
Why Foam?

• 1. Stops lost circulation.
• 2. Improve drilling rate.
• 3. Protects the reservoir.
• 4. Avoid differential sticking.
• 5. Hole cleaning with low fluid volume.

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Lifting Capacity
Powder
Regrinding
And
Mud Ring
Formation
Large
Cuttings
Foam
Air/Mist
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Lost Circulation with Foam

• Reduced the mud density no junk.
• Foam plugs lost zones.

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Lost Circulation with Foam

• The Foam bubbles are lost zone plugging agents!

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Improve Drilling Rate

• Low bottom hole pressure increases drilling rate.
• For hard rock, the new air hammer works with foam.

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Effect of Differential Pressure
Perfect Cleaning
DRILLING RATE
p
b
Bit Flounder not uncommon with foam
p
p
-500
0
500
1000
DIFFERENTIAL PRESSURE (psi)
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Protect Reservoir

• No formation damage with no influx into the well
  bore.
• Minimal pressure surges.
• Controllable pressures.

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Protect ReservoirFoam is Perfect UB Fluid

• In underbalance condition, flow is into the hole.
• Fluid does not ruin the foam.

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Protect ReservoirFoam is perfect UB Fluid

• In overbalance condition, foam bubbles block the
  matrix.
• Foam bubbles also block fractures.

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Differential Pressure Sticking
DRILL PIPE
PH
FILTER CAKE
, K
Pf
PH gt Pf
DRILL COLLAR
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No Differential Pressure Sticking
DRILL PIPE
PH
No FILTER CAKE
, K
Pf
PH gt Pf
DRILL COLLAR
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Foam Lifting CapacityNeeds Only Limited Fluid
Volume
1.0
Stable Foam
Dry
Actually acts like this
0.8
0.6
Wet Foam
Relative Lifting Force
0.4
Relative Velocity
Theory
2
0.2
1
0
1.0
0
0.6
0.4
0.2
0.8
Foam Quality
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Hole Cleaningwith Limited Fluid Volume
Powder
Regrinding
And
Mud Ring
Formation
Large
Cuttings
Foam
Air/Mist
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Theoretical Foam Types

• Stable Foam 1-2 Surfactant.
• Stiff Foam 1 Surfactant, 3-4 Gel, Polymer. Use
  of viscosified water instead of fresh
  non-viscosified water in the incompressible fluid
  component.
• Viscosity additives CMC, Xantan Gum,
  Polymers, etc..

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General Foam Agents

• Foamer to reduce surface tension of water.
• Polymers to strengthen the film around the air
  bubbles.
• Soda Ash to soften water and raise the pH to 10.

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Fluids for Foam Drilling

• Fresh water.
• Saline or brackish water.
• Oils not used to date.

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Small Foam Unit
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Large Foam Job
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Foam Theory
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Foam Structure

• Required Elements
• Gas
• Liquid
• Foaming Agent
• A surface active agent

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The Pattern Of Foam
1/2 inch
1 cm

• Classic static foam pattern on the left.
• Foam in flow probably looks more like the one on
  the right.

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Transfoam (Weatherford)

• All of the following may not apply to transfoam.
• Some of the methods of handling Transfoam may
  vary. It is a slightly different type of foamer.

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Foam Rules

• Smaller bubbles are more stable.
• Polymers make the skin around the bubbles
  tougher.
• Bentonite makes the skin around the bubbles more
  stable.

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Foam Rules

• Soda ash in the water makes the foamer work
  better.
• Soda ash in the water buffers the pH at about 10.
• Different foamer may work best in certain areas.

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Effect Of Pressure On Foam Stability, Correlation
with Bubbles Man Diameter
0.700
1.000
900
0.600
800
0.500
700
600
0.400
Drainage velocity (ml/min)
500
Bubbles mean diameter ( µ m )
0.300
400
0.200
300
200
0.100
100
0.000
0
0 5 10 15 20 25
30 35 40 45 50
Pressure ( bar )
After Saintpere et.al.
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Polyhedral Foam ContactTrue Foam
Plateau Border
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Bubble Pressure Redistribution
Lesser Pressure
Greater Pressure
R
r
From high pressure to lower pressure
Depends on film permeability Gas diffusion.
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Foam Structure Stabilization
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Stronger Bubbles

• Smaller bubbles.
• More foamer.
• Of the right kind.
• Add a surfactant.
• Polymer.
• Other agent.

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Surface Active MaterialsRetard Drainage

• Increase surface viscosity.
• Oxygen reactive additives.
• Migrating surfactants.
• Ionically charged foamers.

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Migrating Surfactant
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Ionically Charged Foamer
-

Most foam system and most foamers are anionic in
nature. If part of the outer wall of the bubble
should become cationically charged the inner and
outer walls would be attracted and the wall would
become thinner at that point.

-

-



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Ionically Charged Foamer
Ionically charged foamers will cause both walls
of each bubble to carry the same electrical
charge. The walls will then repel, becoming
thicker.
-
-
-
-
-
-
-
-
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Foamer Considerations

• Concentration
• Contaminants
• Temperature
• Solubility

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Foamer Concentration
300
250
200
150
Half life in seconds
100
50
0
0 0.2 0.4
0.6 0.8 1 1.2
Foamer concentration
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Major Factors of Foam Stability
All these factors are interdependent if T goes
up, instability increase, solubility of the
foamer increase. If solubility increase,
stability increase.
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Disrupting Factors

• Bubble Size Re-Distribution.
• Bubble Wall Thinning.
• Gravity drainage.
• Evaporation.

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Causes of Bubble Disruption

• Big Bubbles are weaker than small bubbles.
• Salt water weakens the bubble surface.
• Oil weakens the bubble surface.
• Some solids weaken the bubble.

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DEFOAM
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Bubble Disruption Defoamers

• Most defoamers weaken the bubble film - like an
  alcohol or oil.
• Some defoamers use fine silicate solids to
  disrupt the bubble film.
• Time and gravity drainage.

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Foaming Agent Chemicals
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• Straight Foamers

• Anionic in Nature
• Ethoxyl Alcohol Ether Sulfates
• Alpha Olephin Sulfonates
• Widest applicability.
• Excellent solubility.
• Good thermal stability.
• Hydrocarbon tolerance.
• High Costs.

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Amino-Propyl Betaines (Amphoteric)
Foam Boosters

• Will change properties with a change in pH from
  acid to basic.
• Excellent stability.
• Good thermal stability.
• Good brine solubility.
• Fair yield.
• Relatively expensive.

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Alkanol Amides (Cationic)
Foam Boosters

• Good thermal stability.
• Expensive.
• Incompatible with most foam systems.

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Sodium Sulfosuccinates (Anionic)
Foam Stabilizers

• Common.
• Good fresh-water solubility.
• Good thermal stability.
• Extremely poor brine solubility.

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Alkyl-Phenol Ethoxylates (Nonionic)
Foam Stabilizers

• Excellent surface activity.
• Soluble in all waters.
• Good thermal stability.
• Compatible with other additives.
• Provides poor foam quality.

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Quaternary Ammonium Chlorides (Cationic)
Foam Stabilizers

• Provides
• Corrosion inhibition.
• Biocidal properties.
• Clay stability.
• Excellent brine solubility.
• Good foam quantity.
• Poor fresh water solubility.
• Poor lifting capacity.
• Requires high concentration.

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Polymers
Foam Stability Improvement
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Polymer Uses

• Drill solid flocculation.
• Increased viscosity.
• Increased lubricity.
• Stabilize clays.
• Increase foam stability.

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Polymers

• Organic or synthetic.
• Many monomers (repeating units).
• Varied structures.

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Synthetic
Polymers

• Polyacrylamides
• Widely used.
• MW 8-10 million.
• Varied ionic charge.

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Polymers
Synthetic

• Partially-Hydrolyzed Polyacrylamide (PHPA)
• Synthetic polymer.
• Powder or liquid.

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Natural, Organic
Polymers

• Carboxy-methyl Cellulose
• (CMC)
• Natural polymer from plants.
• Cotton.
• Viscosity control.

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Natural, Organic
Polymers

• Hydroxy-Ethyl Cellulose (HEC)
• Anionic.
• Fluid loss control.
• Viscosity control.

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Polymers
Natural, Organic

• Guar Gum
• Natural polymer.
• Non-ionic, Branched chain.
• MW 200,000
• Low temperature.

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Biopolymers
Polymers

• Xanthan gum (XC)
• Viscosity control.
• Fresh or salt water compatible.
• Shear thinning.
• Increase foam stability, but with poor lifting
  ability.

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Clay and Shale Stabilizers
Hole Stability
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Clay Swelling Mechanisms

• Simple adsorption.
• Osmotic swelling.

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Stabilizing Agents

• KCl
• Excludes water attraction.
• Ammonium chlorides.
• Amine salts.
• Cationic polymers.

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General Foam Types

• Stable foam
• Foaming agent
• Polymer
• Stiff foam
• Foaming agent
• Polymer
• Bentonite
• pH sensitive foam (amphoteric)
• Transfoam

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Foam Quality

• Gas phase percent by volume
• Expressed as
• Whole number
• Decimal equivalent
• e.g. 75, 75, or 0.75

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Foam Quality (In theory)

• 0-55 Aerated Fluid
• 55-94 Foam
• 94-99.9 Mist
• 100 Gas/Air

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Hole Cleaning
Powder
Regrinding
And
Mud Ring
Formation
Large
Cuttings
Foam
Air/Mist
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Factors Effecting Foam Quality

• Pressure.
• Depth.
• Gas content.
• Liquid content.

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Maintaining Foam Quality

• Gas and liquid injection rates.
• Back-pressure on the system.
• Measurement.
• Calculation (computer models).

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Foam TextureThe stability of Foam

• Not measured at present.
• Assumed in all the Math.
• A source of error, but we dont know how much.
• Best available guess is half life.

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Foam Texture The Foam Strength

• Small bubbles -mixed at jet bit.
• Good foaming agent.
• Polymer for film strength.

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Liquid Volumes

• Begin with 1/10 of Conventional Mud Rate required
  to give a 120/min (40m/min) annular velocity.
• EXAMPLE In an 8.75 hole, 400 gpm is a normal
  mud rate. For foam start with 40gpm as an
  initial try.

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Liquid Volume

• This may have to be increased up to 50-70 of
  normal mud volume to buffer the steering tool or
  EM-MWD.
• Gas then likewise has to increase.
• Be careful of friction dominate phase.

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Rheological Models
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Bingham Plastic

• The fluid will not flow until a certain minimum
  shear stress is exceeded. Once that minimum
  stress has been exceeded, additional shear stress
  is directly proportional to the shear rate.

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Shear Stress and Shear Rate for a Bingham Plastic
Fluid (Bourgoyne et al., 1986)
t
tg
g 0
Shear Rate,
g
- tg
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Power Law

• A Power-Law fluid with the application of any
  shear stress.
• Shear stress is a function of shear rate for a
  Power-Law fluid, it is not a linear relationship.

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Shear Stress vs. Shear Rate for a Power-Law
Fluid(Bourgoyne et al., 1986)
. n
t k g
n lt 1
.
. n-1
t k g g
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The Published Experts Dont Agree About Foam
Fluid Behavior

• Bingham Plastic
• Mitchell
• Krug
• Beyer
• Power Law
• Okpobiri
• Ikoku
• Sanghani

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Actually

• Foam sometimes flows as a plug.
• And sometimes with a velocity profile across the
  hole cross section.
• Viscosity changes with pressure and temperature
  as well as chemical content.

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Foam Flow

• Foam sometimes flows as a plug.

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Foam Flow

• Foam sometimes flows high viscosity profile.

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Foam Testing

• It is difficult to measure the viscosity of a
  foam.
• Instead a half-life test is used.

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Foam Testing Half Life Procedure
Waring Blender
Stop Watch
1000ml Cylinder
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Foam Testing Half Life Procedure
Foaming Agent 0.5 (0.5ml)
100ml water
Waring Blender
Stop Watch
1000ml Cylinder
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Foam Testing Half Life Procedure
Mix on high for 30 sec
Waring Blender
Stop Watch
1000ml Cylinder
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Foam Testing Half Life Procedure
Pour into cylinder and measure time for 50ml of
water to appear
Foam
Time is half life
Water
Waring Blender
Stop Watch
1000ml Cylinder
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Foam Drilling Equipment
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Stable Foam Mixing System (Hutchison) This is
not a very good method
Detergent
Meter
Blender For Detergent Solution
20 Gpm Positive Displacement Pump
Additives
Foam manifold
Meter
Water
Foam Generator
Annulus
Compressed Air or Gas
Work string
Blowdown
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Modern Foam Mixing System
Metering Pump
Chemical
To Mud Pump
Metering Pump
Chemical
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Foam Drilling Equipment
Rotating Head
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Gas Fluid Mixing System
Foam Drilling Equipment
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Foam Mixing
Foam Drilling Equipment

• The real key to satisfactory operation is the use
  of precision injection pumps.

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Self Contained Foam Unit
Foam Drilling Equipment
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Weatherford Foam Unit
Foam Drilling Equipment
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Compressor Used in Foam Drilling
Foam Drilling Equipment
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Rotary Primary Compressor in a Unitized Package
Foam Drilling Equipment
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Booster Compressor in a Unitized Package
Foam Drilling Equipment
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Baker model Fbit float
Foam Drilling Equipment
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Bakermodel GBstring floatmaybe used every 500
Foam Drilling Equipment
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• Recyclable Foam
• Weatherford TransFoam

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Weatherford Transfoam

• It is an amphoteric material - capable of
  reaction as either an acid or base.
• A combination of two (or more) foaming agents
  that cause foam at a high pH and interfere and
  cause the foam to go flat at a low pH.

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Transfoam Applications

• Environmental concern.
• Space limitations.
• Limited disposal options.

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Transfoam Process Description

• Intentional de-stabilization.
• Decrease pH (10 to lt 5)
• Foam immediately disappears.
• Gas removal in separator.
• Liquid cleaning in shaker, cyclone and
  centrifuge.
• Add make up foamer.
• Re-activation.
• Increase pH

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Simplified Transfoam Foam/DeFoam/ReForm Cycle
Acid
Activator

Foam (100 Volume)
Foam (100 Volume)
Liquid less than 5 Foam
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Transfoam Recyclable Foam System
Supplemental Defoamer Addition (if necessary)
Separator
Blooie Line
To Air Pit
Separator pH Signal to Control Acid Feed
Acid Feed
Acid Storage
Cuttings
Shaker
Recirculation Line
pH Signal to Control Alkaline Feed
Solids Control
pH
Lime Hopper
Lime Feed
Recovered Solution Ready for Reuse
Mud Pits
Polymer Flocculant Addition if Necessary
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Considerations

• Limitless cycles.
• Make-up foamer required for loss to formations
  and solids.
• Water soluble, non-toxic additions.

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Advantages

• Cost Efficient
• Less Chemical Used
• Less Make-up Water
• Less Space
• Environmental
• Offshore
• Less Disposal

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Advantages

• Adaptable fluid.
• Any water base drilling mud can be used.

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Limitations

• Acid environment.
• Corrosion ?
• Good separator required.
• Defoamer possibly required.
• Availability.
• Personnel.
• Equipment.

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CanadaConcord Unit-foam

• A conventional foam used with a defoamer.
• Foam is killed with defoamer, then rebuilt with
  foamer.

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END