lesson 6 foam drilling-1

7/27/2019 Lesson 6 Foam Drilling-1

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Harold Vance Department of Petroleum EngineeringHarold Vance Department of Petroleum Engineering

Lesson 6Foam Drilling

Read: UDMChapter 2.5-2.6, Pages 2.75-2.130

PETE 689 - UnderbalancedDrilling, UBD



Harold Vance Department of Petroleum Engineering




The Pattern Of Foam

Classic static

foam pattern onthe left.Foam in flowprobably looksmore like the oneon the right.

1 cm 1/2 inch




Types of Flow Regimes(Lorenz, 1980)

MISTFOAMLIQUID GAS AERATED

LIQUID




Fluid Phase Continuity

Mist

(97-100% Gas)Foam or Gaseated

(50-97% Gas)

Air/Gas

Water




Mist Aerated Foam

50/1

1000/1500/1

100/1

30/1

10/1

99.8%

90%

Injection Ratio

Foam Quality




Foam and Gaseation

FOAM “Emulsion”.

Hard to Separate. “NO” Pressure Surges. Huge lifting capacity.Plugs lost circulation

and reduces head.

GASEATIONMixture.

Separates easily.Heading and pressuresurges.Normal lifting capacity.

Reduces lost circulationby reducing head.




Reasons for UB Drilling with Foam

1. Stops lost circulation.

2. Improve drilling rate.3. Protects the reservoir.

4. Avoid differential sticking.5. Hole cleaning with low

fluid volume.

Why Foam?




Lifting Capacity

Powder

Regrinding AndMud Ring

Formation

LargeCuttings

Foam Air/Mist




Lost Circulation with Foam

Reduced the mud densityno junk.Foam plugs lost zones.




Lost Circulation with Foam

The Foam

bubbles arelost zoneplugging

agents!




Improve Drilling Rate

Low bottom hole pressureincreases drilling rate.For hard rock, the new airhammer works with foam.




-500 0 +500 +1000

p p

b p

DIFFERENTIAL PRESSURE (psi)

Effect of Differential Pressure

Bit Floundernot

uncommonwith foam

Perfect Cleaning




Protect Reservoir

No formation damage withno influx into the well bore.Minimal pressure surges.

Controllable pressures.




Protect ReservoirFoam is Perfect UB Fluid

In underbalancecondition, flow isinto the hole.Fluid does notruin the foam.




Protect Reservoir

Foam is perfect UB FluidIn overbalancecondition, foambubbles block the matrix.Foam bubblesalso block fractures.




Differential Pressure StickingDRILL PIPE

FILTER CAKE

DRILL COLLAR

, K P f

PH

PH > P f




No Differential Pressure Sticking

DRILL PIPE

NoFILTER CAKE

DRILL COLLAR

, K P f

PH

PH > P f




Foam Lifting CapacityNeeds Only Limited Fluid Volume

0.2

0.6

0.8

1.0

0

0.4

Dry

1.00 0.60.40.2 0.8

WetFoam

Relative Velocity 2

1

StableFoam

Foam Quality

Actually acts likethis

Theory




Powder

Regrinding And

Mud RingFormation

LargeCuttings

Foam Air/Mist

Hole Cleaningwith Limited Fluid Volume




Theoretical Foam Types

Stable Foam: 1-2% Surfactant.Stiff Foam: 1% Surfactant, 3-4% Gel,

Polymer. Use of viscosified waterinstead of fresh non-viscosified waterin the incompressible fluid component.

Viscosity additives: CMC, Xantan Gum,Polymers, etc..




General Foam Agents

Foamer to reduce surface tensionof water.

Polymers to strengthen the filmaround the air bubbles.Soda Ash to soften water andraise the pH to 10.




Fluids for Foam Drilling

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




Small Foam Unit




Large Foam Job




Foam Theory




Foam Structure

Required ElementsGasLiquidFoaming Agent• A surface active agent




The Pattern Of Foam

Classic staticfoam pattern onthe left.Foam in flowprobably looksmore like theone on the right.

1 cm 1/2 inch




Transfoam (Weatherford) All of the following may not applyto transfoam.Some of the methods of handlingTransfoam may vary. It is a slightly

different type of foamer.




Foam Rules

Smaller bubbles are more stable.

Polymers make the skin aroundthe bubbles tougher.Bentonite makes the skin aroundthe bubbles more stable.




Foam Rules

Soda ash in the watermakes the foamer work better.Soda ash in the waterbuffers the pH at about 10.

Different foamer may work best in certain areas.




After Saintpere et.al.

Effect Of Pressure On Foam Stability,Correlation with Bubbles Man Diameter

B u b b l e s m e a n

d i a m e

t e r

(µ

m )

Pressure ( bar )0 5 10 15 20 25 30 35 40 45 50

1.000

900

800

700

600

500

400

300

200

100

0

0.700

0.600

0.500

0.400

0.300

0.200

0.100

0.000

D r a

i n a g e v e

l o c i t y

( m l / m

i n )




Polyhedral Foam ContactTrue Foam

Plateau Border




Bubble

Pressure RedistributionLesser Pressure Greater Pressure

R r

From high pressure to lower pressureDepends on film permeability

Gas diffusion.




Foam StructureStabilization




Stronger Bubbles

Smaller bubbles.More foamer.

Of the right kind. Add a surfactant.

Polymer.Other agent.




Surface Active Materials

Retard DrainageIncrease surface viscosity.

Oxygen reactive additives.Migrating surfactants.

Ionically charged foamers.




Migrating Surfactant




Ionically Charged Foamer

Most foam system and

most foamers are anionicin nature.

If part of the outer wall of the bubble should becomecationically charged theinner and outer wallswould be attracted andthe wall would becomethinner at that point.

+

+++

++

-

- -




Ionically Charged Foamer

Ionically charged foamerswill cause both walls of each bubble to carry the

same electrical charge.The walls will then repel,becoming thicker.

-

-

--

-

--

-




Foamer Considerations

Concentration

Contaminants

Temperature

Solubility




Foamer Concentration

H a

l f l i f e i n s e c o n

d s

% Foamer concentration

300

250

200

150

100

50

0

0 0.2 0.4 0.6 0.8 1 1.2




FACTOR CHANGE EFFECT onDRAINAGE

EFFECT onSTABILITY

Foamer concentration Increase Decrease Increase

Solubility Increase Decrease Increase

Temperature Increase Increase DecreaseContamination Increase ----- Decrease

Major Factors of Foam Stability

All these factors are interdependent if T

goes up, instability increase, solubilityof the foamer increase. If solubilityincrease, stability increase.




Causes of Bubble Disruption

Big Bubbles are weakerthan small bubbles.Salt water weakens thebubble surface.Oil weakens the bubblesurface.Some solids weaken thebubble.




DEFOAM




Bubble Disruption Defoamers

Most defoamers weaken the

bubble film - like an alcohol or oil.Some defoamers use fine silicatesolids to disrupt the bubble film.

Time and gravity drainage.




Foaming AgentChemicals




Straight Foamers

Anionic in NatureEthoxyl Alcohol Ether Sulfates

Alpha Olephin SulfonatesWidest applicability.Excellent solubility.

Good thermal stability.Hydrocarbon tolerance.High Costs.




Amino-Propyl Betaines (Amphoteric)Will change properties with achange in pH from acid to basic.

Excellent stability.Good thermal stability.Good brine solubility.Fair yield.Relatively expensive.

Foam Boosters




Alkanol Amides (Cationic)

Good thermal stability.Expensive.Incompatible with most foam

systems.

Foam Boosters




Sodium Sulfosuccinates (Anionic)

Common.Good fresh-water solubility.Good thermal stability.

Extremely poor brinesolubility.

Foam Stabilizers




Alkyl-Phenol Ethoxylates (Nonionic)

Excellent surface activity.

Soluble in all waters.Good thermal stability.Compatible with other additives.

Provides poor foam quality.

Foam Stabilizers




PolymersFoam Stability Improvement




Polymer Uses

Drill solid flocculation.

Increased viscosity.Increased lubricity.Stabilize clays.Increase foam stability.




Polymers

Organic or synthetic.Many monomers (repeating units).

Varied structures.




Polyacrylamides

Widely used.

MW = 8-10 million.

Varied ionic charge.

Synthetic

Polymers




Partially-Hydrolyzed Polyacrylamide

(PHPA)

Synthetic polymer.

Powder or liquid.

Synthetic

Polymers




Natural, OrganicCar boxy-methyl Cellulose

(CMC)Natural polymer from plants.

Cotton. Viscosity control.

Polymers




Hydroxy-Ethyl Cellulose (HEC)

Anionic.

Fluid loss control.

Viscosity control.

Natural, Organic

Polymers




Guar Gum

Natural polymer.Non-ionic, Branched chain.

MW = 200,000Low temperature.

Natural, Organic

Polymers




Biopolymers Xanthan gum (XC)

Viscosity control. Fresh or salt water compatible.

Shear thinning.Increase foam stability, butwith poor lifting ability.

Polymers




Clay and Shale Stabilizers

Hole Stability




Clay Swelling Mechanisms

Simple adsorption.

Osmotic swelling.




Stabilizing Agents

KClExcludes water attraction.

Ammonium chlorides. Amine salts.

Cationic polymers.




General Foam Types

Stable foamFoaming agentPolymer

Stiff foamFoaming agentPolymerBentonite

pH sensitive foam (amphoteric)Transfoam




Foam Quality

Gas phase percent by volume

Expressed as: %Whole number

Decimal equivalente.g. 75, 75%, or 0.75




Foam Quality (In theory)

0-55% Aerated Fluid

55%-94% Foam94%-99.9% Mist

100% Gas/Air




Powder

Regrinding And

Mud RingFormation

Large

Cuttings

Foam Air/Mist

Hole Cleaning




FactorsEffecting Foam Quality

Pressure.Depth.Gas content.

Liquid content.




Maintaining Foam Quality

Gas and liquid injection rates.

Back-pressure on the system.Measurement.Calculation (computer models).




Foam Texture

The “stability” of Foam

Not measured at present. Assumed in all the Math. A source of error, but we don’tknow how much.Best available guess is “half life”.




Foam Texture

The Foam Strength

Small bubbles -mixed at jet bit.Good foaming agent.

Polymer for film strength.




Liquid Volumes

Begin with 1/10 of ConventionalMud Rate required to give a120 ’/min (40m/min) annularvelocity.

EXAMPLE: In an 8.75 ” hole, 400gpm is a normal mud rate. Forfoam start with 40gpm as aninitial try.




Liquid Volume

This may have to be increased up to50-70% of normal mud volume tobuffer the steering tool or EM-MWD.Gas then likewise has to increase.

Be careful of friction dominatephase.




Rheological Models




Bingham Plastic

The fluid will not flow until acertain minimum shear stress isexceeded. Once that minimumstress has been exceeded,additional shear stress isdirectly proportional to theshear rate.




Shear Stress and Shear Rate for a BinghamPlastic Fluid (Bourgoyne et al., 1986)

g=

0

t

- t g

+ t g

g Shear Rate,

p




Power Law

A Power-Law fluid withthe application of anyshear stress.Shear stress is a functionof shear rate for aPower-Law fluid, it is nota linear relationship.

Sh St Sh R t f P




Shear Stress vs. Shear Rate for a Power-Law Fluid

(Bourgoyne et al., 1986)

t = k g

t

S h e a r

S t r e s s ,

. n

n < 1

Shear Rate, g

t = k g g. . n- 1




The Published Experts Don’t Agree About Foam Fluid Behavior

Bingham Plastic Mitchell

KrugBeyer

Power Law OkpobiriIkoku

Sanghani




ActuallyFoam sometimes flows as a plug.

And sometimes with a velocityprofile across the hole crosssection.

Viscosity changes with pressureand temperature as well aschemical content.




Foam Flow

Foamsometimesflows as aplug.




Foam Flow

Foamsometimesflows highviscosityprofile.




Foam Testing

It is difficult to measure theviscosity of a foam.Instead a half-life test is used.

F T ti g




Foam Testing

Half Life Procedure

Waring Blender Stop Watch 1000ml Cylinder

Foam Testing




100mlwater

Foaming Agent0.5% (0.5ml)


gHalf Life Procedure

Foam Testing




Mix on high for 30 sec


gHalf Life Procedure

Foam Testing




Pour into cylinderand measure timefor 50ml of waterto appear

Water

FoamTime is half life


Foam Testing Half Life Procedure




Foam DrillingEquipment




Stable Foam Mixing System

(Hutchison)This is not a very good method

Detergent

Additives

Water

BlenderFor

DetergentSolution

Compressed Air or Gas

MeterFoamGenerator

Meter

20 Gpm PositiveDisplacementPump

Work string

Annulus

Blowdown

Foammanifold




Modern Foam Mixing System

Chemical

Chemical

MeteringPump

MeteringPump

ToMud Pump

F D illi g Eq i t




Foam Drilling Equipment

Rotating Head





Gas Fluid Mixing System






Foam Mixing

The real key to

satisfactoryoperation is theuse of precision

injectionpumps.





Weatherford Foam Unit






CompressorUsed in Foam Drilling






Rotary Primary Compressor in aUnitized Package






Booster Compressor ina Unitized Package






Bakermodel Fbit float






Bakermodel GBstring floatmaybe usedevery 500’





Recyclable FoamWeatherford TransFoam




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 causefoam at a high pH and interfereand cause the foam to go flat ata low pH.




Transfoam Applications

Environmental concern.

Space limitations.

Limited disposal options.

Transfoam




Process DescriptionIntentional de-stabilization.

Decrease pH (10 to < 5)Foam immediately disappears.

Gas removal in separator.Liquid cleaning in shaker, cycloneand centrifuge.

Add make up foamer.Re-activation.

Increase pH

Si lifi d T f




Simplified Transfoam

Foam/DeFoam/ReForm Cycle

Foam(100% Volume)

Liquidless than 5%

Foam

Activator

Foam(100% Volume)

+ Acid

Transfoam Recyclable Foam System




Recovered SolutionReady for Reuse

Supplemental Defoamer Addition(if necessary)

Separator pH Signal to Control Acid Feed

Acid FeedCuttings

Blooie LineTo Air Pit

Separator

ShakerRecirculation

Line

P

pH Signal to Control Alkaline Feed

P AcidStorage

pH LimeHopper

Lime Feed

Mud Pits

Polymer Flocculant Addition if Necessary

Solids

Control




Considerations

Limitless cycles.Make-up foamer requiredfor loss to formations andsolids.Water soluble, non-toxicadditions.




Advantages

Cost EfficientLess Chemical UsedLess Make-up WaterLess Space

EnvironmentalOffshore

Less Disposal




Advantages

Adaptable fluid. Any water base drilling mudcan be used.

Limitations




Limitations

Acid environment.Corrosion ?

Good separator required.Defoamer possibly required. Availability.

Personnel.Equipment.

Canada




Concord Unit-foam

A conventionalfoam used with

a defoamer.Foam is killedwith defoamer,

then rebuiltwith foamer.



END

lesson 6 foam drilling-1

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