part v filtration control

8/10/2019 Part v Filtration Control

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Advanced Mud School

Part V Filtration Control

Presented By:

Jeff Imrie

August 2006


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Filtration Control

A basic drilling fluid function is to sealpermeable formations and controlfiltration (fluid loss).

Adequate filtration control and thedeposition of a thin, low-permeability

filter cake are often necessary to preventdrilling and production problems.


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Filtration Control

Potential problems from excessive filter-cakethickness:

Tight spots in the hole that cause excessive drag.

Increased surges and swabbing due to reducedannular clearance.

Differential sticking of the drillstring due to

increased contact area and rapid development ofsticking forces caused by higher filtration rate.

Primary cementing difficulties due to inadequate

displacement of filter cake.

Increased difficulty running casing.


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Filtration Control

Potential problems from excessivefiltrate invasion: Formation damage due to filtrate and

solids invasion.

Invalid formation-fluid sampling test. Formation-evaluation difficulties caused

by excessive filtrate invasion, poortransmission of electrical properties

through thick cakes Oil and gas zones may be overlooked

because the filtrate is flushinghydrocarbons away from the wellbore,making detection more difficult.


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Filtration Control - Fundamentals

Drilling fluids are slurries composed of aliquid phase and solid particles.

Filtration refers to the liquid phase of the

drilling mud being forced into a permeable

formation by differential pressure.

During this process, the solid particles arefiltered out, forming a filter cake


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Mud systems should be designed to seal permeablezones as quickly as possible with thin, slick filtercakes.

In highly permeable formations with large pore

throats, whole mud may invade the formation(depending on the size of the mud solids).

In such situations, bridging agents must be usedto block the openings so the mud solids can

form a seal. Bridging agents should be at leastone-half the size of the largest openings.

Such bridging agents include calcium carbonate,ground cellulose and a wide variety of other lost-circulation materials.


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Filtration occurs under bothdynamic and static conditionsduring drilling operations.

Dynamic tests are normally runin a laboratory environmentusing equipment such as aFann 90

Static test are run in the fieldand include the standard APIfilter press and the HPHT filter

press


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For filtration to occur, three conditionsare required:

A liquid or a liquid/solids slurry fluid must

be present.

A permeable medium must be present.

The fluid must be at a higher pressurethan the permeable medium.


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Factors affecting filtration Time

Pressure differential Filter cake permeability

Viscosity

Solids Orientation and composition


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Dynamic Filtration Dynamic filtration is significantly different from

static filtration, often with considerably higherfiltration rates.

No direct correlation exists between API andHTHP static filtration measurements and dynamicfiltration.

Experience has shown that a mud which exhibitsgood static filtration characteristics and stabilitywill have satisfactory performance under actualdrilling conditions, indicating the dynamic fluid

loss is in a satisfactory range.


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Filtration Control Additives For Water Based Muds

Several types of filtration-control additives are used in

water-base muds. Clays

sodium bentonite

Attapulgite and sepiolite are clays but impart no filtrationcontrol


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Filtration Control

Additives For Water Based Muds

Polymers Polymers are the filtration control products

used most often in water-base muds

They can range from natural starches and

modified cellulose to sophisticated

synthetic polymers capable of providing

filtration control under high temperatures

and hostile conditions


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Filtration Control


Polymers reduce fluid loss inseveral ways:

Plugging of openings of the filter

cake by polymer particles.

Encapsulating solids forming a

larger deformable coating or film

which reduces the permeability of

the filter cake.

Viscosification of the liquid phase.


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Filtration Control


Starch, a natural carbohydrate polymer, hasbeen used to control filtration in drilling fluidssince the 1930s.

It is widely available as yellow (untreated) andwhite (modified) starch.

Starches can be used in seawater, salt water,

hard water and complex brines.

The most economical and widely used starches

are made from corn or potatoes, but starches

made from other agricultural products are also

available.


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Filtration Control


Sodium Carboxymethylcellulose (CMC) is a modifiednatural polymer used for filtration control. CMC is an effective fluid-loss control additive in

most water-base muds.

It works particularly well in calcium treatedsystems, where it acts to stabilize properties.

CMC is not subject to bacterial degradation andperforms well at an alkaline pH.

CMCs effectiveness decreases at salt

concentrations greater than 50,000 mg/l. subject to thermal degradation at temperatures

exceeding 250F.

Available in Low, medium and high viscositygrades


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Filtration Control


Polyanionic Cellulose (PAC) is amodified natural polymer used for:freshwater, seawater, salt and low-solids muds.

It is a high-molecular- weight,polyanionic cellulose similar to CMC,but has a higher degree ofsubstitution.

It is the most widely used fluid-losscontrol additive and is generally amuch better product than CMC.

Good to 275F Available as Ultra low viscosity and

regular viscosity


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Filtration Control


Chemical thinners reduce filtration ratesby deflocculating the clays, by increasingthe fluid phase viscosity and by changing

the solids distribution. Desco and Lignite are effective at

deflocculating and lowering fluid loss.


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Filtration Control


Also available for fluid loss control: Complex Resin/lignite blends

For HPHT fluid loss control

Polyacrylites

Not in common use anymore

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Filtration Control

Additives For Oil Based Muds

The API fluid loss of these systems isnormally zero, or too low to be aneffective measure.

The filtration rate of oil muds, unlessotherwise noted, refers to the HTHP

filtration.

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Filtration Control


Most oil- and synthetic-base fluids areemulsions.

Their fluid phase is an emulsion with oil orsynthetic as the continuous phase and brine as

the emulsified phase. These systems contain from 10 to 50 volume

percent brine, usually calcium chloride.

The emulsified brine forms colloid-sized droplets,which are immiscible in the oil or synthetic.

These brine droplets become trapped in the filtercake and reduce filter-cake permeability and fluid

loss.

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Filtration Control


Emulsifiers.

Although emulsifiers are not true filtration-

control additives, they can reduce filtration

by increasing the emulsion strength if theemulsion is unstable.

A sufficiently stable emulsion should be

established before treating with filtration-control additives.

If an emulsifier requires lime to be activated,

excess lime should be maintained in the

mud.

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Filtration Control


Viscosifiers. The primary viscosifier in invert emulsion

muds is organophilic clay.

Although this clay does not hydrate, it will

reduce the filtration rate by providing a

colloidal solid for forming a basic filter

cake.

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Filtration Control


The primary filtration-control additives forinvert emulsion muds are:

asphalt,

gilsonite (natural asphalt), amine treated lignite

various other resins

specialized polymers The asphaltic materials usually provide better

filtration control than the amine-treated lignite

at equal concentrations and temperature.

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Filtration Control

End

part v filtration control

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