Date post: | 02-Jun-2018 |
Category: |
Documents |
Upload: | mohamed-sadek |
View: | 231 times |
Download: | 0 times |
of 24
8/10/2019 Part v Filtration Control
1/24
Advanced Mud School
Part V Filtration Control
Presented By:
Jeff Imrie
August 2006
8/10/2019 Part v Filtration Control
2/24
PFM
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.
8/10/2019 Part v Filtration Control
3/24
PFM
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.
8/10/2019 Part v Filtration Control
4/24
PFM
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.
8/10/2019 Part v Filtration Control
5/24
PFM
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
8/10/2019 Part v Filtration Control
6/24
PFM
Filtration Control - Fundamentals
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.
8/10/2019 Part v Filtration Control
7/24
PFM
Filtration Control - Fundamentals
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
8/10/2019 Part v Filtration Control
8/24
PFM
Filtration Control - Fundamentals
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.
8/10/2019 Part v Filtration Control
9/24
PFM
Filtration Control - Fundamentals
Factors affecting filtration Time
Pressure differential Filter cake permeability
Viscosity
Solids Orientation and composition
8/10/2019 Part v Filtration Control
10/24
PFM
Filtration Control - Fundamentals
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.
8/10/2019 Part v Filtration Control
11/24
PFM
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
8/10/2019 Part v Filtration Control
12/24
PFM
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
8/10/2019 Part v Filtration Control
13/24
PFM
Filtration Control
Additives For Water Based Muds
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.
8/10/2019 Part v Filtration Control
14/24
PFM
Filtration Control
Additives For Water Based Muds
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.
8/10/2019 Part v Filtration Control
15/24
PFM
Filtration Control
Additives For Water Based Muds
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
8/10/2019 Part v Filtration Control
16/24
PFM
Filtration Control
Additives For Water Based Muds
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
8/10/2019 Part v Filtration Control
17/24
PFM
Filtration Control
Additives For Water Based Muds
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.
8/10/2019 Part v Filtration Control
18/24
PFM
Filtration Control
Additives For Water Based Muds
Also available for fluid loss control: Complex Resin/lignite blends
For HPHT fluid loss control
Polyacrylites
Not in common use anymore
PFM
8/10/2019 Part v Filtration Control
19/24
PFM
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.
PFM
8/10/2019 Part v Filtration Control
20/24
PFM
Filtration Control
Additives For Oil Based Muds
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.
PFM
8/10/2019 Part v Filtration Control
21/24
PFM
Filtration Control
Additives For Oil Based Muds
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.
PFM
8/10/2019 Part v Filtration Control
22/24
PFM
Filtration Control
Additives For Oil Based Muds
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.
PFM
8/10/2019 Part v Filtration Control
23/24
PFM
Filtration Control
Additives For Oil Based Muds
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.
PFM
8/10/2019 Part v Filtration Control
24/24
PFM
Filtration Control
End