4 clays chemistry and problems

8/12/2019 4 Clays Chemistry and Problems

http://slidepdf.com/reader/full/4-clays-chemistry-and-problems 1/83

1Agip KCO Well Area Operations

Drilling Supervisors Training Course Drilling Muds RPW2021A

CLAYS CHEMISTRY

AND PROBLEMS





INDEX

• CLAYS CHEMISTRY…. Pag. 03• CLAYS PROBLEMS …. Pag. 41





In drilling fluids industry, certain clay minerals as smectite, a major component of

bentonite, are used to provide viscosity, gel structure and fluid-loss control.

Formation clays are unintentionally incorporated into the mud during drilling and in

this case, they may cause various problems

INTRODUCTION





• Clay minerals can be beneficial (bentonite) or harmful (gumbo) to the fluid system.

• Gumbo clays are encountered in superficial drilling and they are often soft and plastic

when wet, hard when dry and they cause problems of plug in the shale shakers and

flow line or extremely increase the solid contents in the mud if dissolved.

• Bentonite is the term used for a particular smectite (clay) sodium montmorillonite,

used as additive for mud.

INTRODUCTION





TYPES OF CLAYS

There is a great deal of clay minerals, but in drilling fluids, they can be categorized

into three types:

• Attapulgite and sepiolite.

• Needle-shaped, non swelling clays. Used for their shape and their colloidal stability

in sea water based mud.

• Illite, chlorite, kaolinite which have a flattened shape, do not swell out again orcan have a reduced swelling.

• Montmorillonites which have a flattened shape but large swelling properties. In

nature, it is often calcium montmorillonite, but the use in drilling fluids is in thesodium montmorillonite quality (Wyoming).

This is the only type of clay intentionally added to the mud, while the other clay

types can be considered contaminants





Clays exist in nature with a stacked or layered structure, with each unit layer roughly 10

angstroms ( Ǻ) thick. This means there are about a million layers of clay per millimeter of

thickness. Each clay layer is highly flexible, very thin and has a huge surface area. Anindividual clay particle can be thought of as being much like a sheet of paper or a piece of

cellophane. One gram of sodium montmorillonite has a total layer surface area of 8,073

ft2 (750 m2)!

In freshwater, the layers adsorb water and swell to the point where the forces holding

them together become weakened and individual layers can be separated from the packs.

Separating these packs into multiple layers is known as dispersion. This increase in

number of particles, with the resulting increase in surface area, causes the suspension to

thicken.

TYPES OF CLAYS





Photo of bentonite particles

The characteristic shape of the particlesproduces the so-called shingling effectwhich is very important for the fluid-losscontrol

TYPES OF CLAYS

Ideal particle of montmori llonite

Three-layer clays are built of unit layerscomposed of two tetrahedral sheets oneither sides of one octahedral sheet,like a sandwich





Pyrophyllite with neutral chargeThis neutral clay is very similar to the following negativelycharged montmorillonite

TYPES OF CLAYS





The substitution of Mg2+ for Al3+ creates a particle with a negative chargeThe net negative charge is compensated by the adsorption of cations (positive ions)on the unit layer surfaces, and are called the exchangeable cations of the clay. Thequantity of cations per unit weight of the clay is measured and reported as the CEC.

Montmorillonite (Three-layer clays)

TYPES OF CLAYS





Smectite structure (Montmori llonite)The most typical property of

montmorillonites is that of interlayer swelling (hydrating) with water.

TYPES OF CLAYS

Montmori llonite (Three-layer clays)





Ill ites (Three-layer clays)

The structures of the illites are similar to the montmorillonites structures but

they do not show interlayer swelling. Instead of thesubstitution of Mg2+ for

Al3+, as in motmorillonites, Illites have a subsitute Al3+ for Si4+.

The compensating cations are the potassium ions (K+).

The gap among the single layers is 2.8 Å because the ionic diameter of K+ is

2.66 Å, there is a prevention of swelling in presence of water .

TYPES OF CLAYS





Chlorites (Three layer clays)

Chlorites are structurally connected to three layer clays. If pure they will not swell, but it

happens when there are alteration forms.

The cationic exchange capacity of chlorites varies from10 to 20 meq/100 g.Usually, the distance among the intermediate layers of the chlorites is around 14 Å.

Chlorite is often found in old, deeply marine sediments and normally does not cause

significant problems.

TYPES OF CLAYS





Kaolinites (Two-layer clays)

Kaolinite is a non-swelling clay, its layers are closely tied through hydrogen bond.

This prevent the expansion of the particles because water is unable to penetrate the

layers.

Kaolinite has a relatively low cationic exchange (5 to 15 meq/100 g).

Kaolinites are commonly found as minor to moderate constituents in sedimentary

rocks.

TYPES OF CLAYS





Group Structure Tension Cationic

exchange

InteratomicDistance

(Å) Hydratability

Kaolinite 1:1 Layer No No 7.2 No

Talc 2:1 Layer No No 9.3 No

Smectite 2:1 Layer 0.3 - 0.6Na+,Ca2+, K+,Mg2+

11 - 15 Variable

Vermiculite 2:1 Layer 1.0 - 4.0 K+

, Mg2+

14 - 15 Variable

Illite 2:1 Layer 1.3 - 2.0 K+ 10 No

Mica 2:1 Layer 2.0

K+ 10 No

Chlorite 2:2 Layer Variable 14 No

Sepiolite 2:1 chain No No 12 No

Palygorskite

2:1 chain Minor No 10.5 No

Most common clays

TYPES OF CLAYS





Comparison of clay structure

TYPES OF CLAYS





CATIONIC EXCHANGE CAPACITY

CEC

The compensating cations that are adsorbed on the unit-layer surface may be exchanged

for other cations and are called the exchangeable cations of the clay. The quantity of

cations per unit weight of clay is measured and reported as the CEC. The CEC is

expressed in millequivalents per 100 g of dry clay (meq/100 g). The CEC of

montmorillonites is within the range of 80 to 150 meq/11 g of dry clay. The CEC of illites

and chlorites is about 10 to 40 meq/100 g, and for kaolinites it is about 3 to 10 meq/100 g

of clay.

The Methylene Blue Test (MBT) is an indicator of the apparent CEC of a clay.

In order to know which cations will replace the other cations, observing the scheme eachcation on the left will replace a correspondent cation on the right

H+ > Al3+ > Ca2+ > Mg2+ > K+ > NH4+ > Na+ > Li+





• The commercial clays such as Bentonite, are added to water during the preparation

of a water-based mud. They can:

1) give the mud the right viscosity;

2) contribute to create a film which will impermeabilize the formation;

• In the water/clay-muds, water is used as a liquid in a continuous phase in which

certain materials are maintained in suspension and where other materials are

dissolved.

CLAY/WATER-BASED MUD COMPOSITION





Additives for muds used in order to obtain determined characteristics can be divided

in three categories:

1. The continuous phase of the mud is water;

2. The base of the reactive solids is composed of commercial clays, incorporated

hydratable clays and clays coming from drilling cuttings then maintained insuspension in the fluid phase. Some of this solids are treated chemically to

control the properties of the mud;

3. Inert solids are solids in suspension without chemical reaction such aslimestone, dolomite and sandstone. Barite is added to drilling mud in order to

increase its density and it is also an inert solid (high-density solid).






Clay CEC (meq/100 g)

Smectite 80 - 150

Illite 10 - 40

Chlorite 10 - 40

Kaolinite 3 - 10

cec range for pure clay mineral materials


Clays hydration






Depending on the cationspresent, the interlayer spacing of

dry montmorillonite will bebetween 9.8 (sodium) and 12.1 Å (calcium) and filled with tightlybound water. When dry claycontacts freshwater, the

interlayer spacing expands, andthe clay adsorbs a large“envelope” of water. These twophenomena allow clays togenerate viscosity. Calcium-

base bentonites only expand to17 Å, while sodium bentoniteexpands to 40 Å.

Comparison of swelling for Calcium and Sodium Montmorillonite





Cationic influence of the hydration

• As mentioned previously, the substitutive force of a cation with another cation is as

follows:

H+ > Al3+ > Ca2+ > Mg2+ > K+ > NH4+ > Na+ > Li+

Cation Ion Diameter (Å)

HydratedDiameter

(Å)Li+ 1.56 14.6

Na+ 1.90 11.2

K+ 2.66 7.6

NH4+

2.86 5.0Mg2+ 1.30 21.6

Ca2+ 1.98 19.2

Al3+ 1.00 18.0

Ionic radius and hydration radius of

the most recurrent cations. A cation may serve as a bond to holdthe clay mineral particles together,thereby decreasing hydration.Multivalent cations tie layers together

more firmly than monovalent cations,usually resulting in aggregation of theclay particles. Potassium, amonovalent cation, is the exception tothe rule.

CLAY/WATER-BASE MUD COMPOSITION





CLAY/WATER-BASE MUD COMPOSITION

Clay reactions with potassium ions (K+)

The chemical reactions between clay and potassium ions are unique if compared to

other ions. The use of K+ is increasing and it is well known to stabilize reactive

shales, also when concnetration of K+ is below 5%.

According to Eberl (1980), there are two ways that K+ can become associated with

clay minerals:

1. Ion Exchange.

2. Ions Fixing.The ion exchange rate depends on the concentration of the K+ ion; the higher the

ratio of K+ ion to Na+ ion, the faster is the rate of exchange.

The fixation of K+ in montmorillonite clays can happen in particular conditions and is

due to a sort of alteration known as Burial Diagenesis. This diagenetic alteration ina two step reaction, creates a conversion from smectite to illite by the fixation of K+.

The complete reaction to transform smectite to illite, occurs if a large amount of K+

is present.





Clay Particles associated inone of the following states:

• Aggregation• Dispersion• Flocculation• De-Flocculation


Clay – Particle – Linking processes





• Aggregation: leads to the formation of packets. The result is a decrease in the number of

particles and in plastic viscosity. It could happen when drilling in gypsum or anhydrite

formation, due to divalent cations Ca++ . It also occurs when drilling out cement.

• Dispersion: The opposite of aggregation. The increase in the number of particles gives a

higher plastic viscosity value.

The degree of dispersion depends on the electrolyte content of the water. Time, temperature

and exchangeable cations on the clay. Dispersion increases with time, with increase in

temperature and when the water has low salinity and hardness.

• Flocculation: the association of particles edge-to-edge and edge-to-face resulting in a

structure similar to “House of Cards”. This situation is promoted by everything that increases

the repelling force between the particles (e.g. addition of divalent cations, high temperature).

Flocculation causes increase in viscosity, gel strength, fluid loss.






De-Flocculation: when the electrochemical charges on the clays are neutralized,

the attraction between the particles is removed. The result is a decrease in

viscosity and an improvement in the formation of the filter cake to reduce the fluid

loss. The chemicals used as deflocculating action are also called mud thinners.







Clay performance (Yield of clay)

The yield of a clay is defined asthe number of barrels of 15 cPmud that can be obtained from

1 ton of dry material in thisgraph. You can see that for bentonite, only 20 lbs/bbl isrequired to produce a 15 cPviscosity mud. It would contain

less than 6% solid by weight(2,5% by volume) and the yieldis 100 bbl/ton.By comparison, if sub-bentonite is used to prepare a

15 cP visc. Mud, 75 lbs/bbl arerequired, It would contain 18%solid by w. (8,5% by vol.) andthe yield only bbl/ton.





Components Parts per Milion

(mg/l)Sodium 10,550

Chloride 18,970

Sulphate 2,650

Magnesium 1,270

Calcium 400

Potassium 380

Bromide 65Other components 80


Factors which influence the clay performance

NOTE: Brackish water could have the same components but with differentconcentrations

Hydration and dispersion of dryclay are Influenced by the ionscontained in the water used to build

the mud.Many drilling muds off-shore, areprepared using SW for economyand convenience.

Typical seawater composition





Effects on viscosity by additionof bentonite to water whichcontains various concentrationsof salt or calcium.The hydration of clays in freshwater decreases rapidly withincreasing concentrations ofthese ions.The following figures can better explain the different hydration

(and consequent swelling) indifferent water used.






Bentonite hydration with salt water

Bentonite hydration with fresh water






Pre-hydrated bentonite in salt water






Effect of calcium on pre-hydratedbentonite.The initial increase of viscosity is dueto the flocculation caused by theaddition of divalent cation Ca++.

When the concentration of Ca++

reaches the breakover point, itcauses the aggregation of theparticles. The dehydration withreduction of number of particles

decreases also the viscosity.






Salt effect on pre-hydratedbentonite.

This is similar to the previouspicture but due to highconcentration of Na+ cation.






pH effect on Wyoming bentoniteUsually, all the muds work in pHalkaline (above 7). This is for obvious reasons such as safety and

corrosion.Looking at this picture, it isunderstandable why the majority ofmuds are maintained in a range ofpH between 8 and 9.5. Above this

value, the dispersion of clayincreases and as a consequencethe viscosity.


pH effect



CHEMICAL TREATMENT PRINCIPLES





Phosphates

•The main types of phosphates used in drilling fluids are:

1. Sodium pyrophosphate acid with a pH of 4.8

2. Sodium tetra phosphate with a pH of 8.0

All are powerful anionic dispersant and a small amount can strongly reduce the viscosity.

The addition of these products rarely exceed 0.2 lb/bbl (0.5 kg/mc)

They are used in combination with NaOH to avoid alkalinity decrease. They remove Ca++

and Mg++. They cannot be used over the temperature of 175°F (80°C) because of their

transformation in orthophosphates that are flocculants.








Lignite

Acid lignite (pH 3.2) is used to control viscosity. The mud needs to be run

in alkaline range to be effective.

On site the ratio between caustic soda and lignite varies from 1:6 to 1:2.

The best lignite performance is obtained in the muds with a pH from 9 to10.5.

They are moderately effective at higher salt concentration and not effective

at high calcium conc.







Lignins

Lignins are an assembling of products similar to lignite and lignosulfonates and

they are obtained chemically. Their aim is to fluidize the mud and to control the

filtrate in low pH muds.







Linosulfonates

Lignosulfonates include:• Chromium lignosulfonates

• Ferrochromium lignosulfonates.

• Many applications in deflocculated water based-muds.

Characteristics:

• Keep their characteristics in presence of high level of calcium

• Good performance at all alkalinity level

• Can be used with high salt concentrations





CLAYS PROBLEMS

Clays problems

INTRODUCTION





The borehole instability during shales drilling is a common problem.

Shales are sedimentary rocks generally deposited in marin basins.

Shales with sands are called→sandstone shales

The Fluid Supervisor controls the→hydration degree of the shales together with

the cementing materails that connect the shales.

INTRODUCTION





Shales are composed of structurally different clay minerals

The most common are:

Smectite Montmorillonite Illite Chlorite Kaolinite

SHALES: DEFINITIONS





• Shale is a generic term used to describe clay-rich sedimentary rocks. The correctgeneric term is mudrock.

Other terms used to describe shale include:

• Clay

• Claystone

• Mudstone

• Argillite

• Gumbo

• Shales can be massive, interbedded, fissile, silty, swelling, dispersive etc…

• It is estimated that over 75% of footage drilled is through shales

CLASSIFICATION OF SHALES





Shales can be classified according to

• Age

• Mineralogy

• Hardness

• Moisture content

• Type of reaction with drilling fluids / mode of wellbore failure

• Depth of burial / diagenetic history

CLASSIFICATION OF SHALES (AFTER MONDSHINE)





( )

2.5-2.75-30Illite,

Kaolinite,

chlorite

2-50-3BrittleE

2.2-2.520-30Illite +

possiblesmectite

5-153-10HardD

2.3-2.720-30Illite+mixed layer 2-1010-20Firm-hardC

1.5-2.220-30Illite+

mixed layer

15-2510-20FirmB

1.2-1.520-30Smectite+

illite

25-7020-40Soft A

Density

gm/cc

Clay

Wt%

Clay

Minerals

WaterContentwt%

CEC

meq/100 g

TextureClass

CLAYS INSTABILITY FACTORS





• Reactive or chemically stressed shale

• Mechanical stress

• Geopressure

• Hydro-pressure

• Overburden stress

Instability in the formation can be due to:

CONSEQUENCES OF SHALE INSTABILITY





• Hole closure

Repeated reaming

Stuck pipe (in mobile

formations)Stuck casing

Logging difficulties

• Hole enlargement

Stuck pipe due to hole packingoff (cavings)

Poor hole cleaningLoss of directional control

Poor quality coment jobs

Logging difficulties

Poor quality log data

It is estimated that shale problems cost the industry over $600 million / year






CHEMICAL STRESSReactive Clay

Causes:

• Clay susceptibility to water and mud with null or insufficient inhibition.

• Clay, hydrating with water, expands in the borehole

• Time

Chemical problems during drilling shale interval, can be defined as chemical

interactions between shale minerals and mud filtrate






FIG 1. Reactive clays

Clays folding 1 DAY EXPOSITION

ABSORBEB

BY SH ALE

ABSORBEB

BY SH ALE

Hole Wall






3 DAYS EXPOSITION

The reaction depends on time.Clay balls






5 DAYS EXPOSITION

Overpull during POOH.

Impossible or limited circulation.

S T U C KP AC K O F F

O V E R

P U L L

CLAYS INSTABILITY: FACTORS





Reactive clays indicators

Pressure increase→circulation beginningSwabbingMud loss

IncreaseLight increase withweightOverpull without slips

Circulation

Pressure increase→circulation beginning

SwabbingMud loss

IncreaseLight increaseIncrease without slipsBack Reaming

It begins in depthwhere problems arise.Probable mud loss

Light increase withweightOverpull withoutwedges

Running

SwabbingLight increaseWithout wedgesPullin Out

Back pressure beforetheBack flow connection

Increase→ circulationbeginning

Without slipsConnection

Pressure increasingGradual ROP

decreasingProbable mud loss

IncreaseLight increaseLight increase

Drilling

Other PressureTorsionOverpull

Reactive Cuttings IndicatorsPhase






High viscosity funnel. & YP. PV, low gravity solids & increasingCEC. Probable mud density increase.mud eng

Large quantities of hydrated clay cuttings. High value inflating claystest

mud logger

Soft aggregation of shales. Hydrated clay (gumbo). Flow lineblocking

shaker

Visual Indications






Reactive Clays

Preventive actions

• Salts addition (potassium, sodium, calcium, etc.) to reduce water to salt

chemical attraction.

• Encapsulant polymer addition (coating) to reduce water/clay contact.

• Use of oil muds or synthetic base oils to cut water/clay contact out.• Minimize OH permanence.

• Provide reaming at regular intervals or at first signs of reactive clays.

• Correct hydraulic handling for bit and well cleaning.

• Keep ideal mud properties and minimize low gravity solids.






MECHANICAL STRESS

Geo-pressured clay (figure 2)

Cause :

• Drilling of pressurized clays with insufficient mud density• Caving of fractured clays in the hole

Attent ion :

First signs arise when reaching the clays:• Mud logger record indicating porosity pressure increase

• ROP increase at the commencement of drilling

• Connections overpull and torsion increase

• Settlings at the connections, swellings, caving of fractured clays

• Probable gas increase






Indicators :

• It often happens in trip, sometimes in drilling

• Pack-off, caving possibility

• Circulation difficulty or impossibility

First actions :

• Apply pressure moderately (200 – 400 psi)

• Apply torsion, run-in with the maximum weight






FIG 2. Geo-Pressured Clay

H ole W allH ole W all

Hydrostatic

Pressure

6000 Psi5500 Psi

Formation pressure

5500Psi 6000 Psi

Drilling






Trip

Pack-Off

Stuck

Ov er p ul l






Preventive actions for mechanically stressed clays.

• Consider well data off-set a/o computer modules for the simulation of the clays

structural limits in the planning of each hole section.

• Increase the mud density with the increasing of the inclination of the well and TVD to

keep the hole stability.

• In the exploration wells, regularly consult the Mud Logger for formation pressure

changes. Increase gradually the mud density till the symptoms disappearance






• If possible, increase mud density gradually (from 0.1 to 0.2 ppg per day) till the

desired value. The clays sensible to hydrostatic will be counerbalanced.

• Avoid mud density decreasing after more than one exposition day to the clays

sensible to hydrostatic. If this decreasing should be necessary , reduce the density

gradually during a period similar to the exposition one.• Reference to Shaker Handover Notes to determine cuttings volume, block and

cuttings shape






• Keep mud properties during hole cleaning

• Sweeps usage for well cleaning

• Stop drilling and re-start it only after hole conditioning

• Keep OH permanence minimum

• Define action plan if problems arise






Hydro-pressured clay (figures, 3 to 7)

Causes :

• Delayed intervention. The mud invades the formation overloading it

• Imprecise movement the battery can interfere with not stabilized clay

• The clay, folding, falls in the hole causing overpull or drill string stuck

Attention :

• Normally, it happens after a weight drop

• Torsion and overpull increase

• Shaker clay






Indications :

• Probably in trip or drilling phase

• Pack-off, caving possibility• Difficulty or circulation impossibility

First Actions :• Apply pressure moderately (200 – 400 psi)

• Apply torsion, to run-in with maximum weight

• Impossible or drastically limited circulation






Preventive Actions :

• Use OBM, SBM or oil mud in case of trouble

• If necessary, drop mud weight, gradually during the circulation cycles

• Minimize swab / purge pressure






5000 PsiHydrostatic

Pressure

6000 Psi

Stabilized

Shale

FIG 3. Hydro-Pressured clays pattern






Caving formation :

Clay Stability Effect : a good conditions borehole, can loose its stabilitybecause of formation pressure increasing during the swab/surge trips

.

Pressure differential effects on clays stabili ty






FIG 4. Pressure Penetration in Sandstone and Clay

• Pressure differentialcreates filter cake

• Filter cake prevents

pressure transmission

• Pore presure constant

• Flow due to pressure

differential

• Pressure transmitted

• Pore pressure increases

with time

t2

SANDSTONE

Mud Pressure

Borehole

wall

Pore Pressure Distance from

well bore

t2

SANDSTONE

Mud Pressure

Borehole

wall


well bore

t2

SANDSTONE

Mud Pressure

Borehole

wall


well bore

SANDSTONE

Mud Pressure

Borehole

wall


well bore

t0 t1 t2

SHALE

Mud Pressure

Boreholewall


well bore

t0 t1 t2

SHALE

Mud Pressure

Boreholewall


well bore

t0 t1 t2

SHALE

Mud Pressure

Boreholewall


well bore

SHALE

Mud Pressure

Boreholewall


well bore






FIG 5. Pore Pressure in Clay Distribution (water)

1

1

10

20

30

40

50

60

3 5 7 9 11 13 15 17 19 21

Kshale

= 10-7 Darcy

1

1

10

20

30

40

50

60

3 5 7 9 11 13 15 17 19 21

Kshale

= 10-7 Darcy

1 Day

7 Days

45 Days

P r e s s u r e ( B a r )

Normalised distance from borehole wall r/R






FIG 6. Porous clay pressure overloads for hydrostatic over balance effect.

6000 PSI5000 PSI 5000 PSI






FIG 7. Porous clay pressure overloads for hydrostatic over balance effect

S T U C K

P AC K O F F

O V E R

P U L L






Overburden stresses

Causes :

• Insufficient Mud Density

• Mud Density not adequate to the angle increase

• Clays caving in the hole

Attention :

• Borehole cleaning problems

• Overpull and torsion increase

• Clay at the shaker






Indications

• Probably in drilling or trip phase

• Pack-off, caving possibility

• Circulation difficulty or impossibility

First Actions:


• Apply torsion, to drop with maximum weight


• Correct mud density to stabilize the overburden

• As the inclination of the well increases, the mud density increases






FIG 9 Overburden stress






Overburden stress

• Mud density→ not

sufficient to support the

overburden.

• Mud density→ not correct

for the angulation

• Clays caving in the

borehole.






Tectonic Stresses (figure 10)

Causes :

• Lateral natural strngth recurrent in the formation

• Fractures in the stressed clays, the consequent cavings “stick” the string

• The sandstones thrust cause borehole tight






Attent ion :

• Mountainous places

• Known Tectonic• Abnormal torsion and overpull

• Clays blocks subject to caving

• Elliptic hole tendency

Indications :

• Probable in trip or drilling.

• Impossible or limited circulation






First Actions :


• Apply torsion, to run-in with maximum weight


• If possible, increase mud density

• Circulate sweeps at high density

• Minimize swab

• Minimize permanence in OH






FIG 10 Tectonic stresses

CLAYS STABILIZATION: MUDS





Aqueous Mud

Generally, we have aqueous muds stability through ionic inhibition, encapsulation and

physical block. The stability degree won’t be high as in oil-base mud. However, a water

treated mud, can be used with excellent results also with problematic clays.

CLAYS STABILIZATION MUDS





*Not available

*1.14 Al+++

17.62.86Ba++

19.22.12Ca++

21.61.56Mg++

7.62.86NH4+

7.62.66K+

11.21.96Na+

HydratedNot hydrated

Ionic Diameter (Angstroms)Ion

Ionic diameters

CLAYS STABILIZATION: MUDS





Oil-base Muds

Crumbly, dispersible and hydratable clays are sensible to water. The instability can be

reduced when mud water is not in contact with the clay.

A solution is to use an oil-based mud where water is emulsified in the oil-phase






Capil lary Effects

WpPp

WpPp

PpWp PpWp Wp = Wellbore Pressure

Pp = Pore Pressure

Dp = Differential Pressure

OBMWBM

Capillary Action

4 clays chemistry and problems

Documents