1-Pakinstan IWBS.PPT Pakinstan IWBS.PPTS

Pakistan Inhibited Water-Base Fluids Presentation – April 2001
Page 1
© 2001 Baker Hughes Incorporated
All rights reserved.
WHY HAVE
INHIBITED WATER-
BASE
DRILLING FLUIDS?

Page 2
What is INHIBITION?
•Inhibition is essentially PREVENTION and
PROTECTION.
•We are PREVENTING an event, by
PROTECTING ourselves against that event.

Page 3
What are we trying to
PREVENT?
 We are trying to PREVENT undesirable
changes to a number of things:
– The Drilled Cutting!
– The Drilling Fluid Properties!
– The Formation!

Page 4
UNDESIRABLE Changes to
the Drilled Cutting!
 One of the FUNCTIONS of a drilling fluid is
carry the cuttings to the surface and to
remove them.
 If the cutting has been ALTERED in any way,
this function may not be achieved efficiently.
 So, our goal is to get that cutting to the
surface with MINIMAL changes to its shape
and structure.

Page 5
What TYPES of Drilled
Cuttings?
 The type of drilled cutting reflects the type of
formation being drilled.
 The GENERAL types fall into four main
groups:
– Shales: Includes silts, clays and shales.
– Sandstone
– Limestone: Includes dolomite and limestones.
– Others: Includes marl, massive halite, anhydrite,
etc.

Page 6
Different
CHARACTERISTICS!
 Sandstones are virtually INERT!
 Most limestones have little or no adverse
effect!
 Massive salt, extensive halites and anhydrite
are special considerations.
 Our concern is with SHALE!
 However, we will briefly examine the others!

Page 7
What about SANDSTONE?
 Sandstones are generally
INERT!
– They have no reaction!
 They MAY have up to 20-30%
clay minerals contained
within their matrix.
 These clay minerals can
REACT!

Page 8
What of LIMESTONE?
 Limestone formations are mainly
sedimentary rocks formed from the
calcareous remains of marine animals.
 Limestone is primarily CALCIUM
CARBONATE.
 It is largely INERT!
 Dolomite is a CALCIUM MAGNESIUM
CARBONATE.

Page 9
And What of the OTHERS?
 Marl
– A fine-grained sedimentary rock of silts, clays and
calcite.
 Massive Halite
– Salt Domes
– Zechstein (mixed halites)
 Anhydrite
– Consists of ANHYDROUS CALCIUM SULPHATE!
– May be in stringers or as a massive interval.

Page 10
Why are Shales Considered
a PROBLEM?
 Shales are DEPOSITS of clay minerals that
have undergone certain changes to their
structure and chemistry through:
– De-watering
– Compaction
– Formation pressures
 They have TWO undesirable properties:
– Hydration
– Dispersion.

Page 11
What Are SHALES?
 How would you describe a ‘SHALE’?
 A more accurate description might be
MUDSTONES, CLAYSTONES or SILTSTONES!
 However, we will use SHALE to cover all of
these!

Page 12
What Exactly Are SHALES?
 Shales are complex mixtures of CLAY
MINERALS and non-clay minerals.
– The clay minerals include:
• Oxygen Silica Aluminium
• Calcium Magnesium Potassium
– The non-clay minerals include:
• Quartz Feldspar
• Pyrite Calcite
 Shales are rocks composed of more than 50%
clay minerals.

Page 13
The Clay TYPES!
 There are SEVEN major clay types that make
up most of the clay minerals.
 These fall into TWO major groups.
– LAYERED Clays
– CHAIN-TYPE Clays

Page 14
The TYPES of Clay Minerals!
 The MOST common clay minerals are:
– Kaolinite
– Illite
– Chlorite
– Montmorillonite, or smectite
 Each exhibits different characteristics and
was deposited in a different environment!

Page 15
The HYDRATION ABILITY of
Clay Minerals!
 In order of INCREASING hydration ability:
– Chlorite
– Kaolinite
– Illite
– Montmorillonite, or smectite

Page 16
Knowing Your SHALES!
 SHALES are sedimentary deposits of clay
and non-clay minerals!
 They have undergone changes in their
chemistry and their structure, due to age,
compaction and tectonic forces.
 They are generally de-watered!
 They have ONE primary, easily recognised
difference from MUDROCKS!

Page 17
We Have a WORD!
 FISSILITY!
 Another way of looking at this is to say that
they exhibit FRACTURE-PLANES!

Page 18
So! What About
MUDROCKS?
 MUDROCK is a general term used to describe
all sedimentary rocks containing clay
minerals that are not a SHALE.
 Mudrock can be classified into OTHER types
of rocks, based on the particle size.

Page 19
Sediment
PARTICLE SIZE!
Claystone
Mudstone
Clay
Silt
Sand
Sandstone Siltstone
% Clay < 4micron
% Silt (4- 62 microns)
50% 50%
50%
after M.D. Picard

Page 20
So What’s the PROBLEM?
 The problem is simply that boreholes are not
stable when drilled with any drilling fluid
system.
 It is true that they are MORE stable when
OBM or SBM is used!
 It is also true that more problems are
experienced when WBM is used.
 WHY?

Page 21
Defining the PROBLEM!
 The core issue is the reaction that takes
place between the drilling fluid’s EXTERNAL
phase and the formation that is being drilled!
 When water comes into contact with the clay
minerals found in SHALES and MUDROCKS,
these rocks attempt to revert to their original
state.
 We call this HYDRATION and this is the
problem!

Page 22
The Problems with SHALES!
 Many of the problems we have drilling shales
are MECHANICAL!
– Tectonic stresses
– Pore Pressure Transmission
– Sloughing
 We can solve most of the CHEMICAL
problems with the correct fluid!

Page 23
The CHEMICAL Problems
with Shales!
 As we will see, there is effectively just one –
HYDRATION!
 However, hydration leads to DISPERSION!

Page 24
 Hydration is swelling!
– Caused by the shale taking up water - either through
ADSORPTION or ABSORPTION!
 ADSORPTION is basically the attachment of
water to the OUTSIDE of the shale!
 ABSORPTION is essentially the entry of water
INTO the clay structure!
The HYDRATION of Shales!

Page 25
The THREE Hydration
Mechanisms!
 SURFACE HYDRATION:
– The BONDING of water molecules to oxygen atoms
on the surface of the clay platelets.
 IONIC HYDRATION:
– The hydration of INTERLAYER CATIONS with
surrounding shells of water molecules.
 OSMOTIC HYDRATION:
– Occurs on some clays AFTER they are completely
surface and ionically hydrated.

Page 26
Are Shales PREMEABLE?
 Yes!
– The permeability of shales ranges from 10-6 to 10-12
Darcy!
 This very LOW value means that “fluid loss”
as we normally understand it, does not
occur!
 But, a gradual equilibrium between mud
hydrostatic pressure and pore pressure does
occur!

Page 27
A Little MORE on Hydration!
 Water adsorption or hydration can cause the
wellbore to enlarge.
– This in turn leads to problems with drag when trying
to pull out of the hole.
 Wiping the hole - or pulling the bit back
through a section - releases these hydrated
clays into the mud system and also cleans
the hydrated interval.
 It is now free to hydrate new faces.

Page 28
CHARGES on Clay
Particles!
 Charges on clays are important as they
determine properties such as :
– Ion Exchange
– Swelling Behaviour
– Viscosity of Muds
 Charges can arise from :
– Broken edges on clay particles
– Substitution of Ions in the clay structure

Page 29
Some FINAL Points on
Hydration!
 ALL clays experience hydration to some
degree.
 The ILLITES and SMECTITES exhibit varying
degrees of IONIC hydration.
 Shale hydration is essentially SURFACE
ADSORPTION and OSMOTIC ADSORPTION.

Page 30
The AGE of a Shale!
 YOUNG shales tend to soften, swell and
disperse when mixed with water!
 OLD shales have usually undergone
diagenesis and may remain hard when
exposed to water - not easily dispersing into
the drilling fluid.
DIAGENESIS is essentially a satisfying of all electrical
charges - leading to chemical stability!

Page 31
To RECAP!
 When we consider SHALES, we must also
consider each of these UNDESIRABLE
properties:
HYDRATION:
• The swelling of the clays!
DISPERSION:
• The breaking-down into smaller particles!
 BOTH of these mechanisms can, and do,
occur!

Page 32
A SHALE Cutting!
 This drawing
represents a
shale cutting at
the moment it
is released into
the annulus!
 The BLUE is
water in the
shale!

Page 33
A SHALE Cutting!
 In normal
water-base
system, filtrate
begins to
invade the pore
spaces of the
cutting almost
immediately!

Page 34
A SHALE Cutting!
 Causing
weakening of
the clay matrix,
and dispersion!
 Hydration may
also occur,
depending on
the type of
clays!

Page 35
The OVERBURDEN
Pressure!
 Overburden pressure is the weight of the
formations overlying a particular shale
section.
 Weakens the shale when the shale is
penetrated - allowing a combination of
STRESS RELIEF and the OVERBURDEN
PRESSURE to cause the shale to collapse
into the hole.

Page 36
The Development of PORE
PRESSURE!
 Pore pressure is the
pressure that results
from the effects of
OVERBURDEN pressure
pushing DOWN and
FORMATION pressure
pushing UP!
Overburden
Pressure
Formation
Pressure

Page 37
The Effects of PORE
PRESSURE!
 Shales can fail when the OVERBURDEN
pressure exceeds the hydrostatic pressure!
 The strength of the rock determines the
TOLERABLE MAGNITUDE of pressure
differential!
 Normal drilling practise is to maintain the
hydrostatic pressure in BALANCE with the
overburden pressure!

Page 38
PRESSURE SUPPORT and
INVASION!
Pm > Pf
Shale Boreholes are
stabilized by the support
of drilling fluid pressure
Pm > Pf
Pm = Pf
Support Invasion
Pressure invasion.
Pressure invades the shale,
differential pressure support at the
wall is lost

Page 39
Borehole SLOUGHING!
Pm < Pf
Loss of support at the wall
allows overburden stress to
collapse the wall and slough
it off

Page 40
A Look at Borehole STRESS
RELIEF!
 The consolidation process of shale
deposition produces STRESS!
 When a well is drilled through a compacted
sedimentary rock, the stress is relieved
toward the well bore!
 Radial fracturing around the wellbore can
occur!
 This can cause instability!

Page 41
The Formation of MICRO-
FRACTURES!
Try to visualise a shale
section that has just been
drilled.
Stress relief occurs around
the well bore in the form of
micro-fractures!

Page 42
The Effects of BALANCED
Pressures!
When the pore pressure and
hydrostatic pressure are
equalised, the shale will
probably remain stable!
The fluid and formation are in
equilibrium!

Page 43
The Effects of an OVER-
BALANCED Condition!
If the hydrostatic pressure
exceeds the formation
pressure, fluid is forced into
the shale!
This can lead to instability
inside the shale matrix!

Page 44
The Effects of an UNDER-
BALANCED Condition!
If the formation pressure
exceeds the hydrostatic,
sloughing can occur!
The fluid and formation are
NOT in equilibrium!

Page 45
Blocking PORE PRESSURE
TRANSMISSION!
Introduction of materials
designed to reduce, or stop,
this invasion can minimise
any instability!
ALPLEX is one such product,
effectively minimising PPT!
So do CLOUD-POINT
GLYCOLS!

Page 46
The Effects of PORE
PRESSURE Equilibrium!
 As the transfer of water into the shale matrix
takes place, several things happen:
– The effective internal stresses INCREASE!
• Due to the ELEVATION of pore pressure!
– SWELLING pressures are generated within the shale
matrix!
• Caused by WETTING and HYDRATION of clay within the
shale!
 Instability takes TIME to develop!

Page 47
A Look At PORE PRESSURE
TRANSMISSION!
 This is the party line.
 A better way of looking at this might be to call
it ‘PORE PRESSURE DIFUSSION!”
 Can you describe this phenomenon?

Page 48
What is PORE PRESSURE
TRANSMISSION?
 Pore Pressure Transmission, or PPT, is the
condition where the hydrostatic exceeds the
formation pressure and filtrate is forced INTO
the shale!
 The chemistry of the filtrate can reduce the
effects, ANY change to the shale can weaken
the strength of the rock!

Page 49
Pore Pressure
TRANSMISSION!
 Key mechanism for structural destabilisation
of shales
– Can be critical when drilling fractured shales
 Results in hole instability which is frequently
treated by increasing mud density which can
make the problem worse
 Prevention is the only cure!

Page 50
The Effects of TECTONIC
FORCES!
 Tectonic forces are those forces within the
rock that bend, twist and move deposits,
causing instability.
 It can also result in high-angle bedding
planes, allowing the “high” side of the hole to
fall into the well bore.
 Stress relief can also cause the borehole to
become oval, rather than round.

Page 51
What Is An INHIBITED
Drilling Fluid?
 The Baker Hughes INTEQ U.K. Region Fluid
Systems Field Manual offers this definition:
– A Drilling Fluid having an aqueous phase
with a chemical composition that tends to
retard or even prevent (INHIBIT) appreciable
hydration (SWELLING) or dispersion of
formation clays and shales through chemical
and/or physical means (PROTECTION).

Page 52
The FAMILY of Inhibited
Water-Base Drilling Fluids!
 NEW-DRILL:
– Utilises a PHPA and KCl!
 AQUA-DRILL:
– Enhances with GLYCOLS!
 AQUA-DRILL Plus:
– Further enhancement with ALPLEX!
 AQUA-DRILL Plus:
– Leave out the KCl and use POTASSIUM CARBONATE!

Page 53
How do we INHIBIT?
 By understanding the mechanisms of
HYDRATION and DISPERSION, we can design
additives to prevent, or minimise, these
occurrences.
– We can use a SALT to reduce, or prevent, hydration!
– We add ENCAPSLATING POLYMERS to reduce
dispersion!
– We can use a CLOUD-POINT GLYCOL to enhance the
inhibition levels!
– We add a PORE PRESSURE TRANSMISSION reducer!

Page 54
Completing the PACKAGE!
 A typical drilling fluid will be exposed to
BOTH types of clay particles.
 Our INHIBITION mechanisms will prevent
both HYDRATION and DISPERSION!
 The encapsulating polymer coats BOTH
types of clay.

Page 55
The LIMITATIONS of
INHIBITON!
 We must REMOVE that cutting at the
surface the first time it arrives there.
 The importance of an efficient solids
removal package cannot be under-
estimated!

Page 56
The LIMITATIONS of
INHIBITON!
 The Shale Shakers MUST be capable of
handling the maximum flow rate of the
pumps!
 De-sanders, De-silters, Mud Cleaners and
Centrifuges should be used with caution!
 ALWAYS RELY UPON THE SHALE
SHAKER AS THE PRIMARY DEVICE TO
REMOVE SOLIDS!

Page 57
A SHALE Cutting-Revisited!
 Again, a shale
cutting at the
moment it is
released into
the annulus!
 The BLUE is
water in the
shale!

Page 58
A SHALE Cutting -Revisited!
 In an Inhibited
system, like the
AQUA-DRILL
system, each
mechanism
starts to work
immediately!
 The KCl stops
swelling!

Page 59
Reducing HYDRATION with
Salts!
 The addition of a SALT to the water phase
will aid in reducing hydration!
 The most common salt is Potassium
Chloride (KCl)!
 THE ONLY THING THAT POTASSIUM ION
DOES IS REDUCE HYDRATION!

Page 60
 At the same
time, the PHPA
coats the
cutting in a
high viscosity
‘shell’!

Page 61
Reducing DISPERSION!
 The addition of an ENCAPSULATING
polymer can minimise the dispersion of
these clays!
– It accomplishes this through a COATING
mechanism!
 Even though dispersion may still take
place, the polymeric coating CONTAINS
everything in a single, removable solid!

Page 62
 While all of this
is happening,
the CLOUD-
POINT Glycol
as also entered
the pore
throats and
‘solidifies’!

Page 63
We Can IMPROVE This
Inhibition with GLYCOLS!
 Glycols are soluble until a certain
temperature is reached, when they
CLOUD and fill pore spaces with an
INSOLUBLE glycol, but they also COAT
the surface of the particle, as well as the
surface of the well bore.

Page 64
 Both
HYDRATION
and
DISPERSION
are minimised!

Page 65
THE BEAUTY OF IT ALL!
 The AQUA-DRILL system has been run at
densities up to 2.21 sg (18.7 ppg).
 It CAN be run with a minimal set of
components, thus reducing logistic
problems on remote locations.
 It is a highly flexible, highly tolerant system.

Page 66
We Can further IMPROVE
Inhibition with ALPLEX!
 ALPLEX is an Aluminium complex that
effectively PLUGS pore spaces within a
shale structure.

Page 67
We Can further IMPROVE
Inhibition with ALPLEX!
 This plugging mechanism reduces PORE
PRESSURE TRANSMISSION:
– This in turn prevents the invasion of water into the
clay structure.
– It prevents further fracture development.
– It ENHANCES the performance of the basic inhibited
water base system.

Page 68
How Alplex FUNCTIONS!
 Alplex is a mixture of aluminium salts and
organic acids
 Aluminium is in solution at pH values above
10 and below 3
 Precipitates of aluminium hydroxide form at
intermediate pH’s
 Precipitation occurs in shale pores and
microfractures on contact with connate water

Page 69
ALPLEX Pore Plugging!
Filtrate invasion zone
ALPLEXPrecipitate
Uncontaminated formation
External filter cake
FRACTURE
HOLE
Schematic
of Formation

Page 70
Looking at it ANOTHER
Way!
Filtrate WILL invade
the structure of the
clay matrix!

Page 71
Adding ALPLEX Will Block
the Pores!
When the ALPLEX comes in contact with the connate
water, the pH drop causes it to solidify, plugging the
pore spaces in the clay matrix!

Page 72
FAILURE to Address the
PPT Issue is Dangerous!
The Clay Matrix will DE-STABILISE
and begin to fall apart!

Page 73
WHY use Glycol with
Alplex?
 “Belt & braces” approach
 Lubricity contribution above and below cloud
point
 Keeping the bit face clean
 Cuttings protection in annulus
 Contributes to well-bore stability
 Synergistic with Alplex

Page 74
ENHANCEMENT of Glycol
Systems with Alplex!
% Recovery % Hydration % Hardness
0
20
40
60
80
100
KCl/Polymer(A) A+glycol @ 3%(B) B+Alplex (2ppb)

Page 75
The PROOF on Pore
Pressure Transmission!
40
50
60
70
80
90
100
110
120
130
140
150
160
170
0 10 20 30 40 50 60 70 80 90 100 110
HOURS
FORMATION
PRESSURE
(psi)
BOREHOLE: 195 PSI
CONFINING: 315 PSI
TEMPERATURE: 158F (70C)
FORM: 5PPB ALPEX, 0.1% NEWDRILL, 1% PAC LV
CORE: PIERRE II
EQUILIBRATION TIME: 9 HOURS
2% NaCl
5 PPB ALPLEX
+ PHPA + PAC
20% KCl, neat
20% KCl + PHPA + PAC
5 PPB ALPLEX + PHPA
+ PAC
 Salt and polymers
have minimal effect on
PPT
 Alplex completely
eliminates PPT
 Alplex lines are repeat
results to confirm
findings

Page 76
Effect of PENETREX (1)
PDC bit after drilling
Catoosa Shale in a full-
scale drilling simulator
Left: no Penetrex
Right: Penetrex at 3%

Page 77
Effect of PENETREX (2)
PDC bit after drilling Pierre
Shale in a full-scale drilling
simulator
Left: no Penetrex
Right: Penetrex at 3%

Page 78
The BENTONITE Question!
 PHPA inhibits dispersion of ALL clay solids
through encapsulation.
– BENTONITE is a highly dispersible clay solid.
– DRILL CUTTINGS are dispersible clay solids.
 Why add another clay that requires
encapsulation - and takes up part of the
material added to treat drilled cuttings?

Page 79
BENTONITE - To Be or Not
to Be!
 There are only two VALID reasons to add
BENTONITE to a NEW-DRILL system:
– Because the Customer wants it!
– For wall cake building characteristics!
 If you have to add Bentonite, make sure you
use a WYOMING-GRADE PREMIUM
BENTONITE, like MIL-GEL!

Page 80
Performance
CHARACTERISTICS!
CARBODRILL
BIOGREEN
AQUADRILL
NEWDRILL
SYNTEQ
BENTONITE

Page 81
RELATIVE Shale
Inhibition!
1. Gypsum mud
2. Seawater polymer
3. KCl Polymer
4. KCl Polymer/glycol
5. Enhanced glycol mud
6. Oil based/pseudo oil-based
mud
0
10
20
30
40
50
60
70
80
90
100
1 2 3 4 5 6

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