The present invention relates to a method for inhibiting the swelling and
the dispersion of shales in the treatment of subterranean shale
5 formations, i.e. in subterranean formations comprising or releasing
shales. The method comprises the use of a cationic tamarind gum.
In another aspect, the invention relates to fluids for the treatment of
subterranean shale formations comprising a cationic tamarind gum.
BACKGROU ND O F TH E ART
The subterranean treatment fluids, such as drilling fluids, may be
10 classified according to their fluid base. Oil based fluids contain solid
particles suspended in an oil continuous phase and, possibly, water or
brine emulsified with the oil. Alternatively, water base fluids contain solid
particles suspended in water or brine. Various other components may be
added, deliberately or otherwise, to water based drilling fluids: a)
15 organic or inorganic colloids, such as clays, used to impart viscosity and
filtration properties; b) soluble salts or insoluble inorganic minerals used
to increase the fluid density; c) other optional components that may be
added to impart desirable properties, such as dispersants, lubricants,
corrosion inhibitors, defoamers or surfactants; d) formation solids which
20 may disperse into the fluid during the subterranean operations.
Formation solids that become dispersed in a drilling fluid include cuttings
from drilling and soil and/or solids from the surrounding unstable
formation. When the formation yields solids which can swell in water,
hereinafter defined shales, they can potentially compromise drilling time
25 and increase costs. Shales are mainly layered aluminum silicates, in
which the dominant structure consists of layers formed by sheets of silica
and alumina, that can have exposed oxygen atoms and hydroxyls. When
atoms having different valences are positioned within the layers of the
structure, they create a negative potential at the layer surface, which
causes cations t o be adsorbed thereto. These adsorbed cations are called
exchangeable cations because they may chemically exchange places with
other cations when the shale crystal is suspended in water. The type of
substitutions occurring within the layers of the shale and the
exchangeable cations adsorbed on the surface affect shale swelling.
There are different types of water swelling. For example surface
hydration gives swelling with a large number of water molecules
adsorbed by hydrogen interaction on the oxygen atoms exposed on the
layer surfaces. All types of shale can swell in this manner.
Another type of swelling is called osmotic swelling . Where the
concentration of cations between layers in a shale mineral is higher than
the cation concentration in the surrounding water, water is osmotically
drawn between the unit layers. Osmotic swelling results in larger overall
volume increase than surface hydration. The shales that do not give this
inter-layers swelling tend to disperse in water.
All types of shale swelling can cause a series of problems, for example
sticking of the shales onto the drill string and bit, increasing torque and
drag between the drill string and the sides of the borehole, caving or
sloughing of the borehole walls and inducing an uncontrollable increase
of the viscosity of the treatment fluid.
This is why the development of effective substances which reduce or
block the swelling and/or the dispersion of shales, namely shale
inhibitors, is important to the oil and gas industry. The present invention
works towards a solution of these difficulties.
Several patents have been filed which describe techniques or compounds
which can be used to inhibit shales, including inorganic salts such as
potassium chloride, polyalkoxy diamines and their salts, described in US
6,484,821, US 6,609,578, US 6,247,543 and US 2003/0106718,
oligomethylene diamines and their salts, in US 5,771,971 and US
2002/0155956. These compounds are mainly known as shale hydration
inhibitors and principally they inhibit the shale swelling.
Another kind of shale inhibitors works by encapsulating, i.e. coating the
surface of shales and inhibiting the dispersion and, at least partially, the
swelling of the shales. I n the prior art this is accomplished by preparing
a synthetic molecule that has a polymeric backbone made of
hydrocarbon, such as polyethylene onto which polar and/or ionic organic
pendent groups, in particular cationic groups, are attached. These
compounds are known as shale encapsulators and are often used in
combination with shale hydration inhibitors.
While not intending to be bound by any specific theory, it is believed that
the molecular structure of these encapsulators results in their strong
adherence to the shale solid's surface, by way of the polar and/or ionic
organic groups. As a result, the shale particles are encapsulated in a
hydrophobic polymer coating that increases the action of the shale
hydration inhibitors and thus prevents the swelling of the shale and, in
particular, the dispersing of the shale by mechanical action. Alternatively
it has been hypothesized that the strength of the polymer coating stiffly
locks the shale sheets in their relative position and thus swelling and
dispersion of the shales is inhibited.
An example of a shale encapsulator is described in US 2007/129258.
This patent Application describes a drilling fluid comprising, as shale
encapsulator, a cationic polyvinyl alcohol with a molecular weight
comprised between 10,000 and 200,000 AMU.
Very few other patent applications have been filed on shale
encapsulators and, often, the proposed compounds do not show
satisfying performances. Therefore, there is a continuous need for the
development of improved shale encapsulators and methods of using the
same as shale inhibition agent in the treatment of subterranean shale
formations.
The Applicant has now found that a cationic tamarind gum, a cationic
xyloglucan polysaccharide, can be advantageously used as shale
encapsulator in subterranean shale formations.
As far as the Applicant knows, cationic tamarind gum has never been
proposed and described in the previous literature as shale encapsulator.
In the present text, with the expression "cationic degree of substitution"
(DScat) , we mean the average number of hydroxyl groups substituted
with a cationic group on each anhydroglycosidic unit of the
polysaccharide determined by means of ^-NMR.
With the expression "hydroxyalkyl molar substitution" (MS), we mean
the average number of hydroxyalkyl substituents on each
anhydroglycosidic unit of the polysaccharide measured by means of -
NMR.
With the expression "hydrophobic degree of substitution" (DSH) , we
mean average number of hydrophobic substituents on each
anhydroglycosidic unit of the polysaccharide measured by means of gaschromatography
or ^-NMR.
With the expression "carboxyalkyi degree of substitution" (DSan ) , we
mean the average number of hydroxyl groups substituted with a
carboxyalkyi group on each anhydroglycosidic unit of the polysaccharide
measured by means of titration.
As used herein, the expression "subterranean treatment," refers to any
subterranean operation that uses a specific fluid in conjunction with a
desired function and/or for a desired purpose.
DESCRI PTION OFTHEINVENTION
It is therefore an object of the present invention a method for inhibiting
the swelling and the dispersion of shales during the treatment of
subterranean shale formations comprising the steps of:
a) providing a subterranean treatment fluid comprising between 0.2
and 6.0 % wt of a cationic tamarind gum having a cationic degree of
substitution (DScat) from 0.01 to 1.0 and a Brookfield® RV viscosity
at 4.0 % wt water solution, 20 rpm and 20 °C below 2000 mPa*s;
b) introducing said treatment fluid into a wellbore at a pressure
sufficient to treat the subterranean shale formations.
In another aspect the invention relates to a drilling fluid comprising an
aqueous continuous phase, between 0.2 and 6.0 % wt of a cationic
tamarind gum having a cationic degree of substitution (DScat) from 0.01
to 1.0 and a Brookfield® RV viscosity at 4.0 % wt water solution, 20 rpm
and 20 °C below 2000 mPa*s, and between 1 and 70 % wt of a
weighting material.
DETAILED DESCRI PTION O F THE INVENTION
Preferably, the subterranean treatment fluid comprises between 0.5 and
4.0 % wt of said cationic tamarind gum.
Tamarind (Tamarindus Indica) is a leguminous evergreen tall tree which
grows in the tropics. Tamarind gum (tamarind powder or tamarind
kernel powder) is obtained by extracting and purifying the powder
obtained by grinding the seeds of tamarind.
Tamarind gum is a complex mixture containing a xyloglucan
polysaccharide (55-75 % wt), proteins (16-22 %wt ), lipids (6-10 % wt)
and certain minor constituents such as fibres and sugar.
The polysaccharide backbone consists of D-glucose units joined with (1-
4)-p-linkages similar t o that of cellulose, with a side chain of single
xylose unit attached to every second, third and fourth of D-glucose unit
through a -D-(l-6) linkage. One galactose unit is attached to one of the
xylose units through p-D-(l-2) linkage.
There are basically two different grades of tamarind gum which are used
in specific industrial applications like textile and pharmaceutical
industries: oiled tamarind kernel powder and the de-oiled tamarind
kernel powder. Both are useful for the realization of the present
invention.
Other tamarind gums which have been subjected to other kind of
treatment, such as enzymatic treatments or physico-chemical
treatments, are also useful for the realization of the present invention.
The tamarind gum suitable for obtaining the cationic derivative of the
invention has preferably a Brookfield® RV viscosity, measured at 25 °C
and 20 rpm on a 4.0 % by weight water solution, comprised between
100 and 30,000 mPa*s .
The cationization of polysaccharides is well known in the art. Cationic
substituents can be introduced on the tamarind gum by reaction of part
of the hydroxyl groups of the xyloglucan gum with cationization agents,
such as tertiary amino or quaternary ammonium alkylating agents.
Examples of quaternary ammonium compounds include, but are not
limited to, glycidyltrialkyl ammonium salts, 3-halo-2-hydroxypropyl
trialkyi ammonium salts and halo-alkyltrialkyl ammonium salts, wherein
each alkyl can have, independently one of the other, from 1 to 18 carbon
atoms. Examples of such ammonium salts are glycidyltrimethyl
ammonium chloride, glycidyltriethyl ammonium chloride,
gylcidyltripropyl ammonium chloride, glycidylethyldimethyl ammonium
chloride, glycidyldiethylmethyl ammonium chloride, and their
corresponding bromides and iodides; 3-chloro-2-hydroxypropyl trimethyl
ammonium chloride, 3-chloro-2- hydroxypropyltriethyl ammonium
chloride, 3-chloro-2-hydroxypropyltripropyl ammonium chloride, 3-
chloro-2- hydroxypropylethyldimethyl ammonium chloride, 3-chloro-2-
hydroxypropylcocoalkyldimethyl ammonium chloride, 3-chloro-2-
hydroxypropylstearyldimethyl ammonium chloride and their
corresponding bromides and iodides.
Examples of halo-alkyltrialkyl ammonium salts are 2-bromoethyl
trimethyl ammonium bromide, 3-bromopropyltrimethyl ammonium
bromide, 4-bromobutyltrimethyl ammonium bromide and their
corresponding chlorides and iodides.
Quaternary ammonium compounds such as halides of imidazoline ring
containing compounds may also be used.
In the typical embodiments of the invention the cationizing agent is a
quaternary ammonium compound and preferably is 3-chloro-2-
hydroxypropyltrimethyl ammonium chloride. The cationic substituent is
in this case a chloride of a 2-hydroxy-3-trimethylammonium propyl ether
group.
The cationic tamarind gum of the invention may also contain further
substituent groups such as hydroxyalkyl substituents, wherein the alkyl
represents a straight or branched hydrocarbon moiety having 1 to 5
carbon atoms (e.g., hydroxyethyl, or hydroxypropyl, hydroxybutyl) or
hydrophobic substituents or carboxyalkyl substituents or combinations
thereof.
The process for introducing a hydroxyalkyl substituent on a
polysaccharide is well known in the art.
Typically, the hydroxyalkylation of a polysaccharide is obtained by the
reaction with reagents such as alkylene oxides, e.g. ethylene oxide,
propylene oxide, butylene oxide and the like, to obtain hydroxyethyl
groups, hydroxypropyl groups, or hydroxybutyl groups, etc.
The hydroxyalkyl cationic tamarind gum may have a MS comprised
between 0.1 and 3.0, preferably between 0 .1 and 2.0, more preferably
between 0.1 and 1.5.
The hydrophobization of the cationic tamarind gum of the invention is
achieved by the introduction of hydrophobic group.
Examples of the introduction of hydrophobic groups on polysaccharides
is reported for example in EP 323 627 and EP 1 786 840.
Typical derivatizing agents bringing a hydrophobic group include linear or
branched C2-C24 alkyl and alkenyl halides, linear or branched alkyl and
alkenyl epoxides containing a C6-C2 hydrocarbon chain and alkyl and
alkenyl glycidyl ethers containing a C -C2 linear or branched
hydrocarbon chain.
A suitable glycidylether hydrophobizing agent can be, for example, butyl
glycidyl ether, t-butyl glycidyl ether, 2-ethylhexyl glycidyl ether, dodecyl
glycidyl ether, hexadecyl glycidyl ether, behenyl glycidyl ether and
nonylphenyl glycidyl ether .
Representative alkyl epoxides include but are not limited t o 1,2-epoxy
hexane, 1,2-epoxy octane, 1,2-epoxy decane, 1,2-epoxy dodecane, 1,2-
epoxy tetradecane, 1,2-epoxy hexadecane, 1,2-epoxy octadecane and
1,2-epoxy eicosane.
Exemplary halide hydrophobizing agents include but are not limited to
ethyl, propyl, isopropyl, n-butyl, t-butyl, pentyl, neopentyl, hexyl, octyl,
decyl, dodecyl, myristyl, hexadecyl, stearyl and behenyl bromides,
chlorides, and iodides.
Other derivatizing agents suitable for the hydrophobic modification
include alkyl- and alkenyl^-hydroxy-y-chloropropyl ethers and epoxy
derivatives of triglycerides.
In a preferred embodiment of the invention the cationic substituent is 2-
hydroxy-3-trimethylammoniumpropyl ether chloride and the hydrophobic
substituent contains a linear alkyl or alkenyl chain containing between 6
and 24 carbon atoms or a mixture of such alkyls or alkenyls.
The hydrophobically modified cationic tamarind gum of the invention
may have hydrophobic degree of substitution (DSH) of from 1* 10 5 to
5* 10~ preferably from 1* 10 4 to 1* 10~
In a further particular embodiment the cationic tamarind gum of the
invention can contain both hydroxyalkyl substituents and hydrophobic
substituents. In this case the MS is comprised between 0.1 and 3.0 and
the DSH is between 1* 10 5 and 5* 10
In another embodiment the cationic tamarind gum of the invention is
carboxyalkylated, with a degree of carboxyalkyl substitution (DSAN)
ranging from 0.01 to 1.0.
Halo-carboxylic acids or their salts can be used for the preparation of
carboxyalkyl cationic tamarind gum. The preferred halo-carboxylic acid is
monochloro-acetic acid.
The cationic tamarind gum of the present invention can be prepared by
known processes. For example, the cationic substituents can be
introduced by reaction of the tamarind gum with the cationizing agent, in
the presence of a base, such as sodium hydroxide.
The introduction of the different substituents (cationic, carboxyalkyl
hydroxyalkyl and/or hydrophobic) on the tamarind gum backbone can
follow any order.
When the cationic tamarind gum of the invention also contains
hydroxyalkyl substituents, they may also be introduced in the last step,
after the cationization and the optional hydrophobization have occurred.
Further indications about the preparation of the cationic derivatives of
tamarind gum suitable for the realization of the present invention can be
found in the literature, for example in "Industrial Gums: Polysaccharides
and their Derivatives", 3rd Ed., Whistler, Roy L , and BeMiller, James N.,
Academic Press (1993).
In an exemplary production process, the cationic tamarind gum is
obtained operating as follows: tamarind gum, possibly dispersed in
water, or an inert diluent which can be chosen among lower aliphatic
alcohols, ketones, or liquid hydrocarbons, or mixtures of the above, is
treated at ambient temperature with an alkali-hydroxide in aqueous
solution and then heated t o 50-90 °C. The reaction mass system is then
set to about 50°C and the cationizing agent and the optional
hydroxyalkylating agents, for example ethylene oxide and/or propylene
oxide, or carboxyalkylating and/or hydrophobizing agents, are
introduced into the reactor, possibly dispersed in inert organic diluents.
The reaction is completed by setting the temperature at 40-80 °C for 1-3
hours.
In one embodiment of the invention, the cationic tamarind gum is
subjected to an additional treatment with a base after the cationization,
that allows to produce cationic polysaccharide derivatives free from toxic
compounds, such as 3-chloro-2-hydroxypropyltrimethyl ammonium
chloride or 2,3-epoxypropyltrimethyl ammonium chloride. This postcationization
treatment is described more accurately in the patent
application WO 2014/027120.
After the preparation, the cationic tamarind gum can be treated with
several known reagents, for example: caustic; acids; biochemical
oxidants, such as galactose oxidase; chemical oxidants, such as
hydrogen peroxide; and enzymatic reagents; or by physical methods
using high speed agitation machines, thermal methods; and
combinations of these reagents and methods. Reagents such as sodium
metabisulfite or inorganic salts of bisulfite may also be optionally
included.
These treatments can be also performed on the tamarind gum before the
derivatization process.
In a preferred embodiment, the cationic tamarind gum is a
depolymerized cationic tamarind gum, which has been depolymerised by
using chemicals, such as hydrogen peroxide, or cellulase enzymes.
In a further embodiment, a purification step can be performed to obtain
a particularly pure product.
The purification step may take place by extraction of the impurities with
water or aqueous-organic solvent before a final drying step so as to
remove the salts and by-products formed during the reaction.
In a further preferred embodiment, the cationic tamarind gum of the
present invention is left unpurified (usually called "crude" or technical
grade) and still contains by-products generated during its chemical
preparation (that is during cationization of the tamarind gum and the
other possible derivatizations).
This unpurified cationic tamarind gum can contain from 4 to 65 % by dry
weight of by-products such as, cationizing agents and their degradation
products, for example 2,3-dihydroxypropyltrimethyl ammonium chloride,
and inorganic salts deriving from the neutralization of the bases used for
the reaction, glycols and polyglycols deriving from the alkylene oxides,
etc.
Preferably, the cationic tamarind gum of the invention has a DScat
comprised between between 0.05 and 0.55 and a Brookfield® RV
viscosity, measured at 20 °C and 20 rpm in a 4.0 % by weight water
solution, comprised between 30 and 1500 mPa*s .
In a particularly preferred embodiment of the invention, the cationic
tamarind gum contains only cationic substituents and has a DScat
comprised between 0.1 and 0.45 and a Brookfield® RV viscosity,
measured at 20°C and 20 rpm in a 4.0 % by weight water solution,
comprised between 100 and 1000 mPa*s .
The weight average molecular weight (M ) of the cationic tamarind gum
useful for the invention ranges typically between 10,000 and 4,000,000
Dalton, preferably between 100,000 and 1,000,000 Dalton and more
preferably between 350,000 and 750,000 Dalton.
The cationic tamarind gums of the invention can be used as ingredients
in the most different subterranean treatment fluids, where their
capability of binding through their positive charges to substrates having
weak negative charges, such as shales, are fully exploited.
Typically, the subterranean treatment fluid of the invention can comprise
an aqueous continuous phase and a weighting material, which can be
selected from : barite, hematite, ilmenite, iron oxide, calcium carbonate,
magnesium carbonate, magnesium organic and inorganic salts, calcium
chloride, calcium bromide, magnesium chloride, zinc halides, alkali metal
formates, alkali metal nitrates, and combinations thereof. Usually, the
subterranean treatment fluid can contain between 1 and 70 % wt of
weighting material, depending on the desired density.
The aqueous continuous phase may be selected from: fresh water, sea
water, brine, mixtures of water and water-soluble organic compounds,
and mixtures thereof.
In a preferred embodiment of the invention, the subterranean treatment
fluid further comprises from 0.1 to 20 % wt, preferably from 0 .1 to 15 %
wt, of a shale hydration inhibitor.
Any shale hydration inhibitors commonly used in the field can be added
to the subterranean treatment fluid of the present inventions.
Examples are potassium salts; inorganic and organic phosphates;
silicates; polyalkoxy diamines and their salts, for example those sold
with the commercial name of Jeffamine®; choline derivatives; diamines,
triamines, polyamines and their salts; high boiling by-products of
hexamethylenediamine purification and their salts; partially hydrolyzed
(meth)acrylamide copolymers (PHPA) and their cationic derivatives;
dialkyl aminoalkyl (meth)acrylate/(meth)acrylamide copolymers;
quaternary ammonium compounds; cationic polyvinyl alcohols; and
mixtures thereof.
Examples of diamines are diamines with a saturated C2-C8 alkyl chain,
such as 1,6-hexamethylene diamine, 1,2-ethylene diamine, 1,3-
propylene diamine, 1,4-butane diamine, 1,5-pentane diamine, 1,2-
cyclohexane diamine and mixtures thereof.
Examples of triamines and polyamines are diethylene triamine, bishexamethylene-
triamine, triethylene tetramine and tetraethylene
pentamine, higher amines, and mixtures thereof.
Examples of polyalkoxy diamines are those represented by the general
formula I :
in which x has a value from 1 to 25 and R and Ri are, independently one
of the other, alkylene groups having from 1 to 6 carbon atoms.
The amine salts useful for the realization of the invention are of the
inorganic or of the organic kind, the preferred salts being salts formed
with hydrochloric acid, phosphoric acid, formic acid, acetic acid, lactic
acid, adipic acid, citric acid, etc., more preferably with hydrochloric acid
or acetic acid.
Advantageously, the shale hydration inhibitor of the invention is a high
boiling by-product of hexamethylenediamine purification (product that is
commercially known as HMDA bottoms) or a salt thereof. These
products, described in WO 2011/083182, typically comprise variable
amounts of bis-hexamethylene-triamine.
The typical content of amines of HMDA bottoms is the following (% wt) :
Bis-hexamethylene-triamine 20-50
Hexamethylendiamine 20-70
1,2-Cyclohexanediamine 0-30
Higher amines 0-20
Preferred shale hydratation inhibitors are potassium salts, diamines,
triamines, polyamines, polyalkoxy diamine represented by the general
formula I , their salts, and mixture thereof. Potassium salts, such as
potassium chloride, potassium acetate, potassium carbonate, potassium
formate are the most preferred.
The subterranean treatment fluid of the present invention comprises
other normally used additives, well known by those skilled in the art,
such as viscosifying agents, such as xanthan gum, dispersing agents,
lubricants, fluid loss control agents, corrosion inhibitors, defoaming
agents and surfactants.
In an embodiment of the present invention, the treatment fluid further
contains from 0 .1 to 15 % by weight of a defoaming agent.
The defoaming agent can be any defoaming agent known in the art. As
used herein, "defoaming agent" includes any compound, mixture or
formulation that may prevent the formation of foam or reduce or
eliminate previously formed foam.
In exemplary embodiments, the defoaming agent can be: hydrocarbon
materials, for examples mineral oils, liquid paraffins, alpha-olefins,
paraffinic or natural waxes; silicones, such as polyorganosiloxanes;
alkylene oxide derivatives, such as C8-C24 alcohol and C8-C26 carboxylic
acid alkoxylates and ethylene oxide/propylene oxide (EO/PO) block
copolymers and C8-C26 carboxylic acid esters thereof; carboxylic acids
and their salts, for example saturated and unsaturated, linear or
branched, C8-C26 carboxylic acids and Ci8-C5 polycarboxylic acids and
their salts with multivalent metal cation, such as aluminium or alkaline
earth metal salts; organic esters, such as esters of C8-C26 carboxylic
acids with monohydric to polyhydric Ci-C2 alcohols; bis-amidi; higher
alcohols, such as C8-C 8 linear and branched alcohols; trialkyl
phosphates; and mixtures thereof.
In a preferred embodiment, the defoaming agent is premixed with the
cationic tamarind gum before its dissolution in the treatment fluid, for
example at the end of the chemical preparation of the cationic
xyloglucan.
Those skilled in the art know the correct order of addition of the
components to avoid compatibility problems, which may arise in
presence of anionic and cationic materials.
For example, when xanthan gum is used as viscosifying agent, xanthan
gum and the cationic tamarind gum are preferably added into the fluid
after the dissolution of a potassium salt, such as potassium chloride.
The subterranean treatment fluid of the present invention is suitable for
use in any treatment of subterranean formations wherein shale inhibitors
can be necessary. The fluid disclosed herein is useful in the drilling,
completion and working-over of subterranean oil and gas wells and also
in stimulation operations (such as fracturing), gravel packing,
cementing, maintenance, reactivation, cuttings reinjection etc. Preferably
the subterranean treatment fluid is a drilling fluid.
The following examples are included t o demonstrate the preferred
embodiments of the invention.
EXAMPLES
Example 1
I n a 5 litres stirred reactor, 800 g of deoiled tamarind gum were loaded
at room temperature and the atmosphere was made inert by means of
vacuum/nitrogen washings. A mixture of 100 g of water and 316 g of
isopropyl alcohol was added and stirred for 10 minutes. Then 171 g of an
aqueous 50 % wt sodium hydroxide solution were sprayed on the
mixture, which was subsequently homogenized for 15 minutes. The mass
was heated at 70°C for 1 hour and then cooled at 45°C. 396 g of an
aqueous 65 % wt solution of 3-chloro-2-hydroxypropyl trimethyl
ammonium chloride (QUAB® 188 65 % from Quab Chemicals) were
added and the mixture was heated t o 50 °C for 2 hours. After this period
142 g of an aqueous 30 % wt of sodium hydroxide solution and 4 g of
hydrogen peroxide 130 volumes were added. The reaction mass was
heated at 70 °C for one hour then cooled t o 40 °C and the pH was
adjusted t o about 7 with acetic acid. The solvent was distilled off and the
cationic tamarind gum was dried on a fluid bed drier using hot air until
the moisture content was about 3% by weight and then milled.
Example 2
In a 5 litres stirred reactor, 800 g of deoiled tamarind gum and 85 g of
sodium hydroxide were loaded at room temperature and the atmosphere
was made inert by means of vacuum/nitrogen washings. A mixture of
100 g of water and 316 g of isopropyl alcohol was added and stirred for
15 minutes. The reaction mass was heated at 70 °C for one hour then
cooled to 45 °C. 396 g of QUAB® 188 65 % were added and the mixture
was heated to 50 °C for 2 hours. After this period 55 g of an aqueous
30% wt sodium hydroxide solution and a solution of 4 g of hydrogen
peroxide 130 volumes in 20 g of water were added. The reaction mass
was heated at 70°C for one hour then cooled to 40 °C and the pH was
adjusted to about 7 with acetic acid. The solvent was distilled off and the
cationic tamarind gum was dried on a fluid bed drier using hot air until
the moisture content was about 3% by weight and then milled.
Example 3
In a 5 litres stirred reactor, 800 g of deoiled tamarind gum were loaded
at room temperature and the atmosphere was made inert by means of
vacuum/nitrogen washings. A mixture of 270 g of an aqueous 30 % wt
sodium hydroxide solution, 50 g of water and 316 g of isopropyl alcohol
was added and stirred for 15 minutes. Then a solution of 4 g of hydrogen
peroxide 130 volumes in 100 g of water were added and the reaction
mass was heated at 40 °C for 45 minutes and then at 70 °C for one
hour. The mixture was cooled to 45 °C and 396 g of QUAB® 188 65 %
were added and the mixture was heated t o 50°C for 2 hours. After this
period 100 g of an aqueous 30% wt sodium hydroxide solution was
added and reaction mass was heated at 45 °C for one hour. The pH was
adjusted to about 7 with acetic acid, the solvent was distilled off and the
cationic tamarind gum was dried on a fluid bed drier using hot air until
the moisture content was about 3 % by weight and then milled.
Example 4
In a 5 litres stirred reactor, 800 g of deoiled tamarind gum were loaded
at room temperature and the atmosphere was made inert by means of
vacuum/nitrogen washings. A mixture of 180 g of water and 220 g of
isopropyl alcohol was added and stirred for 10 minutes. Then 180 g of an
aqueous 30 % wt sodium hydroxide solution were sprayed on the
mixture, which was then homogenized for 15 minutes. 256 g of QUAB®
188 65 % were added and the mixture was heated to 50°C for 2 hours.
The pH was adjusted t o about 7 with acetic acid. The solvent was
distilled off and the cationic tamarind gum was dried on a fluid bed drier
using hot air until the moisture content was about 3% by weight and
then milled.
Example 5
In a 5 litres stirred reactor, 800 g of deoiled tamarind gum and 100 g of
sodium hydroxide were loaded at room temperature and the atmosphere
was made inert by means of vacuum/nitrogen washings. A mixture of
100 g of water and 316 g of isopropyl alcohol was added and stirred for
15 minutes. The mass was heated at 70°C for 1 hour and then cooled at
45°C. 520 g of QUAB® 188 65 % were added and the mixture was
heated to 50°C for 2 hours. After this period 95 g of an aqueous 30% wt
sodium hydroxide solution and a solution of 4 g of hydrogen peroxide
130 volumes in 20 g of water were added. The reaction mass was heated
at 70°C for one hour then cooled to 40 °C and the pH was adjusted to
about 7 with acetic acid. The solvent was distilled off and the cationic
tamarind gum was dried on a fluid bed drier using hot air until the
moisture content was about 3% by weight and then milled.
Example 6
In a 5 litres stirred reactor, 800 g of tamarind gum and 85 g of sodium
hydroxide were loaded at room temperature and the atmosphere was
made inert by means of vacuum/nitrogen washings. A mixture of 100 g
of water and 316 g of isopropyl alcohol was added and stirred for 15
minutes. The mass was heated at 70°C for 1 hour and then cooled at 45
°C. 396 g of QUAB® 188 65 % were added and the mixture was heated
to 50°C for 2 hours. Then 55 g of an aqueous 30 % wt sodium hydroxide
solution were added and the reaction mass was heated at 50°C for two
hours. The reaction was cooled to 40 °C and the pH was adjusted to
about 7 with acetic acid. The solvent was distilled off and the cationic
tamarind gum was dried on a fluid bed drier using hot air until the
moisture content was about 3% by weight and then milled.
Example 7
In a 5 litres stirred reactor, 800 g of deoiled tamarind gum were loaded
at room temperature and the atmosphere was made inert by means of
vacuum/nitrogen washings. A mixture of 100 g of water and 316 g of
isopropyl alcohol was added. After 10 minutes of stirring, 171 g of an
aqueous 50% wt sodium hydroxide solution were sprayed on the
mixture, which was then homogenized for 15 minutes. The mass was
heated at 70 °C for 1 hour and then cooled at 45 °C. 396 g of QUAB®
188 65 % were added and the mixture was heated to 50°C for 2 hours.
After this period 85 g of an aqueous 50% wt sodium hydroxide solution
and a solution of 3 g of hydrogen peroxide 130 volumes in 57 g of water
were added. The reaction mass was heated at 40°C for 40 minutes and
then at 70°C for one hour. The mixture was cooled to 40 °C and the pH
was adjusted to about 7 with acetic acid. The solvent was distilled off
and the cationic tamarind gum was dried on a fluid bed drier using hot
air until the moisture content was about 3% by weight and then milled.
Example 8
A suspension of 40 g of the cationic tamarind gum of Example 7 in 180
ml of IPA and 20 ml of water was refluxed for 3 hours. The solid was
collected by filtration and dispersed in 160 ml of IPA and 40 ml of water.
The dispersion was refluxed for 3 hours, filtered and the solid was
sequentially washed with IPA/water 6/4, then IPA/water 8/2 and finally
with pure IPA. The purified cationic tamarind gum was dried at 80°C for
16 hours.
Example 9
In a 1 litre stirred reactor, 50 g of a commercial hydroxypropyl tamarind,
gum with a MS of 0.58 and a Brookfield® RV viscosity of 10,150 mPa*s
(7 % water solution, 20 °C and 20 rpm), were loaded at room
temperature and the atmosphere was made inert by means of
vacuum/nitrogen washings. A mixture of 47 g of water, 375 g of
isopropyl alcohol and 28 g of an aqueous 30 % wt sodium hydroxide
solution was added. After 15 minutes of stirring, 29 g of QUAB® 188 65
% were added and the reaction mass was heated to 50 °C for 3 hours.
The resulting suspension was cooled at room temperature and filtered
under vacuum. The obtained cake was sequentially washed with
IPA/water 8/2 and IPA. The solid was dried at 80 °C for 16 hours.
Example 10
In a 1 litre stirred reactor, 50 g of cold-water soluble tamarind gum were
loaded at room temperature and the atmosphere was made inert by
means of vacuum/nitrogen washings. A mixture of 47 g of water, 375 g
of isopropyl alcohol and 28 g of an aqueous 30 % wt sodium hydroxide
solution was added. After 15 minutes of stirring, 12 g of 2-bromoethyl
trimethyl ammonium bromide were added and the obtained mixture was
heated to 50 °C for 3 hours. The resulting suspension was cooled at
room temperature and filtered under vacuum. The cake was sequentially
washed with IPA/water 8/2 and IPA. The product was dried at 80 °C for
16 hours
Cationic Tamarind Gum Characterization
The cationic degree of substitution (DScat) of the cationic tamarind gums
of Examples 1-10 was determined by ^-NMR.
The hydroxypropyl molar substitution (MS) was determined by - MR.
The Brookfield® RV viscosity (RV Viscosity) was measured on a 4.0 %
by weight solution in water at 20 °C and 20 rpm.
The weight average molecular weight (M )was determined by gel
permeation chromatography using a Perkin Elmer Liquid Chromatograph
Series 200 Pump, an Ultrahydrogel® guard column, an Ultrahydrogel®
Linear column and an Evaporative Light Scattering Detector ELSD 3300.
The mobile phase was water containing 1.4 % v/v TEA and 1.0% v/v
glacial acetic acid at a flow of 0.8 ml/min. A pullulan standard kit
(molecular weight range: 5,900 - 788,000 Dalton) was used for the
calibration of the system.
The calculation was performed by the chromatographic software SW
TurboSEC 6.2. 1.0. 104:0104 with a Universal Calibration method. The
following values of the Mark-Houwink constants K and a were assigned :
Table 1 summarizes the characteristics of the cationic tamarind gums of
Examples 1-10.
Table 1
RV Viscosity M
DS MS
(mPa*s) (Dalton)
Example 1 0.27 - 225 612,390
Example 2 0.32 - 316 613,942
Example 3 0.24 - 770 771,355
Example 4 0.12 - 915 758,564
Example 5 0.39 - 155 578,863
Example 6 0.21 - 640 733,605
Example 7 0.30 - 470 737,439
Example 8 0.30 - 591 683,373
Example 9 0.40 0.47 <100 105,857
Example 10 0.12 - <100 23,248
Performance Evaluation
The shale inhibition performances of the cationic tamarind gums were
evaluated with three different kinds of shales: an Arne clay (dispersive),
a Foss Eikeland clay (dispersive) and an Oxford clay (swellable).
Each clay was dried at 70°C for 3 hours.
The dried clays were then ground and sieved through both a 5 mesh (4
mm) sieve and a 10 mesh (2 mm sieve).
The clay particles with a size below 4 mm but larger than 2 mm were
used in this test.
Two different methods of evaluation were used : the "Shale Particle
Disintegration Test" and the "Bulk Hardness Test".
Shale Particle Disintegration Test
The test was performed following the procedure described in the
standard method ISO10416, section 22, with some modifications.
350 ml of typical drilling muds were prepared by means of an Hamilton
Beach Mixer according t o the formulations described in Table 2 .
For the preparation of the muds, the following commercial product were
used :
• Biolam XG, xanthan gum commercialized by Lamberti S.p.A.;
• PREGEFLO M, pre-gelatinezed corn starch commercialized by
Roquette;
• Defoam-X, defoamer commercialized by M-I Swaco;
• Calcitec V/60, CaC03 commercialized by Mineraria Sacilese S.p.A.
The starch was added t o the muds 9-11 in order t o reach the same
viscosity of the other muds, determined with a Fann® 35 at 600 rpm
and 25°C.
All muds were adjusted t o pH 9.0 by adding some drops of NaOH
solution 20 % wt.
30.0 g of sized clay were added t o each mud in a stainless steel ageing
cell which was subsequently closed and vigorously shacked t o disperse
the clay particles.
The ageing cells were then placed in a pre-heated oven and hot-rolled at
80 °C for 16 hours.
After the thermal treatment, each ageing cell was cooled to room
temperature.
The treated muds were then poured onto two sieves: 10 mesh (2 mm)
and 35 mesh (0.5 mm).
The residual clays in the bottles were recovered by washing with a KCI
solution (42.75 g/l).
The sieves were transferred in a bath containing tap water and quickly
but gently submerged in order to rinse both the sieve and the clays.
The recovered clays were then placed in a pre-weighed dish and dried in
oven at 105 °C to constant weight.
After drying, the clays were cooled in a desiccator and weighed. The %
recovery of the clays for each mud was calculated with following
formula :
% recovery = (weight in grams of shale recovered)/ (100-w h) x 100
where wh is the initial moisture content in % by weight of the sized clay.
The initial moisture content of the clay was determined by weight loss at
105 °C.
The results (% recovery) with Arne Clay and Foss Eikeland Clay are
reported in Table 3 and 4, respectively.
The higher the % recovery, in particular on the 10 mesh sieve, the
higher the performance of the shale inhibitors.
The results reported in Tables 3 and 4 demonstrate that the cationic
tamarind gums of the invention show very good inhibition properties on
dispersive shales (Arne and Foss-Eikeland Clays).
Table 2
Comparative
Table 3
% Recovery % Recovery Total
Arne Clay
10 mesh 35 mesh % Recovery
Mud 1 99.7 0.3 100
Mud 2 89.9 2.3 92.2
Mud 3 76.9 3.2 80.1
Mud 4 68.1 5.4 73.5
Mud 5 99.2 0.8 100
Mud 6 71.2 1.6 72.8
Table 3 - continuation
* Comparative
Table 4
* Comparative
Bulk Hardness Test
This test was described by Patel A. et al., in "Designing for the future —
a review of the design, development and inhibitive water-based drilling
fluid"; Drilling and Completion Fluids and Waste Management, Houston
(TX), April 2-3, 2002. Some modifications were introduced.
350 ml of Mud 5 and comparative Mud 11, previously described, were
adjusted to pH 9.0 by adding some drops of NaOH 20 wt% solution.
30.0 g of sized Oxford Clay were added to each mud in a stainless steel
ageing cell which was subsequently closed and carefully shaked t o
disperse the clay particles. The ageing cells were then subjected t o the
same thermal treatment described in the previous test.
The treated muds were then poured onto a 10 mesh sieve. The residual
clays in the bottles were recovered by washing with a KCI solution
(42.75 g/l).
The sieves were transferred in a bath containing tap water and it is
quickly but gently submerged in order to rinse the sieve and the shale.
Using a torque wrench, the recovered clays were extruded through a
perforated plate, measuring the torque required for each turn in
compression. The torque is directly correlated to the hardness of the clay
particles and, since the clay particles which are not inhibited swell in the
fluid and become softer, to the shale inhibitor efficiency. To say, the
higher the torque value, the better the performance of the inhibitor. The
average torque values relative to the 14th, 15th and 16th turn are
reported in Table 5 .
Table 5
The results reported in Table 5 demonstrate that the cationic tamarind
gums of the invention show very good inhibition properties also with
swellable shale (Oxford Clay).
CLAIMS
1) A method for inhibiting the swelling and the dispersion of shales
during the treatment of subterranean shale formations comprising
the step of:
a) providing a subterranean treatment fluid comprising between 0.2
and 6.0 % wt of a cationic tamarind gum having a cationic
degree of substitution (DS cat) from 0.01 to 1.0 and a Brookfield
RV viscosity at 4.0 % wt water solution, 20 rpm and 20 °C below
2000 mPa*s;
b) introducing said treatment fluid into a wellbore at a pressure
sufficient to treat the subterranean shale formations.
2) The method of claim 1), wherein said subterranean treatment fluid
comprises between 0.5 and 4.0 % wt of said cationic tamarind gum.
3) The method of claim 1), wherein said cationic tamarind gum has a
DScat from 0.05 to 0.55 and a Brookfield RV viscosity, at 4.0 % wt
water solution, 20 rpm and 20 °C, of from 30 to 1500 mPa*s .
4) The method of claim 1), wherein said cationic tamarind gum is an
unpurified cationic tamarind gum comprising from 4 to 65 % by dry
weight of by-products generated during its chemical preparation.
5) A subterranean drilling fluid comprising an aqueous continuous
phase, between 0.2 and 6.0 % wt of a cationic tamarind gum having
a cationic degree of substitution (DS cat) from 0.01 to 1.0 and a
Brookfield RV viscosity at 4.0 % wt water solution, 20 rpm and 20
°C below 2000 mPa*s, and between 1 and 70 % wt of a weighting
material.
6) The subterranean drilling fluid of claim 5), further comprising from
0 .1 to 20 % wt of a shale hydration inhibitor.
7) The subterranean treatment fluid of claim 6), wherein said shale
hydration inhibitor is potassium chloride.