Note: Descriptions are shown in the official language in which they were submitted.
CA 02888866 2015-04-24
POLYMERIC ENCAPSULANT FOR AQUEOUS DRILLING FLUID
FIELD OF THE INVENTION
The present invention is directed to the use of a polymer in an aqueous
drilling fluid for
steam assisted gravity drainage operations. More specifically, it is directed
to the use of a
terpolymer in SAGD.
BACKGROUND
Oil sand deposits are found predominantly in the Middle East, Venezuela, and
Western
Canada. The Canadian bitumen deposits, being the largest in the world, are
estimated to contain
between 1.6 and 2.5 trillion barrels of oil, so the potential economic benefit
of this invention
carries significance within this resource class. The term "oil sands" refers
to large subterranean
land formations composed of reservoir rock, water and heavy oil and/or
bitumen.
Bitumen is a heavy, black oil which, due to its high viscosity, cannot readily
be pumped
from the ground like other crude oils. 'Therefore, alternate processing
techniques must be used to
extract the bitumen deposits from the oil sands. The basic principle of known
extraction
processes is to lower the viscosity of the bitumen by applying heat, injecting
chemical solvents,
or a combination thereof, to a deposit layer, thereby promoting flow of the
material throughout
the treated reservoir area, in order to allow for recovery of bitumen from
that layer.
At present there are two main methods that are used to recover bitumen from
the oil
sands in Alberta, Canada. The two methods are truck and shovel surface mining
for subsequent
extraction and steam assisted gravity drainage (SAGD). SAGD is used when the
depth of the
bitumen formation, such as in the Fort McMurray formation in Canada, is too
deep to access and
retrieve via the truck and shovel method. Two horizontal wells are drilled,
one on top of the
other with approximately 5 meters spacing there between. The shallower
horizontal well is the
injector well and is used to pump steam into the formation in order to treat
and soften the
bitumen and allow it to flow. The deeper horizontal well is the production
well which collects
the heated bitumen for pumping to surface. SAGD, as with most recovery
strategies, is focused
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on increasing bitumen temperature within a limited region around a steam
injection well. The
reduced-viscosity oil is then allowed t flow by gravity drainage to an
underlying point of the
reservoir and to be collected by a horizontal production well. The heavy
oil/bitumen is then
brought to the surface for further processing.
In the course of SAGD drilling operations, the drillstring and/or other
equipment come
into contact with zones of rock and/or soil containing bitumen. However,
bitumen is a relatively
sticky substance that may readily adhere to any surface that it contacts,
including the surfaces of
the well-bore and/or any equipment utilized during the drilling operations. If
a sufficient amount
of bitumen adheres to surfaces in the well-bore or drilling equipment, it may,
among other
things, prevent the drillstring from rotating, prevent fluid circulation, or
otherwise impede the
effectiveness of a drilling operation. In some cases, it may become necessary
to remove and/or
disassemble the drillstring in order to remove accretions of bitumen, a
process which may create
numerous cost and safety concerns. The accretion of bitumen on drilling
equipment and/or in the
well-bore also can impede any subsequent operations down hole, including
cementing, acidizing,
fracturing, sand control, and remedial treatments.
SAGD drilling operations were initially plagued with severe issues due to the
sticky
nature of bitumen. Drilling fluids used conventionally at the time contained
no additives to
overcome the problems of drilling in bitumen and, as a result, the bitumen
stuck to everything
including the drill-string, casing and surface equipment which resulted in rig
down-time and
significant expenditure by the operator.
As a result of the earlier experiences with drilling in bitumen-containing
formations, it
became known to use additives within the fluid systems to attempt to inhibit
bitumen accretion
and, as a result, improve ROP. In the last ten years there have been a number
of patents filed for
drilling fluid systems or additives to overcome the problems associated with
drilling SAGD
wells.
Water-based drilling fluids that contain solvents or wetting agents as anti-
accretion
additives and were intended to limit bitumen accretion to metal surfaces are
described in
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Canadian patents 2,454,312; 2,481,543; 2,451,585 and 2,437,522. These solvent
and/or
surfactant systems rely on the solvent's ability to dissolve bitumen. This
approach limits the
number of wells that can be drilled before the drilling fluid must be stripped
of the built-up
bitumen.
More recent anti-accretion drilling fluid additives reported in the patent
literature consist
of polymers such as non-ionic, cationic and hydrophobically associating
polymers. These
polymer additives are believed to prevent accretion of the bitumen or heavy
oil to metal surfaces
via an encapsulation mechanism that involves the formation of an ion pair
between the cationic
functionalities on the encapsulating polymer and the negative charges found in
the composition
of bitumen. This mechanism is supported by the experimental observation that
polymers with
increasing cationic charge provide better encapsulating and anti-accretion
properties.
Encapsulation systems are described in Canadian patents 2,508,339; 2,624,834
and 2,635,300.
Hydrophobically associating polymers have been used in some oilfield
applications, for
example, as viscosifiers in enhanced oil recovery (polymer flooding), in
drilling/completion
fluids, as acid stimulations and as drag reducing agent as described in Han et
al. Soc. of
Petroleum Engineers, 104432, pp. 1-6, 2006 and in Taylor K. C. et al. Canadian
International
Petroleum Conference, Jun. 12-14, 2007, and in oily water cleanup as described
in U.S. Pat. No.
4,734,205.
It has been theorized in US 7,879,768 (CA 2,635,300) to An Ming Wu that the
hydrophobic group of hydrophobically associating polymers strongly adsorbs on
the bitumen
surfaces through its oil affinity force, and the hydrophilic groups of the
hydrophobically
associating polymers make the bitumen surface water wet and provides less
sticking. Further, the
hydrophobically associating polymers can effectively prevent the bitumen from
dispersing.
Accordingly, these hydrophobically associating polymers are excellent bitumen
and/or tar,
flocculent and sticking inhibitors.
While this application is not bound by any theory regarding the bitumen
encapsulation
and anti-accretion properties of hydrophobically modified polymers, it has
been found that the
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dual hydrophobicity of the polymers -ubject to this application remarkably
increase the anti-
accretion and encapsulation performance of these polymers. Moreover, since the
hydrophobically associating polymers subject of this application are anionic,
they are compatible
with conventional drilling fluid additives.
Amphiphilic polymers are increasingly used to control the rheology in aqueous
formulations. These polymers typically include a hydrophilic backbone with
grafted hydrophobic
units or in another type, grafted amphiphilic units that are surfactant-like
and therefore are often
referred to as polysoaps.
In Journal of molecular structure, 2000, vol.554, p.99-108, Chassenieux,
Fundin,
Ducouret and Iliopoulos have reported that it was possible to prepare a new
type of amphiphilic
water soluble polymer based on repeating units of two water insoluble
polymers,
poly(dimethylhexadecyl(vinylbenzyl)ammonium chloride) and polystyrene. At
relatively low
concentration, the solutions behave as viscous fluids whereas for higher
concentration,
viscoelastic properties appear. Though these polymers could be used in SAGD
specific drilling
fluids to prevent bitumen sticking, they are cationic and therefore, are
likely to raise
compatibility issues with anionic components of drilling fluid.
Certain drilling fluids of the prior art that include a cationic polymer have
the
disadvantage that they can be incompatible with other drilling fluid additives
used as viscosiflers.
More specifically, the cationic polymer can coagulate polymers added as
viscosifiers and
decrease the overall viscosity and carrying capacity of the drilling fluid.
This is particularly
problematic in horizontal wells such as those drilled in SAGD operations. In
addition, certain
drilling fluids of the prior art that contain a non-ionic polymer do not
perform well in certain
formations and may not prevent accretion on drilling equipment to a
satisfactory degree.
SUMMARY OF THE PRESENT INVENTION
The present invention relates to the application of anionic amphiphilic
polymers in
SAGD operations. The polymers used according to the present invention are
terpolymers based
on repeating units of two different types of hydrophobic moieties modified
with anionic charged
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groups. In a preferred embodiment, the first hydrophobic moiety is an aromatic
compound such
as styrene and the second hydrophobi:- moiety is a fatty acid. Depending on
the modification
rate, and on the neutralization degree, these polymers behave as highly
hydrophobic but
nevertheless soluble in aqueous solution. The invention also relates to
aqueous drilling fluids
containing the subject polymers that exhibit remarkable bitumen encapsulation
and anti-accretion
properties.
According to one aspect of the present invention, there is provided a drilling
fluid,
comprising a polymer dissolved in an aqueous phase, wherein the polymer is a
terpolymer based
on repeating units of a first type of hydrophobic moiety, a second type of
hydrophobic moiety
and of an anionic charged group. Preferably, the first and second type of
hydrophobic moieties
have different hydrophobic nature. Preferably, the first hydrophobic moieties
type contains an
aromatic group. More preferably, the aromatic hydrophobic moiety is a styrene
derivative.
According to a preferred embodiment, the second hydrophobic moieties type
contains a
fatty acid including an alkyl side chain CnH2n+1, with n being an integer
greater or equal to 6.
Preferably, n is selected from the group consisting of 8, 10, 12, 14 and 16.
More preferably, the
alkyl side chain is grafted to the backbone of the polymer through hetero-
functional groups.
More preferably, hetero-functional group is selected from the list consisting
of amide, ester and
urethane.
According to a preferred embodiment, the anionic charged group is a phosphate.
More
preferably, the anionic charged group is a sulfonate.
According to a preferred embodiment, the polymer is represented by the general
chemical
,
formula:
.., ...
rii,
___________________________ -c-P _ _c-V - C _______
H,
SON.
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where x is the substitution degree and y is between 0.1 and 0.4.
Preferably, the anionic charged group is a carboxylic group.
According to a preferred embodiment, the polymer is represented by the general
chemical
formula:
Ila ____________________________ I I _______
CO2R CO2R
CO211 CO
COI12,,,I _
where n is either 8, 10, 12, 14 or 16, x varies between 0 and 0.5, z varies
from 0.5 to 0.75 and R
is a monovalent cation or a proton. Preferably, the modification rate, defined
as 200x, is 60 and n
is 8, 10, 12, 14 or 16. More preferably, the modification rate, defined as
200x, is 50 and n is 12,
14 or 16. Even more preferably, the modification rate, defined as 200x, is 10
and n is 12. Most
preferably, the modification rate, defined as 200x, is 20 and n is 12, 14 or
16.
According to a preferred embodiment, the polymer concentration is less than 3%
by
weight. Preferably, the polymer concentration is less than 2% by weight, more
preferably, the
polymer concentration is less than 1.5% by weight.
According to another aspect of the present invention, there is provided a use
of a
terpolymer based on repeating units of a first and second type of hydrophobic
moieties and of an
anionic charged group in a SAGD drilling fluid.
BRIEF DESCRIPTION OF THE FIGURES
The invention may be more completely understood in consideration of the
following
description of various embodiments of the invention in connection with the
accompanying
figures, in which:
Figure 1 is a photograph of a carbon steel pipe treated with a solution
according to the present
invention and which was exposed to 100 grams of bitumen and rolled for 24
hours.
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Figure 2 is a photograph of a carbon steel pipe untreated and exposed to 100
grams of bitumen
and rolled for 24 hours.
DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION
The present invention is directed to the novel use of polymers for bitumen
encapsulation
in aqueous drilling fluids. The present invention thus relates to aqueous
solutions of polymers
based on three kinds of repeating units: two moieties preferably of different
hydrophobic nature
and anionic charged groups.
Preferably, the first and second types of hydrophobic moieties show clearly
distinct
hydrophobic properties as exhibited by their limited solubility in water or
their polarity. This can
be achieved, for instance, by selecting for the first moiety an aromatic and
for the second moiety
a fatty acid with a long aliphatic chain (preferably an alkyl chain with at
least 7 carbon atoms).
The alkyl chain may be hydrogenated or perfluorated and is preferably grafted
to the backbone
chain through a hetero-functional group such as an amido, an ester or a
urethane.
The anionic amphiphilic polymers of the present invention may be designed with
various
hydrophobic modification rates while remaining water-soluble. The anionic
group may, for
instance, can be selected from the group consisting of: a carboxylic, a
sulfonate or a phosphate
group. The polymers according to the present invention are terpolymers based
on combination of
a first and second type of hydrophobic groups and of anionic charged groups.
Two types of
anionic charged groups have been studied: carboxylates and sulfonates groups.
In a further embodiment, the invention relates to drilling fluids for drilling
SAGD wells
containing the polymers of the invention as bitumen encapsulator and anti-
accretion additive.
These drilling fluids typically contain less than 30 kg of polymer per cubic
meter of the drilling
fluid.
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While preparation methods for these polymers are not within the scope of this
application
and one skilled in the art may find other suitable synthesis method, the
described method is to be
understood as a reference only.
Example 1
Synthesis of Carboxylated Terpolymer
First, a copolymer styrene and maleic anhydride acid (SMA) is obtained. The
synthesis
was performed with an SMA copolymer in which each monomer unit consist of
exactly one
styrene unit and one maleic anhydride unit (in other words, z=0.5), so that
the molecular mass of
the repeated unit is 102 g/mol. Other commercially available SMA copolymers
have higher
styrene content with z varying from 0.5 to 0.75. The tested SMA copolymer had
a molecular
weight Mw of 150 kg/mol as measured in the laboratory.
In the second step, the SMA polymer is hydrophobically modified with an amine
CnH2n4-11=1H2. Different amines having a purity of 99% were tested with n
being an even number
between 8 and 18.
In a three-necked bottle, 6 g of SMA were dissolved in 150 ml THF
(tetrahydrofuran),
under N2 atmosphere, at 60 C. After two hours, 3.3 g of amine, in 50 ml THF
were added drop
wise. The reaction was allowed to occur for 24h at 60 C. The terpolymer was
recovered by
precipitation in diethylether and drying over vacuum.
The general chemical formula ef the synthetized polymer is thus:
Fl ________________________________ II H ___ Et __
H2
( .02H CO
101 _ 0"rL.0 _I
CI ti
n
with n being either 8, 10, 12 or 16. For a modification rate of 100%, x equals
0.5. Therefore x
varies between 0 and 0.5 (0.5 corresponding to a modification rate equal to
100%, the
modification rate is defined as 200x).
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The last step is the hydrolysis of the polymer allowing its solubilization in
water under
basic conditions (addition of NaOH), at 60 C., over 6 hours under stirring.
Note that sodium
hydroxide can be substituted with other hydroxide of monovalent cation such as
lithium
hydroxide or potassium hydroxide for instance.
Depending on the neutralizatiu-n rate, the polymer formula can be thus
expressed by
where n is either 8, 10, 12, 14 or 16, x varies between 0 and 0.5 and R is a
monovalent cation or
a proton:
H __ H
¨C¨C¨(¨C ________________
Hz I I
c-o2R co,ll CU
-
' -1,ra
Example 2
Sulfonated Terpolymers
Equivalent sulfonated terpolymers, with sulfonate groups replacing the
carboxylate
groups were prepared to improve the thermal stability and the compatibility
with calcium ions.
The main steps of a first synthesis route includes first, the synthesis of a
copolymer based
on styrene and dodecylmethacrylate, using toluene as solvent, at 70 C for a
duration of 30
minutes. This step is followed by a sulfonation at 50 C, using dichloroethane
as solvent in
presence of H2SO4-
The sulfonation reaction is controlled by adjusting the reaction time. The
resulting
polymer is obtained through evaporation and dissolution in DMSO.
Starting with a mixture of 80% styrene and 20% dodecylmethacrylate, a 74%
styrene/26% dodecylmethacrylate copolymer was prepared in the first step,
leading after
sulfonation to the following general chemical formula where x is the
sulfonation degree.
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CH3
_______________ C C __________ C C ________________
H2 H2 H2 ___________
11101 _ C12
_ - 0.74(1-x)
SO3Na
Another synthesis route is based on terpolymerization of styrene, styrene
sulfonate and
alkylacrylamide. The solvent is DMSO. The polymerization was allowed to
proceed for 24 hours
at 65 C. The resulting polymer is obtained by precipitation in ether.
The terpolymer having the following formulae was obtained:
CH3
_______________ C C ____________ C C _______________
H2 H2 H2
_ C12H25
OO
- 0.3
- 0.16 - 0.54
S 03Na
Example 3
A polymer synthesized using a Styrene-Maleic anhydride resin of 1:1 styrene to
maleic anhydride
ratio. This polymer was hydrophobically modified with dodecylamine and the
degree of modification was
approximately 15%. The molecular weight was estimated to be approximately
11000.
Example 4
Two cylinders were filled with 300 ml of water and 0.5 grams of xanthan gum
was added to each.
To one cylinder 0.5 grams of the above polymer was added and the other one was
kept as blank. To each
cylinder a 3/4 " carbon steel pipe of 10 cm in length was placed and 100 grams
of bitumen was added. The
cylinders were rolled for 24 hours and the pipes were removed for visual
examination.
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Visual examination revealed that the treated carbon steel pipe had resisted
the deposition of
bitumen solids to a substantial extent in comparison to the untreated carbon
steel pipe.
The above-described embodiments of the present invention are intended to be
examples
only. Alterations, modifications and variations may be effected to the
particular embodiments by those of
skill in the art without departing from the invention, which is defined by the
claims appended hereto.
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