Note: Descriptions are shown in the official language in which they were submitted.
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FLUID COMPOSITION COMPRISING ANTI-ACCRETION ADDITIVES AND
METHODS OF USE THEREOF
FIELD OF INVENTION
The invention relates to drilling fluids, drilling fluid additives and methods
and, in particular, to
drilling fluids, drilling fluid additives and methods useful for drilling oil
wells through
formations containing heavy oil or bitumen where it is useful to limit oil
sands accretion on
metal surfaces.
BACKGROUND OF THE INVENTION
When drilling through bituminous formations, accretion (or sticking) of the
drill cuttings to the
drill-string, bottom hole assembly or surface handling and solids control
equipment may occur.
Such depositions impair the drilling operations and removal of said deposits
may be required for
continued drilling. Removal of the bituminous material from the drilling
equipment can in some
instances be achieved mechanically; however this requires halting of the
drilling operations with
the consequent decrease in productivity. A more economical solution to the
problem of
accretion may be the addition of certain chemicals to the aqueous-based
drilling fluid that act to
limit or possibly completely eliminate the accumulation of bitumen on drill
components. The
patent literature refers to several additives that act as anti-accretion
additives. See for example
US Patent 7081438 and US Patent Applications 2006/0003899, 2008/0214413,
2008/0217064,
2008/0045420, 2009/0099046 and 2009/0011960.
A desirable anti-accretion additive may improve the bitumen or heavy oil
drilling operations by
preventing the accretion of heavy oil to metal surfaces, preserving or
increasing the heavy oil-
mineral aggregate bond and possibly avoiding foaming of the aqueous-based
drilling fluid to
which is being added.
SUMMARY OF THE INVENTION
Thus, in accordance with a broad aspect of the present invention, there is
provided an oil sand
anti-accretion additive for drilling fluids to limit accretion of oil sands on
metal surfaces
comprising: at least one of an amine, an amide or a nitrogen containing
heterocyclic compound.
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In a further embodiment of the present invention there is provided an aqueous
drilling fluid
comprising an effective amount of an oil sand anti-accretion additive
comprising: an effective
amount of at least one of an amine, an amide or a nitrogen containing
heterocyclic compound.
In accordance with another broad aspect of the present invention, there is
provided a method for
drilling a wellbore through an oil sand containing formation, the method
comprising: operating a
drilling assembly to drill a wellbore and circulating an aqueous-based
drilling fluid through the
wellbore as it is drilled; the aqueous-based drilling fluid including an oil
sand anti-accretion
additive including at least one of an amine, an amide or a nitrogen containing
heterocyclic
compound in an effective amount to limit oil sand accretion on metal surfaces.
In accordance with another broad aspect of the present invention, there is
provided a method for
limiting accretion on metal surfaces in contact with oil sand containing
formations, the method
comprising: washing the metal surfaces with an aqueous based drilling fluid,
the aqueous-based
drilling fluid including an oil sand anti-accretion additive including at
least one of an amine, an
amide or a nitrogen containing heterocyclic compound in an effective amount to
limit oil sand
accretion on metal surfaces.
It is to be understood that other aspects of the present invention will become
readily apparent to
those skilled in the art from the following detailed description, wherein
various embodiments of
the invention are shown and described by way of illustration. As will be
realized, the invention
is capable for other and different embodiments and its several details are
capable of modification
in various other respects, all without departing from the spirit and scope of
the present invention.
Accordingly the drawings and detailed description are to be regarded as
illustrative in nature and
not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a photograph depicting the accretion of oil sand on a steel shim
in the absence of
an anti-accretion additive;
FIGURE 2 is a photograph depicting the effect of 1, 3-propanediamine, Nl-(3-
(tridecyloxy)
propyl)-, branched on oil sand accretion on a steel shim;
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FIGURE 3 is a photograph depicting the effect of fatty acids, tall-oil,
reaction products with
diethylenetriamine on oil sand accretion on a steel shim;
FIGURE 4 is a photograph depicting the effect octadecene dimethyl amine on oil
sand accretion
on a steel shim;
FIGURE 5 a photograph depicting the accretion of oil sand on a steel shim in
the absence of anti-
accretion additive at 50 C;
FIGURE 6 a photograph depicting the effect of fatty acids, tall-oil, reaction
products with
diethylenetriamine on oil sand accretion at 50 C on a steel shim;
FIGURE 7 a photograph depicting the effect of a mixture of fatty acids, tall-
oil, reaction
products with diethylenetriamine and amino triethyl phosphate ester on bitumen
accretion at
50 C on a steel screen;
FIGURE 8 a photograph depicting the accretion of oil sand on a steel screen in
the absence of
anti-accretion additive;
FIGURE 9 a photograph depicting the effect of hexanedinitrile, hydrogenated,
high-boiling
fraction on oil sand accretion on a steel screen;
FIGURE 10 a photograph depicting the effect of a mixture of hexanedinitrile,
hydrogenated,
high-boiling fraction and amino triethyl phosphate ester on oil sand accretion
on a steel screen;
FIGURE 11 a photograph depicting the effect of heavy oil accretions on a steel
sleeve;
FIGURE 12 a photograph depicting the effect of a mixture of 0.5% morpholine on
heavy oil
accretions on a steel sleeve;
FIGURE 13 a photograph depicting the effect of 1.0% morpholine on heavy oil
accretions on a
steel sleeve;
FIGURE 14 a photograph depicting the effect of 0.5% amides of rapeseed oil and
dimethylaminopropyl amine on heavy oil accretions on a steel sleeve;
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FIGURE 15 is a photograph depicting the effect of 1.0% amides of rapeseed oil
and
dimethylaminopropyl amine on heavy oil accretions on a steel sleeve; and
FIGURE 16 is a photograph depicting the effect of 0.5% pyridinium, 1-
(phenylmethyl)-, alkyl
derivatives, chlorides on heavy oil accretions on a steel sleeve.
DETAILED DESCRIPTION
The detailed description set forth below in connection with the appended
drawings is intended as
a description of the present invention and is not intended to represent the
only embodiments
contemplated by the inventor. The detailed description includes specific
details for the purposes
of providing a comprehensive understanding of the present invention. However,
it will be
apparent to those skilled in the art that the present invention may be
practiced without these
specific details.
In horizontal drilling operations, the drill string first bores a
substantially vertical well, then at
some predetermined point deviates from vertical in the build section.
Eventually the borehole
may deviate 90 from vertical to become a horizontal well. The horizontal
section of a well is
designed to have increase well bore intersection with the oil-bearing
formation. The drill string
in a horizontal section of the well experiences increased torque due to the
increased contact
between the string and the horizontal well bore. Horizontal wells are
advantageous in heavy oil,
oil sand or bitumen production due to the low mobility of the oil. Horizontal
wells offer inherent
advantages over vertical wells in steam-assisted oil production. A significant
portion of heavy
oil deposits are found in unconsolidated formations, such as unconsolidated
sand. The mixture
of heavy oil or bitumen with this unconsolidated sand, often referred to as
oil sands, makes the
drill cuttings from these formations malleable. For the purposes of this
description, the terms oil
sand, heavy oil and bitumen and may be used interchangeably.
Deformation of these drill cuttings between the drill string and the formation
or the drill string
and the build section results in the adherence of a coating of the bitumen and
sand on the drill
string and casing. This coating is often referred to as accretion.
The present invention provides several chemicals that may be useful to limit
oil sand accretions
on metal surfaces or remove accretions already deposited. In this application,
the term "limit"
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has been used to mean, in its broadest sense, a reduction or removal of
accretions using the
present additive in comparison to the reduction or removal of accretions using
non-additive
containing fluids. In addition, the additives of the present invention can
also prevent stripping of
the heavy oil from the mineral aggregate. The additives may have limited
foaming abilities, a
property which may be beneficial for the drilling operations. The chemicals
that are useful in the
present invention belong to the chemical class of: an amine, a polyamine, an
oxylated polyamine,
an aminosilane, a nitrogen containing heterocycle, an amide, an
alkylamidopolyamine, a
polyamide, a Mannich amine, a melamine formaldehyde resin, a dicyandiamide
resin, a
polyamideamine, a polyethyleneimine, and a polyvinylamine.
These chemical classes may be useful in the present invention as an effective
additive when
applied in aqueous systems that may limit oil sand accretion on metal surfaces
exposed to oil
sand-containing formations. In addition, the additives of the present
invention may also prevent
stripping of the heavy oil from the mineral aggregate. The additives may have
limited foaming
abilities, a property which is beneficial for the drilling operations.
Possible examples of a suitable amine anti-accretion additive may include:
= polyamine;
= oxylated polyamine;
= aminosilane;
= alkylamidopoliamine;
= Mannich amine;
= melamine formaldehyde resin; and
= polyamideamine.
Possible examples of a suitable polyamine anti-accretion additive may include:
= hexanedinitrile, hydrogenated, high-boiling fraction (CAS # 68411-90-5);
= dihexylenetriamine (CAS# 143-23-7);
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= n-coco alkyl trimethylenediamine (CAS# 61791-63-7);
= fatty acids, tall-oil, reaction products with diethylenetriamine (CAS# 61790-
69-0);
= tall oil reaction products with diethylenetriamine (CAS# 68140-14-7);
= 1,3-Propanediamine, N1-(3-(tridecyloxy)propyl)-, branched (CAS# 68479-04-9);
= n-tallow alkyltripropylene-tetraamine (CAS# 68911-79-5);
= n-tallow alkyl trimethylenediamine (CAS# 61791-55-7);
= 1,2-ethandiamine, polymer with aziridine (CAS#25987-06-8);
= polyethyleneimine (CAS #9002-98-6); and
= polyvinylamines.
Possible examples of a suitable amide anti-accretion additive includes:
= Amides from diethylenetriamines and tall-oil fatty acids;
= Amides of rapeseed oil and dimethylaminopropyl amine;
= Polyamides; and
= Dicyandiamide resins.
A possible example of a suitable nitrogen containing heterocyclic anti-
accretion additive
includes 1-(2-hydroyethyl)-2-alyl-2-imidazoline, alkyl derived from tall oil
fatty acid (CAS#
61791-39-7), pyridinium, 1-(phenylmethyl)-, alkyl derivative chlorides (CAS #
100765-57-9)
and morpholine (CAS# 110-91-8).
As can be noted from the above examples, the anti-accretion additives of the
present invention
may contain in their molecular structure at least one basic nitrogen
functionality. Without being
limited by theory, it is believed that the amine functionality of the anti-
accretion additive may
serve at least one of the following functions: (i) the basic nitrogen can form
a salt with the acidic
functional groups present in bitumen; and (ii) the ion pairing between the
anti-accretion additive
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and the bituminous material may cause an increase in the softening temperature
of bitumen and
consequently the bitumen becomes less sticky. In addition, the anti-accretion
additive may oil
wet the solid aggregates to ensure a strong bond between the bitumen and solid
aggregates
present in oil sands.
Quaternary ammonium salts are known to cause foaming of the drilling fluid and
precipitation of
anionic viscosifying and fluid loss additives such as polycarboxylated
cellulose and xanthan.
The use of the anti-accretion additives of the present invention in
conjunction with quaternary
ammonium salts may result in reduction of foaming and precipitation by
decreasing the amount
of quaternary ammonium salt required for achieving the anti-accretion
activity.
The anti-accretion additives of the present invention can be employed at a
broad concentration
range of 0.2 to 5.0% by weight of drilling fluid that is effective to limit
oil sand accretion on
metal surfaces. While lower concentrations may be effective, the additives are
generally
employed at concentrations of at least 0.5% by weight of the drilling fluid.
With economical
considerations, an upper limit of 5.0% by weight of the drilling fluid has
been employed but a
narrower range of 0.5 to 2% has also demonstrated efficacy. However,
concentrations above
5.0% can be employed if desired.
Aqueous-based drilling fluids, according to the present invention, include
effective amounts of
an amine, a polyamine, an oxylated polyamine, an aminosilane, a nitrogen
containing
heterocycle, an amide, an alkylamidopolyamine, a polyamide, a Mannich amine, a
melamine
formaldehyde resin, a dicyandiamide resin, a polyamideamine, a
polyethyleneimine, and a
polyvinylamine or mixtures thereof. While lower concentrations may be
effective, the additive
is generally employed at concentrations of at least 0.5% by weight of the
drilling fluid. The
drilling fluid may include water and additives such as, for example,
viscosifying and fluid loss
control additives, corrosion inhibitors, along with an oil sand anti-accretion
additive according to
the present invention. The anti-accretion additive can be added to the water
before or after the
addition of the viscosifying and fluid loss control additives. The anti-
accretion additive may be
dissolved in any suitable solvent prior to adding it to the drilling fluid.
The addition of
defoamers may generally not be required as the anti-accretion additives of the
present invention
have none to very limited foaming ability. If foaming is encountered,
defoamers may be added
to the drilling fluid or to the anti-accretion additive. The present anti-
accretion additives can be
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used in conjunction with other known anti-accretion additives such as
phosphonates, phosphate
esters of alkanolamines, quaternary ammonium salts, anionic polymers, cationic
polymers, and
nonionic polymers.
The drilling fluid may be useful to inhibit or remove oil sand accretion on
metal surfaces. In one
aspect, the drilling fluid can be used in a method for drilling a wellbore
through an oil sand-
containing formation. In such a method, without the present additive, drill
cuttings can adhere as
accretions to the metal surfaces of the drilling assembly, metal surfaces in
the wellbore such as
liners and casing and metal surfaces of the surface handling and solids
control equipment. Thus,
the present method includes circulating the aqueous-based drilling fluid, as
described above,
while operating a drilling assembly to drill the wellbore.
It will be appreciated that a drilling assembly can include, for example, a
drill bit, drill string,
and various control and monitoring subs.
It will also be appreciated, that it may not be necessary to use the oil sand
anti-accretion additive-
containing drilling fluid throughout an entire drilling operation. For
example, it may not be
required during drilling through over burden. The method is useful during
drilling wherein oil
sand drill cuttings are being produced and very useful where there is more
frequent contact
between metal surfaces such as, for example, during drilling of the build
section and the
horizontal section of a wellbore.
Where, during drilling using a drilling fluid according to the present
invention, accretions are
being deposited to an undesirable extent, the concentration of additive can be
increased to inhibit
further undesirable amounts of accretion and possibly to remove, at least to
some degree, those
accretions already deposited.
The drilling fluid of the present invention may also be used to reduce or
remove accretions,
which have already been built up on metal surfaces. Thus, in another aspect
the drilling fluid can
be used in a method for removing accretion from metal surfaces that have been
in contact with
oil sand-containing formation cuttings, the method comprising: washing the
metal surfaces with
an aqueous-based drilling fluid, the aqueous-based drilling fluid including an
amount of at least
one of an amine, a polyamine, an oxylated polyamine, an aminosilane, a
nitrogen containing
heterocycle, an amide, an alkylamidopolyamine, a polyamide, a Mannich amine, a
melamine
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formaldehyde resin, a dicyandiamide resin, a polyamideamine, a
polyethyleneimine, and a
polyvinylamine in conjunction with a phosphonate, a phosphate ester of an
alkanolamine, a
quaternary ammonium salt, an anionic polymer, a cationic polymer and a non-
ionic polymer.
In this method, the drilling fluid can be used, for example, to wash
accretions from the drilling
assembly such as the drill string, for the wellbore liners and casing. This
method can also be
used to facilitate running in of liners, such as a slotted liner into a
wellbore where accretions
have occurred. In so doing, the fluid may be circulated through the wellbore
while the liner is
run in. The removal of accretions may require washing over a period of time to
remove a desired
amount of accretions.
EXAMPLES
The following examples are presented to illustrate but not limit the scope of
this invention. All
percentages and parts are by weight unless otherwise noted.
Unless otherwise indicated, the examples are based on the following test
procedure, which was
developed to replicate accretion of the oil sand and heavy oil onto metal
surfaces. In the test
procedure, 350 mL of drilling fluid to be tested was added to a Waring
commercial blender of 1L
capacity. The anti-accretion additive was added to the drilling fluid under
mixing and the pH of
the fluid adjusted to a range of 7 to 11 with sodium hydroxide, for example a
pH of 10. The
mixer was set to high speed and whilst mixing, oil sand of various oil to sand
ratio or bitumen
was added to the drilling fluid. The resultant drilling fluid and oil sand
slurry was then mixed for
a further 5 minutes to disperse the oil sand and ensure homogeneity.
The drilling fluid/tar sand mixture was then transferred into a 500 mL 316
stainless steel drilling
fluid aging cell such as those supplied by Fann Instruments, having an
internal diameter of 6.5
cm and a depth of 15.5. To simulate downhole assembly/shale shaker, pre-
weighed mild steel
shims or 130 mesh steel screen were inserted into the aging cell. The cell was
sealed and placed
horizontally in an aging cell roller oven similar to a Fann Instruments Model
701 Roller Oven
with the temperature set at 25 C or 50 C. The rotary apparatus was turned on
to rotate the cell
at approximately 19rpm. After the desired aging time elapsed, the aging cells
were removed
from the roller oven; the steel shims of the steel screens were removed from
the aging cell, rinsed
under cold water to remove any loose material on the steel, then rinsed with
methanol to remove
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water. The sleeves were left to dry and then reweighed. The heavy oil or
bitumen adhesion was
then calculated on a mass quantity per unit of exposed surface area and the
level of accretion was
visually verified.
Example 1
A sample of a drilling fluid was prepared using 350 mL of tap water containing
0.6% of a
slurried polysaccharide and I% of a starch based fluid loss additive. A slurry
was prepared using
this fluid and 50g of oil sand as described in the test procedure. A steel
shim of 15cm x 21cm
was placed into the aging cell with the slurry and placed in a roller oven for
48 hours at 25 C.
The steel shim was removed and treated as described in the test procedure. oil
sand accretion
was evident on the shim as shown in Figure 1. The oil sand accretion was found
to be 172 g oil
sand/m2 steel, see Table 1. This example demonstrates the accretion of oil
sand on simulated
down-hole equipment when the drilling fluid is not treated with an anti-
accretion additive.
Example 2
A drilling fluid was prepared by hydrating 0.6% of a slurried polysaccharide
and 1% of a starch
based drilling fluid in tap water. To 350 mL fluid 0.5% of an anti-accretion
additive was added
and the pH adjusted to 10. A slurry was prepared using this fluid and 50g of
oil sand as
described in the test procedure. A steel shim of 15cm x 21cm was placed into
the aging cell with
the slurry and placed in a roller oven for 48 hours at 25 C. The steel shim
was removed and
treated as described in the test procedure. The amount of oil sand accretion
was quantified by
calculating the weight difference between the steel shim before and after the
test. The anti-
accretion additives tested along with the amount of oil sand accretion/ m2
exposed surface area
are given in Table 1. Figures 2 to 4 are photographs of the test results using
various anti-
accretion additives.
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TABLE 1
Anti-accretion additive Tar sand accretion (g/m2)
No anti-accretion additive 172
1,3-Propanediamine, N 1-(3-
(tridecyloxy)propyl)-, branched 0
N-tallow alkyltripropylene-tetraamine 0
N-coco alkyl trimethylenediamine 0
Fatty acids, tall-oil, reaction products with
diethylenetriamine 0
Hexanedinitrile, hydrogenated, high-boiling
fraction 0
Tallow trimethyl ammonium chloride* 0
Octadecene dimethyl amine ** 238
*Forms a large amount of foam.
**While not fully understood, it may be possible that a basic nitrogen group
in this molecule, at
the pH tested, does not have adequate oil wetting properties to facilitate
limiting accretion.
Example 3
A drilling fluid was prepared by hydrating 0.6% of a slurried polysaccharide
and I% of a starch
based drilling fluid in tap water. To 350 mL fluid 0.25, 0.5, 1.0, and 2.0 %
of fatty acids, tall-oil,
reaction products with diethylenetriamine or hexanedinitrile, hydrogenated,
high-boiling fraction
were added and the pH adjusted to 10. A slurry was prepared using this fluid
and 50g of oil
sands as described in the test procedure. A steel shim of 15cm x 21cm was
placed into the aging
cell with the slurry and placed in a roller oven for 48 hours at 25 C. The
steel shim was
removed and treated as described in the test procedure. The amount of oil sand
accretion was
quantified by calculating the weight difference between the steel shim before
and after the test.
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In both the tests with fatty acids, tall-oil, reaction products with
diethylenetriamine and the tests
with hexanedinitrile, hydrogenated, high-boiling fraction, all percentages
tested demonstrated
that the amount of accretion was Og/ m2 exposed surface area.
Example 4
A series of tests were performed to test the efficacy of the anti-accretion
additives at elevated
temperatures. A drilling fluid was prepared by hydrating 0.6% of a slurried
polysaccharide and
1% of a starch based drilling fluid in tap water. To 350 mL fluid 0.25% of an
anti-accretion
additive was added and the pH adjusted to 10. A slurry was prepared using this
fluid and 50g of
oil sand or bitumen as described in the test procedure. A steel shim of 15cm x
21 cm was placed
into the aging cell with the slurry and placed in a roller oven for 48 hours
at 50 C. The steel
shim was removed and treated as described in the test procedure. The amount of
oil
sand/bitumen accretion was quantified by calculating the weight difference
between the steel
shim before and after the test. The anti-accretion additives tested along with
the amount of oil
sand or bitumen accretion/ m2 exposed surface area are given in Table 2.
Figures 5 to 7 are
photographs of the test results using various anti-accretion additives.
TABLE 2
Anti-accretion additive Test sample Sample accretion (g/m )
No additive Tar sand 220
Fatty acids, tall-oil, reaction
4.7
products with diethylenetriamine Tar sand
Fatty acids, tall-oil, reaction
8
products with diethylenetriamine Bitumen
Hexanedinitrile, hydrogenated,
22
high-boiling fraction Tar sand
N-coco alkyl trimethylenediamine Tar sand 0
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Mixture of Fatty acids, tall-oil,
reaction products with
Bitumen
diethylenetriamine and amino 0
triethyl phosphate ester
Example 5
The same test procedure was followed as outlined in Example 2 using 130 mesh
steel screen
instead of the steel shim and 1% of anti-accretion additives were added. The
test results are
given in Table 3. Figures 8 to 10 are photographs of the test results in the
absence and in the
presence of the anti-accretion additive.
TABLE 3
Anti-accretion additive Tar sand accretion (g/m )
No additive 189
hexanedinitrile, hydrogenated, high-boiling
fraction 2
Mixture of hexanedinitrile, hydrogenated,
high-boiling fraction and amino triethyl
phosphate ester 30
Example 6
The same test procedure was followed as outlined in Example 2, except 1.0%
polyethyleneimine
or 1,2-ethanediamine, polymer with aziridine were added to the fluid. For
polyethyleneimine, 6
g/m2 of accretion was observed and for the 1,2-ethanediamine, polymer with
aziridine, 9g/m2 of
accretion was observed.
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Example 7
A polymeric Mannich amine, the reaction product of polyacrylamide,
formaldehyde and
dimethylamine was also tested using the test procedure outlines in Example 2.
The additive was
added at 2% and 30g/m2 accretion was observed.
Example 8
A drilling fluid was prepared by adding 0.3% xanthan gum, 0.2% polyanionic
cellulose and 0.8%
starch to tap water while being mixed. The pH of the resulting fluid was
adjusted to 10 using
sodium hydroxide and 350 mL of the resulting fluid was placed in a Waring
blender, to which
35g of an oil sand sample was added along with various amine or amide
additives listed below in
Table 4. The mixture was sheared at high speed for 1 minute and the resulting
slurry was
transferred into a 500 mL drilling fluid ageing cell lined with a mild steel
sleeve. The slurry was
then placed in a roller oven and aged for 16 hours at 35 C. After which the
sleeves were
removed and loose oil rinsed off with water. Observations made on the sleeves
are summarized
in Table 4. FIG. 11 to 16 are photographs of the test results observed for
Example 8.
TABLE 4
Anti-accretion additive Concentration Observation
No additive N/A Heavy Oil Accretion on Sleeve
morpholine 0.5% Slight Accretion on Sleeve
morpholine 1.0% Slight Accretion on Sleeve
amides of rapeseed oil and 0.5%
dimethylaminopropyl Slight Accretion on Sleeve
amine
amides of rapeseed oil and 1.0%
dimethylaminopropyl Slight Accretion on Sleeve
amine
pyridinium, 1- 0.5%
(phenylmethyl)-, alkyl Very Slight Accretion on Sleeve
derivatives, chlorides
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The previous description of the disclosed embodiments is provided to enable
any person skilled
in the art to make or use the present invention. Various modifications to
those embodiments will
be readily apparent to those skilled in the art, and the generic principles
defined herein may be
applied to other embodiments without departing from the spirit or scope of the
invention. Thus,
the present invention is not intended to be limited to the embodiments shown
herein, but is to be
accorded the full scope consistent with the claims, wherein reference to an
element in the
singular, such as by use of the article "a" or "an" is not intended to mean
"one and only one"
unless specifically so stated, but rather "one or more". All structural and
functional equivalents
to the elements of the various embodiments described throughout the disclosure
that are know or
later come to be known to those of ordinary skill in the art are intended to
be encompassed by the
elements of the claims. Moreover, nothing disclosed herein is intended to be
dedicated to the
public regardless of whether such disclosure is explicitly recited in the
claims. No claim element
is to be construed under the provisions of 35 USC 112, sixth paragraph, unless
the element is
expressly recited using the phrase "means for" or "step for".
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