Note: Descriptions are shown in the official language in which they were submitted.
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MAGNETIC POLYMER PELLETS AND A METHOD OF GENERATING
THE BLOCKING GEL PLUG
This invention is related to magnetic polymer pellets represented as a polymer
matrix and solid filler as well as to the application thereof for making gel
plugs.
Polymer (alginate) pellets with para- and ferromagnetic properties and
mathods to obtain them are described in scientific literature. They are gels
crosslilnked with calcium (Lee, D.Y. et al., Ieee Transactions on Magnetics
2004, 40, 2961; Roger, S. et al., Journal of Magnetism and Magnetic Materials
2006, 305, 221) or iron ions (Llanes, F. et al., International Journal of
Biological Macromolecules 2000, 27, 35; Nishio, Y. et al., Polymer 2004, 45,
7129; Naik, R. et al., Journal of Applied Physics 2005, 97, ), and containing
magnetic substance or particles: barium ferrite (Lee, D.Y. et al., Ieee
Transactions on Magnetics 2004, 40, 2961), iron oxide (Llanes, F. et al.,
International Journal of Biological Macromolecules 2000, 27, 35; Nishio, Y. et
al., Polymer 2004, 45, 7129; Naik, R. et al., Journal of Applied Physics 2005,
97, ) and magnetic iron (Tyagi, R. et al., Biocatalysis and Biotransformation
1995) 12, 293; Roger, S. et al., Journal of Magnetism and Magnetic Materials
2006, 305, 221).
The procedure to obtain magnetic alginate pellets includes introduction of
crosslinking ions into the mixture of sodium alginate solution and ferrofluid.
Different introduction options have been described: "internal" and "external".
As applied to calcium-alginate gels the "external" method makes use of the
instillation of the sodium alginate and ferrofluid mixture into the calcium
chloride solution (Lee, D.Y. et al., Ieee Transactions on Magnetics 2004, 40,
2961; Roger, S. et al., Journal of Magnetism and Magnetic Materials 2006, 305,
221). In the "internal" method, first "inactive" calcium as complex with EDTA
is added to the mixture of sodium alginate and ferrofluid mixture and then the
calcium is slowly released by the medium acidification using gluco-6-lactone
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hydrolysis (Roger, S. et al., Journal of Magnetism and Magnetic Materials
2006,
305, 221). With iron-alginate gels "internal" administration method is applied
which is based on alkaline oxidation of ferrous iron in calcium alginate
solution
(Llanes, F. et al., International Journal of Biological Macromolecules 2000,
27,
35). It was demonstrated that in "internal" method of administering the
crosslinking ions more homogenous particles are obtained.
The use of magnetic alginate pellets for biological separation and
treatment of enzymes and cells in the magnetic field has also been described
(Tyagi, R. et al., Biocatalysis and Biotransformation 1995, 12, 293; Ames,
T.T.
et al., Biotechnology Progress 1997, 13, 336; Liu, C.Z. et al., Journal of
Bioscience and Bioengineering 2000, 89, 420), for effluents treatment of heavy
metals (Nestle, N. et al., Colloids and Surfaces A-Physicochemical and
Engineering Aspects 1996, 115, 141; Ngomsik, A.F. et al., Water Research
2006, 40, 1848).
Thus, U.S. Patent No. 4,652,257 describes the method of obtaining
manetically localized polymerizing lipidic vesicles, containing the target
substance (medicine), and the method of the vesicles' destruction and release
of
the contents thereof under the magnetic field effect. The therapeutic
substance
and ferromagnetic particles are encapsulated in the lipidic vesicle, generated
by
the polymerizing lipids. The lipids are polymerized under the effect of
ultraviolet radiation with the formation of the membrane resistant to chemical
and physical effects. Any ferromagnetic substance, preferably single-domain
magnets of bacterial origin, magentites, ferrites or fine-grain iron sawdust
may
be used as magnetic particles. The vesicles are delivered to the target organ
under the effect of the external constant magnetic field. After localization
in the
proper location the vesicle membrane is destroyed or destabilized due to the
application of the variable magnetic field. Frequency and duration of the
variable magnetic field action determine the rate of the vesicle-encapsulated
therapeutic substance release.
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U.S. Patent No. 5,019,372 proposes a method of obtaining solid polymer
pellets filled with stainless steel particles and containing the target
biologically
active substance (water-soluble medicine), the release of which is accelerated
in
the variable magnetic field. The polymer pellet is made of bio-compatible
plastic material non-soluble in the application field, e.g., of ethylene-vinyl
acetate copolymer. The biologically active substance and magnetic particles
are
dispersed in the monomers methylene chloride solution, after which
polymerization and pelletization are conducted. The pellets are places in the
aqueous medium where the target substance is released effected by the
oscillating magnetic field with the intensity of 0.5 to 1,000 Gauss. The rate
of
the release stimulated by the magnetic field is by factor 30 higher than
without
this stimulation and amounts to about 400 micro-Gauss per hour. A water-
soluble substance with the molecular weight exceeding 150 D may be used as
the target substance.
In the proceeding Z. Lu et al. (Langmuir, 2005, 21, 2042-2050) a method
of obtaining magnetically sensitive polyelectrolyte multi-layer micro-pellets
was proposed. The capsule membrane consists of several layers formed by
sodium phosphonated polystyrene and polyallylamine hydrochloride with a
layer of cobalt nano-particles coated with gold between them. The capsule
membrane permeability for dextrane marked with a fluorescent tag was
researched. It was demonstrated that the variable magnetic field with the
frequency of 100-300 Hz and intensity of 1200 Gauss causes intensive rotation
of the cobalt nano-particles which significantly damages the capsule membrane
integrity. The optimum magnetic sensitivity of the membrane sensitivity was
observed in the capsules with the walls formed of 10 layers of
polyelectrolytes
and 1 layer of ferromagnetic nano-particles.
The polymer pellets described are designed for bio-medical application in
the systems of targeted transport of medicines. Their application in other
technologies is limited by the process complexity and their high cost.
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The use of polymers for controlled generation of the plug for zone
insulation is described in Patent RU 2276675. The invention describes the
method of forming a gel plug by gellation of the fluid containing
hydrophobically associating substances and water-soluble gellation inhibitor.
In
case of contact between the fluid and hydrocarbons the inhibitor retains its
properties whereas in case the fluid's contact with the water medium the
inhibitor is dissolved which results in gellation. Therefore, the method
enables
monitoring water influxes in the oil-producing wells by gel plugs' formation.
However, this method has its disadvantages: 1) gellation with the use of this
fluid is irreversible and starts from the first contact with water which could
occur on the surface which creates significant difficulties during the
injection of
water into the well, 2) the already formed gel plugs in certain conditions may
also lock oil-bearing formations making hydrocarbons' production more
difficult.
The invention claimed covers polymer pellets containing ferromagnetic
microparticles and having optimum mechanical properties enabling gel plug
formation resulting from their swelling in the external magnetic field. The
polymer granules may be used when zone insulation is required. Influenced by
the magnetic field these pellets migrate to the location where zone insulation
is
required and are destroyed due to swelling in the confined volume where they
are held by the magnetic field and form the gel plug.
As per this invention, the polymer pellet is a gel matrix of anionic
polymer cross-linked with cations of multivalent metals in which ferromagnetic
particles are dispersed at the concentration of ferromagnetic micro-particles
of
0.5 - 5%. The concentration of ferromagnetic particles below 0.5% does not
provide the particles' required ferromagnetic properties whereas the
particles'
concentration of >5% results in heavier pellets which swell worse. Anionic
polysaccharide with the concentration from 0.1 to 2% is used as the anionic
polymer. The anionic polysaccharide may be sodium alginate, pectin with
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etherification degree of maximum 30%, carboxymethyl cellulose or
oxyethylcarboxymethyl cellulose. As the ferromagnetic particles spherical or
bar-shaped particles of iron or oxides thereof with the minimum size of 40 -
300 nm, e.g., magnetite or magenite are used.
As per this invention, the polymer pellets are used to form the locking gel
plug, e.g., to provide the formation insulation. In accordance with the
invention,
the method of making the locking gel plug includes delivery of the gellating
compound made as polymer pellets to the gel plug formation zone; each pellet
being a gel matrix of anion polymer cross-linked with the cations of
multivalent
metals in which ferromagnetic particles are dispersed with the ferromagnetic
particles' concentration from 0.5 to 5%. The locking gel plug is formed due to
the pellets' intensive swelling provided by the ambient pH increase to pH>7 in
the confined volume where they are retained by the external magnetic field
with
the intensity of 5,000-20,000 Oersted.
The polymer pellets may be pre-dried. The humidity of the dried pellets is
15-25%. A substance stimulating the polymer pellets' swelling may be added to
the medium in which the pellets are swelled; as this substance soda as well as
phosphates, polyphosphates, citrates or chelating agents like
ethylenediaminotetraacetic acid (EDTA) sodium salt. To speed up the swelling
the pellets' surface may be pre-wetted with ethyl alcohol. To intensify the
swelling of the pellets cross-linked with barium ions their surface is treated
with
0.1 M hydrochloric acid. The pellets may be delivered by the application of
the
external magnetic field providing the polymer pellets' migration to the gel
plug
formation zone.
As per this invention, the polymer pellets may be obtained by dispersing
ferromagnetic particles stirred in the water solution of anionic
polysaccharide
capable of ionotropic gellation, after that the suspension is dripped into the
multivalent metal salt water solution. As the multivalent metal salts water-
soluble salts of calcium, barium or aluminum may be used.
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The essence of the invention may be illustrated by the following non-limiting
examples.
Example 1
Making Magnetite-Containing Alginate Pellets
0.3 g of magnetite (powder of irregular shape Fe304 particles with the
size of about 300 nm) is dispersed by stirring in 9.7 g of 1.4 %-solution of
sodium alginate in 0.01 M solution of the buffer mixture tris-(hydroxymethyl)-
aminomethane - HCl with pH 7.4. The sodium alginate solution magnetite
suspension obtained is dripped into 100 ml of 3 % solution of calcium chloride
in the buffer mixture tris-(hydroxymethyl)-aminomethane - HCl above at pH
7.4. Simultaneously calcium alginate pellets with the diameter of 3 mm are
formed. The pellets' suspension is kept at 4 C for 24 hours and then washed
five times with 20 ml of bidistilled water and stored in the refrigerator for
further use or dried using any method until the residual humidity is 15-25%.
Example 2
MakingMagenite-Containing Alginate Pellets
0.3 g of magenite (powder of needle-shaped y-Fe203 particles with the
diameter of 40-60 nm and length of 400-800 nm) is dispersed by stirring in 9.7
g of 1.4 % solution of sodium alginate in 0.01 M solution of the buffer
mixture
tris-(hydroxymethyl)-aminomethane - HCl with pH 7.4. The sodium alginate
solution magenite suspension obtained is dripped into 100 ml of 3 % solution
of
calcium chloride in the buffer mixture tris-(hydroxymethyl)-aminomethane -
HCl above at pH 7.4. The suspension of the pellets (diameter 3 mm) formed is
kept at 4 C for 24 hours and then washed five times with 20 ml of bidistilled
water and stored in the refrigerator for further use.
Example 3
Gel Plug Formation
Dried alginate pellets containing ferromagnetic particles are introduced
into the system with the capillaries with the diameter of 2-6 mm and fluid
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circulating with the rate of max. 700 ml/min. Under the influence of the
magnetic field with the intensity of 7,000-10,000 Oersted the pellets are
localized in the magnet area swell with the gel plug. The pressure in the
capillaries is increased to 250 kPa using compressed gas. The pressure formed
withstands the pressure.
Example 4
Drying of Alginate Pellets Containing Magnetite at Room Temperature
The magnetic pellets made as shown in Example 1 are dried at the room
temperature for 24 hours. Hereby the average weight of one pellet is reduced
from 12.8 to 1.1 micrograms within the first 3 hours and then virtually does
not
change. The pellets retain spherical shape. Weight reduction during the drying
is
accompanied by the diameter reduction from 3.1 mm to 0.7-0.9 mm.
Example 5
Drying of Alginate Pellets Containing Magnetite at 80 C
The magnetic pellets made as shown in Example 1 are dried at 80 C B for
1 hour. Hereby the average weight of one pellet is reduced from 12.8 to 1.1
micrograms within the first 0.5 hours and then virtually does not change. The
pellets retain spherical shape. Weight reduction during the drying is
accompanied by the diameter reduction from 3.1 mm to 0.7-0.9 mm.
Example 6
Drying of Alginate Pellets Containing Magnetite using Sublimation
Dehydration Method
The magnetic pellets made as shown in Example 1 are frozen at -50 C
and then dried in the sublimation dehydration unit at the residual pressure of
1.1
Pa (Martin Chrict model ALFA 1-2 LD; Osterode am Harz, W, Germany) for 14
hours. Hereby the average weight of one pellet is reduced from 12.8 to 1.1
micrograms within the first 5 hours and then virtually does not change. The
weight loss during the drying is accompanied by the pellets' shape change,
they
become disc-shaped (diameter 2.4 mm and thickness 0.25 mm).
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Example 7
Drying of Alginate Pellets Containing Magnetite at Room Temperature in
Vacuum
The magnetic pellets made as shown in Example 1 are dried at the room
temperature in vacuum (1-10-3 mm Hg) for 22 hours. Hereby the average
weight of one pellet is reduced from 12.8 to 1.1 micrograms within the first 5
hours and then virtually does not change. The pellets retain spherical shape.
The
weight loss during the drying is accompanied by the pellets' diameter
reduction
from 3.1 mm to 0.9-1.0 mm.
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