CA1102030A - Process for the treatment of aqueous solutions of partially hydrolyzed polyacrylamides - Google Patents
Process for the treatment of aqueous solutions of partially hydrolyzed polyacrylamidesInfo
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- CA1102030A CA1102030A CA308,150A CA308150A CA1102030A CA 1102030 A CA1102030 A CA 1102030A CA 308150 A CA308150 A CA 308150A CA 1102030 A CA1102030 A CA 1102030A
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- solutions
- solution
- partially hydrolyzed
- water
- polyacrylamide
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J3/00—Processes of treating or compounding macromolecular substances
- C08J3/02—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques
- C08J3/03—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques in aqueous media
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
- C09K8/58—Compositions for enhanced recovery methods for obtaining hydrocarbons, i.e. for improving the mobility of the oil, e.g. displacing fluids
- C09K8/588—Compositions for enhanced recovery methods for obtaining hydrocarbons, i.e. for improving the mobility of the oil, e.g. displacing fluids characterised by the use of specific polymers
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2333/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers
- C08J2333/24—Homopolymers or copolymers of amides or imides
- C08J2333/26—Homopolymers or copolymers of acrylamide or methacrylamide
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Health & Medical Sciences (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Dispersion Chemistry (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
- Separation Of Suspended Particles By Flocculating Agents (AREA)
- Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method for treating an aqueous solution of a partially hydrolyzed polyacrylamide to be utilized in enhanced oil recovery wherein the polyacrylamide solution is sheared at a shear rate between 20,000 and 50,000 s-1.
A method for treating an aqueous solution of a partially hydrolyzed polyacrylamide to be utilized in enhanced oil recovery wherein the polyacrylamide solution is sheared at a shear rate between 20,000 and 50,000 s-1.
Description
~2~30 FIELD OF THE INVENTION
This invention relates to a method for treating aqueous solutions of partially hydrolyzed polyacrylamides prior to their use in enhanced oil recovery operations.
DESCRIPTION OF THE PRIOR ART
Among the more widely practiced methods for the recovery of oil from an oil-bearing reservoir is water-flooding. In this method, flood water is injected into the reservoir via one or more injection wells, which water displaces the oil in the formation toward one or more production wells. More recently, improvements in water-flooding methods have included the use of water-soluble polymers whereby the viscosity of the flood water is increased. The "thickened" water results in a more favorable mobility ratio and leads to improved oil recovery.
Only materials with very high molecular weights of one to ten million and rod-shaped molecules are suitable for this purpose, and only such materials are effective in increasing the viscosity of the water in the desired manner at very small concentrations of less than 1 kg/m3. Two types 20 of such polymers that have been found suitable as thickeners are the polyacrylamides, which may be partially hydrolyzed, and polysaccharides which are mainly produced by means of the bacteria Xanthomonas Campestris.
The polyacrylamides are long chain polymers of the acrylamide with the general formula:
ECH2-CH ~CONH2~ ]n with n = about 50,000 or more. The molecular weight is 3 to 6 million. With partially hydrolyzed polyacrylamides, a part of the amide group - CONH2 ~ is converted into the carboxylate group - COONa - by saponification reaction.
~J2~!30 Polyacrylamides that are hydrolyzed to 10 - 60 percent or preferably 20 - 35 percent are especially well-suited for polymer flooding.
The molecules of partially hydrolyzed polyacryl-amides possess their elongated rod-like shape only in practically non-conductive, i.e. salt-free water, because of the repulsive energy of the negatively loaded carboxyl group and behave like very long stretched elastic fibers.
The length is about 10,000 times the thickness and is about 10~ m.
Solutions of partially hydrolyzed polyacrylamides in fresh water are considerably more viscous than solutions of polysaccharides at the same concentration. Apart from this, the price per kilo is only half as much and polymer solutions of suitable viscosity with partially hydrolyzed polyacrylamides can be produced at a quarter of the cost per cubic meter ~m3~ of flooding liquid compared to that of the polysaccharide. In reservoirs that contain salt water, a polyacrylamide solution using fresh water can be favorably applied after preconditioning the reservoir by flooding with fresh water. Other advantages of the partially hydrolyzed polyacrylamide include, better stability against bacteria and against high temperatures of up to 100C compared to 70C for a polysaccharide.
Solutions of such high molecular materials are not genuine liquids in the rheological sense, The viscosity depends on the velocity gradient. The flow characteristics of this pseudo plastic solution follows the power law:
~ = shear rate ~s 1~
~ ~ ~ = shear strength (dyn~cm2) 3~
n and ~ are constants, ~ is the apparent viscosity at a shear rate of 1 s 1, The exponent, n, is smaller than 1.
For genuine liquids n = 1.
Pseudo plastic liquids are less suitable than genuine liquids of constant viscosity for displacing oil from reservoirs with heterogeneous permeability which is the case for more or less all natural reservoirs. The Darcy law generalized to incorporate pseudo plastic liquids is:
lo 2) ~ 4n . 1 ~ ~ ( p )/n 3~+1 71 ~/n ~ ~
= average velocity = permeability (cm2) = porosity ~/~ = pressure gradient The flow velocity depends, therefore, more strongly on permeability than that of genuine liquids (n = 1).
It is therefore desirable to achieve constant viscosity within the range of the velocity gradient that occurs in an oil reservoir. The velocity gradient along 20 the walls of the pore channel is:
3) ~= ~n l 1 . nr ~n When 1 m of polymer solution per hour, per meter of reservoir thickness is injected into the injection well, a radial flow yields, at a distance of 100 m, a velocity of = 1 cm/h = 2 .8 x 10 4 cm/s. For~ = 10 8 cm2 (1 Darcy), ~ = 0.25 and n = 0.5 the shear rate becomes ~= 7 s 1. In this case the flow curve in the shear rate range below 7 s 1 is decisive. With lower permeabilities, greater distances, lower injection rates the area of interest is still lower, ~30 in other cases also higher.
In practice there occur considerable deviations from the theoretically correct relationships shown above.
As a result of the more difficult passage of the very large molecules through the narrow parts of the pore channels the pressure losses are greater than predicted by theory. At low flow velocities they are a multiple of 1.2 to 1.5 with polysaccharide solutions and a multiple of 2 to 5 with hydrolyzed polyacrylamide solutions. The pore cross section is reduced by adsorption of polymer molecules on the surface of the rock. Therefore, during two phase flow of oil and water or oil and polymer solution only the effective permeability for water should be applied. The lower the absolute permeability, the stronger is the permeability reduction by polymer adsorption.
The usual form of commercial hydrolyzed polyacryl-amides is a fine grained, solid product. Even though it is a water-soluble polymer it is practically impossible to produce a completely molecular dispersed solution. In water, the polymer grains swell and tend to form lumps which require long periods of stirring or special dissolution methods before an apparently homogeneous solution is obtained. Even optically clear solutions contain micro gel particles or aggregates of 10 or 30 molecules which cling to the narrow parts of the pore channeI and lead to a partial blockage.
Multivalent cations ~Fe, Ca, Mg~ especially, can produce larger particles or even lead to coagulation through the cross linking of several molecules C'Mobility of Polymer Solutions in Porous Media", SPE 3683, I. Ershachi and 0 L. L. Handy, Los Angeles, November 1971).
111;3Z~3~
Even though the removal of the undesirable micro particles by means of filtration through a packing of very fine grained material such as diatomacious earth or silica flour is possible, it is only suited for laboratory quantities, not for field applications. The following method for the production of aqueous polysaccharide solutions from polysaccharide is known ~"Improved Injectability of Biopolymer Solution" SPE 5099, D. Lipton, Denver, April 1976).
The fine grained polymer trickles into a blender through a 10 water spray whereby practically every grain is individually ~-wetted. The highly concentrated solution produced (stock solution), e.g. 1 percent, in fresh water is stirred vigorously for several minutes. The solution is subsequently homogenized in a simple manner, whereby it is pumped through perforated plates under high pressure, e.g. with a pressure loss of 10 bar per plate. In order to destroy the insoluble remnants of the bacteria, an enzyme treatment is necessary which lasts for several hours at an increased temperature of 50C. After this treatment has been completed, the stock 2a solution can be diluted with brine, process water or reservoir water available. The injectability in reservoirs with low permeability is not really good in spite of the extensive treatment, as the solution still contains aggregates from a large number of molecules which cling to the narrow parts of the pore channels and cause a partial blockage.
The production of solutions from hydrolyzed polyacrylamides, which is in fine grained form, also takes place with the aid of a blender. As the polyacrylamides are Q very sensitive, they are not forced through a perforated plate.
~2~30 An enzyme treatment is not necessary. A great number ofcommercially available polyacrylamides are either too slowly or incompletely soluble as a result of drying and/or grinding procedure during manufacturing of the product. Some manufacturers therefore supply the product as a concentrated aqueous gel which is a suspension of fine globules in mineral oil. Such liquid polymers are therefore pre-swollen and dissolve much quicker in water. But even with these products, an efficient injectability is not assured. The molecule aggregates that are formed from the polyacrylamides, and partly also from cross-linking by bivalent cations, are trapped in the pore space. In order to obtain the best possible molecular dispersed solution the manufacturers recommend that a stock solution, e.g. 1 percent, be mixed and then be diluted to the required concentration after 24 hours. It is known that solutions of partially hydrolyzed polyacrylamide of high molecular weight are subject to a viscosity reduction caused by shearing when a high shear rate is applied. The longest molecules rupture as a result of the high tensile strain. In using these solutions, it has been recommended that such solutions not be pumped through narrow jets, and that only stirring apparatus with a low revolution ~ate should be used, i.e. centrifugal pumps should not be used. Also the injection rate in flood wells should ~e kept within limits in order to keep the loss of viscosity as low as possible during entry of the polymer solution into the formation. ~See: "The Oil & Gas Journal", July 12, 1976, p. 541. In another publication, it is pointed out that hydrolyzed polyacrylamide is ~1~2~30 disadvantageously influenced by shearing. (See "Fundamentalsof Tertiary Oil Recovery", Petroleum Engineer, July 1976, E. F. Herbeck et al, p. 48-59, 54).
It is an object of the present invention to overcome the problems associated with the pretreatment of polyacrylamide solutions prior to their employment in oil recovery operations by subjecting the polyacrylamide solutions to a controlled, limited shearing treatment.
The Figure shows the result of the change in shear rate on the apparent viscosity of polyacrylamide solutions.
According to the invention there is provided a process for the treatment of aqueous solutions of partially hydrolyzed polyacrylamides prior to the employment of said solutions in enhanced oil recovery operations wherein said solutions contain said polyacrylamide at a concentration less than 1 kg/m3 and said solutions are sheared at shear rates in the range of about 20,000 to about 50,000 s 1.
In a preferred embodiment said shearing is achieved by forcing said aqueous polyacrylamide solutions through perforated plates having holes 1 to 4 mm diameter and said shear rate is selected so as to maintain a pressure loss of between 1 and 3 bar per perforated plate.
Thus there is provided a method for the pretreatment of polyacrylamide solutions by a controlled, limited shearing action wherein solutions of partially hydrolyzed polyacrylamides are sheared at a shear gradient of 20,000 to 50,000 s 1 corresponding to a shearing stress of 500 to 2,000 dynes/cm2.
By the treatment thus described it has been found that solutions of partially hydrolyzed polyacrylamides that are to be used in ~ , enhanced recovery operations were improved and trouble-free injectability was achieved.
The improvement has been demonstrated in the following laboratory tests. A core from a reservoir, or a sandpack with comparable pore space is flooded at a constant rate with the polymer solution. With the sheared solution, ; in accordance with the invention, the flow pressure, except for the first few minutes, (a certain increase in pressure is produced due to adsorption) remains constant even after .
-, ~ .
1~, , ;~ 20 - 7(a) -' , ll~Z~3~
the throughput of large volumes. With unsheared solutions good injecta~ility was achieved only after filtration through fine pored filter media or after a very long stirring period.
Referring to the accompanying Figure, it can be seen that the flow curve of the sheared solution of partially hydrolyzed polyacrylamide is more suited for polymer flooding, as with small velocity gradients, such as prevail in the reservoir, practically constant viscosity is produced ~curve 2~, while the unsheared solution (curve 1) is strongly pseudo plastic. This means that the apparent viscosity at decreasing shear rates increases to values which are too high. A sheared solution at a given pressure gradient is forced more quickly into the reservoir and sweeps a larger part of its lower permeability region. This leads to a higher degree of oil recovery than with an unsheared solution.
Further, according to the method of invention, the injection pressure is considerably reduced by the shearing of the solution of the partially hydrolyzed polyacrylamide.
During flooding through a sandpack with a grain size of 60 - 90Jwm and at a shear rate of 100 s 1 the injection pressure for an unsheared solution of partially hydrolyzed polyacrylamide was Q.38 bar. If the same solution is sheared ~n accordance with the invention the injection pressure is reduced to Q.16 bar. The apparent viscosities at a shear rate of lOQ s shows practically no difference ~7.5 and 7,3 cPl, This effect of the shear treatment on the injection pressure is of special importance for 0 reservoirs with relatively low permeabilities. As the
This invention relates to a method for treating aqueous solutions of partially hydrolyzed polyacrylamides prior to their use in enhanced oil recovery operations.
DESCRIPTION OF THE PRIOR ART
Among the more widely practiced methods for the recovery of oil from an oil-bearing reservoir is water-flooding. In this method, flood water is injected into the reservoir via one or more injection wells, which water displaces the oil in the formation toward one or more production wells. More recently, improvements in water-flooding methods have included the use of water-soluble polymers whereby the viscosity of the flood water is increased. The "thickened" water results in a more favorable mobility ratio and leads to improved oil recovery.
Only materials with very high molecular weights of one to ten million and rod-shaped molecules are suitable for this purpose, and only such materials are effective in increasing the viscosity of the water in the desired manner at very small concentrations of less than 1 kg/m3. Two types 20 of such polymers that have been found suitable as thickeners are the polyacrylamides, which may be partially hydrolyzed, and polysaccharides which are mainly produced by means of the bacteria Xanthomonas Campestris.
The polyacrylamides are long chain polymers of the acrylamide with the general formula:
ECH2-CH ~CONH2~ ]n with n = about 50,000 or more. The molecular weight is 3 to 6 million. With partially hydrolyzed polyacrylamides, a part of the amide group - CONH2 ~ is converted into the carboxylate group - COONa - by saponification reaction.
~J2~!30 Polyacrylamides that are hydrolyzed to 10 - 60 percent or preferably 20 - 35 percent are especially well-suited for polymer flooding.
The molecules of partially hydrolyzed polyacryl-amides possess their elongated rod-like shape only in practically non-conductive, i.e. salt-free water, because of the repulsive energy of the negatively loaded carboxyl group and behave like very long stretched elastic fibers.
The length is about 10,000 times the thickness and is about 10~ m.
Solutions of partially hydrolyzed polyacrylamides in fresh water are considerably more viscous than solutions of polysaccharides at the same concentration. Apart from this, the price per kilo is only half as much and polymer solutions of suitable viscosity with partially hydrolyzed polyacrylamides can be produced at a quarter of the cost per cubic meter ~m3~ of flooding liquid compared to that of the polysaccharide. In reservoirs that contain salt water, a polyacrylamide solution using fresh water can be favorably applied after preconditioning the reservoir by flooding with fresh water. Other advantages of the partially hydrolyzed polyacrylamide include, better stability against bacteria and against high temperatures of up to 100C compared to 70C for a polysaccharide.
Solutions of such high molecular materials are not genuine liquids in the rheological sense, The viscosity depends on the velocity gradient. The flow characteristics of this pseudo plastic solution follows the power law:
~ = shear rate ~s 1~
~ ~ ~ = shear strength (dyn~cm2) 3~
n and ~ are constants, ~ is the apparent viscosity at a shear rate of 1 s 1, The exponent, n, is smaller than 1.
For genuine liquids n = 1.
Pseudo plastic liquids are less suitable than genuine liquids of constant viscosity for displacing oil from reservoirs with heterogeneous permeability which is the case for more or less all natural reservoirs. The Darcy law generalized to incorporate pseudo plastic liquids is:
lo 2) ~ 4n . 1 ~ ~ ( p )/n 3~+1 71 ~/n ~ ~
= average velocity = permeability (cm2) = porosity ~/~ = pressure gradient The flow velocity depends, therefore, more strongly on permeability than that of genuine liquids (n = 1).
It is therefore desirable to achieve constant viscosity within the range of the velocity gradient that occurs in an oil reservoir. The velocity gradient along 20 the walls of the pore channel is:
3) ~= ~n l 1 . nr ~n When 1 m of polymer solution per hour, per meter of reservoir thickness is injected into the injection well, a radial flow yields, at a distance of 100 m, a velocity of = 1 cm/h = 2 .8 x 10 4 cm/s. For~ = 10 8 cm2 (1 Darcy), ~ = 0.25 and n = 0.5 the shear rate becomes ~= 7 s 1. In this case the flow curve in the shear rate range below 7 s 1 is decisive. With lower permeabilities, greater distances, lower injection rates the area of interest is still lower, ~30 in other cases also higher.
In practice there occur considerable deviations from the theoretically correct relationships shown above.
As a result of the more difficult passage of the very large molecules through the narrow parts of the pore channels the pressure losses are greater than predicted by theory. At low flow velocities they are a multiple of 1.2 to 1.5 with polysaccharide solutions and a multiple of 2 to 5 with hydrolyzed polyacrylamide solutions. The pore cross section is reduced by adsorption of polymer molecules on the surface of the rock. Therefore, during two phase flow of oil and water or oil and polymer solution only the effective permeability for water should be applied. The lower the absolute permeability, the stronger is the permeability reduction by polymer adsorption.
The usual form of commercial hydrolyzed polyacryl-amides is a fine grained, solid product. Even though it is a water-soluble polymer it is practically impossible to produce a completely molecular dispersed solution. In water, the polymer grains swell and tend to form lumps which require long periods of stirring or special dissolution methods before an apparently homogeneous solution is obtained. Even optically clear solutions contain micro gel particles or aggregates of 10 or 30 molecules which cling to the narrow parts of the pore channeI and lead to a partial blockage.
Multivalent cations ~Fe, Ca, Mg~ especially, can produce larger particles or even lead to coagulation through the cross linking of several molecules C'Mobility of Polymer Solutions in Porous Media", SPE 3683, I. Ershachi and 0 L. L. Handy, Los Angeles, November 1971).
111;3Z~3~
Even though the removal of the undesirable micro particles by means of filtration through a packing of very fine grained material such as diatomacious earth or silica flour is possible, it is only suited for laboratory quantities, not for field applications. The following method for the production of aqueous polysaccharide solutions from polysaccharide is known ~"Improved Injectability of Biopolymer Solution" SPE 5099, D. Lipton, Denver, April 1976).
The fine grained polymer trickles into a blender through a 10 water spray whereby practically every grain is individually ~-wetted. The highly concentrated solution produced (stock solution), e.g. 1 percent, in fresh water is stirred vigorously for several minutes. The solution is subsequently homogenized in a simple manner, whereby it is pumped through perforated plates under high pressure, e.g. with a pressure loss of 10 bar per plate. In order to destroy the insoluble remnants of the bacteria, an enzyme treatment is necessary which lasts for several hours at an increased temperature of 50C. After this treatment has been completed, the stock 2a solution can be diluted with brine, process water or reservoir water available. The injectability in reservoirs with low permeability is not really good in spite of the extensive treatment, as the solution still contains aggregates from a large number of molecules which cling to the narrow parts of the pore channels and cause a partial blockage.
The production of solutions from hydrolyzed polyacrylamides, which is in fine grained form, also takes place with the aid of a blender. As the polyacrylamides are Q very sensitive, they are not forced through a perforated plate.
~2~30 An enzyme treatment is not necessary. A great number ofcommercially available polyacrylamides are either too slowly or incompletely soluble as a result of drying and/or grinding procedure during manufacturing of the product. Some manufacturers therefore supply the product as a concentrated aqueous gel which is a suspension of fine globules in mineral oil. Such liquid polymers are therefore pre-swollen and dissolve much quicker in water. But even with these products, an efficient injectability is not assured. The molecule aggregates that are formed from the polyacrylamides, and partly also from cross-linking by bivalent cations, are trapped in the pore space. In order to obtain the best possible molecular dispersed solution the manufacturers recommend that a stock solution, e.g. 1 percent, be mixed and then be diluted to the required concentration after 24 hours. It is known that solutions of partially hydrolyzed polyacrylamide of high molecular weight are subject to a viscosity reduction caused by shearing when a high shear rate is applied. The longest molecules rupture as a result of the high tensile strain. In using these solutions, it has been recommended that such solutions not be pumped through narrow jets, and that only stirring apparatus with a low revolution ~ate should be used, i.e. centrifugal pumps should not be used. Also the injection rate in flood wells should ~e kept within limits in order to keep the loss of viscosity as low as possible during entry of the polymer solution into the formation. ~See: "The Oil & Gas Journal", July 12, 1976, p. 541. In another publication, it is pointed out that hydrolyzed polyacrylamide is ~1~2~30 disadvantageously influenced by shearing. (See "Fundamentalsof Tertiary Oil Recovery", Petroleum Engineer, July 1976, E. F. Herbeck et al, p. 48-59, 54).
It is an object of the present invention to overcome the problems associated with the pretreatment of polyacrylamide solutions prior to their employment in oil recovery operations by subjecting the polyacrylamide solutions to a controlled, limited shearing treatment.
The Figure shows the result of the change in shear rate on the apparent viscosity of polyacrylamide solutions.
According to the invention there is provided a process for the treatment of aqueous solutions of partially hydrolyzed polyacrylamides prior to the employment of said solutions in enhanced oil recovery operations wherein said solutions contain said polyacrylamide at a concentration less than 1 kg/m3 and said solutions are sheared at shear rates in the range of about 20,000 to about 50,000 s 1.
In a preferred embodiment said shearing is achieved by forcing said aqueous polyacrylamide solutions through perforated plates having holes 1 to 4 mm diameter and said shear rate is selected so as to maintain a pressure loss of between 1 and 3 bar per perforated plate.
Thus there is provided a method for the pretreatment of polyacrylamide solutions by a controlled, limited shearing action wherein solutions of partially hydrolyzed polyacrylamides are sheared at a shear gradient of 20,000 to 50,000 s 1 corresponding to a shearing stress of 500 to 2,000 dynes/cm2.
By the treatment thus described it has been found that solutions of partially hydrolyzed polyacrylamides that are to be used in ~ , enhanced recovery operations were improved and trouble-free injectability was achieved.
The improvement has been demonstrated in the following laboratory tests. A core from a reservoir, or a sandpack with comparable pore space is flooded at a constant rate with the polymer solution. With the sheared solution, ; in accordance with the invention, the flow pressure, except for the first few minutes, (a certain increase in pressure is produced due to adsorption) remains constant even after .
-, ~ .
1~, , ;~ 20 - 7(a) -' , ll~Z~3~
the throughput of large volumes. With unsheared solutions good injecta~ility was achieved only after filtration through fine pored filter media or after a very long stirring period.
Referring to the accompanying Figure, it can be seen that the flow curve of the sheared solution of partially hydrolyzed polyacrylamide is more suited for polymer flooding, as with small velocity gradients, such as prevail in the reservoir, practically constant viscosity is produced ~curve 2~, while the unsheared solution (curve 1) is strongly pseudo plastic. This means that the apparent viscosity at decreasing shear rates increases to values which are too high. A sheared solution at a given pressure gradient is forced more quickly into the reservoir and sweeps a larger part of its lower permeability region. This leads to a higher degree of oil recovery than with an unsheared solution.
Further, according to the method of invention, the injection pressure is considerably reduced by the shearing of the solution of the partially hydrolyzed polyacrylamide.
During flooding through a sandpack with a grain size of 60 - 90Jwm and at a shear rate of 100 s 1 the injection pressure for an unsheared solution of partially hydrolyzed polyacrylamide was Q.38 bar. If the same solution is sheared ~n accordance with the invention the injection pressure is reduced to Q.16 bar. The apparent viscosities at a shear rate of lOQ s shows practically no difference ~7.5 and 7,3 cPl, This effect of the shear treatment on the injection pressure is of special importance for 0 reservoirs with relatively low permeabilities. As the
2~30 injection pressure must not exceed the fracture pressureof the rock, the sheared solution of partially hydrolyzed polyacrylamide, - according to the invention, - allows higher injection rates to be realized and the duration of the flooding project to be reduced.
The shearing equipment should be selected in such a way as to permit the determination of the shear rate.
Stirrers or whirling sections built into pipelines are unsuitable. During pumping through jets, perforated plates or slits, the velocity gradient and the shearing stress are not constant, but do not exceed in the entire flow region a maximum that depends on flow rate or on pressure loss. As during a single passage through a jet not all particles are subjected to the same shearing stress, a multiple throughput is recommended in order to destroy all particles above the critical molecular size.
The pressure loss ~ in jets at high rates of flow is in accordance with the Bernoulli law:
_ 4) ~ _ ~ . C ) p = Density, g/cm3 ~V = Average velocity, cm/s ~ = Pressure, dyne/cm2 C is a ~et factor, which, however, is also dependent on the viscosity at high viscosities. In perforated plates of 2 mm thickness with holes from 1 to 3 mm diameter C is 0.85 for water, 0.65 for an aqueous solution of 0,5 g~l of partially hydrolyzed polyacrylamide and 0.55 for a water solution of 5 g/l.
_g_ ~lV2~3~
In practice the use of perforated plates proved successful for the homogenization of the stock solution and also of the diluted solution. Best results were obtained with 4 perforated plates with a pressure loss of 1.5 to 2 bar.
Improved in;ectability was attained as compared to using homogenization equipment such as whirling sections, static mixers or colloid mills and is also simpler and cheaper.
The concentration of the stock solution is chosen as the highest possible multiple ~5 to 20) of the diluted solution. Concentrations between 100 and 1000 ppm of polyacrylamide are suitable for flooding. Thus, the range of the concentration of the stock solution lies between 2 and lQ g/l ~6 - 30 g/l liquid polymer) as long as the viscosity of the stock solution is not too high which depends princi-pally on the molecular weight of the polymer and the salinity of the water.
As an example, for the continuous production of injectable polymer solutions of about 30 percent partially hydrolyzed polyacrylamide produced from the commercial liquid polymer NALCO Q 41 F ~a product of NALCO Co.), an apparatus was constructed that is capable of a throughput of 5 m3 polymer solution per hour and concentrations of 1.5 g/l liquid polymer = 0.5 g/l polymer in fresh water ~based on dry polymerl.
The liquid polymer is an emulsion of the water-in-oil type. To ensure that the geI pellets are wetted as quickly as possible and can hydrate during the injection of the emulsion into the water an activator must be added.
This process takes place more quickly and completely when the 3Q activator concentration is higher. Therefore, a stock 3g;~
solution with a high concentration ~5 g/l polymer) is first produced, which is diluted with water to the required end concentration ~0.5 g/l polymer) only after it is inverted.
The throughput rate in the bypass of the aforementioned apparatus has been set at 500 liters per hour.
On the suction side of the transportation centrifugal pump the activator and a biocide is added, followed by the dosage of liquid polymer. Three perforated plates each with
The shearing equipment should be selected in such a way as to permit the determination of the shear rate.
Stirrers or whirling sections built into pipelines are unsuitable. During pumping through jets, perforated plates or slits, the velocity gradient and the shearing stress are not constant, but do not exceed in the entire flow region a maximum that depends on flow rate or on pressure loss. As during a single passage through a jet not all particles are subjected to the same shearing stress, a multiple throughput is recommended in order to destroy all particles above the critical molecular size.
The pressure loss ~ in jets at high rates of flow is in accordance with the Bernoulli law:
_ 4) ~ _ ~ . C ) p = Density, g/cm3 ~V = Average velocity, cm/s ~ = Pressure, dyne/cm2 C is a ~et factor, which, however, is also dependent on the viscosity at high viscosities. In perforated plates of 2 mm thickness with holes from 1 to 3 mm diameter C is 0.85 for water, 0.65 for an aqueous solution of 0,5 g~l of partially hydrolyzed polyacrylamide and 0.55 for a water solution of 5 g/l.
_g_ ~lV2~3~
In practice the use of perforated plates proved successful for the homogenization of the stock solution and also of the diluted solution. Best results were obtained with 4 perforated plates with a pressure loss of 1.5 to 2 bar.
Improved in;ectability was attained as compared to using homogenization equipment such as whirling sections, static mixers or colloid mills and is also simpler and cheaper.
The concentration of the stock solution is chosen as the highest possible multiple ~5 to 20) of the diluted solution. Concentrations between 100 and 1000 ppm of polyacrylamide are suitable for flooding. Thus, the range of the concentration of the stock solution lies between 2 and lQ g/l ~6 - 30 g/l liquid polymer) as long as the viscosity of the stock solution is not too high which depends princi-pally on the molecular weight of the polymer and the salinity of the water.
As an example, for the continuous production of injectable polymer solutions of about 30 percent partially hydrolyzed polyacrylamide produced from the commercial liquid polymer NALCO Q 41 F ~a product of NALCO Co.), an apparatus was constructed that is capable of a throughput of 5 m3 polymer solution per hour and concentrations of 1.5 g/l liquid polymer = 0.5 g/l polymer in fresh water ~based on dry polymerl.
The liquid polymer is an emulsion of the water-in-oil type. To ensure that the geI pellets are wetted as quickly as possible and can hydrate during the injection of the emulsion into the water an activator must be added.
This process takes place more quickly and completely when the 3Q activator concentration is higher. Therefore, a stock 3g;~
solution with a high concentration ~5 g/l polymer) is first produced, which is diluted with water to the required end concentration ~0.5 g/l polymer) only after it is inverted.
The throughput rate in the bypass of the aforementioned apparatus has been set at 500 liters per hour.
On the suction side of the transportation centrifugal pump the activator and a biocide is added, followed by the dosage of liquid polymer. Three perforated plates each with
3 holes of 2.5 mm diameter support the homogenizing effect of the centrifugal pump; a destruction of the molecule does not take place at this stage, as the gel pellets have not yet dissolved in the water. This takes place after the solution has been diluted and requires a certain amount of time. One perforated plate with 18 holes of 3.0 mm diameter which is situated just behind the stock solution inlet point into the main flowline primarily serves for the homogeniza-tion of the solution. The actual shearing treatment takes place after dilution and after this diluted polymer solution has flowed through the field flowline to the injection well where it has had about 15 minutes time to hydrate. This shearing treatment is performed with 2 perforated plates with 19 holes each of 2.5 mm diameter, each with a pressure loss of 1.8 bar, and a perforated plate with 22 holes of 2.5 mm diameter with a pressure loss of 1.4 bar. A
trouble-free injectability was achieved and the flow characteristics of the polymer solution were as desired.
trouble-free injectability was achieved and the flow characteristics of the polymer solution were as desired.
Claims (2)
1. A process for the treatment of aqueous solutions of partially hydrolyzed polyacrylamides prior to the employment of said solutions in enhanced oil recovery operations wherein said solutions contain said polyacrylamide at a concentration less than 1 kg/m3 and said solutions are sheared at shear rates in the range of about 20,000 to about 50,000 s-1.
2. The process according to Claim 1 wherein said shearing is achieved by forcing said aqueous polyacrylamide solutions through perforated plates having holes of 1 to 4 mm diameter and said shear rate is selected so as to maintain a pressure loss of between 1 and 3 bar per perforated plate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19772733852 DE2733852B2 (en) | 1977-07-27 | 1977-07-27 | Process for the shear treatment of aqueous solutions of partially hydrolyzed polyacrylamides |
| DEP2733852.9 | 1977-07-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1102030A true CA1102030A (en) | 1981-05-26 |
Family
ID=6014952
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA308,150A Expired CA1102030A (en) | 1977-07-27 | 1978-07-26 | Process for the treatment of aqueous solutions of partially hydrolyzed polyacrylamides |
Country Status (5)
| Country | Link |
|---|---|
| AT (1) | AT365737B (en) |
| CA (1) | CA1102030A (en) |
| DE (1) | DE2733852B2 (en) |
| FR (1) | FR2398769A1 (en) |
| GB (1) | GB2001999B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3422612A1 (en) * | 1984-06-19 | 1985-12-19 | Basf Ag, 6700 Ludwigshafen | METHOD FOR IMPROVING THE DEPOSIT RELATED TO THE PROPERTIES OF AQUEOUS POLYMER SOLUTIONS THAT SERVE THE POLYMER |
| US5139087A (en) * | 1991-05-31 | 1992-08-18 | Union Oil Company Of California | Method for ensuring injectivity of polymer solutions |
| DE4338870C1 (en) * | 1993-11-13 | 1994-11-17 | Rwe Dea Ag | Polymer flooding process for the recovery of oil from underground deposits |
| DE4402547C1 (en) * | 1994-01-28 | 1995-03-23 | Stockhausen Chem Fab Gmbh | Apparatus and process for dissolving water-soluble, pulverulent polymers |
-
1977
- 1977-07-27 DE DE19772733852 patent/DE2733852B2/en active Granted
-
1978
- 1978-07-26 CA CA308,150A patent/CA1102030A/en not_active Expired
- 1978-07-26 FR FR7822187A patent/FR2398769A1/en active Granted
- 1978-07-27 AT AT548178A patent/AT365737B/en not_active IP Right Cessation
- 1978-07-27 GB GB7831355A patent/GB2001999B/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2733852B2 (en) | 1980-02-21 |
| GB2001999B (en) | 1982-02-17 |
| AT365737B (en) | 1982-02-10 |
| FR2398769A1 (en) | 1979-02-23 |
| DE2733852A1 (en) | 1979-02-08 |
| FR2398769B1 (en) | 1982-08-20 |
| GB2001999A (en) | 1979-02-14 |
| ATA548178A (en) | 1981-06-15 |
| DE2733852C3 (en) | 1980-10-09 |
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