EA044351B1 - POLYMER EMULSIONS FOR APPLICATION IN CRUDE OIL EXTRACTION - Google Patents

Description

Field of technology

The present invention relates to improved emulsions of mobility control polymers that can be used to enhance the recovery of crude oil from a subterranean hydrocarbon containing formation. A flooding fluid containing polymer emulsions is injected into a well in contact with a subterranean hydrocarbon-bearing formation. Polymers can be temporarily cross-linked due to labile cross-linking fragments, which leads to shear protection and improved well injection. Shear protection can be measured based on shear viscosity loss, and improved pumpability can be measured based on filtration coefficient, flow rate, and flood fluid viscosity.

State of the art

When extracting oil from petroleum reservoirs, usually in situ using primary recovery methods that use only the natural forces present in the reservoir, only minute portions of the original oil can be recovered. Accordingly, various additional methods have been developed and used to increase the amount of oil recovered. A commonly used secondary method is waterflooding, which involves injecting water into an oil reservoir. As water moves through the reservoir, it displaces the oil in it into one or more production wells, from which the oil is recovered.

One of the problems encountered in waterflooding operations is the relatively low efficiency of water displacement of oil, i.e. water, when moving from the injection well(s) to the production well(s), can channel through certain parts of the reservoir, thereby bypassing other parts of the reservoir. . Poor displacement efficiency may be due, for example, to differences in water mobility relative to oil mobility and changes in permeability within the reservoir that favor flow through some parts of the reservoir and impede flow through other parts.

Various enhanced oil recovery techniques have been used to improve displacement efficiency. To improve the displacement efficiency, aqueous solutions containing high molecular weight water-soluble polymers were used. Such media are more viscous than ordinary water or brine, but are often subject to molecular weight breakdown or decomposition due to shear, temperature, oxidative stress and physical forces acting in the wellbore. This decomposition leads to a decrease in viscosity and a decrease in oil recovery when using secondary and tertiary methods for extracting oil from underground formations. What is needed are waterflood fluids with improved well injection ability, as measured by filtration coefficient, flow rate and viscosity of the waterflood, and waterfloods with improved resistance to viscosity loss due to shear forces.

Brief description of the invention

In one aspect, the present invention is directed to increasing the recovery of crude oil from a subterranean hydrocarbon containing formation. The proposed method involves injecting an aqueous flooding fluid into a well in contact with a subterranean hydrocarbon-containing formation. The aqueous flooding fluid contains injection water and a mobility control agent, wherein the mobility control agent comprises a cross-linked water-soluble polymer. The cross-links are broken to form a water-soluble polymer containing fewer cross-links; wherein the aqueous flooding fluid, when injected into the well, has a filtration coefficient of 1 to about 1.2 and a flow rate of at least 0.1 g/s at a membrane filter size of 5 μm and a pressure of 20 psi (about 138 kPa).

When employing methods to enhance the recovery of crude oil from a subterranean hydrocarbon containing formation, the mobility control agent may comprise an emulsion consisting of an aqueous phase and an oil phase. The aqueous phase may contain a cross-linked water-soluble polymer and the oil phase may contain a hydrocarbon oil and a surfactant, wherein said surfactant comprises a high molecular weight cross-linked multiester and/or multiether polyol.

A further aspect of the present invention is an aqueous flooding fluid comprising an emulsion consisting of an aqueous phase and an oil phase, wherein the aqueous phase contains a cross-linked water-soluble polymer and the oil phase contains a hydrocarbon oil and a surfactant. The surfactant contains a high molecular weight structured multiester and/or multiether polyol wherein the cross-links are broken to form a water-soluble polymer containing fewer cross-links. According to such a method, the aqueous flooding fluid when injected into a well has a filtration coefficient of from about 0.8 to about 1.5 or from about 1 to about 1.5 and a flow rate of at least 0.1 g/s with a membrane filter size of 5 microns and a pressure of 20 psi (approximately 138 kPa).

Brief description of drawings

Fig. 1 is a plot of viscosity at 10.2 s ^-1 (cP) versus shear rate of polymer VII and a commonly used HPAM polymer.

Fig. 2 is a plot of viscosity at 10.2 s ^-1 (cP) versus shear time in seconds at speeds from 14,000 to 16,000 rpm.

Description of preferred embodiments of the invention

The present invention relates to water-soluble, shear-resistant, high molecular weight, cross-linked polymers having improved pumpability and used to enhance the recovery of crude oil from a subterranean hydrocarbon containing formation. According to methods for recovering oil from subterranean hydrocarbon-containing formations, the aqueous flooding fluid contains injection water and a mobility control agent, wherein the mobility control agent contains cross-linked water-soluble polymers, wherein the cross-links are broken to form a water-soluble polymer containing a smaller number of cross-links . The aqueous flooding fluid, when injected into a well, may have a filtration coefficient of from about 0.8 to about 1.1, from 0.95 to about 1.2, or from about 1 to about 1.2 and a flow rate of at least 0.1 g/s at a membrane filter size of 5 µm and a pressure of 20 psi (approximately 138 kPa).

In addition, the aqueous flooding fluid, when injected into a well, may have a filtration coefficient of from about 0.8 to about 1.1, from 0.95 to about 1.2, or from about 1 to about 1.2 and a flow rate of at least 0.1 g/s at 1.2 µm membrane filter size and 20 psi (approximately 138 kPa).

Crosslinkers can be degraded by breaking one or more of the cross-links between the polymer strands under the action of heat, hydrolysis, catalysis, enzymatic catalysis, oxidation, light, reduction, pH, biological influence, electrolysis, or a combination thereof.

The crosslinks can undergo hydrolysis, which allows the viscosity of the composition to change after it is injected into a subterranean hydrocarbon containing formation.

The mobility controlling agent may comprise an emulsion consisting of an aqueous phase and an oil phase, wherein the aqueous phase contains a cross-linked water-soluble polymer and the oil phase contains a hydrocarbon oil and a surfactant, wherein the surfactant contains high molecular weight structured multiesters and /or polyol multiethers.

The aqueous flooding fluid contains an emulsion consisting of an aqueous phase and an oil phase, wherein the aqueous phase contains a cross-linked water-soluble polymer and the oil phase contains a hydrocarbon oil and an emulsifying surfactant or mixture of surfactants. The emulsifying surfactant contains high molecular weight cross-linked polyol multiesters and/or multiethers wherein the cross-links are broken to form a water-soluble polymer containing fewer cross-links and the aqueous flooding fluid when injected into the well has a filtration factor of 1 to about 1 .5 and a flow rate of at least 0.1 g/s with a 5 µm membrane filter size and a pressure of 20 psi (approximately 138 kPa).

The aqueous flooding fluid, when injected into a well, may have a filtration coefficient of from about 0.8 to about 1.4, from about 0.8 to about 1.3, from about 0.8 to about 1.2, from about 0.8 to about 1.2, from about 1 to about 1.4, from about 1 to about 1.3, from about 1 to about 1.2, or from about 1 to about 1.2 at a membrane filter size of 5 μm and a pressure of 20 psi (approximately 138 kPa).

The high molecular weight structured multiesters and/or multiether polyols may have a molecular weight of from about 950 daltons to about 500,000 daltons, from about 950 daltons to about 100,000 daltons, from about 950 daltons to about 50,000 daltons, from about 950 daltons to about 25,000 daltons, from about 950 dalton to about 10,000 dalton, from about 950 dalton to about 5,000 dalton, from about 950 dalton to about 2,500 dalton, from about 1,000 dalton to about 10,000 dalton, from about 1,500 dalton to about 10,000 dalton, from about 2,000 dalton to about 10,000 daltons, about 2,500 daltons to about 10,000 daltons, about 3,000 daltons to about 10,000 daltons, about 4,000 daltons to about 10,000 daltons, or about 5,000 daltons to about 10,000 daltons.

The high molecular weight structured multiesters and/or polyol multiethers may have a molecular weight greater than about 900 daltons, greater than about 1000 daltons, greater than about 1500 daltons, greater than about 2000 daltons, or greater than about 2500 daltons.

The high molecular weight structured surfactant may be a fatty acid, a fatty acid ester, an alcohol, an alkylated alcohol, an oxalkylated alcohol, an alkylated polyol, an oxyalkylated polyol, an alkylated amine, an oxyalkylated amine, an alkylated polyamine, an oxyalkylated polyamine, an alkylated amide, an oxyalkylated amide, an alkylated polyamide, oxyalkylated polyamide, alkylated sulfur compound, oxyalkylated sulfur compound, alkylated phosphorus compound, oxyalkylated phosphorus compound, alkylated silicone-based polymer, oxyalkylated silicone-based polymer, or a combination thereof.

The high molecular weight structured multiester polyol may contain polyoxyethylene sorbitan dioleate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitan tetraoleate, polyoxypropylene sorbitan dioleate, polyoxypropylene sorbitan trioleate, polyoxypropylene sorbitan tetraoleate, polyoxyethylene sorbitan distearate, polyoxyethylene sorbitan tristearate, poly oxyethylene sorbitan tetrastearate, polyoxypropylene sorbitan distearate, polyoxypropylene sorbitan tristearate , polyoxypropylene sorbitan tetrastearate, sorbitol trioleate, sorbitol tetraoleate, sorbitol pentaoleate, sorbitol hexaoleate, sorbitol tristearate, sorbitol tetrastearate, sorbitol pentastearate, sorbitol hexastearate, polyoxyethylene sorbitol dioleate, polyoxyethylene sorbitol trioleate, polyoxyeth ylene sorbitol tetraoleate, polyoxyethylene sorbitol pentaoleate, polyoxyethylene sorbitol hexaoleate, polyoxypropylene sorbitol dioleate, polyoxypropylene sorbitol trioleate, polyoxypropylene sorbitol tetraoleate, polyoxypropylene sorbitol pentaoleate, polyoxypropylene sorbitol hexaoleate, polyoxyethylene sorbitol distearate, polyoxyethylene sorbitol tristearate, polyoxyethylene sorbitol tetrastearate, polyoxyethylene sorbitol pentastearate, polyoxyethylene sorbitol hexastearate, polyoxypropylene sorbitol distearate, polyoxypropylene sorbitol tristearate, polyoxypropylene sorbitol tetrastearate , polyoxypropylene sorbitol pentastearate, polyoxypropylene sorbitol hexastearate, copolymer of poly(12-hydroxystearic acid) and polyethylene oxide or their combined polyol multiethers may contain an alkylated polyglycerol, an oxyalkylated polyglycerol, an alkylated polyglycoside, an oxyalkylate polyglycoside, an alkylated polysaccharide, oxyalkylated polysaccharide or a combination thereof.

The emulsifying surfactant or surfactant mixture may have a hydrophilic-lipophilic balance (HLB) of at least about 8, at least about 9, or at least about 10.

In addition, the emulsifying surfactant or surfactant mixture may have an HLB of from about 8 to about 19.5; from about 9 to about 19.5; or from about 10 to about 19.5.

The emulsifying surfactant may comprise polyoxyethylene sorbitan trioleate, poly(12-hydroxystearic acid)-polyethylene oxide copolymer, polyoxyethylene sorbitol hexaoleate, or a combination thereof.

The aqueous flooding fluid may further contain a surfactant that is sorbitan monooleate, sorbitan dioleate, sorbitan trioleate, or a combination thereof.

The aqueous flooding fluid may further contain a surfactant that is sorbitan monostearate, sorbitan distearate, sorbitan tristearate, or a combination thereof.

The aqueous flooding fluid may further comprise a surfactant having a branched structure, a hyperbranched structure, a dendrimer structure, or a combination of these structures.

The surfactant may be a nonionic surfactant, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, or a combination thereof.

At least one of the surfactants may be an inverting surfactant.

When at least one of the surfactants is an inverting surfactant, the hydrophilic-lipophilic balance of said inverting surfactant is (HLB) at least about 8, at least about 9, or at least about 10.

In addition, the HLB of the inverting surfactant can be from about 8 to about 19.5; from about 9 to about 19.5; or from about 10 to about 19.5.

When at least one of the surfactants is an inverting surfactant, the hydrophilic-lipophilic balance of said inverting surfactant is (HLB) greater than 10, preferably greater than 13.

When the mobility controlling agent contains an emulsion consisting of an aqueous phase and an oil phase, said aqueous phase contains a cross-linked water-soluble polymer and said oil phase contains a hydrocarbon oil and a surfactant, wherein the average size of water droplets in the emulsion is from about 0. 01 µm to about 100 µm, from about 0.01 µm to about 50 µm, from about 0.01 µm to about 40 µm, from about 0.01 µm to about 30 µm, from about 0.01 µm to about 20 µm , from about 0.01 μm to about 10 μm, from about 0.01 μm to about 5 μm, or from about 0.01 μm to about 1 μm, or from about 0.01 μm to about 0.1 μm.

When the mobility controlling agent contains an emulsion consisting of an aqueous phase and an oil phase, said aqueous phase contains a cross-linked water-soluble polymer and said oil phase contains a hydrocarbon oil and a surfactant, wherein the middle

- 3 044351 the size of the water droplets in the emulsion is less than about 5 μm, less than about 4 μm, less than about 3 μm, less than about 2 μm or less than about 1 μm or less than about 0.1 μm.

The hydrocarbon oil may be a mineral oil, a biodiesel oil, an organic solvent, or the like.

The mobility-controlling agent may be a low-viscosity solution that is resistant to the drop in viscosity caused by the high shear experienced during injection. But after injection, higher temperatures and longer residence times within the subterranean formation promote hydrolysis of the cross-linking agents, resulting in increased solution viscosity due to the increased hydrodynamic volume of the mobility-controlling agents (cross-linked water-soluble polymers) that are not cross-linked after hydrolysis. The viscosity of such a resulting solution is equal to or higher than the viscosity of a solution containing an almost identical polymer in which labile cross-links are absent. The higher viscosity of the solution in the formation ensures its effective use in controlling the mobility of hydrocarbons in the formation, improving the secondary/tertiary recovery of hydrocarbons from the formation. Thus, the compositions of the invention, when activated over time by heating/hydrolysis, provide viscosity values in formations that are much higher than those of polymers previously used for hydrocarbon recovery, which can degrade much more quickly under the influence of shear when introduced through the wellbore.

Water-soluble polymers.

Cross-linked water-soluble polymers may contain thermally labile, catalytically labile, enzyme labile, oxidation/reduction labile, optically labile, pH labile, aging labile, biologically labile, hydrophobically labile, hydrolytically labile, or electrolytically labile cross connections. In addition, cross-linking can be achieved by physically intertwining polymer chains, the weaves of which undergo unraveling after the polymer enters the collector.

The polymer emulsion can be prepared by starting with a monomer emulsion, which is polymerized to produce a water-soluble polymer. The starting monomer emulsion is prepared by any suitable means, for example, by the use of emulsifying surfactants (optionally by high shear mixing) or by phase inversion emulsification. Typically, the monomer emulsion is a water-in-oil emulsion, but an oil-in-water emulsion, a bicontinuous emulsion, a triple emulsion, a heterogeneous emulsion, or any combination thereof can also be used. The end result, after polymerization of the original monomer emulsion, is a water-in-oil emulsion or microsuspension of water-swellable polymer granules suspended in a continuous oil phase. The polymer emulsion may be a macroemulsion, a nanoemulsion, a microemulsion, or a combination thereof. The polymer emulsion is applied by diluting it in injection water and then pumping it into the oil reservoir. Typically, the polymer emulsion is inverted or converted into an aqueous continuous emulsion by a high HLB surfactant and high shear during the dilution process. However, such an inversion step is not necessary if the properties of the finished emulsion allow it to pass through the collector without prior inversion. In this latter case, it is expected that the emulsion will invert in the reservoir, causing an increase in the viscosity of the injected fluid.

The water-soluble polymer may be a synthetic polymer or it may be a biopolymer. A common synthetic polymer used as a mobility control polymer is an anionic high molecular weight polyacrylamide prepared by copolymerizing acrylamide with an anionic monomer such as sodium acrylate or sodium 2-acrylamido-2-methylpropanesulfonate. An example of a biopolymer that has been used as a mobility-controlling polymer is xanthan. Other biopolymers, such as diutane or schizophyllan, can also be used as mobility-controlling polymers.

The mobility-regulating polymer may also contain a pH-activated cross-linking monomer (ie, pH labile). The pH-activated cross-linking agent may contain an alkyl boronic acid functional group in the cross-linking agent. Alkylboronic acids, arylboronic acids and alkenylboronic acids, together with borate salts, form borate esters at high pH with polymers containing at least one diol or 1,2-vicinyl-diols, or with a polyol as a cross-linking agent and thus they can serve as pH-activated cross-links. For example, if the reservoir pH is about 7 or lower, the borate ester cross-link will be broken down by hydrolysis. 4 Vinylphenylboronic acid is an example of a monomer that can be incorporated into a polymer to serve as a polymeric, pH-activated cross-linking agent with 1,2-diol-containing biopolymers.

In addition, ionically cross-linked polymers can also be prepared from conventional mobility-controlling polymers by combining them with an ionic cross-linker that will cross-link the polymer such that the cross-links will dissociate or break upon injection of the polymer/ionic cross-linker into the layer The amount of crosslinker and the crosslinker/polymer ratio can be adjusted such that ionic cross-links are stable in the finished form of the polymer or formed when the polymer is injected into the formation, but are unstable and break down once the polymer passes shear points during injection and enters the reservoir. In this case, crosslink instability will be activated due to a change in the crosslinker/polymer environment upon injection (ie, changes in concentration, salinity, temperature, pH, etc.). Examples of ionic cross-linkers that can be used in this manner include multivalent metal ions such as zirconium, chromium, calcium, lithium, cerium and aluminum, or polyelectrolytes such as water-soluble polymers having cationic charges (i.e. cationic polyamine (polyEPI) -DMA) or polydiallyl dimethylammonium chloride (polyDADMAC).Examples of such polymers include, but are not limited to, polymers derived from amine-containing monomers such as N,N-dimethylamine, aziridine, N,N-dimethylaminoethyl acrylate or its quaternized salt, N, N-dimethylaminoethyl methacrylate or its quaternized salt, N,N-dimethylaminoethyl methacrylate or its quaternized salt, N,N-dimethylaminopropylacrylamide or its quaternized salt, N,N-dimethylaminopropyl methacrylamide or its quaternized salt, N,N-dimethyldiallylammonium chloride, N,N-diallylamine Under suitable conditions, these types of ionic cross-linkers form ionic cross-links with typical anionic polyacrylamide mobility control polymers by complexation or Coulomb interaction. For example, a poly(acrylamide/sodium acrylate) copolymer mixture at a concentration of about 100 to 10,000 ppm can form suitable cross-links with zirconium at a concentration of about 3 to 300 ppm in seawater.

In particular, labile cross-linked monomer units are disrupted upon exposure to a stimulus, such as a change in temperature or chemical environment (eg, pH, concentration, or ionic strength). For example, water-soluble polymers may be introduced into an aqueous flood fluid and may undergo hydrolysis after the aqueous flood fluid is introduced into a subterranean hydrocarbon containing formation. Labile cross-linked monomer units can be cross-linked using a covalently hydrolyzable cross-linker, or through ionic interactions between a monomer unit containing a charged hydrolyzable moiety and a monomer unit having an opposite charge, or through hydrophobic interactions resulting from the use of a hydrolytically labile hydrophobic monomer.

When these polymers are dissolved in an aqueous solution, they provide an aqueous polymer solution with significant shear strength as well as relatively low viscosity. If an aqueous solution is exposed to altered conditions, such as injection into a subterranean formation, or elevated temperatures, the viscosity may increase to a value greater than the viscosity of the original solution or to a value greater than the viscosity of an aqueous solution containing the same polymer that lacks hydrolyzable cross-links. communications.

The water-soluble polymers of the present invention may contain from about 1 mol.% to about 99 mol.% acrylamide monomer units. For example, the polymer may contain acrylamide monomers in amounts of about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98 or 99 mol.%. Water-soluble polymers may contain from about 20 mol.% to about 80 mol.% acrylamide monomers. In addition, the water-soluble polymers contain from about 60 mol.% to about 80 mol.% acrylamide monomers.

The water-soluble polymer may contain additional monomer units, which can be selected from the group consisting of acrylic acid or a salt thereof, methacrylic acid or a salt thereof, 2-acrylamido-2-methylpropane sulfonic acid or a salt thereof, acrolein, styrene sulfonic acid or a salt thereof, N-vinylformamide, N-vinylpyrrolidone, N,N-dimethylaminoethyl acrylate or its quaternized salt, N,N-dimethylaminoethyl methacrylate or its quaternized salt, N,N-dimethylaminopropylacrylamide or its quaternized salt, N,N-dimethylaminopropyl methacrylamide or its quaternized salt, N,N chloride -dimethyldiαlylammonium, N,N-diallylamine and a hydrophobic monomer such as lauryl methacrylate. For example, the water-soluble copolymer may further contain monomer units selected from the group consisting of acrylic acid or a salt thereof, 2-acrylamido-2-methylpropane sulfonic acid or a salt thereof, 2-acrylamido-tert-butyl sulfonic acid (ATBS) or a salt thereof , acrolein, dimethylaminoethyl acrylate methyl chloride quaternary (DMAEA.MCQ) and dimethylaminoethyl methacrylate methyl chloride quaternary (DMAEM.MCQ).

If present, each of the monomer units described herein may be included in the polymer in an amount of from about 1 mol.% to about 99 mol.%. For example, the polymer may contain about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,

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26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98 or 99 mol.% the monomer units listed above. Water-soluble polymers may contain from about 10 mol.% to about 60 mol.% of the above monomer units. Water-soluble polymers may contain from about 20 mol.% to about 40 mol.% of the above monomer units.

The water-soluble polymer may be a homopolymer (eg, an acrylamide homopolymer) or a copolymer or terpolymer. In the case of copolymers and terpolymers, the polymer can be any form of copolymer or terpolymer, such as an alternating copolymer, periodic copolymer, random copolymer, or block copolymer (eg, diblock copolymer or triblock copolymer).

The polymer may be a linear polymer or a branched polymer (eg, a hyperbranched polymer or a dendritic polymer).

After exposing a solution containing a water-soluble polymer to an external stimulus, such as an increase in temperature or a change in the chemical environment, such as a change in pH, concentration or ionic strength (for example, after injection into a subterranean formation), and hydrolysis of any cross-linked monomer units, the water-soluble polymer of the invention may have a molecular weight greater than about 500 kDa, or from about 500 kDa to about 50,000 kDa, or from about 1000 kDa to about 25,000 kDa. For example, the molecular weight of a water-soluble polymer may be about 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2 300, 2400, 2500 , 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700,

3800, 3900, 4000, 4100, 4200, 4300, 4400, 4500, 4600, 4700, 4800, 4900, 5000, 5100, 5200, 5300, 5400,5500,

5600, 5700, 5800, 5900, 6000, 6100, 6200, 6300, 6400, 6500, 6600, 6700, 6800, 6900, 7000, 7100, 7200,7300,

7400, 7500, 7600, 7700, 7800, 7900, 8000, 8100, 8200, 8300, 8400, 8500, 8600, 8700, 8800, 8900, 9000,9100,

9200, 9300, 9400, 9500, 9600, 9700, 9800, 9900, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 200 00, 21000, 22000, 23000, 24000, 25000, 26000, 27000, 28000, 29000, 30000, 31000, 32000, 33000, 34000, 35000, 36000, 37000, 38000, 39000, 40000, 41000, 42000, 43000, 44 000, 45000, 46000, 47000, 48000, 49000 or 50000 kDa. Molecular weights can be higher than 50,000 kDa, in the case where some of the cross-links remain unhydrolyzed.

After injection into a subterranean hydrocarbon-containing formation and hydrolysis of any cross-linked monomer units, the water-soluble polymer of the invention may have a charge level (eg, anionic charge level) from about 10 mol.% to about 75 mol.%. For example, the charge level of a water-soluble polymer may be approximately 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 , 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55 , 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74 or 75 mol%. The charge level of water-soluble polymers can be from about 10 mol.% to about 60 mol.% In particular, the charge level of water-soluble polymers can be from about 10 mol.% to about 40 mol.%.

Water-soluble polymers may contain monomer units that are cross-linked using a covalent hydrolyzable cross-linking agent. As an example of a hydrolyzable covalent cross-link, two monomer units can be cross-linked by a moiety containing at least one hydrolyzable group, such as an ester group, carbonate, oxalate, acetal, hemiacetal, hemiaminal or the like. The cross-linking moiety may contain up to about 1000 constituent atoms and may include straight and/or branched chains, ring structures, and optional substituents. Any suitable fragment capable of cross-linking two monomer units and containing at least one hydrolyzable group can be used.

Covalently linked monomer units may have the following formula (IIa):

O OH OH O (Pa) wherein each R is independently selected from the group consisting of -H and -CH3;

Z is selected from the group consisting of a bond and a C ₁ -C ₁ 2-alkylenyl group; and each σννν represents a site of attachment to the first polymer backbone; and each λλλλ represents a site of attachment to a first polymer backbone or a second polymer backbone.

According to one embodiment of formula (IIa), the covalently linked monomer units may have the following formula (IIb):

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(lib).

The cross-linked monomer units listed above can be prepared in several different ways. For example, two acrylamide or methacrylamide monomer units can be cross-linked by adding a dialdehyde compound to the polymer solution. Suitable dialdehyde compound includes, but is not limited to, glyoxal, glutaraldehyde, dialdehyde starch, or any compound containing two or more aldehyde groups.

Hydrolyzable covalently cross-linked monomer units are incorporated into the polymer either by introducing a bifunctional hydrolyzable monomer unit during polymerization or by adding a dialdehyde compound as a cross-linking agent, wherein the cross-linked monomer units may be incorporated into the polymer in an amount of from about 0.1 ppm to approximately 20,000 ppm based on the weight of the polymer. For example, the cross-linked monomer units may be included in the polymer in an amount of from about 0.1 ppm to about 10,000 ppm, from about 0.1 ppm to about 5,000 ppm, from about 0.1 ppm to about 1,000 ppm, or from about 0 .1 ppm to approximately 100 ppm. For example, cross-linked monomer units may be included in the polymer in amounts of about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 , 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700 , 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000 or 20000 ppm.

Water-soluble polymers can be synthesized using any method known in the art, such as, for example, radical polymerization. For example, corresponding polymers can be prepared by free radical polymerization of acrylamide and other vinyl monomers, including an optionally hydrolyzable cross-linking monomer such as glyoxal bis(acrylamide). Optionally, other additives can be added, including additives that can form the desired hydrolyzable cross-links in the polymer before, during or after the polymerization reaction.

In addition, the polymer can be obtained in the form of a dry polymer, an oil-in-water emulsion polymerization polymer, or an invert emulsion polymerization polymer.

The monomer solution can be suspended in a water-immiscible solvent, such as a hydrocarbon oil, together with a high molecular weight structured surfactant described herein. Polymerization is then initiated by adding a small amount of free radical polymerization initiator.

Free radical polymerization initiators typically degrade to form free radicals through thermal, photochemical, redox, or hybrid mechanisms. One example of a thermal initiator includes, but is not limited to, azo compounds such as 2,2'-azobisisobutyronitrile. An example of a redox initiator includes, but is not limited to, tert-butyl hydroperoxide/ferrous ion and ammonium persulfate/sodium bisulfite.

The polymerization reaction is most often carried out at temperatures ranging from about 10°C to about 110°C.

After completion of the polymerization reaction, an optional step may be performed to reduce the residual monomer content of the product. Such a step is carried out, if necessary, by heating the reaction product for additional time or by adding additional initiators or other additives that will react with the residual monomer, or by a combination of both. Optionally, additional processing steps can be performed, for example, to adjust the pH of the product or remove water or other solvents from the reaction product to obtain a solid polymer product. Thus, the form of the final polymer product is determined by the choice of formula and the process steps employed, so that a polymer product may be prepared containing a liquid solution, a liquid emulsion, or a dry solid.

To effectively displace crude oil from a subterranean hydrocarbon containing formation using the methods discussed above, the aqueous flooding fluid has a sufficiently high viscosity. When injected into a subterranean formation, the low-viscosity waterflood fluid can seek the path of least resistance in the reservoir rock and can thereby bypass large quantities of oil. As viscosity increases to a value approaching that of oil, the mobility of the water flooding fluid decreases and it is more effective at displacing oil from the reservoir. Therefore, the aqueous flooding fluid of the present invention contains a high molecular weight water-soluble polymer which, after activation in the subterranean formation (as will be further described below), has a large hydrodynamic volume which has a major effect on the bulk viscosity of such solution. The high bulk viscosity of the waterflood fluid promotes the displacement of oil from the reservoir, ultimately into one or more production reservoirs.

Although high bulk viscosity is desirable when the aqueous flood fluid is in a subterranean hydrocarbon containing formation, high viscosity solutions are difficult to inject into the formation at a sufficiently high rate. Thus, filterability of the aqueous flooding fluid as described above is desirable.

In addition, water-soluble polymers can undergo significant shear deformation during the injection process, resulting in a decrease in the molecular weight and hydrodynamic volume of the polymer and the viscosity of the aqueous flooding fluid, which ultimately affects oil displacement. Thus, the aqueous flooding fluid contains high molecular weight, shear-resistant polymers that are temporarily cross-linked before the aqueous flooding fluid is injected into the subterranean formation. The size of the emulsion droplets primarily affects the ability of the aqueous flooding fluid to be injected into the hydrocarbon containing formation. These properties provide greater ease of injection down into the wellbore and also give the polymer significant shear resistance.

Once the aqueous flooding fluid reaches the subterranean formations, the cross-links hydrolyze over time and upon exposure to higher temperatures in the formation, the cross-links undergo further hydrolysis such that the high molecular weight polymers are no longer cross-linked. Removal of cross-links results in an increase in hydrodynamic volume, resulting in a viscosity equal to or greater than that of the aqueous flooding fluid prior to injection. Next, the high-viscosity aqueous flooding fluid can effectively displace hydrocarbons from the subterranean formation.

Aqueous flooding liquid.

The aqueous flooding fluid contains injection water and a mobility control agent. The mobility controlling agent comprises a cross-linked water-soluble polymer as described above.

Before injection, the viscosity of the aqueous flooding fluid may range from about 0 cP to about 100 cP. After injecting the aqueous flooding fluid into a hydrocarbon-containing subterranean formation, the viscosity of the aqueous flooding fluid may range from about 1 cP to about 5000 cP. This increase in viscosity is due to the decomposition of the cross-linked water-soluble polymer in which the cross-links are broken, resulting in the formation of a water-soluble polymer that is not cross-linked or has fewer cross-links than the cross-linked water-soluble polymer before injection.

The aqueous flooding fluid may contain hydrolyzable cross-linked monomer units. The hydrolyzable cross-linked monomer units are hydrolyzed after injection of an aqueous flooding fluid into a hydrocarbon-containing subterranean formation, wherein the viscosity of the solution after hydrolysis is approximately the same as or higher than the viscosity of the composition before injection.

The water-soluble polymer may be added to the aqueous flooding fluid in an amount from about 100 ppm to about 10,000 ppm. For example, the polymer may be added to the aqueous flooding fluid in an amount of about 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7 500, 8000, 8500, 9000, 9500 or 10000 ppm. In some embodiments, the water-soluble polymer may be added to the aqueous flood fluid in an amount of from about 100 ppm to about 3000 ppm.

Before injection into the subterranean formation, the viscosity of the aqueous flooding fluid may range from about 0 cP to about 100 cP. For example, the viscosity of an aqueous flooding fluid may be approximately 0, 0.001, 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 cP. In addition, the viscosity of the aqueous flooding fluid may range from about 0.001 cP to about 100 cP; from about 0.01 cP to about 100 cP; or from about 0.1 cP to about 20 cP. The viscosity of the aqueous flooding fluid may preferably be from about 0.1 cP to about 10 cP.

After exposure to a stimulus or change in conditions such as temperature, pH, concentration, salt content, or the like. (e.g., when injected into a subterranean formation or added to synthetic seawater), the viscosity of the aqueous flooding fluid may be approximately the same as or greater than the viscosity of the aqueous flooding fluid prior to stimulus application, or the viscosity may be approximately the same as or greater than the viscosity of the aqueous flooding fluid , containing a corresponding water-soluble polymer in which there are no hydrolyzable cross-links. For example, after injection, the viscosity of the aqueous flooding fluid may range from about 1 cP to about 5000 cP, such as 1, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250 , 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1 800, 1900, 2000 , 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, 4100, 4200, 4300, 4400, 4500 , 4600, 4700, 4800, 4900 or 5000 cP.

- 8 044351

Aqueous flooding fluids containing the water-soluble polymers described above remain water-soluble after being introduced into the subterranean formation. Once injected into the reservoir, environmental conditions in the reservoir cause hydrolysis of the cross-links in the water-soluble polymers described above, providing a viscous aqueous fluid for flooding. To improve the mobility of oil in the formation with an aqueous flooding fluid and improve the oil displacement efficiency of an aqueous polymer flooding, the water-soluble polymer that provides the viscosity of the flooding fluid must be able to move freely through the formation without blocking the pores of the formation.

Accordingly, mobility control agents, such as the water-soluble polymers described above, remain water-soluble and do not interfere with the flow of aqueous flooding fluid into the formation. A commonly accepted laboratory test to measure the ability of an aqueous flooding fluid to move through a subterranean formation without clogging the formation pores is called the filtration coefficient test. An example of this type of test is described in American Petroleum Institute standards RP 63. In the filtration coefficient test, a volume under normal conditions of an aqueous flooding fluid with a specified polymer concentration is passed through a filter at constant pressure. After certain volumes of solution have passed through the filter, the time required for the solution to pass through said filter is recorded. The filtration coefficient is calculated as the ratio of the filtration time for the final part of the solution relative to the filtration time for the initial part of the solution of equal volume. Ideally, the water flooding fluid should flow through the filter at a constant rate throughout the test without causing clogging of the pores during filtration, so that the filtration coefficient should be equal to unity. However, the actual measured filtration coefficient is usually greater than unity, so the upper limit of the filtration coefficient under a certain set of conditions is usually used to determine the suitability of an aqueous flooding fluid for mobility control applications.

The aqueous flooding fluid, when injected into a well, may have a filtration coefficient of from about 0.8 to about 1.5, from about 0.8 to about 1.2, from about 0.8 to about 1.2, from about 0.95 to about 1.5, from about 0.95 to about 1.2, from about 0.95 to about 1.2, from about 1 to about 1.5, from 1 to about 1.4, from 1 to about 1 ,3, from 1 to about 1.2 or from 1 to about 1.2 with a 5 µm membrane filter size and a pressure of 20 psi (about 138 kPa).

The aqueous flooding fluid contains the water-soluble polymers described above and exhibits enhanced shear strength. Polymers used for mobility control in enhanced oil recovery are typically high molecular weight, non-crosslinked polymers that are sensitive to the shear forces experienced by the polymer-containing aqueous flooding fluid as it is injected into the formation and as it moves through the formation near the wellbore. Any tight spots in such a high-flow region can cause shear-induced mechanical degradation of the polymer molecular weight, resulting in an undesirable decrease in the viscosity of the aqueous flood fluid. High molecular weight viscous polymer solutions of this type, required for mobility control, are particularly sensitive to mechanical degradation under shear stress. Even if engineering measures are taken to minimize mechanical degradation under shear stresses of the injected aqueous flooding fluid, viscosity loss of up to 25% of the original polymer viscosity is not unusual during shear deformation, with much greater viscosity loss of up to about 80% or more possible.

The shear-induced drop in fluid viscosity can be measured using an industry standard test, such as the test described in American Petroleum Institute standards RP 63, in which an aqueous flooding fluid is passed through a small orifice at high pressure. To determine the magnitude of mechanical destruction under shear stress, the viscosity of the flooding fluid is measured by measuring the difference in the viscosity of the fluid before and after the difficult section. Alternatively, a simple Waring mixer test can be used to induce mechanical shear failure of the aqueous flooding fluid. The amount of viscosity loss experienced with increasing mixer shear time can be measured and used to determine the relative shear strength of flood fluids containing different types of polymers.

Aqueous flooding fluids containing water-soluble polymers can exhibit significant shear resistance. For example, when exposed to shear conditions such as a mixer test, a standard RP 63 test, or injection into a subterranean formation, the aqueous flooding fluids of the present invention may experience a viscosity loss of less than 50%, less than 49%, less than 48%, less 47%, less than 46%, less than 45%, less than 44%, less than 43%, less than 42%, less than 41%, less than 40%, less than 39%, less than 38%, less than 37%, less than 36%, less than 35% , less than 34%, less than 33%, less than 32%, less than 31%, less than 30%, less than 29%, less than 28%, less than 27%, less than 26%, less than 25%, less than 24%, less than 23%, less 22%, less than 21%, less than 20%, less than 19%, less than 18%, less than 17%, less than 16%, less than 15%, less than 14%, less than 13%, less than 12%, less than 11%, less than 10% , less than 9%, less than 8%,

- 9 044351 less than 7%, less than 6%, less than 5%, less than 4%, less than 3%, less than 2% or less than 1%.

When added to the water-soluble polymer, the aqueous flooding fluid may optionally further contain one or more additives. Suitable additives include, but are not limited to, asphaltene inhibitor, wax inhibitor, corrosion inhibitor, scale inhibitor, emulsifier, water clarifier, dispersant, emulsion breaker, hydrogen sulfide scavenger, hydrogen sulfide absorption enhancer, gas hydrate inhibitor, biocide, pH modifier, surfactant -active substance, antioxidant or solvent.

The aqueous flooding fluid may further contain a corrosion inhibitor. Suitable corrosion inhibitors include, but are not limited to, an amidoamine, a quaternary amine, an amide, a phosphate ester, or a combination thereof.

The aqueous flooding fluid may further contain a scale inhibitor. Suitable scale inhibitors include, but are not limited to, phosphate, phosphate ester, phosphoric acid, phosphonate, phosphonic acid, polyacrylamide, acrylamidomethylpropanesulfonate/acrylic acid copolymer salt (AMPS/AA), phosphinated maleic copolymer (PHOS/MA), polymaleic acid terpolymer salt /acrylic acid/acrylamidomethylpropane sulfonate (PMA/AMPS) or a combination thereof.

The aqueous flooding fluid may further contain an emulsifier. A suitable emulsifier includes, but is not limited to, a carboxylic acid salt, an acylation reaction product of a carboxylic acid or a carboxylic anhydride and an amine, an alkyl, acyl or amide derivative of a saccharide (alkylsaccharide emulsifier), or a combination thereof.

The aqueous flooding fluid may further contain a water clarifier. A suitable water clarifier may include, but is not limited to, an inorganic metal salt such as potassium alum, aluminum chloride and aluminum hydrochloride, or an organic polymer such as acrylic acid polymer, acrylamide polymer, polymerized amine, alkanolamine, thiocarbamate and cationic a polymer such as diallyldimethylammonium chloride (DADMAC).

The aqueous flooding liquid may further contain a dispersant. A suitable dispersant may include, but is not limited to, an aliphatic phosphonic acid containing from 2 to 50 carbon atoms, such as hydroxyethyl diphosphonic acid and aminoalkylphosphonic acid, for example, polyaminomethylene phosphonate containing from 2 to 10 nitrogen atoms, wherein, for example, each the nitrogen atom bears at least one methylenephosphonic acid group; examples of the latter compound are ethylenediamine tetra(methylenephosphonate), diethylenetriamine penta(methylenephosphonate), and triamine and tetramine polymethylene phosphonates containing 2 to 4 methylene groups between each nitrogen atom, with at least two of the number of methylene groups in each phosphonate are different. Other suitable dispersing agents include lignin or a lignin derivative such as lignosulfonate, and naphthalene sulfonic acid and a derivative.

The aqueous flooding fluid may additionally contain an emulsion breaking agent. Suitable emulsion breaking agents may include, but are not limited to, dodecyl benzyl sulfonic acid (DDBSA), sodium xylene sulfonic acid (NAXSA), epoxylated and propoxylated compound, anionic surfactant, cationic surfactant, nonionic surfactant, a resin such as phenolic resin or epoxy resin.

The aqueous flooding liquid may further contain a hydrogen sulfide absorbent. A suitable additional hydrogen sulfide scavenger may include, but is not limited to, an oxidizing agent (for example, an inorganic peroxide such as sodium peroxide or chlorine dioxide), an aldehyde (for example, containing from 1 to 10 carbon atoms, such as formaldehyde or glutaraldehyde or (meth)acrolein ), triazine (eg, monoethanolamine triazine and monomethylamine triazine), glyoxal, or a combination thereof. The addition of monomethylamine (MMA) triazines may result in the reduction or elimination of unpleasant MMA odors.

The aqueous flooding fluid may further contain a gas hydrate inhibitor. A suitable gas hydrate inhibitor may include, but is not limited to, a thermodynamic inhibitor (THI), a kinetic inhibitor (KHI), an anti-agglomeration agent (AA), or a combination thereof. A suitable thermodynamic inhibitor may include, but is not limited to, NaCl salt, KCl salt, CaCl ₂ salt, MgCl ₂ salt, NaBr salt, formate saline (eg, potassium formate), polyol (such as glucose, sucrose, fructose, maltose, lactose, gluconate, monoethylene glycol, diethylene glycol, triethylene glycol, monopropylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, monobutylene glycol, dibutylene glycol, tributylene glycol, glycerin, diglycerin, triglycerin, sugar alcohol (eg sorbitol, mannitol)), methanol, propanol, ethanol , glycol ether (such as diethylene glycol monomethyl ether, ethylene glycol monobutyl ether), an alkyl or cyclic alcohol ester (such as ethyl lactate, butyl lactate, methyl ethyl benzoate), or a combination thereof. Suitable kinetic inhibitor and anti-agglomer agent

- 10 044351 tions include, but are not limited to, polymer, copolymers, polysaccharide (such as hydroxyethylcellulose (HEC), carboxymethylcellulose (CMC), starch, starch derivatives and xanthan), lactam (such as polyvinylcaprolactam, polyvinyl lactam), pyrrolidone (such as polyvinylpyrrolidone with different molecular weights), surfactant (such as fatty acid salt, ethoxylated alcohol, propoxylated alcohol, sorbitan ester, ethoxylated sorbitan ester, polyglycerol fatty acid ester, alkyl glucoside, alkyl polyglucoside, alkyl sulfate, alkyl sulfonate, alkyl ether sulfonate, aromatic alkyl sulfonate , alkyl betaine, alkyl amidobetaine), a hydrocarbon-based dispersant (such as lignosulfonate, iminodisuccinate, polyaspartate), an amino acid, proteins, or a combination thereof.

The aqueous flooding fluid may further contain a biocide. Any biocide suitable for use in oil fields can be used. The biocide may be included in the composition in an amount from about 0.1 ppm to about 1000 ppm, for example 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900 or 1000 ppm.

Suitable biocide includes, but is not limited to, an oxidizing or non-oxidizing biocide. Suitable non-oxidizing biocide includes, for example, an amine compound (eg, a quaternary amine compound and cocodiamine), a halogenated compound (eg, bronopol and 2,2-dibromo-3nitrilopropionamide (DBNPA)), a sulfur compound (eg, isothiazolone, carbamate, and metronidazole), and phosphonium quaternary salt (eg tetrakis(hydroxymethyl)phosphonium sulfate (THPS)). Suitable oxidizing biocide includes, for example, sodium hypochlorite, trichloroisocyanuric acid, dichloroisocyanuric acid, calcium hypochlorite, lithium hypochlorite, chlorinated hydantoin, stabilized sodium hypobromite, activated sodium bromide, brominated hydantoin, chlorine dioxide, ozone, peroxide, or a combination thereof.

The aqueous flooding fluid may further contain a pH modifier. Suitable pH modifier includes, but is not limited to, an alkali metal hydroxide, an alkali metal carbonate, an alkali metal bicarbonate, an alkaline earth metal hydroxide, an alkaline earth metal carbonate, an alkaline earth metal bicarbonate, or a combination thereof. Typical pH modifiers include NaOH, KOH, Ca(OH) ₂ , CaO, _Na2CO3 , _KHCO3 , _K2CO3 , _{NaHCO3 ,} MgO and Mg(OH) ₂ .

The aqueous flooding fluid may further contain a surfactant. The surfactant may be a cationic surfactant, an anionic surfactant, an amphoteric surfactant, a zwitterionic surfactant, or a nonionic surfactant. A surfactant can help improve oil recovery from a reservoir. The surfactant may be added to the aqueous flooding fluid in an amount from about 100 ppm to about 10,000 ppm, such as 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000 or 10000 ppm.

Suitable surfactant includes, but is not limited to, an anionic surfactant, cationic surfactant or nonionic surfactant. The anionic surfactant may be an alkylaryl sulfonate, olefin sulfonate, paraffin sulfonate, alcohol sulfate, alcohol ether sulfate, alkyl carboxylate, alkyl ether carboxylate, alkyl and ethoxylated alkyl phosphate ether, mono- and dialkyl sulfosuccinate and sulfosuccinamate, alkyl or alkyl ether sulfate and sulfonate. such as a C ₁ 4-C ₂ 4-alpha olefin sulfonate, a C ₁₃ -C ₁₈ alcohol ether sulfate, a C ₁₅ -C ₁₇ internal olefin sulfonate or a C ₁₂ -C ₁₈ ester sulfonate.

The cationic surfactant may be a quaternary alkyltrimethyl ammonium salt, a quaternary alkyldimethylbenzyl ammonium salt, a quaternary dialkyldimethyl ammonium salt, an imidazolinium salt, or a combination thereof.

The nonionic surfactant may be an alcohol alkoxylate, an alkylphenol alkoxylate, an ethylene oxide-propylene oxide-butylene oxide block copolymer, an alkyl dimethyl amine oxide, an alkyl bis(2-hydroxyethyl) amine oxide, an alkyl amidopropyl dimethyl amine oxide, an alkyl amidopropyl bis(2-hydroxyethyl) amine oxide, an alkyl polyglucoside. , polyalkoxylated glyceride, sorbitan ether, polyalkoxylated sorbitan ether, alkyl polyethylene glycol ether and diester. Also included are betaine and sultan, an amphoteric surfactant such as alkyl amphoacetate and amphodiacetate, alkyl amphopropionate and amphodipropionate, alkyl iminodipropionate, or a combination thereof.

The aqueous flooding fluid may further contain a solvent. Suitable solvent includes, but is not limited to, water, isopropanol, methanol, ethanol, 2-ethylhexanol, heavy aromatic naphtha, toluene, ethylene glycol, ethylene glycol monobutyl ether (EGMBE), diethylene glycol monoethyl ether, xylene, or a combination thereof. Suitable polar solvents suitable for the composition of the above composition include water, saline, seawater, alcohol (including straight chain or branched aliphatic alcohol such as methanol, ethanol, propanol, isopropanol, butanol, 2-ethylhexanol, hexanol , octanol, decanol, 2-butoxyethanol, etc.), glycol or derivative (ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, monobutyl

- 11 044351 ethylene glycol ether, etc.), ketone (cyclohexanone, diisobutyl ketone), N-methylpyrrolidinone (NMP), N,N-dimethylformamide, etc. A suitable non-polar solvent suitable for the composition of the above composition includes an aliphatic solvent such as pentane, hexane, cyclohexane, methylcyclohexane, heptane, decane, dodecane, diesel fuel and the like; an aromatic solvent such as toluene, xylene, heavy aromatic naphtha, a fatty acid derivative (acid, ester, amide) and the like.

The solvent may be monoethylene glycol, methanol, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), tetrahydrofuran (THF), or a combination thereof.

The aqueous flooding fluid may further contain a compound that enhances the hydrogen sulfide scavenging activity of the composition described. Such a compound may be a quaternary ammonium compound, an amine oxide, an ionic or nonionic surfactant, or a combination thereof. Suitable quaternary amine compound may include, but is not limited to, alkyl benzyl ammonium chloride, benzyl cocoalkyl (C ₁₂ -C ₁₈ )dimethylammonium chloride, dicocoalkyl (C ₁₃ -C ₁₈ )dimethyl ammonium chloride, dital dimethyl ammonium chloride, di(hydrogenated tall alkyl) methyl chloride dimethyl quaternary ammonium, methyl bis(2hydroxyethyl cocoalkyl(C ₁₂ -C ₁ 8) quaternary ammonium chloride, dimethyl (2-ethyl) tallow ammonium methyl sulfate, n-dodecylbenzyldimethylammonium chloride, n-octadecylbenzyldimethyl ammonium chloride, ndodecyltrimethylammonium sulfate, soy alkyltrichloride methylammonium, hydrogenated tallow alkyl(2-ethylhexyl)dimethyl quaternary ammonium methyl sulfate or a combination thereof.

A suitable amine oxide compound may include, but is not limited to, a fatty amine oxide such as stearyl dimethyl amine oxide, lauryl dimethyl amine oxide, cocamidopropyl amine oxide, ether amine oxide such as bis-(2-hydroxyethyl) isodecyloxypropyl amine oxide, or a combination thereof. A suitable nonionic surfactant may include, but is not limited to, polyoxyethylene glycol alkyl ether, polyoxypropylene glycol alkyl ether, polyoxyethylene glycol nonylphenol ether, poloxamer, diethanolamine cocamide, polyethoxylated tallowamine, or a combination thereof.

The listed compounds may be present in an amount of from about 0.01 wt.% to about 20 wt.%, from about 1 wt.% to about 10 wt.%, from about 2 wt.% to about 9 wt.%, from about 3 wt.% to about 8 wt.%, from about 4 wt.% to about 7 wt.%, or from about 5 wt.% to about 6 wt.%.

The hydrogen sulfide absorption enhancer compound may be added to the liquid or gas at the same time as the flooding liquid, or it may be added separately.

The aqueous flooding fluid may further contain an asphaltene inhibitor. Suitable asphaltene inhibitors include, but are not limited to, aliphatic sulfonic acid; alkylaryl sulfonic acid; arylsulfonate; lignosulfonate; alkylphenol/aldehyde resin and the like sulfonated resin; polyolefin ester; polyolefin imide; a polyolefin ester with an alkyl, alkylenephenyl or alkylenepyridyl functionality; polyolefin amide; polyolefin amide with an alkyl, alkylenephenyl or alkylenepyridyl functional group; polyolefin imide with an alkyl, alkylenephenyl or alkylenepyridyl functional group; alkenyl/vinyl pyrrolidone copolymer; graft copolymer of polyolefin with maleic anhydride or vinylimidazole; hyperbranched polyesteramide; a polyalkoxylated asphaltene, an amphoteric fatty acid, an alkyl succinate salt, sorbitan monooleate, polyisobutylene succinic anhydride, or a combination thereof.

The aqueous flooding fluid may further contain a wax inhibitor. A suitable wax inhibitor includes, but is not limited to, a wax crystal modifier, a dispersant/wax crystal modifier combination, or a combination thereof. Suitable wax crystal modifiers include, but are not limited to, alkyl acrylate copolymer, alkyl acrylate vinyl pyridine copolymer, ethylene vinyl acetate copolymer, maleic anhydride ester copolymer, branched polyethylene, naphthalene, anthracene, microcrystalline wax, asphaltene, or a combination thereof. Suitable dispersant includes, but is not limited to, dodecylbenzenesulfonate, oxyalkylated alkylphenol, oxyalkylated alkylphenol resin, or a combination thereof.

The aqueous flooding fluid may further contain an antioxidant. Any antioxidant suitable for use in oil fields can be used. A typical antioxidant includes, but is not limited to, sulfite, thiocyanate, thiosulfate, or a combination thereof. The antioxidant may be included in the composition in an amount from about 1 ppm to about 1000 ppm, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70 , 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900 or 1000 ppm.

The compositions prepared according to the present invention may further contain additional functional agents or additives that provide a beneficial property. Additional agents or additives will vary depending on the aqueous flood fluid being produced and its intended use, as will be appreciated by one skilled in the art.

As used herein, the term alkyl refers to a linear or branched hydrocarbon radical preferably containing 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 , 17, 18, 19,

20, 21, 22, 23, 24, 25, 26, 27, 28, 39, 30, 31 or 32 carbon atoms. Alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl. Alkyl groups may be unsubstituted or contain one or more suitable substituents as defined below.

As used herein, the term alkylenyl or alkylene refers to a divalent group derived from a saturated, straight or branched hydrocarbon chain of 1 to 50 carbon atoms. The term C ₁ -C ₆ -alkylene refers to those alkylene or alkylenyl groups that contain from 1 to 6 carbon atoms. Suitable examples of alkylenyl groups include, but are not limited to, -CH ₂ -, -CH(CH3)-, -CHSi)-, -CH(CH(CH3)(C2H5))-, -C(H)(CH3)CH2CH2 -, -C(CH3)2-, -CH2CH2-, -CH2CH2CH2-, -CH2CH2CH2CH2- and -CH2CH(CH3)CH2-. Alkylenyl groups may be unsubstituted or contain one or more suitable substituents as defined below.

As used herein, the term alkenyl refers to a straight or branched hydrocarbon radical preferably containing 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 , 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 39, 30, 31 or 32 carbon atoms and having one or more carbon-carbon double bonds. The alkenyl group includes, but is not limited to, ethenyl, 1-propenyl, 2-propenyl (allyl), isopropenyl, 2-methyl-1-propenyl, 1-butenyl and 2-butenyl. Alkenyl groups may be unsubstituted or contain one or more suitable substituents as defined below.

As used herein, the term alkenylenyl or alkenylene refers to a divalent group derived from a straight or branched chain hydrocarbon of 2 to 50 carbon atoms that contains at least one carbon-carbon double bond. Suitable examples of alkenylenyl groups include, but are not limited to, -C(H)=C(H)-, -C(H)=C(H)-CH2-, -C(H)=C(H)-CH2- CH2—, —CH2—C(H)=C(H)—CH2—, —C(H)=C(H)—CH(CH3)— and —CH ₂ —C(H)=C(H)— CH (CH ₂ CH _h )—. Alkenylenyl groups may be unsubstituted or contain one or more suitable substituents as defined below.

As used herein, the term alkynyl refers to a straight or branched hydrocarbon radical preferably containing 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 , 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 39, 30, 31 or 32 carbon atoms and having one or more carbon-carbon triple bonds. The alkynyl group includes, but is not limited to, ethynyl, propynyl and butynyl. Alkynyl groups may be unsubstituted or contain one or more suitable substituents as defined below.

As used herein, the term alkynylenyl or alkynylene refers to a divalent unsaturated hydrocarbon group derived from a straight or branched chain hydrocarbon containing from 2 to 50 carbon atoms and having at least one carbon-carbon triple bond. Suitable examples of alkynylene groups include, but are not limited to, CC, CCSI; , S S SI; SI; .. SI; S S SI; , S SSISiz) and —SSH—

C=C—CH(CH ₂ CH ₃ )—. Alkynylenyl groups may be unsubstituted or contain one or more suitable substituents as defined below.

As used herein, the term alkoxy refers to an alkyl group, as defined herein, attached to the host molecular moiety via an oxygen atom.

As used herein, the term aryl refers to monocyclic, bicyclic or tricyclic aromatic radicals such as phenyl, naphthyl, tetrahydronaphthyl, indanyl and the like; optionally containing one or more suitable substituents, preferably from 1 to 5 suitable substituents as defined below.

The term carbonyl, (C=O) or -C(O)- (as used in expressions such as alkylcarbonyl, alkyl -(C=O)— or alkoxycarbonyl) refers to the addition of a >C=O moiety to a second moiety, such as an alkyl group or amino group (i.e., amido group). Alkoxycarbonylamino (i.e. alkoxy(C=O)—NH—) refers to the alkylcarbamate group. Herein, a carbonyl group is also equivalently defined as (C=O). Alkylcarbonylamino belongs to groups such as acetamide.

As used herein, the term cross-link refers to a bond that connects one monomer unit of a polymer chain to another monomer unit of a polymer chain. Said bond may be a covalent bond or an ionic bond.

As used herein, the term cycloalkyl refers to a monocyclic, bicyclic or tricyclic carbocyclic radical (e.g., cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclopentenyl, cyclohexenyl, bicyclo[2,2,1]heptanyl, bicyclo[3,2 ,1]octanyl and bicyclo[5,2,0]nonanyl, etc.), optionally containing 1 or 2 double bonds. The cycloalkyl groups may be unsubstituted or contain one or more suitable substituents, preferably from 1 to 5 suitable substituents as defined above.

- 13 044351

As used herein, the term halo or halogen refers to a fluorine, chlorine, bromine or iodine radical.

As used herein, the term heteroalkylenyl or heteroalkylene refers to a divalent group derived from a saturated, straight or branched hydrocarbon chain in which at least one atom is a heteroatom such as O, S, N, Si or P. The terms CrCmheteroalkylenyl, Cl- Cl ₂ -heteroalkylenyl and C ₁ -C ₆ -heteroalkylene refer to those heteroalkylene or heteroalkylenyl groups containing from 1 to 24 atoms, from 1 to 12 atoms or from 1 to 6 constituent atoms, respectively, wherein said atoms are either carbon, or heteroatom. Suitable examples of heteroalkylenyl groups include, but are not limited to, -O(CH ₂ CH ₂ O) _n - and -O(CH ₂ CH ₂ CH ₂ O) _n -, where each n is independently from 1 to 12. Heteroalkylenyl groups may be unsubstituted or contain one or more suitable substituents as defined below.

As used herein, the term heteroaryl refers to a monocyclic, bicyclic or tricyclic aromatic heterocyclic group containing on the ring(s) one or more heteroatoms selected from O, S and N. Heteroaryl groups include, but are not limited to, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, thienyl, furyl, imidazolyl, pyrrolyl, oxazolyl (e.g. 1,3-oxazolyl, 1,2-oxazolyl), thiazolyl (e.g. 1,2-thiazolyl, 1,3-thiazolyl), pyrazolyl, tetrazolyl, triazolyl ( e.g. 1,2,3-triazolyl, 1,2,4-triazolyl), oxadiazolyl (e.g. 1,2,3-oxadiazolyl), thiadiazolyl (e.g. 1,3,4-thiadiazolyl), quinolyl, isoquinolyl, benzothienyl , benzofuryl and indolyl. Heteroaryl groups may be unsubstituted or contain one or more suitable substituents, preferably from 1 to 5 suitable substituents as defined below.

As used herein, the term heterocycle refers to a monocyclic, bicyclic or tricyclic group containing from 1 to 4 heteroatoms selected from N, O, S(O) _n , NH or ^NRx , where ^Rx is a suitable substituent. Heterocyclic groups optionally contain 1 or 2 double bonds. The heterocyclic group includes, but is not limited to, azetidinyl, tetrahydrofuranyl, imidazolidinyl, pyrrolidinyl, piperidinyl, piperazinyl, oxazolidinyl, thiazolidinyl, pyrazolidinyl, thiomorpholinyl, tetrahydrothiazinyl, tetrahydrothiadiazinyl, morpholinyl, oxetanyl, tetrahydrodiazinyl, o xazinil, oxathiazinyl, indolinil, isoindolinyl, quinuclidinil, chromanil , isochromanil and benzoxazinil. Examples of monocyclic saturated or partially saturated ring systems are tetrahydrofuran-2-yl, tetrahydrofuran-3-yl, imidazolidin-1-yl, imidazolidin-2-yl, imidazolidin-4-yl, pyrrolidin-1-yl, pyrrolidin-2-yl , pyrrolidin-3-yl, piperidin-1-yl, piperidin-2-yl, piperidin-3-yl, piperazin-1-yl, piperazin-2-yl, piperazin-3-yl, 1,3-oxazolidin-3 -yl, isothiazolidinyl, 3-thiazolidin-3-yl, 1,2-pyrazolidin-2-yl, 1,3-pyrazolidin-1-yl, thiomorpholin-yl, 1,2-tetrahydrothiazin-2-yl, 1,3 -tetrahydrothiazin-3-yl, tetrahydrothiadiazin-yl, morpholin-yl, 1,2-tetrahydrodiazin-2-yl, 1,3-tetrahydrodiazin-1-yl, 1,4-oxazin-2-yl and 1,2,5 -oxathiazin-4-yl. Heterocyclic groups may be unsubstituted or contain one or more suitable substituents, preferably 1 to 3 suitable substituents as defined below.

As used herein, the term high molecular weight, when referring to a water-soluble polymer, refers to a polymer having a molecular weight of at least about 500 kDa. In some embodiments, the term high molecular weight refers to a polymer that has a molecular weight of at least about 5000 kDa.

As used herein, the term hydrocarbon liquid refers to an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons may be aromatic hydrocarbons (arenes), alkanes, alkenes, cycloalkanes and alkyne-based compounds. Most naturally occurring hydrocarbons are found in crude oil, where decayed organic matter provides an abundance of carbon and hydrogen, which when bound can chain together to form seemingly endless chains. Hydrocarbons may be saturated hydrocarbons (alkanes) consisting entirely of single bonds, and these hydrocarbons are saturated with hydrogen. The general formula for saturated hydrocarbons is C _n H _2n+2 (if they are non-cyclic structures). Saturated hydrocarbons are the basis of petroleum fuels and occur in the form of both linear and branched compounds. Hydrocarbons with the same molecular formula but different structural formulas are called structural isomers. As indicated in the example of 3-methylhexane and its higher homologues, branched hydrocarbons can be chiral. Chiral saturated hydrocarbons make up the side chains of biomolecules such as chlorophyll and tocopherol. Hydrocarbons may be unsaturated hydrocarbons containing one or more double or triple bonds between carbon atoms, such as alkenes and alkynes, as defined above. The hydrocarbons may be cycloalkanes, which are hydrocarbons containing one or more carbon rings to which hydrogen atoms are attached. The hydrocarbons may be aromatic hydrocarbons, also known as arenes, which are hydrocarbons containing at least one aromatic ring. Hydrocarbons may be gases (for example, methane and propane), liquids (for example, hexane and benzene), waxes or low melting point solids (for example, paraffin wax and naphthalene), or polymers (for example, polyethylene, polypropylene and polystyrene). The hydrocarbons may be a liquid hydrocarbon. The liquid hydrocarbon may be any type of liquid hydrocarbon, including, but not limited to, crude oil, heavy oil, processed residual oil, bituminous oil, coker oil, coker gas oil, catalytic cracker feedstock, gas oil, naphtha, fluid catalytic cracking slurry, diesel fuel, heating oil, jet fuel, gasoline and kerosene.

As used herein, the term hydrodynamic volume refers to a measure of the size of the polymer in solution, with such volume having a major effect on the bulk viscosity of the polymer solution. Hydrodynamic volume can further refer to the volume of the polymer chain when it is in solution. In the case of a polymer, this volume may vary depending on how well the polymer interacts with the solvent and depending on the molecular weight of the polymer. The properties of a solvent can be influenced by the concentration and type of ionic compounds dissolved in the solvent.

As used herein, the term hydrolyzable refers to a bond or moiety that can be cleaved when water is added.

As used herein, the term hydrolyzable cross-link refers to a cross-link as defined above that can be cleaved upon hydrolysis (addition of water).

As used herein, the term hydroxy refers to a -OH group.

As used herein, a constituent atom refers to a multivalent atom (eg, a C, O, N, S, or P atom) in a chain or ring system forming part of a chain or ring. For example, in pyridine, five carbon atoms and one nitrogen atom are the constituent atoms of the ring. In diethyl ether, four carbon atoms and one oxygen atom are the constituent atoms of the chain. The constituent atoms will be replaced to their normal valency. For example, in an alkylenyl chain, each carbon atom will contain two hydrogen atoms, or one hydrogen atom and one other substituent (eg, an alkyl group or hydroxyl group) or two substituents (eg, two alkyl groups). Alternatively, the carbon atom may be replaced by an oxo group to form a -C(O)- group.

As used herein, the term oxo refers to a double-bonded oxygen (=O) radical where the bonding partner is a carbon atom. Such a radical can also be considered a carbonyl group.

As used herein, the term substituent is meant to mean a chemically acceptable functional group that is substituted on any suitable atom of such group. Suitable substituents include, but are not limited to, halo groups, perfluoroalkyl groups, perfluoroalkoxy groups, alkyl groups, alkenyl groups, alkynyl groups, hydroxy groups, oxo groups, mercapto groups, alkylthio groups, alkoxy groups, aryl or heteroaryl groups, aryloxy or heteroaryloxy groups, aralkyl or heteroaralkyl groups, aralkoxy or heteroaralkoxy groups, HO—(C=O)— groups, heterocyclic groups, cycloalkyl groups, amino groups, alkyl and dialkylamino groups, carbamoyl groups, alkylcarbonyl groups, alkoxycarbonyl groups, alkylaminocarbonyl groups, dialkylamino carbonyl groups groups, arylcarbonyl groups, aryloxycarbonyl groups, alkylsulfonyl groups, arylsulfonyl groups, groups according to the formula -(OCH2)tOH, where t is from 1 to 25, and groups according to the formula -alkylenyl-(OCH ₂ ) _tOH , where t is from 1 to 25. Those skilled in the art will understand that many substituents may contain additional substituents.

As used herein, the term reservoir refers to any suitable container that can receive hydrocarbon fluid displaced from a subterranean formation. An example of a suitable reservoir includes, but is not limited to, pipelines, tanks, ships, floating production, storage and offloading (FPSOs), floating storage and offloading (FSOs) or any installation in which a hydrocarbon liquid can be transported and stored.

As used herein, the term viscosity, expressed as the ratio of shear stress (force per unit area) to shear rate (rate of change of shear strain), refers to a fluid's resistance to flow. Viscosity can be further described as the internal friction of a moving fluid. A fluid with high viscosity can resist movement because its molecular composition provides significant internal friction. A fluid with low viscosity can move easily because when it is in motion, its molecular composition results in very little friction.

In this document, for listing numeric ranges, each intermediate value within the range is explicitly given to the same degree of precision. For example, for the range from 6 to 9, in addition to the values 6 and 9, the values 7 and 8 are assumed, and for the range from 6.0 to 7.0, the values 6.0, 6.1, 6.2, 6.3 are explicitly considered. 6.4, 6.5, 6.6, 6.7, 6.8, 6.9 and 7.0.

Unless otherwise specified, all technical and scientific terms used herein have the same meanings as commonly understood by one skilled in the art. When

- 15 044351 contradictions this document, including definitions, will govern. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein may be used in the practice or testing of the present invention. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods and examples described herein are illustrative only and are not intended to be limiting.

As used herein, the terms constitute, include, have, has, may, contain, and variations thereof are intended to be non-limiting transitional phrases, terms or words that do not preclude the possibility of additional actions or structures. Singular forms include references to the plural unless the context clearly indicates otherwise. The present invention also includes other embodiments comprising, consisting of, and essentially consisting of embodiments of the invention or elements presented herein, whether explicitly stated or not.

The compounds, compositions, methods and processes of the present invention will be better understood by reference to the following examples, which are intended to illustrate and not limit the scope of the present invention.

Examples

The foregoing description may be better understood by reference to the following examples, which are provided for purposes of illustration and are not intended to limit the scope of the present invention. All reagents were purchased from commercial sources and used as received unless otherwise stated. K,K'-(1,2-dihydroxyethylene)bisacrylamide, also known as glyoxal bis(acrylamide), is abbreviated herein as GBA.

Example 1: General procedure for preparing poly(acrylic acid-acrylamide).

The poly(acrylic acid-acrylamide) product was prepared by polymerizing a water-in-oil emulsion containing an aqueous monomer phase and an external hydrocarbon oil phase. The monomer phase contained an aqueous mixture of about 29 mol% acrylic acid and 71 mol% acrylamide, neutralized in an ice bath with sodium hydroxide solution to a pH of 7 to 8.5. In addition, a glyoxal bisacrylamide-containing solution as a cross-linking agent, sodium formate as a chain transfer agent and diethylenediaminetetrasodium tetraacetate as a chelating agent were added to the monomer phase. A solution containing glyoxal bisacrylamide was prepared by adding glyoxal to an aqueous acrylamide solution neutralized with sodium hydroxide solution to a pH of 8 to 8.5 and stirring the resulting mixture at 37°C for 2 to 3 hours. The oil phase contained a hydrocarbon oil and one or more surfactants.

The emulsion was prepared by adding the monomer phase to the oil phase while shaking at 38 to 44°C and stirring for a minimum of 30 min.

Polymerization was initiated by adding 2,2'-azobisobutyronitrile and purging with nitrogen at a reaction temperature of 38 to 44°C. After the conversion of the polymerization reaction reached 85%, the emulsion was subjected to subsequent heating at 57°C or higher for at least one hour to complete the polymerization and reduce the amount of monomer residues.

Dissolution of the polymer emulsion in synthetic sea salt water was accomplished by shear mixing the emulsion in sea salt water in the presence of a nonionic surfactant with a high hydrophilic-lipophilic balance (HLB) at a concentration of less than 10% based on the weight of the emulsion polymer. A portion of the freshly prepared polymer solution was used immediately to determine the filtration coefficient and measure bulk viscosity. Another part of the solution was activated in an oven at 70°C for 5 to 22 hours to determine the filtration coefficient and measure the bulk viscosity.

Example 2. Product I.

Product I was prepared following the general procedure described in example 1.

The monomer phase consisted of 370.676 g of 50.30 wt.% acrylamide, 137.082 g of deionized water and 78.730 g of acrylic acid neutralized in an ice bath containing 84.000 g of 50 wt.% aqueous sodium hydroxide solution. In addition, a glyoxal bisacrylamide-containing solution consisting of 0.120 g of 1 wt.% glyoxal solution, 9.940 g of 50.3 wt.% acrylamide and 0.80 g of 1 wt.% sodium hydroxide solution, 0.350 g of sodium formate and 0.090 g tetrasodium diethylenediaminetetraacetate. The oil phase consisted of 280,000 g of paraffin solvent (Exxsol D80), 13,060 g of sorbitan monooleate (Span® (Span) 80) and 21,940 g of polyoxyethylene sorbitan trioleate (Tween® (Tween) 85). 0.528 g of 2,2'-azobisisobutyronitrile was used for polymerization.

Example 3 Product II.

Product II was prepared following the general procedure described in Example 1. The monomer phase consisted of 370.676 g of 50.30 wt.% acrylamide, 137.257 g of deionized water and 78.730 g of acrylic acid,

- 16 044351 neutralized in an ice bath containing 84,000 g of 50 wt.% aqueous sodium hydroxide solution. In addition, a solution containing glyoxal bisacrylamide was added to the monomer phase, consisting of 0.120 g of 1 wt.% glyoxal solution, 9.940 g of 50.3 wt.% acylamide and 0.80 g of 1 wt.% sodium hydroxide solution, 0.175 g of sodium formate and 0.090 g tetrasodium diethylenediaminetetraacetate. The oil phase consisted of 280,000 g of paraffin solvent (Exxsol D80), 13,060 g of sorbitan monooleate (Span® (Span) 80) and 21,940 g of polyoxyethylene sorbitan trioleate (Tween® (Tween) 85). 0.528 g of 2,2'-azobisisobutyronitrile was used for polymerization.

Example 4 Product III.

Product III was prepared following the general procedure described in Example 1. The monomer phase consisted of 370.040 g of 50.40 wt.% acrylamide, 139.853 g of deionized water and 78.730 g of ice bath neutralized acrylic acid containing 84.000 g of 50 wt.% aqueous sodium hydroxide solution. In addition, a glyoxal bisacrylamide-containing solution consisting of 0.120 g of 1 wt.% glyoxal solution, 9.821 g of 50.4 wt.% acrylamide and 0.80 g of 1 wt.% sodium hydroxide solution, 0.350 g of sodium formate and 0.090 g tetrasodium diethylenediaminetetraacetate. The oil phase consisted of 280,000 g of paraffin solvent (Exxsol D80), 11,754 g of sorbitan monooleate (Span® (Span) 80), 23,246 g of polyoxyethylene sorbitan trioleate (Tween® (Tween) 85) and 0,200 g of Hypermer™ B210. 0.396 g of 2,2'-azobisobutyronitrile was used for polymerization.

Example 5 Product IV.

Product IV was prepared following the general procedure described in Example 1. The monomer phase consisted of 370.676 g of 50.30 wt.% acrylamide, 137.082 g of deionized water and 78.730 g of ice bath neutralized acrylic acid containing 84.000 g of 50 wt.% aqueous sodium hydroxide solution. In addition, a glyoxal bisacrylamide-containing solution consisting of 0.120 g of 1 wt% glyoxal solution, 9.940 g of 50.3% acrylamide and 0.80 g of 1 wt% sodium hydroxide solution and 0.090 g of tetrasodium diethylenediaminetetraacetate was added to the monomer phase. The oil phase consisted of 280,000 g of paraffin solvent (Exxsol D80), 13,060 g of sorbitan monooleate (Span® (Span) 80) and 21,940 g of polyoxyethylene sorbitan trioleate (Tween® (Tween) 85). 0.528 g of 2,2'-azobisisobutyronitrile was used for polymerization.

Example 6. Product V.

Product V was prepared following the general procedure described in Example 1. The monomer phase consisted of 370.040 g of 50.40 wt.% acrylamide, 140.053 g of deionized water and 78.730 g of acrylic acid neutralized in an ice bath containing 84.000 g of 50 wt.% aqueous sodium hydroxide solution. In addition, a glyoxal bisacrylamide-containing solution consisting of 0.120 g of 1 wt.% glyoxal solution, 9.821 g of 50.4 wt.% acrylamide and 0.80 g of 1 wt.% sodium hydroxide solution, 0.350 g of sodium formate and 0.090 g tetrasodium diethylenediaminetetraacetate. The oil phase consisted of 280,000 g of paraffin solvent (Exxsol D80), 10,085 g of sorbitan monooleate (Span® (Span) 80) and 24,915 g of polyoxyethylene sorbitan hexaoleate. 0.396 g of 2,2'-azobisobutyronitrile was used for polymerization.

Example 7. Product VI.

Product VI was prepared following the general procedure described in Example 1. The monomer phase consisted of 378.963 g of 49.20 wt.% acrylamide, 15.516 g of deionized water and 78.730 g of ice bath neutralized acrylic acid containing 82.700 g of 50 wt.% aqueous sodium hydroxide solution. In addition, a glyoxal bisacrylamide-containing solution consisting of 0.120 g of 1 wt% glyoxal solution, 10.163 g of 49.20 wt% acrylamide and 0.310 g of 1 wt% sodium hydroxide solution and 0.090 g of diethylenediaminetetrasodium tetraacetate was added to the monomer phase. The oil phase consisted of 331.800 g paraffin solvent (Exxsol D80), 11.200 g sorbitan sesquioleate (Arlacel® (Arlaser) 83 or Span® (Span) 83) and 88.800 g polyoxyethylene sorbitan hexaoleate. 0.528 g of 2,2'-azobisisobutyronitrile was used for polymerization.

Example 8. Product VII.

Product VII was prepared following the general procedure described in Example 1. The monomer phase consisted of 900.184 g of 47.90 wt.% acrylamide, 325.501 g of deionized water and 183.449 g of acrylic acid neutralized in an ice bath containing 190.240 g of 50 wt.% aqueous sodium hydroxide solution. In addition, a glyoxal bisacrylamide-containing solution consisting of 5.592 g of 1 wt.% glyoxal solution, 49.603 g of 47.90 wt.% acrylamide and 1.841 g of 1 wt.% sodium hydroxide solution, 0.816 g of sodium formate and 0.209 g was added to the monomer phase. tetrasodium diethylenediaminetetraacetate. The oil phase consisted of 652.428 g paraffin solvent (Exxsol D80), 27.388 g sorbitan monooleate (Span® (Span) 80), 54.123 g polyoxyethylene sorbitan trioleate and 0.466 g Hypermer™ B210. 0.691 g of 2,2'-azobisobutyronitrile was used for polymerization.

Using a modified version of the mechanical shear degradation procedure described in API RP63, a 2000 ppm polymer solution was prepared in synthetic seawater and forced through a 0.01 inch (0.254 mm) ID capillary tube at various flow rates/shear rates and The viscosity of the effluent/sheared samples was immediately measured at 25° C. and 10.2 s ^-1 . Next, the output samples of product VII are activated

- 17 044351 and measured the viscosity values again. In fig. 1 shows viscosity versus shear rate. Another shear test was carried out using a Waring mixer, with viscosity versus shear time shown in FIG. 2. For fig. 1 and 2 SSW stands for synthetic salt water. It is known in the industry that traditional hydrolyzed polyacrylamides (HPAMs) lose 20 to 50% of their original viscosity when exposed to significant shear. This was confirmed in the experiment described above; however, Product VII in its unactivated form did not show a loss of its original viscosity when subjected to shear and also did not show a loss of viscosity after its thermal activation.

Example 9. Product VIII.

Product VIII was prepared following the general procedure described in Example 1. The monomer phase consisted of 280.123 g of 50.00 wt.% acrylamide, 154.059 g of deionized water and 76.437 g of ice bath neutralized acrylic acid containing 82.452 g of 50 wt.% aqueous sodium hydroxide solution. In addition, a glyoxal bisacrylamide-containing solution consisting of 0.500 g of 40 wt.% glyoxal solution, 99.000 g of 50.00 wt.% acrylamide and 0.2578 g of 10 wt.% acrylamide was added to the monomer phase. sodium hydroxide solution, 0.340 sodium formate and 0.087 g of tetrasodium diethylenediaminetetraacetate. The oil phase consisted of 271.845 g of paraffin solvent (Exxsol D80), 11.412 g of sorbitan monooleate (Span® (Span) 80) and 22.569 g of polyoxyethylene sorbitan trioleate. 0.288 g of 2,2'-azobisobutyronitrile was used for polymerization. Before subsequent heating, 1.610 g of a 2.8% aqueous solution of tert-butyl hydroperoxide and 1.330 g of a 10% aqueous solution of sodium metabisulfite were added for 30 minutes.

Example 10. Filtration coefficients and flow rates of various products I-VIII.

The instrument used to measure the filtration coefficient of the waterflood fluids was a steel housing (from OFI) connected to a pressurized nitrogen line to provide a constant nitrogen pressure of 20 psi (approximately 138 kPa) for filtration coefficient and flow rate measurements. For filtration, a membrane filter with a pore size of 1.2 to 5.0 μm was used, and a computer was connected to the digital balancing device to record the mass of the polymer solution passing through the filter and the time spent passing through said filter. Using approximately 250 g of a 3000 or 1000 ppm polymer active solution prepared in synthetic seawater, the filtration coefficient was calculated by the time used to filter from 180.0 to 210.0 g of the polymer solution divided by the time used to filter from 90.0 to 120.0 g of polymer solution, and the flow rate was calculated based on the mass of 210.0 g divided by the total time used to filter 210.0 g of polymer solution.

Filtration coefficients and flow rates for both fresh and activated polymer solutions were determined using the method described above. The method used fully complies with the American Petroleum Institute standard (API 63). Bulk viscosities for both solutions were measured in a programmable viscometer at 25°C and a shear rate of 10.2/s.

Data for products I-VIII described in examples 2-9 are presented below.

Product Droplet size (µm) I 0.642 II 0.732 III 0.590 IV 0.755 V 0.551 VI 75.3 VII 0.581 VIII 0.612

- 18 044351

Product Concentration (PPt) Activation time at 70°C Bulk viscosity (cP) at 25°C after activation Filtration coefficient Membrane filter (µm) Flow rate (g/s) I 3000 0* 1.77 1.05 5.0 1.38 0* 1.77 1.13 1.2 0.96 5 67.24 1.02 5.0 0.10 22 54.24 1.04 5.0 0.17 22 54.24 1.07 1.2 0.16 II 3000 0* 1.41 1.00 5.0 1.60 22 83.23 1.01 5.0 0.15 22 83.23 1.09 1.2 0.11 III 3000 0* 1.17 1.09 1.2 1.00 22 64.44 1.04 1.2 0.12 IV 3000 0* 0.78 1.10 h,o 1.01 22 116.51 1.10 h,o 0.16 V 3000 0* 0 1.04 5.0 1.63 22 57.08 1.02 5.0 0.26 22 57.08 1.04 1.2 0.13 VI 3000 0* 1.72 1.06 h,o 1.68 22 73.04 1.08 1.2 0.16 VII 3000 0 (not activated) 3.12 1.08 1.2 0.16 1.02 5.0 3.00 18 64.83 1.12 1.2 1.83 1.01 5.0 0.093 VIII 1000 0 (not activated) 1.56 1.05 5.0 5,198 1.05 1.2 3,376 18 10.15 1.03 5.0 0.316 0.95 1.2 0.151

*Not activated.

Example 11. Shear protection.

The shear protection of the polymer has been demonstrated using two types of testing methods. One test method is a modified API standard method RP63. In this test, 2000 ppm solutions of Polymer VII and T07 (standard 30/70 sodium acrylate/acrylamide emulsion polymer) were prepared in synthetic seawater. Each solution was forced through a capillary tube with an internal diameter of 0.01 inch (0.254 mm) and the solution viscosity of each sheared effluent sample was immediately measured after passing through the orifice at each flow rate/shear rate in a programmable Brookfield viscometer at 25°C and speed shift 10.2 s ^-1 . Next, each sheared polymer VII outlet sample was activated by heating at 70°C for 18 hours and after cooling to room temperature, the viscosity was measured at 25°C and a shear rate of 10.2 s ^-1 . Another test was performed using a Waring mixer. In this test, 3000 ppm polymer active solutions of Polymer VII and T07 were prepared in synthetic seawater, the resulting polymer solutions were sheared at a constant shear strain of 14,000 to 16,000 rpm for 0 to 40 s, and the viscosity of each sheared polymer was immediately measured. solution at 25°C and a shear rate of 10.2 s ^-1 . For polymer product VII, each sheared polymer solution was then activated by heating at 70° C. for 18 hours and, after cooling to room temperature, the viscosity was measured at 25° C. and a shear rate of 10.2 s ^-1 .

The results shown in Fig. 1 show that the control polymer (T07) exhibited up to approximately a 50% drop in initial viscosity when the shear rate was increased to 100,000 s ^-1 . Re

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Claims (1)

Results for non-activated Product VII and activated Product VII polymer solutions after shear showed that the temporary cross-linking of the present invention protected the polymer from mechanical shear degradation under conditions that caused significant mechanical shear degradation in the T07 polymer solutions. When a polymer solution in non-activated, transiently cross-linked form is sheared, the VII non-activated polymer solution retains its original viscosity and can be activated after shear deformation to produce a polymer solution (shear activated product VII) exhibiting the same initial high viscosity regardless of the shift it underwent in its non-activated form. The results of the shear test method using a mixer are shown in FIG. 2. Under test conditions, the control polymer (T07) exhibited a 75% reduction in viscosity after shearing for 40 s. Polymer VII behaved differently. When exposed to shear in its non-activated form, non-activated polymer VII maintained its low viscosity. When polymer VII was activated after shear deformation (after exposure to shear), the viscosity remained high and unchanged. The results obtained showed that Polymer VII is shear stable when subjected to shear on its non-activated form. It is to be understood that the foregoing detailed description and the accompanying examples are merely illustrative and are not to be construed as limiting the scope of the invention, which is defined solely by the appended claims and their equivalents. Various changes and modifications to the described embodiments will be apparent to those skilled in the art. Such changes and modifications, including without limitation changes and modifications related to the chemical structures, substituents, derivatives, intermediates, syntheses, compositions, formulations or methods of using the invention, may be made without departing from the spirit and scope of the present invention. CLAIM 1. A polymer composition for recovering crude oil from a subterranean hydrocarbon-containing formation, comprising an emulsion of an aqueous phase and an oil phase, wherein the aqueous phase contains a cross-linked water-soluble polymer and the oil phase contains a surfactant and an organic solvent or hydrocarbon oil, wherein the cross-linked water-soluble polymer contains from 1 to 100 mol.% acrylamide monomers and from 0.1 to 1000 ppm hydrolyzable cross-linking monomer units based on the weight of the water-soluble polymer, wherein said hydrolyzable cross-linking monomer units are covalently cross-linked and said covalently linked cross-linking monomer units the units have the structure of formula (IIb) wherein each R is independently hydrogen or methyl; and each σννν represents a site of attachment to the first polymer backbone; and each LM represents a site of attachment to a first polymer backbone or to a second polymer backbone, wherein said surfactant comprises a high molecular weight structured polyol multiether having a molecular weight of from 950 to 500,000 daltons, or a high molecular weight structured polyol multiether having a molecular weight weight from 950 to 500,000 daltons, and the specified high molecular weight structured multiester polyol is selected from the group consisting of polyoxyethylene sorbitan dioleate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitan tetraoleate, polyoxypropylene sorbitan dioleate, polyoxypropylene sorbitan trioleate, polyoxypropylene sorbitan tetraoleate, polyoxyethylene ylene sorbitan distearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan tetrastearate, polyoxypropylene sorbitan distearate, polyoxypropylene sorbitan tristearate, polyoxypropylene sorbitan tetrastearate, sorbitol trioleate, sorbitol tetraoleate, sorbitol pentaoleate, sorbitol hexaoleate, sorbitol tristearate, sorbitol tetrastearate, sorbitol pentastearate, sorbitol hexastearate, polyoxyethylene sorbitol dioleate, polyoxyethylene sorbitol trioleate, polyoxyethylene sorbitol tetraoleate, polyoxyethylene sorbitol pentaoleate, polyoxyethylene sorbitol hexaoleate, polyoxypropylene sorbitol dioleate, polyoxypropylene sorbitol trioleate, polyoxypropylene sorbitol tetraoleate, polyoxypropylene sorbitol pentaoleate, polyoxypropylene sorbitol hexaoleate, polyoxyethylene sorbitol dis thearate, polyoxyethylene sorbitol tristearate, polyoxyethylene sorbitol tetrastearate, polyoxyethylene sorbitol -