Process

Abstract

A process for reducing the permeability to water of a thief zone of a porous and permeable subterranean petroleum reservoir includes injecting a composition comprising a dispersion of betainised crosslinked polymeric microparticles in an aqueous fluid down a well and into a thief zone. The betainised crosslinked polymeric microparticles have a transition temperature that is at or below the maximum temperature encountered in the thief zone and greater than the maximum temperature encountered in the well. The betainised crosslinked polymeric microparticles are solvated by water, expand in size and optionally aggregate in the thief zone when they encounter a temperature greater than the transition temperature so as to reduce the permeability of the thief zone to water.

Claims

1. A process for reducing the permeability to water of a thief zone of a porous and permeable subterranean petroleum reservoir, said process comprising: injecting a composition comprising a dispersion of betainised crosslinked polymeric microparticles in an aqueous fluid down a well and into a thief zone, wherein the betainised crosslinked polymeric microparticles have a transition temperature which is at or below the maximum temperature encountered in the thief zone and greater than the maximum temperature encountered in the well, and wherein the betainised crosslinked polymeric microparticles are solvated by water and expand in size in the thief zone when they encounter a temperature at or greater than the transition temperature so as to reduce the permeability of the thief zone to water.

2. A process for recovering hydrocarbon fluids from a porous and permeable subterranean petroleum reservoir comprising at least one higher permeability layer of reservoir rock and at least one lower permeability layer of reservoir rock that are penetrated by at least one injection well and at least one production well, the process comprising: i) injecting into the higher permeability layer of reservoir rock a composition comprising betainised crosslinked polymeric microparticles dispersed in an aqueous fluid wherein the higher permeability layer has a region between the injection well and production well having a temperature at or above the transition temperature of the betainised crosslinked microparticles; ii) propagating said composition through the higher permeability layer until the composition reaches the region of the higher permeability layer having a temperature at or above the transition temperature such that betainised crosslinked microparticles become solvated and expand in size thereby reducing the permeability of the higher permeability layer of the reservoir and diverting subsequently injected aqueous fluid into the lower permeability layer of the reservoir; and iii) recovering hydrocarbon fluids from said at least one production well.

3. The process of claim 2, wherein the higher permeability layer(s) of reservoir rock has a permeability at least 50% greater than the permeability of the lower permeability layer(s) of reservoir rock.

4. The process of claim 2, wherein the composition comprising betainised microparticles is injected into the injection well at a temperature in the range of 4 to 30 C. and the transition temperature of the betainised microparticles is in the range of 20 C. to 120 C. with the proviso that the transition temperature is greater than the injection temperature.

5. The process of claim 2, wherein the composition comprising betainised microparticles is injected in a pore volume amount in the range of 0.05 to 1, preferably 0.2 to 0.5.

6. The process of claim 2, wherein the initial average particle diameter of the betainised microparticles is in the range of 0.1 to 1 m and the average particle diameter of the expanded betainised microparticles is in the range of 1 to 10 microns.

7. A method for preparing betainised microparticles, said method comprising: reacting precursor polymeric microparticles comprising crosslinked polymer chains having pendant groups comprising a betainisable functional group with a betainising reagent to convert at least a portion of the betainisable functional groups to betainised functional groups thereby forming betainised microparticles comprising crosslinked polymer chains having pendant groups comprising a betainised functional group and optionally having pendant groups comprising an unreacted betainisable functional group.

8. The method of claim 7, wherein the precursor polymeric microparticles are reacted with a betainising reagent selected from sulfobetainising, carboxybetainising, phosphobetainising, phosphonobetainising and sulfabetainising reagents to form betainised microparticles in which at least a portion of the betainisable functional groups are converted to betainised functional groups.

9. The method of claim 7, wherein the precursor microparticles are prepared by emulsion polymerization or dispersion polymerization of a mixture of monomers comprising: (a) monomers having betainisable functional groups; (b) crosslinking monomers; and (c) optionally, hydrophobic comonomers that do not contain a betainisable functional group.

10. The method of claim 9, wherein the monomers having betainisable functional groups are selected from the group consisting of dialkylaminoalkyl acrylates; dialkylaminoalkyl alkacrylates; dialkylaminoalkyl acrylamides; dialkylaminoalkyl alkacrylamides; vinylaryldialkylamines; and vinyl-N-heterocyclic amines.

11. The method of claim 10, wherein the monomers having betainisable functional groups are vinyl-N-heterocyclic amines and the resulting precursor microparticles have structural units with pendant N-heterocyclic amine rings that are reacted with the betainising reagent to form betainised N-heterocyclic ammonium rings.

12. The method of claim 10, wherein the monomers having betainisable functional groups are dialkylaminoalkyl acrylates and alkacrylates of general formula (I):
[H.sub.2CC(R.sup.1)CO.sub.2R.sup.2NR.sup.3R.sup.4] wherein R.sup.1 is selected from hydrogen and methyl; R.sup.2 is a straight chain alkylene moiety having from 2 to 10 carbon atoms or a branched chain alkylene moiety having a main chain having from 2 to 10 carbons atoms and at least one branched chain having from 2 to 10 carbon atoms with the proviso that the straight or branched chain alkylene moiety is optionally substituted by methyl; and R.sup.3 and R.sup.4 are independently selected from methyl, ethyl, n-propyl and isopropyl, or N, R.sup.3 and R.sup.4 together form an N-heterocyclic amine ring, optionally, including an oxygen heteroatom.

13. The method of claim 10, wherein the monomers having betainisable functional groups are dialkylaminoalkyl acrylamides and alkacrylamides of the formula (II):
[H.sub.2CC(R.sup.1)CONHR.sup.2NR.sup.3R.sup.4] wherein R.sup.1R.sup.2R.sup.3 and R.sup.4 are as defined in claim 12.

14. The method of claim 10, wherein the monomers having betainisable functional groups are vinylbenzyldialkylamines of the general formula (III):
[H.sub.2CC(R.sup.1)C.sub.6H.sub.4R.sup.2NR.sup.3R.sup.4] wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are as defined in claim 12 or are vinylbenzyldialkylamines analogues of those of general formula (III) in which the benzyl group has from one to three substituents selected from methyl, ethyl, halogen, alkoxy and nitro groups.

15. The method of claim 12, wherein the crosslinking monomer comprises from 0.1 to 10 mol %, preferably 0.5 to 3 mol % of the mixture of monomers used to prepare the precursor microparticles.

16. The method of claim 9, wherein the crosslinking monomers are selected from diacrylamides and methacrylamides of diamines such as the diacrylamide or dimethacrylamide of piperazine or diacrylamide or dimethacrylamide of methylenediamine; methacrylate esters of di, tri, tetra hydroxy compounds including ethyleneglycol dimethacrylate, polyethyleneglycol dimethacrylate, trimethylolpropane trimethacrylate, and the like; divinylbenzene, 1,3-diisopropenylbenzene, and the like; the vinyl or allyl esters of di or trifunctional acids; and, diallylamine, triallylamine, divinyl sulfone, diethyleneglycol diallyl ether, and the like.

17. The method of claim 9, wherein the hydrophobic comonomers are selected from benzyl methacrylate, benzyl acrylate, benzyl acrylamide, benzyl methacrylamide, n-butyl methacrylate, n-butyl acrylate, n-butyl acrylamide, n-butyl methacrylamide, and the like; and styrenic monomers substituted with branched alkyl, straight chain alkyl or aryl groups and comprise up to 50 mol % of the mixture of monomers used to prepare the precursor microparticles.

18. The method of claim 7, wherein the betainisation reagent is of general formula V:
XRA.sup.M.sup.+ wherein X is a halogen selected from F, Cl, Br and I, preferably, CI and Br; R is a hydrocarbylene group having up to 30 carbon atoms wherein the hydrocarbylene group may be selected from: branched or unbranched alkylene groups; arylene groups; alkarylene groups (an alkyl substituted arylene group wherein the alkyl substituent may be branched or unbranched); and arylalkylene groups (an aryl substituted alkylene group where the alkylene group may be branched or unbranched); and wherein the alkylene, arylene, alkarylene or arylalkylene groups may be optionally substituted with functional groups selected from hydroxyl, ether, ester, amide, and the like; A.sup. is an anionic functional group selected from SO.sub.3.sup. (sulfonate), PO.sub.3.sup. (phosphonate), OPO.sub.3.sup. (phosphate), CO.sub.3.sup. (carboxylate) and OSO.sub.3.sup. (ether sulfonate; also referred to as sulfate) functional groups, preferably, SO.sub.3.sup. (sulfonate); and M.sup.+ is selected from H.sup.+, Group IA metal cations and ammonium cations.

19. The method of claim 18, wherein the betainisation reagent is a betainisation reagent having a halide leaving group of general formula Va:
XCH.sub.2(CH.sub.2).sub.nCH.sub.2A.sup.M.sup.+ wherein X, A.sup. and M.sup.+ are as defined above; and n is an integer in the range of 0 to 20, preferably 0 to 10, in particular, 0 to 3.

20. The method of claim 7, wherein the betainising reagent is a cyclic betainising reagent selected from the group consisting of sultones; lactones; dioxaphospholane oxides; dioxathiolane dioxides; and dioxathiane dioxides.

21. Betainised microparticles comprising: crosslinked polymer chains in the form of microparticles, wherein the crosslinked polymer chains have: pendant groups comprising betainised functional groups, and pendant groups comprising unreacted betainisable functional groups, wherein the betainised functional groups are present in the microparticles in an amount of from 50% to 95% based on the total amount of betainised and unreacted betainisable functional groups.

22. Betainised microparticles of claim 21, wherein the microparticles are selected from sulfobetainised microparticles, carboxybetainised microparticles phosphobetainised microparticles, phosphonobetainised microparticles and sulfabetainised microparticles, preferably selected from sulfobetainised microparticles and sulfabetainised microparticles.

23. Betainised microparticles of claim 22, wherein the betainised microparticles comprise betainised groups selected from: (2-sulfoethyl)-ammonium betaine groups, (3-sulfopropyl)-ammonium betaine groups, (4-sulfobutyl)-ammonium betaine groups, (2-carboxyethyl)-ammonium betaine groups, (3-carboxypropyl)-ammonium betaine groups, (4-carboxybutyl)-ammonium betaine groups, (2-phosphoethyl)-ammonium betaine groups, (3-phosphopropyl)-ammonium betaine groups, (4-phosphobutyl)-ammonium betaine groups, (2-phosphonoethyl)-ammonium betaine groups, (3-phosphonopropyl)-ammonium betaine groups, (4-phosphonobutyl)-ammonium betaine groups, (2-sulfaethyl)-ammonium betaine groups, (3-sulfapropyl)-ammonium betaine groups, and (4-sulfabutyl)-ammonium betaine groups.

24. A composition comprising: an aqueous fluid; and a dispersion of betainised microparticles in the aqueous fluid, where the betainised microparticles comprise: crosslinked polymer chains in the form of microparticles, wherein the crosslinked polymer chains have: pendant groups comprising betainised functional groups, and pendant groups comprising unreacted betainisable functional groups, wherein the betainised functional groups are present in the microparticles in an amount of from 50% to 95% based on the total amount of betainised and unreacted betainisable functional groups.

25. The composition of claim 24, wherein the composition comprises from 0.01 to 20% by weight, preferably from 0.01 to 10% by weight, more preferably from 0.02 to 5% by weight, and most preferably from 0.05 to 3% by weight of the betainised microparticles based on the total weight of the composition.

26. The composition of claim 24, wherein the aqueous fluid has a total dissolved solids (TDS) content in the range of 200 to 250,000 mg/L, preferably, in the range of 500 to 50,000 mg/L, more preferably, 1500 to 35,000 mg/L.

27. The composition of claim 29, wherein the aqueous fluid is selected from seawater, estuarine water, brackish water, lake water, river water, desalinated water, produced water, aquifer water or mixtures thereof, preferably seawater.

28. The process of claim 1, wherein the composition comprising betainised microparticles is injected into the injection well at a temperature in the range of 4 C. to 30 C. and the transition temperature of the betainised microparticles is in the range of 20 C. to 120 C. with the proviso that the transition temperature is greater than the injection temperature.

29. The process of claim 1, wherein the composition comprising betainised microparticles is injected in a pore volume amount in the range of 0.05 to 1, preferably 0.2 to 0.5.

30. The process of claim 1, wherein the initial average particle diameter of the betainised microparticles is in the range of 0.1 to 1 m and the average particle diameter of the expanded betainised microparticles is in the range of 1 to 10 microns.

Description

[0170] The invention will now be demonstrated by reference to the following Examples and Figures.

[0171] FIG. 1 shows the synthesis of poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) precursor microparticles using different stabilizers.

[0172] FIG. 2 shows the reactions of dialkylaminoalkylene (betainisable) functional groups of the precursor microparticles with 1,3 propane sultone and with sodium 3-bromopropane-1-sulfonate.

[0173] FIG. 3 shows changes in the diameter of sulfobetainised crosslinked microparticles (having 50, 75 and 100% betainisation) with changing temperature when the microparticles are dispersed in ultra-pure water.

[0174] FIG. 4 shows changes in the diameter of polysulfobetaine microparticles with changing temperature when the microparticles are dispersed in a 0.3 M sodium chloride solution (for microparticles comprising pendant betainised groups having an n-propyl or n-butyl group linking the ammonium and sulfonate groups).

[0175] FIG. 5 shows the reversible microparticle expansion and aggregation of polysulfobetaine microparticles in a 0.3M solution of NaCl.

[0176] FIG. 6a shows DLS analytical data at a temperature of 25 C. for polysulfobetaine microparticles synthesised at two different scales (10 g and 40 g procedures).

[0177] FIG. 6b shows how the hydrodynamic diameter (D.sub.h) of hydroxysulfobetainised microparticles change with temperature when dispersed in ultra-pure water having a resistivity of 18.2 M.Math.cm water.

[0178] FIG. 6c shows how the hydrodynamic diameter (D.sub.h) of carboxybetainised microparticles change with temperature when dispersed in ultra-pure water having a resistivity of 18.2 M.Math.cm water.

[0179] FIGS. 7a and 7b show the test temperatures for sandpack sections for Sandpack Tests 1 to 3.

[0180] FIG. 8 shows injection profiles for Sandpack Tests 1 and 3 (for compositions with a microparticle concentration of 1000 ppm).

[0181] FIGS. 9a and 9b show blocking profiles for Sandpack Tests 1 to 3 (for compositions with a microparticle concentration of 5000 ppm).

[0182] FIG. 10 shows dispersion of a block in sequential sandpack sections, upon cooling, for Sandpack Test 1.

EXAMPLES

[0183] Unless otherwise stated, emulsion polymerization was used in the syntheses of the crosslinked polymeric microparticles.

Direct Synthesis of Poly(N,N-dimethyhmethacryloylethyl)ammonium propane sulfonate) (PDMAPS) Microparticles by Inverse Emulsion Polymerization

[0184] Polyoxyethylene sorbitan monooleate (Tween 80) surfactant (1.7 g, 2 wt. % based on the total weight of the emulsion), N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate (DMAPS) monomer (1.9 g), poly(ethylene glycol) dimethacrylate (PEGDMA) cross-linking monomer having a number average molecular weight (M.sub.n) of 550 Da (0.1 g, 5 wt. % of the total weight of DMAPS and PEGDMA monomers) and radical initiator 4,4-azobis(4-cyanovaleric acid) (ACVA) (0.02 g, 1 wt. % of the total weight of DMAPS and PEGDMA monomers) were dissolved by stirring in water (6 mL) having a resistivity of 18.2 M.Math.cm. Toluene (80 mL) was added to the resulting aqueous solution and the mixture was sonicated in an ice bath for 10 minutes. The resulting emulsion was purged with nitrogen for 30 minutes and then heated in an oil bath with stirring (750 rpm) at a temperature of 65 C. for 16 hours.

[0185] The resulting polymeric microparticles were found to be ill-defined with a broad size distribution as determined by dynamic light scattering (DLS) and scanning electron microscopy (SEM) analyses. The microparticle diameters were found to be in the range of 70 to 160 nm by SEM. These microparticles are not suitable for use in the method of the present invention.

Direct Synthesis of Poly(N,N-dimethyhmethacryloylethyl)ammonium propane sulfonate) (PDMAPS) Microparticles by Dispersion Polymerization

[0186] Polyoxyethylene sorbitan monooleate (Tween 80) surfactant (2 g, 2 wt. % based on the total weight of the dispersion), DMAPS monomer (5 g, 5 wt. % based on the total dispersion), N,N-methylenebisacrylamide (MBAc) crosslinking monomer (0.025 g, 0.5 wt. % based on the weight of the DMAPS monomer) and the radical initiator 2,2-azobis(2-methylpropionamidine)dihydrochloride (V-50) (0.04 g, 0.8 wt. % based on the weight of the DMAPS monomer) were dissolved in water (93 mL) having a resistivity of 18.2 M.Math.cm (in the order listed) by stirring. The mixture was purged with nitrogen for 30 minutes and then heated in an oil bath with stirring (600 rpm) at a temperature of 65 C. for 16 hours.

[0187] The resulting microparticles were found to be ill-defined with a broad size distribution as determined by dynamic light scattering (DLS) and scanning electron microscopy (SEM) analyses. The microparticle diameters were found to be in the range of 500 to 900 nm by SEM. These microparticles are not suitable for use in the method of the present invention.

Synthesis of Stabilizers for Use in the Synthesis of Precursor Microparticles

[0188] Poly(N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate) (PDMAPS) polymeric stabilizers were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization according to the procedures described below.

[0189] The resulting PDMAPS polymeric stabilizers have a dithiobenzoate end group arising from the chain transfer agent (CTA) used in this synthetic procedure. It was found that retention of the dithiobenzoate end-group in the PDMAPS stabilizer allowed for covalent attachment of the stabilizer to the polymeric microparticles during polymerization.

(a) Synthesis of Poly(N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate)(PDMAPS) Polymeric Stabilizer with Number Average Molecular Weight (MO of 5000 Daltons (Da)

[0190] N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate (DMAPS) monomer (5 g, 18 equivalents based on the amount of chain transfer agent), 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid chain transfer agent (CTA) (1 equivalent) and 4,4-azobis(4-cyanovaleric acid) (ACVA) radical initiator (0.2 equivalents based on the amount of CTA) were dissolved in 0.5 M aqueous solution of NaCl and the resulting solution was adjusted to a pH value of 7 by the addition of dilute aqueous NaOH. After transferring the solution to an ampoule provided with a stirrer bar, the solution was degassed by purging with nitrogen for 30 minutes while stirring. The polymerisation reaction was started by immersion of the ampoule in an oil bath heated to a temperature of 65 C. and the polymerization mixture was stirred at this temperature for 4 hours. The polymerization reaction was then stopped by cooling and exposing the polymerization mixture to air. The resulting polymer was purified by extensive dialysis against deionized water (1 kDa MWCO dialysis tubing) with at least 6 changes of water, and was recovered as a pink solid by freeze-drying. The resulting polymer had a number average molecular weight (M.sub.n) of 5 kDa as determined by .sup.1H NMR spectroscopy.

(b) Synthesis of Poly(N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate) (PDMAPS Polymeric Stabilizer with Number Average Molecular Weight (M.SUB.n.) of 20,000 Daltons (Da)

[0191] N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate (DMAPS) monomer (5 g, 72 equivalents based on the amount of chain transfer agent), 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid chain transfer agent (CTA) (1 equivalent) and 4,4-azobis(4-cyanovaleric acid) (ACVA) radical initiator (0.2 equivalents based on the amount of CTA) were dissolved in a 0.5 M aqueous solution of NaCl and the resulting solution was adjusted to a pH value of 7 by the addition of dilute aqueous NaOH. After transferring the solution to an ampoule provided with a stirrer bar, the solution was degassed by purging with nitrogen for 30 minutes while stirring. The polymerisation reaction was started by immersion of the ampoule in an oil bath heated to a temperature of 65 C. and the polymerization mixture was stirred at this temperature for 4 hours. The polymerization reaction was then stopped by cooling and exposing the polymerization mixture to air. The resulting polymer was purified by extensive dialysis against deionized water (1 kDa MWCO dialysis tubing) with at least 6 changes of water, and was recovered as a pink solid by freeze-drying. The resulting polymeric stabilizer had a number average molecular weight (M.sub.n) of 20 kDa as determined by .sup.1H NMR spectroscopy.

Synthesis of Poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) Precursor Microparticles

[0192] A number of syntheses of poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) precursor microparticles were performed using different stabilizers.

Synthesis of Poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) Precursor Microparticles using Sodium dodecyl sulfate (SDS) as a Surfactant Stabilizer

[0193] SDS surfactant (0.24 g, 20 wt. % based on the weight of the DEAEMA monomer), 2-(diethylamino)ethyl methacrylate (DEAEMA) monomer (1.2 g) and ethylene glycol dimethacrylate (EGDMA) cross-linking monomer (0.012 g, 1 wt. % based on the weight of DEAEMA monomer) were dispersed in water (38 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator potassium persulfate (KPS) (0.012 g, 1 wt. % of the DEAEMA monomer) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and purged for 10 minutes with nitrogen. The degassed KPS solution was added to the degassed surfactant and monomer solution to initiate polymerization. The resulting polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 60 nm with a dispersity of 0.19.

Synthesis of Poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) Precursor Microparticles using Poly(ethylene glycol) methacrylate (M.SUB.n.=360 Da) as a Polymeric Stabilizer

[0194] Poly(ethylene glycol) methacrylate (PEGMA) stabilizer (M.sub.n=360 Da) (0.04 g, 1.6 wt. % based on the weight of the DEAEMA monomer), 2-(diethylamino)ethyl methacrylate (DEAEMA) monomer (2.5 g) and ethylene glycol dimethacrylate (EGDMA) cross-linking monomer (0.025 g, 1 wt. % based on the weight of DEAEMA monomer) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator potassium persulfate (KPS) (0.025 g, 1 wt. % of the DEAEMA monomer) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and the resulting solution was purged for 10 minutes with nitrogen. The degassed KPS solution was then added to the degassed surfactant and monomer solution to initiate polymerization. The resulting polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 190 nm with a dispersity of 0.03.

Synthesis of Poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) Precursor Microparticles using Poly(ethylene glycol) methacrylate (M.SUB.n.=950 Da) as a Polymeric Stabilizer

[0195] Poly(ethylene glycol) methacrylate (PEGMA) stabilizer (M.sub.n=950 Da) (0.10 g, 4 wt. % based on the weight of DEAEMA monomer), 2-(diethylamino)ethyl methacrylate (DEAEMA) monomer (2.5 g) and ethylene glycol dimethacrylate (EGDMA) cross-linking monomer (0.025 g, 1 wt. % based in the weight of DEAEMA monomer) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator potassium persulfate (KPS) (0.025 g, 1 wt. % based on the weight of DEAEMA monomer) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and purged for 10 minutes with nitrogen. The degassed KPS solution was added to the degassed surfactant and monomer solution to initiate polymerization. The resulting polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 215 nm with a dispersity of 0.10.

Synthesis of Poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) Precursor Microparticles using Poly(N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate) DMAPS (M.SUB.n.=5000 Da) as Polymeric Stabilizer

[0196] Poly(N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate) (PDMAPS) stabilizer having a dithiobenzoate chain transfer agent (CTA) end-group (M.sub.n=5000 Da) prepared according to the procedure described above (0.1 g, 4 wt. % based on the weight of DEAEMA monomer), 2-(diethylamino)ethyl methacrylate (DEAEMA) monomer (2.5 g) and ethylene glycol dimethacrylate (EGDMA) cross-linking monomer (0.025 g, 1 wt. % based on the weight of DEAEMA monomer) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring.

[0197] The radical initiator potassium persulfate (KPS) (0.025 g, 1 wt. % based on the weight of DEAEMA monomer) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and purged for 10 minutes with nitrogen. The degassed KPS solution was added to the degassed surfactant and monomer solution to initiate polymerization. The polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 110 nm with a dispersity of 0.07.

Synthesis of Poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) Precursor Microparticles using Poly(N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate) (DMAPS) (M.SUB.n.=20,000 Da) as a Polymeric Stabilizer

[0198] Poly(N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate) (PDMAPS) stabilizer (M.sub.n=20,000 Da) prepared according to the procedure described above (0.1 g, 4 wt. % based on the weight of DEAEMA monomer), 2-(diethylamino)ethyl methacrylate monomer (DEAEMA) (2.5 g), and ethylene glycol dimethacrylate (EGDMA) cross-linking monomer (0.025 g, 1 wt. % based on the weight of DEAEMA monomer) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator potassium persulfate (KPS) (0.025 g, 1 wt. % based on the weight of DEAEMA monomer) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and purged for 10 minutes with nitrogen. The degassed KPS solution was added to the degassed surfactant and monomer solution to initiate polymerization. The polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 160 nm with a dispersity of 0.04.

Variation of Cross-Linking Density of the Poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) Precursor Microparticles

[0199] A number of experiments were performed in which the cross-linking density of the PDEAEMA precursor microparticles was varied:

(a) 0.5 wt. % Cross-Linker (EGDMA) with PEGMA Stabilizer

[0200] Poly(ethylene glycol) methacrylate (PEGMA) stabilizer (M.sub.n=360 Da) (0.04 g, 1.6 wt. % based on the weight of DEAEMA), 2-(diethylamino)ethyl methacrylate (DEAEMA) monomer (2.5 g) and ethylene glycol dimethacrylate (EGDMA) cross-linking monomer (0.012 g, 0.5 wt. % based on the weight of DEAEMA) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator potassium persulfate (KPS) (0.025 g, 1 wt. % based on the weight of DEAEMA) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and purged for 10 minutes with nitrogen. The degassed KPS solution was added to the degassed surfactant and monomer solution to initiate polymerization. The polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 470 nm with a dispersity of 0.16.

(b) 5 wt. % Cross-Linker (EGDMA) with PEGMA Stabilizer

[0201] Poly(ethylene glycol) methacrylate (PEGMA) stabilizer (M.sub.n=360 Da) (0.04 g, 1.6 wt. % based on the weight of DEAEMA), 2-(diethylamino)ethyl methacrylate (DEAEMA) monomer (2.5 g), and ethylene glycol dimethacrylate (EGDMA) cross-linking monomer (0.125 g, 5 wt. % based on the weight of DEAEMA) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator potassium persulfate (KPS) (0.025 g, 1 wt. % to DEAEMA) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and purged for 10 minutes with nitrogen. The degassed KPS solution was added to the degassed surfactant and monomer solution to initiate polymerization. The polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 150 nm with a dispersity of 0.19.

[0202] Poly(N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate) (PDMAPS) stabilizer (M.sub.n=20,000 Da) having a dithiobenzoate chain transfer agent (CTA) end-group prepared according to the procedure described above (0.1 g, 4 wt. % based on the weight of DEAEMA), 2-(diethylamino)ethyl methacrylate (DEAEMA) monomer (2.5 g) and ethylene glycol dimethacrylate (EGDMA) cross-linking monomer (0.012 g, 0.5 wt. % based on the weight of DEAEMA) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator potassium persulfate (KPS) (0.025 g, 1 wt. % based on the weight of DEAEMA) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and purged for 10 minutes with nitrogen. The degassed KPS solution was added to the degassed surfactant and monomer solution to initiate polymerization. The polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 130 nm with a dispersity of 0.40.

(d) 5 wt. % Cross-Linker (EGDMA) with PDMAPS Stabilizer

[0203] Poly(N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate) (PDMAPS) stabilizer (M.sub.n=20,000 Da) having a dithiobenzoate chain transfer agent (CTA) end-group prepared according to the procedure described above (0.1 g, 4 wt. % based on the weight of DEAEMA), 2-(diethylamino)ethyl methacrylate (DEAEMA) monomer (2.5 g) and ethylene glycol dimethacrylate (EGDMA) cross-linking monomer (0.125 g, 5 wt. % based on the weight of DEAEMA) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator potassium persulfate (KPS) (0.025 g, 1 wt. % based on the weight of DEAEMA) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and purged for 10 minutes with nitrogen. The degassed KPS solution was added to the degassed surfactant and monomer solution to initiate polymerization. The polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 130 nm with a dispersity of 0.08.

Synthesis of Precursor Microparticles Comprising Copolymers of 2-(diethylamino)ethyl methacrylate (DEAEMA) and benzyl methacrylate (BnMA)

[0204] Precursor microparticles comprising copolymers of 2-(diethylamino)ethyl methacrylate (DEAEMA) and benzyl methacrylate (BnMA) were prepared using different weight ratios of DEAEMA and BnMA.

(a) 1:1 Weight Ratio of DEAEMA:BnMA

[0205] Poly(N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate) (PDMAPS) (M.sub.n=5000 Da) having a dithiobenzoate chain transfer agent (CTA) end-group prepared according to the procedure described above (0.1 g, 4 wt. % based on the total weight of monomer), the monomers benzyl methacrylate (BnMA) (1.25 g) and 2-(diethylamino)ethyl methacrylate (DEAEMA) (1.25 g) and the cross-linking monomer ethylene glycol dimethacrylate (EGDMA) (0.025 g, 1 wt. % based on the total weight of monomer) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator potassium persulfate (KPS) (0.025 g, 1 wt. % based on the total weight of monomer) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and purged for 10 minutes with nitrogen. The degassed KPS solution was added to the degassed surfactant and monomer solution to initiate polymerization. The mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 70 nm with a dispersity of 0.03.

(b) 0.7:0.3 Weight Ratio of DEAEMA:BnMA

[0206] Poly(N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate) (PDMAPS) (M.sub.n=5000 Da) having a dithiobenzoate chain transfer agent (CTA) end-group prepared according to the procedure described above (0.1 g, 4 wt. % based on the total weight of monomer), the monomers benzyl methacrylate (BnMA) (0.75 g) and 2-(diethylamino)ethyl methacrylate (DEAEMA) (1.75 g) and the cross-linking monomer ethylene glycol dimethacrylate (EGDMA) (0.025 g, 1 wt. % based on the total weight of monomer) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator potassium persulfate (KPS) (0.025 g, 1 wt. % to overall monomer) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and purged for 10 minutes with nitrogen. The degassed KPS solution was added to the degassed surfactant and monomer solution to initiate polymerization. The polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 75 nm with a dispersity of 0.05.

Synthesis of Precursor Microparticles by Varying the Dialkylaminoalkyl (Alkyl)acrylate Monomer

[0207] A number of experiments were performed in which the dialkylaminoalkyl (alkyl)acrylate used in the preparation of the precursor microparticles was varied:

Synthesis of Poly(2-(diisopropylamino)ethyl methacrylate) (PDPAEMA) Precursor Microparticles

[0208] A number of syntheses of poly 2-(diisopropylamino)ethyl methacrylate (PDPAEMA) precursor microparticles were prepared using different polymeric stabilizers.

(a) Synthesis of Poly(2-(diisopropylamino)ethyl methacrylate) (PDPAEMA) Precursor Microparticles Using PEGMA (M.SUB.n.=360 Da) as a Polymeric Stabilizer

[0209] Poly(ethylene glycol) methacrylate (PEGMA) stabilizer (M.sub.n=360 Da) (0.08 g, 3.2 wt. % based on the weight of the DPAEMA monomer), 2-(diisopropylamino)ethyl methacrylate (DPAEMA) monomer (2.5 g) and ethylene glycol dimethacrylate (EGDMA) cross-linking monomer (0.025 g, 1 wt. % based on the weight of DPAEMA monomer) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator potassium persulfate (KPS) (0.025 g, 1 wt. % of the DPAEMA monomer) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and the resulting solution was purged for 10 minutes with nitrogen. The degassed KPS solution was then added to the degassed surfactant and monomer solution to initiate polymerization. The resulting polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 360 nm with a dispersity of 0.03.

(b) Synthesis of Poly(2-(diisopropylamino)ethyl methacrylate) (PDPAEMA) Precursor Microparticles Using PEGMA (M.SUB.n.=2000 Da) as a Polymeric Stabilizer

[0210] PEGMA stabilizer (M.sub.n=2000 Da) (0.20 g, 8 wt. % based on the weight of the DPAEMA monomer), DPAEMA monomer (2.5 g) and EGDMA cross-linking monomer (0.025 g, 1 wt. % based on the weight of DPAEMA monomer) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator KPS (0.025 g, 1 wt. % of the DPAEMA monomer) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and the resulting solution was purged for 10 minutes with nitrogen. The degassed KPS solution was then added to the degassed surfactant and monomer solution to initiate polymerization. The resulting polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 260 nm with a dispersity of 0.06.

(c) Synthesis of Poly(2-(diisopropylamino)ethyl methacrylate) (PDPAEMA) Precursor Microparticles Using PDMAPS (M.SUB.n.=5000 Da) as Polymeric Stabilizer

[0211] Poly(N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate) (PDMAPS) stabilizer having a dithiobenzoate chain transfer agent (CTA) end-group (M.sub.n=5000 Da) prepared using the procedure described above (0.1 g, 4 wt. % based on the weight of DPAEMA monomer), 2-(diisopropylamino)ethyl methacrylate (DPAEMA) monomer (2.5 g) and EGDMA cross-linking monomer (0.025 g, 1 wt. % based on the weight of DPAEMA monomer) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator KPS (0.025 g, 1 wt. % of the DPAEMA monomer) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and the resulting solution was purged for 10 minutes with nitrogen. The degassed KPS solution was then added to the degassed surfactant and monomer solution to initiate polymerization. The resulting polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 130 nm with a dispersity of 0.01.

Synthesis of Poly(2-(dimethylamino)ethyl methacrylate) (DMAEMA) Precursor Microparticles

[0212] SDS surfactant (0.24 g, 20 wt. % based on the weight of DMAEMA), 2-(dimethylamino)ethyl methacrylate (DMAEMA) monomer (1.2 g) and ethylene glycol dimethacrylate (EGDMA) cross-linking monomer (0.012 g, 1 wt. % based on the weight of DMAEMA) were dispersed in water (38 mL) having a resistivity of 18.2 M.Math.cm (with the pH adjusted to a value of 9 to ensure the DMAEMA was deprotonated and water insoluble) by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator potassium persulfate (KPS) (0.012 g, 1 wt. % based on the weight of DMAEMA) was dispersed separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and purged for 10 minutes with nitrogen. The degassed KPS solution was added to the degassed surfactant and monomer solution to initiate polymerization. The polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting particles were obtained as a dispersion in water. DLS analysis revealed the particles were ill-defined with a size range of D.sub.h=10-20 nm.

Synthesis of Poly(3-(dimethylamino)propyl methacrylamide) (PDMAPMA) Precursor Microparticles Using sodium dodecyl sulfate (SDS) as a Surfactant Stabilizer by Dispersion Polymerization

[0213] SDS surfactant (0.10 g, 20 wt. % based on the weight of the DMAPMA monomer), 3-(dimethylamino)propyl methacrylamide (DMAPMA) monomer (0.5 g) and N,N-methylenebisacrylamide (MBAc) cross-linking monomer (0.005 g, 1 wt. % based on the weight of DMAPMA monomer) were dispersed in water (49 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator potassium persulfate (KPS) (0.005 g, 1 wt. % of the DMAPMA monomer) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and purged for 10 minutes with nitrogen. The degassed KPS solution was added to the degassed surfactant and monomer solution to initiate polymerization. The resulting polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 11 nm with a dispersity of 0.26.

Synthesis of Poly(N-(4-vinylbenzyl)-N,N-dimethylamine) (PVBDMA) Precursor Microparticles

[0214] N-(4-Vinylbenzyl)-N,N-dimethylamine (VBDMA) was selected as an example of a vinylbenzyldialkylamine monomer. This example also demonstrates variation of the cross-linking monomer with use of a styrenic cross-linker divinylbenzene (DVB).

Synthesis of Poly(N-(4-vinylbenzyl)-N,N-dimethylamine) (PVBDMA) Precursor Microparticles Using Sodium Dodecylsulfate (SDS) as a Surfactant Stabilizer

[0215] SDS surfactant (0.10 g, 20 wt. % based on the weight of the VBDMA monomer), N-(4-vinylbenzyl)-N,N-dimethylamine (VBDMA) monomer (0.5 g) and divinylbenzene (DVB) cross-linking monomer (0.005 g, 1 wt. % based on the weight of VBDMA monomer) were dispersed in water (49 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator potassium persulfate (KPS) (0.005 g, 1 wt. % of the VBDMA monomer) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and purged for 10 minutes with nitrogen. The degassed KPS solution was added to the degassed surfactant and monomer solution to initiate polymerization. The resulting polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 48 nm with a dispersity of 0.08.

Synthesis of Poly(N-(4-vinylbenzyl)-N,N-dimethylamine) (PVBDMA) Precursor Microparticles Using PEGMA (M.SUB.n.=2000 Da) as a Polymeric Stabilizer

[0216] PEGMA stabilizer (M.sub.n=2000 Da) (0.13 g, 7.6 wt. % based on the weight of the VBDMA monomer), VBDMA monomer (2.5 g) and divinylbenzene (DVB) cross-linking monomer (0.025 g, 1 wt. % based on the weight of VBDMA monomer) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator KPS (0.025 g, 1 wt. % of the VBDMA monomer) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and the resulting solution was purged for 10 minutes with nitrogen. The degassed KPS solution was then added to the degassed surfactant and monomer solution to initiate polymerization. The resulting polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting microparticles were obtained as a dispersion in water, however a large amount of particle aggregation was observed. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 250 nm with a dispersity of 0.29.

Synthesis of Polyvinyl-N-heterocyclic amine Precursor Microparticles

[0217] Poly(4-Vinylpyridine) (P4VP) was selected as an example of a vinyl-N-heterocyclic amine monomer.

Synthesis of Poly(4-vinylpyridine) (P4VP) Precursor Microparticles by Emulsion Polymerization Using PDMAPS (M.SUB.n.=5000 Da) as Polymeric Stabilizer

[0218] Poly(N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate) (PDMAPS) stabilizer having a dithiobenzoate chain transfer agent (CTA) end-group (M.sub.n=5000 Da) prepared according to the procedure described above (0.1 g, 4 wt. % based on the weight of 4-VP monomer), 4-vinylpyridine (4-VP) monomer (2.5 g) and divinylbenzene (DVB) cross-linking monomer (0.025 g, 1 wt. % based on the weight of 4-VP monomer) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator KPS (0.025 g, 1 wt. % of the 4-VP monomer) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and the resulting solution was purged for 10 minutes with nitrogen. The degassed KPS solution was then added to the degassed surfactant and monomer solution to initiate polymerization. The resulting polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 150 nm with a dispersity of 0.07.

Synthesis of Poly(4-vinylpyridine) (P4VP) Precursor Microparticles using Surfactant Free Emulsion Polymerization

[0219] 4-Vinylpyridine (4-VP) monomer (1 g) and divinylbenzene (DVB) cross-linking monomer (0.005 g, 0.5 wt. % based on the weight of 4-VP monomer) were dispersed in water (44 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring. The radical initiator KPS (0.01 g, 1 wt. % of the 4-VP monomer) was dissolved separately in water (1 mL) having a resistivity of 18.2 M.Math.cm and the resulting solution was purged for 10 minutes with nitrogen. The degassed KPS solution was then added to the degassed surfactant and monomer solution to initiate polymerization. The resulting polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 200 nm with a dispersity of 0.04.

Betainisation Reactions

Sulfobetainisation of PDEAEMA Precursor Microparticles

(a) Use of Propane Sultone as Sulfobetainisation Reagent

[0220] HPLC grade tetrahydrofuran (THF)(4 mL) was added dropwise to a dispersion of PDEAEMA precursor microparticles having a PEGMA shell (PEGMA M.sub.n=360 Da) dispersed in water (4 mL) having a resistivity of 18.2 M.Math.cm (particle concentration=50 mg/mL) with stirring. 1,3-propane sultone (0.069 g, 0.5 molar equivalents based on the structural units derived from DEAEMA in the precursor microparticles) was added and the solution stirred for 16 hours at a temperature of 60 C. Trimethylamine (0.3 mL of a 1M solution in THF, 1 molar equivalent based on the molar amount of 1,3-propane sultone) was added (to react with any unreacted 1,3-propane sultone) and the dispersion stirred for a further 16 hours. The betainised microparticles were purified by extensive dialysis against deionised water (using dialysis tubing having a 1-14 kDa molecular weight cut-off (MWCO)) with at least 6 changes of water.

[0221] In an alternative synthetic method, HPLC grade THF (25 mL) was added to freeze-dried PDEAEMA particles (0.5 g) to give a concentration of precursor microparticles of 20 mg/mL and the mixture was sonicated to disperse the precursor microparticles. 1,3-propane sultone (0.16 g, 0.5 molar equivalents based on the structural units derived from DEAEMA repeat in the precursor microparticles) was added and the dispersion stirred for 16 hours at a temperature of 60 C. Trimethylamine (0.3 mL of a 1M solution in THF, 1 molar equivalent based on the molar amount of 1,3-propane sultone) was added (to react with any unreacted 1,3-propane sultone) and the dispersion stirred for a further 16 hours. The sulfobetainised microparticles were purified by extensive dialysis against deionised water (using dialysis tubing having a 12-14 kDa molecular weight cut-off (MWCO)) with at least 6 changes of water. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 150 nm with a dispersity of 0.03.

(b) Use of Sodium 3-Bromopropane Sulfonate as Sulfobetainisation Reagent

[0222] Propan-2-ol (300 mL), sodium 3-bromopropane sulfonate (6.0 g, 0.33 molar equivalents based on the structural units derived from DEAEMA in the precursor microparticles) and NaOH (20 mL of 0.2M aqueous solution, 0.05 molar equivalents based on the structural units derived from DEAEMA in the precursor microparticles) were added portion-wise to a dispersion of PDEAEMA particles in water (300 mL) having a resistivity of 18.2 M.Math.cm (precursor microparticle concentration=50 mg/mL). The dispersion was heated to a temperature of 75 C. and stirred for 40 hours. Unreacted sodium 3-bromopropane sulfonate reactant, propan-2-ol solvent and NaBr by-product were removed via extensive dialysis against deionised water (using dialysis tubing having a 12-14 kDa MWCO) with at least 6 changes of water. The resulting well-defined sulfobetainised microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 100 nm with a dispersity of 0.05.

[0223] The above procedure was modified by using 0.25. 0.5, 0.75 and 3 molar equivalents of the betainisation reagent sodium 3-bromopropane sulfonate (based on the structural units derived from DEAEMA in the precursor microparticles) to target 25%, 50%, 75% and 100% betainisation respectively of the precursor microparticles. The resulting well-defined sulfobetainised microparticles were obtained as dispersions in water. The hydrodynamic diameter (D.sub.h) of the 25%, 50%, 75% and 100% betainised microparticles were determined to be 100, 110, 110 and 190 nm respectively by DLS.

[0224] Propan-2-ol (300 mL), sodium 4-bromobutane sulfonate (6.5 g, 0.33 molar equivalents based on the structural units derived from DEAEMA in the precursor microparticles) and NaOH (20 mL of 0.2M aqueous solution, 0.05 molar equivalents based on the structural units derived from DEAEMA in the precursor microparticles) were added portion-wise to a dispersion of PDEAEMA particles in water (300 mL) having a resistivity of 18.2 M.Math.cm (precursor microparticle concentration=50 mg/mL). The dispersion was heated to a temperature of 75 C. and stirred at this temperature for 40 hours. Unreacted sodium 4-bromobutane sulfonate, propan-2-ol solvent and NaBr by-product were removed via extensive dialysis against deionised water (using dialysis tubing having a 14 kDa MWCO) with at least 6 changes of water. The resulting well-defined sulfobetainised microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 120 nm with a dispersity of 0.08.

(d) Use of Sodium 2-Bromo-1-Ethane Sulfonate as Sulfobetainisation Reagent

[0225] Propan-2-ol (3 mL), sodium 2-bromo-1-ethane sulfonate (0.043 g, 0.25 molar equivalents based on the structural units derived from DEAEMA in the precursor microparticles) and NaOH (0.80 mL of 0.2M aqueous solution, 0.05 molar equivalents based on the structural units derived from DEAEMA in the precursor microparticles) were added portion-wise to a dispersion of PDEAEMA particles with a PDMAPS shell (M.sub.n=5000 Da) dispersed in water (3 mL) having a resistivity of 18.2 M.Math.cm (precursor microparticle concentration=50 mg/mL). The dispersion was heated to a temperature of 75 C. and stirred for 40 hours. Unreacted sodium 2-bromo-1-ethane sulfonate, propan-2-ol solvent and NaBr by-product were removed via extensive dialysis against deionized water (using dialysis tubing having a 14 kDa MWCO) with at least 6 changes of water. The resulting sulfobetainised microparticles were found to aggregate and precipitate in both ultrapure water (resistivity of 18.2 M.Math.cm) and 0.3M NaCl.

(e) Use of Sodium 3-chloro-2-hydroxy-1-propane sulfonate as Sulfobetainisation Reagent

[0226] Propan-2-ol (3 mL), sodium 3-chloro-2-hydroxy-1-propane sulfonate (0.055 g, 0.33 molar equivalents based on the structural units derived from DEAEMA in the precursor microparticles) and NaOH (0.80 mL of 0.2M aqueous solution, 0.05 molar equivalents based on the structural units derived from DEAEMA in the precursor microparticles) were added portion-wise to a dispersion of PDEAEMA particles with a PDMAPS shell (M.sub.n=5000 Da) dispersed in water (3 mL) having a resistivity of 18.2 M.Math.cm (precursor microparticle concentration=50 mg/mL). The dispersion was heated to a temperature of 75 C. and stirred for 40 hours. Unreacted sodium 3-chloro-2-hydroxy-1-propane sulfonate, propan-2-ol solvent and NaCl by-product were removed via extensive dialysis against deionized water (using dialysis tubing having a 14 kDa MWCO) with at least 6 changes of water. The resulting well-defined sulfobetainised microparticles were obtained as a dispersion in water. The microparticles were found to have a betainisation level of ca. 30%.

[0227] The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 96 nm with a dispersity of 0.28. Variable temperature dynamic light scattering (DLS) experiments were performed to determine how the size (D.sub.h) of the hydroxysulfobetained microparticles varied with temperature when dispersed in ultra-pure water having a resistivity of 18.2 M.Math.cm water. The results are shown in FIG. 6b

Sulfabetainisation of PDEAEMA Precursor Microparticles

Use of 1,3,2-Dioxathiane 2,2-dioxide as a Sulfabetainisation Reagent

[0228] Tetrahydrofuran (THF) (3 mL) was added dropwise to a dispersion of PDEAEMA precursor microparticles with a PDMAPS shell (M.sub.n=5000 Da) dispersed in water having a resistivity of 18.2 M.Math.cm (3 mL, particle concentration=50 mg/mL) with stirring. 1,3,2-Dioxathiane 2,2-dioxide (0.056 g, 0.5 molar equivalents based on the structural units derived from DEAEMA in the precursor microparticles) was added and the solution stirred for 16 hours at a temperature of 65 C. The resulting sulfabetainised microparticles were purified by extensive dialysis against deionized water (using dialysis tubing having a 12-14 kDa molecular weight cut-off (MWCO)) with at least 6 changes of water. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 240 nm with a dispersity of 0.02.

Carboxybetainisation of PDEAEMA Precursor Microparticles

[0229] Propan-2-ol (3 mL), sodium iodoacetate (0.084 g, 0.50 molar equivalents based on the structural units derived from DEAEMA in the precursor microparticles) and NaOH (0.80 mL of 0.2M aqueous solution, 0.05 molar equivalents based on the structural units derived from DEAEMA in the precursor microparticles) were added portion-wise to a dispersion of PDEAEMA particles with a PDMAPS shell (M.sub.n=5000 Da) dispersed in water (3 mL) having a resistivity of 18.2 M.Math.cm (precursor microparticle concentration=50 mg/mL). The dispersion was stirred at room temperature for 24 hours. Unreacted sodium iodoacetate, propan-2-ol solvent and NaI by-product were removed via extensive dialysis against deionized water (using dialysis tubing having a 14 kDa MWCO) with at least 6 changes of water. The resulting well-defined carboxybetainised microparticles were obtained as a dispersion in water.

[0230] The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 140 nm with a dispersity of 0.02. Variable temperature dynamic light scattering (DLS) experiments were performed to determine how the size (D.sub.h) of the carboxybetainised microparticles varied with temperature when dispersed in deionised water. The results are shown in FIG. 6c

Dynamic Light Scattering Temperature Experiments

[0231] Dynamic light scattering (DLS) experiments were performed to determine how polysulfobetaine particle size (D.sub.h) varied with temperature. DLS experiments were performed using a Malvern Zetasizer NanoS instrument with a 4 mW HeNe 633 nm laser module and the data was analyzed using Malvern DTS v7.3.0 software. Polysulfobetainised microparticle dispersions were analyzed at a concentration of 1 mg/mL (in a quartz cuvette). Data was collected a temperature intervals of 5 C. over a temperature range (for example, over a temperature range of 5 C. to 90 C.) and the microparticle dispersion was allowed to equilibrate for at least five minutes at each temperature. At least 3 measurements were made at each temperature and data was reported as an average of these measurements.

[0232] FIG. 3 shows how the hydrodynamic diameter (D.sub.h) of polysulfobetaine microparticles change with temperature when dispersed in ultra-pure water having a resistivity of 18.2 M.Math.cm water. The results presented in FIG. 3 are for microparticles with 50%, 75% and 100% levels of sulfobetainisation.

[0233] FIG. 4 shows how polysulfobetained microparticle hydrodynamic diameter (D.sub.h) changes with temperature for microparticles dispersed in a 0.3M solution of sodium chloride. The microparticles have a 50% level of betainisation and either a n-propyl or n-butyl group linking the ammonium and sulfonate groups of the betaine moiety.

[0234] To test the reversibility of microparticle expansion and aggregation by DLS, the polysulfobetaine dispersions were cycled between two temperatures, one below the transition temperature and one above the transition temperature, for example, 35 and 70 C. respectively for a transition temperature of 50 C. The microparticles were heated at the higher temperature for 10 minutes per cycle and then allowed to cool to the lower temperature for up to 3 hours per cycle. FIG. 5 shows the reversible microparticle expansion and aggregation of polysulfobetaine microparticles in a 0.3M solution of NaCl (wherein the microparticles have a target betainisation level of 50%) where the microparticles were subjected to three heating and cooling cycles and microparticle size (hydrodynamic diameter, D.sub.h) was determined by dynamic light scattering at temperatures of 35 and 70 C. during these heating and cooling cycles.

Scaled-Up Synthesis of PDEAEMA Precursor Microparticles and Betainisation of the Precursor Microparticles

[0235] To prepare larger volumes of polysulfobetaine microparticle dispersions, the emulsion polymerization of DEAEMA was performed on a larger scale using 10 g DEAEMA monomer, compared with previous examples using 2.5 g of DEAEMA monomer.

Precursor Microparticle Synthesis (10 g Scale)

[0236] PDEAEMA precursor microparticles were prepared at an increased scale (4 original scale) using 10 g of DEAEMA as follows:

[0237] Poly(N,N-dimethyl(methacryloylethyl)ammonium propane sulfonate) (PDMAPS) stabilizer having a dithiobenzoate chain transfer agent (CTA) end-group (M.sub.n=5000 Da) (0.40 g, 4 wt. % based on the weight of DEAEMA monomer), 2-(diethylamino)ethyl methacrylate (DEAEMA) monomer (10 g) and ethylene glycol dimethacrylate (EGDMA) cross-linking monomer (0.10 g, 1 wt. % based on the weight of DEAEMA monomer) were dispersed in water (176 mL) having a resistivity of 18.2 M.Math.cm by stirring (in the order listed). The resulting mixture was purged with nitrogen for 30 minutes with stirring and then heated for 30 minutes in an oil bath at a temperature of 65 C. with stirring.

[0238] The radical initiator potassium persulfate (KPS) (0.10 g, 1 wt. % based on the weight of DEAEMA monomer) was dissolved separately in water (4 mL) having a resistivity of 18.2 M.Math.cm and purged for 10 minutes with nitrogen. The degassed KPS solution was added to the degassed surfactant and monomer solution to initiate polymerization. The polymerization mixture was heated in an oil bath with stirring (magnetic stirrer with oval shaped bar, 600 rpm) at a temperature of 65 C. for 16 hours. The resulting well-defined microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 105 nm with a dispersity of 0.04.

Sulfobetainisation of the Precursor Microparticles

[0239] The resulting PDEAEMA microparticles were betainised using the procedure given in Example 5(a). The resulting well-defined polysulfobetaine microparticles were obtained as a dispersion in water. The hydrodynamic diameter (D.sub.h) of the microparticles was determined by dynamic light scattering and found to be 120 nm with a dispersity of 0.07.

[0240] FIG. 6 shows the DLS analytical data at a temperature of 25 C. for polysulfobetaine microparticles synthesised using the 2.5 g, and 10 g procedures.

Sandpack Experiments

[0241] Sandpack tests were performed using a pack of a granular material (often referred to in the art as sand) located in a cylindrical tubing (often referred to in the art as a column) designed to simulate reservoir rock.

[0242] The sandpack comprised a 6.95 mm internal diameter, 9.53 mm external diameter column having a length of approximately 5 feet (152 cm) containing a dry sand. The column had four equally spaced pressure taps arranged along its length as shown in FIGS. 7a and 7b. The sandpack was provided with trace heating for heating the sandpack. Sections of the sandpack between adjacent pressure taps may be heated to different temperatures using the trace heating (as shown in FIGS. 7a and 7b). The compositions of the sands used for the sandpack tests are given below in Table 1 and the particle size distributions (screen analyses) in Tables 2 and 3. Sand A (RH110 DRY sand supplied by SIBELCO UK Ltd) was used for high permeability tests and Sand B (a sand supplied by AGSCO Corporation) was used for low permeability tests. The sands were retained in the column by means of: a 316L stainless steel mesh (25 m, 500 mesh size) arranged at each of the pressure taps; a 316L stainless steel mesh (100 m, 140 mesh size) arranged at the inlet of the column; and, a 316L stainless steel mesh (25 m, 500 mesh size) arranged at the outlet of the column.

TABLE-US-00001 TABLE 1 Compositions of Sands A and B Sand B Sand A Typical Amount Mineral Typical Amount (weight %) (weight %) SiO.sub.2 99.38 99.5 Fe.sub.2O.sub.3 0.091 0.05 Al.sub.2O.sub.3 0.18 0.02 TiO.sub.2 0.15 0.005 K.sub.2O 0.02 Na.sub.2O <0.05 0.05 ZrO.sub.2 0.01 MgO 0.002 CaO 0.01 SrO 0.002 Cr <0.002 P <0.01 CO.sub.3.sup.2 <0.01 Loss on ignition 0.12 0.1

TABLE-US-00002 TABLE 2 Typical Particle size distribution of Sand A: Cumulative Cumulative Amount of Amount of Sieve Amount of Sand A Sand A Mesh Sand A Passing Retained by Retained by Retained Size through Sieve Sieve (weight Each Sieve Sand A (microns) (weight %) %) (weight %) (weight %) 1000 100.0 0.0 0.0 0.0 710 100.0 0.0 0.0 0.1 500 99.9 0.1 0.1 355 99.8 0.2 0.1 1.0 250 98.9 1.1 0.9 180 83.2 16.8 15.7 65.2 125 33.7 66.3 49.5 90 9.1 90.0 24.6 32.6 63 1.1 98.9 8.0 <63 100.0 1.1 1.1

TABLE-US-00003 TABLE 3 Typical Screen Analysis (Percent Retained) Sand B: US Sieve #4 #3 #2 #1 #1/2 #2/0 #3/0 #4/0 12 11.0 14 25.4 16 26.0 18 21.3 20 11.9 25.3 25 4.3 31.7 30 0.1 25.6 3.6 35 10.6 13.4 40 4.2 25.8 50 2.6 41.6 1.6 60 10.3 33.5 1.5 70 4.3 38.7 13.5 80 1.0 18.4 22.2 100 4.4 18.1 1.9 120 1.0 18.8 21.0 140 0.4 15.4 36.5 6.5 0.6 170 7.5 21.1 19.5 1.0 200 2.6 9.8 19.9 1.9 230 0.4 5.5 21.0 1.4 270 2.8 18.3 2.0 325 0.9 5.0 8.3 Pan Trace Trace Trace Trace Trace 0.5 9.8 83.9 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Sandpack Test Methodology

[0243] The sandpack containing either Sand A or Sand B was saturated with a test brine (0.3M solution of NaCl), delivered by a high pressure liquid chromatography (HPLC) pump, at a constant flow rate of 1.0 ml/min for a minimum of 16 hours, until stable differential pressures were obtained across the entire sandpack and across each individual section of the sandpack (i.e. the sections of the sandpack located between adjacent pressure taps). During this time, the sandpack and test fluids were maintained at an ambient temperature of between 18 and 21 C. The permeability of the entire sandpack and of each individual section of the sandpack to the test brine was determined at flow rates of 0.025, 0.05, 0.1, 0.2 and 0.4 ml/min and at ambient temperature.

[0244] The sandpack was then heated to a test temperature (approximately 5 C. greater than the maximum transition temperature of the betainised crosslinked polymeric microparticles of the test composition, which temperature was reached within 1 hour) and baseline differential pressures for the test brine at a flow rate of 0.1 ml/min were obtained across the whole sandpack and across each individual section of sandpack.

[0245] The sandpack was then cooled to ambient temperature. Once at ambient temperature, the test brine was reinjected into the sandpack at a flow rate of 0.1 ml/min until stable differential pressures were achieved across the entire sandpack and each individual section of the sandpack.

[0246] The test composition comprising a dispersion of the sulfobetainised crosslinked polymeric microparticles (1000, 2500 or 5000 ppm wt/vol) in an aqueous fluid (0.3 M solution of sodium chloride) was then injected at a flow rate of 0.1 ml/min until the sandpack was saturated with the composition (typically, after 40 to 48 hours). This saturation point was determined by visual comparison of the sandpack effluent with the pre-injected composition as well as from the stability of the differential pressures obtained across the entire sandpack and across the individual sections of the sandpack. Having saturated the sandpack with the test composition, the temperature of the sandpack was increased to the test temperature until a block of expanded microparticles was formed (typically, 12 to 24 hours) as evidenced by an increase in differential pressure across one or more sections of the sandpack (where the block has formed) that is equal to, or in excess of, a resistance factor (RF) of 20, i.e.,

[00001] $RF = \frac{_{w}}{_{p}} 20$

and .sub.w and .sub.p are the mobilities of the test brine and of the test composition. Once an RF>20 had been formed in one or more sections of the sandpack, the sandpack was cooled back to ambient temperature (over typically 2 to 3 hours) whilst continuing to inject the test composition at a constant flow rate of 0.1 ml/min until the block had dissipated (dispersed) and/or had been flushed from the sandpack.

[0247] The test brine was then re-injected at a flow rate of 0.1 ml/min and at ambient temperature until any remaining test composition was flushed from the sandpack. The permeability of the sandpack and of each individual section of the sandpack was again determined by injecting the test brine at flow rates of 0.025, 0.05, 0.1, 0.2 and 0.4 ml/min and at ambient temperature.

[0248] The difference between the initial and final permeabilities of the sandpack, measured as residual resistance factor (RRF), was then taken as an indication of the reversibility of the formed block:

[00002] $RRF = \frac{_{w}}{_{wp}}$

where .sub.w and .sub.wp are the mobilities to the test brine before and after injection of the dispersion of polymeric microparticles, when measured at the same flow rate.

Sandpack Experiments Using the Five Foot Sandpack

[0249] Three sandpack tests (Tests 1 to 3) were performed using the five foot (152 cm) sandpack. The compositions used in the tests comprised sulfobetainised crosslinked microparticles having a transition temperature of 60 C. (Tests 1 and 3) or a transition temperature of 80 C. (Test 2). The sandpack used in Tests 1 and 2 comprised Sand A having a permeability of approximately 6.5D (Darcy). The sandpack used in Test 3 comprised Sand B having a permeability of 280 mD (milliDarcy).

[0250] Initial permeabilities for a 0.3 M NaCl brine across the sandpacks were determined at ambient temperature and were averaged for all test flow rates. These average initial permeabilities are given in Table 4 below.

[0251] After the initial permeabilities to the 0.3 M NaCl brine had been obtained, the trace heating for the sandpacks was switched on, thereby achieving the temperatures given in FIG. 7a (Tests 1 and 3) and FIG. 7b (Test 2). Baseline differential pressures using the 0.3M NaCl brine, at a test flow rate of 0.1 ml/min and at the test temperature, were then obtained. The sandpacks were then cooled to ambient temperature and a test composition comprising sulfobetainized crosslinked microparticles dispersed in the sodium chloride brine was then injected.

[0252] In Test 1, the sandpack was initially injected with a composition having a concentration of microparticles of 1000 ppm before injecting a composition having a test concentration of microparticles of 5000 ppm (the microparticles having a transition temperature of 60 C.). In Test 2, the sandpack was injected with a composition having a test concentration of microparticles of 5000 ppm (the microparticles having a transition temperature of 80 C.). In Test 3, three different microparticle test compositions were injected having initial, intermediate and final (test) concentrations of microparticles of 1000 ppm, 2500 ppm and 5000 ppm respectively (the microparticles having transition temperatures of 60 C.).

[0253] In each of Tests 1 to 3, the microparticles were found to both successfully inject into and propagate through the sandpacks. In Test 3, with the low permeability 250 mD sandpack, consecutive rises in differential pressures across successive pack sections provided evidence that the microparticles propagated through each section of the pack. A rise in differential pressure was not seen in the more permeable 6.5D packs (Tests 1 and 2). FIG. 8 shows the differential pressures for Tests 1 and 3 (for the high and low permeability sandpacks) during injection of microparticle compositions having concentrations of microparticles of 1000 ppm (the microparticles having a transition temperature of 60 C.).

[0254] Once the sandpacks were saturated with the microparticle composition, i.e., the concentration of microparticles in the effluent removed from the column was equivalent to the concentration of microparticles in the stock microparticle composition (the composition prior to injection into the column), the trace heating for the sandpacks was turned on, to achieve the temperatures given in FIG. 7a or 7b. Microparticle compositions continued to be injected at a flow rate of 0.1 ml/min as the sandpacks were heated to the test temperatures. Injection of the microparticles at the test temperatures was continued until a resistance factor (RF) equal to or in excess of 20 was obtained. The trace heating was then turned off and, during cooling of the sandpack, injection of the microparticle composition was continued at a flow rate of 0.1 ml/min.

[0255] FIGS. 9a and 9b show the differential pressures during heating (block formation) and cooling (at about 43 hours) for Tests 1, 2 and 3. Block formation occurred in all cases in the sandpack section where the microparticles first reached the trigger temperature. This occurred in the second section of the sand packs (dP2 in FIGS. 7a and 7b). For Test 1 (having a sandpack permeability of 6.5D, and a microparticle transition temperature of 60 C.), an RF of 30 was achieved with a dp of about 10 psi. For Test 2 (having a sandpack permeability of 6.5D, and a microparticle transition temperature of 80 C.), an RF of 25 was achieved with a dp of about 5.5 psi. For Test 3 (having a sandpack permeability of 0.28D, and microparticle transition temperature of 60 C.), an RF of 20 was achieved with a dp of about 150 psi. It can be seen that for all three sandpacks, the blocks of microparticles dispersed upon cooling and the differential pressures returned to those similar to pre-blocking measurements. Further evidence for dispersion of the blocks is shown in FIG. 10 where the block becomes progressively smaller in size as it moves through subsequent sandpack sections (as evidenced by lower differential pressures with distance and with cooling).

[0256] Final permeabilities for a 0.3 M NaCl brine across the sandpacks for Tests 1 to 3 were determined at ambient temperature and were averaged for all test flow rates. These final permeabilities are also given in Table 4 below.

[0257] A measure of the reversibility of the microparticle block formation is given by the Residual Resistance Factor (RRF), with an RRF of 1 showing complete reversibility (and also no particle retention or adsorption). An RRF of up to 1.2 is an indication of good block reversibility. Table 5 below gives RRF values for Tests 1 to 3. It can be seen that for tests employing the 6.5D sandpacks (Tests 1 and 2) the RRF value was about 1.1 indicative of good block reversal. For Test 3 using the less permeable sandpack having a permeability of 0.28D, the RRF was higher at about 1.4. This may be due to microparticle retention in the low permeability sandpack rather than poor block reversal (poor dispersion of the microparticles). Table 5 also shows that the RRF in the section of the sandpack where the block was formed was higher than in other sections.

TABLE-US-00004 TABLE 4 Initial and final brine (0.3M NaCl) permeabilities for 5 foot sandpacks Sandpack Microparticle Initial or Final Permeability (D) Test UCST ( C.) Permeability 320dP dP1 dP2 dP3 dP4 dP5 1 60 Initial 6.62 6.63 5.84 6.22 7.39 8.00 Final 4.62 2.50 5.43 5.76 6.97 7.33 2 80 Initial 6.19 6.56 5.83 6.31 6.12 7.02 Final 5.73 5.78 5.58 5.73 5.53 6.28 Permeability (D) Inlet- PT4- PTdP PT1 PT1-PT2 PT2-PT3 PT3-PT4 outlet 3 60 Initial 0.281 0.258 0.273 0.283 0.285 0.312 Final 0.178 0.104 0.213 0.239 0.244 0.215 dP = differential pressure measured from a differential pressure transducer reading across the pack section. PTdP = differential pressure calculated as the difference of two single point pressure readings either side of a pack section.

TABLE-US-00005 TABLE 5 RRF (at flow rate of 0.1 ml/min) for 5 foot sandpacks, at ambient temperature Sandpack Microparticle RRF Test UCST ( C.) 320dP dP1 dP2 dP3 dP4 dP5 1 60 1.38 2.86 1.03 1.04 1.02 1.05 2 80 1.11 1.16 1.06 1.12 1.13 1.14 RRF Inlet- PT4- PTdP PT1 PT1-PT2 PT2-PT3 PT3-PT4 outlet 3 60 1.42 2.41 1.26 1.12 1.10 1.11 dP = differential pressure measured from a differential pressure transducer reading across a pack section PTdP = differential pressure calculated as the difference of two single point pressure readings either side of a pack section

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