Method for reducing the viscosity of viscosified fluids for applications in natural gas and oil fields

1. A method of reducing the viscosity of a viscosified treatment fluid in natural gas and/or oilfield stimulation processes comprising the steps of:

(i) providing a viscosified treatment fluid containing a water soluble polymeric gelling agent wherein the viscosified treatment fluid is prepared using natural occurring brines selected from the group consisting of formation water, produced water and/or flow back from a well after a stimulation process, and mixtures thereof, wherein the natural occurring brine has a total organic carbon (TOC) in the range of 310-5000 mg/I and a total dissolved solids (TDS) salt of at least 10,000 ppm, the water soluble polymeric gelling agent including at least structural units of formula (I)

wherein

R1, R2 and R3 independently are hydrogen or C 1 -C 6 -alkyl,

up to 95% by weight of the water soluble polymeric gelling agent of structural units of formula (II)

wherein

R4 is hydrogen or C 1 -C 6 -alkyl,

R5 is hydrogen, a cation of an alkaline metal, of an earth alkaline metal, of ammonia and/or of an organic amine,

A is a covalent C—S bond or a two-valent organic bridging group, and

up to 20% by weight of the water soluble polymeric gelling agent of structural units of formula (V)

wherein

R17 is hydrogen or, C 1 -C 6 -alkyl, and

R18 and R19 are independently of one another hydrogen, a cation of an alkaline metal, of an earth alkaline metal, of ammonia and/or of an organic amine,

B is a covalent C—P bond or a two-valent organic bridging group,

(ii) providing a breaker composition containing an aliphatic azo-compound selected from the group consisting of: 2,2′-Azobis[2-(2-imidazolin-2-yl)propane], 2,2′-Azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 2,2′-Azobis[2-(2-imidazolin-2-yl)propane]disulfate dihydrate, 2,2′-Azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}dihydrochloride, 2,2′-Azobis(2-methyl propionamidine) dihydrochloride, 2,2′-Azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate, 2,2′-Azobis(1-imino-1-pyrrolidino-2-ethylpropane)dihydrochloride, 2,2′-Azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2′-Azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethl]propionamide}, 2,2′-Azobis(2.4-dimethyl valeronitrile), 2,2′-Azobis(4-methoxy-2.4-dimethyl valeronitrile), Dimethyl 2,2′-azobis(2-methylpropionate), 1,1′-Azobis(cyclohexane-1-carbonitrile), 2,2′-Azobis[N-(2-propenyl)-2-methylpropionamide], 1-[(1-cyano-1-methylethyl)azo]formamide 2,2′-Azobis(N-butyl-2-methylpropionamide), 2,2′-Azobis(N-cyclohexyl-2-methylpropionamide), and mixtures thereof,

(iii) mixing said viscosified treatment fluid and said breaker composition and injecting the mixture of viscosified treatment fluid and breaker composition into a natural gas or oil reservoir,

(iv) allowing said viscosified treatment fluid and said breaker composition to interact whereby the viscosity of the viscosified treatment fluid is reduced.

2. The method of claim 1 wherein a concentration of the aliphatic azo compound ranges from 0.01 to 10% by weight, of the total mass of the aqueous polymer solution.

3. The method of claim 1 wherein the viscosified treatment fluid is injected at a temperature below 90° C.

4. The method of claim 1 wherein the viscosified treatment fluid is injected as hydraulic fracturing fluid.

5. A method of stimulating a natural gas and/or oil reservoir comprising the steps of:

(i) providing a viscosified treatment fluid containing a water soluble polymeric gelling agent wherein the viscosified treatment fluid is prepared using natural occurring brines selected from the group consisting of formation water, produced water and/or flow back from a well after a stimulation process, and mixtures thereof, wherein the natural occurring brine has a total organic carbon (TOC) in the range of 310-5000 mg/I and a total dissolved solids (TDS) salt of at least 10,000 ppm, the water soluble polymeric gelling agent including at least structural units of formula (I)

wherein

R1, R2 and R3 independently are hydrogen or C 1 -C 6 -alkyl,

up to 95% by weight of the water soluble polymeric gelling agent of structural units of formula (II)

wherein

R4 is hydrogen or C 1 -C 6 -alkyl,

R5 is hydrogen, a cation of an alkaline metal, of an earth alkaline metal, of ammonia and/or of an organic amine,

A is a covalent C—S bond or a two-valent organic bridging group, and

up to 20% by weight of the water soluble polymeric gelling agent of structural units of formula (V)

wherein

R17 is hydrogen or, C 1 -C 6 -alkyl, and

R18 and R19 are independently of one another hydrogen, a cation of an alkaline metal, of an earth alkaline metal, of ammonia and/or of an organic amine,

B is a covalent C—P bond or a two-valent organic bridging group,

(ii) providing a breaker composition containing an aliphatic azo-compound selected from the group consisting of: 2,2′-Azobis[2-(2-imidazolin-2-yl)propane], 2,2′-Azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 2,2′-Azobis[2-(2-imidazolin-2-yl)propane]disulfate dihydrate, 2,2′-Azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}dihydrochloride, 2,2′-Azobis(2-methyl propionamidine) dihydrochloride, 2,2′-Azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate, 2,2′-Azobis(1-imino-1-pyrrolidino-2-ethylpropane)dihydrochloride, 2,2′-Azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2′-Azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethl]propionamide}, 2,2′-Azobis(2.4-dimethyl valeronitrile), 2,2′-Azobis(4-methoxy-2.4-dimethyl valeronitrile), Dimethyl 2,2′-azobis(2-methylpropionate), 1,1′-Azobis(cyclohexane-1-carbonitrile), 2,2′-Azobis[N-(2-propenyl)-2-methylpropionamide], 1-[(1-cyano-1-methylethyl)azo]formamide 2,2′-Azobis(N-butyl-2-methylpropionamide), 2,2′-Azobis(N-cyclohexyl-2-methylpropionamide), and mixtures thereof,

(iii) mixing said viscosified treatment fluid and said breaker composition and injecting the mixture of viscosified treatment fluid and breaker composition into a natural gas or oil reservoir,

(iv) allowing said viscosified treatment fluid and said breaker composition to interact whereby the viscosity of the viscosified treatment fluid is reduced,

(v) removing the viscosity reduced fluid from step (iv) from the natural gas or oil reservoir.

6. A method for the production of oil and/or natural gas which includes the stimulation of the natural gas and/or oil reservoir by the steps of:

(i) providing a viscosified treatment fluid containing a water soluble polymeric gelling agent wherein the viscosified treatment fluid is prepared using natural occurring brines selected from the group consisting of formation water, produced water and/or flow back from a well after a stimulation process, and mixtures thereof, wherein the natural occurring brine has a total organic carbon (TOC) in the range of 310-5000 mg/I and a total dissolved solids (TDS) salt of at least 10,000 ppm, the water soluble polymeric gelling agent including at least structural units of formula (I)

wherein

R1, R2 and R3 independently are hydrogen or C 1 -C 6 -alkyl,

up to 95% by weight of the water soluble polymeric gelling agent of structural units of formula (II)

wherein

R4 is hydrogen or C 1 -C 6 -alkyl,

R5 is hydrogen, a cation of an alkaline metal, of an earth alkaline metal, of ammonia and/or of an organic amine,

A is a covalent C—S bond or a two-valent organic bridging group, and

up to 20% by weight of the water soluble polymeric gelling agent of structural units of formula (V)

wherein

R17 is hydrogen or, C 1 -C 6 -alkyl, and

R18 and R19 are independently of one another hydrogen, a cation of an alkaline metal, of an earth alkaline metal, of ammonia and/or of an organic amine,

B is a covalent C—P bond or a two-valent organic bridging group,

(ii) providing a breaker composition containing an aliphatic azo-compound selected from the group consisting of: 2,2′-Azobis[2-(2-imidazolin-2-yl)propane], 2,2′-Azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 2,2′-Azobis[2-(2-imidazolin-2-yl)propane]disulfate dihydrate, 2,2′-Azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}dihydrochloride, 2,2′-Azobis(2-methyl propionamidine) dihydrochloride, 2,2′-Azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate, 2,2′-Azobis(1-imino-1-pyrrolidino-2-ethylpropane)dihydrochloride, 2,2′-Azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2′-Azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethl]propionamide}, 2,2′-Azobis(2.4-dimethyl valeronitrile), 2,2′-Azobis(4-methoxy-2.4-dimethyl valeronitrile), Dimethyl 2,2′-azobis(2-methylpropionate), 1,1′-Azobis(cyclohexane-1-carbonitrile), 2,2′-Azobis[N-(2-propenyl)-2-methylpropionamide], 1-[(1-cyano-1-methylethyl)azo]formamide 2,2′-Azobis(N-butyl-2-methylpropionamide), 2,2′-Azobis(N-cyclohexyl-2-methylpropionamide), and mixtures thereof,

(iii) mixing said viscosified treatment fluid and said breaker composition and injecting the mixture of viscosified treatment fluid and breaker composition into a natural gas or oil reservoir,

(iv) allowing said viscosified treatment fluid and said breaker composition to interact whereby the viscosity of the viscosified treatment fluid is reduced,

(v) removing the viscosity reduced fluid from step (iv) from the natural gas or oil reservoir.