Scale inhibitor

A method of inhibiting the formation of scale comprising the measures

• (i) providing a viscosified treatment fluid containing at least water, a water soluble polymeric gelling agent and a breaker compound,
• (ii) pumping the treatment fluid into a formation,
• (iii) allowing the breaker compound to degrade the gelling agent and to form polymer fragments that inhibit scaling,
• the polymeric gelling agent being a synthetic polymer comprising:
• (I) at least structural units of formula (I)
• wherein
• R1, R2 and R3 independently are hydrogen or C1-C6-alkyl,
• (II) from 1 to 95% by weight structural units of formula (II)
• wherein
• R4 is hydrogen or C1-C6-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,
• (III) from 0 to 20% by weight structural units of formula (III)
• wherein
• R6 and R7 are independently of one another hydrogen, C1-C6-alkyl, —COOR9 or —CH2—COOR9, with R9 being hydrogen, a cation of an alkaline metal, of an earth alkaline metal, of ammonia and/or of an organic amine,
• R8 is hydrogen, a cation of an alkaline metal, of an earth alkaline metal, of ammonia and/or of an organic amine, or is C1-C6-alkyl, a group —CnH2n—OH with n being an integer between 2 and 6, or is a group —CoH2o—NR10R11, with o being an integer between 2 and 6, and
• R10 and R11 are independently of one another hydrogen or C1-C6-alkyl,
• (IV) from 0 to 95% by weight structural units of formula (IV)
• wherein
• R12 and R13 are independently of one another hydrogen, C1-C6-alkyl, —COOR16 or —CH2—COOR16, with
• R16 being hydrogen, a cation of an alkaline metal, of an earth alkaline metal, of ammonia and/or of an organic amine,
• R14 is hydrogen or, C1-C6-alkyl, and
• R15 is —COH, —CO—C1-C6-alkyl or
• R14 and R15 together with the nitrogen atom to which they are attached form a heterocyclic group with 4 to 6 ring atoms,
• (V) from 0 to 20% by weight structural units of formula (V)
• wherein
• R17 is hydrogen or, C1-C6-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,
• with the proviso that the percentage of the structural units of formulae (I) to (V) refer to the total mass of the copolymer and the percentage of the structural units of formulae (I) to (V) amounts to 100%.

A scale inhibitor included in hydraulic fracturing fluids has a degraded synthetic polymer, said synthetic polymer comprising:

• (I) at least structural units of formula (I)
• wherein
• R1, R2 and R3 independently are hydrogen or C1-C6-alkyl,
• (II) from 1 to 95% by weight structural units of formula (II)
• wherein
• R4 is hydrogen or C1-C6-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,
• (III) from 0 to 20% by weight structural units of formula (III)
• wherein
• R6 and R7 are independently of one another hydrogen, C1-C6-alkyl, —COOR9 or —CH2—COOR9, with R9 being hydrogen, a cation of an alkaline metal, of an earth alkaline metal, of ammonia and/or of an organic amine,
• R8 is hydrogen, a cation of an alkaline metal, of an earth alkaline metal, of ammonia and/or of an organic amine, or is C1-C6-alkyl, a group —CnH2n—OH with n being an integer between 2 and 6, or is a group —CoH2o—NR10R11, with o being an integer between 2 and 6, and
• R10 and R11 are independently of one another hydrogen or C1-C6-alkyl, preferably hydrogen,
• (IV) from 0 to 95% by weight structural units of formula (IV)
• wherein
• R12 and R13 are independently of one another hydrogen, C1-C6-alkyl, —COOR16 or —CH2—COOR16, with
• R16 being hydrogen, a cation of an alkaline metal, of an earth alkaline metal, of ammonia and/or of an organic amine,
• R14 is hydrogen or, C1-C6-alkyl, and
• R15 is —COH, —CO—C1-C6-alkyl or
• R14 and R15 together with the nitrogen atom to which they are attached form a heterocyclic group with 4 to 6 ring atoms,
• (V) from 0 to 20% by weight structural units of formula (V)
• wherein
• R17 is hydrogen or, C1-C6-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,
• with the proviso that the percentage of the structural units of formulae (I) to (V) refer to the total mass of the copolymer and the percentage of the structural units of formulae (I) to (V) amounts to 100%,
• wherein the scale inhibitor applied in formations or resources containing crude oil and natural gas.