SUBTERRANEAN FORMATIONS

1 . A method of treating a subterranean formation, the method comprising:

(i) selecting a subterranean formation which is susceptible to formation of an undesirable gel like goo or in which an undesirable gel like goo has been observed or in which an undesirable gel like goo has formed; and

(ii) contacting the formation with a fluid (A) comprising a polymer (PP) which includes a pendent group which includes a moiety

O—S═O  (I)

wherein the sulphur atom of the moiety is covalently bonded, optionally via a linking atom or group, to the backbone of the polymer.

2 . The method according to claim 1 , the method comprising selecting a subterranean formation in which an undesirable gel like goo has been observed.

3 . The method according to claim 1 , wherein said goo is a rubbery semi-solid.

4 . The method according to claim 1 , wherein said goo comprises a quasi cross-linked friction reducer or residue of a friction reducer quasi crosslinked by a multivalent cation present within the formation.

5 . The method according to claim 1 , wherein said goo comprises iron or an iron compound.

6 . The method according to claim 1 , wherein moiety (I) is part of a moiety of formula

7 . The method according to claim 6 , wherein moiety (I) and/or moiety (II) is pendent from a repeat unit of formula

wherein the carbon atom attached to the oxygen atom is covalently bonded to a moiety which includes said moiety (I) and/or said moiety (II), wherein R 1 , R 2 and R 3 independently represent a hydrogen atom or an optionally-substituted alkyl group.

8 . The method according to claim 6 , wherein said moiety (I) is part of a moiety

XO—S═O  (IV)

and said moiety (II) is part of a moiety

wherein X is a hydrogen atom, an alkali metal or NH 4 ;

wherein said polymer (PP) includes a repeat unit which includes a moiety

wherein the carbon atom bonded to R 2 is bonded to a pendent group which includes said moiety (I) and/or said moiety (II) and R 1 , R 2 and R 3 independently represent a hydrogen atom or an optionally-substituted alkyl group.

9 . The method according to claim 1 , wherein polymer (PP) includes a repeat unit derived or derivable from a monomer of the formula

10 . The method according to claim 1 , wherein said moiety (I) is part of a moiety —SO 3 − and is part of a zwitterion and said polymer (PP) includes a repeat unit which includes a moiety

wherein the carbon atom bonded to R 7 is bonded to a pendent group which includes said SO 3 − moiety and R 6 , R 7 and R 8 independently represent a hydrogen atom or an optionally-substituted alkyl group; and, optionally,

said repeat unit of formula (XIII) is part of a moiety of formula

wherein L 2 is a linking group, wherein L 2 represents

wherein n2 is an integer in the range 1 to 5, n3 is an integer in the range 1 to 6 and R 9 and R 10 independently represent C 1-4 alkyl groups.

11 . The method according to claim 1 , wherein polymer (PP) is a copolymer which includes an acrylamide repeat unit and/or a repeat unit comprising a vinylpyrrolidone moiety.

12 . The method according to claim 1 , wherein polymer (PP) includes a repeat unit of formula

wherein R 11 and R 12 are independently selected from a hydrogen atom and an optionally-substituted, alkyl group.

13 . The method according to claim 1 , wherein said polymer (PP) is a copolymer of acrylamido-methyl-propane sulfonate and acrylamide which includes 5 to 40 mol % of acrylamido-methyl-propane sulfonate repeat units and 60 to 90 mol % of acrylamide repeat units.

14 . The method according to claim 13 , wherein said polymer (PP) does not include any phosphonate moiety; and/or does not include any cationic moiety except as part of a zwitterion; and/or does not include any free quaternary ammonium groups.

15 . The method according to claim 14 , wherein said polymer (PP) has a molecular weight in the range 1,000,000 to 50,000,000 Daltons; and/or a polydispersity in the range 1-7.

16 . The method according to claim 1 , wherein the only polymer for friction reduction in said fluid (A) is said polymer (PP) and/or said fluid (A) does not include:

any cationic polymer containing a hydrolysable group within a group pendent from the polymer backbone; and/or

any anionic polymer comprising a pendent group that will complex with iron; and/or

any polymer which includes a P-containing functional group such as a phosphonic acid-based group.

17 . The method according to claim 1 , wherein:

(a) a pulverized core sample of the formation has one or more of the following characteristics:

Total acid solubility of 15-60 wt %

HCl solubility of 2-25 wt %;

HF solubility of 12-50% wt %; and/or

(b) said formation rock includes pyrite and/or marcasite; and/or

(c) the formation rock includes feldspar; and/or

(d) the Total Organic Content in the formation rock is between 0.5 and 9 wt %; and/or

(e) formation water includes Total Dissolved Solids (TDS) of at least 5,000 ppm; and/or

(f) ICP Flowback water analysis yields a fluid comprising one or more of the following after fracturing:

Al: at least 5 ppm;

B: between 0 and 150 ppm;

Ba: between 0-50 ppm;

Ca: at least 50 ppm;

Fe: at least 100 ppm; and less than 1500 ppm;

K: at least 100 ppm;

Sr: 0-100 ppm.

18 . The method according to claim 1 , wherein the method comprises fracturing a subterranean formation in a method comprising contacting the formation with a fluid (A) and fracturing the subterranean formation by pumping the fluid (A) into the wellbore at a pressure sufficient to create a fracture network.

19 . The method according to claim 1 , wherein said polymer (PP) is a copolymer of 2-acrylamido-2-methylpropane sulfonic acid and acrylamide which includes 5 to 40 mol % of acrylamido-methyl-propane sulfonate repeat units and 60 to 90 mol % of acrylamide repeat units.

20 . A method of treating a subterranean formation susceptible to formation of an undesirable gel like goo, the method comprising:

(i) selecting a subterranean formation in the state of Oklahoma; and

(ii) contacting the formation with a fluid (A) comprising a polymer (PP) which includes a pendent group which includes a moiety

O—S═O  (I)

wherein the sulphur atom of the moiety is covalently bonded, optionally via a linking atom or group, to the backbone of the polymer.

21 . An assembly positioned adjacent a subterranean formation which is susceptible to formation of a undesirable gel-like goo as referred to in SPE-173594-MS, said assembly being arranged to deliver a fluid (A) into the formation, said assembly comprising:

(I) a receptacle containing a fluid (A) comprising a polymer (PP) as described in claim 1 ;

(II) a water supply;

(III) a pump (PI) for dosing fluid (A) from said receptacle into said water supply, to define at least part of a fracturing fluid;

(IV) a conduit for delivering fracturing fluid into the formation; and

(V) a pump (P2) for injecting the fracturing fluid via said conduit into the formation.