Families of scale-inhibitors having different absorption profiles and their application in oilfield

1. A method for imparting scale inhibition in an oilfield, the method comprising the steps of:

a) injecting at least two inflow streams of a fluid into at least two production zones of an oil producing well that is linked to the oilfield, or into at least two different oil producing wells that are linked to the oilfield,

wherein scale inhibitor having detectable moieties is introduced into the oilfield and/or into the fluid, so as to be present in the two zones or wells,

wherein two different scale inhibitors are introduced, one for each of the two zones or wells, said different scale inhibitors having different detectable moieties, such that these different scale inhibitors have distinct absorption maxima that can be determined by an absorption analytical method;

b) displacing oil from the oil producing well;

c) recovering an outflow stream of fluid comprising the oil;

wherein at least two outflow streams, one from each of the two zones or one from each of the two wells, are combined before said recovering; and

d) measuring the amounts of the different scale inhibitors present in the recovered stream of fluid, or in a fluid derived from the recovered stream of fluid, by an absorption analytical method;

and wherein one of the two scale inhibitors is a polymer (P1) as obtained by polymerization of:

an ethylenically unsaturated carboxylic monomer;

an ethylenically unsaturated sulphonic acid monomer or water soluble salts thereof;

a styrene monomer, optionally substituted by one to three groups;

in the presence of an hypophosphorous adduct of the formula (A1):

(X 2 O 3 P) 2 CHYPO 2 X 2   (A1)

wherein:

X is H or an alkali metal, alkaline earth or ammonium,

Y is an alkylene group, which may be linear or branched, having from 1 to 5 carbon atoms;

and wherein the other one of the two scale inhibitors is a polymer (P2) as obtained by polymerization of:

an ethylenically unsaturated carboxylic monomer;

an ethylenically unsaturated sulphonic acid monomer or water soluble salts thereof;

a vinyl heteroaromatic monomer comprising at least one heteroatom selected from N, P and O, which can be substituted by at least one hydrocarbon group having 1 to 6 carbon atoms, and which optionally contains functional groups;

in the presence of an hypophosphorous adduct of the formula (A1):

(X 2 O 3 P) 2 CHYPO 2 X 2   (A1)

wherein:

X is H or an alkali metal, alkaline earth or ammonium,

Y is an alkylene group, which may be linear or branched, having from 1 to 5 carbon atoms,

whereby the hypophoshorous adducts of the formula (A1) are identical or distinct.

2. The method of claim 1 , wherein if in step (d) the amount of one of the two scale inhibitors is below a predetermined value, the method further comprises the step of:

e) addressing a scale formation problem in the zone or well that is associated with said scale inhibitor.

3. The method of claim 1 , wherein the absorption analytical method is UV/VIS spectroscopy.

4. The method of claim 1 , wherein in formula (A1) Y is a methylene or an ethylene group.

5. The method of claim 1 , wherein in formula (A1) X is sodium (Na).

6. The method of claim 1 , wherein the vinyl heteroaromatic monomer contains sulphate, carboxylate, phosphonate and/or phosphinate functional groups.

7. A polymer having an absorption maximum between 215 and 240 nm and having an average general formula (1):

(X 2 O 3 P) 2 CHYPO 2 XZ1  (1)

wherein

X is H or an alkali metal, alkaline earth or ammonium,

Y is an alkylene group, which may be linear or branched, having from 1 to 5 carbon atoms, and

Z1 is a polymer chain obtained by polymerization of an ethylenically unsaturated carboxylic monomer with an ethylenically unsaturated sulphonic acid monomer or water soluble salts thereof and a styrene monomer, which can be substituted by one to three groups that may be identical or different, and which are selected to provide said absorption maximum, in the presence of an hypophosphorous adduct of the formula (A1):

(X 2 O 3 P) 2 CHYPO 2 X 2   (A1)

wherein X and Y have the same meaning as in formula (1).

8. A polymer as defined in claim 7 , wherein the substituent groups of the styrene monomer are chosen from H, SO 3 H, SO 3 Na, NH 2 , Me 2 N, COOH, CH 2 Cl, CH 2 OH and OH.

9. A polymer as defined in claim 7 , wherein the ethylenically unsaturated carboxylic monomer is selected from the group consisting of: acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, aconitic acid, mesaconic acid, citraconic acid, crotonic acid isocrotonic acid, angelic acid and tiglic acid.

10. A polymer as defined in claim 7 , wherein the ethylenically unsaturated sulphonic acid monomer is selected from the group consisting of: vinyl sulphonic acid, 2-acrylamido-2-methyl propane sulphonic acid, allyl sulphonic acid, and methallyl sulphonic acid.

11. A polymer as defined in claim 7 , wherein the polymer is selected from the group consisting of: copolymers of vinyl sulphonic acid with acrylic and/or maleic acid and/or vinyl phosphonic and/or vinylidene diphosphonic acid.

12. A polymer having an absorption maximum between 240 and 400 nm and having an average general formula (2):

(X 2 O 3 P) 2 CHYPO 2 XZ 2   (2)

wherein

X is H or an alkali metal, alkaline earth or ammonium,

Y is an alkylene group, which may be linear or branched, having from 1 to 5 carbon atoms, and

Z2 is a polymer chain obtained by polymerization of an ethylenically unsaturated carboxylic monomer with an ethylenically unsaturated sulphonic acid monomer or water soluble salts thereof and a vinyl heteroaromatic monomer, which can be substituted by one to three groups that may be identical or different, and selected to provide said absorption maximum, in the presence of an hypophosphorous adduct of the formula (A2):

(X 2 O 3 P) 2 CHYPO 2 X 2   (A2)

wherein X and Y have the same meaning as in formula (2).

13. A polymer as defined in claim 12 , wherein the ethylenically unsaturated carboxylic monomer is selected from the group consisting of: acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, aconitic acid, mesaconic acid, citraconic acid, crotonic acid, isocrotonic acid, angelic acid and tiglic acid.

14. A polymer as defined in claim 12 , wherein the ethylenically unsaturated sulphonic acid monomer is selected from the group consisting of: vinyl sulphonic acid, 2-acrylamido-2-methyl propane sulphonic acid, allyl sulphonic acid, and methallyl sulphonic acid.

15. A polymer as defined in claim 12 , wherein the polymer is selected from the group consisting of: copolymers of vinyl sulphonic acid with acrylic and/or maleic acid and/or vinyl phosphonic and/or vinylidene diphosphonic acid.