FORMULATIONS AND METHODS FOR MINERAL SCALE REMOVAL

Abstract

A composition is provided for sulfate scale removal, said composition comprising one or more chelants and one or more accelerants, wherein said accelerants serve to occupy reactive sites of cations of the sulfate scale. The composition is preferably provided wherein said one or more chelants comprise a mixture of two or more polyaminopolycarboxylic acids. The composition if further preferably provided, wherein said one or more accelerants promote rapid complexation of cations of the sulphate scale. The composition is further still preferably provided, wherein said one or more accelerants comprise substances that have a smaller molecule size than that of said one or more chelants.

Claims

1. Composition for sulfate scale removal, said composition comprising; a. one or more chelants; and b. one or more accelerants, wherein said accelerants serve to occupy reactive sites of cations of the sulfate scale.

2. The composition of claim 1 wherein said one or more chelants comprise a mixture of two or more polyaminopolycarboxylic acids.

3. The composition of claim 2, wherein said one or more polyaminopolycarboxylic acids are selected from the group consisting of ethylene diamine tetraacetic acid (EDTA), diethylene triamine pentaacetic acid (DTPA), polyaspartic acid (PAA) and methylglycine diacetic acid (MGA) and mixtures thereof.

4. The composition of claim 2, wherein said one or more accelerants promote rapid complexation of cations of the sulphate scale.

5. The composition of claim 4, wherein said one or more accelerants have a smaller molecule size than that of said one or more chelants.

6. The composition of claim 5, wherein said one or more accelerants comprise small molecule substances selected from the group consisting of monocarboxylic acids; dicarboxylic acids; potassium, sodium or ammonium salts of monocarboxylic acids; potassium, sodium or ammonium salts of dicarboxylic acids and combinations thereof.

7. The composition of claim 6, wherein the formula for the monocarboxylic acids is R—C(O)OH, wherein R═C2 to C6.

8. The composition of claim 6, wherein the formula for the dicarboxylic acids is HO2C—R—CO2H, wherein R is an aliphatic or aromatic ring of length C2 to C6.

9. The composition of claim 8 wherein said aromatic is a five-member furan.

10. The composition of claim 5, wherein said one or more accelerants comprise small molecule antioxidants.

11. The composition of claim 10, wherein said accelerants are selected from the group consisting of tocopherol, ascorbic acid, isothiocyanates, tannins and polyphenols.

12. The composition of claim 11, wherein the tannins comprise gallic acid.

13. The composition of claim 3, wherein said one or more polyaminopolycarboxylic acids comprise a mixture of EDTA and DTPA.

14. The composition of claim 11, wherein the concentration of the accelerant in the composition is between 0.10 wt. % to 1.0 wt. %.

15. The composition of claim 14, wherein the concentration of the one or more polyaminopolycarboxylic acids in the composition is between 1.0 wt. % to 20.0 wt. %.

16. The composition of claim 15, wherein the one or more polyaminopolycarboxylic acids are present in the form of acid salts in solution.

17. The composition of claim 15, further comprising one or more surfactants.

18. The composition of claim 15, wherein said composition is applied under alkaline conditions.

19. The composition of claim 18, wherein said alkaline conditions comprise maintaining the composition at a pH of from 9 to 13.

20. The composition of claim 19, wherein said alkaline conditions comprise maintaining the composition at a pH of from 11 to 12.5.

21. The composition of claim 1, for use in continuous treatment down producing wells, with water flush and continuous injection into surface lines.

22. The composition of claim 1, for use in formation squeeze treatment of oil wells.

23. The composition of claim 1, for us in an aqueous solution at a concentration of from 50 to 100 ppm.

24. The composition of claim 1, for use in a fill and soak or circulation method of application.

Description

DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENT

[0017] The description that follows and the embodiments described therein are provided by way of illustration of an example, or examples, of particular embodiments of the principles of various aspects of the present invention. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the invention in its various aspects.

[0018] In accordance with the present invention, alkaline earth scales, and more particularly sulfate scales such as barium sulfate scales can be chemically removed from surface equipment and oil and gas bearing formations by a chemical process employing a composition comprising a mixture of chelants, more preferably a mixture of polyaminopolycarboxylic acids, and accelerants to promote more rapid dissolution.

[0019] Polyaminopolycarboxylic acids of the present invention include but are not limited to ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), polyaspartic acid (PAA) and methylglycinediacetic acid (MGA) among others, and mixtures thereof

[0020] Accelerants have been found by the present inventors to be useful to promote higher rates of scale dissolution and markedly more rapid complexation of the cations of the scale deposit. Accelerants of the present invention include any number of small molecule groups that act as bridging compounds to facilitate occupying the reactive sites of the cations of the scale deposits. The accelerants of the present invention are relatively smaller molecules than the chelant materials. In this way they can fill in reactive sites on the alkaline earth scale that are otherwise not reachable by the larger chelant materials, due to steric hindrance. In this way, the accelerants of the present invention react with the alkaline earth molecules more quickly and promote more rapid access by the chelants.

[0021] Accelerants of the present invention include any smaller molecule groups, including but not limited to any member of mono or dicarboxlic acids and/or their respective salts from potassium, sodium or ammonium where the formula is: [0022] Monocarboxylic acid: R—C(O)OH, wherein R═C2 to C6 [0023] Dicarboxylic acid: HO2C—R—CO2H, wherein R is aliphatic or aromatic ring of C2 to C6 length. More preferably, the aromatic ring is a five-member furan.

[0024] Single component and multiple component mixtures of accelerants would also be understood by those skilled in the art to be useful in the present invention.

[0025] Accelerants of the present invention preferably comprise antioxidants. More preferably, the accelerants include, but are not limited to, tocopherol, ascorbic acid, isothiocyanates, tannins such as gallic acid and polyphenols.

[0026] According to one embodiment of the present invention, scale removal can be effected with an aqueous solution of a mixture of polyaminopolycarboxylic acids such as EDTA and DTPA which act as chelating agents, together with the accelerant, to form stable complexes with the metal cations of the scale deposits.

[0027] Complexation occupies cation reactive sites of the scale deposits. Blocking the reactive sites of the cations prevents them from redepositing on surface equipment once being dissolved. The chelating agents have multiple reactive sites that serve to react with multiple cation sites and form more than one bond between the alkaline earth scale material and a molecule of the chelating agent, resulting in the formation of a ring structure incorporating the cation thereby dissolving the scale and preventing it from rescaling onto equipment surfaces.

[0028] While single component chelant solutions can be employed, the present inventors have surprisingly discovered that mixtures of more than one polyaminopolycarboxylic acids, in the form of salts of polyaminopolycarboxylic acid in solution, function more favorably to form stable complexes of the scale deposits and can sequester high concentrations of alkaline earth scales at higher rates than single component chelant solutions.

[0029] Accelerants used in the present invention can preferably be added to an aqueous solution of one or more polyaminopolycarboxylic acid salts to increase the speed of complex formation and the efficiency of scale removal. The concentration of the accelerant in the aqueous solution can preferably be at least 0.10% to 1.0% by wt. Higher concentrations of accelerant may also be used, however, no economic nor functional increase in performance is observed.

[0030] As is typical with most chelation reactions, scale removal is preferably performed under alkaline conditions ranging from a solution pH of 9-13 and most preferably at a pH of 11-12.5. It would be well understood by a person of skill in the art that alkaline conditions can be created in any suitable way known in the art for example, by the addition of any suitable alkaline components to the solution.

[0031] The preferred compositions and solutions of the present invention comprise about 1.0% to 20.0% of a mixture of various polyaminopolycarboxylic acid salts. One example of a preferred aqueous solution for scale removal is composed of the following:

TABLE-US-00001 Percentage Ingredient by Weight Ethylenediaminetetraacetic Acid, Na.sup.+ or K.sup.+ Salt    1-5% Diethylenetriaminepentaacetic Acid, Na.sup.+ Salt    3-10% Polyaspartic Acid, Na.sup.+ or K.sup.+ Salt    1-5% Polyphenol  0.1-.5% Surfactant 0.1-0.5%

[0032] The surfactant is preferably present to reduce surface tension in the composition, but it would be well understood by a person of skill in the art that a surfactant would not be required for the compositions or methods of the present invention.

[0033] To those skilled in the art, this invention may be embodied in many different forms and it should not be construed as limited to the embodiment herein disclosed. It will be recognized to those skilled in the art that other suitable chelants and other polyaminopolycarboxylic acids and various forms of salts and various other accelerants maybe employed and interchanged for those materials herein disclosed.

[0034] The present invention may be used in downhole or surface installations. Methods of suggested application include continuous treatment down the annulus or treating string of producing wells, with water flush and continuous injection into surface lines. It can also be used for formation squeeze treatment of oil wells, which is a well-known industrial cleaning method involving using chemical compositions to protect the well downhole from scale deposition and formation damage.

[0035] An initial high dosage of the solution of the present invention of between 50-100 ppm (8-16 litres/1000 bbls of well product) based on well production rate can also be used to remove scale build-up in downhole or surface equipment and facilities, in cases of severe scaling problem. A fill and soak or circulation method of application is recommended, which is a well-known industrial chemical cleaning method involving filling up vessel or pipe system with cleaning composition and letting it soak for several hours in order to dissolve scaling. The duration of contact required for scale deposit removal will depend on the scale composition and barium sulfate content.

[0036] The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 USC 112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or “step for”.