WO2009080498A1

WO2009080498A1 - Scale inhibition

Info

Publication number: WO2009080498A1
Application number: PCT/EP2008/067121
Authority: WO
Inventors: Gareth Collins; Brian Downward; Chris Jones
Original assignee: Rhodia Operations SAS
Current assignee: Rhodia Operations SAS
Priority date: 2007-12-21
Filing date: 2008-12-09
Publication date: 2009-07-02
Anticipated expiration: 2010-06-21
Also published as: GB0724962D0; GB2455776A

Abstract

The present invention relates to a method of inhibiting scale in an aqueous system, the method comprising adding to the aqueous system a scale inhibiting composition comprising an effective amount of ethanolamine- N,N-bis(methylene phosphonate) compound of formula (I): wherein X is hydrogen or a cation such that the resulting salt is water soluble; wherein the aqueous system is at a temperature of 12O0C or higher when the composition is added, or wherein the aqueous system will be at a temperature of 12O0C or higher after the composition is added; application to aqueous systems like an oil or a gas well system.

Description

SCALE INHIBITION

The present invention relates to methods of scale inhibition, in particular methods of scale inhibition at high temperatures.

The problem of scale formation in aqueous systems is well known. In particular, the need to inhibit or prevent the formation of scale in systems containing high concentration of alkaline earth metal is well recognised.

Oil and gas well systems can in particular suffer from the build-up of undesirable scale deposits. In oil and gas well systems these deposits can form in the oil and gas wells themselves, as well as in their flow lines and in auxiliary equipment, such as heat exchangers and cooling towers.

Compounds for inhibiting, i.e. for reducing or preventing, scale formation in aqueous environments are known.

However, there is a need to be able to achieve scale inhibition at high temperatures, such as 12O⁰C or higher, in particular 15O⁰C and higher. This would then allow use in applications such as oil and gas well systems.

The present invention provides, in a first aspect, a method of inhibiting scale in an aqueous system, the method comprising adding to the aqueous system a scale inhibiting composition comprising an effective amount of ethanolamine-N,N-bis(methylene phosphonate) compound of formula (I):

s CH₂PO₃X₂ HOCH₂CH₂N (I)

^^ CH₂PO₃X₂

wherein X is hydrogen or a cation such that the resulting salt is water soluble; wherein the aqueous system is at a temperature of 12O⁰C or higher, or wherein the aqueous system will be at a temperature of 12O⁰C or higher after the composition is added.

Surprisingly, the compounds of formula (I) are effective scale inhibitors at high temperatures. Many phosphates are, in contrast, degraded at high temperatures.

The high temperature efficacy of the compounds of formula (I) permits their use in applications such as oil and gas well systems.

The compounds of formula (I) are known and may be produced from the reaction of ethanolamine, formaldehyde and phosphorous acid. This method produces a mixture of the compound of formula (I) and its corresponding cyclic ester.

As discussed in WO00/18695, a mixture of the compound of formula (I) and its corresponding cyclic ester can be converted to give a higher ratio of the non-esterified product, i.e. the compound of formula (I), to the cyclic ester product. This can be achieved by heating the mixture in strongly alkaline aqueous solution, for example using 3.5 to 10 molar proportions of alkali, e.g. sodium hydroxide, in aqueous solution at a temperature of greater than 100⁰C for a time sufficient to hydrolyse at least 30% of the weight of the cyclic ester. A time of from 4 hours to 4 days may be required; for example a time of from 2 to 10 hours at reflux.

For example, the scale inhibiting composition may comprise 20% or less by weight of the cyclic ester, based on the total weight of ethanolamine-N,N- bis(methylene phosphonate), such as 15% or less by weight. Preferably, the scale inhibiting composition comprises 10% or less by weight of the cyclic ester, based on the total weight of ethanolamine-N,N-bis(methylene phosphonate), such as 7% or less by weight; more preferably 5% or less by weight; such as 3% or less by weight, e.g. 2% or less by weight; most preferably 1% or less by weight, such as 0.5% or less by weight.

In one embodiment, the scale inhibiting composition consists essentially of ethanolamine-N,N-bis(methylene phosphonate) of formula (I).

In the embodiment wherein the aqueous system will be at a temperature of 12O⁰C or higher after the composition is added, it is preferred that the aqueous system will be at a temperature of 12O⁰C or higher after the composition is added but before the composition has biodegraded. More preferably, the aqueous system will be at a temperature of 12O⁰C or higher within 24 hours of the composition being added, such as within 12 hours of the composition being added, for example within 5, 4, 3, 2 or 1 hours of the composition being added.

In one embodiment, the aqueous system is, or will be, at a temperature of 13O⁰C or higher, such as 14O⁰C or higher.

Preferably, the aqueous system is, or will be, at a temperature of 15O⁰C or higher, for example from 150 to 200⁰C or higher, such as 16O⁰C or higher. Most preferably, the aqueous system is, or will be, at a temperature of 165⁰C or higher, for example from 170 to 19O⁰C or higher, such as 18O⁰C or higher.

The system may be a system that already contains scale, or a system where scale is expected to develop.

The scale may, in particular, be calcium, strontium or barium based scale, such as calcium carbonate, calcium sulphate or barium sulphate.

The aqueous system may be any system that is potentially vulnerable to scale formation. In particular, systems containing high concentrations of alkaline earth metal may be considered. These may be aqueous systems that contain one or more of barium, calcium or strontium. They may in particular contain 3000ppm or higher of alkaline earth metal, e.g. 5000ppm or higher, such as lOOOOppm or higher.

Preferably, the aqueous system contains 5000ppm or higher Ca or Ba, such as 7000ppm or higher, preferably lOOOOppm or higher, such as 15000ppm or higher.

In one embodiment, the aqueous system contains lOOOOppm or more Ca, such as 12000ppm or more Ca, e.g. 15000ppm or more Ca.

In one embodiment, the aqueous system is an oil or gas well system. In this regard, the scale inhibiting composition may, for example, be added to the oil and gas wells themselves, their flow lines, or auxiliary equipment, such as heat exchangers and cooling towers.

In one embodiment, the aqueous system is in contact with iron or an iron alloy. Surprisingly, the compounds of formula (I) have excellent iron tolerance. In particular, the compounds of formula (I) have better iron tolerance than other phosphonates.

Iron tolerance is an important characteristic for scale inhibitors in a number of applications. In particular, it is important for systems where aquifer water is injected, as this will often contain high levels of dissolved iron; in reservoirs with high iron ore mineralogy, e.g. siderite or pyrite; or where there is significant corrosion debris. Therefore the scale inhibitor having good iron tolerance is key to its potential use in such applications.

In one embodiment, the aqueous system is one that requires the scale inhibitor to be readily biodegraded under ambient aerobic conditions. Surprisingly, the compounds of formula (I) have good biodegradation under ambient aerobic conditions. In particular, the compounds of formula (I) have better biodegradation under ambient aerobic conditions than other phosphonates.

For example, monoethanolamine methylenebis phosphonic acid exhibited 39% biodegradation in an OECD306 seawater test. As the skilled man would appreciate, seawater tests are more difficult to pass than freshwater tests. It also exhibited biodegradation of 17% after 28 days in an aerobic inherent degradation test (OECD No 306).

Many applications require treatment with a scale inhibitor that will be stable in the treatment system but biodegradable when subsequently discharged from the system following treatment. Therefore it is desirable that the scale inhibitor is chemically stable under high temperature, anaerobic conditions and biodegradable under ambient, aerobic conditions.

Accordingly, it is extremely beneficial for a scale inhibitor to have good biodegradation under the ambient aerobic conditions it will encounter following discharge from the treatment system.

Biodegradability is an important characteristic for scale inhibitors in the offshore oil and gas industry. There are international concerns over marine pollution and increased restrictions imposed on offshore oil and gas rigs relating to chemical discharges. Therefore the scale inhibitor having good biodegradability is key to its potential use in such applications.

Biodegradability is also an important characteristic for scale inhibitors in geothermal scale control.

The aqueous system may have any suitable pH. In one embodiment, the pH is 6 or higher, preferably 6.5 or higher, such as from 6.5 to 9.5; preferably 7 or higher, for example from 7 to 9. In the compound of formula (I), each X is the same.

In one embodiment, X is hydrogen, and therefore compound (I) is monoethanolamine methylenebis phosphonic acid.

In another embodiment, X is a cation such that the resulting salt is water soluble. In this regard, X may be a metal cation, such as an alkali metal. For example, X may be sodium or potassium.

The compound of formula (I) is preferably used in an effective amount that gives a concentration in the aqueous system of from 5 to lOOOppm, such as from 10 to 800ppm, e.g. from 20 to 700ppm; preferably from 30 to 600ppm; more preferably from 50 to 500ppm.

The invention also provides, in a second aspect, the use of an ethanolamine-N,N-bis(methylene phosphonate) compound of formula (I):

/ CH₂PO₃X₂

HOCH₂CH₂N (I) ^^\

^ CH₂PO₃X₂

wherein X is hydrogen or a cation such that the resulting salt is water soluble to inhibit the formation of scale in an aqueous system at a temperature of 12O⁰C or higher.

In one embodiment, the use is in oilfield and gasfield systems, such as offshore oil and gas rigs.

Features of preferred embodiments are as described above in relation to the first aspect. The invention will be further described, by means of example only, in the following Example.

Example

The efficacy of the compounds of formula (I) as scale inhibitors at high temperatures, of 12O⁰C or higher, can be assessed as follows:

Tube blocking apparatus is used, comprising one or more bottle to hold brine samples to be tested; stainless steel or polymer capillary tubing; one or more pump to pump the samples through the tubing; a heat source; pressure detectors to detect the pressure in the capillary tubing; and data recording equipment.

The capillary tube coil used is generally made of UNS S31600 (type 316SS) or polyetheretherketone (PEEK), with a coil size of approximately 1.0 to 1.1mm for the inside diameter and Im in length.

The heat source may suitably be a pressure rated oven which contains the capillary tube coil, with the coils being held at a temperature of 12O⁰C or above during each test.

A field water brine is used for the test, which induces a severe calcium carbonate problem.

Flow rates (laminar flow) of 0.2 ml/minute to 25 ml/minute can suitably be used, but even higher rates can be considered, such as up to 75ml/minute. Typical flow rates would be around 5 to lOml/minute.

Untreated brine is firstly tested in the apparatus, to establish baseline conditions for scale formation. Then brine which has a compound of formula (I) added, e.g. by injection, prior to entry into the coil is tested.

Differential pressure across the capillary tube coil is measured in each test. An increase in pressure indicates the formation of scale, as scale adheres to the wall and constricts the capillary tubing. Adequate scale inhibition can be seen to be achieved when there is no increase in pressure across the capillary tube coil. The minimum concentration required to achieve adequate inhibition is known as the minimum scale inhibitor concentration.

Following each test, the capillary tube coil is flushed clean, so as to be ready for use in a subsequent test. For example, a cleaning solution, such as an aqueous solution of EDTA salt, formic acid or dilute nitric acid, may be used to flush the coil clean.

Claims

1. A method of inhibiting scale in an aqueous system, the method comprising adding to the aqueous system a scale inhibiting composition comprising an effective amount of ethanolamine-N,N-bis(methylene phosphonate) compound of formula (I):

/ CH₂PO₃X₂

HOCH₂CH₂N (I) ^ CH₂PO₃X₂

wherein X is hydrogen or a cation such that the resulting salt is water soluble; wherein the aqueous system is at a temperature of 12O⁰C or higher when the composition is added, or wherein the aqueous system will be at a temperature of 12O⁰C or higher after the composition is added.

2. The method of Claim 1, wherein the scale inhibiting composition comprises 10% or less by weight of the corresponding cyclic ester of the compound of formula (I), based on the total weight of ethanolamine-N,N- bis(methylene phosphonate).

3. The method of Claim 2, wherein the scale inhibiting composition consists essentially of ethanolamine-N,N-bis(methylene phosphonate) of formula (I).

4. The method of any one of Claims 1 to 3, wherein the aqueous system is at, or will be at, a temperature of 15O⁰C or higher.

5. The method of Claim 4, wherein the aqueous system is at, or will be at, a temperature of 165⁰C or higher.

6. The method according to any one of Claims 1 to 5 wherein the scale is a calcium, strontium or barium based scale.

7. The method of Claim 6 wherein the scale is calcium carbonate, calcium sulphate or barium sulphate.

8. The method of Claim 6 or Claim 7 wherein there is 5000ppm or higher Ca or Ba in the aqueous system.

9. The method of Claim 8 wherein there is lOOOOppm or higher Ca or Ba in the aqueous system.

10. The method of any one of Claims 1 to 9 wherein the aqueous system is in contact with iron or an iron alloy.

11. The method of any one of Claims 1 to 10 wherein the aqueous system is one that requires the scale inhibitor to be chemically stable under high temperature, anaerobic conditions and biodegradable under ambient, aerobic conditions.

12. The method of any one of Claims 1 to 11 wherein the aqueous system is an oil or gas well system.

13. The method of any one of Claims 1 to 12 wherein the aqueous system has a pH of 6 or higher.

14. The method of Claim 13, wherein the pH is 6.5 or higher.

15. The method of any one of Claims 1 to 14 wherein X is hydrogen.

16. The method of any one of Claims 1 to 15 wherein the compound of formula (I) is used in an effective amount that gives a concentration in the aqueous system of from 5 to lOOOppm.

17. The use of an ethanolamine-N,N-bis(methylene phosphonate) compound of formula (I):

/ CH₂PO₃X₂

HOCH₂CH₂N (I) ^ CH₂PO₃X₂

18. The use of Claim 17 to inhibit the formation of scale in an aqueous system at a temperature of 15O⁰C or higher.

19. The use according to Claim 17 or Claim 18 wherein the scale is a calcium, strontium or barium based scale.

20. The use of Claim 19 wherein there is lOOOOppm or higher Ca or Ba in the aqueous system.

21. The use of any one of Claims 17 to 20 wherein the aqueous system is in contact with iron or an iron alloy.

22. The use of any one of Claims 17 to 21 wherein the aqueous system is one that requires the scale inhibitor to be chemically stable under high temperature, anaerobic conditions and biodegradable under ambient, aerobic conditions.

23. The use of any one of Claims 17 to 22 wherein the aqueous system is an oil or gas well system.

24. The use of any one of Claims 17 to 23 wherein the aqueous system has a pH of 6.5 or higher.

25. The use of any one of Claims 17 to 24 wherein X is hydrogen.