Sulfonated lignin for scale inhibition

Abstract

The present invention relates to an oxidized sulfonated lignin scale inhibitor, its use in inhibiting scale formation in oilfield applications, a method of inhibiting scale formation in oilfield applications, and a method of preparing the oxidized sulfonated lignin scale inhibitor of the present invention.

Description

TECHNICAL FIELD

[0001] The present invention relates to an oxidized sulfonated lignin scale inhibitor, its use to inhibit scale formation in oilfield applications, a method of inhibiting scale formation in oilfield applications, and a method of making the oxidized sulfonated lignin scale inhibitor of the invention. BACKGROUND

[0002] Scale formation is a major challenge faced by the oil and gas industry. When certain minerals, such as calcium carbonate, calcium sulfate, or barium sulfate, exceed their solubility limit, they precipitate and form scale deposits. These scales accumulate on the surfaces of production equipment, wellbore, and reservoir formations, leading to reduced production rates, reduced efficiency, and equipment damage.

[0003] Various methods have been employed to address the scale formation problem in the oil and gas industry. Traditional methods involve reactive measures, such as using acid treatment or mechanical intervention to remove or dissolve scale deposits. However, these methods are often costly, time-consuming, and can cause production interruptions and environmental issues.

[0004] Another approach to control scale formation in the oil and gas industry is to actively use scale inhibitors. For example, scale inhibitors can be added to production fluids or drilling muds, thereby improving production rates, extending equipment life, and improving operational efficiency.

[0005] However, in the oil and gas industry, a large amount of liquid is discharged into the environment. In addition, challenging conditions, such as concentrated brines and high temperatures and / or high pressures, are often present in the oil and gas industry, particularly in oilfield applications.

[0006] Therefore, in the oil and gas industry, there is a need and a search for scale inhibitors that are efficient (i.e., work at very low dosage) under challenging conditions (high temperature and / or high pressure; concentrated brines).

[0007] In addition, due to the environmental risks of oil and gas field activities, the use of scale inhibitors is subject to increasingly stringent regulations. In sensitive areas such as the North Sea, only scale inhibitors registered as PLONOR are allowed. The PLONOR list is a compilation of chemicals considered by the OSPAR Commission to have little or no risk to the environment, providing a regulatory framework for water treatment additives in the oil and gas industry. In addition to new environmental regulations, there is a general trend in the industry to move from petroleum-based raw materials to renewable raw materials.

[0008] Commonly used scale inhibitors are, for example, anionic polymers (e.g., polyacrylates, polyvinyl sulfonates) or organic phosphonate molecules (e.g., 1-hydroxyethylidene-1,1-diphosphonic acid). However, these compounds are fossil-based, are not environmentally friendly, and are not considered PLONOR acceptable. Therefore, scale inhibitors commonly used in oil and gas fields are increasingly less popular.

[0009] Another class of compounds that were in the past considered to be scale inhibitors are lignin based materials. For example, US 2,297,670 describes the use of lignin materials to protect boilers from embrittlement and, as an aspect, to prevent the adhesion of boiler scale. Further, US 3,849,328 mentions the use of sulfonated alkali lignin to inhibit the accumulation of mineral scale deposits in waters prone to scale formation. However, US 3,849,328 teaches that sulfite lignin does not impart unusual scale inhibition properties and thus teaches against the use of such compounds. US 2,505,457 discloses the use of lignin derivatives prepared by heating sodium lignosulfonate in the presence of caustic soda for inhibiting scale formation in evaporators, feedwater heaters, economizers, boilers and other steam generating systems. However, the lignin derivatives of US 2,505,457 have very low performance and do not perform well enough to be used for commercial purposes. Finally, lignosulfonates have been mixed or grafted with synthetic moieties known to inhibit scale formation (e.g. acrylic acid and polyacrylates) (see US 2013 / 0137799 and Ind. Eng. Chem. Res. 2006, 45, 16, 5716-5721). However, it is doubtful that such complex mixtures of petroleum based and lignosulfonate based materials meet the PLONOR criteria. Further, these compounds are associated with rather high production costs which make them economically not suitable for commercial large scale applications, e.g. in the oil and gas industry.

[0010] Thus, there is a great need for new scale inhibitors that meet the following requirements:

[0011] environmentally friendly and PLONOR registered

[0012] resistant to high temperatures and high pressures

[0013] resistant to high calcium brines

[0014] high efficiency, i.e. performance at least as good as the state of the art

[0015] easy to handle and deploy (i.e. in the form of a pumpable concentrated liquid)

[0016] economically efficient and available in large quantities

[0017] based on renewable raw materials. SUMMARY

[0018] It is an object of the present invention to achieve all or some of the above-mentioned objects.

[0019] In particular, it is an object of the present invention to provide new scale inhibitors suitable for use in the oil and gas industry and meeting the above-mentioned requirements. In particular, it is an object of the present invention to provide scale inhibitors that are efficient under the extreme conditions present in the oil and gas industry and that are environmentally harmless.

[0020] The performance / efficiency of a scale inhibitor is usually expressed as the failure inhibitor concentration (FIC). This is the inhibitor concentration at which scale onset is detected. A lower FIC value indicates a better performing scale inhibitor. Commonly used scale inhibitors usually have a FIC value of about 10 ppm or lower, depending on the severity of the scale conditions, and it is desirable that new scale inhibitors have about the same efficiency.

[0021] These and other objects have been achieved by the novel scale inhibitor of the present invention, which is based on the biomolecule lignin, in particular sulfonated lignin.

[0022] Sulfonated lignin, in particular lignosulfonate, is a known dispersant in the oil industry for dilution of drilling muds. Lignosulfonates are PLONOR registered, bio-based, and are available in large quantities in concentrated liquid form. However, as has been recognized in US 3,849,328, currently available lignin materials, in particular common sulfonated lignin such as lignosulfonates obtained from sulfite pulping, are not suitable as scale inhibitors due to rather low performance.

[0023] However, through extensive research, the inventors of the present invention have found that sulfonated lignin can be converted into a highly efficient scale inhibitor by providing a certain amount of -COOH groups and methoxyl groups. In particular, it has been found that the amount of -COOH groups should be higher than 4 wt%, while the amount of methoxyl groups should be lower than 6 wt%, based on the total weight of the lignin material. The required amounts of -COOH and methoxyl can be provided by oxidizing the sulfonated lignin.

[0024] Such highly oxidized sulfonated lignin was unknown prior to the present invention, let alone their high efficiency in inhibiting scale under extreme conditions. For example, the sulfonated lignin derivatives disclosed in WO 2021 / 165298 only have 3 wt% -COOH groups and thus show insufficient scale inhibition performance (FIC of about 50 ppm; see Table 6).

[0025] Thus, in a first aspect, the present invention relates to an oxidized sulfonated lignin scale inhibitor characterized by a -COOH group content of more than 4.0 wt%, based on the total weight of the oxidized sulfonated lignin, and a methoxyl content of less than 6.0 wt%, based on the total weight of the oxidized sulfonated lignin.

[0026] In a second aspect, the present invention relates to the use of the oxidized sulfonated lignin scale inhibitor of the present invention for inhibiting scale formation in oilfield applications.

[0027] In a third aspect, the present invention relates to a method for inhibiting scale formation in oilfield applications.

[0028] In a fourth aspect, the present invention relates to a method for preparing the oxidized sulfonated lignin scale inhibitor of the present invention. Detailed Implementation

[0029] As stated above, this invention is based on the surprising discovery that sulfonated lignin, particularly lignin sulfonates, can be used as effective scale inhibitors if a certain amount of -COOH groups and methoxy groups are provided. Specifically, it has been found that, based on the total weight of the modified lignin, the amount of -COOH groups should be greater than 4% by weight, while the amount of methoxy groups should be less than 6% by weight.

[0030] Lignin sulfonates are traditionally produced through a process called "sulfite pulping" of wood and other plant biomass. This "pulping" is typically achieved by extracting lignin from lignocellulosic biomass using various sulfites in a large pressure vessel called a digester. During sulfite pulping, lignin molecules are sulfonated, thus becoming negatively charged and water-soluble. Figure 1 A representative description of lignin sulfonates obtained by sulfite pulping is shown. Another common route for sulfonating lignin is the sulfonation of lignin that has already been extracted from biomass by other methods, such as sulfate processing or organic solvent lignin. Direct sulfonation of extracted lignin can be achieved by sulfite pulping or other reactions known in the art to introduce sulfonate groups, such as sulfonylation.

[0031] Depending on the pulping reaction conditions, feedstock, and post-treatment, sulfonated lignin polymers can be designed with different structures and chemical functionalities, such as molecular weight, degree of sulfonation, degree of conjugation, density of -COOH groups, phenolic groups, methoxy groups, etc. Therefore, sulfonated lignin represents a highly diverse class of materials, primarily involving lignin extracted from biomass and functionalized with charged sulfonate groups.

[0032] In this invention, a large number of -COOH groups are introduced through the oxidation of sulfonated lignin (preferably a multi-step oxidation process). The oxidation must be carried out in a manner that achieves the desired amounts of -COOH and methoxy groups; not every oxidation of the sulfonated lignin material will produce the advantageous oxidized sulfonated lignin of this invention. During the oxidation process, it is preferable to avoid the decomposition of lignin derivatives into smaller fragments. An exemplary method for preparing the oxidized sulfonated lignin scale inhibitor of this invention will be further described below.

[0033] In a preferred embodiment, the oxidized sulfonated lignin scale inhibitor is an oxidized lignin sulfonate. This means that the oxidized sulfonated lignin scale inhibitor is preferably prepared by oxidizing lignin sulfonates obtained from sulfite pulping. Since lignin sulfonates are typically obtained as a byproduct of the papermaking industry, this makes the oxidized sulfonated lignin scale inhibitor particularly environmentally friendly and cost-effective.

[0034] Preferably, the carbon atom of the -COOH group is already contained in the natural lignin from which the oxidized sulfonated lignin scale inhibitor is derived. This means that no additional portion is grafted onto the lignin skeleton to introduce the -COOH group.

[0035] As stated above, the inventors of this invention have discovered that sulfonated lignin, particularly lignin sulfonates, are effective scale inhibitors when the amount of -COOH groups is greater than 4% by weight and the amount of methoxy groups is less than 6% by weight (both based on the total weight of the modified lignin). In particular, it has been found that if the amount of methoxy groups is not within the desired range, an amount of COOH groups greater than 4% by weight is insufficient, and vice versa. Therefore, the combination of the amounts of -COOH and methoxy groups results in the high efficiency of the oxidized sulfonated lignin of this invention.

[0036] In a preferred embodiment, the amount of -COOH groups is equal to or greater than 5.0% by weight, preferably greater than 5.0% by weight, based on the total weight of the sulfonated lignin. In another preferred embodiment, the amount of -COOH groups is equal to or greater than 6.0% by weight, preferably greater than 6.0% by weight, based on the total weight of the sulfonated lignin.

[0037] Regarding the amount of methoxy groups, it is preferably equal to or less than 5.0% by weight, more preferably less than 5.0% by weight, based on the total weight of the oxidized sulfonated lignin. More preferably, based on the total weight of the oxidized sulfonated lignin, the amount of methoxy groups is equal to or less than 4.0% by weight, more preferably less than 4.0% by weight.

[0038] In a preferred embodiment, the amount of -COOH groups is greater than 4.0% by weight and the amount of methoxy groups is equal to or less than 5.0% by weight.

[0039] In another preferred embodiment, the amount of -COOH groups is greater than 4.0% by weight and the amount of methoxy groups is less than 5.0% by weight.

[0040] In another preferred embodiment, the amount of -COOH groups is greater than 4.0% by weight and the amount of methoxy groups is equal to or less than 4.0% by weight.

[0041] In another preferred embodiment, the amount of -COOH groups is greater than 4.0% by weight and the amount of methoxy groups is less than 4.0% by weight.

[0042] In another preferred embodiment, the amount of -COOH groups is equal to or greater than 5.0% by weight and the amount of methoxy groups is less than 6.0% by weight.

[0043] In another preferred embodiment, the amount of -COOH groups is equal to or greater than 5.0% by weight and the amount of methoxy groups is equal to or less than 5.0% by weight.

[0044] In another preferred embodiment, the amount of -COOH groups is equal to or greater than 5.0% by weight and the amount of methoxy groups is less than 5.0% by weight.

[0045] In another preferred embodiment, the amount of -COOH groups is equal to or greater than 5.0% by weight and the amount of methoxy groups is equal to or less than 4.0% by weight.

[0046] In another preferred embodiment, the amount of -COOH groups is equal to or greater than 5.0% by weight and the amount of methoxy groups is less than 4.0% by weight.

[0047] In another preferred embodiment, the amount of -COOH groups is greater than 5.0% by weight and the amount of methoxy groups is less than 6.0% by weight.

[0048] In another preferred embodiment, the amount of -COOH groups is greater than 5.0% by weight and the amount of methoxy groups is equal to or less than 5.0% by weight.

[0049] In another preferred embodiment, the amount of -COOH groups is greater than 5.0% by weight and the amount of methoxy groups is less than 5.0% by weight.

[0050] In another preferred embodiment, the amount of -COOH groups is greater than 5.0% by weight and the amount of methoxy groups is equal to or less than 4.0% by weight.

[0051] In another preferred embodiment, the amount of -COOH groups is greater than 5.0% by weight and the amount of methoxy groups is less than 4.0% by weight.

[0052] In another preferred embodiment, the amount of -COOH groups is equal to or greater than 6.0% by weight and the amount of methoxy groups is less than 6.0% by weight.

[0053] In another preferred embodiment, the amount of -COOH groups is equal to or greater than 6.0% by weight and the amount of methoxy groups is equal to or less than 5.0% by weight.

[0054] In another preferred embodiment, the amount of -COOH groups is equal to or greater than 6.0% by weight and the amount of methoxy groups is less than 5.0% by weight.

[0055] In another preferred embodiment, the amount of -COOH groups is equal to or greater than 6.0% by weight and the amount of methoxy groups is equal to or less than 4.0% by weight.

[0056] In another preferred embodiment, the amount of -COOH groups is equal to or greater than 6.0% by weight and the amount of methoxy groups is less than 4.0% by weight.

[0057] In another preferred embodiment, the amount of -COOH groups is greater than 6.0% by weight and the amount of methoxy groups is less than 6.0% by weight.

[0058] In another preferred embodiment, the amount of -COOH groups is greater than 6.0% by weight and the amount of methoxy groups is equal to or less than 5.0% by weight.

[0059] In another preferred embodiment, the amount of -COOH groups is greater than 6.0% by weight and the amount of methoxy groups is less than 5.0% by weight.

[0060] In another preferred embodiment, the amount of -COOH groups is greater than 6.0% by weight and the amount of methoxy groups is equal to or less than 4.0% by weight.

[0061] In another preferred embodiment, the amount of -COOH groups is greater than 6.0% by weight and the amount of methoxy groups is less than 4.0% by weight.

[0062] It has been found that a combination of 5.0% by weight of -COOH groups and 5.0% by weight of methoxy groups results in particularly good efficiency (FIC=5ppm).

[0063] Furthermore, the organic sulfur content (i.e., the amount of sulfur associated with sulfonate groups attached to lignin, i.e., the degree of sulfonation) has been found to play a role, particularly regarding the calcium compatibility of oxidized sulfonated lignin scale inhibitors. In particular, it has been found that an organic sulfur content greater than 0.5% by weight is advantageous. Preferably, the organic sulfur content is greater than 1% by weight, more preferably greater than 3% by weight. The weight percentage is based on the total weight of the oxidized sulfonated lignin scale inhibitor. Specifically, it has been found that an organic sulfur content greater than 3% by weight, combined with the desired amounts of -COOH and methoxy groups, results in particularly good calcium compatibility.

[0064] Surprisingly, the oxidized sulfonated lignin scale inhibitor of the present invention has the same range of efficiencies as conventionally used scale inhibitors, while possessing many further advantages, particularly PLONOR adaptability and high-temperature and calcium tolerance, and is also bio-based. This is summarized in Table 1 below:

[0065] Table 1: Comparison of the sulfonated lignin of the present invention with some common scale inhibitors.

[0066]

[0067] Table 2: Performance of common oilfield scale inhibitors, tested in the same manner as sulfonated lignin in Table 6 for comparison.

[0068]

[0069] According to a preferred embodiment, the oxidized sulfonated lignin scale inhibitor of the present invention has a failure inhibitor concentration (FIC) of less than 50 ppm, preferably less than 40 ppm, more preferably less than 30 ppm, more preferably less than 20 ppm, more preferably less than 10 ppm, more preferably equal to or less than 5 ppm, and more preferably less than 5 ppm. The FIC can be determined according to the scalerig test described further below.

[0070] As mentioned above, an early method for imparting scale-inhibiting properties to lignin sulfonates was simply to graft known scale-inhibiting synthetic components, such as acrylic acid and polyacrylate, onto the lignin sulfonate. However, it is questionable whether such complex mixtures of petroleum-based and lignin sulfonate-based materials meet PLONOR standards. Furthermore, such compounds are associated with considerably high production costs, making them economically unsuitable for large-scale commercial applications, such as in the oil and gas industry. The present invention overcomes this drawback. Therefore, it is preferable that the oxidized sulfonated lignin scale inhibitor does not contain the acrylic acid or polyacrylate grafted thereon.

[0071] Furthermore, as described above, it is preferable to avoid the decomposition of lignin derivatives into smaller fragments during the oxidation reaction. Therefore, the oxidized sulfonated lignin scale inhibitor of the present invention preferably has a number average molecular weight of 1000-100000 g / mol, more preferably 5000-60000 g / mol, and even more preferably 15000-40000 g / mol. As those skilled in the art will know, the number average molecular weight can be determined using gel permeation chromatography.

[0072] Furthermore, the oxidized sulfonated lignin scale inhibitor of the present invention has been found to have excellent thermal stability. In particular, the oxidized sulfonated lignin scale inhibitor of the present invention has been found to be stable under long-term high-temperature conditions. Therefore, in a preferred embodiment, the oxidized sulfonated lignin scale inhibitor of the present invention has an inactivation inhibitor concentration (FIC) of less than 50 ppm, preferably less than 40 ppm, more preferably less than 30 ppm, more preferably less than 20 ppm, more preferably less than 10 ppm, and more preferably less than 5 ppm after being stored at 130°C for 14 days.

[0073] The advantageous properties of oxidized sulfonated lignin scale inhibitors make them particularly suitable for oilfield applications, especially for inhibiting the formation of calcite and barite scale. Therefore, according to a preferred embodiment, oxidized sulfonated lignin scale inhibitors are used to inhibit the formation of calcite and barite scale in oilfield applications.

[0074] The present invention further relates to the use of the oxidized sulfonated lignin scale inhibitor of the present invention in oilfield applications to inhibit scale formation.

[0075] Preferably, oxidized sulfonated lignin scale inhibitors are used in oilfield applications to inhibit the formation of calcite and barite scale.

[0076] Furthermore, the present invention relates to a method for inhibiting scale formation in oilfield applications. This method includes using the oxidized sulfonated lignin scale inhibitor of the present invention.

[0077] Preferably, the oxidized sulfonated lignin scale inhibitor is added to the production enhancement fluid or completion fluid, or used for extrusion treatment.

[0078] Furthermore, the present invention relates to a method for preparing the oxidized sulfonated lignin scale inhibitor of the present invention. The method comprises the following steps: (a1) providing sulfonated lignin raw material, and (a2) oxidizing the sulfonated lignin raw material with an oxidizing agent to obtain the oxidized sulfonated lignin scale inhibitor.

[0079] Preferably, the sulfonated lignin raw material is lignin sulfonate, and more preferably lignin sulfonate obtained from sulfite pulping.

[0080] Preferably, the oxidation step (a2) is performed as a multi-step oxidation using multiple oxidants.

[0081] In this multi-step oxidation process, one of the oxidants is preferably ozone or molecular oxygen.

[0082] Also preferably, one of the oxidants used in multi-step oxidation is hydrogen peroxide.

[0083] Also preferably, one of the oxidants used in multi-step oxidation is sodium hydroxide.

[0084] Preferably, the multi-step oxidation method is characterized in that one oxidant is sodium hydroxide and the other oxidant is ozone or molecular oxygen.

[0085] Preferably, the multi-step oxidation method is characterized by being a two-step oxidation method and involving the sequential application of two oxidizing agents. Preferably, one of the two oxidizing agents is sodium hydroxide, and the other is ozone. Preferably, sodium hydroxide is applied first.

[0086] According to another preferred embodiment, the multi-step oxidation is a three-step oxidation and includes the sequential application of three oxidizing agents. Preferably, one of the three oxidizing agents is sodium hydroxide, and the other is ozone. More preferably, one of the three oxidizing agents is sodium hydroxide, the other is ozone, and the third is hydrogen peroxide. More preferably, sodium hydroxide is applied first, followed by ozone, and then hydrogen peroxide.

[0087] According to another preferred embodiment, the oxidant is ozone, molecular oxygen, or a peracid, wherein the peracid is preferably selected from peracetic acid, perpropionic acid, and perbenzoic acid. More preferably, the peracid is peracetic acid.

[0088] According to the above disclosure, the method preferably does not include the step of grafting acrylic acid or polyacrylate onto lignin sulfonate.

[0089] Furthermore, the method is preferably carried out in a manner that avoids the decomposition of the sulfonated lignin raw material. Preferably, the number average molecular weight of the oxidized lignin sulfonate scale inhibitor is at least 10% of the number average molecular weight of the sulfonated lignin raw material, more preferably at least 50%, more preferably at least 70%, and even more preferably at least 80%.

[0090] Furthermore, the present invention relates to an oxidized sulfonated lignin scale inhibitor obtained by the method according to the present invention.

[0091] The invention will now be further described through the following items:

[0092] Project 1. Oxidized sulfonated lignin scale inhibitor, characterized in that:

[0093] • The content of -COOH groups is greater than 4.0% by weight, based on the total weight of oxidized sulfonated lignin.

[0094] The -COOH group content is determined by phosphorylation of the -COOH group and subsequent steps as described in the specification. 31 P-NMR measurements, and

[0095] • The methoxy content is less than 6.0% by weight, based on the total weight of oxidized sulfonated lignin, wherein the methoxy content is determined as described in the instructions.

[0096] Project 2. The oxidized sulfonated lignin scale inhibitor according to Project 1, wherein the oxidized sulfonated lignin scale inhibitor is an oxidized lignin sulfonate.

[0097] Project 3. Oxidized sulfonated lignin scale inhibitor according to Project 1 or 2, wherein the carbon atom of the -COOH group is already contained in the natural lignin from which the oxidized sulfonated lignin scale inhibitor originates.

[0098] Project 4. An oxidized sulfonated lignin scale inhibitor according to any of the preceding projects, wherein the amount of -COOH groups is equal to or greater than 5.0% by weight, preferably greater than 5.0% by weight.

[0099] Project 5. An oxidized sulfonated lignin scale inhibitor according to any of the preceding projects, wherein the amount of -COOH groups is equal to or greater than 6.0% by weight, preferably greater than 6.0% by weight.

[0100] Item 6. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of methoxy group is equal to or greater than 5.0% by weight, preferably greater than 5.0% by weight.

[0101] Item 7. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of methoxy groups is equal to or greater than 4.0% by weight, preferably greater than 4.0% by weight.

[0102] Project 8. An oxidized sulfonated lignin scale inhibitor according to any of the preceding projects, wherein the amount of -COOH groups is greater than 4.0 wt% and the amount of methoxy groups is equal to or less than 5.0 wt%.

[0103] Project 9. An oxidized sulfonated lignin scale inhibitor according to any of the preceding projects, wherein the amount of -COOH groups is greater than 4.0 wt% and the amount of methoxy groups is less than 5.0 wt%.

[0104] Item 10. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is greater than 4.0 wt% and the amount of methoxy groups is equal to or less than 4.0 wt%.

[0105] Project 11. An oxidized sulfonated lignin scale inhibitor according to any of the preceding projects, wherein the amount of -COOH groups is greater than 4.0 wt% and the amount of methoxy groups is less than 4.0 wt%.

[0106] Item 12. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is equal to or greater than 5.0 wt%, and the amount of methoxy groups is less than 6.0 wt%.

[0107] Item 13. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is equal to or greater than 5.0% by weight, and the amount of methoxy groups is equal to or less than 5.0% by weight.

[0108] Item 14. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is equal to or greater than 5.0% by weight, and the amount of methoxy groups is less than 5.0% by weight.

[0109] Item 15. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is equal to or greater than 5.0 wt%, and the amount of methoxy groups is equal to or less than 4.0 wt%.

[0110] Item 16. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is equal to or greater than 5.0% by weight, and the amount of methoxy groups is less than 4.0% by weight.

[0111] Item 17. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is greater than 5.0 wt% and the amount of methoxy groups is less than 6.0 wt%.

[0112] Item 18. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is greater than 5.0 wt% and the amount of methoxy groups is equal to or less than 5.0 wt%.

[0113] Item 19. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is greater than 5.0 wt% and the amount of methoxy groups is less than 5.0 wt%.

[0114] Item 20. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is greater than 5.0 wt% and the amount of methoxy groups is equal to or less than 4.0 wt%.

[0115] Project 21. An oxidized sulfonated lignin scale inhibitor according to any of the preceding projects, wherein the amount of -COOH groups is greater than 5.0 wt% and the amount of methoxy groups is less than 4.0 wt%.

[0116] Item 22. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is equal to or greater than 6.0 wt%, and the amount of methoxy groups is less than 6.0 wt%.

[0117] Item 23. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is equal to or greater than 6.0 wt%, and the amount of methoxy groups is equal to or less than 5.0 wt%.

[0118] Item 24. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is equal to or greater than 6.0 wt%, and the amount of methoxy groups is less than 5.0 wt%.

[0119] Item 25. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is equal to or greater than 6.0 wt%, and the amount of methoxy groups is equal to or less than 4.0 wt%.

[0120] Item 26. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is equal to or greater than 6.0 wt%, and the amount of methoxy groups is less than 4.0 wt%.

[0121] Item 27. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is greater than 6.0 wt% and the amount of methoxy groups is less than 6.0 wt%.

[0122] Item 28. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is greater than 6.0 wt% and the amount of methoxy groups is equal to or less than 5.0 wt%.

[0123] Item 29. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is greater than 6.0 wt% and the amount of methoxy groups is less than 5.0 wt%.

[0124] Item 30. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the amount of -COOH groups is greater than 6.0 wt% and the amount of methoxy groups is equal to or less than 4.0 wt%.

[0125] Project 31. An oxidized sulfonated lignin scale inhibitor according to any of the preceding projects, wherein the amount of -COOH groups is greater than 6.0 wt% and the amount of methoxy groups is less than 4.0 wt%.

[0126] Item 32. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, having an organic sulfur content greater than 0.5% by weight, based on the total weight of the oxidized sulfonated lignin, wherein the organic sulfur content is determined as described in the specification.

[0127] Item 33. The oxidized sulfonated lignin scale inhibitor according to Item 32, wherein the organic sulfur content is greater than 1% by weight, preferably greater than 3% by weight.

[0128] Item 34. An oxidized sulfonated lignin scale inhibitor according to any one of the preceding items, having a failure inhibitor concentration (FIC) of less than 50 ppm, preferably less than 40 ppm, more preferably less than 30 ppm, more preferably less than 20 ppm, more preferably less than 10 ppm, more preferably equal to or less than 5 ppm, more preferably less than 5 ppm, wherein the FIC is determined according to the scaling device test described in the specification.

[0129] Item 35. An oxidized sulfonated lignin scale inhibitor according to any of the preceding items, wherein the oxidized sulfonated lignin scale inhibitor does not contain an acrylic portion or a polyacrylate portion grafted thereon.

[0130] Item 36. An oxidized sulfonated lignin scale inhibitor according to any one of the preceding items, having a number average molecular weight of 1,000-100,000 g / mol, preferably 5,000-60,000 g / mol, more preferably 15,000-40,000 g / mol.

[0131] Item 37. The oxidized sulfonated lignin scale inhibitor according to any one of the preceding items has an inactivation inhibitor concentration (FIC) of less than 50 ppm, preferably less than 40 ppm, more preferably less than 30 ppm, more preferably less than 20 ppm, more preferably less than 10 ppm, and more preferably less than 5 ppm after being stored at 130°C for 14 days, wherein the FIC is determined according to the scaling device test described in the specification.

[0132] Project 38. An oxidized sulfonated lignin scale inhibitor according to any of the preceding projects, wherein the oxidized sulfonated lignin scale inhibitor is used to inhibit the formation of calcite and barite scale in oilfield applications.

[0133] Item 39. The use of an oxidized sulfonated lignin scale inhibitor according to any one of Items 1-38 for inhibiting scaling in oilfield applications.

[0134] Project 40. Based on the application of Project 39, the oxidized sulfonated lignin scale inhibitor is used in oilfield applications to inhibit the formation of calcite and barite scale.

[0135] Item 41. A method for inhibiting scale formation in oilfield applications, the method comprising using an oxidized sulfonated lignin scale inhibitor according to any one of Items 1-38.

[0136] Project 42. The method of Project 41, wherein an oxidized sulfonated lignin scale inhibitor is added to a production enhancement fluid, a completion fluid, or used for a squeeze treatment.

[0137] Item 43. A method for preparing an oxidized sulfonated lignin scale inhibitor according to any one of Items 1-38, the method comprising the following steps:

[0138] (a1) Provides sulfonated lignin raw materials,

[0139] (a2) Oxidize the sulfonated lignin raw material with an oxidizing agent to obtain the oxidized sulfonated lignin scale inhibitor.

[0140] Project 44. According to the method of Project 43, wherein the sulfonated lignin raw material is lignin sulfonate, preferably lignin sulfonate obtained from sulfite pulping.

[0141] Item 45. According to the method of Item 43 or 44, wherein the oxidation step (a2) is carried out as a multi-step oxidation using multiple oxidants.

[0142] Project 46. According to the method of Project 45, the multi-step oxidation is characterized in that one of the oxidants is ozone or molecular oxygen.

[0143] Project 47. According to the method of Project 45 or 46, the multi-step oxidation is characterized in that one of the oxidants is hydrogen peroxide.

[0144] Project 48. The method according to any one of Projects 45-47, wherein the multi-step oxidation is characterized in that one of the oxidants is sodium hydroxide.

[0145] Project 49. According to any one of Projects 45-48, the multi-step oxidation is characterized in that one of the oxidizing agents is sodium hydroxide and the other oxidizing agent is ozone.

[0146] Project 50. The method of any one of Projects 45-49, wherein the multi-step oxidation is characterized by being a two-step oxidation method and involving the sequential application of two oxidizing agents.

[0147] Project 51. According to the method of Project 50, one of the two oxidants is sodium hydroxide and the other of the two oxidants is ozone.

[0148] Project 52. According to the method of Project 51, wherein sodium hydroxide is first applied.

[0149] Project 53. The method according to any one of Projects 45-49, wherein the multi-step oxidation is characterized by being a three-step oxidation method and involving the sequential application of three oxidizing agents.

[0150] Project 54. According to the method of Project 53, one of the three oxidants is sodium hydroxide, and the other of the three oxidants is ozone.

[0151] Project 55. According to the method of Project 54, one of the three oxidants is sodium hydroxide, another of the three oxidants is ozone, and the third of the three oxidants is hydrogen peroxide.

[0152] Project 56. According to the method of Project 55, sodium hydroxide is applied first, ozone is applied second, and hydrogen peroxide is applied third.

[0153] Item 57. The method according to any one of Items 43 or 44, wherein the oxidant is ozone, molecular oxygen or peracid, wherein the peracid is preferably selected from peracetic acid, perpropionic acid and perbenzoic acid.

[0154] Project 58. According to the method in Project 57, the peracid is peracetic acid.

[0155] Item 59. The method of any one of items 43-58, wherein the method does not include the step of grafting acrylic acid or polyacrylate onto lignin sulfonate.

[0156] Item 60. The method according to any one of Items 43-59, wherein the number average molecular weight of the oxidized lignin sulfonate scale inhibitor is at least 10% of the number average molecular weight of the sulfonated lignin raw material, preferably at least 50%, more preferably at least 70%, and even more preferably at least 80%.

[0157] Item 61. Oxidized sulfonated lignin scale inhibitor, obtained by any one of the methods in Items 43-60.

[0158] Example

[0159] Synthesis of lignin sulfonates (sulfonated lignin F and G) according to the present invention

[0160] Lignin F: Sodium lignin sulfonate, produced from commercial sulfite waste, was dissolved in water at a solids content of 30% and reacted with 20% sodium hydroxide in a Par reactor at 160°C for 3 hours. The mixture was then oxidized with ozone gas (15% ozone relative to lignin solids) at 50°C using a laboratory ozone generator and reactor. Finally, the product was treated with a 30% aqueous hydrogen peroxide solution (30% peroxide relative to lignin solids) in a round-bottom flask heated to 66°C.

[0161] Lignin G: Sodium lignin sulfonate produced from commercial sulfite waste liquid is dissolved in water with a solid content of 25% and treated at 71°C with a premixed solution of peracetic acid (peracetic acid composition = 40% w / w hydrogen peroxide dosage (relative to dry lignin mass) + glacial acetic acid (¼ of the total volume of peroxide used) + catalytic amount of 50% H2SO4 solution).

[0162] Fouling device test

[0163] The inhibition performance was tested using a high-pressure dynamic scaling apparatus. This apparatus, located at the University of Stavanger in Norway, was manufactured by the PMAC Group in Aberdeen, UK. This is an effective laboratory method for determining the inhibition efficiency of scale inhibitors on calcite and barite scale in oilfields.

[0164] The device has a main control unit consisting of two pumps that allow the aqueous solution to flow at the desired rate through a stainless steel coil (1 m long, 1 mm inner diameter). The coil is placed inside an oven connected to the main control unit via steel tubing. The main control unit also contains a pH probe and a conductivity meter for measuring the pH and conductivity of the mixed aqueous solution passing through the coil. For the experimental method developed by the University of Stavanger, experiments were conducted at 100°C and a line pressure of approximately 1200 psi, but the device is designed to withstand higher temperature and pressure variations.

[0165] Figure 2A schematic diagram of the control unit is shown, explaining typical conditions during a single-tube blockage test run. Pump 1 injects a cationic salt solution, while pump 2 is responsible for pumping four different solutions controlled by valves A, B, C, and D. Valve A pumps anionic salt solution, and valve B injects an inhibitor solution (dissolved in anionic salt solution) at a controlled flow rate, which is then mixed and pumped into the scaling coil. Valves A and B must be opened and closed simultaneously to maintain the flow rate within the coil. Additionally, valves C and D in pump 2 are responsible for injecting a cleaning solution, an alkaline EDTA solution (pH=12), and distilled water, respectively.

[0166] A complete run consists of two consecutive tests, controlled by an automatic scaling device:

[0167] The first test was "chemical," in which cationic and anionic saline solutions were mixed with an inhibitor solution and pumped into the scaling coil at a flow rate of 10 mL / min. The test consisted of multiple automated cycles, each lasting 1 hour. In each test, the inhibitor concentration was gradually reduced until rapid tube blockage occurred at a certain inhibitor concentration.

[0168] The second is "repetitive chemistry," where the initial inhibitor concentration is the same as that in the stage leading to rapid scale formation. The initial concentration of the stock inhibitor solution (SLS dissolved in anionic brine) is approximately 200 ppm, with a pH of 7.

[0169] In the first "chemical" stage of the test, saline and inhibitor solutions are mixed in a specific ratio to obtain the required inhibitor concentration within the test coil.

[0170] Starting with an initial inhibitor concentration of 100 ppm, the flow rate is automatically adjusted hourly to gradually reduce the concentration (e.g., 50, 20, 10, 5, 2, and 1 ppm) until rapid scaling is observed, triggering a cleaning cycle. The concentration that causes rapid scaling in the test coil is called the ineffective inhibitor concentration (FIC). This is typically indicated by a sudden increase in differential pressure across the test coil (approximately 10 psi from a baseline pressure of 0.4–0.5 psi). Depending on the test conditions, inhibitors with an FIC range of 2–10 ppm are considered to have excellent to fairly good scale inhibition efficiency.

[0171] The synthetic brine used in this study was simulated based on water produced from the Heidrun oil field in Norway. Formation water was used only for calcite scale testing. The salt composition of the brine is given in Table 3 below. Before each experiment, the brine, scale inhibitor solution, and cleaning fluid were freshly prepared and thoroughly degassed to avoid complications during automated operation.

[0172] Table 3. Salt composition of brine 1 and 2 for calcite scaling.

[0173]

[0174] Brine compatibility test

[0175] Formation water may contain high levels of Ca. 2+ If the injected scale inhibitor is incompatible with the brine, this can cause serious problems. If incompatible, the scale inhibitor itself can cause problems during the extrusion process by forming insoluble calcium ions. 2+ Scale inhibitors can precipitate as a complex. This can clog the pores of formation rocks, causing severe formation damage. Therefore, all scale inhibitors are screened to determine their calcium tolerance limits.

[0176] Use a simple test method to check the initial compatibility of the scale inhibitor with cationic brine, especially with Ca ions. Mix approximately 1 mL of a 1 wt% scale inhibitor solution in distilled water with an equal volume of cationic brine, and heat the resulting solution to 90°C. Then check the solution for any precipitation or turbidity.

[0177] Clear brown solution = compatible

[0178] Opaque solution = poor compatibility

[0179] Brown precipitate = incompatible

[0180] Temperature stability test

[0181] Temperature stability testing was conducted to assess whether the scale inhibitor maintained its inhibitory performance under reservoir conditions, including extrusion treatment. A 5 wt% solution of the scale inhibitor in distilled water, equipped with a magnetic stir bar, was placed in a hard glass tube fitted with a Teflon stopcock. The solution was then subjected to three repeated vacuum refill (with nitrogen) cycles, followed by sealing under a nitrogen atmosphere. The tube was then placed in an oil bath preheated to 130°C or 160°C and maintained at this temperature for 14 or 10 days. The water was then evaporated, and the solid sample was tested in a scaling apparatus. The inhibitory performance of the thermally aged inhibitor was compared with that of the non-aged inhibitor to determine their stability under high-temperature conditions.

[0182] Methoxyl analysis

[0183] Approximately 30 mg of scale inhibitor was dissolved in 1000 mg of deuterated methanol (MeOD-d4), and then added to Amberlite IR-120 resin. The solution was stirred for at least 30 min, and then 620 μL was transferred to an NMR tube using an automated pipette. Samples were prepared twice (two in parallel, each parallel was performed separately, and the average result was used as the final result for MeO content). HSQC experiments were then performed, where the methoxy content was calculated relative to a linear curve prepared using an internal methoxy standard. NMR experiments were performed on a Bruker Avance III 500 MHz spectrometer using a selectively reversed (SEI) probe to obtain maximum 1H sensitivity. All spectra were recorded in MeOH-d4 at 300 K. Optimization for methoxy groups was performed. 1 H- 13 CHSQC spectra (1JC, H coupling constant 145 Hz) were recorded in phase-sensitive mode using echo-antiecho with a standard Bruker pulse sequence. A 200t1 experiment (24 scans and 16 virtual scans) was conducted recording 1k real data points, with a relaxation delay of 3 seconds, a proton spectral width of 9 ppm, and a carbon spectral width of 130 ppm. The total experimental time was 4.5 hours. (The last sentence appears to be incomplete and possibly refers to a separate experiment.) * After zero-padding the matrix of 1k data points, squared sinusoidal window functions were applied in both directions. The spectrum underwent phase correction in the F2 direction, baseline correction was performed in the F1 and F2 directions using an automatic 5th-order polynomial function, and the summative projection in the F1 direction was calculated. The amount of methoxy groups was determined by the signal intensity in the 53–58 ppm region.

[0184] Organic sulfur analysis

[0185] The amount of "organic" sulfur (org.S), i.e., the amount of sulfur associated with sulfonate groups attached to lignin, i.e., the degree of sulfonation, is determined based on the difference between total sulfur %S (tot) and inorganic sulfur %S (inorg), using the following relationship:

[0186] %S(org) = %S(tot) – %S(inorg)

[0187] Total sulfur was determined using an elemental analyzer (e.g., ThermoQuest NCS2500). An appropriate sample amount (e.g., 1-2 mg) was placed in a tin capsule containing a suitable catalyst (e.g., vanadium pentoxide). The total sulfur in the sample was then quantified using the 2,5-bis(5-tert-butyl-2-benzoxazol-2-yl)thiophene (BBOT) standard or other suitable sulfur standard. The sample was then burned at 1400 °C, and all sulfur was oxidized to SO2 and quantified.

[0188] Inorganic sulfur was determined by measuring sulfate in oxidized samples using ion chromatography and conductivity detection (Dionex instrument, using an Ion Pac AS11-HC column and 13 mM OH- eluent). 30 mg of sample was weighed and placed in a 50 mL volumetric flask. 10 mL of 0.5% NaOH and 5 mL of 3% H₂O₂ were added to oxidize the sulfur-containing inorganic anions to sulfate. The sample was then allowed to stand for 12–16 hours to allow for reaction. Milli-Q water was added, and the pH was neutralized by adding 2 mL of 5% CH₃COOH, followed by dilution to the mark with Milli-Q water. Sulfate standards ranging from 5 mg / L to 80 mg / L were prepared. The sulfate content in the oxidized sample was then determined by ion chromatography according to the instrument manual.

[0189] -COOH was determined using P-NMR.

[0190] Characterizing the molecular structure of lignin sulfonates is often challenging due to the presence of unknown impurities. Specifically, low molecular weight carboxylic acids, such as formic acid and acetic acid, which are formed from xylose and are commonly found in lignin sulfonates, can interfere with -COOH measurements.

[0191] Therefore, a slightly modified phosphorus NMR (P-NMR) method, originally developed by Argyropoulos, DS; Abacherli, A.; Rincón, AG; Arx, UV [Quantitative 31 P nuclear magnetic resonance (NMR) spectra of lignin. In Analytical Methods for Lignin Characterisation; International Lignin Institute: Lausanne, Switzerland, 2009], was used to quantify the density of -COOH groups on the lignin framework.

[0192] Specifically, the method includes a purification step to remove low molecular weight carboxylic acid impurities (e.g., formic acid, acetic acid), followed by the method of Argyropoulos et al., using a phosphorylation reagent and 31 P-NMR was used to measure the density of -COOH groups on lignin polymers.

[0193] Chemicals:

[0194] Internal standard: 99% cholesterol

[0195] Phosphorylation reagent: 95% 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxophosphazenecyclopentane

[0196] Deuterated solvent: CDCl3

[0197] Solvents: 99.8% anhydrous pyridine and 99.8% anhydrous N,N-dimethylformamide

[0198] Desiccant: Molecular sieve 13X, beads, 8-12 mesh

[0199] Resin: Amberlite IR120 H+ form

[0200] The analysis will be conducted over two days:

[0201] Day 1:

[0202] Fill a glass pipette with Amberlite. Then rinse the resin twice with deionized water and elute 2 × 1 mL through the pipette.

[0203] Weigh the sample (200 mg) in a glass vial, add deionized water (3 mL), and stir for approximately 10 minutes. Filter the resulting solution through a glass pipette filled with Amberlite and collect the filtrate in a round glass flask. Rinse the resin twice with water, 2 x 1 mL each time, and collect the filtrate in the flask. Freeze and lyophilize the filtered sample overnight.

[0204] Phosphorylation is highly sensitive to water, and all reagents and components must be dried. Hamilton syringes are used to add the solvent to the reaction mixture and therefore must be completely dry. Molecular sieves are washed in pure acetone in glass beakers and then dried overnight in an oven (105°C). They will be used for drying the solvent the following day.

[0205] Day 2:

[0206] A solvent mixture of N,N-dimethylformamide (DMF) and pyridine (1:1) was prepared in a glass vial containing a dried molecular sieve. The vial was sealed to prevent moisture.

[0207] Pyridine was also added to another glass vial containing a dried molecular sieve, and the vial was sealed. This will be used to prepare a solution of 40 mg / mL cholesterol (internal standard) in dried pyridine.

[0208] The dried solution of the deuterated solvent CDCl3 was also prepared by adding deuterated chloroform to a glass vial containing a molecular sieve and sealing the vial. Then, in a 2 mL glass vial, 400 μL of dried CDCl3 was transferred, followed by 100 μL of the phosphorylation reagent 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxophosphazenecyclopentane.

[0209] The freeze-dried sample (30 mg ± 3 mg) was added to a 2 mL glass vial, followed by a magnetic stirrer and a solvent mixture of DMF:pyridine (1:1) (100 μL), and the mixture was stirred for 30 minutes. Next, a cholesterol solution (100 μL) was added to the reaction mixture, and stirring was continued for 15–30 minutes. Finally, a solution of freshly prepared derivatizing reagent in CDCl3 (500 μL) was added dropwise, and the reaction mixture was stirred for 1 hour before NMR analysis.

[0210] NMR experiment:

[0211] 31 PNMR experiments were performed using a BBO probe at 300 K. The NMR experimental setup for the 500 MHz Avance III Bruker instrument is as follows:

[0212] Table 4

[0213]

[0214] After obtaining the fid and performing a Fourier transform, the phase (ph) of the frequency domain spectrum was manually corrected, followed by automatic phase correction (efp) using an apodized Fourier transform, and finally, fundamental correction (abs). Spectral calibration was performed using the peak at 132.20 ppm of the reaction byproduct between the phosphorylation reagent and water. The cholesterol peak at 144.8 ppm was first integrated between 145.0 and 144.4 ppm and calibrated at 1. Then, other signals were integrated as follows:

[0215] Table 5

[0216]

[0217] The concentration of each type of OH group (mmol OH / g sample) was determined using the following formula:

[0218]

[0219] C: Concentration of internal standard (mg / mL)

[0220] A: Area of ​​functional OH groups (when the integral calibration of the cholesterol peak is 1).

[0221] IS: Volume of internal standard solution added to pyridine (0.1 mL)

[0222] M: Molecular weight of the internal standard (386.65 g / mol)

[0223] L: Weight (g) of the freeze-dried sample added to the vial

[0224] P: Purity of the internal standard (0.99)

[0225] The mass of the -COOH functional group on the lignin polymer can then be calculated using the molecular weight of the -COOH functional group (45.0174 g / mol), and the weight can be calculated based on the total weight of the oxidized sulfonated lignin.

[0226] result

[0227] The inventors of this invention have studied the scale inhibition properties and calcium compatibility of a series of sulfonated lignins with different characteristics.

[0228] Sulfonated lignin A and B are lignin sulfonates produced from sulfite waste liquid raw materials, without further modification.

[0229] Sulfonated lignin C and D are alkaline lignin sulfonates produced according to the hydrothermal caustic treatment described in the prior art (see US3,849,328 and US2,505,457, respectively).

[0230] Sulfonated lignin E is an oxidized lignin sulfonate as described in WO2021 / 165298.

[0231] Sulfonated lignins F and G are according to the present invention and have been prepared as described above.

[0232] Sulfonated lignins LS6, LS7 and LS8 are the same samples as LS6, LS7 and LS8 in Table 1 of WO2021 / 165298.

[0233] Sulfonated lignin A10 corresponds to sample A treated with 10% NaOH.

[0234] Sulfonated lignin A20 corresponds to sample A treated with 20% NaOH.

[0235] Laboratory methods for determining scale inhibitor performance must simulate industrial conditions as closely as possible. For oilfield applications, high-pressure dynamic pipe clogging and scaling test apparatuses allow for direct comparison of different scale inhibitors under process-related conditions. These apparatuses are used as standard equipment in the oilfield industry, replicating specific scaling conditions by programming temperature, pressure, brine composition, and flow rate. The performance of the scale inhibitor is expressed as the failure inhibitor concentration (FIC). The results are shown in Table 6 below:

[0236] Table 6: Properties and molecular characteristics of selected ranges of lignin sulfonates tested.

[0237]

[0238] To consider commercial relevance, sulfonated lignin scale inhibitors should have FIC values ​​comparable to or better than commercially available synthetic scale inhibitors (see Table 2 above) and good compatibility with calcium brine. The data in Table 6 indicate that only sulfonated lignins with a combination of high -COOH content and low methoxy content perform well enough to be considered commercially relevant (lignin sulfonates F and G). Unmodified lignin sulfonates (A and B) and prior art hydrothermally causticized lignin sulfonates (C and D) do not possess this combination of properties and perform poorly enough to be considered relevant for oilfield scale inhibition applications. Oxidized lignin sulfonate E is not sufficiently oxidized, does not possess a favorable combination of properties, and performs poorly enough to be considered relevant for oilfield scale inhibition applications.

[0239] Sulfonated lignins LS6, LS7, and LS8 do not exhibit the combination of high COOH content and low methoxy content, and perform poorly in terms of FIC and calcium compatibility; therefore, they cannot be considered relevant to oilfield scale inhibition applications. Sulfonated lignins A10 and A20 also do not exhibit the combination of high COOH content and low methoxy content, and perform poorly in terms of FIC and calcium compatibility; therefore, they cannot be considered relevant to oilfield scale inhibition applications. Furthermore, the results for these samples indicate that single-step oxidation with NaOH does increase the -COOH content (compared to sample A), but not significantly. The results also show that the methoxy content does not change significantly due to single-step oxidation.

[0240] Further testing of the thermal stability of lignin sulfonate F (Table 7) revealed that it is stable under long-term high-temperature conditions.

[0241] Table 7: Properties of Lignosulfonate F after heat treatment

[0242]

[0243] * Determined based on the following scaling device test.

Claims

1. An oxidized sulfonated lignin scale inhibitor, characterized in that: The content of ·-COOH groups is greater than 4.0% by weight, based on the total weight of oxidized sulfonated lignin. The -COOH group content is determined by phosphorylation of the -COOH group as described in the specification, and subsequently... 31 P-NMR measurements, and • The methoxy content is less than 6.0% by weight, based on the total weight of oxidized sulfonated lignin, wherein the methoxy content is determined by NMR testing as described in the instructions.

2. The oxidized sulfonated lignin scale inhibitor according to claim 1, wherein the oxidized sulfonated lignin scale inhibitor is an oxidized lignin sulfonate.

3. The oxidized sulfonated lignin scale inhibitor according to claim 1 or 2, wherein the carbon atom of the -COOH group is already contained in the natural lignin from which the oxidized sulfonated lignin scale inhibitor originates.

4. The oxidized sulfonated lignin scale inhibitor according to any one of the preceding claims, wherein the amount of the -COOH group is equal to or greater than 5.0% by weight, preferably greater than 5.0% by weight.

5. The oxidized sulfonated lignin scale inhibitor according to any one of the preceding claims, wherein the amount of the -COOH group is equal to or greater than 6.0% by weight, preferably greater than 6.0% by weight.

6. The oxidized sulfonated lignin scale inhibitor according to any one of the preceding claims, wherein the amount of methoxy groups is equal to or less than 5.0% by weight, preferably less than 5.0% by weight.

7. The oxidized sulfonated lignin scale inhibitor according to any one of the preceding claims, wherein the amount of methoxy groups is equal to or less than 4.0% by weight, preferably less than 4.0% by weight.

8. The oxidized sulfonated lignin scale inhibitor according to any one of the preceding claims, having an organic sulfur content of greater than 0.5% by weight, preferably greater than 1% by weight, and preferably greater than 3% by weight, based on the total weight of the oxidized sulfonated lignin, wherein the organic sulfur content is determined as described in the specification.

9. The oxidized sulfonated lignin scale inhibitor according to any one of claims 1-8 is used to inhibit scale formation in oilfield applications, preferably for inhibiting the formation of calcite scale and barite scale.

10. A method for inhibiting scale formation in oilfield applications, the method comprising using an oxidized sulfonated lignin scale inhibitor according to any one of claims 1-8, preferably wherein the oxidized sulfonated lignin scale inhibitor is added to a production enhancement fluid, a completion fluid, or used for extrusion treatment.

11. A method for preparing an oxidized sulfonated lignin scale inhibitor according to any one of claims 1-8, the method comprising the following steps: (a1) Provides sulfonated lignin raw materials, (a2) Oxidize the sulfonated lignin raw material with an oxidizing agent to obtain the oxidized sulfonated lignin scale inhibitor.

12. The method according to claim 11, wherein the oxidation step (a2) is performed as a multi-step oxidation using a variety of oxidants.

13. The method according to any one of claims 11 and 12, wherein the multi-step oxidation is characterized in that it is a two-step oxidation method and includes the sequential application of two oxidizing agents.

14. The method according to any one of claims 11 and 12, wherein the multi-step oxidation is characterized in that it is a three-step oxidation method and includes the sequential application of three oxidizing agents.

15. An oxidized sulfonated lignin scale inhibitor, obtained by the method according to any one of claims 11-14.

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