Low-molecular-weight filtrate reducer and preparation method thereof

Abstract

The invention discloses a low-molecular-weight filtrate reducer and a preparation method thereof, and relates to the technical field of oilfield chemistry. The method comprises the following steps: dissolving chitosan oligosaccharide in water, adding a small amount of a cross-linking agent under the condition of continuous stirring at 50-70 DEG C to realize light cross-linking, adding N, N-dimethylacrylamide, N-vinyl imidazole, sodium p-styrenesulfonate and unsaturated carboxylic acid after the reaction is finished, carrying out free radical polymerization under the action of an initiator, and after the polymerization is finished, carrying out suction filtration, washing and drying to obtain chitosan oligosaccharide. And drying and crushing the mixture to obtain the traditional Chinese medicine composition. The filtrate reducer prepared by the preparation method disclosed by the invention is relatively small in molecular weight, and compared with a filtrate reducer with relatively large molecular weight, the filtrate reducer disclosed by the invention has the advantages that a formed filter cake is more compact, the filtrate reduction effect is relatively good, and the filtrate reducer has good temperature resistance and salt tolerance.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield chemistry, and in particular to a low-molecular-weight fluid loss additive and a preparation method thereof. Background Art

[0002] During the wellbore construction process, drilling fluid forms a filter cake through filtration, which protects the wellbore and prevents further fluid loss. However, excessive filter cake loss during the formation process not only increases drilling costs, but also easily leads to shale hydration and expansion, which in turn can cause wellbore instability. Furthermore, increased filter loss and thickening of the filter cake reduce the wellbore diameter, creating greater torque on the rotating drill string. This can cause swabbing and pressure fluctuations during tripping, which can easily lead to differential pressure sticking.

[0003] Obviously, filter cake forms as drilling fluid is lost. Any further loss of drilling fluid must pass through the already formed filter cake. Therefore, the primary factor determining fluid loss is the permeability of the filter cake. Creating a high-quality, low-permeability filter cake to prevent further fluid loss is a key consideration in drilling fluid formulation. Therefore, fluid loss control agents are typically added to drilling fluids to control fluid loss during the wall-building process, keeping fluid loss within a reasonable range.

[0004] Existing fluid loss control agents are divided into modified natural polymer fluid loss control agents and artificial polymer fluid loss control agents. Modified natural polymer fluid loss control agents are favored by researchers due to their environmental performance. Modified natural polymer fluid loss control agents typically have matrices such as starch, cellulose, humic acid, and chitosan. These are generally macromolecular matrices, and while effective, they suffer from slow dissolution in drilling fluids, typically requiring high-speed stirring for a period of time. While some modified natural polymer fluid loss control agents, such as chitosan quaternary ammonium salt, dissolve relatively quickly in water, their solubility decreases rapidly after further modification to graft multiple monomers. Summary of the Invention

[0005] In view of the above technical problems, the purpose of the present invention is to provide a low molecular weight fluid loss additive and a preparation method thereof to address the defects of the prior art.

[0006] The present invention adopts the following technical scheme: a preparation method of a low molecular weight fluid loss additive, which comprises the following steps, in parts by weight: taking 100 parts of chitosan oligosaccharide and dissolving it in water; adding 0.01-0.1 parts of a cross-linking agent at 50-70°C and continuously stirring; and simultaneously dropwise adding 0.5-1 parts of an alkaline catalyst; continuing the reaction for 10-18 hours; after the reaction is completed, adding 60-90 parts of N,N-dimethylacrylamide, 20-40 parts of N-vinylimidazole, 30-50 parts of sodium p-styrenesulfonate and 30-50 parts of an unsaturated carboxylic acid; carrying out free radical polymerization under the action of an initiator; and after the polymerization is completed, drying and pulverizing the fluid loss additive to obtain the fluid loss additive; the cross-linking agent is one of polyethylene glycol acrylate and polyethylene glycol dimethacrylate.

[0007] The difference from conventional fluid loss additives is that in this embodiment, the substrate used is chitosan oligosaccharide, a low-molecular hydrolyzate of chitosan. Chitosan oligosaccharide refers to an oligosaccharide polymer with a degree of polymerization of 2-20 and a molecular weight of less than 3200. Compared with conventional substrates, such as chitosan and starch with a molecular weight of hundreds of thousands, its molecular weight is much lower. Chitosan oligosaccharide contains a large number of hydroxyl and amino groups and has good water solubility. At the same time, the hydroxyl and amino groups can provide a large number of active sites for subsequent grafting reactions. However, the disadvantage of chitosan oligosaccharide is that it is not water-resistant and is very easy to degrade in water. Therefore, in the present invention, before using chitosan oligosaccharide for grafting polymerization, it is first modified.

[0008] In the present invention, first utilize cross-linking agent to carry out light cross-linking of chitosan oligosaccharide, in this process, the dosage of cross-linking agent cannot be too much, when the dosage of cross-linking agent is too much, cross-linking degree is too high, it can form gel state, and water absorption expansion rate is slow;Meanwhile, for cross-linking agent, the present invention discloses that it is one of polyethylene glycol acrylate or polyethylene glycol dimethacrylate, for similar cross-linking agent, such as diethanol dimethacrylate, diallyldimethylammonium chloride etc., its chain length is too short, cross-linking network is too dense, can cause the product of second step to be more concentrated in the polymerization of each monomer rather than graft polymerization, grafting rate is low, and the performance of final product is poor.The dosage of cross-linking agent is equally unsuitable, within the preferred range, the dosage of cross-linking agent can be set to 0.05~0.08 part, such as 0.05 part, 0.06 part, 0.07 part and 0.08 part.Meanwhile, in cross-linking reaction process, reaction time needs to be extended as much as possible, to avoid remaining a large amount of cross-linking agent in product.

[0009] Theoretically, this step can use oil-in-water emulsion polymerization to produce more uniform cross-linked chitosan oligosaccharides. However, in the present invention, the amount of cross-linking agent added is low, the concentration of chitosan oligosaccharides is low, and the cross-linking agent is one of polyethylene glycol acrylate or polyethylene glycol dimethacrylate, which contains less double bonds. Therefore, the inventors found through experiments that whether the reaction is directly in an aqueous solution or in an emulsion, the performance of the final product is relatively similar, and the aqueous solution reaction is lower in cost and takes less time.

[0010] In the second step, the present invention uses N,N-dimethylacrylamide as the primary polymerization monomer, supplemented with N-vinylimidazole, sodium p-styrenesulfonate, and an unsaturated carboxylic acid, to graft polymerize the product from the first step. The imidazole group, benzene ring, sulfonic acid group, and carboxylic acid group in the polymerization monomer can all reduce the degradation of chitosan oligosaccharide to a certain extent. This ultimately results in a fluid loss additive produced by the present invention having excellent temperature and salt resistance.

[0011] In one embodiment of the present invention, the alkaline catalyst is sodium hydroxide or potassium hydroxide, which is prepared into an aqueous solution with a concentration of 10-20 wt% before use.

[0012] In one embodiment of the present invention, the unsaturated carboxylic acid is one of acrylic acid, itaconic acid, and maleic anhydride. These are common unsaturated carboxylic acids in the art. Preferably, a dicarboxylic acid has a better effect, such as itaconic acid.

[0013] In one embodiment of the present invention, the initiator is a persulfate initiator or a redox initiator, both of which are common water-soluble initiators in the art. The amount of initiator added is typically 1-3% of the total monomer mass. The reaction temperature after adding the initiator can be selected based on the type of initiator. For example, for a redox initiator (persulfate / sulfite with a mass ratio of 1:1), the reaction temperature can be 20-50°C, and the polymerization reaction time can be 1-3 hours. For potassium persulfate, the reaction temperature can be 55-70°C, and the reaction time can be 1-5 hours. This is a common setting in the art.

[0014] One embodiment of the present invention is that the amount of N,N-dimethylacrylamide added is 70-80 parts, the amount of N-vinylimidazole added is 25-30 parts, the amount of sodium p-styrenesulfonate added is 35-45 parts, and the amount of unsaturated carboxylic acid added is 35-45 parts.

[0015] One embodiment of the present invention is that when chitosan oligosaccharides are dissolved in water, their concentration is 5-10 wt %. During free radical polymerization, the total monomer concentration in water is no more than 25 wt %. This is primarily due to the monomer concentrations in the two reactions: for the first reaction (cross-linking of chitosan oligosaccharides), if the chitosan oligosaccharide concentration is too high, there is a risk of forming a gel state (a highly aqueous solid phase) after cross-linking, which is detrimental to subsequent reactions. For the second reaction (graft polymerization), if the monomer concentration in the second step is too high, there is a risk of implosion. Based on the inventors' practical experience, the total concentration of all monomers (including cross-linked chitosan oligosaccharides) in water in the second step is preferably no more than 25 wt %, preferably 13-18 wt %. Of course, in actual reactions, some water may be added in the first reaction and some in the second reaction.

[0016] In one embodiment of the present invention, the average molecular weight of the polyethylene glycol acrylate or polyethylene glycol dimethacrylate is 400 to 600. Common polyethylene glycol dimethacrylates also have an average molecular weight of 200, but the inventors have found that when polyethylene glycol dimethacrylates of this molecular weight are used, the effect is poor.

[0017] Another object of the present invention is to disclose a low molecular weight fluid loss additive prepared by any of the above methods, which has a good fluid loss reduction effect.

[0018] The beneficial effect of the present invention is that the fluid loss reducer prepared by the present invention has a relatively small molecular weight. It is known to those skilled in the art that, compared with fluid loss reducers with larger molecular weights, the advantages of the present invention are that the filter cake formed is denser, the fluid loss reduction effect is better, and the filter loss reducer has good temperature and salt resistance. DETAILED DESCRIPTION

[0019] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is described in detail below in conjunction with the embodiments, but it should not be understood as limiting the scope of implementation of the present invention.

[0020] In the following examples, unless otherwise specified, the methods used are conventional methods in the art.

[0021] In the following examples, unless otherwise specified, the drugs used are conventional commercial products.

[0022] In the following examples, unless otherwise specified, all parts are by weight.

[0023] Example 1: Take 100g of chitosan oligosaccharide and add it to 1150mL of water and dissolve it. Take 0.7g of sodium hydroxide and add it to 5mL of water to prepare a sodium hydroxide solution. At 60°C and under continuous stirring, add 0.05g of polyethylene glycol dimethacrylate (molecular weight 600) to the chitosan oligosaccharide solution. Then, add the aforementioned sodium hydroxide solution dropwise and continue to react for 14 hours. After the reaction is completed, cool to room temperature. Under continuous stirring, add 75g of N,N-dimethylacrylamide, 28g of N-vinyl imidazole, 40g of sodium p-styrene sulfonate, and 40g of itaconic acid. After stirring evenly, add water to control the total concentration of chitosan oligosaccharide, N,N-dimethylacrylamide, N-vinyl imidazole, sodium p-styrene sulfonate and itaconic acid to 17wt%. Then, add 6.0g of potassium persulfate and heat to 65°C. Continue to react for 2 hours. After the reaction is completed, dry and crush it. The average molecular weight is measured to be about 58×10 3 g / mol.

[0024] Example 2: 100g of chitosan oligosaccharide was added to 1150mL of water and dissolved. 0.7g of sodium hydroxide was added to 5mL of water to prepare a sodium hydroxide solution. 0.12g of polyethylene glycol dimethacrylate (molecular weight 400) was added to the chitosan oligosaccharide solution at 60°C and under continuous stirring. The sodium hydroxide solution was then added dropwise and the reaction was continued for 16h. After the reaction was completed, it was cooled to room temperature. Under continuous stirring, 75g of N,N-dimethylacrylamide, 28g of N-vinylimidazole, 40g of sodium p-styrenesulfonate, and 40g of itaconic acid were added. After stirring evenly, water was added to control the total concentration of chitosan oligosaccharide, N,N-dimethylacrylamide, N-vinylimidazole, sodium p-styrenesulfonate, and itaconic acid to 15wt%. 6.0g of potassium persulfate was then added and the temperature was raised to 70°C. The reaction was continued for 1.5h. After the reaction was completed, it was dried and crushed to obtain the product. The average molecular weight was measured to be approximately 120×10 3 g / mol.

[0025] Example 3: Take 100g of chitosan oligosaccharide and add it to 1150mL of water and dissolve it. Take 0.7g of sodium hydroxide and add it to 5mL of water to prepare a sodium hydroxide solution. At 60°C and under continuous stirring, add 0.08g of polyethylene glycol dimethacrylate (molecular weight 200) to the chitosan oligosaccharide solution. Then, add the aforementioned sodium hydroxide solution dropwise and continue to react for 12h. After the reaction is completed, cool to room temperature. Under continuous stirring, add 75g of N,N-dimethylacrylamide, 28g of N-vinyl imidazole, 40g of sodium p-styrene sulfonate, and 40g of itaconic acid. After stirring evenly, add water to control the total concentration of chitosan oligosaccharide, N,N-dimethylacrylamide, N-vinyl imidazole, sodium p-styrene sulfonate and itaconic acid to 15wt%. Then, add 6.0g of potassium persulfate and heat to 70°C. Continue to react for 1.5h. After the reaction is completed, dry and crush it. The average molecular weight is measured to be approximately 34×10 3 g / mol.

[0026] Example 4, compared with Example 1, the difference is that the amount of N,N-dimethylacrylamide added is 65g, the amount of N-vinylimidazole added is 35g, the amount of sodium p-styrenesulfonate added is 35g, and the amount of itaconic acid added is 35g, and the rest are the same. The average molecular weight is measured to be about 52×10 3 g / mol.

[0027] Example 5, compared with Example 1, the difference is that itaconic acid is replaced by 45g acrylic acid, the total concentration of chitosan oligosaccharide, N,N-dimethylacrylamide, N-vinylimidazole, sodium p-styrenesulfonate and acrylic acid is 22wt%, and the rest are the same. The average molecular weight is measured to be about 69×10 3 g / mol.

[0028] Comparative Example 1 is compared with Example 1, except that 0.05 g of polyethylene glycol dimethacrylate (molecular weight 600) is replaced by 0.05 g of diethanol dimethacrylate, and the rest are the same.

[0029] Comparative Example 2 is compared with Example 1, except that when chitosan oligosaccharide is dissolved in water, the concentration of the chitosan oligosaccharide is 20 wt %, and the rest are the same. It is found that after the chitosan oligosaccharide is cross-linked, it agglomerates into agglomerates.

[0030] Comparative Example 3 is compared with Example 1, except that N-vinylimidazole is not added, and the rest are the same.

[0031] Comparative Example 4 is compared with Example 1, except that the chitosan oligosaccharide was not cross-linked before the graft polymerization reaction, and the rest are the same.

[0032] In order to further illustrate the effects of the embodiments of the present invention, a specific method is used to test them below.

[0033] 1. Configure speed test The fluid loss additives prepared in Examples 1 to 4 were added to water with a pH of 9 (pH adjusted with sodium carbonate) at a mass ratio of 4 wt %. The mixture was stirred rapidly at 100 r / min and its dissolution time was observed (the solution was considered to be completely dissolved when it was transparent). The time interval was recorded at 30 s, and the final results were shown in Table 1.

[0034] Table 1 Dissolution rate test table

[0035] As can be seen from Table 1, the fluid loss additive prepared in the embodiment of the present invention has a cross-linked chitosan in the middle that can quickly absorb water and swell, and the grafted polymer can make the fluid loss additive well dispersed in water; referring to Comparative Document 1, after replacing the short-chain cross-linking agent, it has some insoluble matter, which only absorbs water and swells but does not dissolve.

[0036] 2. Fluid loss reduction performance Freshwater and brine drilling fluids were prepared according to the method outlined in "Q / SH 0047-2007 General Technical Requirements for Salt-Resistant and High-Temperature-Resistant Fluid Loss Reducers for Drilling Fluids." 8 g of the fluid loss reducers prepared in Examples 1-5 and Comparative Examples 1-6 were added to the freshwater and brine drilling fluids, respectively, and rapidly stirred until fully dispersed. Their fluid loss reduction performance was evaluated at a hot rolling temperature of 150°C and a hot rolling time of 16 hours. The results are shown in Table 2.

[0037] Table 2 Fluid loss reduction performance test table

[0038] As can be seen from Table 2, the fluid loss reducer prepared in the embodiment of the present invention has good temperature and salt resistance, and at the same time, has good fluid loss reduction performance; referring to Comparative Examples 1 and 2, it can be seen that in the embodiments of the present invention, the concentration of the polymerization monomer and the type of the cross-linking agent have a great influence on the performance of the fluid loss reducer; referring to Comparative Example 3, it can be seen that the added materials have corresponding effects; referring to Comparative Example 4, it can be seen that the cross-linked chitosan has a better effect.

[0039] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a low molecular weight fluid loss additive, characterized in that: The method comprises the following steps, in parts by weight: dissolving 100 parts of chitosan oligosaccharide in water, adding 0.01-0.1 parts of a cross-linking agent at 50-70° C. and continuously stirring, and simultaneously dropwise adding 0.5-1 parts of a basic catalyst, continuing the reaction for 10-18 hours; after the reaction is completed, adding 60-90 parts of N,N-dimethylacrylamide, 20-40 parts of N-vinyl imidazole, 30-50 parts of sodium p-styrene sulfonate and 30-50 parts of unsaturated carboxylic acid, carrying out free radical polymerization under the action of an initiator, and drying and crushing the mixture after the polymerization is completed to obtain the product; the cross-linking agent is one of polyethylene glycol acrylate and polyethylene glycol dimethacrylate.

2. The method according to claim 1, characterized in that The alkaline catalyst is sodium hydroxide or potassium hydroxide, which is prepared into an aqueous solution with a concentration of 10-20 wt% before use.

3. The method according to claim 1, characterized in that The unsaturated carboxylic acid is one of acrylic acid, itaconic acid and maleic anhydride.

4. The method according to claim 1, wherein The initiator is a persulfate initiator or a redox initiator.

5. The method according to claim 1, wherein The amount of N,N-dimethylacrylamide added is 70-80 parts, the amount of N-vinylimidazole added is 25-30 parts, the amount of sodium p-styrenesulfonate added is 35-45 parts, and the amount of unsaturated carboxylic acid added is 35-45 parts.

6. The method according to claim 1, wherein When chitosan oligosaccharide is dissolved in water, its concentration is 5-10wt%; when free radical polymerization is carried out, the total monomer concentration in water is not more than 25wt%.

7. The method according to claim 1, characterized in that The molecular weight of the polyethylene glycol acrylate or polyethylene glycol dimethacrylate is 400-600.

8. A low molecular weight fluid loss additive prepared by the method according to any one of claims 1 to 7.

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