Low molecular weight fluid loss additives and methods for making the same

Abstract

The application discloses a low-molecular-weight fluid loss additive and a preparation method thereof, and relates to the technical field of oil fields. The method comprises the following steps: chitooligosaccharide is dissolved in water, a small amount of crosslinking agent is added to slightly crosslink the chitooligosaccharide under the condition that the temperature is 50-70 DEG C and continuous stirring is carried out, after the reaction is completed, N, N-dimethyl acrylamide, N-vinylimidazole, sodium p-styrenesulfonate and unsaturated carboxylic acid are added, and free radical polymerization is carried out under the action of an initiator, and after the polymerization is completed, drying and crushing are carried out, and the low-molecular-weight fluid loss additive is obtained. The fluid loss additive prepared by the application has a small molecular weight, compared with the fluid loss additive with a large molecular weight, the application has the advantages that the filter cake formed is more compact, the fluid loss reducing effect is better, and the fluid loss additive has good temperature resistance and salt resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oilfield chemical technology, and particularly relates to a low-molecular-weight fluid loss additive and a preparation method thereof. BACKGROUND

[0002] In the process of wall building, the drilling fluid can form a filter cake through fluid loss, thereby protecting the well wall and avoiding further fluid loss of the drilling fluid. However, when the filter cake fluid loss is too large in the process of forming the filter cake by the drilling fluid, not only the drilling cost is increased, but also the drilling fluid fluid loss into the reservoir can easily cause shale hydration and swelling, thereby causing well wall instability. In addition, the increased filter loss thickens the filter cake, which reduces the hole diameter and causes a large torque to the rotating drilling tool, and causes swabbing and pressure fluctuation when tripping, which can easily cause differential pressure sticking.

[0003] Obviously, the filter cake is formed at the same time when the drilling fluid fluid loss occurs, and the drilling fluid fluid loss must pass through the formed filter cake. Therefore, the main factor determining the fluid loss amount is the permeability of the filter cake. How to form a high-quality filter cake with low permeability to prevent further fluid loss of the drilling fluid is one of the main problems to be considered in the preparation of the drilling fluid. Therefore, in the drilling fluid, a fluid loss additive is usually added to control the fluid loss amount of the drilling fluid in the wall building process, so that the fluid loss amount of the drilling fluid is controlled within a reasonable range.

[0004] Among the existing fluid loss additives, there are modified natural polymer fluid loss additives and artificial polymer fluid loss additives. Among them, the modified natural polymer fluid loss additive is favored by researchers due to its environmental protection performance. For the modified natural polymer fluid loss additive, the matrix usually has starch, cellulose, humic acid and chitosan. These matrices are usually macromolecular matrices. Although the effect is good, the problem is that the dissolution speed in the drilling fluid is slow, and it usually needs to be stirred at high speed for a certain time to dissolve. Although the dissolution speed of some modified natural polymer fluid loss additives, such as chitosan quaternary ammonium salt, in water is relatively fast, but after further modification to graft a plurality of monomers, the dissolution speed decreases rapidly. SUMMARY

[0005] In view of the above technical problems, the present application aims at the defects of the prior art, and provides a low-molecular-weight fluid loss additive and a preparation method thereof.

[0006] The application adopts the following technical scheme: a preparation method of a low molecular weight fluid loss additive, including the following steps: taking 100 parts of chitooligosaccharide and dissolving in water, under the condition of 50-70 DEG C and continuous stirring, adding 0.01-0.1 parts of a crosslinking agent, and simultaneously adding 0.5-1 parts of an alkaline catalyst dropwise, continuously reacting for 10-18 hours, after the reaction is completed, adding 60-90 parts of N, N-dimethyl acrylamide, 20-40 parts of N-vinyl imidazole, 30-50 parts of sodium p-styrene sulfonate and 30-50 parts of an unsaturated carboxylic acid, and performing free radical polymerization under the action of an initiator, after the polymerization is completed, drying and crushing the product to obtain the low molecular weight fluid loss additive; the crosslinking agent is one of polyethylene glycol acrylate or polyethylene glycol dimethyl acrylate.

[0007] The difference between the application and the conventional fluid loss additive is that, in the application, the substrate is chitooligosaccharide, which is an oligosaccharide polymer with a degree of polymerization of 2-20 and a molecular weight of less than 3200, and the molecular weight of chitooligosaccharide is much lower than that of the conventional substrate such as chitosan and starch with a molecular weight of hundreds of thousands. Chitooligosaccharide contains a large number of hydroxyl groups and amino groups, and has good water solubility, and the hydroxyl groups and amino groups can provide a large number of active sites for subsequent grafting reaction. However, chitooligosaccharide has the disadvantage of being not resistant to water and easily degrading in water. Therefore, in the application, the chitooligosaccharide is modified before being used for grafting polymerization.

[0008] In the application, the chitooligosaccharide is first lightly crosslinked by using a crosslinking agent, and in the process, the amount of the crosslinking agent should not be too much, because when the amount of the crosslinking agent is too much, the crosslinking degree is too high, and the crosslinking agent will form a gel state and swell in water at a slow speed. Meanwhile, the crosslinking agent is one of polyethylene glycol acrylate or polyethylene glycol dimethyl acrylate, and for similar crosslinking agents such as diethanol dimethyl acrylate and diallyl dimethyl ammonium chloride, the chain length is too short, and the crosslinking network is too dense, which will cause the product of the second step to be more concentrated in the polymerization of the monomers rather than in the grafting polymerization, and the grafting rate is low, and the performance of the final product is poor. The amount of the crosslinking agent should also not be too much, and in the preferred range, the amount of the crosslinking agent can be set to 0.05-0.08 parts, such as 0.05 parts, 0.06 parts, 0.07 parts and 0.08 parts. Meanwhile, the reaction time needs to be as long as possible in the crosslinking reaction process, so as to avoid a large amount of residual crosslinking agent in the product.

[0009] Theoretically, this step can be prepared by water-in-oil emulsion polymerization to obtain more uniform cross-linked chitosan oligosaccharide, however, in the present application, the amount of cross-linking agent is low, the concentration of chitosan oligosaccharide is low, and the cross-linking agent is one of polyethylene glycol acrylate or polyethylene glycol dimethyl acrylate, which contains less double bond content, therefore, the inventors found through experiments that whether the reaction is directly in an aqueous solution or by emulsion, the performance of the final product is similar, and the aqueous solution reaction has lower cost and less time.

[0010] In the reaction process of the second step, the present application uses N,N-dimethyl acrylamide as the main polymerization monomer, supplemented by N-vinyl imidazole, sodium p-styrene sulfonate and unsaturated carboxylic acid, to carry out graft polymerization reaction on the product of the first step, wherein 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. Finally, the filtrate loss reducer prepared by the present application has good temperature resistance and salt resistance.

[0011] An embodiment of the present application is that the basic catalyst is sodium hydroxide or potassium hydroxide, which is configured into an aqueous solution with a concentration of 10-20wt% before use.

[0012] An embodiment of the present application is that the unsaturated carboxylic acid is one of acrylic acid, itaconic acid and maleic anhydride. These are common unsaturated carboxylic acids in the field, and preferably, the effect of dicarboxylic acid is better, such as itaconic acid.

[0013] An embodiment of the present application is that the initiator is one of persulfate initiator or redox initiator, which is a common water-soluble initiator in the field, and the amount of initiator is usually 1-3% of the total mass of monomers. The reaction temperature after adding the initiator can be selected according to the type of initiator, such as the redox initiator (mass ratio of persulfate / sulfite is 1:1), the reaction temperature of which can be 20-50℃, and the polymerization reaction time is 1-3h; for potassium persulfate, the reaction temperature can be 55-70℃, and the reaction time is 1-5h. These are conventional settings in the field.

[0014] An embodiment of the present application is that the amount of N,N-dimethyl acrylamide is 70-80 parts, the amount of N-vinyl imidazole is 25-30 parts, the amount of sodium p-styrene sulfonate is 35-45 parts, and the amount of unsaturated carboxylic acid is 35-45 parts.

[0015] One embodiment of the present application is that when chitosan oligosaccharide is dissolved in water, the concentration is 5-10wt%; when free radical polymerization is carried out, the total concentration of monomers in water is not more than 25wt%. This is mainly to consider the concentration of monomers in the two-step reaction: for the first step reaction (crosslinking of chitosan oligosaccharide), if the concentration of chitosan oligosaccharide is too high, there is a risk of forming a gel state (high water content solid phase) after crosslinking, which is not conducive to the subsequent reaction; for the second step reaction (graft polymerization), if the concentration of monomers in the second step is too high, there is a risk of explosive polymerization. From the practical experience of the inventor, in the second step reaction, the total concentration of all monomers (including crosslinked chitosan oligosaccharide) in water is preferably not more than 25wt%, preferably 13-18wt%. Of course, in the actual reaction process, a part of water can be added in the first step reaction, and another part of water can be added in the second step reaction.

[0016] One embodiment of the present application is that the average molecular weight of the polyethylene glycol acrylate or polyethylene glycol dimethacrylate is 400-600. The molecular weight of the commonly used polyethylene glycol dimethacrylate has an average molecular weight of 200 materials, but the inventor found that when using polyethylene glycol dimethacrylate with this molecular weight, the effect is poor.

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

[0018] The beneficial effects of the present application are: the fluid loss additive prepared by the present application has a small molecular weight, and the person skilled in the art knows that compared with the fluid loss additive with a large molecular weight, the present application has the advantages of forming a more dense filter cake, having a better fluid loss effect, and having good temperature resistance and salt resistance. DETAILED DESCRIPTION

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

[0020] In the following examples, if not specifically stated, the methods used are conventional operation methods in the art.

[0021] In the following examples, if not specifically stated, the drugs used are conventional commercial products.

[0022] In the following examples, if not specifically stated, the parts are all weight parts.

[0023] Example 1, take 100 g of chitooligosaccharide into 1150 mL of water and dissolve, take 0.7 g of sodium hydroxide and add 5 mL of water to configure into sodium hydroxide solution, under the condition of 60 °C and continuous stirring, add 0.05 g of polyethylene glycol dimethyl acrylate (molecular weight 600) into the chitooligosaccharide solution, then drop the aforementioned sodium hydroxide solution and continue to react for 14 h, after the reaction is completed, cool to room temperature, under the condition of continuous stirring, add 75 g of N,N-dimethyl acrylamide, 28 g of N-vinyl imidazole, 40 g of sodium p-styrene sulfonate, 40 g of itaconic acid, after stirring uniformly, add water to control the total concentration of chitooligosaccharide, N,N-dimethyl acrylamide, N-vinyl imidazole, sodium p-styrene sulfonate and itaconic acid to be 17 wt%, then add 6.0 g of potassium persulfate and warm up to 65 °C, continue to react for 2 h, after the reaction is completed, dry and crush it to obtain. The average molecular weight is about 58 x 10 3 g / mol.

[0024] Example 2, take 100 g of chitooligosaccharide into 1150 mL of water and dissolve, take 0.7 g of sodium hydroxide and add 5 mL of water to configure into sodium hydroxide solution, under the condition of 60 °C and continuous stirring, add 0.12 g of polyethylene glycol dimethyl acrylate (molecular weight 400) into the chitooligosaccharide solution, then drop the aforementioned sodium hydroxide solution and continue to react for 16 h, after the reaction is completed, cool to room temperature, under the condition of continuous stirring, add 75 g of N,N-dimethyl acrylamide, 28 g of N-vinyl imidazole, 40 g of sodium p-styrene sulfonate, 40 g of itaconic acid, after stirring uniformly, add water to control the total concentration of chitooligosaccharide, N,N-dimethyl acrylamide, N-vinyl imidazole, sodium p-styrene sulfonate and itaconic acid to be 15 wt%, then add 6.0 g of potassium persulfate and warm up to 70 °C, continue to react for 1.5 h, after the reaction is completed, dry and crush it to obtain. The average molecular weight is about 120 x 10 3 g / mol.

[0025] Example 3, take 100 g of chitooligosaccharide and add 1150 mL of water and dissolve, take 0.7 g of sodium hydroxide and add 5 mL of water to configure a sodium hydroxide solution, under the condition of 60℃ and continuous stirring, add 0.08 g of polyethylene glycol dimethacrylate (molecular weight 200) to the chitooligosaccharide solution, then add the aforementioned sodium hydroxide solution dropwise and continue to react for 12 h, after the reaction is completed, cool to room temperature, under the condition of continuous stirring, add 75 g of N,N-dimethyl acrylamide, 28 g of N-vinylimidazole, 40 g of sodium p-styrene sulfonate, 40 g of itaconic acid, stir uniformly, then add water to control the total concentration of chitooligosaccharide, N,N-dimethyl acrylamide, N-vinylimidazole, sodium p-styrene sulfonate and itaconic acid to be 15 wt%, then add 6.0 g of potassium persulfate and heat to 70℃, continue to react for 1.5 h, after the reaction is completed, dry and crush to obtain. The average molecular weight is about 34×10 3 g / mol.

[0026] Example 4, compared with example 1, the difference lies in that the amount of N,N-dimethyl acrylamide is 65 g, the amount of N-vinylimidazole is 35 g, the amount of sodium p-styrene sulfonate is 35 g, and the amount of itaconic acid is 35 g, and the rest are the same. The average molecular weight is about 52×10 3 g / mol.

[0027] Example 5, compared with example 1, the difference lies in that the itaconic acid is replaced by 45 g of acrylic acid, and the total concentration of chitooligosaccharide, N,N-dimethyl acrylamide, N-vinylimidazole, sodium p-styrene sulfonate and acrylic acid is 22 wt%, and the rest are the same. The average molecular weight is about 69×10 3 g / mol.

[0028] Comparative example 1, compared with example 1, the difference lies in that 0.05 g of polyethylene glycol dimethacrylate (molecular weight 600) is replaced by 0.05 g of ethylene glycol dimethacrylate, and the rest are the same.

[0029] Comparative example 2, compared with example 1, the difference lies in that when the chitooligosaccharide is dissolved in water, the concentration of the chitooligosaccharide is 20 wt%, and the rest are the same. It is found that the chitooligosaccharide is crosslinked and agglomerated into a group.

[0030] Comparative example 3, compared with example 1, the difference lies in that N-vinylimidazole is not added, and the rest are the same.

[0031] Comparative example 4, compared with example 1, the difference lies in that the chitooligosaccharide is not crosslinked before the graft polymerization reaction, and the rest are the same.

[0032] In order to further illustrate the effect of the embodiment of the present application, the following specific method is used for testing.

[0033] 1、Configuration speed test

[0034] The filtrate reducer prepared in Examples 1-4 was added into water with pH of 9 (pH was adjusted by sodium carbonate) at a mass ratio of 4 wt%, and was stirred rapidly under the condition of 100 r / min, and the dissolving time (solution transparent was regarded as complete dissolving) was observed, and the interval time was recorded as 30 s, and finally, the results were shown in Table 1.

[0035] Table 1: Dissolving speed test table

[0036]

[0037] From Table 1, the crosslinked chitosan in the filtrate reducer prepared in the examples of the present application could quickly absorb water and swell, and the grafted polymer could make the filtrate reducer well dispersed in water; referring to Comparative Example 1, after changing the short-chain crosslinking agent, there were some insoluble substances, which only absorbed water and swelled without dissolving.

[0038] 2、Filtrate reduction performance

[0039] Fresh water drilling fluid and salt water drilling fluid were configured according to the method shown in Q / SH 0047-2007 General Technical Requirements for Salt-Resistant and High-Temperature-Resistant Filtrate Reducers for Drilling Fluids, and then 8 g of the filtrate reducers prepared in Examples 1-5 and Comparative Examples 1-6 were added into the fresh water drilling fluid and the salt water drilling fluid, respectively, and were stirred rapidly until they were fully dispersed, and the filtrate reduction performance was evaluated, wherein the hot rolling temperature was 150℃, and the hot rolling time was 16 h. The final results were shown in Table 2.

[0040] Table 2: Filtrate reduction performance test table

[0041]

[0042] From Table 2, the filtrate reducer prepared in the examples of the present application had good temperature resistance and salt resistance, and at the same time, had good filtrate reduction performance; referring to Comparative Example 1 and Comparative Example 2, the concentration of the polymer monomer and the type of the crosslinking agent had a great influence on the performance of the filtrate reducer; referring to Comparative Example 3, the added material had a corresponding effect; referring to Comparative Example 4, the crosslinked chitosan had better effect.

[0043] The above description is only the preferred specific implementation of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can easily think of changes or replacements within the technical range disclosed in the examples of the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing a low molecular weight fluid loss additive, characterized by, The method comprises the following steps in parts by weight: 100 parts of chitosan oligosaccharide is dissolved in water, 0.01-0.1 parts of a crosslinking agent is added under the condition of 50-70 DEG C and continuous stirring, and 0.5-1 parts of an alkaline catalyst is added dropwise, and the reaction is continued for 10-18 hours; after the reaction is completed, 60-90 parts of N,N-dimethyl acrylamide, 20-40 parts of N-vinyl imidazole, 30-50 parts of sodium p-styrene sulfonate and 30-50 parts of an unsaturated carboxylic acid are added, and free radical polymerization is carried out under the action of an initiator; after the polymerization is completed, drying and crushing are carried out to obtain the product; the crosslinking agent is polyethylene glycol dimethacrylate; when the chitosan oligosaccharide is dissolved in water, the concentration is 5-10 wt%; when the free radical polymerization is carried out, the total concentration of monomers in water is not more than 25 wt%; and the molecular weight of the polyethylene glycol dimethacrylate is 400-600.

2. The method of claim 1, wherein, The alkaline catalyst is sodium hydroxide or potassium hydroxide, and is configured into an aqueous solution with a concentration of 10-20 wt% before use.

3. The method of claim 1, wherein, The unsaturated carboxylic acid is one of acrylic acid, itaconic acid and maleic anhydride.

4. The method of claim 1, wherein, The initiator is one of persulfate initiator and redox initiator.

5. The method of claim 1, wherein, The addition amount of the N,N-dimethyl acrylamide is 70-80 parts, the addition amount of the N-vinyl imidazole is 25-30 parts, the addition amount of the sodium p-styrene sulfonate is 35-45 parts, and the addition amount of the unsaturated carboxylic acid is 35-45 parts.

6. A low molecular weight fluid loss additive prepared by the method of any one of claims 1-5.

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