Modified carboxymethyl cellulose viscosifier, suspension for fracturing fluid, and method of making

Abstract

This application provides a modified carboxymethyl cellulose (CMC) thickener, a fracturing fluid suspension, and a preparation method thereof, belonging to the field of hydraulic fracturing in oil and gas fields. The structural formula of the modified CMC thickener is shown in Formula 1: In Formula 1, n is 5500–6000. Two modifiers containing sulfonic acid groups and quaternary ammonium groups are incorporated into the CMC molecular structure, transforming it into zwitterionic CMC, thus forming a zwitterionic structure. This structural transformation allows the CMC molecular chains to maintain stable performance and a stretched state under high-salt conditions, thereby improving the salt resistance of the fracturing fluid thickener.

Description

Technical Field

[0001] This application relates to the field of hydraulic fracturing technology in oil and gas fields, and in particular to a modified carboxymethyl cellulose thickener, a fracturing fluid suspension, and a preparation method thereof. Background Technology

[0002] In recent years, with the depletion of conventional oil and gas resources, shale gas, coalbed methane, and tight gas have become hot areas for petrochemical energy development in China. Due to the low pressure and low permeability characteristics of these reservoirs, the residue formed by conventional fracturing fluid systems under reservoir conditions can easily cause reservoir damage. At the same time, hydraulic fracturing operations have a large demand for freshwater resources, and the scarcity of freshwater resources in mountainous areas can significantly increase the cost of operations.

[0003] However, the high salinity of gas fields produces a large amount of water, which is difficult to treat and puts pressure on local environmental protection. Therefore, in response to the current challenges faced by hydraulic fracturing operations in unconventional gas reservoirs, the main problems that water-based fracturing fluid systems need to overcome include: (1) reducing the residue of thickeners and preparing clean fracturing fluid systems; (2) developing salt-resistant fracturing thickeners that can be directly mixed with high salinity formation water, reducing freshwater consumption and reusing formation water; and (3) continuous on-site mixing to avoid pre-mixing. Carboxymethyl cellulose, as a water-based fracturing fluid thickener, has good salt resistance and extremely low residue, thus it has the potential to prepare ultra-high salt-resistant clean fracturing fluids. Currently, in order to achieve real-time on-site mixing and avoid pre-mixing, the thickener is suspended in the oil phase or prepared as an emulsion system for continuous on-site mixing. Summary of the Invention

[0004] This application provides a modified carboxymethyl cellulose thickener, a fracturing fluid suspension, and a preparation method to solve the following technical problem: how to improve the salt resistance of the fracturing fluid thickener so that the fracturing fluid system can use fluids with a salinity of 10 × 10⁻⁶. 4 mg / L to 25×10 4 Formation produced water within the mg / L range can be directly prepared.

[0005] In a first aspect, this application provides a modified carboxymethyl cellulose thickener, the structural formula of which is shown in Formula 1:

[0006]

[0007] In Equation 1, n is 5500 to 6000.

[0008] Optionally, the particle size of the modified carboxymethyl cellulose thickener is 100 mesh to 140 mesh.

[0009] Secondly, this application provides a method for preparing the modified carboxymethyl cellulose thickener described in the embodiments of the first aspect, the method comprising:

[0010] Carboxymethyl cellulose, quaternary ammonium salt cationic modifier, sulfonic acid group modifier and catalyst of a set concentration are etherified in a mixed solvent to obtain a reaction mixture;

[0011] The mixed solvent is removed from the reaction mixture to obtain the modified carboxymethyl cellulose thickener.

[0012] Optionally, the carboxymethyl cellulose has a mass concentration of 10% to 16%; and / or,

[0013] The mass concentration of the quaternary ammonium salt cationic modifier is 2% to 4.5%; and / or,

[0014] The mass concentration of the sulfonic acid modifier is 1.5% to 3.5%; and / or,

[0015] The mass concentration of the catalyst is 1% to 3%.

[0016] Optionally, the degree of substitution of the carboxymethyl cellulose is 0.5 to 1.5; and / or,

[0017] The carboxymethyl cellulose has a particle size of 100 mesh to 140 mesh; and / or,

[0018] The quaternary ammonium salt cationic modifier is 2-chloroethyltrimethylammonium chloride; and / or,

[0019] The catalyst comprises one or more of sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, and sodium ethoxide; and / or,

[0020] The mixed solvent is a mixture of deionized water, isopropanol and dimethylformamide, and the mass ratio of the deionized water, isopropanol and dimethylformamide is (1-3):(3-4):(1-5).

[0021] Optionally, the preparation method of the sulfonic acid modifier includes:

[0022] Epichlorohydrin and taurine were subjected to a ring-opening reaction to obtain an intermediate product.

[0023] The intermediate product was purified to obtain a sulfonic acid-based modifier; wherein...

[0024] The mass ratio of epichlorohydrin to taurine is (0.8–1.3):1; and / or,

[0025] The ring-opening reaction is carried out at a temperature of 35℃ to 50℃ for a duration of 3.5h to 5h.

[0026] Optionally, the etherification reaction temperature is 40℃~60℃, and the etherification reaction time is 5h~8h.

[0027] Thirdly, this application provides a fracturing fluid suspension, which, by mass, comprises the following chemical components: 25 to 45 parts of the modified carboxymethyl cellulose thickener described in the first aspect embodiment, 35 to 55 parts of hydrocarbon dispersion medium, 2 to 5 parts of organic bentonite, 5 to 10 parts of drag-reducing agent, 1 to 3 parts of dispersant, 0.5 to 1.5 parts of phase inversion agent, 1.5 to 3 parts of clay stabilizer, 3 to 5 parts of drainage aid, 1 to 2.5 parts of temperature stabilizer, and 1.5 to 2.5 parts of demulsifier.

[0028] Optionally, the hydrocarbon dispersion phase is mineral oil, wherein the aromatic hydrocarbon content of the mineral oil is <0.01%, and the kinematic viscosity of the mineral oil is 1.5 mm. 2 / s~3mm 2 / s; and / or,

[0029] The organic bentonite meets at least one of the following properties: a colloidal value of 800 mL / 15 g to 1500 mL / 15 g, a blue absorption capacity of 36 g / 100 g to 40 g / 100 g, a montmorillonite content of 82% to 90%, a whiteness > 80%, a particle size of 350 to 400 mesh, and a moisture content ≤ 5%; and / or,

[0030] The drag-reducing agent is a highly salt-resistant polyacrylamide polymer, which contains one or more of sulfonic acid groups, quaternary ammonium groups, and hydrophobic groups. The molecular weight of the highly salt-resistant polyacrylamide polymer is 1 million to 10 million, and the particle size is 120 mesh to 140 mesh; and / or,

[0031] The dispersant is composed of alkylphenol polyoxyethylene ether, alkyl alcohol polyoxyethylene ether, fatty acid sorbitan monoester, and fatty acid isopropyl ester, wherein the mass ratio of the alkylphenol polyoxyethylene ether, the alkyl alcohol polyoxyethylene ether, the fatty acid sorbitan monoester, and the fatty acid isopropyl ester is (3-7):(1-2):(1-3):(2-5); and / or,

[0032] The phase-transfer agent is composed of ethoxylated isotridecyl alcohol, glycerol, and isopropanol, wherein the mass ratio of the ethoxylated isotridecyl alcohol, the glycerol, and the isopropanol is (2-5):(1-3):(1-2); and / or,

[0033] The clay stabilizer comprises one or more of potassium chloride, polyquaternium salts, and polyamines; and / or,

[0034] The drainage aid includes one or more of fatty alcohol polyoxyethylene ether and perfluorooctyl sulfonate; and / or

[0035] The temperature stabilizer includes one or more of triethanolamine, sodium bisulfite, and sodium thiosulfate; and / or,

[0036] The demulsifier includes one or more of polyethylene polyamine polyoxyethylene polyoxypropylene ether and polyethylene polyamine polyoxyethylene ether.

[0037] Fourthly, this application provides a method for preparing the suspension described in the third aspect embodiment, the method comprising:

[0038] Organic bentonite is added to a hydrocarbon dispersion medium at a first set stirring speed and a first set temperature to obtain a viscous liquid mixture; the first set stirring speed is 1200 r / min to 1800 r / min and the first set temperature is 40℃ to 55℃.

[0039] At a second set stirring speed, the formulated amounts of dispersant, phase inversion agent, drainage aid, clay stabilizer, temperature stabilizer, and demulsifier are added to a viscous liquid mixture at a second set temperature to obtain a mixture; the second set stirring speed is 1000 r / min to 1200 r / min, and the second set temperature is room temperature;

[0040] At a third set stirring speed, the formulated amount of modified carboxymethyl cellulose and drag-reducing agent are added to the mixture at a third set temperature to obtain a suspension; the third set stirring speed is 1500 r / min to 1800 r / min, and the third set temperature is 45℃ to 55℃.

[0041] The technical solutions provided in this application have the following advantages compared with the prior art:

[0042] This application provides a modified carboxymethyl cellulose (CMC) thickener. Through an etherification reaction, two modifiers containing sulfonic acid groups and quaternary ammonium groups are incorporated into the CMC molecular structure, transforming it into a zwitterionic CMC. This transformation introduces cationic groups (quaternary ammonium groups) into the originally single anionic CMC molecular chain, while retaining the original anionic groups (sulfonic acid groups and carboxymethyl groups), thus forming a zwitterionic structure. This structural transformation allows the CMC molecular chain to maintain stable performance and a stretched state under high-salt environments, exhibiting excellent salt resistance. This, in turn, improves the salt resistance of the fracturing fluid thickener. Attached Figure Description

[0043] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0044] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 A schematic flowchart illustrating a method for preparing a modified carboxymethyl cellulose thickener provided in this application embodiment;

[0046] Figure 2 A schematic flowchart illustrating a method for preparing a suspension provided in this application embodiment;

[0047] Figure 3 The effect of calcium chloride concentration on the viscosity of fracturing fluid prepared from suspension is shown in Example 3 of this application.

[0048] Figure 4 The effect of calcium chloride concentration on the dissolution rate of the suspension is shown in Example 4 of this application;

[0049] Figure 5 The rheological curve of the high-viscosity fracturing fluid prepared in simulated formation water by the suspension provided in Example 5 of this application. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0051] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0052] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple. "Parts representation," such as parts by weight or parts by mass, indicates the proportional relationship between components. In the proportional relationships discussed in this article, parameters described by proportion should be understood as the first term of the proportion in the order of description, while the proportion figure should be understood as the second term. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substances A, B, and C should correspond one-to-one with the proportion figure in the proportion in the order of description, i.e., the mass of substance A : the mass of substance B : the mass of substance C = 1:2:3.

[0053] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0054] This application provides a modified carboxymethyl cellulose thickener, the structural formula of which is shown in Formula 1:

[0055]

[0056] In Equation 1, n is 5500 to 6000.

[0057] In some embodiments, the particle size of the modified carboxymethyl cellulose thickener is 100 mesh to 140 mesh.

[0058] Through etherification, two modifiers containing sulfonic acid groups and quaternary ammonium groups are incorporated into the molecular structure of carboxymethyl cellulose (CMC), transforming it into zwitterionic carboxymethyl cellulose. This transformation introduces cationic groups (quaternary ammonium groups) into the originally single anionic CMC molecular chain, while retaining the original anionic groups (sulfonic acid groups and carboxymethyl groups), thus forming a zwitterionic structure.

[0059] In high-salt environments, the anionic groups on the molecular chains of ordinary CMCs readily interact with cations in the solution, leading to a charge shielding effect and causing the CMC molecular chains to shrink, thus affecting their performance. However, zwitterionic CMCs, containing both anionic and cationic groups, can form internal salt bonds between these groups in high-salt environments, thereby offsetting to some extent the effects of added salt on the CMC molecular chains. This ionic balance mechanism allows zwitterionic CMCs to maintain stable performance in high-salt environments.

[0060] Meanwhile, in high-salt solutions, the addition of salt may disrupt the hydrogen bonds and other interactions on the molecular chains of ordinary CMCs, leading to chain shrinkage and decreased viscosity. However, for zwitterionic CMCs, due to the presence of internal salt bonds, the addition of salt, while disrupting some hydrogen bonds, may also enhance the interaction between the CMC molecules and the solvent, making the molecular chains more free and extended. This extended state of the molecular chains helps maintain their performance stability in high-salt environments.

[0061] Furthermore, the salt tolerance mechanism of zwitterionic CMC differs significantly from that of ordinary polysaccharide polyelectrolyte solutions. Ordinary polysaccharide polyelectrolyte solutions often exhibit polyelectrolyte characteristics under high salt conditions, meaning their intrinsic viscosity decreases with increasing salt concentration. However, zwitterionic CMC exhibits pronounced anti-polyelectrolyte characteristics. Its intrinsic viscosity not only does not decrease with increasing salt concentration but actually increases. This is mainly because the added salt disrupts the internal salt bonds formed by the interaction between carboxymethyl anionic groups and quaternary ammonium cation groups on the CMC molecular chain, making the CMC molecular chain more free and extended, thereby improving its salt tolerance.

[0062] In summary, the high salinity resistance of the super salt-resistant modified carboxymethyl cellulose thickener is mainly attributed to the transformation of its zwitterionic structure. This structural transformation allows the CMC molecular chains to maintain stable performance and a stretched state under high salt conditions, thus exhibiting excellent super salt resistance. For example, the particle size of this modified carboxymethyl cellulose thickener can be 100 mesh, 110 mesh, 120 mesh, 130 mesh, 140 mesh, etc.

[0063] Figure 1 This is a schematic flowchart illustrating a method for preparing a modified carboxymethyl cellulose thickener, as provided in an embodiment of this application.

[0064] like Figure 1 As shown, this application provides a method for preparing the modified carboxymethyl cellulose thickener described in the above embodiments, the method comprising:

[0065] S11. Etherification reaction of carboxymethyl cellulose, quaternary ammonium salt cationic modifier, sulfonic acid group modifier and catalyst at a set concentration in a mixed solvent to obtain a reaction mixture;

[0066] S12. Remove the mixed solvent from the reaction mixture to obtain the modified carboxymethyl cellulose thickener.

[0067] In some embodiments, the carboxymethyl cellulose has a mass concentration of 10% to 16%; and / or,

[0068] The mass concentration of the quaternary ammonium salt cationic modifier is 2% to 4.5%; and / or,

[0069] The mass concentration of the sulfonic acid modifier is 1.5% to 3.5%; and / or,

[0070] The mass concentration of the catalyst is 1% to 3%.

[0071] The mass concentration of carboxymethyl cellulose (CMC) is limited to 10%–16%. CMC forms a stable, high-viscosity colloidal solution, which is beneficial for subsequent etherification reactions and the product's application performance. Simultaneously, it can improve the product's thickening, suspension, and stability, meeting the application requirements of various fields. The mass concentration of the quaternary ammonium salt cationic modifier is limited to 2%–4.5%. This modifier effectively reacts with CMC, introducing cationic groups, improving the product's cationic and hydrophilic properties, and ensuring the uniformity and stability of the modification reaction, avoiding over-modification or under-modification. The mass concentration of the sulfonic acid modifier is limited to 1.5%–3.5%. This modifier effectively reacts with CMC, introducing sulfonic acid groups, improving the product's anionic and hydrophilic properties. It also ensures the uniformity and stability of the modification reaction, improving the product's overall performance. For example, the mass concentration of carboxymethyl cellulose can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, etc., the mass concentration of quaternary ammonium salt cationic modifier can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, etc., the mass concentration of sulfonic acid group modifier can be 1.5%, 2%, 2.5%, 3%, 3.5%, etc., and the mass concentration of catalyst can be 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0072] In some embodiments, the degree of substitution of the carboxymethyl cellulose is 0.5 to 1.5; and / or,

[0073] The carboxymethyl cellulose has a particle size of 100 mesh to 140 mesh; and / or,

[0074] The quaternary ammonium salt cationic modifier is 2-chloroethyltrimethylammonium chloride; and / or,

[0075] The catalyst comprises one or more of sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, and sodium ethoxide; and / or,

[0076] The mixed solvent is a mixture of deionized water, isopropanol and dimethylformamide, and the mass ratio of the deionized water, isopropanol and dimethylformamide is (1-3):(3-4):(1-5).

[0077] Limiting the degree of substitution of carboxymethyl cellulose (CMC) to 0.5–1.5 improves its water solubility and allows for the formation of a more uniform colloidal solution. Limiting the particle size of CMC to 100–140 mesh facilitates its dissolution and dispersion, improving its uniformity in the reaction system. The mixed solvent ratio is (1–3):(3–4):(1–5) by mass of deionized water, isopropanol, and dimethylformamide, providing good solubility and a favorable reaction environment for sufficient contact and reaction between CMC and the modifier. For example, the degree of substitution of CMC can be 0.5, 0.7, 0.9, 1, 1.2, 1.4, 1.5, etc., and the particle size of CMC can be 100 mesh, 110 mesh, 120 mesh, 130 mesh, 140 mesh, etc.

[0078] In some embodiments, the method for preparing the sulfonic acid modifier includes:

[0079] Epichlorohydrin and taurine were subjected to a ring-opening reaction to obtain an intermediate product.

[0080] The intermediate product was purified to obtain a sulfonic acid-based modifier; wherein...

[0081] The mass ratio of epichlorohydrin to taurine is (0.8–1.3):1; and / or,

[0082] The ring-opening reaction is carried out at a temperature of 35℃ to 50℃ for a duration of 3.5h to 5h.

[0083] The mass ratio of epichlorohydrin to taurate is limited to (0.8–1.3):1, ensuring sufficient reaction between the two to generate the desired intermediate product. Excess or insufficient epichlorohydrin may lead to incomplete reaction or the formation of byproducts, affecting the purity and performance of the product. The ring-opening reaction temperature is limited to 35°C–50°C, and the reaction time to 3.5 h–5 h, ensuring a stable and moderate reaction rate. Excessively high temperatures may increase side reactions, while excessively low temperatures may decrease the reaction rate and prolong the reaction time. Exemplary mass ratios of epichlorohydrin to taurate can be 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, etc. The temperature for the ring-opening reaction can be 35℃, 38℃, 40℃, 42℃, 45℃, 50℃, etc., and the reaction time can be 3.5h, 3.8h, 4h, 4.2h, 4.5h, 5h, etc.

[0084] In some embodiments, the etherification reaction is carried out at a temperature of 40°C to 60°C for 5 hours to 8 hours.

[0085] The etherification reaction is limited to a temperature of 40℃ to 60℃ and a time of 5h to 8h. This allows for efficient etherification, producing the desired modified carboxymethyl cellulose thickener. Appropriate reaction time ensures complete reaction and avoids unreacted raw material residue. For example, the etherification reaction temperature can be 40℃, 45℃, 50℃, 55℃, 60℃, etc., and the reaction time can be 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, etc.

[0086] The product prepared by the method of preparing the modified carboxymethyl cellulose thickener is the modified carboxymethyl cellulose thickener described above. The chemical composition and microstructure of the modified carboxymethyl cellulose thickener prepared by the method of preparing the modified carboxymethyl cellulose thickener can be referred to the above embodiments. Since the method of preparing the modified carboxymethyl cellulose thickener adopts some or all of the technical solutions of the modified carboxymethyl cellulose thickener embodiments, it has at least all the beneficial effects brought about by the technical solutions of the modified carboxymethyl cellulose thickener embodiments, which will not be elaborated here.

[0087] Based on a general inventive concept, this application provides a fracturing fluid suspension, which, by mass, comprises the following chemical components: 25 to 45 parts of the modified carboxymethyl cellulose thickener described in the above embodiments, 35 to 55 parts of hydrocarbon dispersion medium, 2 to 5 parts of organobentonite, 5 to 10 parts of drag-reducing agent, 1 to 3 parts of dispersant, 0.5 to 1.5 parts of phase inversion agent, 1.5 to 3 parts of clay stabilizer, 3 to 5 parts of drainage aid, 1 to 2.5 parts of temperature stabilizer, and 1.5 to 2.5 parts of demulsifier.

[0088] The functions of each component in fracturing fluid suspension are as follows:

[0089] Modified carboxymethyl cellulose (25-45 parts): As a thickener, modified carboxymethyl cellulose can significantly increase the viscosity of fracturing fluid, enabling it to better suspend and carry sand or other proppant. Simultaneously, the high viscosity helps maintain the suspension of particles such as sand in the fracturing fluid, preventing premature settling. For example, the mass fraction of this carboxymethyl cellulose thickener can be 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, etc.

[0090] Hydrocarbon dispersion medium (35-55 parts): The hydrocarbon dispersion medium provides a good dissolution or dispersion environment for other chemical components. It also helps reduce the flow resistance of fracturing fluid in the pipeline and formation. For example, the mass fraction of this hydrocarbon dispersion medium can be 35 parts, 40 parts, 45 parts, 50 parts, 55 parts, etc.

[0091] Organic bentonite (2-5 parts): Organic bentonite has good thickening and suspension stability, which can further enhance the viscosity of fracturing fluid and maintain the suspension of particles. Simultaneously, it gives the fracturing fluid a high viscosity when at rest, while reducing viscosity under shear, which is beneficial for the injection and flow of the fracturing fluid. For example, the mass fraction of this organic bentonite can be 2, 3, 4, or 5 parts, etc.

[0092] Drag-reducing agent (5-10 parts): The drag-reducing agent can significantly reduce the resistance of fracturing fluid during flow, thereby improving fracturing efficiency. Simultaneously, by reducing pressure and flow velocity, it reduces damage to the formation structure and protects reservoir integrity. For example, the mass fraction of this drag-reducing agent can be 5, 6, 7, 8, 9, or 10 parts.

[0093] Dispersant (1 to 3 parts): The dispersant helps to uniformly disperse other solid particles or additives in the fracturing fluid. Simultaneously, it prevents particle aggregation and sedimentation, maintaining the stability of the fracturing fluid. For example, the dispersant can be present in parts by weight of 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, etc.

[0094] Phase inversion agent (0.5 parts to 1.5 parts): The phase inversion agent can change the phase state of the fracturing fluid, making it better adaptable to different formation conditions. By adjusting the phase state of the fracturing fluid, its fluidity and permeability in different formations can be improved. For example, the mass fraction of the phase inversion agent can be 0.5 parts, 0.8 parts, 1 part, 1.2 parts, 1.5 parts, etc.

[0095] Clay stabilizer (1.5 to 3 parts): The clay stabilizer can adsorb onto the surface of clay particles, preventing their hydration, swelling, dispersion, and migration. Simultaneously, by stabilizing the clay particles, it reduces damage to oil and gas reservoirs, thereby improving oil recovery. For example, the mass fraction of this clay stabilizer can be 1.5 parts, 2 parts, 2.5 parts, 3 parts, etc.

[0096] Drainage aid (3-5 parts): The drainage aid reduces the interfacial tension between the fracturing fluid and the formation rock, promoting the drainage of the fracturing fluid. Simultaneously, by reducing the amount of fracturing fluid remaining in the formation, it improves oil and gas recovery. For example, the mass fraction of this drainage aid can be 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, etc.

[0097] Temperature stabilizer (1 to 2.5 parts): The temperature stabilizer enhances the stability of fracturing fluid under high-temperature conditions, preventing degradation or failure. Simultaneously, it ensures that the fracturing fluid maintains good viscosity and suspension capacity at high temperatures. For example, the mass fraction of the temperature stabilizer can be 1 part, 1.5 parts, 2 parts, 2.5 parts, etc.

[0098] Demulsifier (1.5 to 2.5 parts): The demulsifier can disrupt the emulsion structure in the fracturing fluid, causing it to separate into oil and water phases. Through demulsification, it helps to displace more oil and gas from the formation, improving oil recovery. For example, the demulsifier can be present in quantities of 1.5 parts, 1.8 parts, 2 parts, 2.2 parts, 2.5 parts, etc.

[0099] In summary, the various components in this fracturing fluid suspension work synergistically to achieve the various functions in the fracturing process.

[0100] In some embodiments, the hydrocarbon dispersion phase is mineral oil, wherein the aromatic hydrocarbon content of the mineral oil is <0.01%, and the kinematic viscosity of the mineral oil is 1.5 mm. 2 / s~3mm 2 / s; and / or,

[0101] The organic bentonite meets at least one of the following properties: a colloidal value of 800 mL / 15 g to 1500 mL / 15 g, a blue absorption capacity of 36 g / 100 g to 40 g / 100 g, a montmorillonite content of 82% to 90%, a whiteness > 80%, a particle size of 350 to 400 mesh, and a moisture content ≤ 5%; and / or,

[0102] The drag-reducing agent is a highly salt-resistant polyacrylamide polymer, which contains one or more of sulfonic acid groups, quaternary ammonium groups, and hydrophobic groups. The molecular weight of the highly salt-resistant polyacrylamide polymer is 1 million to 10 million, and the particle size is 120 mesh to 140 mesh; and / or,

[0103] The dispersant is composed of alkylphenol polyoxyethylene ether, alkyl alcohol polyoxyethylene ether, fatty acid sorbitan monoester, and fatty acid isopropyl ester, wherein the mass ratio of the alkylphenol polyoxyethylene ether, the alkyl alcohol polyoxyethylene ether, the fatty acid sorbitan monoester, and the fatty acid isopropyl ester is (3-7):(1-2):(1-3):(2-5); and / or,

[0104] The phase-transfer agent is composed of ethoxylated isotridecyl alcohol, glycerol, and isopropanol, wherein the mass ratio of the ethoxylated isotridecyl alcohol, the glycerol, and the isopropanol is (2-5):(1-3):(1-2); and / or,

[0105] The clay stabilizer comprises one or more of potassium chloride, polyquaternium salts, and polyamines; and / or,

[0106] The drainage aid includes one or more of fatty alcohol polyoxyethylene ether and perfluorooctyl sulfonate; and / or

[0107] The temperature stabilizer includes one or more of triethanolamine, sodium bisulfite, and sodium thiosulfate; and / or,

[0108] The demulsifier includes one or more of polyethylene polyamine polyoxyethylene polyoxypropylene ether and polyethylene polyamine polyoxyethylene ether.

[0109] Figure 2 This is a schematic flowchart illustrating a method for preparing a suspension according to an embodiment of this application.

[0110] like Figure 2 As shown, this application provides a method for preparing the suspension described in the above embodiments, the method comprising:

[0111] S21. At a first set stirring speed, organic bentonite is added to a hydrocarbon dispersion medium at a first set temperature to obtain a viscous liquid mixture; the first set stirring speed is 1200 r / min to 1800 r / min, and the first set temperature is 40℃ to 55℃.

[0112] S22. At a second set stirring speed, the formulated amounts of dispersant, phase inversion agent, drainage aid, clay stabilizer, temperature stabilizer, and demulsifier are added to the viscous liquid mixture at a second set temperature to obtain a mixture; the second set stirring speed is 1000 r / min to 1200 r / min, and the second set temperature is room temperature;

[0113] S23. At a third set stirring speed, the formulated amount of modified carboxymethyl cellulose and drag-reducing agent are added to the mixture at a third set temperature to obtain a suspension; the third set stirring speed is 1500 r / min to 1800 r / min, and the third set temperature is 45℃ to 55℃.

[0114] The first set stirring speed of 1200 r / min to 1800 r / min facilitates the rapid dispersion and uniform mixing of organobentonite in the hydrocarbon dispersion medium, forming a viscous liquid. The first set temperature of 40℃ to 55℃ promotes the swelling and dispersion of organobentonite, improving the viscosity and stability of the mixture. The second set stirring speed of 1000 r / min to 1200 r / min reduces air bubbles and shear forces in the mixture, preventing additive failure due to over-stirring. The second set temperature of room temperature simplifies the operation and avoids the adverse effects of high temperatures on additive performance. The third set stirring speed of 1500 r / min to 1800 r / min facilitates the rapid dispersion and uniform mixing of modified carboxymethyl cellulose and drag-reducing agents in the mixture, forming a stable suspension. The third set temperature of 45℃ to 55℃ promotes the dissolution and dispersion of modified carboxymethyl cellulose while maintaining the stability and flowability of the suspension.

[0115] The product prepared by the method of preparing the suspension is the suspension described above. The chemical composition and microstructure of the suspension prepared by the method of preparing the suspension can be referred to the above embodiments. Since the method of preparing the suspension adopts some or all of the technical solutions of the suspension embodiments, it has at least all the beneficial effects brought about by the technical solutions of the suspension embodiments, which will not be elaborated here.

[0116] The advantages of this method in the embodiments of this application are summarized as follows:

[0117] (1) Excellent high-salt resistance: By incorporating two modifiers containing sulfonic acid groups and quaternary ammonium groups into the molecular structure of carboxymethyl cellulose (CMC), zwitterionic carboxymethyl cellulose is formed, which effectively improves the stability and performance of CMC in high-salt environments. At the same time, the zwitterionic structure can counteract the effect of added salt on the CMC molecular chain, maintain the extended state of the molecular chain, and thus maintain stable viscosity and suspension ability in high-salt environments.

[0118] (2) Precise control of the preparation process: Precise control of the concentrations of carboxymethyl cellulose, modifier, and catalyst, as well as the reaction temperature and time, ensures the uniformity and stability of the modification reaction, avoiding problems of over-modification or under-modification. At the same time, a specific mixed solvent ratio provides good solubility and reaction environment, which is conducive to sufficient contact and reaction between CMC and modifier.

[0119] (3) Synergistic effect of suspension components: The various components in the fracturing fluid suspension work synergistically to achieve various functions in the fracturing process, such as thickening, suspension, drag reduction, dispersion, phase inversion, clay stabilization, drainage assistance, temperature stabilization, and demulsification. At the same time, the mass and proportion of each component are carefully selected to ensure the overall performance and stability of the suspension.

[0120] (4) Environmentally friendly and efficient: The hydrocarbon dispersion medium used (such as mineral oil) has a low aromatic hydrocarbon content, which is environmentally friendly. At the same time, the selection and design of modified carboxymethyl cellulose thickener and other additives take into account environmental protection and efficiency, reducing pollution to the environment.

[0121] (5) High adaptability: Modified carboxymethyl cellulose thickener and suspension are suitable for different formation conditions and fracturing requirements, and have a wide range of adaptability. By adjusting the proportion and type of each component, fracturing fluid suspensions that meet specific needs can be customized.

[0122] (6) Improved oil recovery: Additives such as clay stabilizers, drainage aids and demulsifiers in the suspension help reduce damage to the formation structure and reduce the residue of fracturing fluid in the formation, thereby improving the oil and gas recovery rate.

[0123] In summary, the modified carboxymethyl cellulose thickener and its fracturing fluid suspension prepared by this method possess advantages such as excellent high-salt resistance, precise control of the preparation process, synergistic effect of suspension components, environmental friendliness and high efficiency, strong adaptability, and improved oil recovery. These advantages make this method promising for broad application and of significant value in oil and gas field fracturing operations.

[0124] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0125] Example 1

[0126] This embodiment provides a method for preparing a modified carboxymethyl cellulose thickener, the method comprising the following steps:

[0127] Step 1: Dissolve epichlorohydrin and sodium taurate in a mixture of ethanol and deionized water at a molar ratio of 1.1:1 (ethanol to deionized water ratio is 1:3). Stir magnetically at 40°C for 4 hours. After the reaction is complete, remove the solvent and excess epichlorohydrin by vacuum distillation to obtain the sulfonic acid-based modifier. The synthetic route of the sulfonic acid-based modifier is shown in Formula 2.

[0128]

[0129] Step 2: Select carboxymethyl cellulose with a degree of substitution of 0.8 and a particle size of 120 mesh as raw material. Disperse the carboxymethyl cellulose in a mixture of DMF and propanol (3:1) at a concentration of 15 wt%. Add the above-mentioned sulfonic acid modifier and 2-chloroethyltrimethyl at concentrations of 2 wt% and 3.5 wt%, respectively. Stir the mixture magnetically at 60°C for 8 hours. The synthesis route is shown in Formula 3.

[0130]

[0131] Step 3: After the reaction is complete, the solvent is removed by vacuum distillation, and the product is dried in a vacuum drying oven at 40°C for 24 hours to obtain super salt-resistant modified carboxymethyl cellulose powder.

[0132] Example 2

[0133] Based on the modified carboxymethyl cellulose thickener of Example 1, this example also provides a method for preparing a suspension, including the following steps:

[0134] Step 1: Place 50 parts of No. 5 white oil into the reaction vessel;

[0135] Step 2: Raise the temperature inside the reactor to 45°C, control the stirring speed to 1500 r / min, add 2 parts of organic bentonite, and continue until the viscosity of the mixture stabilizes.

[0136] Step 3: Reduce the temperature inside the reactor to 30°C, reduce the stirring speed to 1000 r / min, and add 1.5 parts of dispersant, 1.5 parts of phase inversion agent, 3 parts of drainage aid, 1.5 parts of clay stabilizer, 1 part of temperature stabilizer and 1.5 parts of demulsifier according to the formula, until fully dissolved;

[0137] Step 4: Increase the temperature inside the reactor to 50℃, increase the stirring speed to 1600r / min, add 35 parts of modified carboxymethyl cellulose and 8 parts of drag-reducing agent according to the formula, until the mixture is evenly mixed and dispersed, and finally a stable dispersion system is obtained.

[0138] The hydrocarbon dispersion phase has an aromatic hydrocarbon content of 0.005% and a kinematic viscosity of 2 mm. 2 / s of mineral oil;

[0139] The parameters of the organic bentonite are as follows: colloidal value of 1200mL / 15g, blue absorption of 38g / 100g, montmorillonite content of 85%, whiteness of 90%, particle size of 380 mesh, and moisture content of 3%.

[0140] The drag-reducing auxiliary agent is a high salt-resistant polyacrylamide polymer (polyacrylamide FP3530S), with a molecular weight between 5 million and 10 million and a particle size in the range of 120 to 140 mesh.

[0141] The dispersant is composed of alkylphenol polyoxyethylene ether, alkyl alcohol polyoxyethylene ether, fatty acid sorbitan monoester, and fatty acid isopropyl ester in a mass ratio of 5:1.5:2:3.

[0142] The phase inversion agent is composed of ethoxylated isotridecyl alcohol, glycerol and isopropanol in a mass ratio of 3:2:1.5;

[0143] The clay stabilizer is potassium chloride;

[0144] The drainage aid is fatty alcohol polyoxyethylene ether;

[0145] The temperature stabilizer is triethanolamine;

[0146] The demulsifier is polyethylene polyamine polyoxyethylene polyoxypropylene ether.

[0147] Example 3

[0148] Using the super-salt-resistant modified carboxymethyl cellulose suspension system prepared in Example 2, the effect of calcium chloride concentration on the apparent viscosity of the solution was tested. Solutions were prepared with deionized water and different amounts of the suspension system, and different amounts of calcium chloride were added. After complete dissolution, the apparent viscosity was measured, and the results were plotted as follows: Figure 3 As shown, under different amounts of calcium chloride added to the suspension system, it can be observed that the apparent viscosity of the solution does not change significantly with the increase of calcium chloride concentration, demonstrating excellent tolerance to divalent salts.

[0149] Example 4

[0150] The dissolution time of the super-salt-resistant modified carboxymethyl cellulose suspension system prepared in Example 2 in clean water and high-saltification brine was tested. The experimental method used a fracturing fluid friction tester. The time it took for the pressure difference across the pipeline to stabilize after adding the super-salt-resistant modified carboxymethyl cellulose suspension system during water circulation was measured to characterize the dissolution time of the suspension system. The pump flow rate of the friction tester was controlled at 20 L / min, and simulated formation water was pumped in. 0.1% of the polymer suspension system was added to the storage tank and stirred. The change in pressure difference across the friction tester over time was observed to analyze the dissolution time. The test results are as follows: Figure 4 The salt-resistant modified carboxymethyl cellulose suspension system, with an addition of 0.1 wt%, showed good solubility in deionized water, 10000 mg / L calcium chloride solution, and 50000 mg / L calcium chloride solution, with dissolution times of 70 s, 55 s, and 71 s, respectively, and is suitable for continuous on-site mixing.

[0151] Example 5

[0152] As shown in Table 1, based on the mineral composition of the water produced by a gas well platform, simulated formation water was prepared. High viscosity (0.8wt% of suspension system added) fracturing fluid was prepared using simulated formation water, and its temperature and shear resistance under 120℃ and 170s-1 conditions was tested using a rotational rheometer.

[0153] Table 1. Mineral composition of water produced from a gas well platform.

[0154]

[0155] Rheological test results as follows Figure 5 As shown, at 120℃ and 170s -1 After continuous shearing for 120 minutes under the specified conditions, the apparent viscosity can still be maintained above 50 mPas, and the high viscosity system exhibits good temperature and shear resistance.

[0156] Example 6

[0157] Using the mineral components listed in Table 1 of Example 5, simulated formation water was prepared. Low-viscosity fracturing fluid (0.1 wt% suspension), medium-viscosity fracturing fluid (0.4 wt% suspension), and high-viscosity fracturing fluid (0.8 wt% suspension) were prepared using this simulated formation water. The three fracturing fluids were then subjected to gel breaking at 90°C for 2 hours using 100 ppm ammonium persulfate as a breaker. The viscosity, surface / interfacial tension, and core damage rate of the fluids after gel breaking were tested. The results obtained using a six-speed viscometer, surface / interfacial tension meter, and core displacement experiment are shown in Table 2.

[0158] Table 2. Test of properties of the colloid breaking solution

[0159]

[0160]

[0161] Experimental results show that fracturing fluids with low, medium, and high viscosity prepared from a super salt-resistant modified carboxymethyl cellulose suspension system in simulated formation water can achieve complete gel breaking at 90°C for 2 hours with an addition of 100 ppm ammonium persulfate breaker. The apparent viscosity of the gel-breaking fluid is less than 3 mPas, and the core damage rate is less than 10%, demonstrating low damage.

[0162] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages:

[0163] In this embodiment, the modified carboxymethyl cellulose thickener exhibits superior salt resistance, with a tolerance to divalent calcium salts reaching 20 × 10⁻⁶. 4 mg / L, can be used with a mineralization degree of 0~25×10 4 mg / L formation produced water is directly used for solution preparation.

[0164] In this embodiment, the prepared suspension system is easy to mix continuously online on-site and can be completely dissolved within 45s to 80s in a mineralization of 0 to 25×10⁻⁶. 4 In formation produced water at a concentration of mg / L, the maximum drag reduction rate can reach over 70%.

[0165] In this embodiment, during the fluid preparation process, the real-time viscosity of the fracturing fluid system can be achieved by changing the amount of suspension added. A salinity of 0–25 × 10⁻⁶ is used. 4 The fracturing fluid directly prepared from formation produced water at a concentration of mg / L has the following characteristics: when the amount of the super salt-resistant modified carboxymethyl cellulose suspension added is 0.05wt%–0.2wt%, the viscosity of the fracturing fluid system is 10–40 mPas, which is a low-viscosity fracturing fluid system; when the amount added is 0.3wt%–0.5wt%, the viscosity of the fracturing fluid system is 50–100 mPas, which is a medium-viscosity fracturing fluid system; and when the amount added is 0.6wt%–1.0wt%, the viscosity of the fracturing fluid system is 120–200 mPas, which is a high-viscosity fracturing fluid system. The type of fracturing fluid can be changed in real time by changing the amount of suspension added.

[0166] In this embodiment, after the fracturing fluid breaks down, core damage experiments revealed that the fracturing fluid system has an extremely low damage rate, less than 8%. This achieves the goal of saving freshwater resources and protecting the environment by directly preparing the fracturing fluid using high-salinity formation water or flowback fluid. At the same time, it has ultra-low damage to unconventional reservoirs and can achieve rapid on-site preparation and continuous mixing.

[0167] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A modified carboxymethyl cellulose thickener, wherein the modified carboxymethyl cellulose thickener has the structural formula shown in Formula 1: In Equation 1, n is 5500 to 6000.

2. The modified carboxymethyl cellulose thickener according to claim 1, characterized in that, The particle size of the modified carboxymethyl cellulose thickener is 100 mesh to 140 mesh.

3. A method for preparing the modified carboxymethyl cellulose thickener according to claim 1 or 2, the method comprising: Carboxymethyl cellulose, quaternary ammonium salt cationic modifier, sulfonic acid group modifier and catalyst of a set concentration are etherified in a mixed solvent to obtain a reaction mixture; The mixed solvent is removed from the reaction mixture to obtain the modified carboxymethyl cellulose thickener.

4. The method according to claim 3, characterized in that, The carboxymethyl cellulose has a mass concentration of 10% to 16%; and / or, The mass concentration of the quaternary ammonium salt cationic modifier is 2% to 4.5%; and / or, The mass concentration of the sulfonic acid modifier is 1.5% to 3.5%; and / or, The mass concentration of the catalyst is 1% to 3%.

5. The method according to claim 3, characterized in that, The degree of substitution of the carboxymethyl cellulose is 0.5 to 1.5; and / or, The carboxymethyl cellulose has a particle size of 100 mesh to 140 mesh; and / or, The quaternary ammonium salt cationic modifier is 2-chloroethyltrimethylammonium chloride; and / or, The catalyst comprises one or more of sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, and sodium ethoxide; and / or, The mixed solvent is a mixture of deionized water, isopropanol and dimethylformamide, and the mass ratio of the deionized water, isopropanol and dimethylformamide is (1-3):(3-4):(1-5).

6. The method according to claim 3, characterized in that, The preparation method of the sulfonic acid-based modifier includes: Epichlorohydrin and taurine were subjected to a ring-opening reaction to obtain an intermediate product. The intermediate product was purified to obtain a sulfonic acid-based modifier; wherein... The mass ratio of epichlorohydrin to taurine is (0.8–1.3):1; and / or, The ring-opening reaction is carried out at a temperature of 35℃ to 50℃ for a duration of 3.5h to 5h.

7. The method according to claim 3, characterized in that, The etherification reaction is carried out at a temperature of 40℃ to 60℃ for 5 hours to 8 hours.

8. A fracturing fluid suspension, comprising, by weight, the following chemical components: 25-45 parts of the modified carboxymethyl cellulose thickener as described in claim 1 or 2, 35-55 parts of a hydrocarbon dispersion medium, 2-5 parts of organic bentonite, 5-10 parts of a drag-reducing agent, 1-3 parts of a dispersant, 0.5-1.5 parts of a phase inversion agent, 1.5-3 parts of a clay stabilizer, 3-5 parts of a flow aid, 1-2.5 parts of a temperature stabilizer, and 1.5-2.5 parts of a demulsifier.

9. The suspension according to claim 8, characterized in that, The hydrocarbon dispersion phase is mineral oil, the aromatic hydrocarbon content of the mineral oil is <0.01%, and the kinematic viscosity of the mineral oil is 1.5 mm. 2 / s~3mm 2 / s; and / or, The organic bentonite meets at least one of the following properties: a colloidal value of 800 mL / 15 g to 1500 mL / 15 g, a blue absorption capacity of 36 g / 100 g to 40 g / 100 g, a montmorillonite content of 82% to 90%, a whiteness > 80%, a particle size of 350 to 400 mesh, and a moisture content ≤ 5%; and / or, The drag-reducing agent is a highly salt-resistant polyacrylamide polymer, which contains one or more of sulfonic acid groups, quaternary ammonium groups, and hydrophobic groups. The molecular weight of the highly salt-resistant polyacrylamide polymer is 1 million to 10 million, and the particle size is 120 mesh to 140 mesh; and / or, The dispersant is composed of alkylphenol polyoxyethylene ether, alkyl alcohol polyoxyethylene ether, fatty acid sorbitan monoester, and fatty acid isopropyl ester, wherein the mass ratio of the alkylphenol polyoxyethylene ether, the alkyl alcohol polyoxyethylene ether, the fatty acid sorbitan monoester, and the fatty acid isopropyl ester is (3-7):(1-2):(1-3):(2-5); and / or, The phase-transforming agent is composed of ethoxylated isotridecyl alcohol, glycerol and isopropanol, wherein the mass ratio of ethoxylated isotridecyl alcohol, glycerol and isopropanol is (2-5):(1-3):(1-2); And / or, The clay stabilizer comprises one or more of potassium chloride, polyquaternium salts, and polyamines; and / or, The drainage aid includes one or more of fatty alcohol polyoxyethylene ether and perfluorooctyl sulfonate; and / or The temperature stabilizer includes one or more of triethanolamine, sodium bisulfite, and sodium thiosulfate; and / or, The demulsifier includes one or more of polyethylene polyamine polyoxyethylene polyoxypropylene ether and polyethylene polyamine polyoxyethylene ether.

10. A method for preparing the suspension according to claim 8 or 9, the method comprising: At a first set stirring speed, organic bentonite is added to a hydrocarbon dispersion medium at a first set temperature to obtain a viscous liquid mixture. The first set stirring speed is 1200 r / min to 1800 r / min, and the first set temperature is 40℃ to 55℃; At a second set stirring speed, the formulated amounts of dispersant, phase inversion agent, drainage aid, clay stabilizer, temperature stabilizer, and demulsifier are added to a viscous liquid mixture at a second set temperature to obtain a mixture; the second set stirring speed is 1000 r / min to 1200 r / min, and the second set temperature is room temperature; At a third set stirring speed, the formulated amount of modified carboxymethyl cellulose and drag-reducing agent are added to the mixture at a third set temperature to obtain a suspension; the third set stirring speed is 1500 r / min to 1800 r / min, and the third set temperature is 45℃ to 55℃.

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