An ultrafine particle suspension and its preparation process

Abstract

This application relates to the field of petroleum extraction technology, specifically disclosing an ultrafine particle suspension and its preparation process. The ultrafine particle suspension comprises the following raw materials: anionic polyacrylamide, a compound co-solvent, sodium alkylnaphthalene sulfonate, thiourea, and water; the compound co-solvent is a complex of urea and acetamide. The ultrafine particle suspension obtained by this application has a minimum dissolution time of 30 seconds, improving the dissolution rate, and achieves a maximum viscosity retention rate and drag reduction rate of 96.0% and 83.9%, respectively, enhancing the dissolution effect. As a drag-reducing agent for fracturing, it not only has a high drag reduction rate but also a high dissolution rate and effect. Furthermore, after standing for 30 days, it exhibits good properties without stratification, demonstrating high stability. It can be used immediately upon collection, is easy to inject, and is suitable for drilling environments with limited space.

Description

Technical Field

[0001] This application relates to the field of oil extraction, and more specifically, to an ultrafine particle suspension and its preparation process. Background Technology

[0002] Currently, fracturing has become the mainstream method for oil extraction. It involves pumping fracturing fluid into the oil reservoir through the wellbore. When the injection pressure exceeds the formation fracturing pressure, the rock is fractured, creating artificial fractures. With continued injection of fracturing fluid, the fractures extend deeper and laterally into the oil reservoir, forming a network of fractures with a certain length, width, and height, connecting the oil and gas reservoir to the wellbore, thereby increasing production. However, when the fracturing fluid flows at high speed in the pipeline or fracture, resistance is generated due to internal friction between fluid molecules and external friction between the fluid and the pipe wall, leading to increased pumping pressure and significant energy loss. To reduce energy loss during pumping, drag-reducing agents are added to the fracturing fluid system to reduce frictional resistance as the fracturing fluid flows through the wellbore and fractures, thus reducing energy loss during pumping.

[0003] In related technologies, polyacrylamide polymers are often used as drag-reducing agents for fracturing due to their controllable cost and good water solubility. However, in the face of emergencies such as blowouts and lost circulation, polyacrylamide polymers have a slow dissolution rate, requiring approximately 120 minutes to completely dissolve in the freshwater environment of some onshore oilfields. This leads to insufficient capacity to handle emergencies, increasing safety risks. Moreover, when polyacrylamide polymer powder is dissolved, the fine dry powder does not disperse well during the dissolution process, easily forming "fish eyes" that clog filters or pipelines, making it difficult to inject into the ground and affecting the construction effect. In addition, in some emerging drilling environments such as offshore drilling platforms, the construction space is limited, making it difficult to configure large dissolution equipment. The increased use of polyacrylamide polymers inevitably requires larger and more numerous dissolution equipment, which contradicts the limited space of the drilling platform. At the same time, the excessively long dissolution time will inevitably affect the efficiency of the entire construction process and increase costs.

[0004] Therefore, it is necessary to develop an ultrafine particle suspension with a high dissolution rate and effectiveness as a drag-reducing agent for fracturing. Summary of the Invention

[0005] In order to simultaneously improve the dissolution rate and effect of drag-reducing agents for fracturing, this application provides an ultrafine particle suspension and its preparation process.

[0006] In a first aspect, this application provides an ultrafine particle suspension, which adopts the following technical solution: An ultrafine particle suspension comprises the following raw materials in parts by weight: 0.1-0.15 parts of anionic polyacrylamide, 0.05-0.1 parts of compound co-solvent, 0.03-0.05 parts of sodium alkylnaphthalene sulfonate, 0.01-0.03 parts of thiourea, and 99.5-99.7 parts of water; wherein the compound co-solvent is a complex of urea and formamide.

[0007] By adopting the above scheme, anionic polyacrylamide is used as the main raw material. As an anionic polymer, its molecular chains fully expand after dissolving in water. During high-speed fluid flow, the anionic polyacrylamide chains will align with the direction of water flow, suppressing the turbulent pulsation of the water flow and reducing the frictional resistance between the fluid and the pipe wall and inside the fluid, thereby playing a drag reduction role.

[0008] A complex of urea and acetamide is used as a co-solvent in this compounding process. Urea acts as a strong hydrogen bond donor and acceptor, competitively disrupting the self-associative hydrogen bonds between anionic polyacrylamide molecular chains, reducing the surface tension of anionic polyacrylamide, promoting water molecule penetration, and improving dissolution efficiency. Acetamide has better compatibility and can further disrupt the intermolecular hydrogen bond network. At the same time, the methyl groups of acetamide have weak hydrophobicity, forming hydrophilic channels on the surface of anionic polyacrylamide molecular chains, accelerating water molecule penetration. Both can bind to anionic polyacrylamide at different sites, achieving comprehensive dismantling of the hydrogen bond network, thereby improving the dissolution effect. In addition, the methyl groups of acetamide can weaken the intermolecular forces on the surface of anionic polyacrylamide particles, making the surface structure of anionic polyacrylamide more porous. Combined with the hydrogen bond disrupting effect of urea, water molecules can quickly diffuse into the interior, significantly shortening the dissolution time and increasing the dissolution rate. This effectively avoids the phenomenon of anionic polyacrylamide easily agglomerating and forming "fish eyes," making it more suitable for a wider range of applications and meeting the needs of emerging drilling environments such as offshore drilling platforms.

[0009] Adding sodium alkylnaphthalene sulfonate allows it to adsorb onto the surface of anionic polyacrylamide, further preventing its aggregation through electrostatic repulsion and improving dissolution. Adding thiourea eliminates reactive oxygen free radicals generated during fracturing fluid preparation and application, preventing oxidative breakage of the anionic polyacrylamide molecular chains and extending the shelf life and operational effectiveness of the ultrafine particle suspension.

[0010] Preferably, the ultrafine particle suspension comprises the following raw materials in parts by weight: 0.12-0.14 parts of anionic polyacrylamide, 0.07-0.09 parts of compound co-solvent, 0.035-0.045 parts of sodium alkylnaphthalene sulfonate, 0.015-0.025 parts of thiourea, and 99.55-99.65 parts of water.

[0011] The raw materials for the ultrafine particle suspension of this application include 0.12-0.14 parts of anionic polyacrylamide, 0.07-0.09 parts of compound co-solvent, 0.035-0.045 parts of sodium alkylnaphthalene sulfonate, 0.015-0.025 parts of thiourea, and 99.55-99.65 parts of water. Any value within the range can improve the dissolution rate and effect of the drag-reducing agent for fracturing to varying degrees.

[0012] Preferably, the mass ratio of urea to acetamide is 1:(2-3).

[0013] By adopting the above scheme and adjusting the mass ratio of acetamide and urea, the rate and effect of dissolving anionic polyacrylamide can be further improved.

[0014] Preferably, the compound co-solvent is prepared by modification, specifically: S1. Mix nano-silica with deionized water, add alkyl glycosides, and disperse by ultrasonication to obtain nano-silica dispersion; S2. Mix urea and acetamide and add them to deionized water. Stir and dissolve at 50-60℃. During the stirring process, add nano-silica dispersion dropwise at a rate of 1-2 mL / min. After the addition is complete, raise the temperature to 60-70℃ and continue stirring for 30 min to obtain the modified compound cosolvent.

[0015] By employing the above-mentioned scheme, urea and acetamide are modified with nano-silica. The hydroxyl groups on the surface of the nano-silica form strong hydrogen bonds with urea and acetamide molecules, and the compound co-solvent molecules are firmly adsorbed onto the surface of the nano-silica, forming highly active composite microspheres. When the modified compound co-solvent comes into contact with anionic polyacrylamide, it can quickly penetrate into the interior of the anionic polyacrylamide, increasing the diffusion rate of the compound co-solvent. Furthermore, urea and acetamide are responsible for breaking the self-associative hydrogen bonds between the anionic polyacrylamide molecular chains, allowing the molecular chains to initially untangle. The rigid particles of nano-silica embed themselves in the gaps between the anionic polyacrylamide molecules, preventing secondary entanglement of the untangled molecular chains through steric hindrance, thereby further improving the dissolution effect.

[0016] Preferably, the amount of nano-silica used accounts for 3%-5% of the total mass of urea and acetamide.

[0017] By adopting the above scheme and adjusting the amount of nano-silica, it is more conducive to improving the diffusion rate of the compounded co-solvent and the stability after dissolution, thereby further improving the dissolution rate and dissolution effect of the drag-reducing agent for fracturing.

[0018] Preferably, the ultrafine particle suspension also includes sodium carboxymethyl starch.

[0019] By adopting the above scheme, the addition of sodium carboxymethyl starch molecules with a large number of carboxymethyl hydrophilic groups disrupts the self-associative hydrogen bonds between anionic polyacrylamide molecular chains, promoting the rapid penetration of water molecules into the interior of anionic polyacrylamide particles. The branched structure of sodium carboxymethyl starch has a good steric hindrance effect, which can be interspersed between the initially unfolded anionic polyacrylamide molecular chains, preventing secondary entanglement of molecular chains, further shortening the dissolution time and improving the dissolution rate.

[0020] Preferably, the weight ratio of the carboxymethyl starch to the anionic polyacrylamide is 1:(2-6).

[0021] By adopting the above scheme and adjusting the weight ratio of carboxymethyl starch to anionic polyacrylamide, the dissolution rate of the drag-reducing agent for fracturing can be further improved.

[0022] Secondly, this application provides a preparation process for the ultrafine particle suspension according to any one of claims 1-7, which is specifically achieved through the following technical solution: A process for preparing an ultrafine particle suspension according to any one of claims 1-7 includes the following steps: heating water to 40-50°C, magnetically stirring, adding a compound co-solvent and stirring to dissolve, adding other raw materials, stirring to dissolve, and obtaining an ultrafine particle suspension.

[0023] In summary, this application includes at least one of the following beneficial technical effects: This application improves the dissolution rate and effect of ultrafine particle suspension by controlling the types and amounts of each raw material in the ultrafine particle suspension, so that the dissolution time of the ultrafine particle suspension is 1 minute, and the viscosity retention rate and drag reduction rate are 93.2-93.5% and 80.7-81.5%, respectively.

[0024] This application modifies urea and acetyl with nano-silica and adjusts the amount of nano-silica to achieve a dissolution time of 37-41 s for the ultrafine particle suspension, with viscosity retention rate of 94.1-94.5% and drag reduction rate of 82.3-82.7%, further improving the dissolution rate and effect of the ultrafine particle suspension.

[0025] This application further improves the dissolution rate and effect of ultrafine particle suspension by adding sodium carboxymethyl starch to the ultrafine particle suspension raw material and adjusting the amount of sodium carboxymethyl starch, so that the dissolution time of ultrafine particle suspension is 30-33s, and the viscosity retention rate and drag reduction rate are 95.4-96.0% and 83.4-83.9%, respectively. Detailed Implementation

[0026] The following detailed description, in conjunction with specific embodiments, further illustrates this application. All the raw materials used in this application are commercially available products and are intended to fully disclose the raw materials used in this application; they should not be construed as limiting the source of the raw materials. Specifically: anionic polyacrylamide, particle size 50 mesh; sodium alkylnaphthalene sulfonate, active ingredient content 99%; thiourea, active ingredient content 99%; urea, total nitrogen content ≥46%; acetamide, active ingredient content 99%; nano-silica, particle size 50 nm; sodium carboxymethyl starch, active ingredient content 99%.

[0027] The following are examples of the preparation of modified compound cosolvents. Preparation Example 1 The modified compound cosolvent of Preparation Example 1 is prepared as follows: S1. Mix 2g of nano-silica with 20mL of deionized water, add 0.04g of alkyl glycoside, and disperse by ultrasonication to obtain a nano-silica dispersion; S2. Mix 100g of urea and 150g of acetamide and add them to 250mL of deionized water. Stir and dissolve at 50℃. During the stirring process, add nano-silica dispersion dropwise at a rate of 1mL / min. After the addition is complete, raise the temperature to 60℃ and continue stirring for 30min to obtain the modified compound cosolvent.

[0028] Preparation Examples 2-5 The modified compound cosolvents in Preparation Examples 2-5 are exactly the same as those in Preparation Example 1 in terms of raw material types and preparation methods. The difference lies in the amount of nano-silica added, which is 4g, 5g, 6g and 7g respectively. The remaining steps are the same as those in Preparation Example 1. Example

[0029] Example 1: An ultrafine particle suspension was prepared through the following steps: According to the dosage of each raw material in Table 1, heat the water to 40°C, stir magnetically, add the raw materials and stir to dissolve, then add the other raw materials and stir to dissolve to obtain an ultrafine particle suspension.

[0030] Examples 2-5 The preparation methods and raw material types of the ultrafine particle suspensions in Examples 2-5 are exactly the same as those in Example 1, except that the dosage of each raw material is different, as detailed in Table 1.

[0031] Table 1. Dosage of each raw material in the ultrafine particle suspensions of Examples 1-5 (unit: g)

[0032] Examples 6-10 The preparation methods of the ultrafine particle suspensions in Examples 6-10 are the same as those in Example 3, except that the modified compound co-solvents prepared in Examples 1-5 are used in the raw materials, while the types and amounts of the other raw materials are the same as in Example 3.

[0033] Examples 11-15 The preparation methods of the ultrafine particle suspensions in Examples 11-15 are the same as those in Example 8, except that sodium carboxymethyl starch is also included in the raw materials, with specific dosages of 0.13g, 0.065g, 0.032g, 0.022g and 0.019g, respectively. The types and dosages of the other raw materials are the same as those in Example 8.

[0034] Comparative Example 1 The preparation method of the ultrafine particle suspension in Comparative Example 1 is exactly the same as that in Example 1, except that urea is replaced with acetamide in equal amounts, and the remaining raw materials and dosages are the same as in Example 1.

[0035] Comparative Example 2 The preparation method of the ultrafine particle suspension in Comparative Example 2 is exactly the same as that in Example 1, except that acetamide is replaced with urea in equal amounts, while the other raw materials and dosages are the same as in Example 1.

[0036] Performance testing The solubility of ultrafine particle suspensions of different Examples 1-15 and Comparative Examples 1-2 were tested using the following testing standards or methods. The test results are shown in Table 2.

[0037] Dissolution time: Record the time from the start of stirring and dissolving after adding the compound co-solvent until the raw material is added and completely dissolved.

[0038] Viscosity retention rate: The viscosity of the ultrafine particle suspension at 25℃ was tested and recorded as A0. The fracturing fluid drag reducer was stored at 90℃ for 30 days and the viscosity was tested again and recorded as A1. Viscosity retention rate = A1 / A0×100%. The results are shown in Table 1.

[0039] Drag reduction rate: The drag reduction rate of the ultrafine particle suspension was tested according to the industry standard NB / T14003.2-2016 "Shale gas fracturing fluid Part 2: Performance indicators and test methods of drag reducing agents".

[0040] Stability: Weigh 200g of the ultrafine particle suspension and let it stand at 25℃ for 30 days. Observe whether there is any visible stratification of the suspension.

[0041] Table 2 Performance test results of different ultrafine particle suspensions

[0042] The test results in Table 2 show that the dissolution time of the ultrafine particle suspension obtained by this application is as low as 30s, which improves the dissolution rate. The viscosity retention rate and drag reduction rate are as high as 96.0% and 83.9% respectively, which improves the dissolution effect. As a drag reduction agent for fracturing, it not only has a high drag reduction rate, but also a high dissolution rate and effect. After standing for 30 days, it has good properties and no stratification is observed. It has high stability and can be used immediately. It is sufficient to cope with sudden situations such as well blowout and well leakage. It is suitable for drilling environments with limited construction space.

[0043] Based on the performance test data of the ultrafine particle suspensions in Examples 1-5, it was found that the dissolution time of the ultrafine particle suspensions in Examples 2-4 was 1 min, which was lower than that in Examples 1 and 5. The viscosity retention rate and drag reduction rate were 93.2-93.5% and 80.7-81.5%, respectively, which were higher than those in Examples 1 and 5. This indicates that it is more appropriate to use urea and acetamide with a mass ratio of 1:(1-2) as the co-solvent in the raw materials of the ultrafine particle suspension, which improves the dissolution rate and effect of the ultrafine particle suspension.

[0044] Based on the performance test data of the ultrafine particle suspensions in Examples 6-10, it was found that the dissolution time of the ultrafine particle suspensions in Examples 7-9 was 37-41s, which was lower than that in Examples 6 and 10. The viscosity retention rate and drag reduction rate were 94.1-94.5% and 82.3-82.7%, respectively, which were higher than those in Examples 6 and 10. This indicates that modifying urea and acetamide with nano-silica and adjusting the amount of nano-silica to 3%-5% of the total mass of urea and acetamide can further improve the dissolution rate and effect of the ultrafine particle suspension.

[0045] Based on the performance test data of the ultrafine particle suspensions in Examples 11-15, it was found that the dissolution time of the ultrafine particle suspensions in Examples 12-14 was 30-33s, which was lower than that in Examples 11 and 15. The viscosity retention rate and drag reduction rate were 95.4-96.0% and 83.4-83.9%, respectively, which were higher than those in Examples 11 and 15. This indicates that adding sodium carboxymethyl starch to the raw materials of the ultrafine particle suspension and adjusting the amount of sodium carboxymethyl starch, and controlling the weight ratio of carboxymethyl starch to anionic polyacrylamide to be 1:(2-6), can further improve the dissolution rate and effect of the ultrafine particle suspension.

[0046] Based on the performance test data of the ultrafine particle suspensions in Example 1 and Comparative Examples 1-2, it was found that adding acetamide and urea to the raw materials of the ultrafine particle suspension can improve the dissolution rate and effect of the ultrafine particle suspension to varying degrees.

[0047] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A suspension of ultrafine particles, characterized in that, It comprises the following raw materials in parts by weight: 0.1-0.15 parts of anionic polyacrylamide, 0.05-0.1 parts of compound co-solvent, 0.03-0.05 parts of sodium alkylnaphthalene sulfonate, 0.01-0.03 parts of thiourea, and 99.5-99.7 parts of water; wherein the compound co-solvent is a complex of urea and acetamide.

2. The ultrafine particle suspension according to claim 1, characterized in that, The ultrafine particle suspension comprises the following raw materials in parts by weight: 0.12-0.14 parts of anionic polyacrylamide, 0.07-0.09 parts of compound co-solvent, 0.035-0.045 parts of sodium alkylnaphthalene sulfonate, 0.015-0.025 parts of thiourea, and 99.55-99.65 parts of water.

3. The ultrafine particle suspension according to claim 1, characterized in that, The mass ratio of urea to acetamide is 1:(1-2).

4. The ultrafine particle suspension according to claim 1, characterized in that, The compound co-solvent is prepared by modification, specifically as follows: S1. Mix nano-silica with deionized water, add alkyl glycosides, and disperse by ultrasonication to obtain nano-silica dispersion; S2. Mix urea and acetamide and add them to deionized water. Stir and dissolve at 50-60℃. During the stirring process, add nano-silica dispersion dropwise at a rate of 1-2 mL / min. After the addition is complete, raise the temperature to 60-70℃ and continue stirring for 30 min to obtain the modified compound cosolvent.

5. The ultrafine particle suspension according to claim 4, characterized in that, The amount of nano-silica used accounts for 3%-5% of the total mass of urea and acetamide.

6. The ultrafine particle suspension according to claim 1, characterized in that, The ultrafine particle suspension also includes sodium carboxymethyl starch.

7. The ultrafine particle suspension according to claim 6, characterized in that, The weight ratio of carboxymethyl starch to anionic polyacrylamide is 1:(2-6).

8. A process for preparing the ultrafine particle suspension according to any one of claims 1-7, characterized in that, Heat water to 40-50℃, stir magnetically, add compound co-solvent and stir to dissolve, then add other raw materials and stir to dissolve to obtain an ultrafine particle suspension.

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