A biomass polymer suspension dispersion system for variable viscosity fracturing fluid and its preparation method and application

Abstract

The present invention discloses a biomass polymer suspension dispersion system for variable viscosity fracturing fluid, its preparation method, and application, belonging to the field of hydraulic fracturing in unconventional oil and gas fields. Pure biomass materials account for more than 90% of the polymer suspension dispersion system. The biomass materials include: modified sodium carboxymethyl cellulose, fatty alcohol polyoxyethylene ether, polylactic acid, polyethylene glycol diester, fatty amide propyl betaine, and monohydric alcohol ester; non-biomass materials are polyacrylamide drag reducers, potassium chloride, and persulfate, accounting for less than 10% of the suspension dispersion system. The polymer suspension dispersion system, which is compounded with multiple biomass raw materials, quickly dissolves in water or mineralized water by changing the added amount, achieving real-time viscosity change of the fracturing fluid.

Description

Technical Field

[0001] The present invention belongs to the field of hydraulic fracturing in unconventional oil and gas fields, and specifically relates to a biomass polymer suspension dispersion system for variable viscosity fracturing fluid, and a preparation method and application thereof, which has excellent performance, ultra-low damage and excellent environmental friendliness. Background Art

[0002] With the increasing demand for energy from economic development, conventional oil and gas resources are no longer sufficient to meet today's development needs; therefore, the development of unconventional oil and gas resources has, to some extent, filled this gap. However, the ultra-low permeability and low porosity physical properties of unconventional oil and gas reservoirs make their development more difficult. Large-scale "volume fracturing" technology has become a highly effective means of developing unconventional oil and gas. Currently, to achieve large-scale volume fracturing operations on-site, "integrated" continuous mixing technology is often used. Unlike traditional pre-mixed fluids placed in storage tanks, "integrated" fracturing technology uses an on-site, ready-to-use method. Because powdered fracturing fluid thickeners and additives require a certain amount of time to hydrate and tend to aggregate in the aqueous phase to form "fisheyes," "integrated" continuously mixed fracturing fluids are often formulated using polymers in emulsion form or suspended dispersions in which polymers are dispersed in the oil phase for fracturing. Field applications have found that the content of effective polymer components in emulsion-form polymer systems is relatively low, generally not exceeding 30%; while the polyacrylamide polymer suspension dispersion system prepared with mineral oil as the dispersion medium can have an effective solid content of more than 40%. The prepared fracturing fluid forms residue after gel breaking and is less environmentally friendly. Summary of the Invention

[0003] In order to overcome the above technical defects and retain the advantages of the polymer suspension dispersion system, while avoiding the residue damage caused by its preparation of fracturing fluid and improving the environmental friendliness of the system, one of the objectives of the present invention is to provide a biomass polymer suspension dispersion system for variable viscosity fracturing fluid, which uses biomass monohydric alcohol ester as a suspending dispersant, polylactic acid and polyethylene glycol diester as stabilizers, fatty alcohol polyoxyethylene ether and fatty amide betaine as auxiliary agents, and modified sodium carboxymethyl cellulose powder and polyacrylamide powder are suspended and dispersed in the monohydric alcohol ester, that is, the biomass suspension dispersion system.

[0004] Pure biomass materials account for more than 90% of the polymer suspension and dispersion system, including modified sodium carboxymethyl cellulose, fatty alcohol polyoxyethylene ether, polylactic acid, polyethylene glycol diester, fatty amide propyl betaine and monohydric alcohol ester; non-biomass materials are polyacrylamide drag reducers, potassium chloride and persulfate, accounting for less than 10% of the suspension and dispersion system.

[0005] Specifically, the biomass polymer suspension dispersion system for variable viscosity fracturing fluid provided by the present invention is composed of the following components in percentage by weight:

[0006] Modified sodium carboxymethyl cellulose 25-45%

[0007] Fatty alcohol polyoxyethylene ether 5-15%

[0008] Stabilizer 3-6%

[0009] Fatty acid amide propyl betaine 5%~10%

[0010] Drag reducer 1~5%

[0011] Gel breaker 0.5%~2%

[0012] Anti-swelling agent potassium chloride 2% to 5%

[0013] The balance is biomass monohydric alcohol ester.

[0014] Furthermore, the modified sodium carboxymethyl cellulose can be sodium sulfonate-modified sodium carboxymethyl cellulose, hydroxypropyl-modified sodium carboxymethyl cellulose or hydroxyethyl carboxymethyl cellulose, etc., with a total proportion of 25% to 45% in the polymer suspension dispersion system, a degree of substitution between 0.3 and 1.8, and a particle size of 80 to 140 meshes. The main function of the modified sodium carboxymethyl cellulose is to hydrate and thicken after dissolving in water, and it has strong salt resistance.

[0015] Furthermore, the fatty alcohol polyoxyethylene ether can be myristyl alcohol polyoxyethylene ether, lauryl alcohol polyoxyethylene ether, stearic acid polyoxyethylene ether, palmitic acid polyoxyethylene ether, oleic acid polyoxyethylene ether or a composite system thereof, etc., which mainly helps the polymer powder to disperse in the monohydric alcohol ester solvent, avoids agglomeration, and increases the speed at which the polymer suspension dispersion system dissolves in water, while also playing the role of assisting in the drainage of fracturing fluid, and accounts for 5% to 15% of the total amount of the biomass polymer suspension dispersion system;

[0016] Furthermore, the biomass polymer suspension dispersion system stabilizer is composed of polylactic acid and polyethylene glycol diester, which is used to increase the viscosity of the suspension dispersion system and ensure that the suspension dispersion system does not stratify during long-term standing. The polylactic acid has a molecular weight of 5,000 to 50,000; the polyethylene glycol diester component can be, but is not limited to, polyethylene glycol diethyl ester, polyethylene glycol dibutyl ester, polyethylene glycol diisopropyl ester, or polyethylene glycol diisooctyl ester, wherein the polyethylene glycol degree of polymerization is 200 to 2,000. The amount of the two components added accounts for 3% to 6% of the total biomass polymer suspension dispersion system. Furthermore, the mass ratio of polylactic acid to polyethylene glycol diester is 1 to 5:2 to 3.

[0017] Furthermore, fatty amide propyl betaine mainly plays a phase inversion role, accelerating the process of contact between the polymer and water in the suspended dispersion system. It may include but is not limited to lauryl amide propyl betaine, palmitamide propyl betaine, oleyl amide propyl betaine, myristamide propyl betaine, cocoamide propyl betaine, etc., and its added amount accounts for 5% to 10% of the total amount of the biomass polymer suspended dispersion system.

[0018] Furthermore, the drag reducer is a polyacrylamide powder with a molecular weight of 10 million to 15 million and a particle size of 100 to 140 meshes. It accounts for 1% to 5% of the total suspended dispersion system, and its drag reduction rate for mineralized water should be above 80%.

[0019] Furthermore, the gel breaker is mainly persulfate, which destroys the long chain structure of the polymer under high temperature conditions in the formation. It can include but is not limited to ammonium persulfate, sodium persulfate and potassium persulfate, which accounts for 0.5% to 2% in the total suspended dispersion system.

[0020] Furthermore, potassium chloride is an anti-swelling agent, which accounts for 2% to 5% in the total suspension dispersion system.

[0021] Furthermore, the biomass monohydric alcohol ester is a dispersion medium of the suspension dispersion system, which can be but not limited to isooctyl laurate, isooctyl myristate, isooctyl palmitate, isooctyl stearate, isopropyl laurate, isopropyl myristate or a mixed solvent thereof, and its viscosity is required to be 4.5 to 6.6 m 2 / s, surface tension range is 24~31mN / m, density is 0.8~0.92g / cm 3 .

[0022] A second object of the present invention is to provide a method for preparing the above-mentioned biomass polymer suspension dispersion system for variable viscosity fracturing fluid.

[0023] Specifically, the preparation method of the biomass polymer suspension dispersion system is as follows: heat the biomass monohydric alcohol ester to 30-100°C, stir at 800-900 r / min, add fatty alcohol polyoxyethylene ether, stabilizer, and fatty amide propyl betaine until completely dissolved, and then cool to 10-40°C to obtain a continuous phase of the suspension dispersion system; increase the stirring speed to 900-1000 r / min, add modified sodium carboxymethyl cellulose powder, drag reducer, gel breaker, and anti-swelling agent, and continue stirring for 30-90 minutes to obtain the biomass polymer suspension dispersion system.

[0024] A third object of the present invention is to provide an application of the above-mentioned biomass polymer suspension and dispersion system for variable viscosity fracturing fluid.

[0025] Specifically, the application method of the above biomass polymer suspension dispersion system in variable viscosity fracturing fluid is as follows: the water salinity range of the prepared fracturing fluid is 0 to 10×10 4 mg / L, pumping volume is 1~20m 3 / h, and control the dripping rate of the polymer dispersion system at the wellhead according to the displacement, so that the addition amount of the polymer dispersion system in water is 0.02wt%~0.5wt%, of which 0.02wt%~0.06wt% is a low viscosity system, 0.06wt%~0.3wt% is a medium viscosity system, and 0.1wt%~0.5wt% is a high viscosity system.

[0026] The biomass polymer suspension dispersion system provided by the present invention has excellent fracturing fluid additive functions, and is characterized by low residue and environmental friendliness. More than 90% of the components in the suspension dispersion system are derived from biomass. The residue rate is extremely low under high temperature and high pressure environments, with a residue content of less than 5 mg / L and a core damage rate of less than 5%, with minimal damage to low-permeability reservoirs. Various biomass additives have the characteristics of low residue, low damage, zero pollution, and resistance to mineralization. They can be used in 10×10 4 The maximum drag reduction rate of the biomass polymer suspension dispersion system can reach 81%. After the modified sodium cellulose is fully dissolved, the high viscosity system can be directly mixed with the formation water with a mineralization degree of mg / L, thus getting rid of the dependence on fresh water resources. -1 At the same shear rate, after 2 hours of shearing, the apparent viscosity remains above 50 mPa·s, indicating excellent sand-carrying performance even in high-temperature environments. This technology not only meets the needs of ultra-low permeability tight oil and gas and shale gas development for high displacement, low damage, and integrated continuous liquid mixing, but also complies with the "dual carbon" goals and environmental protection policies that promote the use of renewable green materials in production and processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be described in further detail below with reference to the accompanying drawings.

[0028] Figure 1 This is a curve showing the change in pressure difference between the two ends of the friction meter circulation pipeline over time after the bio-based suspension dispersion system prepared in Example 1 is added to the water phase;

[0029] Figure 2 This is a curve showing the change in drag reduction rate with increasing displacement after the bio-based suspension dispersion system prepared in Example 1 is added to the water phase;

[0030] Figure 3 This is a curve showing the change in apparent viscosity over time at different temperatures after the bio-based suspension dispersion system prepared in Example 1 is added to the aqueous phase;

[0031] Figure 4 The high viscosity fracturing fluid prepared by the bio-based suspension dispersion system prepared in Example 1 was heated at 160°C for 170s. -1Temperature and shear resistance test under conditions;

[0032] Figure 5 This is a curve showing the change of the core damage rate of the high-viscosity fracturing fluid prepared in Example 1 at different temperatures as a function of the injection multiple;

[0033] Figure 6 This is a curve showing the change in apparent viscosity over time at different temperatures after the bio-based suspension dispersion system prepared in Example 5 is added to the water phase;

[0034] Figure 7 This is the dissolution time and drag reduction rate change curve of the bio-based suspension dispersion system prepared in Example 6 after adding the water phase;

[0035] Figure 8 This is the drag reduction rate, i.e., the apparent viscosity change curve at 40° C., of the bio-based suspension dispersion system prepared in Example 7 after adding the aqueous phase. DETAILED DESCRIPTION

[0036] The present invention will be described below in conjunction with specific examples and accompanying drawings. The examples are intended only to explain the present invention and are not intended to limit the scope of the present invention. Where specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0037] Example 1

[0038] The preparation method of the bio-based polymer suspension dispersion system is as follows:

[0039] S1: Place 25 parts of isooctyl laurate and 20 parts of isopropyl laurate in a reaction kettle and heat to 60°C;

[0040] S2: 3 parts of myristyl alcohol polyoxyethylene ether, 2 parts of polylactic acid (molecular weight 10,000), 2 parts of polyethylene glycol dioctyl ester (degree of polymerization 1,000), and 3 parts of cocamidopropyl betaine were added to a reactor and stirred at a mechanical speed of 800 r / min for 30 minutes until they were completely dissolved. Then, the system temperature was lowered to 40°C.

[0041] S3: Increase the mechanical stirring speed to 1000 r / min, evenly mix 3 parts of potassium chloride solid powder (200 mesh), 2 parts of ammonium persulfate powder (200 mesh), 5 parts of polyacrylamide drag reducer powder (molecular weight 10 million, particle size 120 mesh) and 35 parts of sulfonic acid modified sodium carboxymethyl cellulose powder (degree of substitution 0.9, molecular weight 5 million, particle size 140 mesh), and slowly add them into the reactor to fully suspend and disperse the powder in the monohydric alcohol ester system. Continue stirring for 90 minutes to obtain a bio-based suspension dispersion system.

[0042] Example 2

[0043] The bio-based suspension dispersion system prepared in Example 1 was dissolved in the simulated produced water of Well A to prepare a fracturing fluid.

[0044] The mineral composition of water produced from Well A in a certain formation in the Ordos Basin was tested, and its mineralization is shown in Table 1.

[0045] Table 1 Ion concentration of produced water from well A in a certain block of the Ordos Basin

[0046]

[0047] The bio-based suspension dispersion prepared in Example 1 was dissolved in the simulated produced water from Well A to prepare a fracturing fluid. A fracturing fluid friction meter was used to analyze and test the time it took for the viscous fracturing fluid to achieve optimal drag reduction and the highest drag reduction rate. The test method is as follows:

[0048] 10L of simulated produced water from well A in a certain formation in the Ordos Basin was added to the fracturing fluid friction tester circulation tank, and the mechanical stirring in the tank was turned on at a stirring speed of 100r / min. The circulation displacement was set to 35L / min, and the simulated formation water circulated in the pipeline. 10g of the bio-based suspension dispersion system was dripped into the circulation tank. The pressure difference between the two ends of the circulation pipeline was recorded until the pressure difference stabilized. The drag reduction rate at this displacement was calculated according to the following formula. The test results are as follows: Figure 1 .

[0049]

[0050] Wherein, ΔP0 is the pressure drop of pure water, Pa; ΔP1 is the stable pressure drop after adding the dispersed system, Pa.

[0051] like Figure 1 As shown, the test results show that after 48 seconds of adding the bio-based suspended dispersion system prepared in Example 1 to the simulated produced water of Well A, the pressure difference of the circulation pipeline can be stabilized, that is, the maximum drag reduction rate is achieved, and the drag reduction rate can reach 76%. The results show that the polyacrylamide polymer drag reducer in the suspended dispersion system can achieve the best effect within 48 seconds.

[0052] Adjust the displacement of the fracturing fluid friction meter and test the drag reduction rate of the medium viscosity fracturing fluid in the displacement range of 20 to 45 L / min. The test results are as follows: Figure 2 As shown in the figure, the drag reduction rate increases with the increase of displacement, and tends to be stable when the displacement reaches 40L / min, and the drag reduction rate can reach 79.8%.

[0053] Example 3

[0054] Take a 1000mL beaker, add 500mL of simulated produced water from well A in a certain formation in the Ordos Basin mentioned in Example 2, place the beaker in a water bath and set it to a certain temperature, use mechanical stirring to continuously stir at a speed of 1000r / min, add 6g of the biomass suspension dispersion system prepared in Example 1 to the beaker to prepare a high-viscosity fracturing fluid, and then stir it every 30s and test it for 170s. -1 The apparent viscosity under the conditions, the test results are as follows Figure 3 .

[0055] like Figure 3 As shown in the figure, the reason why the apparent viscosity of high-viscosity fracturing fluid increases with time is that the hydration of modified sodium carboxymethyl cellulose takes a certain amount of time. At low temperature of 20°C, it takes 270 seconds to achieve complete hydration and the apparent viscosity reaches a stable level of 245 mPa·s. At 40°C, it takes 120 seconds to achieve complete hydration and the apparent viscosity reaches a stable level of 239 mPa·s.

[0056] The prepared high-viscosity fracturing fluid was subjected to temperature and shear resistance tests using a high-temperature and high-pressure rheometer. The target temperature was set at 160°C and the shear rate was 170s. -1 , continue shearing for 120 minutes, observe the apparent viscosity remaining, the test results are as follows Figure 4 As shown in the figure, it can be seen that the high viscosity fracturing fluid is heated at 160℃ and a shear rate of 170s -1 Under the same conditions, after 120 minutes of continuous shearing, the apparent viscosity remained above 50 mPa·s, showing excellent temperature resistance.

[0057] Example 4

[0058] High-viscosity fracturing fluids were prepared according to the method of Example 3, and their gel breaking performance was tested at 60°C, 90°C, 120°C, and 160°C. The test results are shown in Table 2. As can be seen from Table 2, the surface tension of the high-viscosity fracturing fluids was less than 28 mN / m, the interfacial tension was less than 0.1 mN / m, and the residue content was less than 5 mg / L.

[0059] Table 2 Gel breaking of high viscosity fracturing fluid at different temperatures

[0060]

[0061] Core displacement tests were conducted using breakers formed at 60°C, 90°C, and 120°C to evaluate their damage rate. The evaluation method used artificial cores with a porosity of 8.7% and a permeability of 0.9 mD. The test method involved driving saturated sodium chloride brine into the artificial core at a specific temperature to reach equilibrium. The initial permeability, K0, was calculated using Darcy's equation. The permeability, K1, was then calculated after the breakers reached equilibrium at the corresponding temperature. The core damage rate (η) was then calculated using the following formula.

[0062]

[0063] The relationship between core damage rate and injection multiple is as follows: Figure 5 The damage rate of the breaker to the low-permeability core was less than 5%, which shows that the fracturing fluid prepared by the bio-based suspension dispersion system has excellent cleanliness and low damage.

[0064] Example 5

[0065] The preparation method of the bio-based polymer suspension dispersion system is as follows:

[0066] S1: Place 25 parts of isooctyl myristate and 20 parts of isopropyl myristate in a reaction kettle and heat to 60°C;

[0067] S2: 3 parts of lauryl alcohol polyoxyethylene ether, 2 parts of polylactic acid (molecular weight 10,000), 2 parts of polyethylene glycol dibutyl ester (degree of polymerization 1,000), and 3 parts of cocamidopropyl betaine were added to a reactor and stirred at a mechanical speed of 800 r / min for 30 min until they were completely dissolved, and then the system temperature was lowered to 40°C;

[0068] S3: Increase the mechanical stirring speed to 1000 r / min, evenly mix 3 parts of potassium chloride solid powder (200 mesh), 2 parts of ammonium persulfate powder (200 mesh), 5 parts of polyacrylamide drag reducer powder (molecular weight 10 million, particle size 120 mesh) and 35 parts of sulfonic acid modified sodium carboxymethyl cellulose powder (degree of substitution 0.9, molecular weight 5 million, particle size 140 mesh), and slowly add them into the reactor to fully suspend and disperse the powder in the monohydric alcohol ester system. Continue stirring for 90 minutes to obtain a bio-based suspension dispersion system.

[0069] The prepared bio-based suspension dispersion system was tested for dissolution rate and drag reduction effect according to the evaluation method in Example 2. The test results showed that the pressure difference reached stability within 49 seconds, that is, the dissolution time was 49 seconds, and the maximum drag reduction rate reached 80.5%.

[0070] The relationship between the viscosity of the high-viscosity fracturing fluid prepared with the bio-based suspension dispersion system and time was evaluated with reference to Example 3. Figure 6 As shown in the figure, the reason why the apparent viscosity of high-viscosity fracturing fluid increases with time is that the hydration of modified sodium carboxymethyl cellulose takes a certain amount of time. At low temperature of 20°C, it takes 250 seconds to achieve complete hydration and the apparent viscosity reaches a stable level of 253 mPa·s. At 40°C, it takes 120 seconds to achieve complete hydration and the apparent viscosity reaches a stable level of 258 mPa·s.

[0071] The results of the temperature and shear resistance test show that the high viscosity fracturing fluid is-1 Under the same conditions, after 120 minutes of continuous shearing, the apparent viscosity remained above 56 mPa·s, showing excellent temperature resistance.

[0072] The high-viscosity fracturing fluid was evaluated using the same method as in Example 4, and the results of gel breaking performance testing are shown in Table 3. As shown in Table 3, the gel breaking fluids used to prepare the high-viscosity fracturing fluid in this example exhibited surface tensions below 28 mN / m, interfacial tensions below 0.1 mN / m, and residue contents below 5 mg / L. Core damage rate testing revealed that the gel breaking fluids exhibited core damage rates below 5%.

[0073] Table 3 Gel breaking of high viscosity fracturing fluid at different temperatures

[0074]

[0075] Example 6

[0076] Keeping the other conditions in Example 1 unchanged, while keeping the added type and total proportion of the stabilizers polylactic acid and polyethylene glycol diester, only the mass ratio of polylactic acid to polyethylene glycol diester was changed, and the mass ratio was set to 1:3, 1:2, 2:2, 5:3, and 5:2, to prepare 5 bio-based suspension dispersions.

[0077] The dissolution rate and drag reduction effect were tested according to the evaluation method in Example 2. The dissolution rate and drag reduction effect were plotted against the mass ratio of polylactic acid to polyethylene glycol diester. Figure 7 The results show that bio-based suspensions formulated with polylactic acid to polyethylene glycol diester mass ratios within this range dissolve in mineralized water at rates below 49 seconds and achieve slickwater drag reduction rates exceeding 74%. The overall pattern is that a higher polylactic acid ratio results in a longer dissolution time but higher drag reduction, while a lower polylactic acid ratio results in a shorter dissolution time but lower drag reduction.

[0078] Example 7

[0079] The effect of modified carboxymethyl cellulose dosage on product performance was studied. As a thickener, modified carboxymethyl cellulose has a significant impact on the preparation of highly viscous fracturing fluids. Maintaining all other conditions unchanged from Example 1 and the combined ratio of modified carboxymethyl cellulose to drag reducer, five bio-based suspension dispersions were prepared by adding modified sodium carboxymethyl cellulose at 25, 30, 35, 40, and 45 parts, respectively.

[0080] The drag reduction rate and the maximum viscosity at 40°C were tested according to Example 2 and Example 3, and the test results are as follows: Figure 8The results show that the drag reduction rate gradually decreases, but will not fall below 70%. Furthermore, as the proportion of modified carboxymethyl cellulose increases and the amount of drag reducer decreases, the maximum apparent viscosity of the high-viscosity fracturing fluid increases, reaching a maximum of over 290 mPa·s at 40°C.

[0081] Example 8

[0082] The materials and proportions in Example 1 remain unchanged, and only the heating temperatures of S1 and S2 are changed during the preparation process. The heating temperature in S1 is changed to 50°C, and the heating temperature in S2 is changed to 70°C. The prepared bio-based suspension dispersion is tested for dissolution rate and drag reduction effect according to the evaluation method in Example 2. The test results show that the pressure difference reaches stability within 46 seconds, that is, the dissolution time is 46 seconds, and the maximum drag reduction rate reaches 79.85%. Referring to Example 3, the high-viscosity fracturing fluid prepared with the bio-based suspension dispersion system requires 259 seconds to achieve complete hydration at a low temperature of 20°C, and the apparent viscosity reaches a stable level, which can reach 243mPa·s; under 40°C conditions, it requires 112 seconds to achieve complete hydration, and the apparent viscosity reaches a stable level, which can reach 273mPa·s. Subsequently, the high-viscosity fracturing fluid is tested for heat and shear resistance according to the evaluation method in Example 3. The experimental results show that the high-viscosity fracturing fluid has a high shear resistance at 160°C and a shear rate of 170s. -1 Under these conditions, after 120 minutes of continuous shearing, the apparent viscosity remained above 51 mPa·s, demonstrating excellent temperature resistance. Referring to the evaluation method in Example 4, the breaker prepared for the high-viscosity fracturing fluid in this example exhibited surface tensions below 28 mN / m, interfacial tensions below 0.1 mN / m, residue contents below 5 mg / L, and core damage rates below 5%.

[0083] Example 9

[0084] Keeping other conditions in Example 1 unchanged, the degree of polymerization of polyethylene glycol diisooctyl ester added to S2 was adjusted to 1500, and the prepared bio-based suspension dispersion was tested for dissolution rate and drag reduction effect according to the evaluation method in Example 2. The test results showed that the pressure difference reached stability within 43 seconds, that is, the dissolution time was 43 seconds, and the maximum drag reduction rate reached 80.31%. Referring to Example 3, the high-viscosity fracturing fluid prepared with the bio-based suspension dispersion system required 234 seconds to achieve complete hydration at a low temperature of 20°C, and the apparent viscosity reached a stable value of 252mPa·s; at 40°C, it required 117 seconds to achieve complete hydration, and the apparent viscosity reached a stable value of 279mPa·s. Subsequently, the high-viscosity fracturing fluid was tested for heat and shear resistance according to the evaluation method in Example 3. The experimental results showed that the high-viscosity fracturing fluid had a high shear resistance at 160°C and a shear rate of 170s. -1Under these conditions, after 120 minutes of continuous shearing, the apparent viscosity remained above 50.5 mPa·s, demonstrating excellent temperature resistance. Referring to the evaluation method in Example 4, the breaker prepared for the high-viscosity fracturing fluid in this example exhibited surface tensions below 28 mN / m, interfacial tensions below 0.1 mN / m, residue contents below 5 mg / L, and core damage rates below 5%.

[0085] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A biomass polymer suspension dispersion system for variable viscosity fracturing fluid, characterized in that: The biomass polymer suspension dispersion system is composed of the following components in terms of weight percentage: Modified sodium carboxymethyl cellulose 25~45% Fatty alcohol polyoxyethylene ether 5~15% Stabilizer 3~6% Fatty acid amide propyl betaine 5%~10% Drag reducer 1~5% Gel breaker 0.5%~2% Anti-swelling agent potassium chloride 2%~5% The balance is biomass monohydric alcohol ester; The modified sodium carboxymethyl cellulose is sulfonic acid-modified sodium carboxymethyl cellulose with a degree of substitution of 0.3-1.8 and a particle size of 80-140 meshes; the stabilizer is composed of polylactic acid and polyethylene glycol diester in a mass ratio of 1-5:2-3; the drag reducer includes polyacrylamide powder, which has a drag reduction rate of more than 80% for mineralized water; and the biomass monohydric alcohol ester includes one or more of isooctyl laurate, isooctyl myristate, isooctyl palmitate, isooctyl stearate, isopropyl laurate, and isopropyl myristate.

2. The biomass polymer suspension dispersion system for variable viscosity fracturing fluid according to claim 1, characterized in that: The molecular weight of the polylactic acid is 5000-50000, and the degree of polymerization of the polyethylene glycol in the polyethylene glycol diester is 200-2000.

3. The biomass polymer suspension dispersion system for variable viscosity fracturing fluid according to claim 1, characterized in that: The molecular weight of polyacrylamide powder is 10 million to 15 million, and the particle size is 100 to 140 mesh.

4. The biomass polymer suspension dispersion system for variable viscosity fracturing fluid according to claim 1, characterized in that: The gel breaker is a persulfate; the persulfate includes ammonium persulfate, sodium persulfate or potassium persulfate.

5. The biomass polymer suspension dispersion system for variable viscosity fracturing fluid according to claim 1, characterized in that: The viscosity of the biomass monohydric alcohol ester is 4.5~6.6 m 2 / s, surface tension is 24~31mN / m, density is 0.8~0.92g / cm 3 .

6. A method for preparing a biomass polymer suspension dispersion system for variable viscosity fracturing fluid according to claim 1, characterized in that: The preparation method comprises the following steps: heating the biomass monohydric alcohol ester to 30-100° C., stirring at 800-900 r / min, adding fatty alcohol polyoxyethylene ether, a stabilizer, and fatty amide propyl betaine until completely dissolved, and then cooling to 10-40° C. to obtain a continuous phase of the dispersed system; The stirring speed was increased to 900-1000 r / min, and modified sodium carboxymethyl cellulose powder, drag reducer, gel breaker and anti-swelling agent were added, and the stirring was continued for 30-90 min to obtain a biomass polymer suspension dispersion system.

7. An application of the biomass polymer suspension dispersion system for variable viscosity fracturing fluid according to claim 1, characterized in that: The salinity range of water used in preparing fracturing fluid is 10×10 4 mg / L, pumping volume is 1~20m 3 / h, and control the dripping rate of the polymer dispersion system at the wellhead according to the displacement, so that the addition amount of the polymer dispersion system in water is 0.02wt%~0.5wt%, of which 0.02wt%~0.06wt% is a low viscosity system, 0.06wt%~0.3wt% is a medium viscosity system, and 0.1wt%~0.5wt% is a high viscosity system.

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