Method for improving performance of resistance reducing agent based on cyclodextrin solubilization modification and application

Abstract

The application discloses a method for improving the performance of a resistance reducing agent based on cyclodextrin solubilization modification and application, and belongs to the technical field of fracturing fluids, and comprises the following steps: S1, mixing a hydrophobic associated polymer dry powder and cyclodextrin to prepare a mixed liquid; S2, stirring the mixed liquid, and testing the particle size in the mixed liquid at the same interval of time; and ending the stirring after the particle size is reduced to a stable size, so as to obtain a hydrophobic associated polymer solution. The cyclodextrin polymer not only has a high molecular effect, but also retains the inclusion ability of the cavity of the cyclodextrin, and has good inclusion performance in the case that the guest molecules are large. The hydrophobic associated polymer is modified through host-guest inclusion technology, the solubility of the hydrophobic associated polymer is improved on the basis of ensuring the resistance reducing effect, and the prepared hydrophobic associated polymer resistance reducing agent has the advantages of fast dissolution, good shear resistance and good resistance reducing effect.

Description

Technical Field

[0001] This invention relates to the field of fracturing fluid technology, and in particular to a method and application for improving the drag-reducing performance of drag-reducing agents based on cyclodextrin solubilization modification. Background Technology

[0002] Shale gas, tight gas, and other unconventional resources are gradually becoming a crucial component of current and future oil and gas supply. With the development of unconventional gas reservoirs, fracturing technology has improved significantly, and volumetric fracturing has become the primary method for developing these reservoirs. Large-scale volumetric fracturing of slickwater and other fracturing fluids in shale gas and tight gas reservoirs is currently a key technology for the effective development of shale gas and tight gas in China. Slickwater is formulated with drag reducers, surfactants, and bactericides according to formation conditions and operational requirements, with drag reducers being the most critical additive.

[0003] After years of development, the performance of slickwater drag reducers has made significant progress, with excellent products emerging, represented by hydrophobic associating polymers. These polymers further enhance the drag reduction performance of slickwater through intermolecular and intramolecular association. Currently, the most commonly used hydrophobic associating polymer drag reducers in the field are mainly inverse emulsions and suspension emulsions. These require large on-site dosages and introduce a significant amount of oil phase, stabilizers, and emulsifiers, which not only increases the cost of use but also poses a potential risk of damage to the reservoir and further complicates the handling of fracturing flowback fluid.

[0004] Dry powder hydrophobic associating polymer drag reducers are a preferred method for solving the above problems. Not only do they significantly reduce usage costs due to their high effective concentration, but they also avoid introducing undesirable components such as oil phases, stabilizers, and emulsifiers. However, dry powder hydrophobic associating polymer drag reducers have poor solubility (slow dissolution rate), making complete dissolution difficult within a limited time. This forces an increase in the amount of drag reducer used on-site to meet drag reduction performance requirements, which actually increases usage costs and can also lead to problems such as the formation of "fisheyes" that affect the quality of slickwater.

[0005] Therefore, the following application is submitted. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to improve the existing dry powder drag-reducing agents, which have good drag-reducing effects but are slow to dissolve, difficult to operate and have low construction efficiency.

[0007] This invention is achieved through the following technical solution:

[0008] This application proposes a method for improving the performance of drag-reducing agents based on cyclodextrin solubilization modification, comprising the following steps:

[0009] S1: Prepare a liquid mixture by mixing hydrophobic associative polymer dry powder and cyclodextrin;

[0010] S2: Stir the mixed liquid and test the particle size in the mixed liquid at the same time intervals. Stop stirring when the particle size decreases to a stable size to obtain a hydrophobic associative polymer solution.

[0011] Preferably, the hydrophobic associating polymer powder is one or a combination of quaternary ammonium salt hydrophobic associating polymers, nonionic hydrophobic associating polymers, and rigid structure hydrophobic associating polymers.

[0012] Preferably, the quaternary ammonium salt-type hydrophobic associating polymer is PAAD, and the PAAD has the following molecular structural formula:

[0013] Wherein, 70≤x≤90, 5≤y≤30, 0≤z≤5.

[0014] Preferably, the nonionic hydrophobic associative polymer is PAAO, and PAAO has the following molecular structural formula:

[0015] Where 70≤x≤90, 5≤y≤30, 0≤z≤5, and n represents the amount of ethylene oxide, 9≤n≤30.

[0016] Preferably, the rigid-structure hydrophobic associating polymer is PSEM, and the PSEM has the following molecular structural formula:

[0017] Where 70≤x≤90, 5≤y≤30, 0≤z≤5, and n represents the amount of ethylene oxide, 9≤n≤30.

[0018] Preferably, the cyclodextrin is one or a combination of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin.

[0019] Preferably, in the hydrophobic associating polymer solution, the molar ratio of the cyclodextrin to the hydrophobic associating polymer dry powder in the mixed liquid of S1 is 1-2: 1-2;

[0020] The concentration of the hydrophobic associating polymer in the S2 hydrophobic associating polymer solution is 400 mg / L to 600 mg / L.

[0021] Preferably, the ambient temperature for stirring in S2 is 20℃~40℃;

[0022] The stirring speed is 150 rpm to 400 rpm;

[0023] In the particle size test, a laser particle size analyzer was used for measurement, with a measurement interval of 4 to 6 minutes.

[0024] Preferably, the molecular weight of the hydrophobic associative polymer is 1 million to 20 million g / mol.

[0025] To achieve the above objectives, the present invention also provides the application of hydrophobic associative polymer solutions prepared by the method described above for improving drag-reducing agent performance based on cyclodextrin solubilization modification in oil and gas field development.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] (1) This application utilizes the property of cyclodextrin being hydrophilic on the outside and hydrophobic on the inside to solubilize poorly soluble substances. Cyclodextrin polymers not only have a polymer effect but also retain the inclusion capacity of cyclodextrin cavities, exhibiting good inclusion performance when the guest molecules are large. By modifying the hydrophobic associating polymer through host-guest inclusion technology, its solubility is improved while ensuring its drag reduction effect. The prepared hydrophobic associating polymer drag reducer has the advantages of fast dissolution, shear resistance, and good drag reduction effect.

[0028] (2) This invention establishes the Langmuir isothermal adsorption equation through rheological testing, and analyzes and calculates the inclusion constant, entropy change, and enthalpy change from a molecular dynamics perspective to determine its accurate inclusion constant and ratio. Specifically, through a combination of molecular dynamics simulations, theoretical equations, and experiments, the inclusion effect of hydrophobic segments of hydrophobic associative polymers with cyclodextrin cavities was systematically studied. The interaction energy, radial distribution function, and radius of gyration of the inclusion process were obtained, and the matching relationship between the hydrophobic associative structure and the cyclodextrin cavity was derived. A highly matched cyclodextrin cavity can promote the dissolution of dry powder hydrophobic associative polymers and, to a certain extent, improve the drag reduction effect of polymer aqueous solutions, making it widely applicable in the field.

[0029] (3) This invention is based on the difference in hydrophilicity and hydrophobicity inside and outside the cyclodextrin cavity, and conducts solubilization modification research through host-guest inclusion. The effects of cyclodextrin type, concentration, dissolution temperature and stirring time on the solubility of dry powder hydrophobic associating polymers were systematically studied. It was confirmed that with β-CD (β-cyclodextrin) as the main substance and its ratio to hydrophobic segments of 2:1, the dry powder hydrophobic associating polymers could be completely dissolved by stirring at 25 ℃ for 45 min. The inclusion constant was calculated to be 0.8065, 1.1114 and 1.4911 at 25 ℃, 35 ℃ and 45 ℃, respectively, by establishing the Langmuir isotherm adsorption equation through rheological testing. The entropy change of the process was -78.12 J / mol∙K and the enthalpy change was -23.41. kJ / mol; Molecular simulations calculated the interaction energy, radial distribution function, and radius of gyration of the inclusion process from a molecular dynamics perspective. The introduction of β-CD increased the interaction energy between the dry powder hydrophobic associating polymer and water, increased the hydrogen bond content of the system, and increased the hydrodynamic radius of the dry powder hydrophobic associating polymer, proving that β-CD can promote the dissolution of the dry powder hydrophobic associating polymer. β-CD recognizes the hydrophobic structure in the system through host-guest interaction and rapidly includes it, changing its hydrophilicity and hydrophobicity, thereby accelerating dissolution. By controlling the amount of β-CD added, the generation of hydrophobic segment association can be regulated, thus balancing the dissolution performance and drag reduction performance of the dry powder hydrophobic associating polymer. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0031] Figure 1 This is a graph showing the dissolution time of the hydrophobic associating polymer in Example 1;

[0032] Figure 2 This is a graph showing the dissolution time of the hydrophobic associating polymer in Example 2;

[0033] Figure 3 This is a graph showing the dissolution time of the hydrophobic associating polymer in Example 3;

[0034] Figure 4 This is a graph showing the dissolution time of the hydrophobic associating polymer in Example 4;

[0035] Figure 5 This is a graph showing the dissolution time of the hydrophobic associating polymer in Example 5;

[0036] Figure 6This is a graph showing the dissolution time of the hydrophobic associating polymer in Example 6;

[0037] Figure 7 This is a subject-object inclusion conformation diagram of the system in an embodiment of the present invention;

[0038] Figure 8 This is a diagram illustrating the host-guest inclusion and solubilization mechanism in an embodiment of the present invention.

[0039] Figure 9 This is a schematic diagram illustrating the solubility properties of hydrophobic associating polymers in the prior art.

[0040] Figure 10 This is a schematic diagram illustrating the solubility of the hydrophobic associating polymer in an embodiment of the present invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0042] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0043] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0044] The differences between the embodiments of the present invention and the prior art CN114605982A are as follows:

[0045] (1) Solubility and Inclusion Optimization: Patent CN114605982A uses a combination of cyclodextrin and surfactant. First, Tween-80, sodium dodecyl sulfonate, and cyclodextrin β-CD are mixed in a certain proportion, and then a certain concentration of hydrophobic associating polymer is added. The viscosity of the solution is tested at the same time intervals using a viscometer. The embodiments of this invention are based on multi-method synergistic research and have obtained an implementation scheme that achieves the inclusion of hydrophobic associating polymer in cyclodextrin without the use of surfactant, thereby achieving the purpose of solubility promotion. Moreover, the improvement in solubility does not damage the drag reduction performance, but rather improves the drag reduction performance to a certain extent. Patent CN114605982A only focuses on the improvement of solubility performance.

[0046] (2) Technological Optimization: Patent CN114605982A increases the solubility of hydrophobically associated polymers by shielding the hydrophobic association of polymers and utilizing the synergistic effect of cyclodextrin and surfactants to change the polarity of the polymer aqueous solution. For example... Figure 7-8 As shown, this invention, for the first time, systematically studies the inclusion effect of hydrophobic segments of hydrophobic associative polymers with cyclodextrin cavities through a combination of molecular dynamics simulations, theoretical equations, and experiments. The interaction energy, radial distribution function, and radius of gyration of the inclusion process were obtained, revealing the matching relationship between the hydrophobic associative structure and the cyclodextrin cavity. The highly matched cyclodextrin cavity can promote the dissolution of dry powder hydrophobic associative polymers.

[0047] (3) Key Solution: Patent CN114605982A determined better preparation conditions through experimental comparison. However, this result is affected by experimental errors and changes in the system, and the influence of surfactants is unclear. This invention, through thermodynamic analysis, studies the changes in state functions from a macroscopic perspective, calculating the inclusion constant and thermodynamic parameters of the inclusion process. Based on this, the inclusion constant of the system under different conditions and environments can be accurately determined by measuring the rheological properties of the system, thus obtaining the optimal inclusion ratio. The inclusion constants of β-CD with dry powder hydrophobic associating polymers are shown in Table 1 below:

[0048]

[0049] (4) Performance improvement: such as Figure 9-10 As shown, under the same polymer concentration and the same amount of cyclodextrin, the dissolution time of the present invention embodiment is shortened by more than 40 minutes compared with the dissolution time of patent CN114605982A, which is a significant improvement, and the drag reduction performance is improved by 5.76% compared with the performance without the addition of cyclodextrin.

[0050] To better understand the technical solution of the present invention, the experimental methods, samples, and instruments of the embodiments are described below:

[0051] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available. In the following embodiments, the cyclodextrins used are α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin, provided by Sichuan Kelong Pharmaceutical Co., Ltd. The hydrophobic associating polymer was prepared in the laboratory, with a viscosity-average molecular weight of 100-2000 million g / mol. The concentration of the hydrophobic associating polymer in the solution was 400 mg / L to 600 mg / L, and the preparation volume was 500 mL.

[0052] Cyclodextrin: α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, wherein the molar concentration ratio of cyclodextrin to hydrophobic associating polymer powder is 1-2: 1-2. The dissolution method is as follows: the hydrophobic associating polymer powder and cyclodextrin are prepared according to a certain ratio and concentration, and the particle size of the solution is tested at the same time intervals using a laser particle size analyzer. Stirring is stopped when the particle size gradually decreases and tends to stabilize, and the hydrophobic associating polymer solution is obtained. Example

[0053] Prepare a 500 mL mixture of quaternary ammonium salt hydrophobic associating polymers. Heat the mixture to the prepared temperature. Add α-cyclodextrin at a molar ratio of 1:2 (quaternary ammonium salt hydrophobic associating polymer powder to cyclodextrin). Adjust the mechanical stirrer speed to 150 rpm and stir. At 40 °C, measure the particle size change of the polymer solution every five minutes using a laser particle size analyzer. Stop stirring when the particle size gradually decreases and tends to stabilize, thus obtaining the hydrophobic associating polymer solution. The dissolution time curve of 500 mg / L hydrophobic associating polymer is shown below. Figure 4 As shown, based on the criterion of measuring the particle size of the polymer solution every five minutes and ending the experiment when the particle size gradually decreases and tends to stabilize, the dissolution time of the 500 mg / L hydrophobic associative polymer is less than 18 min, and the drag reduction rate is increased by 4.74%. Example

[0054] Prepare 500 mL of a nonionic hydrophobic-associated polymer mixture. Heat the mixture to the prepared temperature. Add β-cyclodextrin at a ratio of nonionic hydrophobic-associated polymer to cyclodextrin of 1.1:1.8. Adjust the mechanical stirrer speed to 200 rpm and stir. At 35°C, measure the particle size change of the polymer solution every five minutes using a laser particle size analyzer. Stop stirring when the particle size gradually decreases and tends to stabilize, thus obtaining the hydrophobic-associated polymer solution. The dissolution time curve of 500 mg / L hydrophobic-associated polymer is shown below. Figure 5 As shown, based on the criterion of measuring the particle size of the polymer solution every five minutes and ending the experiment when the particle size gradually decreases and tends to stabilize, the dissolution time of the 500 mg / L hydrophobic associative polymer is less than 15 min, and the drag reduction rate is increased by 5.76%. Example

[0055] Prepare 500 mL of a rigid-structure hydrophobic associating polymer mixture. Heat the mixture to the prepared temperature. Add g-cyclodextrin at a ratio of 1.5:1.5 (rigid-structure hydrophobic associating polymer dry powder:cyclodextrin). Adjust the mechanical stirrer speed to 250 rpm and stir. At 30°C, measure the particle size change of the polymer solution every five minutes using a laser particle size analyzer. Stop stirring when the particle size gradually decreases and tends to stabilize, thus obtaining the hydrophobic associating polymer solution. The dissolution time curve of 500 mg / L hydrophobic associating polymer is shown below. Figure 6As shown, based on the criterion of measuring the particle size of the polymer solution every five minutes and ending the experiment when the particle size gradually decreases and tends to stabilize, the dissolution time of the 500 mg / L hydrophobic associative polymer was less than 21 min, and the drag reduction rate was increased by 4.12%. Example

[0056] Prepare a 500 mL mixture of quaternary ammonium salt hydrophobic associating polymers. Heat the mixture to the prepared temperature. Add α-cyclodextrin at a ratio of quaternary ammonium salt hydrophobic associating polymer to cyclodextrin of 1.6:1.3. Adjust the mechanical stirrer speed to 300 rpm and stir. At 30°C, measure the particle size change of the polymer solution every five minutes using a laser particle size analyzer. Stop stirring when the particle size gradually decreases and tends to stabilize, thus obtaining the hydrophobic associating polymer solution. The dissolution time curve of 500 mg / L hydrophobic associating polymer is shown below. Figure 7 As shown, based on the criterion of measuring the particle size of the polymer solution every five minutes and ending the experiment when the particle size gradually decreases and tends to stabilize, the dissolution time of the 500 mg / L hydrophobic associative polymer is less than 29 min, and the drag reduction rate is increased by 1.36%. Example

[0057] Prepare 500 mL of a nonionic hydrophobic associating polymer mixture. Heat the mixture to the prepared temperature. Add β-cyclodextrin at a ratio of nonionic hydrophobic associating polymer to cyclodextrin of 1.8:1.1. Adjust the mechanical stirrer speed to 350 rpm and stir. At 35°C, measure the particle size change of the polymer solution every five minutes using a laser particle size analyzer. Stop stirring when the particle size gradually decreases and tends to stabilize, thus obtaining the hydrophobic associating polymer solution. The dissolution time curve of 500 mg / L hydrophobic associating polymer is shown below. Figure 8 As shown, based on the criterion of measuring the particle size of the polymer solution every five minutes and ending the experiment when the particle size gradually decreases and tends to stabilize, the dissolution time of the 500 mg / L hydrophobic associative polymer was less than 23 min, and the drag reduction rate was increased by 3.11%. Example

[0058] Prepare 500 mL of a rigid-structure hydrophobic associating polymer mixture. Heat the mixture to the prepared temperature. Add g-cyclodextrin at a ratio of 2:1 (rigid-structure hydrophobic associating polymer to cyclodextrin). Stir the mixture at 400 rpm using a mechanical stirrer. At 20°C, measure the particle size change of the polymer solution every five minutes using a laser particle size analyzer. Stop stirring when the particle size gradually decreases and tends to stabilize, thus obtaining the hydrophobic associating polymer solution. The dissolution time curve for 500 mg / L hydrophobic associating polymer is shown below. Figure 9As shown, based on the criterion of measuring the particle size of the polymer solution every five minutes and ending the experiment when the particle size gradually decreases and tends to stabilize, the dissolution time of the 500 mg / L hydrophobic associative polymer is less than 27 min, and the drag reduction rate is increased by 1.47%.

[0059] The experimental verification results of Examples 1-6 above are summarized in Table 2 below:

[0060]

[0061] This invention provides a method and application for improving the drag reduction rate of drag-reducing agents based on cyclodextrin solubilization modification. The hydrophobic associating polymers include quaternary ammonium salt type hydrophobic associating polymer PAAD, nonionic hydrophobic associating polymer PAAO, and rigid structure type hydrophobic associating polymer PSEM. The concentration of the hydrophobic associating polymer is 500 mg / L, and the molar ratio of cyclodextrin to hydrophobic groups is 1-2:1-2. The dissolution method is as follows: the hydrophobic associating polymer dry powder and cyclodextrin are prepared according to a certain ratio and concentration. The polymer particle size in the solution is measured at the same time intervals using a laser particle size analyzer. The test is stopped when the particle size decreases to a stable level, and the hydrophobic associating polymer solution is obtained.

[0062] A slickwater system was developed using a solubilized and modified dry powder drag-reducing agent as the main agent, and its various properties were studied. Rheological testing confirmed that the system has good viscoelasticity. Under the same stirring conditions, a system of 0.025 wt% SW-41 (b-CD) and SW-4 (dry powder hydrophobic associating polymer + b-CD) was prepared and stirred in water for 10 min. The drag reduction rates were 40.76% and 71.43%, respectively, confirming that the introduction of b-CD can achieve high-efficiency drag reduction at low concentrations, only accelerating the dissolution process, and also helping to improve the stability and drag reduction performance of the system. The NaCl concentration was 1.2 × 10⁻⁶. 5 mg / L, CaCl2 concentration 1×10 3 At mg / L, the drag reduction rates of the 0.075 wt% SW-4 system were 72.28% and 74.23%, respectively, indicating good salt resistance and excellent temperature and shear resistance.

[0063] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for improving the performance of drag-reducing agents based on cyclodextrin solubilization modification, characterized in that, Includes the following steps: S1: Prepare a liquid mixture by mixing hydrophobic associative polymer dry powder and cyclodextrin; S2: Stir the mixed liquid and test the particle size in the mixed liquid at the same time intervals. Stop stirring when the particle size decreases to a stable size to obtain a hydrophobic associating polymer solution. The hydrophobic associating polymer powder is one or a combination of quaternary ammonium salt hydrophobic associating polymers and rigid structure hydrophobic associating polymers. In the hydrophobic associating polymer solution, the molar ratio of the cyclodextrin to the hydrophobic associating polymer dry powder in the mixed liquid of S1 is 1-2: 1-2; The concentration of the hydrophobic associating polymer in the S2 hydrophobic associating polymer solution is 400 mg / L to 600 mg / L; The quaternary ammonium salt-type hydrophobic associative polymer is PAAD, and PAAD has the following molecular structural formula: ； Where 70≤x≤90, 5≤y≤30, 0≤z≤5; The rigid-structured hydrophobic associative polymer is PSEM, and the PSEM has the following molecular structural formula: ； Where 70≤x≤90, 5≤y≤30, 0≤z≤5, and n represents the amount of ethylene oxide, 9≤n≤30.

2. The method for improving drag-reducing agent performance based on cyclodextrin solubilization modification according to claim 1, characterized in that, The cyclodextrin is one or a combination of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin.

3. The method for improving drag-reducing agent performance based on cyclodextrin solubilization modification according to claim 1, characterized in that, The ambient temperature for stirring in S2 is 20℃~40℃; The stirring speed is 150 rpm to 400 rpm; In the particle size test, a laser particle size analyzer was used for measurement, with a measurement interval of 4 to 6 minutes.

4. The method for improving drag-reducing agent performance based on cyclodextrin solubilization modification according to claim 1, characterized in that, The molecular weight of the hydrophobic associative polymer is 1 million to 20 million g / mol.

5. The application of the hydrophobic associative polymer solution prepared by the method of improving drag-reducing agent performance based on cyclodextrin solubilization modification as described in any one of claims 1-4 in oil and gas field development.

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