A delayed swelling pre-crosslinked gel particle based on gel microenvironment hydrolysis self-inhibition and a preparation method thereof

Abstract

The application provides a pre-crosslinking gel particle with a delayed swelling effect and a preparation method thereof, and belongs to the field of oil exploitation. The delayed swelling performance of the gel particle is reflected in that the gel particle has a small swelling multiple at room temperature, and the swelling multiple gradually increases in a high temperature (greater than 60 DEG C) environment, and the delayed swelling function is realized based on the hydrolysis self-inhibition in a gel microenvironment. Main components include acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, an acrylate monomer, and crosslinking agents N,N-methylenebisacrylamide (MBA) and polyethylene glycol diacrylate (PEGDA). The gel particle of the application uses a double crosslinking structure. The MBA is a stable crosslinking agent, remains relatively stable in a high temperature environment, and maintains the gel structure. The PEGDA belongs to an unstable crosslinking agent, is prone to hydrolysis of a carboxylic acid ester bond in a high temperature environment, and thus makes the gel particle have the delayed swelling capacity. The addition of the acrylate monomer can change the gel microenvironment, produce the self-inhibition PEGDA hydrolysis effect, thus the delayed swelling time of the PEGDA is controllable, and the problem of insufficient injection depth of the pre-crosslinking gel particle is effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of petroleum extraction technology and relates to a pre-crosslinked gel particle used for reservoir profile control and water shut-off, and more particularly to a time-controllable delayed swelling pre-crosslinked gel particle and its preparation method. Background Technology

[0002] As exploration and development of oil and gas resources in my country continue to deepen, many oil and gas fields have entered the mid-to-late stages of development, urgently requiring measures to improve oil and gas recovery rates. However, with increasingly complex formation conditions, fractures and large pores are frequently appearing. The presence of these fractures and large pores, along with the inherent characteristics of the formations, means that injected water and polymers tend to advance rapidly along high-permeability layers, while low-permeability layers are difficult to be affected. Therefore, developing strong plugging agents that can effectively seal fractures has become a key measure for developing fractured reservoirs.

[0003] Various types of plugging agents can be selected to address different degrees of reservoir heterogeneity. Among them, gel treatment is considered one of the most cost-effective chemical profile control and water shut-off methods. Gel treatment is mainly divided into subsurface cross-linked polymer gel systems and pre-cross-linked gel systems. Pre-cross-linked gel particles have advantages such as no need to consider gelation time, controllable gel strength, short mixing time, and simple injection process. The injection depth of gel particles is affected by their swollen particle size; smaller particle sizes are easier to inject but have poorer plugging ability. Therefore, it is necessary to develop a pre-cross-linked gel particle system with delayed swelling to achieve deeper injection depth and stronger plugging ability.

[0004] Several patents have reported on delayed-swelling pre-crosslinked gel particles (slow-swelling particles). Chinese patent document CN110922951B discloses a coated microgel particle profile modifier and its preparation method, the core technology of which is the coated structure. Chinese patent document CN111087998B proposes a method using graftable copolymers to prepare slow-swelling particles. Currently, the most common method to achieve delayed swelling is through a double-crosslinked structure, where the selection of an unstable crosslinking agent is crucial. For example, Chinese patent document CN114478897B uses 1,5-pentanediol diacrylate as an unstable crosslinking agent, while patent CN111394075B reports polyethylene glycol diacrylate as an unstable crosslinking agent. However, none of these patents provide specific methods for enhancing the delayed swelling effect.

[0005] This invention is based on the principle of self-inhibition of hydrolysis in the gel microenvironment. It proposes a method using acrylate monomers to inhibit the hydrolysis rate of unstable crosslinking agents, achieving controllable delay time for the swelling of pre-crosslinked gel particles. While acrylate monomers are commonly used to prepare pre-crosslinked gel particles or slow-swelling particles, previous patent documents have only used them as hydrophobic monomers, and the dosage is often quite high. For example, patent document CN114933674A mentions the use of various acrylate monomers (methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate) as hydrophobic monomers, but their role is to achieve temperature-controlled hydrophobic association. Patent document CN10305247B uses acrylate monomers as oil-soluble monomers to control the initial water absorption capacity of the gel particles. Therefore, there are currently no reports of using acrylate monomers to inhibit the hydrolysis of unstable crosslinking agents to achieve controlled delayed swelling. Summary of the Invention

[0006] The purpose of this invention is to address the problem that conventional pre-crosslinked gel particles swell too quickly, resulting in insufficient injection depth and poor plugging ability. To address this, a novel delayed-swelling pre-crosslinked gel particle is proposed, which utilizes stable / unstable crosslinking structures and acrylates as self-inhibitors of hydrolysis in the gel microenvironment. The preparation method is also specifically optimized based on the type and dosage of monomers.

[0007] The stable crosslinking agent used in the delayed swelling pre-crosslinked gel particles of the present invention is N,N-methylenebisacrylamide (MBA) and the unstable crosslinking agent is polyethylene glycol diacrylate (PEGDA, structural formula see below). Figure 1 The main monomers are acrylamide (AM) and 2-acrylamide-2-methylpropanesulfonic acid (AMPS), and the hydrolysis self-inhibitors of the gel microenvironment are acrylates, such as methyl acrylate, ethyl acrylate, hydroxypropyl acrylate, etc.

[0008] In this invention, MBA maintains the gel's network structure. PEGDA gradually hydrolyzes over time at higher reservoir temperatures. After localized disruption of the gel network, the water absorption and swelling capacity of the gel particles is enhanced, thus achieving a delayed swelling effect. The main agent AM and AMPS constitute the main chain structure of the gel network, with the sulfonate groups of AMPS providing strong water-absorbing side groups. The acrylate monomers, through pH changes caused by their own hydrolysis within the gel's microenvironment, inhibit the hydrolysis of PEGDA, thereby achieving a controllable delayed swelling time.

[0009] To achieve the above objectives, this invention provides a method for preparing delayed swelling pre-crosslinked gel particles. The main raw material components of the gel particles have the following content (calculated as molar percentage): crosslinking agent n(MBA) is 0.005-0.05 mol%, n(PEGDA) is 0.1-1 mol%, n(AM) is 80-95 mol%, n(AMPS) is 5-20 mol%, and acrylate monomers are 1-5 mol%. The content of acrylate monomers is key to controlling the self-inhibition of hydrolysis in the gel microenvironment.

[0010] The preparation method of this invention mainly involves the polymerization and cross-linking of raw material monomers initiated by an initiator, followed by cutting, granulation, drying, crushing, and screening to obtain the gel particle product. The specific implementation steps for preparing the gel particles of this invention are as follows:

[0011] (1) Weigh the specified mass of AM, AMPS and acrylate monomers into a beaker, add distilled water to dissolve them, and add the specified mass of MBA and PEGDA crosslinking agent;

[0012] (2) After the medicine has been fully dissolved, adjust the pH to about 7 using NaOH;

[0013] (3) During the integration and configuration process, the initial temperature should be controlled at 10-15℃;

[0014] (4) Transfer the monomer reaction solution to a heat-insulated container, remove oxygen by passing N2, add the initiator, and finally stop passing N2, seal the container, and record the temperature change of the reaction solution.

[0015] (5) After the temperature reaches the highest point, wait for 1 hour before taking out the rubber block, cutting it into pieces, and drying it in a 50℃ oven for 24 hours. Grind it into powder and sieve it to remove the specified mesh size for later use.

[0016] The above steps require explanation.

[0017] In step (1), the monomer content was optimized: crosslinking agent n(MBA) was 0.005–0.05 mol%, n(PEGDA) was 0.1–1 mol%, n(AM) was 80–95 mol%, n(AMPS) was 5–20 mol%, and acrylate monomers were 1–5 mol%. The ratio of MBA to PEGDA determined the final delayed swelling capacity of the product, the content of AM and AMS determined the initial swelling capacity of the product at room temperature, and the amount of acrylate monomers determined the delayed swelling time.

[0018] In step (2), adjusting the pH to around 7 is beneficial for the polymerization of monomers and the particles are less prone to side group hydrolysis under neutral conditions.

[0019] In step (3), the initial temperature of the reaction solution needs to be controlled at 10-15℃. The purpose is to control the temperature of the system during the polymerization reaction from being too high, which would cause the monomer to hydrolyze.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This delayed-swelling pre-crosslinked gel particle utilizes a dual-crosslinked network structure composed of MBA and PEGDA, allowing for control over the delayed swelling capacity through their ratio. Most importantly, it innovatively employs acrylate monomers as hydrolysis inhibitors in the gel microenvironment. By regulating the pH of the gel microenvironment through their own hydrolysis, they inhibit the hydrolysis of PEGDA, thus achieving controllable delayed swelling time. Attached Figure Description

[0022] The accompanying drawings, which constitute a part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0023] Figure 1 The molecular formula for unstable crosslinking agents, such as polyethylene glycol diacrylates;

[0024] Figure 2 To evaluate the effect of delayed swelling of pre-crosslinked gel particles. Detailed Implementation

[0025] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0026] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0027] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0028] Unless otherwise specified, the instruments, reagents, and materials used in the following embodiments are all conventional instruments, reagents, and materials already available in the prior art and can be obtained through legitimate commercial channels. Unless otherwise specified, the experimental methods and detection methods used in the following embodiments are all conventional experimental methods and detection methods already available in the prior art.

[0029] (I) Examples of Preparation Methods

[0030] Example 1:

[0031] Weigh 25.588 g of AM and 8.29 g of AMPS into a beaker (total molars: 0.4 mol, molar ratio AM:AMPS: 9:1). Add 0.01 mol% MBA and 0.2 mol% PEGDA (as monomers), and dissolve in 100 ml of water. After the reagents are fully dissolved, weigh 1.6 g of NaOH and add it to the solution, adjusting the pH to approximately 7 using liquid alkali. Finally, transfer the solution to an insulated container and maintain the initial temperature of the reaction solution at 10–15 °C. After purging with N2 gas for at least 10 minutes, add 0.4 mL of 10% ammonium persulfate solution (oxidant), 0.2 mL of 10% tetramethylethylenediamine solution (catalyst), and 0.2 mL of 10% sodium bisulfite solution (reducing agent) sequentially. Finally, stop purging with N2 gas, seal the container, and record the temperature change of the reaction solution. After reaching the maximum temperature, wait for 1 hour before removing the gel block. Post-processing: Cut the rubber blocks into small pieces, dry them in a 50℃ oven for 24 hours, grind them into powder and sieve out 40-80 mesh for later use.

[0032] Example 2:

[0033] Weigh 25.588 g of AM and 8.29 g of AMPS into a beaker (total molars: 0.4 mol, molar ratio AM:AMPS: 9:1), add 0.01 mol% MBA and 0.2 mol% PEGDA (as a percentage of monomers), and dissolve in 100 ml of water. Weigh 0.344 g, 1.032 g, and 1.72 g of methyl acrylate (MAA, or other acrylate monomers can be substituted) to prepare delayed-swelling pre-crosslinked gel particles with different MAA contents. After the reagents are fully dissolved, weigh 1.6 g of NaOH and add it to the solution, adjusting the pH to approximately 7 using liquid alkali. Finally, transfer the solution to an insulated container and maintain the initial reaction temperature at 10–15 °C. After purging with N2 gas for at least 10 minutes, 0.4 mL of a 10% ammonium persulfate solution (oxidant), 0.2 mL of a 10% tetramethylethylenediamine solution (catalyst), and 0.2 mL of a 10% sodium bisulfite solution (reducing agent) were added sequentially. Finally, the N2 gas purging was stopped, the container was sealed, and the temperature change of the reaction solution was recorded. After reaching the maximum temperature, the container was allowed to stand for another hour before removing the gel block. Post-processing: The gel block was cut into small pieces, dried in a 50℃ oven for 24 hours, ground into powder, and sieved through a 40-80 mesh screen for later use. Three modified products with different MAA contents were finally obtained.

[0034] (II) Evaluation of delayed swelling effect

[0035] First, weigh 0.2g of dry gel particles into a pressure-resistant test tube, add 25mL of 1wt% NaCl, and allow it to swell completely for 1 hour. Then, place the pressure-resistant test tube in an 80℃ water bath and observe the change in the swelling volume of the gel particles at regular intervals.

[0036] The delayed swelling effect of the invention in Example 1 was compared with that in Example 2 using Example 1 as the basic system. The experimental results are shown in [Figure 1]. Figure 2 It can be seen that as the content of MAA increases, the delayed swelling effect of the pre-crosslinked gel particles gradually improves, extending the swelling time from the initial 10 hours to tens to hundreds of hours. Especially when the content of MAA is greater than 5 mol%, the delayed swelling time is greatly extended, which is why the amount of acrylate monomer added in this invention is extremely important.

Claims

1. A delayed swelling pre-crosslinked gel particle based on self-inhibition of hydrolysis in a gel microenvironment, characterized in that, The monomers used include acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), acrylate monomers, and crosslinking monomers N,N-methylenebisacrylamide (MBA) and polyethylene glycol diacrylate (PEGDA). The monomers involved in polymerization are expressed in mole fractions, with n(AM) being 80-95 mol%; n(AMPS) being 5-20 mol%; acrylate monomers being 1-5 mol%; crosslinking agent n(MBA) being 0.005-0.05 mol%; and n(PEGDA) being 0.1-1 mol%. Selectable acrylate monomers include methyl acrylate, ethyl acrylate, and hydroxypropyl acrylate. The content of acrylate monomers is key to controlling the self-inhibition of hydrolysis in the gel microenvironment, which can delay the hydrolysis rate of unstable crosslinking agents in gel particles and achieve the goal of controllable delayed swelling time.

2. The method for preparing delayed swelling pre-crosslinked gel particles according to claim 1, characterized in that, Includes the following steps: (1) Weigh the specified mass of AM, AMPS and acrylate monomers into a beaker, add distilled water to dissolve them, and add the specified mass of MBA and PEGDA crosslinking agent; (2) After the medicine has been fully dissolved, adjust the pH to about 7 using NaOH; (3) During the integration and configuration process, the initial temperature should be controlled at 10~15℃; (4) Transfer the monomer reaction solution to a heat-insulated container, remove oxygen by passing N2 through it, add the initiator, and finally stop passing N2 through it, seal the container, and record the temperature change of the reaction solution. (5) After the temperature reaches the maximum, wait for 1 hour, then take out the rubber block, cut it into pieces, put it in a 50℃ oven to dry for 24 hours, grind it into powder and sieve it to remove the specified mesh size for later use.

3. The method for preparing delayed swelling pre-crosslinked gel particles as described in claim 2, characterized in that, In step (3), the initial temperature of the reaction solution needs to be controlled at 10~15℃. The purpose is to control the temperature of the system during the polymerization reaction from being too high and causing the monomer to hydrolyze.

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