Preparation method, product and application of polymer gel particles

Abstract

The present invention relates to the fields of oilfield chemistry and high-temperature and high-salinity reservoir profile control and water plugging technology, and in particular to a preparation method, product, and application thereof of polymer gel particles with enhanced mechanical properties through a double-crosslinked domain structure. The preparation method comprises the following steps: dissolving a monomer, a crosslinking agent, and an initiator in water to carry out a free radical polymerization reaction to obtain a polymer hydrogel; drying the polymer hydrogel to obtain the polymer gel particles; the monomers include acrylamide, acrylic acid, N-(hydroxymethyl)acrylamide, and 2-acrylamide-2-methylpropanesulfonic acid; the crosslinking agent includes methacrylated lignin sulfonate and / or N,N'-methylenebisacrylamide. The preparation method of the present invention is simple, and the polymer gel particles prepared by the method have a unique double-crosslinked domain structure, excellent mechanical properties, excellent temperature and salt resistance, and are suitable for high-temperature and high-salinity reservoir profile control and water plugging.

Description

Technical Field

[0001] The present invention relates to the technical fields of oilfield chemistry and high-temperature and high-salt oil reservoir profile control and water plugging, and in particular to a preparation method, product and application of polymer gel particles with enhanced mechanical properties through a double-crosslinked domain structure. Background Art

[0002] As oilfield development deepens, long-term waterflooding operations lead to the formation of highly permeable channels within the reservoir, gradually increasing the water-to-oil ratio and increasing the costs of subsequent processing and separation. Furthermore, water flooding can lead to uneven fluid distribution within the reservoir, resulting in low waterflooding efficiency and even ineffective circulation, which in turn reduces oil recovery efficiency. To address this issue, pre-crosslinked gel particles, an effective profile control and water plugging material, absorb water and swell within the reservoir, blocking high-permeability areas and promoting water flow to low-permeability zones, thereby increasing crude oil recovery.

[0003] Pre-crosslinked gel particles are a three-dimensional cross-linked polymer network system synthesized in-house. They can be injected into oil reservoirs to plug high-permeability channels, improving water flooding sweep efficiency and oil recovery. However, with the advancement of exploration and development, reservoir conditions are becoming increasingly complex, especially in high-temperature, high-salinity reservoirs. Traditional pre-crosslinked gel particles often suffer from insufficient heat and salt resistance and low mechanical properties, resulting in reduced plugging effectiveness and difficulty meeting the requirements for profile control and water blocking in harsh environments. These particles are poorly stable in high-temperature, high-salinity conditions, have insufficient mechanical properties, and are prone to failure, resulting in failure to achieve the expected profile control and water blocking results.

[0004] Therefore, providing a polymer gel particle with good mechanical properties and high temperature and high salt resistance to improve the shortcomings of traditional pre-crosslinked gel particles under complex reservoir conditions is of great significance to the fields of oilfield chemistry and high temperature and high salt reservoir profile control and water plugging technology. Summary of the Invention

[0005] Based on the above content, the present invention provides a preparation method, product and application of polymer gel particles with enhanced mechanical properties through a double cross-linked domain structure, so as to overcome the problems of insufficient mechanical properties, poor stability in high temperature and high salt environments and easy failure of blocking in existing pre-cross-linked gel particles.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is a method for preparing polymer gel particles, comprising the following steps:

[0008] dissolving a monomer, a cross-linking agent and an initiator in water to carry out a free radical polymerization reaction to obtain a polymer hydrogel; and drying the polymer hydrogel to obtain the polymer gel particles;

[0009] The monomers include acrylamide (AM), acrylic acid (AA), N-(hydroxymethyl)acrylamide (NMA) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS);

[0010] The crosslinking agents include methacrylated lignin sulfonate (MLS) and N,N'-methylenebisacrylamide (MBAA).

[0011] The second technical solution of the present invention is a polymer gel particle prepared according to the above preparation method.

[0012] The third technical solution of the present invention is the application of the above-mentioned polymer gel particles in profile control and water plugging in high-temperature and high-salinity oil reservoirs.

[0013] A fourth technical solution of the present invention is a profile control and water plugging agent suitable for high-temperature and high-salinity oil reservoirs, the raw materials of which include the above-mentioned polymer gel particles.

[0014] The present invention discloses the following technical effects:

[0015] The polymer gel particles of the present invention have a unique double cross-linked domain structure and excellent mechanical properties, including excellent elastic modulus (G′=48478Pa), high strength (0.14MPa) and excellent toughness (2.96MJ·m -3 ).

[0016] The preparation process of the polymer gel particles with a double cross-linked domain structure of the present invention is simpler, and the particles have excellent temperature and salt resistance. 4 The gel swelling ratio can reach 3.45 under the conditions of 1% (mg / L) solution and 140℃.

[0017] After the polymer gel particles with a double-crosslinked domain structure of the present invention are injected into the formation as a profile control and water plugging agent, the gel particles can block water in the high permeability area, improve the heterogeneity of the formation, increase the water flooding swept area, and thus achieve the effect of improving the recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 This is a schematic diagram of the process flow for preparing polymer gel particles having a double-crosslinked domain structure according to the present invention.

[0020] Figure 2This is the SEM image of the PAANA-L1B1 hydrogel in Example 2.

[0021] Figure 3 FT-IR images of the PAANA-L1B1 hydrogel in Example 2, the PAANA-L1B0 hydrogel in Comparative Example 1, and the PAANA-L0B1 hydrogel in Comparative Example 2.

[0022] Figure 4 This is a diagram showing the plugging performance of PAANA-L1B1 gel particles in Example 2. DETAILED DESCRIPTION

[0023] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0024] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0025] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0026] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0027] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0028] The "room temperature" mentioned in the present invention, unless otherwise specified, refers to 20-30°C.

[0029] In order to overcome this shortcoming, the present invention proposes polymer gel particles based on a double-crosslinked domain network structure. By introducing two crosslinking agents (MLS and MBAA), a double-crosslinked structure is formed, which not only ensures the flexibility and water absorption of the hydrogel, but also significantly improves its mechanical strength and high temperature and high salt resistance. The double-crosslinked domain network structure effectively enhances the stability of the hydrogel in the high-temperature and high-salt oil reservoir environment, enabling it to maintain an excellent sealing effect in complex oil reservoirs, thereby greatly improving the recovery rate of the oil reservoir. Therefore, the polymer gel particles with a double-crosslinked domain structure, by virtue of their excellent mechanical properties and high temperature and high salt resistance, significantly improve the shortcomings of traditional pre-crosslinked gel particles under complex oil reservoir conditions, and become an ideal material for profile control and water blocking in high-temperature and high-salt composite oil reservoirs, and have broad application prospects.

[0030] A first aspect of the present invention provides a method for preparing polymer gel particles, comprising the following steps:

[0031] dissolving a monomer, a cross-linking agent and an initiator in water to carry out a free radical polymerization reaction to obtain a polymer hydrogel; and drying the polymer hydrogel to obtain the polymer gel particles;

[0032] The monomers include acrylamide (AM), acrylic acid (AA), N-(hydroxymethyl)acrylamide (NMA) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS);

[0033] The cross-linking agent includes methacrylated lignin sulfonate (MLS) and / or N,N'-methylenebisacrylamide (MBAA).

[0034] In a specific embodiment, the monomer may be first dissolved in water and nitrogen gas may be introduced to remove air from the solution. Then, an initiator may be added to the solution, and the solution may be stirred while nitrogen gas is introduced, and then a free radical polymerization reaction may be carried out.

[0035] In a preferred embodiment of the present invention, the concentration of the monomers in the mixed solution for the free radical polymerization reaction is 15 wt % to 30 wt %.

[0036] In a preferred embodiment of the present invention, the initiator is at least one of potassium persulfate, ammonium persulfate and azobisisobutylimidazoline hydrochloride.

[0037] In a preferred embodiment of the present invention, the mass ratio of acrylamide, acrylic acid, N-(hydroxymethyl)acrylamide and 2-acrylamide-2-methylpropanesulfonic acid is 5:3:1:1.

[0038] In a preferred embodiment of the present invention, the added amount of the cross-linking agent is 1%-4% of the mass of the monomer; when the cross-linking agent is a mixture of methacrylated lignin sulfonate and N,N'-methylenebisacrylamide, the mass ratio of methacrylated lignin sulfonate to N,N'-methylenebisacrylamide is (1-3):1.

[0039] When the cross-linking agent is a mixture of MLS and MBAA, the mass ratio of the two, MLS:MBAA, is (1-3):1, which can be 1:1, 2:1 or 3:1. At this time, the amount of MBAA added to the cross-linking agent is 1wt% of the monomer mass; when the cross-linking agent is a single MLS or a single MBAA, the amount of the cross-linking agent MLS or MBAA added is 1wt% of the monomer mass respectively.

[0040] In a preferred embodiment of the present invention, the cross-linking agent is a mixture of MLS:MBAA in a mass ratio of 1:1, and the added amount of the cross-linking agent is 2% of the mass of the monomer.

[0041] In a preferred embodiment of the present invention, the added amount of the initiator is 1% of the mass of the monomer.

[0042] In a preferred embodiment of the present invention, the temperature of the free radical polymerization reaction is 55-75° C., and the time is 3-6 hours; the temperature of the drying is 60° C., and the time is 12 hours.

[0043] After the drying, the method further comprises the step of crushing and grinding the mixture to pass through a 100-mesh sieve.

[0044] The second aspect of the present invention provides polymer gel particles prepared according to the above preparation method.

[0045] A third aspect of the present invention provides the use of the above-mentioned polymer gel particles in profile control and water plugging in high-temperature and high-salinity oil reservoirs.

[0046] A fourth aspect of the present invention provides a profile control and water plugging agent suitable for high-temperature and high-salinity oil reservoirs, the raw material of which includes the above-mentioned polymer gel particles.

[0047] The present invention proposes a novel polymer gel particle with enhanced mechanical properties through a double cross-linked domain structure, which has significant advantages in profile control and water blocking, and improving oil field recovery. The gel particle is prepared by a one-pot method, in which methacrylated lignin sulfonate (MLS) is mixed with N,N'-methylenebisacrylamide (MBAA) cross-linker and monomer, and a free radical polymerization reaction is performed in an aqueous solution to generate a polymer hydrogel (PAANA-L x B y), and then dried, crushed, ground and screened to obtain uniform gel particles. MLS, as a macromolecular cross-linking agent, can form low-density cross-linking points in the hydrogel network, and then construct a three-dimensional network structure with loose and flexible characteristics, thereby giving the hydrogel good toughness, water absorption and expansibility, and effectively improving its fracture resistance and ductility. The small molecule cross-linking agent MBAA, through its structure with multiple cross-linking sites, prompts the hydrogel to form a high-density cross-linked network, significantly enhancing the mechanical strength, heat resistance and stability of the hydrogel in complex oil reservoir environments. The double cross-linked domain structure enables the polymer gel particles to maintain high mechanical strength and stability in high-temperature and high-salt environments, effectively solving the problems of poor stability and insufficient mechanical properties of traditional pre-cross-linked gel particles. The preparation method is simple in process, can maintain good sealing effect and water drive control performance under complex oil reservoir conditions, significantly improves the recovery rate of complex oil reservoirs, and has important application value.

[0048] Unless otherwise specified, the technical solutions described in the present invention are all conventional solutions in the field, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0049] The preparation steps of methacrylated lignin sulfonate (MLS) used in the examples of the present invention are as follows:

[0050] First, sodium lignin sulfonate (SLS, 3.5 g), methacrylic anhydride (MAA, 8.5 g), and N,N-diisopropylethylamine (DIPEA, 1 g) were dissolved in 60 mL of deionized water. The solution was heated to 70°C and stirred for 24 hours. After cooling to room temperature, the reaction mixture was poured into ethanol and washed three times with excess ethanol to obtain a brown precipitate. The precipitate was then freeze-dried in a vacuum freeze dryer to obtain methacrylated lignin sulfonate, which was then stored in a refrigerator until use.

[0051] The test methods involved in the present invention are as follows: the swelling rate test refers to the GB / T 1033.1-2008 standard, the rheological property test refers to the ISO 11443:2006 standard, and the uniaxial compression property test refers to the GB / T 1041-2008 standard.

[0052] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0053] Example 1

[0054] A method for preparing polymer gel particles having a double cross-linked domain structure, comprising the following steps:

[0055] Step 1: Dissolve 5g of acrylamide, 3g of acrylic acid, 1g of N-(hydroxymethyl)acrylamide, and 1g of 2-acrylamido-2-methylpropanesulfonic acid in 40mL of deionized water and stir with a magnetic stirrer until completely dissolved. Then, add 0.1g of methacrylated ligninsulfonate and 0.1g of N,N'-methylenebisacrylamide to the mixture. Nitrogen is continuously injected for 15 minutes while stirring to remove oxygen from the mixture.

[0056] Step 2: Then, 0.1 g of potassium persulfate was added to the above mixed solution and stirring was continued until the initiator was completely dissolved, while nitrogen was continuously introduced into the mixed solution for 15 minutes.

[0057] Step 3: Pour the completely dissolved mixed solution into a glass bottle, transfer it to a 55°C forced air drying oven to react for 4 hours to obtain a polymer hydrogel, then dry it in a 60°C oven for 12 hours, and then crush and grind it through a 100-mesh sieve to obtain polymer gel particles with a double-cross-linked domain structure.

[0058] The process flow diagram of preparing polymer gel particles with double cross-linked domain structure in this embodiment is as follows: Figure 1 shown.

[0059] Example 2

[0060] The only difference from Example 1 is that the reaction temperature in step 3 is 65° C.; the remaining steps and parameters are the same as those in Example 1. The polymer hydrogel prepared in this example is labeled PAANA-L1B1.

[0061] Figure 2 The SEM images of the PAANA-L1B1 hydrogel prepared in Example 2 at different magnifications are shown below: Figure 2 It can be seen that the interior of the gel presents an ordered porous structure, which helps to regulate fluid flow, thereby increasing the oil-water ratio and improving the recovery rate. Figure 2 Middle (b) is a high-magnification magnified image of the PAANA-L1B1 hydrogel, where it can be observed that the internal network of the gel is arranged in an orderly manner and evenly distributed.

[0062] Figure 3 FT-IR image of PAANA-L1B1 hydrogel prepared in Example 2; Figure 3 It can be seen that 2934cm -1 The peak at 1620 cm corresponds to the symmetrical stretching vibration of the -CH2 group. -1 、1181cm -1 and 1038cm -1The peaks at 1660 cm-1 are attributed to the vinyl C=C stretching vibration, the symmetric stretching vibration of S=O, and the CO stretching vibration. -1 With PAANA-L x B y As the MLS content in the hydrogel increases, the peak areas of S=O, -C=O and CO groups also increase. The FTIR spectrum of PAAN-L0B1 is similar to that of other PAAN-L x B y Comparison of the FTIR spectra of the hydrogels (PAAN-L1B0 and PAAN-L1B1) showed that there were significant differences between the two spectra. In addition, the changes in the characteristic absorption peaks (such as vinyl and carbonyl groups) indicated that PAAN-L x B y MLS and MBA cross-linking mechanisms exist in the hydrogel.

[0063] Note: To simplify understanding, the prepared hydrogel is named PAANA-L x B y , where L and B represent the cross-linking agents MLS and MBAA, respectively. x and y represent the mass ratio of MLS to MBAA.

[0064] Example 3

[0065] The only difference from Example 1 is that the reaction temperature in step 3 is 75° C.; the remaining steps and parameters are the same as those in Example 1.

[0066] Example 4

[0067] The only difference from Example 2 is that the amount of methacrylated lignin sulfonate added in step 1 is 0.2 g; the remaining steps and parameters are the same as those in Example 1.

[0068] Example 5

[0069] The only difference from Example 2 is that the amount of methacrylated lignin sulfonate added in step 1 is 0.3 g; the remaining steps and parameters are the same as those in Example 1.

[0070] Comparative Example 1

[0071] The only difference from Example 2 is that the addition of N,N'-methylenebisacrylamide in step 1 is omitted; the remaining steps and parameters are the same as those in Example 2. The prepared polymer hydrogel is labeled PAAN-L1B0.

[0072] Comparative Example 2

[0073] The only difference from Example 2 is that the addition of methacrylated lignin sulfonate in step 1 is omitted; the remaining steps and parameters are the same as those in Example 2. The resulting polymer hydrogel is labeled PAAN-LOB1.

[0074] The test results are shown in Table 1:

[0075] Table 1

[0076]

[0077]

[0078] Plugging performance test:

[0079] The experiment used a natural rock core with a diameter of 2.51 cm and a length of 5.02 cm for fracture design, and a rough fracture surface was created using the Brazilian splitting test. To create a 0.5 mm crack in the core and prevent closure, stainless steel plates were clamped on both sides of the core, and a hole was drilled at the entrance to improve injection capacity. The experimental steps are as follows:

[0080] (1) Place the crushed core in a holder and load the surrounding pressure to maintain 3 MPa higher than the injection pressure. Inject 2% NaCl solution at a rate of 0.5 mL / min until the injection pressure and flow rate are stable. Calculate the permeability before plugging (K) using Darcy's law. b ).

[0081] (2) Inject 2% PAANA-L1B1 gel particle solution (carried by guar gum) at the same injection rate until the injection pressure stabilizes and particles are observed to flow out of the outlet. The core temperature is raised to 80°C and aged for 24 hours.

[0082] (3) Re-inject 2% NaCl solution at a rate of 0.5 mL / min until the pressure and flow rate stabilize and gel particles are observed flowing out of the outlet, then stop the process;

[0083] (4) Then the core temperature was raised to 120°C and aged for 24 h. 2% NaCl solution was injected for the third time at a rate of 0.5 mL / min, and the permeability after plugging (K a The maximum pressure achieved during each process was recorded as the breakthrough pressure, and the plugging effect of the gel particles was evaluated by the breakthrough pressure gradient and the plugging efficiency (E).

[0084] E=(K b -K a ) / K b ×100 (1)

[0085] The blocking performance of the PAANA-L1B1 gel particles in Example 2 was tested, and the results were as follows: Figure 4To evaluate the effectiveness of reservoir fracture plugging, 0.5 mm steel plates were added to natural cores to simulate fractures, and then filled with 100 mesh PAANA-L1B1 gel particles. Figure 4 The results show that the first injection of 2 wt% NaCl solution resulted in high permeability and stable pressure changes in the fractures. After the injection of the PAANA-L1B1 gel particles, the injection pressure rapidly rose to a maximum of 194 psi / ft, then decreased and stabilized at 168 psi / ft as the particles flowed out. The core temperature was raised to 80°C, and the gel particles expanded further. After the second injection of NaCl solution, the breakthrough pressure gradient was 260 psi / ft, and the stable pressure gradient was 195 psi / ft. The core temperature was raised again to 120°C, and after the third injection of NaCl solution, the breakthrough pressure gradient was 235 psi / ft, and the stable pressure gradient was 179 psi / ft. After the injection of the PAANA-L1B1 gel particles, the plugging efficiency was 96.8%. After the second injection of NaCl solution, the plugging efficiency increased to 98.1%, and after the third injection of NaCl solution, the plugging efficiency increased to 97.2%. These results demonstrate that the PAANA-L1B1 gel particles prepared in Example 2 can effectively plug the high-permeability layer and expand at high temperatures, forming a stable plug.

[0086] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing polymer gel particles, characterized in that: The following steps are involved: dissolving a monomer, a cross-linking agent and an initiator in water to carry out a free radical polymerization reaction to obtain a polymer hydrogel; and drying the polymer hydrogel to obtain the polymer gel particles; The monomers include acrylamide, acrylic acid, N-(hydroxymethyl)acrylamide and 2-acrylamide-2-methylpropanesulfonic acid; The cross-linking agent includes methacrylated lignin sulfonate and N,N'-methylenebisacrylamide; The amount of the cross-linking agent added is 2% of the weight of the monomer; the weight ratio of methacrylated lignin sulfonate to N,N'-methylenebisacrylamide is 1:1; The temperature of the free radical polymerization reaction is 65° C. and the time is 3-6 hours.

2. The preparation method according to claim 1, characterized in that The initiator is at least one of potassium persulfate, ammonium persulfate and azobisisobutylimidazoline hydrochloride.

3. The preparation method according to claim 1, characterized in that The mass ratio of the acrylamide, acrylic acid, N-(hydroxymethyl)acrylamide and 2-acrylamide-2-methylpropanesulfonic acid is 5:3:1:

1.

4. The preparation method according to claim 1, characterized in that The added amount of the initiator is 1% of the mass of the monomer.

5. The preparation method according to claim 1, characterized in that The drying temperature is 60° C. and the drying time is 12 h.

6. The polymer gel particles prepared according to the preparation method according to any one of claims 1 to 5.

7. Use of the polymer gel particles according to claim 6 in profile control and water plugging in high-temperature and high-salinity oil reservoirs.

8. A profile control and water plugging agent suitable for high-temperature and high-salinity oil reservoirs, characterized in that: The raw material comprises the polymer gel particles according to claim 6.

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