A composite weak gel, its preparation method and application

Abstract

The application belongs to the technical field of composite weak gel material, and discloses a composite weak gel material, a preparation method and application thereof, and the preparation method is as follows: step 1, uniformly dispersing graphene oxide in an aqueous solvent to obtain a graphene oxide suspension; step 2, under the action of stirring, adding partially hydrolyzed polyacrylamide to the graphene oxide suspension, adding a covalent bond type crosslinking agent after swelling treatment, and curing treatment to obtain the composite weak gel material; or adding an ionic bond type crosslinking agent to the graphene oxide suspension, adding partially hydrolyzed polyacrylamide under the action of stirring, and then carrying out swelling treatment and curing treatment to obtain the composite weak gel material. The application adopts a physical blending method, does not need to add any other surfactants and additives, and can make the composite weak gel formed by GO and HPAM have high fluid viscosity, good temperature resistance and mechanical properties, the operation process is simple and easy to implement, and the application is extremely suitable for water control and deep profile control of ultra-low permeability reservoirs.

Description

Technical Field

[0001] This invention relates to the field of composite weak gel materials technology, and in particular to a composite weak gel material, its preparation method, and its application. Background Technology

[0002] With declining production in older oilfields, most have now entered the medium-to-high water-cut stage, leading to an accelerated decline in oil production. Long-term water-drive development has exacerbated reservoir heterogeneity, making it difficult to significantly improve oil recovery rates using conventional water injection techniques. In these heterogeneous oilfields, high-permeability zones exhibit extremely high permeability, resulting in massive water production; while ultra-low permeability zones, due to their poor reservoir properties, suffer from small pore throats and high flow resistance, easily leading to flow bypass and blockage phenomena, resulting in significant oil retention. Conventional development techniques can only achieve high production in the initial stages of development and cannot establish a long-term stable production cycle, resulting in a low final oil recovery rate. Using polymers as oil displacement agents in oilfield development has shown that polymer aqueous solutions can block high-permeability zones, thereby reducing water permeability in these areas and helping to reduce water production. Simultaneously, after passing through the formation, polymer molecules are moderately adsorbed on the rock surface, creating residual resistance to subsequently injected water, forcing it to change its flow path and enter medium-, low-, and ultra-low-permeability zones, thus improving oil recovery rates. However, due to the influence of the formation environment, polymers are easily subjected to high shear forces and high temperatures during the process, leading to their degradation. Therefore, improving the viscosity, temperature resistance, and shear strength of polymer aqueous solutions is a current research direction for enhancing oil recovery.

[0003] There are three main types of polymers used: comb-type polymers (KYPAM) have good thickening properties, but their polymerization is extremely difficult and costly; hydrophobic associative polymers (HAP) have a fast gelation rate, but they are difficult to dissolve, and the hydrophobic groups are prone to aggregation due to hydrophobic interactions, leading to molecular chain coiling and a significant decrease in viscosity under high shear; partially hydrolyzed polyacrylamide (HPAM), as a linear water-soluble polymer, has low initial viscosity, good thickening properties, thermal stability, and non-toxic and odorless characteristics. It has broad application prospects in flocculation, thickening, drag reduction, gelation, bonding, and scale inhibition processes in water treatment, petroleum, papermaking, mining, geology, textiles, and construction industries, and is one of the key research hotspots in new materials and polymer materials. Although partially hydrolyzed polyacrylamide has better thermal stability than other electrolytes, it will still decompose under prolonged high-temperature heating, and the molecular chain breakage will lead to a significant decrease in the viscosity of the polymer aqueous solution. Typically, a weakly cross-linked system with a three-dimensional network structure can be formed by cross-linking and polymerization with partially hydrolyzed polyacrylamide using an appropriate cross-linking agent. This system is characterized by intermolecular cross-linking as the main component and intramolecular cross-linking as the secondary component. The cross-linking agent generates chemical bonds between the linear molecular chains of partially hydrolyzed polyacrylamide, causing the linear molecular chains to entangle with each other and form a network structure, thereby improving the gel strength.

[0004] There are many types of crosslinking agents. HPAM can be crosslinked with covalent (aldehyde compounds, phenolic resins, urea-formaldehyde resins, etc.) and ionic (Al) crosslinking systems. 3+ Cr 3+ Zr 4+ Ti 4+ Crosslinking systems. Phenolic resin crosslinking systems possess advantages such as good mechanical properties, excellent durability, and water resistance. The weak gels formed by crosslinking phenolic resin with HPAM exhibit excellent viscoelasticity, making it an effective method for preparing weak gels. However, the raw materials used to synthesize phenolic resin crosslinking agents—formaldehyde, phenol, and resorcinol—are toxic, and the process also suffers from disadvantages such as high cost and slow gelation speed.

[0005] To further reduce costs and accelerate the reaction rate, existing technologies utilize chromium acetate as a crosslinking agent. 3+ When HPAM enters the solution, it promotes intramolecular cross-linking reactions between different branches on the HPAM molecular chain. The molecular chain coils to form a dense coil, and can continue to cross-link with other molecular chains. The increase in cross-linking points leads to the enlargement of the molecular coil, which in turn causes the viscosity of the system to increase rapidly until it stabilizes. However, the temperature resistance and shear resistance of the currently developed weak gels urgently need further improvement.

[0006] Therefore, the present invention provides a composite weak gel material, its preparation method and application. Summary of the Invention

[0007] To address the shortcomings of the prior art, this invention provides a composite weak gel material, its preparation method, and its application.

[0008] The present invention provides a composite weak gel material, its preparation method, and its application, which are achieved through the following technical solutions:

[0009] The first objective of this invention is to provide a method for preparing a composite weak gel material, comprising the following steps:

[0010] Step 1: Graphene oxide is uniformly dispersed in an aqueous solvent to obtain a graphene oxide suspension.

[0011] Step 2: Under stirring, partially hydrolyzed polyacrylamide is added to the graphene oxide suspension to obtain a mixture; after swelling treatment, a covalent crosslinking agent is added, followed by curing treatment to obtain the composite weak gel material.

[0012] Alternatively, an ionic crosslinking agent can be added to the graphene oxide suspension, followed by the addition of partially hydrolyzed polyacrylamide under stirring. After swelling and curing treatments, the composite weak gel material is obtained.

[0013] Furthermore, the ratio of the amount of graphene oxide to the amount of water solvent is 0.1–2 g: 100 mL;

[0014] The ratio of the partially hydrolyzed polyacrylamide to the aqueous solvent is 0.3–0.5 g: 100 mL.

[0015] Furthermore, the ionic crosslinking agent is a chromium acetate crosslinking agent, and the mass ratio of the chromium acetate crosslinking agent to the partially hydrolyzed polyacrylamide is 0.05-0.07:0.3-0.5.

[0016] Furthermore, the covalent crosslinking agent is a mixture of oligophenolic resin crosslinking agent and crosslinking promoter, and the ratio of the oligophenolic resin crosslinking agent and crosslinking promoter to the partially hydrolyzed polyacrylamide is 0.5-0.7 mL: 0.1-0.3 mL: 0.3-0.5 g.

[0017] Furthermore, the oligomeric phenolic resin crosslinking agent is a linear resin synthesized from formaldehyde, phenol, and resorcinol under the action of a catalyst.

[0018] Furthermore, the main components of the cross-linking promoter are thiourea and resorcinol, which have antioxidant effects.

[0019] Furthermore, the temperature of the curing treatment is 65–75°C, and the treatment time is 20–28 hours.

[0020] Furthermore, the stirring process is as follows:

[0021] The graphene oxide suspension is stirred at a stirring rate of 200-300 r / min until a vortex of 1.5-2.0 cm is generated. Then, the partially hydrolyzed polyacrylamide is added. After the addition is completed, the mixture is stirred at a stirring rate of 100-150 r / min for 10-30 min.

[0022] The second objective of this invention is to provide a composite weak gel material prepared by the above-described preparation method.

[0023] A third objective of this invention is to provide an application of the aforementioned composite weak gel material in an oil displacement agent for oilfield development.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] This invention disperses graphene oxide in an aqueous solvent. The surface and boundaries of graphene oxide (GO) contain a large number of oxygen-containing groups such as hydroxyl, carboxyl, and epoxy groups, which enable it to be uniformly dispersed in deionized water to form a homogeneous graphene oxide suspension. Using the graphene oxide suspension as a reinforcing phase and carbon source, after adding partially hydrolyzed polyacrylamide, the partially hydrolyzed polyacrylamide can combine well with the graphene oxide in the graphene oxide suspension. Furthermore, under the crosslinking action of covalent or ionic crosslinking agents, a composite weak gel material with both high viscosity and fluidity is formed.

[0026] This invention employs a physical blending method, without the need for any other surfactants or additives, to create a composite weak gel with high fluid viscosity, good temperature resistance, and mechanical properties from a graphene oxide suspension and partially hydrolyzed polyacrylamide. The process is simple and easy to implement, making it highly suitable for water control and deep profile control in ultra-low permeability reservoirs.

[0027] Compared with single HPAM weak gel, the composite weak gel material prepared by this invention can exert the synergistic effect of GO, HPAM and crosslinking agent, thereby increasing the fluid viscosity of HPAM weak gel by about 25000 mPa·s. In addition, its temperature resistance, shear resistance and chemical stability are also improved. Attached Figure Description

[0028] Figure 1 SEM image of the weak gel prepared in Comparative Example 1 of this invention;

[0029] Figure 2 This is a SEM image of the composite weak gel prepared in Example 4 of the present invention;

[0030] Figure 3 The fluid viscosity diagrams are for the composite weak gels prepared in Comparative Example 1 and Examples 1-8 of this invention.

[0031] Figure 4 Rheological curves of the weak gels in Comparative Example 1 and Example 7;

[0032] Figure 5 These are photographs showing the suspension effect of the weak gels in Comparative Example 1 and Examples 1-8 of the present invention on a glass rod;

[0033] Figure 6 These are photographs showing the suspension effect of the composite weak gels of Comparative Example 6 and Examples 18-23 of the present invention on a glass rod;

[0034] Figure 7 The graph shows the continuous monitoring of the viscosity of the three weak gels (Comparative Example 1, Example 6, and Example 7) over 30 days.

[0035] Figure 8The viscosity changes of the weak gels of Comparative Examples 1-10, Examples 2, 9-12 and Examples 21, 24-27 of this invention under curing conditions at 60-100℃ are shown in the graphs. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0037] This invention provides a composite weak gel material, and its preparation method is as follows:

[0038] Step 1, Preparation of graphene oxide suspension:

[0039] Graphene oxide is uniformly dispersed in an aqueous solvent to obtain a graphene oxide suspension.

[0040] It should be noted that this invention does not limit the specific dispersion method used when dispersing graphene oxide in an aqueous solvent, as long as the graphene oxide is uniformly dispersed in the aqueous solvent to form a homogeneous suspension. Ultrasonic exfoliation can be used for dispersion.

[0041] Step 2, forming a composite weak gel material:

[0042] It should be noted that the crosslinking agent of the present invention can be a covalent crosslinking agent or an ionic crosslinking agent.

[0043] 2.1 When using a covalent crosslinking agent, the following steps are taken to form a composite weak gel material:

[0044] Under stirring, partially hydrolyzed polyacrylamide is added to the graphene oxide suspension to obtain a mixture; after swelling treatment, a covalent crosslinking agent is added, followed by curing treatment to obtain the composite weak gel material.

[0045] The stirring process used in this invention when adding partially hydrolyzed polyacrylamide is as follows:

[0046] First, the graphene oxide suspension is stirred at a stirring rate of 200–300 rpm until a vortex of 1.5–2.0 cm is formed. Then, the partially hydrolyzed polyacrylamide is added. After the addition is complete, the mixture is stirred at a stirring rate of 100–150 rpm for 10–30 minutes to ensure sufficient contact between the partially hydrolyzed polyacrylamide and the graphene oxide suspension. It should be noted that to avoid clumping of the partially hydrolyzed polyacrylamide due to excessively rapid addition, it must be added slowly, completing the addition process in approximately 5–6 minutes.

[0047] This invention does not limit the specific process of swelling treatment, as long as it allows the partially hydrolyzed polyacrylamide to fully contact the graphene oxide suspension and absorb the water solvent in the graphene oxide suspension for swelling. To avoid interference from external factors, during the swelling treatment, the container opening can be sealed with plastic wrap and left to stand at room temperature for 1-3 hours to allow it to swell.

[0048] 2.2 When using an ionic crosslinking agent, the following steps are used to form a composite weak gel material:

[0049] An ionic crosslinking agent is added to the graphene oxide suspension obtained in step 1. Then, under stirring, a portion of hydrolyzed polyacrylamide is added. After swelling and curing treatments are performed sequentially, the composite weak gel material is obtained.

[0050] The stirring process used when adding partially hydrolyzed polyacrylamide is as follows:

[0051] First, the graphene oxide suspension containing the ionic crosslinking agent is added while stirring at a rate of 200–300 rpm to ensure uniform mixing. Once a vortex of 1.5–2.0 cm is formed in the graphene oxide suspension containing the ionic crosslinking agent, partially hydrolyzed polyacrylamide is added. After addition, the mixture is stirred at a rate of 100–150 rpm for 10–30 minutes to ensure sufficient contact between the partially hydrolyzed polyacrylamide and the graphene oxide suspension. It should be noted that to prevent clumping of the partially hydrolyzed polyacrylamide due to rapid addition, it must be added slowly, completing the addition process in approximately 5–6 minutes.

[0052] This invention does not limit the specific process of swelling treatment, as long as it allows the partially hydrolyzed polyacrylamide to fully contact the graphene oxide suspension and absorb the water solvent in the graphene oxide suspension for swelling. To avoid interference from external factors, during the swelling treatment, the container opening can be sealed with plastic wrap and left to stand at room temperature for 1-3 hours to allow it to swell, after which it can be directly subjected to curing treatment.

[0053] Example 1

[0054] This embodiment provides a composite weak gel material, and its preparation method is as follows:

[0055] Weigh 0.0050g of GO and add it to 100mL of deionized water. Disperse the GO by ultrasonication at 480-550W for 2 hours to form a uniform dispersion, thus obtaining a graphene oxide suspension.

[0056] Subsequently, the graphene oxide suspension was stirred at a stirring rate of 250 r / min using a magnetic stirrer until a vortex of 1.5–2.0 cm was formed. Then, 0.4000 g of HPAM was slowly added over 5–6 minutes to avoid agglomeration of HPAM due to excessively rapid addition. After the HPAM was added, the stirring rate was reduced to 130 r / min and the stirring time was 15 minutes. The mixture was then allowed to stand for 2 hours to swell, resulting in a swollen gel.

[0057] Then, using a mixture of oligophenolic resin crosslinking agent and crosslinking promoter as a covalent crosslinking agent, 0.6 mL of oligophenolic resin crosslinking agent and 0.2 mL of crosslinking promoter were added sequentially to the gel liquid after the above swelling treatment using a pipette, and stirred to obtain a viscous gel-like liquid.

[0058] Finally, the viscous gel-like liquid obtained above is transferred to an aging bottle, sealed, and placed in a 70°C oven for curing to form a gel for 24 hours, thus obtaining a brown viscous GO / HPAM composite weak gel.

[0059] It should be noted that in this embodiment, the oligophenolic resin crosslinking agent used is a linear resin synthesized from formaldehyde, phenol, and resorcinol under the action of a catalyst. The preparation method of the above-mentioned oligophenolic resin crosslinking agent adopts the alkaline catalytic method: First, according to the molar ratio of phenol, resorcinol, and formaldehyde of 1:1:3, the corresponding masses of phenol, resorcinol, and formaldehyde are weighed and set aside. Then, phenol and resorcinol are mixed and heated to 45-50°C, and stirred to ensure thorough mixing. Subsequently, 40% NaOH solution is added, and the mixture is kept at a constant temperature of 50-60°C and stirred for 20 minutes. Then, 3 / 4 of the weighed formaldehyde solution is slowly added dropwise, the temperature is raised to 70-75°C, and the temperature is kept constant for 30 minutes. Then, 2% Ba(OH)2 and the remaining 1 / 4 of the formaldehyde solution are added, the temperature is set to 80-85°C, and the reaction is kept constant for 1.5-2 hours. After cooling, a transparent light yellow solution with a pungent odor is obtained, which is the oligophenolic resin crosslinking agent.

[0060] In this embodiment, the main components of the crosslinking promoter are thiourea and resorcinol, which have the functions of accelerating the reaction rate and anti-oxidation. The preparation method of the crosslinking promoter used in this embodiment is as follows: First, 100 mL of deionized water is measured and 0.5% sodium bisulfite is added. The mixture is stirred at room temperature until completely dissolved. Then, thiourea and resorcinol (total amount of 16%) are added at a ratio of 1:1. The temperature is raised to 35°C and stirred for 1 to 1.5 h until completely dissolved to obtain a transparent, colorless solution with a pungent odor, which is the crosslinking promoter.

[0061] Example 2

[0062] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 1 only in that:

[0063] In this embodiment, the amount of GO used is 0.0100g.

[0064] Example 3

[0065] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 1 only in that:

[0066] In this embodiment, the amount of GO used is 0.0500g.

[0067] Example 4

[0068] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 1 only in that:

[0069] In this embodiment, the amount of GO used is 0.1000g.

[0070] Example 5

[0071] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 1 only in that:

[0072] In this embodiment, the amount of GO used is 0.5000g.

[0073] Example 6

[0074] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 1 only in that:

[0075] In this embodiment, the amount of GO used is 1.0000g.

[0076] Example 7

[0077] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 1 only in that:

[0078] In this embodiment, the amount of GO used is 1.5000g.

[0079] Example 8

[0080] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 1 only in that:

[0081] In this embodiment, the amount of GO used is 2.0000g.

[0082] Example 9

[0083] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 1 only in that:

[0084] In this embodiment, the amount of GO used was 0.0100g; the curing temperature was 60℃.

[0085] Example 10

[0086] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 1 only in that:

[0087] In this embodiment, the amount of GO used is 0.0100g; the curing temperature is 80℃.

[0088] Example 11

[0089] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 1 only in that:

[0090] In this embodiment, the amount of GO used is 0.0100g; the curing temperature is 90℃.

[0091] Example 12

[0092] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 1 only in that:

[0093] In this embodiment, the amount of GO used is 0.0100g; the curing temperature is 100℃.

[0094] Example 13

[0095] This embodiment provides a composite weak gel material, and its preparation method is as follows:

[0096] In this embodiment, chromium acetate is used as a crosslinking agent. 0.0200g of chromium acetate is weighed and added to 100mL of deionized water. The mixture is stirred and dissolved to form a uniform blue-green solution.

[0097] Subsequently, the blue-green solution was stirred at a stirring rate of 250 r / min using a magnetic stirrer until a vortex of 1.5-2.0 cm was formed. Then, 0.4000 g of HPAM was slowly added over 5-6 minutes to avoid clumping of HPAM due to excessively rapid addition. After the HPAM was added, the stirring rate was reduced to 130 r / min and the stirring time was 15 minutes. The mixture was then allowed to stand and swell for 2 hours to obtain a viscous gel-like liquid.

[0098] Then, the viscous gel-like liquid obtained above is transferred to an aging bottle, sealed, and placed in a 70°C oven for curing to form a gel for 12 hours, thus obtaining a lake-blue viscous HPAM weak gel.

[0099] Example 14

[0100] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 13 only in that:

[0101] In this embodiment, the amount of chromium acetate used is 0.0400g.

[0102] Example 15

[0103] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 13 only in that:

[0104] In this embodiment, the amount of chromium acetate used is 0.0600g.

[0105] Example 16

[0106] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 13 only in that:

[0107] In this embodiment, the amount of chromium acetate used is 0.0800g.

[0108] Example 17

[0109] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 13 only in that:

[0110] In this embodiment, the amount of chromium acetate used is 1.0000g.

[0111] Example 18

[0112] This embodiment provides a composite weak gel material, and its preparation method is as follows:

[0113] Weigh 0.0050g of GO and add it to 100mL of deionized water. Disperse the GO by ultrasonication at 480-550W for 2 hours to form a uniform dispersion, thus obtaining a graphene oxide suspension.

[0114] In this embodiment, chromium acetate was used as a crosslinking agent. 0.0600g of chromium acetate was weighed and added to the graphene oxide suspension obtained above. Then, the graphene oxide suspension containing chromium acetate was stirred at a stirring rate of 250r / min using a magnetic stirrer to ensure that the chromium acetate was fully dissolved in the graphene oxide suspension. After stirring continued until a vortex of 1.5-2.0cm was generated, 0.4000g of HPAM was slowly added and the addition was completed within 5-6 minutes to avoid the formation of clumps due to the excessively fast addition rate of HPAM. After the HPAM was added, the stirring rate was reduced to 130r / min and the stirring time was 15 minutes. After standing and swelling for 2 hours, a viscous gel-like liquid was obtained.

[0115] Then, the viscous liquid of the above-obtained lake-blue viscous HPAM weak gel is transferred to an aging bottle, sealed, and placed in a 70°C oven for curing to form a gel for 24 hours.

[0116] Example 19

[0117] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 18 only in that:

[0118] In this embodiment, the amount of GO used is 0.0500g;

[0119] Example 20

[0120] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 18 only in that:

[0121] In this embodiment, the amount of GO used is 0.1000g.

[0122] Example 21

[0123] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 18 only in that:

[0124] In this embodiment, the amount of GO used is 0.2000g.

[0125] Example 22

[0126] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 18 only in that:

[0127] In this embodiment, the amount of GO used is 0.4000g.

[0128] Example 23

[0129] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 18 only in that:

[0130] In this embodiment, the amount of GO used is 0.5000g.

[0131] Example 24

[0132] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 18 only in that:

[0133] In this embodiment, the amount of GO used is 0.2000g; the curing temperature is 60℃.

[0134] Example 25

[0135] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 18 only in that:

[0136] In this embodiment, the amount of GO used is 0.2000g; the curing temperature is 80℃.

[0137] Example 26

[0138] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 18 only in that:

[0139] In this embodiment, the amount of GO used is 0.2000g; the curing temperature is 90℃.

[0140] Example 27

[0141] This embodiment provides a composite weak gel material, and its preparation method differs from that of Example 18 only in that:

[0142] In this embodiment, the amount of GO used is 0.2000g; the curing temperature is 100℃.

[0143] Comparative Example 1

[0144] This comparative example provides a weak gel material, and its preparation method is as follows:

[0145] Measure 100 mL of deionized water and stir it at a stirring rate of 250 r / min using a magnetic stirrer until a vortex of 1.5–2.0 cm is formed. Then, slowly add 0.4000 g of HPAM over 5–6 minutes to avoid clumping of HPAM due to rapid addition. After the HPAM is added, reduce the stirring rate to 130 r / min and stir for 15 minutes. Let it stand for 2 hours to swell and obtain the swollen gel.

[0146] Add 0.6 mL of oligophenolic crosslinking agent and 0.2 mL of crosslinking accelerator to the above gel solution in sequence using a pipette, and stir to obtain a viscous gel-like liquid.

[0147] The obtained gel solution was transferred to an aging bottle, sealed, and placed in a 70°C oven for 24 hours to cure into a gel, thus obtaining a brown, viscous HPAM weak gel.

[0148] Comparative Example 2

[0149] This comparative example provides a weak gel material, and its preparation method differs from that of Comparative Example 1 only in that:

[0150] The curing temperature is 60℃.

[0151] Comparative Example 3

[0152] This comparative example provides a weak gel material, and its preparation method differs from that of Comparative Example 1 only in that:

[0153] The curing temperature is 80℃.

[0154] Comparative Example 4

[0155] This comparative example provides a weak gel material, and its preparation method differs from that of Comparative Example 1 only in that:

[0156] The curing temperature is 90℃.

[0157] Comparative Example 5

[0158] This comparative example provides a weak gel material, and its preparation method differs from that of Comparative Example 1 only in that:

[0159] The curing temperature is 100℃.

[0160] Comparative Example 6

[0161] This comparative example provides a weak gel material, and its preparation method differs from that of Example 18 only in that:

[0162] GO is not added in this comparative example.

[0163] Comparative Example 7

[0164] This comparative example provides a weak gel material, and its preparation method differs from that of Comparative Example 6 only in that:

[0165] The curing temperature is 60℃.

[0166] Comparative Example 8

[0167] This comparative example provides a weak gel material, and its preparation method differs from that of Comparative Example 6 only in that:

[0168] The curing temperature is 80℃.

[0169] Comparative Example 9

[0170] This comparative example provides a weak gel material, and its preparation method differs from that of Comparative Example 6 only in that:

[0171] The curing temperature is 90℃.

[0172] Comparative Example 10

[0173] This comparative example provides a composite weak gel material, and its preparation method differs from that of Comparative Example 6 only in that:

[0174] The curing temperature is 100℃.

[0175] Experimental Section

[0176] (I) SEM Testing

[0177] The cross-sectional morphology of the HPAM weak gels prepared in Comparative Example 1 and Example 4 was measured by SEM, and the test results are as follows: Figure 1 and Figure 2 As shown.

[0178] Figure 1 The SEM image of the HPAM weak gel prepared for Comparative Example 1 shows that the cross-sectional morphology of the HPAM weak gel without GO in Comparative Example 1 exhibits numerous three-dimensional pores with pore sizes ranging from 11.0 to 134 μm and a maximum thickness of 13.5 μm. In addition, there are some linear materials connecting the pores, which are three-dimensional networks formed by HPAM molecular chains during cross-linking. The uneven distribution of these pores on the cross-section is caused by the non-uniform pores formed during freeze-drying.

[0179] Figure 2 The SEM image of the GO / HPAM composite weak gel prepared in Example 4 shows that a large number of three-dimensional pores of varying sizes appeared in the cross-section of the HPAM composite weak gel with 0.1000% GO added in Example 4. The largest diameter was measured to be 233.5 μm, and the smallest diameter was 7.7 μm. Furthermore, the cross-sectional thickness was less than 5.0 μm, and a large amount of lamellar material (GO) was observed to enter the pores. The two-dimensional lamellar GO was connected to the HPAM gel, causing the pores to expand and the cross-sectional walls to thin during the freeze-drying process due to the effect of GO.

[0180] (II) Viscosity Test

[0181] The viscosities of the composite weak gels prepared in Examples 1-8 and Comparative Example 1 were tested in this invention, and the test results are as follows: Figure 3 As shown, curve Test1 is the viscosity test result of the composite weak gel using a digital rotational viscometer NDJ-1S, and curve Test2 is the viscosity test result of the composite weak gel using an intelligent gel analyzer. The intelligent gel analyzer used in this invention is based on existing technology (Xi'an Petroleum University. A device and evaluation method for evaluating gel performance: 201611189905.3 [P]. 2017-11-14).

[0182] Depend on Figure 3It can be seen that different mass concentrations of GO have a significant impact on the viscosity of the composite weak gel. When the GO mass concentration is low (0.0001–0.0100%), the viscosity of the HPAM composite weak gel decreases with increasing GO mass concentration. When the GO mass concentration is between 0.0100 and 0.0500%, the viscosity of the composite weak gel fluctuates between 16000 and 19000 mPa·s. When the GO mass concentration increases to between 0.0500 and 1.5000%, the viscosity increases to 88041 mPa·s. Further increasing the GO mass concentration leads to gel agglomeration and loss of fluidity. Therefore, increasing the GO mass concentration from 0% to 1.5000% results in a viscosity increase of approximately 25000 mPa·s compared to the original viscosity, significantly increasing the viscosity of the composite weak gel.

[0183] (III) Shear Performance Test

[0184] This invention uses the weak gels of Comparative Example 1 and Example 7 as examples, and tests their rheological curves respectively. The test results are as follows: Figure 4 As shown.

[0185] Depend on Figure 4 It can be seen that, compared to the pure weak gel without GO in Comparative Example 1, the HPAM composite weak gel with 1.5000% GO in Example 7 of this invention exhibits excellent shear resistance. That is, at low shear rates, the apparent viscosity of the composite weak gel is much higher than that of the weak gel without GO. The reason for the high apparent viscosity at low shear rates is mainly due to the three-dimensional network structure formed by GO, HPAM, and the crosslinking agent, resulting in a higher structural viscosity than the weak gel without GO. This high viscosity at low shear rates is beneficial for forming a temporary plugging layer on the surface of ultra-low permeability wellbores, thus stabilizing the wellbore. As the shear rate increases, the network structure is disrupted, and the viscosity gradually decreases, which also helps to accelerate the weak gel's penetration into deep formations.

[0186] (iv) Liquidity Testing

[0187] This invention takes the weak gels of Comparative Example 1 and Examples 1-8, namely weak gels formed by polymerization of different mass concentrations of GO and HPAM and oligophenolic crosslinking agents, as examples. They were suspended on glass rods, and their suspension effects were observed. The suspension effects are as follows: Figure 5 As shown.

[0188] Depend on Figure 5It can be seen that when the GO concentration is low, it disperses extremely uniformly in deionized water, and the gel is light brown in color. However, as the GO concentration increases, the gel color darkens until it becomes dark black. Simultaneously, the inventors found that the synthesized weak gel exhibited agglomeration, mainly because the increased GO content led to uneven dispersion in deionized water, with many layers even stacking together, resulting in GO being distributed within the weak gel in single-layer, multi-layer, and aggregated forms. In Example 7, when the GO concentration was 1.5%, the fluid viscosity of the composite weak gel reached a maximum of 88041 mPa·s. The inventors speculate that this is because the introduction of GO can react with the carboxyl groups of HPAM, resulting in more cross-linking points and increasing the fluid viscosity. Although the viscosity of the composite weak gel increased significantly, it can still be seen from the image that it can be suspended on a glass rod, indicating that it has fluidity.

[0189] This invention takes the composite weak gels of Examples 18-23, namely weak gels formed by polymerization of different mass concentrations of GO, HPAM, and chromium acetate crosslinking agent, as examples. The gels were suspended on glass rods, and their suspension effects were observed. The suspension effects are as follows: Figure 6 As shown.

[0190] Depend on Figure 6 It can be seen that the viscosity of the synthesized weak gel system continuously increases with the increase of GO mass concentration. In Example 23, when the GO mass concentration was increased to 0.5% based on crosslinking with chromium acetate, the fluid viscosity of the composite weak gel increased by approximately 30,000 mPa·s compared to the original viscosity. This is because Cr... 3+ After hydrolysis and polymerization to form polynuclear hydroxybridged complexes, HPAM undergoes cross-linking polymerization with these complexes. Simultaneously, the introduction of GO increases the number of cross-linking points, and their synergistic effect improves the fluid viscosity. Furthermore, the system retains fluidity even at maximum viscosity. The inventors discovered that using chromium acetate as a cross-linking agent significantly reduces the amount of GO required, simplifying the process and lowering application costs.

[0191] (V) Gel stability test

[0192] This invention uses three weak gels—Examples 6, 7, and Comparative Example 1—as examples, and continuously monitors their viscosity for 30 days. The monitoring results are as follows: Figure 7 As shown.

[0193] Depend on Figure 7As shown, in Comparative Example 1, without the addition of GO, the initial viscosity of the weak gel was very high, but it decreased with prolonged storage at room temperature. This was mainly because HPAM degraded over time, disrupting the network structure of the weak gel and reducing the viscosity to approximately half of its initial viscosity. In Examples 6 and 7, the viscosity change curves of the composite weak gels with GO mass concentrations of 1.0% and 1.5% showed relatively stable trends, with smaller viscosity decreases. The 30-day storage period did not significantly affect the viscosity of the composite weak gel, indicating that the combined effect of the oxygen-containing groups on GO, HPAM, and the crosslinking agent slowed down polymer chain degradation. Compared to the effect of the pure crosslinking agent, the addition of GO significantly improved the chemical stability of the HPAM composite weak gel.

[0194] (vi) Temperature resistance analysis

[0195] like Figure 8 As shown in Figure a, the weak gel is polymerized from a covalent crosslinking agent. By comparing Comparative Examples 1-5 and Examples 9-12, it was found that the viscosity of the composite weak gel system containing 0.01% GO hardly changed when the temperature was increased to 100°C. However, the viscosity of the HPAM weak gel without GO decreased by approximately 30,000 mPa·s when the temperature was increased from 70°C to 100°C.

[0196] like Figure 8 As shown in b, the weak gel is polymerized using an ionic crosslinking agent. By comparing the composite weak gel systems containing 0.2% GO (Examples 21 and 24-27), it can be seen that the viscosity of the composite weak gel containing 0.2% GO decreases by approximately 20,000 mPa·s when the temperature rises to 90°C. When the temperature rises to 95-100°C, the weak gel system dehydrates.

[0197] By comparing the HPAM weak gel without added GO (Comparative Examples 6-10), it can be seen that the viscosity of the HPAM weak gel without added GO decreased by approximately 23,000 mPa·s when the temperature was raised to 80℃. The system dehydrated directly when the temperature was only raised to 85-90℃. Therefore, compared to the original weak gel, the addition of GO is beneficial to improving the temperature resistance of the HPAM composite weak gel system in both types of composite weak gels formed by the two crosslinking agents.

[0198] Obviously, the above embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a composite weak gel material, characterized in that, Includes the following steps: Step 1: Graphene oxide is uniformly dispersed in an aqueous solvent to obtain a graphene oxide suspension. Step 2: Under stirring, partially hydrolyzed polyacrylamide is added to the graphene oxide suspension to obtain a mixture; after swelling treatment, a covalent crosslinking agent is added, followed by curing treatment to obtain the composite weak gel material. Alternatively, an ionic crosslinking agent can be added to the graphene oxide suspension, followed by the addition of partially hydrolyzed polyacrylamide under stirring. After swelling and curing treatments, the composite weak gel material can be obtained. The ratio of the amount of graphene oxide to the amount of water solvent is 0.1~2 g:100 mL; The ratio of the partially hydrolyzed polyacrylamide to the aqueous solvent is 0.3~0.5 g:100 mL; The ionic crosslinking agent is a chromium acetate crosslinking agent, and the mass ratio of the chromium acetate crosslinking agent to the partially hydrolyzed polyacrylamide is 0.05~0.07:0.3~0.5; The covalent crosslinking agent is a mixture of oligophenolic resin crosslinking agent and crosslinking promoter, and the ratio of the oligophenolic resin crosslinking agent and crosslinking promoter to the partially hydrolyzed polyacrylamide is 0.5~0.7 mL: 0.1~0.3 mL: 0.3~0.5 g.

2. The preparation method according to claim 1, characterized in that, The oligomeric phenolic resin crosslinking agent is a linear resin synthesized from formaldehyde, phenol, and resorcinol under the action of a catalyst.

3. The preparation method according to claim 1, characterized in that, The main components of the cross-linking promoter include thiourea and resorcinol.

4. The preparation method according to claim 1, characterized in that, The curing treatment is performed at a temperature of 65-75 ℃ for 20-28 h.

5. The preparation method according to claim 1, characterized in that, The stirring process is as follows: The graphene oxide suspension was stirred at a stirring rate of 200-300 r / min until a vortex of 1.5-2.0 cm was generated. Then, the partially hydrolyzed polyacrylamide was added. After the addition was completed, the mixture was stirred at a stirring rate of 100-150 r / min for 10-30 min.

6. A composite weak gel material prepared by the preparation method according to any one of claims 1-5.

7. The application of the composite weak gel material according to claim 6 in an oil displacement agent for oilfield development.

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