A polymer gel for deep plugging in high-temperature oil reservoirs, its preparation method and application

Abstract

This invention provides a polymer gel for deep plugging in high-temperature oil reservoirs, its preparation method, and its application. The polymer gel comprises the following components by mass percentage: hydrolysis-resistant polymer, 0.6%–0.9%; nanocapsule crosslinking agent, 6%–9%; oxygen scavenger, 0.6%–0.9%; water-soluble high-molecular-weight polysaccharide, 0.06%–0.09%; water-retaining agent, 0.06%–0.09%; and water, the balance; the sum of all components is 100%. This polymer gel for deep plugging possesses characteristics such as temperature resistance and good injectability. It can undergo a crosslinking reaction at deep formation depth to form a polymer gel, achieving deep plugging and effectively sealing heterogeneous high-permeability zones, natural / artificial fractures, and other advantageous channels in deep high-temperature oil reservoirs. This achieves targeted and efficient deep plugging, expands the swept volume, and improves oil recovery.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas extraction technology, specifically relating to a polymer gel suitable for deep plugging and sealing in high-temperature oil reservoirs, its preparation method, and its application. Background Technology

[0002] During water injection development in oilfields, water channeling is highly likely to occur between oil and water wells due to reservoir heterogeneity and differences in water-oil mobility ratios. Profile control and water shut-off are effective technologies to address this issue. Subsurface cross-linked polymer gel systems are widely used in profile control and water shut-off operations in high water-cut reservoirs both domestically and internationally due to their controllable gelation time, high gel strength, and simple construction process. The polymer gel system mainly consists of polymers, cross-linking agents (inorganic or organic), and other additives (stabilizers, retarders, oxygen scavengers, etc.). Through cross-linking reactions in the formation, a stable three-dimensional network structure is formed to seal pores or fractures, diverting subsequent injected fluids (water or displacement fluid) to unaffected high oil-saturation areas, thereby increasing the swept volume and oil recovery rate.

[0003] As oilfields gradually tap into deeper reservoirs, facing increasingly demanding high-temperature reservoir conditions, commonly used polymer gel plugging agents often improve their temperature resistance by increasing polymer concentration. However, this increases costs, injection difficulty, and shortens gel formation time, making it difficult to seal deep reservoir areas and severely impacting profile control and water shut-off effectiveness. Therefore, there is an urgent need to develop a polymer gel plugging agent suitable for deep profile control and water shut-off in high-temperature oil reservoirs to meet the requirements of high-temperature reservoir profile control and water shut-off.

[0004] Chinese patent document CN105504158A discloses a smart gel particle that can be re-crosslinked under formation conditions, its preparation method, and its application. The smart gel particle is formulated with acrylamide, anionic monomers, cationic monomers, N,N-vinylpyrrolidone, a pH adjuster, an initiator, crosslinking agent I, crosslinking agent II, a stabilizer, nanoparticle materials, and water. This gel particle is used for oilfield profile control and water shut-off, filtration control, and / or wellbore sealing during drilling and well completion. After entering the formation, the gel particle can re-crosslink under formation conditions to form a high-strength gel, achieving effective sealing. However, this gel particle is only suitable for environments up to 80℃; its sealing performance cannot be guaranteed as the temperature rises. Furthermore, since the injected material is granular, the granules are prone to causing blockage and retention near the wellbore, affecting the deep sealing effect of the gel particle in the formation. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a polymer gel suitable for deep plugging in high-temperature oil reservoirs, its preparation method, and its application. The polymer gel for deep plugging of this invention possesses characteristics such as high-temperature resistance and good injectability. It can undergo a cross-linking reaction at deep formation depth to form a polymer gel, achieving deep plugging and effectively sealing heterogeneous high-permeability zones, natural / artificial fractures, and other advantageous channels in deep high-temperature oil reservoirs. This enables targeted and efficient deep plugging, expands the swept volume, and improves oil recovery.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A polymer gel for deep plugging and sealing in high-temperature oil reservoirs comprises the following components by weight percentage: hydrolysis-resistant polymer, 0.6%–0.9%; nanocapsule crosslinking agent, 6%–9%; oxygen scavenger, 0.6%–0.9%; water-soluble high-molecular-weight polysaccharide, 0.06%–0.09%; water-retaining agent, 0.06%–0.09%; water, balance; the sum of the contents of all components is 100%.

[0008] According to a preferred embodiment of the present invention, the hydrolysis-resistant polymer is a copolymer of acrylamide, acrylic acid and N-vinylpyrrolidone, with a viscosity-average molecular weight of 10 million to 15 million, a degree of hydrolysis of 3 to 10%, and a particle size of 10 μm to 1 mm.

[0009] According to a preferred embodiment of the present invention, the hydrolysis-resistant polymer is prepared from the following raw materials: acrylamide, acrylic acid, N-vinylpyrrolidone, urea, photoinitiator N-diisobutylamidine hydrochloride, and water. The urea used in this invention is a co-solvent, which enhances the solubility of the synthesized polymer.

[0010] Preferably, the mass ratio of acrylamide, acrylic acid, and N-vinylpyrrolidone is 96.6-99.2:0.3-0.4:0.5-3, more preferably 96.66:0.34:3; the mass ratio of acrylamide to water is 1:3-5; urea accounts for 2-3% of the total mass of acrylamide, acrylic acid, and N-vinylpyrrolidone; and the photoinitiator, N-diisobutylamidine hydrochloride, accounts for 0.05-0.5% of the total mass of acrylamide, acrylic acid, and N-vinylpyrrolidone.

[0011] Preferably, the preparation method of the hydrolysis-resistant polymer includes the following steps: fully dispersing acrylamide, acrylic acid, N-vinylpyrrolidone, and urea in water; adding photoinitiator N-diisobutylamidine hydrochloride under inert gas protection and mixing evenly; and undergoing polymerization under inert gas protection and ultraviolet light conditions, followed by washing, drying, and pulverizing to obtain the hydrolysis-resistant polymer.

[0012] Further preferably, the ultraviolet light conditions are provided by an ultraviolet high-pressure mercury lamp; the polymerization reaction temperature is room temperature, the polymerization reaction time is 2-4 hours; and the inert gas is nitrogen or argon.

[0013] According to a preferred embodiment of the present invention, the nanocapsule crosslinking agent is an aqueous solution of a phenolic resin-aluminum citrate composite crosslinking agent encapsulated in thermosensitive modified nano-silica, wherein the mass concentration of the phenolic resin-aluminum citrate is 10-30%. Using the encapsulated phenolic resin-aluminum citrate composite crosslinking agent, controlled release can be achieved at temperatures of 50-160°C, achieving high injectability and deep formation sealing. The phenolic resin is crosslinked with the amide groups on the polymer chain, and the aluminum citrate is crosslinked with the carboxyl groups on the polymer chain, improving crosslinking efficiency and polymer gel strength.

[0014] According to a preferred embodiment of the present invention, the nanocapsule crosslinking agent is prepared from the following raw materials: water-soluble phenolic resin, aluminum citrate, thermosensitive modified nano-silica, and water.

[0015] Preferably, the mass ratio of thermosensitive modified nano-silica, water-soluble phenolic resin, aluminum citrate and water is 5-15:5-15:5-15:70-85, and more preferably 10:10:10:70.

[0016] Preferably, the particle size of the temperature-sensitive modified nano-silica is 20–40 nm. The temperature-sensitive modified nano-silica of this invention possesses temperature-sensitive properties. As a capsule wall material, hydrophobic nano-SiO2 is grafted with temperature-sensitive monomers. At reservoir temperatures of 50–160°C, the molecular chains on the surface of the nano-SiO2 shrink, forming cross-linking agent release microchannels between the nanoparticles, thereby releasing phenolic resin and aluminum citrate. These react with the polymer to achieve cross-linking reactions, improving injectability and sealing deep formations. The introduction of temperature-sensitive monomers enables temperature release switching control under reservoir conditions. Furthermore, precise control of the switching temperature and release rate can be achieved by adjusting the amount and ratio of the temperature-sensitive monomers grafted onto the SiO2 surface and other polymerizable monomers.

[0017] Preferably, the preparation method of temperature-sensitive modified nano-silica includes the following steps: fully dispersing nano-SiO2 in ethanol, adding water, and mixing evenly; adding silane coupling agent γ-methacryloxypropyltrimethoxysilane, adding ammonia water dropwise, and stirring the reaction under nitrogen protection; adding isopropylacrylamide, acrylamide, and potassium persulfate initiator, stirring the reaction, washing, and drying to obtain temperature-sensitive modified nano-silica.

[0018] Further preferably, the particle size of nano-SiO2 is 5-20 nm; the mass ratio of nano-SiO2 to ethanol is 0.005-0.1 g / mL; the volume ratio of ethanol to water is 8-12:1; the mass ratio of the silane coupling agent γ-methacryloyloxypropyltrimethoxysilane to nano-SiO2 is 1-1.1:1; the mass concentration of ammonia water is 25%, and the mass ratio of ammonia water to nano-SiO2 is 0.4-0.5:1; silane coupling agent is added. The stirring reaction temperature after adding γ-methacryloxypropyltrimethoxysilane is 45-55℃, and the stirring reaction time is 10-30h; the mass ratio of isopropylacrylamide, acrylamide, potassium persulfate initiator and nano-SiO2 is 0.8-1.5:0.5-0.9:0.002-0.003:1; the stirring reaction temperature after adding isopropylacrylamide, acrylamide and potassium persulfate initiator is 45-55℃, and the stirring reaction time is 5-10h.

[0019] According to the present invention, in the preparation of thermosensitive modified nano-silica, commonly used hydrophilic nano-SiO2 is first polymerizable and hydrophobically modified using a silane coupling agent. The degree of surface modification of the nanoparticles is precisely controlled by changing the amount of modifier added, reaction time, and reaction temperature. Adding more modifier increases the contact between the modifier and the surface of the silica particles, thereby improving the modification effect; however, excessive addition of modifier increases the number of silane groups formed after the hydroxyl groups on the SiO2 surface are replaced, increasing the steric hindrance of the nano-SiO2 and hindering further contact between the SiO2 particles and the modifier, thus slowing down the rate of increase in the degree of modification. Extending the reaction time increases the reaction time between the modifier and the particles, which is beneficial for the full adsorption and surface reaction of the modifier; however, it should not be too long, mainly because the reaction is accompanied by stirring. If the stirring time is too long, some of the modifier that is not completely grafted or is not stably grafted onto the SiO2 surface will detach under stress. Changing the reaction temperature can alter the reaction rate and equilibrium position, thus affecting the degree of modification. The degree of modification on the surface of SiO2 particles increases rapidly with increasing temperature. This is because as temperature rises, molecular thermal motion intensifies, the proportion of activated molecules increases, and the reaction rate accelerates. However, when the temperature continues to rise, the degree of modification does not change significantly. This is because at excessively high temperatures, molecular motion becomes too intense, and the silanol groups on the surface of SiO2 particles undergo condensation reactions, competing with the main reaction and thus hindering further improvement in the degree of modification. Then, based on reservoir temperature conditions, hydrophobic nano-SiO2 was subjected to thermosensitive modification. Isopropylacrylamide was used as the thermosensitive monomer, acrylamide monomer as the comonomer, and persulfate as the initiator. Thermosensitive long chains were grafted onto the surface of the hydrophobic nano-SiO2 to serve as the wall material for microcapsules.

[0020] The preparation of temperature-sensitive modified nano-silica according to the present invention is illustrated below:

[0021]

[0022] Preferably, the preparation method of the nanocapsule crosslinking agent includes the following steps: fully dissolving water-soluble phenolic resin and aluminum citrate in water, adding thermosensitive modified nano-silica, and stirring at high speed to obtain the nanocapsule crosslinking agent. The phenolic resin is industrial-grade water-soluble phenolic resin, and the aluminum citrate is industrial-grade solid aluminum citrate particles. The thermosensitive modified nano-silica is hydrophobic, and through self-assembly in aqueous solution, the crosslinking agent solution is encapsulated inside capsules composed of thermosensitive modified nano-silica, achieving the purpose of slow crosslinking.

[0023] Further preferably, the high-speed stirring speed is 15000-25000 r / min, the high-speed stirring temperature is room temperature, and the high-speed stirring time is 0.5-20 min.

[0024] According to a preferred embodiment of the present invention, the oxygen scavenger is one or both of thiourea and sodium sulfite, preferably thiourea. As an oxygen scavenger, it reduces the oxygen content in the gel and improves the stability of the polymer gel.

[0025] According to a preferred embodiment of the present invention, the water-soluble polymeric polysaccharide is one or a combination of two or more of stearin, konjac glucomannan, or sodium alginate, preferably stearin. The water-soluble polymeric polysaccharide, as a complex biopolymer, enhances gel stability through the reaction of its chain hydroxyl groups with phenolic resin.

[0026] According to a preferred embodiment of the present invention, the water-retaining agent is cobalt chloride. This water-retaining agent can improve the strength of the gel and reduce the dehydration rate by locking in moisture within the gel network structure.

[0027] According to a preferred embodiment of the present invention, the water is mineralized water with a mineralization degree of 10,000 mg / L or higher, wherein the total content of calcium and magnesium ions is 50-100 mg / L.

[0028] The above-mentioned method for preparing polymer gels suitable for deep plugging and sealing in high-temperature oil reservoirs includes the following steps:

[0029] The hydrolysis-resistant polymer is fully dissolved in water, and then nanocapsule crosslinking agent, oxygen scavenger, water-soluble high molecular weight polysaccharide, and water-retaining agent are added. After thorough mixing and uniform dispersion, a polymer gel suitable for deep plugging in high-temperature oil reservoirs is obtained.

[0030] The above-mentioned polymer gels for deep profile control and water shut-off in high-temperature reservoirs are used for deep profile control and water shut-off in high-temperature reservoirs.

[0031] According to a preferred embodiment of the present invention, the application method includes the steps of: injecting a polymer gel into the formation, and at the formation temperature, the polymer gel undergoes a cross-linking reaction to form a gel, thereby achieving profile control and water shut-off.

[0032] Preferably, the formation temperature is less than or equal to 160℃, more preferably 50-160℃; the crosslinking reaction time is 0.5d to 5d.

[0033] The technical features and beneficial effects of this invention are as follows:

[0034] 1. The polymer gel for profile control and water shut-off in high-temperature reservoirs provided by this invention has simple components, is environmentally friendly, and has a simple preparation method with low cost.

[0035] 2. This invention uses a nanocapsule crosslinking agent. Since the crosslinking agent does not release under low-temperature conditions at ground level, the injection of the plugging agent mainly involves injecting a polymer aqueous solution. The initial viscosity is much lower than that of conventional polymer gel systems, resulting in good injectability, lower performance requirements for the surface pump, and low injection pressure that is less likely to cause the opening of new microcracks. The low viscosity system facilitates the migration of the system to the deep reservoir, thereby achieving deep plugging. In the nanocapsule crosslinking agent of this invention, hydrophobic temperature-sensitive nano-silica particles are used as the capsule wall material. This allows the crosslinking agent to release phenolic resin and aluminum citrate in a controlled and slow manner at reservoir temperatures of 50–160°C, achieving the purpose of slow crosslinking. After the capsule breaks, the temperature-sensitive nano-silica particles can also enhance the gelation effect of the polymer gel, thereby enhancing gel stability. This invention uses a composite crosslinking system of phenolic resin and aluminum citrate. The phenolic resin crosslinks with the amide groups on the polymer chain, and the aluminum citrate crosslinks with the carboxyl groups on the polymer chain, improving crosslinking efficiency and polymer gel strength.

[0036] 3. This invention uses a hydrolysis-resistant polymer containing NVP monomers, thus the resulting polymer gel system exhibits high-temperature resistance and can be used in environments up to 160℃. The oxygen scavenger used in this invention reduces the oxygen content in the gel and improves the stability of the polymer gel. The water-soluble high-molecular-weight polysaccharide used in this invention, as a compound biopolymer, reacts with phenolic resin through its chain hydroxyl groups to improve the stability and strength of the gel. The water-retaining agent in this invention can significantly improve the strength of the gel and reduce the dehydration rate by locking in the moisture in the gel network structure. The raw materials of this invention work together as a whole, giving the plugging agent high high-temperature resistance, effectively sealing high-permeability layers and natural / artificial fractures in deep formations, with high sealing strength, good stability, increased swept volume, and improved oil recovery.

[0037] 4. In the preparation method of this invention, each step and condition works together as a whole to achieve the excellent effects mentioned above. Changing the raw material ratio will cause a loss of gel performance. In the hydrolysis-resistant polymer, the NVP content needs to be appropriate. Increasing the NVP content will increase the temperature resistance of the polymer gel, allowing the gel to maintain its stability at higher temperatures. However, the NVP content cannot be too high, otherwise the molecular weight of the synthesized polymer will decrease, resulting in a poorer thickening effect and a worse temperature resistance of the formed gel. The molecular weight of the hydrolysis-resistant polymer affects the strength of the gel after gelation, and the degree of hydrolysis affects the stability of the polymer after gelation. Therefore, the molecular weight of the hydrolysis-resistant polymer in this invention needs to be appropriate to ensure that the polymer has high strength and stability after gelation. In the nanocapsule crosslinking agent, the thermosensitive modified nano silica plays a role in delaying crosslinking, phenolic resin plays a major crosslinking role and is indispensable, and aluminum citrate plays an auxiliary crosslinking role. Reducing the amount will reduce the stability and strength of the polymer gel. The particle size of the thermosensitive modified nano silica affects the degree of slow crosslinking. The larger the particle size, the worse the encapsulation effect and the lower the slow crosslinking effect. Attached Figure Description

[0038] Figure 1 These are state diagrams of the polymer gels prepared in Examples 1-5 and Comparative Examples 2-3 at different crosslinking times;

[0039] Figure 2 These are the viscoelastic property test results of the gels obtained by gelation of the polymer gels prepared in Examples 1-4;

[0040] Figure 3 These are the thermal stability test results of the gels obtained from the polymer gelation of Examples 1-4. Detailed Implementation

[0041] To provide a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but this should not be construed as limiting the scope of implementation of the present invention.

[0042] In this invention, the preparation methods are all conventional unless otherwise specified; the raw materials used can be obtained from publicly available commercial sources unless otherwise specified.

[0043] Example 1

[0044] A polymer gel for deep plugging in high-temperature oil reservoirs comprises the following components by weight percentage: hydrolysis-resistant polymer, 0.6%; nanocapsule crosslinking agent, 6%; oxygen scavenger thiourea, 0.6%; water-soluble high molecular weight polysaccharide stearin, 0.06%; water-retaining agent cobalt chloride, 0.06%; water, balance; the sum of the contents of all components is 100%.

[0045] The hydrolysis-resistant polymer is a copolymer of acrylamide, acrylic acid, and N-vinylpyrrolidone, with a molecular weight (viscosity average) of 15 million and a degree of hydrolysis of 3%, wherein the mass content of N-vinylpyrrolidone structural units is 3%. The preparation method of the hydrolysis-resistant polymer includes the following steps: acrylamide, acrylic acid, N-vinylpyrrolidone, and urea are fully dispersed in water, with a mass ratio of acrylamide, acrylic acid, N-vinylpyrrolidone, urea, and water of 96.66:0.34:3:2.5:397.5; under nitrogen protection, a photoinitiator, N-bisisobutyramidine hydrochloride, is added, with the mass of N-bisisobutyramidine hydrochloride being 0.1% of the total mass of acrylamide, acrylic acid, and N-vinylpyrrolidone, and the mixture is thoroughly mixed; under nitrogen protection and ultraviolet high-pressure mercury lamp radiation, the polymerization reaction is carried out at room temperature for 3 hours, followed by washing with ethanol, drying, and pulverizing to obtain a hydrolysis-resistant polymer with a particle size of 10-1000 micrometers.

[0046] The nanocapsule crosslinking agent is an aqueous solution of a phenolic resin-aluminum citrate composite crosslinking agent encapsulated in thermosensitive modified nano-silica.

[0047] The preparation method of the nanocapsule crosslinking agent includes the following steps: water-soluble phenolic resin and aluminum citrate are added sequentially to water, stirred and dissolved, and then thermosensitive modified nano-silica (the particle size of the thermosensitive modified nano-silica is 20 nm) is added. The mixture is stirred at 20,000 r / min at room temperature for 1 min to obtain the nanocapsule crosslinking agent encapsulating the phenolic resin-aluminum citrate composite crosslinking agent. The mass ratio of thermosensitive modified nano-silica, water-soluble phenolic resin, aluminum citrate and water is 10:10:10:70.

[0048] Thermosensitive modified nano-silica was prepared by the following method:

[0049] Unmodified nano-SiO2 particles with a diameter of 10 nm were accurately weighed and ultrasonically dispersed in ethanol. The mixture was then combined with distilled water and poured into a four-necked flask equipped with a condenser. The constant temperature water bath was set at 50 °C, and the mechanical stirring speed was 500 r / min. Subsequently, a silane coupling agent (γ-methacryloyloxypropyltrimethoxysilane) was added to the system, followed by dropwise addition of 25% ammonia solution. Under nitrogen protection, the mixture was stirred continuously for 24 h. Isopropylacrylamide and acrylamide were then added, along with potassium persulfate as an initiator. The mixture was stirred continuously for 8 h. After the reaction was complete, the mixture was washed multiple times with ethanol and centrifuged to separate the supernatant. The lower product was dried to obtain the thermosensitive modified nano-silica. The mass ratio of nano-SiO2 to ethanol was 0.01 g / mL; the volume ratio of ethanol to water was 10:1; the mass ratio of silane coupling agent γ-methacryloxypropyltrimethoxysilane to nano-SiO2 was 1.03:1; the mass ratio of ammonia to nano-SiO2 was 0.46:1; and the mass ratio of isopropylacrylamide, acrylamide, initiator potassium persulfate, and nano-SiO2 was 1.23:0.81:0.0024:1.

[0050] The water is mineralized water with a mineralization of 10568.32 mg / L, and its composition is as follows: Ca 2+ 39.34 mg / L; Mg 2+ 21.86 mg / L; Na + 3641.66 mg / L; HCO3 - : 2289.59mg / L; Cl - 3852.71 mg / L; SO4 2- 723.16 mg / L.

[0051] The above-mentioned method for preparing polymer gels suitable for deep plugging and sealing in high-temperature oil reservoirs includes the following steps:

[0052] The hydrolysis-resistant polymer is fully dissolved in water, and then nanocapsule crosslinking agent, oxygen scavenger, water-soluble high molecular weight polysaccharide, and water-retaining agent are added. After thorough mixing and uniform dispersion, a polymer gel suitable for deep plugging in high-temperature oil reservoirs is obtained.

[0053] Example 2

[0054] A polymer gel for deep plugging in high-temperature oil reservoirs comprises the following components by weight percentage: hydrolysis-resistant polymer, 0.7%; nanocapsule crosslinking agent, 7%; oxygen scavenger thiourea, 0.7%; water-soluble high molecular weight polysaccharide stearin, 0.07%; water-retaining agent cobalt chloride, 0.07%; and water, balance; the sum of the contents of all components is 100%.

[0055] The types and preparation methods of the hydrolysis-resistant polymers and nanocapsule crosslinking agents are the same as in Example 1; the composition of the water is the same as in Example 1.

[0056] The preparation method of the polymer gel for deep plugging and sealing in high-temperature reservoirs is the same as in Example 1.

[0057] Example 3

[0058] A polymer gel for deep plugging in high-temperature oil reservoirs comprises the following components by weight percentage: hydrolysis-resistant polymer, 0.8%; nanocapsule crosslinking agent, 8%; oxygen scavenger thiourea, 0.8%; water-soluble high molecular weight polysaccharide stearin, 0.08%; water-retaining agent cobalt chloride, 0.08%; and water, balance; the sum of the contents of all components is 100%.

[0059] The types and preparation methods of the hydrolysis-resistant polymers and nanocapsule crosslinking agents are the same as in Example 1; the composition of the water is the same as in Example 1.

[0060] The preparation method of the polymer gel for deep plugging and sealing in high-temperature reservoirs is the same as in Example 1.

[0061] Example 4

[0062] A polymer gel for deep plugging in high-temperature oil reservoirs comprises the following components by weight percentage: hydrolysis-resistant polymer, 0.9%; nanocapsule crosslinking agent, 9%; oxygen scavenger thiourea, 0.9%; water-soluble high-molecular-weight polysaccharide stearin, 0.09%; water-retaining agent cobalt chloride, 0.09%; and water, balance; the sum of the contents of all components is 100%.

[0063] The types and preparation methods of the hydrolysis-resistant polymers and nanocapsule crosslinking agents are the same as in Example 1; the composition of the water is the same as in Example 1.

[0064] The preparation method of the polymer gel for deep plugging and sealing in high-temperature reservoirs is the same as in Example 1.

[0065] Example 5

[0066] A polymer gel suitable for deep plugging in high-temperature oil reservoirs, as described in Example 1, except that: the mass content of N-vinylpyrrolidone structural units in the hydrolysis-resistant polymer is 0.5%; in the preparation method of the hydrolysis-resistant polymer, the mass ratio of acrylamide, acrylic acid, and N-vinylpyrrolidone is 99.15:0.35:0.5; the preparation steps and conditions of other hydrolysis-resistant polymers are the same as in Example 1.

[0067] The type and preparation method of the nanocapsule crosslinking agent are the same as in Example 1; the composition of water is the same as in Example 1.

[0068] The preparation method of the polymer gel for deep plugging and sealing in high-temperature reservoirs is the same as in Example 1.

[0069] Example 6

[0070] A polymer gel suitable for deep plugging in high-temperature oil reservoirs, as described in Example 1, differs in that the temperature-sensitive modified nano-silica particles have a diameter of 40 nm in the preparation method of the nanocapsule crosslinking agent. The specific preparation method is as follows: Unmodified nano-SiO2 particles with a diameter of 20 nm are accurately weighed, ultrasonically dispersed in ethanol, and mixed with distilled water. The mixture is then poured into a four-necked flask equipped with a condenser. The constant temperature water bath temperature is set to 50°C, and the mechanical stirring speed is 500 r / min. Subsequently, a silane coupling agent (γ-methacryloyloxypropyltrimethoxysilane) is added to the system, and 25% ammonia solution is added dropwise. Under nitrogen protection, the mixture is continuously stirred and reacted for 18 h. Isopropylacrylamide and acrylamide are then added, along with the initiator potassium persulfate. The mixture is continuously stirred and reacted for 8 h. After the reaction, the mixture is repeatedly washed with ethanol and centrifuged to separate the upper layer solution. The lower layer product is dried to obtain the temperature-sensitive modified nano-silica. The mass ratio of nano-SiO2 to ethanol was 0.01 g / mL; the volume ratio of ethanol to water was 10:1; the mass ratio of silane coupling agent γ-methacryloxypropyltrimethoxysilane to nano-SiO2 was 1.03:1; the mass ratio of ammonia to nano-SiO2 was 0.46:1; and the mass ratio of isopropylacrylamide, acrylamide, initiator potassium persulfate, and nano-SiO2 was 0.86:0.54:0.0024:1.

[0071] The other preparation steps and conditions for the nanocapsule crosslinking agent are the same as in Example 1.

[0072] The types and preparation methods of the hydrolysis-resistant polymers are the same as in Example 1; the composition of the water is the same as in Example 1.

[0073] The preparation method of the polymer gel for deep plugging and sealing in high-temperature reservoirs is the same as in Example 1.

[0074] Comparative Example 1

[0075] A polymer gel for deep plugging in high-temperature oil reservoirs, as described in Example 1, except that phenolic resin is not added in the preparation method of the nanocapsule crosslinking agent; the other preparation steps and conditions of the nanocapsule crosslinking agent are the same as in Example 1.

[0076] The types and preparation methods of the hydrolysis-resistant polymers are the same as in Example 1; the composition of the water is the same as in Example 1.

[0077] The preparation method of the polymer gel for deep plugging and sealing in high-temperature reservoirs is the same as in Example 1.

[0078] Comparative Example 2

[0079] A polymer gel for deep plugging in high-temperature oil reservoirs, as described in Example 1, except that aluminum citrate is not added in the preparation method of the nanocapsule crosslinking agent; the other preparation steps and conditions of the nanocapsule crosslinking agent are the same as in Example 1.

[0080] The types and preparation methods of the hydrolysis-resistant polymers are the same as in Example 1; the composition of the water is the same as in Example 1.

[0081] The preparation method of the polymer gel for deep plugging and sealing in high-temperature reservoirs is the same as in Example 1.

[0082] Comparative Example 3

[0083] A polymer gel for deep plugging in high-temperature oil reservoirs, as described in Example 1, except that: no water-retaining agent cobalt dichloride is added; other raw material composition is the same as in Example 1.

[0084] The types and preparation methods of the hydrolysis-resistant polymers and nanocapsule crosslinking agents are the same as in Example 1; the composition of the water is the same as in Example 1.

[0085] The preparation method of the polymer gel for deep plugging and sealing in high-temperature reservoirs is the same as in Example 1.

[0086] Experimental Example 1

[0087] Polymer gelation time and gel strength testing:

[0088] The polymer gels prepared in Examples 1-6 and Comparative Examples 1-3 were placed in an oven at 160°C, and the gelation time was observed and recorded. The gel strength was evaluated using the "visual code evaluation method" commonly used in the petroleum industry, and the changes in gel strength were recorded after 10 days, 60 days, 150 days, and 360 days. The gel strength was tested using the breakthrough vacuum method.

[0089] Evaluation criteria for gel strength: Grade A indicates no gel formation at all; Grade B indicates increased viscosity of the gel system, but still high fluidity; Grade C indicates a highly fluid gel with slight wall adhesion; Grade D indicates a moderately fluid gel with significant wall adhesion; Grade E indicates a low-flow gel; Grade F is a high-deformation-flow gel; Grade G is a moderately deformable-flow gel; Grade H is a low-deformation-flow gel, essentially non-flowing, with a short tongue; Grade I is a rigid gel, non-flowing, and without a long tongue. (Zhu Daoyi. Development and Gelation Mechanism Study of Polymer Gel System in High-Temperature Oil Reservoirs [D]. China University of Petroleum (Beijing), 2018)

[0090] The polymer gel prepared in Example 1 gelled after 24 hours, changing from a liquid to a gel and losing its flow properties. Figure 1As shown in (a), the gel gradually changed from yellow to black over time. After gelation, the gel strength was H grade at 10 days, 60 days, 150 days and 360 days. The breakthrough vacuum degree of the gel at 360 days was 55 Pa. When placed at 160℃ for 360 days, the gel had almost no dehydration, with a dehydration rate of 4%.

[0091] The polymer gel prepared in Example 2 gelled after 22 hours, changing from a liquid to a gel and losing its flow properties. Figure 1 As shown in (b), the gel gradually changed from yellow to black over time. After gelation, the gel strength was H grade at 10 days, 60 days, 150 days and 360 days. The breakthrough vacuum degree of the gel at 360 days was 61 Pa. When placed at 160℃ for 360 days, the gel was almost dehydrated, with a dehydration rate of 3%.

[0092] The polymer gel prepared in Example 3 gelled after 24 hours, changing from a liquid to a gel and losing its flow properties. Figure 1 As shown in (c), the gel gradually changed from yellow to black over time. The gel strength at 10, 60, 150 and 360 days after gelation was all grade H. The breakthrough vacuum degree of the gel at 360 days was 71 Pa. The gel did not dehydrate after being placed at 160℃ for 360 days, and the dehydration rate was 0%.

[0093] The polymer gel prepared in Example 4 gelled after 24 hours, changing from a liquid to a gel and losing its flow properties. Figure 1 As shown in (d), the gel gradually changed from yellow to black over time. After gelation, the gel strength was H grade at 10 days, 60 days, 150 days and 360 days. The breakthrough vacuum degree of the gel at 360 days was 73 Pa. The gel did not dehydrate after being placed at 160℃ for 360 days, and the dehydration rate was 0%.

[0094] The polymer gel prepared in Example 5 gelled after 24 hours, changing from a liquid to a gel and losing its flow properties. Figure 1 As shown in (e), the gel strength was H grade at 10 days and 60 days after gelation. The gel was dehydrated and destroyed on day 125, with a dehydration rate of 40%.

[0095] The polymer gel prepared in Example 6 gelled at 13 hours, and its gel properties were not significantly different from those of the polymer gel prepared in Example 1, except that the gelation time was reduced.

[0096] The polymer gel prepared in Comparative Example 1 could not form a gel.

[0097] The polymer gel prepared in Comparative Example 2 gelled after 24 hours, with a gel strength of G, as shown. Figure 1 As shown in (f), the product was dehydrated and destroyed after being placed at 160°C for 18 days, with a dehydration rate of 28%.

[0098] The polymer gel prepared in Comparative Example 3 gelled after 27 hours, with a gel strength of F, as shown. Figure 1 As shown in (g), the product was dehydrated and destroyed after being placed at 160°C for 7 days, with a dehydration rate of 35%.

[0099] As shown above, the polymer gel prepared by this invention exhibits excellent gel strength and stability after gelation.

[0100] Test Example 2

[0101] Viscoelasticity test of the gel obtained after polymer gelation:

[0102] The polymer gels prepared in Examples 1-4 were placed in a 160°C oven and allowed to gel. After gelation, the gels were kept at 160°C for 10 days. The viscoelasticity (storage modulus and loss modulus) of the polymer gels was measured using an Austrian MCR302 rheometer and a cone-plate system. Oscillating frequency scanning was performed, selecting 10%–30% of the upper limit stress value in the linear viscoelastic region as the stress value. To accelerate the testing, scanning was conducted within the frequency range of 0.01–10 Hz to determine the relationship between the storage modulus G', loss modulus G”, and frequency f. The testing temperature was 160°C.

[0103] Test results are available Figure 2 .from Figure 2 It can be seen that the storage modulus G' of the polymer gel obtained in Example 1 is higher than the loss modulus G”. At a frequency of 10 Hz, the storage modulus G' is stable at 50.5 Pa, and the loss modulus G” is 3.4 Pa. The storage modulus G' of the polymer gel obtained in Example 2 is higher than the loss modulus G”. At a frequency of 10 Hz, the storage modulus G' is stable at 54.8 Pa, and the loss modulus G” is 2.9 Pa. The storage modulus G' of the polymer gel obtained in Example 3 is higher than the loss modulus G”. At a frequency of 10 Hz, the storage modulus G' is stable at 103 Pa, and the loss modulus G” is 4.9 Pa. The storage modulus G' of the polymer gel obtained in Example 4 is higher than the loss modulus G”. At a frequency of 10 Hz, the storage modulus G' is stable at 107.0 Pa, and the loss modulus G” is 9.5 Pa. Therefore, it can be seen that as the concentration of each component increases, the storage modulus G' and the loss modulus G” show an increasing trend, indicating better viscoelasticity of the gel.

[0104] Experimental Example 3

[0105] Thermal stability test of the gel obtained after polymer gelation:

[0106] The polymer gels prepared in Examples 1-4 were placed in a 160°C oven and dried at 160°C for 10 days after gelation. Then, they were placed in a 200°C oven for 48 hours until completely dried and pulverized. 1-2 mg samples were placed in a thermogravimetric analyzer to test the mass fraction change of the polymer gel within the range of 0-600°C, with a testing frequency of 6°C per test. The test results are shown below. Figure 3 .

[0107] from Figure 3 It can be seen that the polymer gel exhibits two distinct weight loss steps. The first weight loss step occurs between 200 and 300°C, with weight changes ranging from approximately 15% (Example 1), 10% (Example 2), 15% (Example 3), and 15% (Example 4), primarily attributed to thermal dissipation of the polymer itself. The second weight loss step occurs between 300 and 400°C, at which point the amide groups formed by the polymer and phenolic resin in the gel structure begin to decompose, resulting in weight losses of approximately 20% (Example 1), 25% (Example 2), 20% (Example 3), and 20% (Example 4). The final remaining mass of the polymer gel is 50.37% (Example 1), 43.64% (Example 2), 43.86% (Example 3), and 45.93% (Example 4).

[0108] Test Example 4

[0109] Blocking test:

[0110] Fracture core plugging experiments were conducted on the polymer gels prepared in Examples 1-4, corresponding to core numbers 1-4. The experimental steps are as follows:

[0111] 1. Select a length of 10cm and a cross-sectional area of ​​4.9cm². 2 The core samples were weighed dry, vacuumed for 24 hours, saturated with simulated formation water, and pressurized to 10 MPa for 24 hours. The wet weight of the core samples was then weighed, and the porosity of the core model was measured.

[0112] 2. Split the artificial core along the longitudinal axis, and lay a 0.5mm spacer along the edge of the core. Attach a small amount of double-sided tape to both sides of the spacer to fix its position, and close the two halves of the core to obtain a fractured core.

[0113] 3. Apply a confining pressure of 10 MPa to the core and inject simulated formation water at a flow rate of 0.5 mL / min. Record the pressure difference after the injection pressure stabilizes.

[0114] 4. Inject 1 PV of plugging agent into the core at a flow rate of 0.5 mL / min and age it at 120℃ for 24 hours until it is completely gelled. Inject formation water again at a flow rate of 0.5 mL / min until the pressure breaks through and stabilizes, and calculate the plugging rate η.

[0115] The blocking rate η is calculated as follows:

[0116]

[0117] Where: η—formation plugging rate, %; Δp0—stable pressure difference between the inlet and outlet during the initial water drive, kPa; Δp1—stable pressure difference between the inlet and outlet during subsequent water drive after the injection of plugging agent, kPa;

[0118] The experimental results are shown in Table 1.

[0119] Table 1. Results of the sealing experiment

[0120]

[0121] As shown above, the polymer gel of the present invention exhibits excellent sealing performance, with all levels exceeding 99%.

Claims

1. A polymer gel suitable for deep plugging in high-temperature oil reservoirs, characterized in that, It comprises the following components by weight percentage: hydrolysis-resistant polymer, 0.6%~0.9%; nanocapsule crosslinking agent, 6%~9%; oxygen scavenger, 0.6%~0.9%; water-soluble high molecular weight polysaccharide, 0.06%~0.09%; water-retaining agent, 0.06%~0.09%; water, balance; the sum of the contents of all components is 100%. The hydrolysis-resistant polymer is a copolymer of acrylamide, acrylic acid, and N-vinylpyrrolidone, with a viscosity-average molecular weight of 10-15 million, a degree of hydrolysis of 3-10%, and a particle size of 10 μm-1 mm. The hydrolysis-resistant polymer is prepared from the following raw materials: acrylamide, acrylic acid, N-vinylpyrrolidone, urea, photoinitiator N-bisisobutyramidine hydrochloride, and water. The nanocapsule crosslinking agent is an aqueous solution of a phenolic resin-aluminum citrate composite crosslinking agent encapsulated in thermosensitive modified nano-silica, wherein the mass concentration of phenolic resin-aluminum citrate is 10-30%. The nanocapsule crosslinking agent is prepared from the following raw materials: water-soluble phenolic resin, aluminum citrate, thermosensitive modified nano-silica, and water. The preparation method of thermosensitive modified nano-silica includes the following steps: fully dispersing nano-SiO2 in ethanol, adding water, and mixing evenly; adding silane coupling agent γ-methacryloyloxypropyltrimethoxysilane, adding ammonia dropwise, and stirring the reaction under nitrogen protection; adding isopropylacrylamide, acrylamide, and potassium persulfate initiator, stirring the reaction, washing, and drying to obtain thermosensitive modified nano-silica. The water-soluble high-molecular-weight polysaccharide is one or a combination of two or more of the following: stearin, konjac glucomannan, or sodium alginate; the water-retaining agent is cobalt dichloride.

2. The polymer gel for deep plugging and sealing in high-temperature reservoirs according to claim 1, characterized in that, Includes one or more of the following conditions: i. The mass ratio of acrylamide, acrylic acid, and N-vinylpyrrolidone is 96.6-99.2:0.3-0.4:0.5-3; the mass ratio of acrylamide to water is 1:3-5; urea accounts for 2-3% of the total mass of acrylamide, acrylic acid, and N-vinylpyrrolidone; the mass of the photoinitiator N-diisobutylamidine hydrochloride is 0.05-0.5% of the total mass of acrylamide, acrylic acid, and N-vinylpyrrolidone. ii. The preparation method of the hydrolysis-resistant polymer includes the following steps: acrylamide, acrylic acid, N-vinylpyrrolidone, and urea are fully dispersed in water; under inert gas protection, photoinitiator N-diisobutylamidine hydrochloride is added and mixed evenly; under inert gas protection and ultraviolet light conditions, a polymerization reaction is carried out, followed by washing, drying, and pulverization to obtain the hydrolysis-resistant polymer; the ultraviolet light conditions are provided by an ultraviolet high-pressure mercury lamp; the polymerization reaction temperature is room temperature, and the polymerization reaction time is 2-4 hours; the inert gas is nitrogen or argon.

3. The polymer gel for deep plugging and sealing in high-temperature reservoirs according to claim 1, characterized in that, Includes one or more of the following conditions: i. The mass ratio of thermosensitive modified nano-silica, water-soluble phenolic resin, aluminum citrate and water is 5-15:5-15:5-15:70-85. ii. The particle size of the temperature-sensitive modified nano-silica is 20~40nm; iii. The particle size of nano-SiO2 is 5-20 nm; the mass ratio of nano-SiO2 to ethanol is 0.005-0.1 g / mL; the volume ratio of ethanol to water is 8-12:1; the mass ratio of silane coupling agent γ-methacryloyloxypropyltrimethoxysilane to nano-SiO2 is 1-1.1:1; the mass concentration of ammonia is 25%, and the mass ratio of ammonia to nano-SiO2 is 0.4-0.5:1; γ-methacryloyloxypropyltrimethoxysilane is added. The stirring reaction temperature after adding methacryloyloxypropyltrimethoxysilane is 45-55℃, and the stirring reaction time is 10-30h; the mass ratio of isopropylacrylamide, acrylamide, potassium persulfate initiator and nano-SiO2 is 0.8-1.5:0.5-0.9:0.002-0.003:1; the stirring reaction temperature after adding isopropylacrylamide, acrylamide and potassium persulfate initiator is 45-55℃, and the stirring reaction time is 5-10h. iv. The preparation method of the nanocapsule crosslinking agent includes the following steps: dissolving water-soluble phenolic resin and aluminum citrate in water, adding thermosensitive modified nano-silica, and obtaining the nanocapsule crosslinking agent by high-speed stirring; the high-speed stirring speed is 15000-25000 r / min, the high-speed stirring temperature is room temperature, and the high-speed stirring time is 0.5-20 min.

4. The polymer gel for deep plugging and sealing in high-temperature reservoirs according to claim 1, characterized in that, Includes one or more of the following conditions: i. The oxygen scavenger is one or both of thiourea or sodium sulfite; ii. The water-soluble high-molecular-weight polysaccharide is sclerosotan; iii. The water is mineralized water with a mineralization degree of 10,000 mg / L or higher, and the total content of calcium and magnesium ions is 50-100 mg / L.

5. The method for preparing the polymer gel for deep plugging and sealing in high-temperature reservoirs as described in any one of claims 1-4, comprising the steps of: The hydrolysis-resistant polymer is fully dissolved in water, and then nanocapsule crosslinking agent, oxygen scavenger, water-soluble high molecular weight polysaccharide, and water-retaining agent are added. After thorough mixing and uniform dispersion, a polymer gel suitable for deep plugging in high-temperature oil reservoirs is obtained.

6. The application of the polymer gel for deep profile control and water shut-off in high-temperature reservoirs as described in any one of claims 1-4, for use in deep profile control and water shut-off in high-temperature reservoirs.

7. The application according to claim 6, wherein the application method includes the steps of: injecting polymer gel into the formation, and at the formation temperature, the polymer gel undergoes a cross-linking reaction to form a gel, thereby achieving profile control and water shut-off.

8. In the application according to claim 7, the formation temperature is less than or equal to 160°C; the crosslinking reaction time is 0.5 days to 5 days.

9. The application according to claim 8, wherein the formation temperature is 50-160°C.

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