Preparation and application method of hydrophobic polyionic anti-swelling plugging agent

Abstract

The application provides a hydrophobic polyionic anti-swelling plugging agent preparation and application method, which comprises the following steps: step 1, preparing an ionic liquid precursor, wherein the ionic liquid precursor is prepared by mixing 1-methyl-2-vinylimidazole, 1,4-p-dichlorobenzyl and dimethyl sulfoxide; step 2, preparing low-molecular-weight hydrophobic polyionic liquid and high-molecular-weight hydrophobic polyionic liquid, wherein the low-molecular-weight hydrophobic polyionic liquid and the high-molecular-weight hydrophobic polyionic liquid are both prepared by mixing the ionic liquid precursor, water and dimethyl sulfoxide; step 3, preparing a solution of the low-molecular-weight hydrophobic polyionic liquid and injecting the solution into a reservoir; and step 4, preparing a solution of the high-molecular-weight hydrophobic polyionic liquid and injecting the solution into an oil reservoir. The hydrophobic polyionic anti-swelling plugging agent preparation and application method can be applied to oilfield development and production, can be used as an anti-swelling agent when injected into a reservoir and can be injected into an oil reservoir, greatly reduces the water phase permeability without affecting the oil phase permeability and realizes the selective water plugging effect.

Description

Technical Field

[0001] This invention relates to the field of oilfield reservoir protection and production enhancement measures, and in particular to a method for preparing and applying a hydrophobic polyionic anti-swelling and plugging agent. Background Technology

[0002] Currently, with the continued development and production of old oilfields in eastern my country, most oilfields have entered the ultra-high water-cut stage. Among them, the Shengli Oilfield's onshore integrated oil reservoirs have recoverable reserves of 1.29 billion tons, with a current recovery rate of 37.6% and an overall water cut of 95.6%, indicating that it has entered the late-stage development phase of ultra-high water cut. Therefore, how to further improve crude oil recovery rate is an urgent problem to be solved for old oilfields.

[0003] In oilfield development and production, two issues significantly impact recovery rates. First, for reservoirs with high clay content and high water sensitivity, water injection or production enhancement injection can lead to clay mineral hydration and swelling, reducing the flow radius of pore throats, decreasing reservoir permeability, and affecting oilfield development. Therefore, anti-swelling agents must be used for reservoir protection. Second, due to reservoir heterogeneity, the selective adsorption of oil and water by rocks, and differences in oil and water viscosity, water channeling often occurs during water injection development, resulting in high water cuts at lower recovery stages and decreased oil production. Water shut-off measures are needed to adjust the production fluid structure to increase oil production and reduce water content.

[0004] To address these two issues, the most widely used anti-swelling agents are inorganic salts and cationic surfactants. The metal cations in inorganic salts can diffuse into the interlayer of clay crystals, neutralizing the negative charge of the clay, reducing the repulsive force of the electric double layer, and thus achieving charge neutralization. Simultaneously, the cations provided by inorganic salts have low hydration energy, preferentially combining with water in clay particles, causing dehydration between clay layers and effectively inhibiting clay hydration. These clay stabilizers are low-cost, readily available, and easy to use, and were widely used in the early stages of oilfield development. However, inorganic salt clay stabilizers are prone to cation exchange in solution, causing the clay to revert to a dispersible form, resulting in poor long-term effectiveness. Furthermore, they cannot form multi-point adsorption, have poor erosion resistance, and their anti-swelling effect disappears after repeated erosion. In oilfields, quaternary ammonium salt-type cationic surfactants are also frequently used as anti-swelling agents. After hydration, they can generate cationic groups, neutralize the negative charge of clay particles, adsorb onto the surface of clay particles, and replace metal cations. At the same time, the hydrophobic chains in the molecular chain can form a hydrophobic layer, separating water molecules and clay particles. The larger molecular weight of cationic surfactants and the stronger intermolecular forces can make the adsorption system more stable and significantly reduce the dispersion and migration of clay. However, because cationic surfactants have the property of reducing the interfacial tension between oil and water, there is a possibility that they can cause the reservoir to change from water-wet to oil-wet and reduce the permeability of the aqueous phase.

[0005] On the other hand, conventional water shut-off systems mainly include gels, gels, particles, sediments, and foams. Their characteristic is that they preferentially enter and block high-permeability areas along with the injected working fluid. Therefore, the channels for oil and water in high-permeability areas are blocked, resulting in the loss of crude oil production in high-permeability channels. That is, existing water shut-off systems have selective blocking properties for reservoir permeability, but no selective blocking properties for oil and water.

[0006] Currently, among conventional anti-swelling agents, inorganic salt clay stabilizers easily undergo cation exchange in solution, causing the clay to revert to a dispersible form. This results in poor long-term effectiveness, an inability to form multi-point adsorption, and poor erosion resistance; the anti-swelling effect disappears after repeated erosion. Cationic surfactants, on the other hand, have the property of reducing the interfacial tension between oil and water, potentially causing the reservoir to change from water-wet to oil-wet and reducing the permeability of the aqueous phase. Furthermore, conventional water-blocking agents can block both oil and water channels in high-permeability areas, resulting in the loss of crude oil production from these channels. In other words, existing water-blocking systems exhibit selective blocking based on reservoir permeability, but not selective blocking based on oil-water ratio. Therefore, in development and production, we need better anti-swelling agents for reservoir protection, as well as water-blocking agents with selective blocking capabilities.

[0007] Chinese patent application CN109184615B discloses a selective water shut-off method and its application in conglomerate reservoirs. The method involves: selecting candidate wells for water shut-off based on production needs and the characteristics of wells in conglomerate reservoirs; preparing a selective water shut-off agent suitable for conglomerate reservoirs; designing a mathematical model to calculate the amount of water shut-off agent based on reservoir porosity and / or fracture factors; designing a five-stage water shut-off agent slug; designing the maximum injection pressure for water shut-off based on formation fracture pressure; designing the injection rate of the water shut-off agent based on formation permeability and injection equipment performance; and injecting the water shut-off agent slug into the candidate wells for water shut-off. This method achieves safe operation, comprehensive injection, and increased oil production while reducing water loss, providing strong technical support for water control and oil stabilization in horizontal wells of the Kunbei Oilfield in Qinghai Province, and providing a model for water shut-off process design in horizontal wells of conglomerate reservoirs in China. This patent prepares a water-blocking agent by monomer polymerization, cross-linking reaction, and repolymerization to gelation. The resulting water-blocking agent is a colloidal microparticle. Its blocking mechanism is that the microparticles expand when they come into contact with water and block the pore throat. After blockage, neither oil nor water can pass through. Therefore, it does not have the selectivity of "blocking water but not oil".

[0008] Chinese patent application CN104449627B discloses a reservoir protection promoter and its preparation method. This promoter comprises the following components by weight percentage: 0.1%–1.0% polyepoxychloropropane-dimethylamine, 0.5%–2.0% ammonium chloride, 0.1%–0.5% surfactant, 5%–15% ethanol, and the balance being water. This reservoir protection promoter exhibits high anti-swelling rate and strong erosion resistance, while simultaneously reducing the surface tension of the working fluid and improving its permeability. It significantly reduces water sensitivity and water-locking damage to the reservoir, achieving the goal of protecting the reservoir from external working fluid intrusion. It meets the reservoir protection requirements during construction operations in low-porosity, low-permeability reservoirs and can be used in various working fluids during oilfield production. It can also be used as an additive in working fluids for acidizing, fracturing, water shut-off, and profile control, playing a role in protecting the formation and preventing formation damage during operations. This patent simply combines commonly used inorganic salt clay stabilizers such as ammonium chloride, surfactants, polyepoxychloropropane-dimethylamine, and ethanol in oil fields. It does not offer any clear innovation in the anti-swelling mechanism and still faces the problems that inorganic salt clay stabilizers cannot form multi-point adsorption, have poor erosion resistance, and lose their anti-swelling effect after repeated erosion. Although its surfactant component can reduce the interfacial tension between oil and water, there is still a risk of causing the reservoir to change from water-wet to oil-wet and reducing the permeability of the aqueous phase.

[0009] Chinese patent application CN101037933A discloses a method for scale and corrosion inhibition combining chemical injection and water shut-off. This method involves providing a scale and corrosion inhibitor, a selective plugging agent, and a corresponding working fluid injection process. The scale and corrosion inhibitor is diethylenetriaminepentamethylphosphonic acid, and the selective plugging agent is a copolymer of acrylamide and 3-acrylamido-3-methylbutyltrimethylammonium chloride. The injection process involves first injecting brine containing a clay anti-swelling agent into the formation as a pre-fluid, followed by the injection of the scale and corrosion inhibitor, then injecting an appropriate amount of formation water or brine as a post-fluid, and finally injecting the selective plugging agent. After injection, the well is shut in and left to simmer for 16-24 hours before being reopened to resume production. Through this process, the scale and corrosion inhibitor is forced into the near-wellbore zone of the oil well. The selective plugging agent seals the scale and corrosion inhibitor within the porous media of the formation, allowing the scale and corrosion inhibitor to be continuously carried by formation fluids to the wellbore, surface pipelines, and equipment, achieving continuous release and long-lasting scale and corrosion inhibition. The plugging agent used in this patent is a copolymer of acrylamide and 3-acrylamido-3-methylbutyltrimethylammonium chloride, which belongs to the category of polymer plugging agents. It mainly relies on the high viscosity of the plugging agent solution to reduce the mobility of the aqueous phase, thereby inhibiting the movement of water. Its adsorption capacity on the rock wall is relatively weak. During the production process, it will be sheared and destroyed by the produced fluid. The produced fluid will carry the scale and corrosion inhibitor to the wellbore, surface pipelines and equipment. Its function and purpose are not to "block water but not oil", but to seal the scale and corrosion inhibitor in the porous medium of the formation through the plugging agent. This allows the scale and corrosion inhibitor to be continuously, rather than once, carried to the wellbore, surface pipelines and equipment by the formation fluid, so as to achieve continuous release and long-term scale and corrosion inhibition effect.

[0010] The existing technologies described above are significantly different from this invention. A search reveals no literature of the XY category, indicating that this invention is innovative. Since no solution exists in the existing technologies to address the technical problem we seek to solve, we have invented a novel method for preparing and applying a hydrophobic polyionic anti-swelling and anti-blocking agent. Summary of the Invention

[0011] The purpose of this invention is to provide a method for preparing and applying a hydrophobic polyionic anti-swelling and plugging agent that can reduce the permeability of the aqueous phase without affecting the permeability of the oil phase, thereby achieving water-blocking without oil-blocking.

[0012] The objective of this invention can be achieved through the following technical measures: a method for preparing and applying a hydrophobic polyionic anti-swelling and anti-blocking agent, the method comprising:

[0013] Step 1: Prepare the ionic liquid precursor, which is made by mixing 1-methyl-2-vinylimidazolium, 1,4-dichlorobenzyl, and dimethyl sulfoxide.

[0014] Step 2: Prepare low molecular weight hydrophobic polyionic liquid and high molecular weight hydrophobic polyionic liquid. Both low molecular weight hydrophobic polyionic liquid and high molecular weight hydrophobic polyionic liquid are prepared by mixing ionic liquid precursor, water and dimethyl sulfoxide.

[0015] Step 3: Prepare the low molecular weight hydrophobic polyionic liquid into a solution and inject it into the reservoir;

[0016] Step 4: Prepare a solution from the high molecular weight hydrophobic polyionic liquid and inject it into the oil reservoir.

[0017] The objective of this invention can also be achieved through the following technical measures:

[0018] In step 1, 1-methyl-2-vinylimidazole and 1,4-dichlorobenzyl were uniformly stirred and dissolved in dimethyl sulfoxide, and heated at high temperature under a nitrogen atmosphere. After the reaction was completed, the supernatant was filtered, the solid was collected, the solid was rotary evaporated, and then dried in a vacuum drying oven to obtain an ionic liquid, which was used as the precursor for the reaction in step 2. The ionic liquid was ground into particles and added to a mixed solution of water and dimethyl sulfoxide, and stirred continuously at room temperature until completely dissolved to obtain the ionic liquid precursor.

[0019] In step 1, the molar volume ratio of 1-methyl-2-vinylimidazole, 1,4-dichlorobenzyl, and dimethyl sulfoxide is 4-7 mmol: 5 mmol: 5-10 ml.

[0020] In step 2, the ionic liquid precursor was taken, and azobisisobutyronitrile and hydroxyethyl methacrylate were added. Under nitrogen protection, the mixture was first stirred at high temperature to ensure complete dissolution of the reactants, and then heated and stirred to ensure sufficient reaction. The resulting blocky solid was washed multiple times with dimethyl sulfoxide to remove unreacted reactants, and then vacuum dried and ground to obtain black solid particles. The black solid particles were centrifuged multiple times with alternating anhydrous ethanol and deionized water. After centrifugation, the supernatant was removed, the precipitate was collected, and the precipitate was vacuum dried at high temperature. The obtained solid particles were then ground to obtain solid powder, thus preparing the hydrophobic polyionic liquid.

[0021] In step 2, the addition ratio of ionic liquid precursor, water, and dimethyl sulfoxide is controlled to be 0.35-0.62 g: 0.38-0.86 ml: 3.0-3.3 ml, the addition ratio of azobisisobutyronitrile is 1.8-2.4 wt.%, and the molar ratio of ionic liquid precursor and hydroxyethyl methacrylate is 0.85-1.05 mmol: 0.45-0.65 mmol, to obtain a hydrophobic polyionic liquid with a low molecular weight of 20,000-30,000.

[0022] In step 2, the addition ratio of ionic liquid precursor, water, and dimethyl sulfoxide is controlled to be 1.2-1.8 g: 0.4-0.9 ml: 3.2-3.8 ml, the addition ratio of azobisisobutyronitrile is 1.8-2.4 wt.%, and the molar ratio of ionic liquid precursor and hydroxyethyl methacrylate is 2-2.5 mmol: 1.2-1.5 mmol, to obtain a hydrophobic polyionic liquid with a high molecular weight of 300,000-500,000.

[0023] In step 3, the prepared low molecular weight hydrophobic polyionic liquid is formulated into a solution and injected into the reservoir. The polyionic liquid can be adsorbed on the negatively charged clay minerals on the surface of the reservoir rock under electrostatic action, preventing water from entering the interlayer structure of the clay minerals.

[0024] In step 3, the prepared low molecular weight hydrophobic polyionic liquid is formulated into a 0.05-0.15% solution and injected into the reservoir.

[0025] In step 4, the prepared high molecular weight hydrophobic polyionic liquid is formulated into a solution and injected into the reservoir. The polyionic liquid preferentially enters the high permeability area along with the solution and is adsorbed on the rock. A hydrophobic film is formed on the rock wall and in the pore throat, making it difficult for the water phase to pass through while the oil phase can pass through easily. This significantly reduces the water phase permeability without affecting the oil phase permeability, thus playing a selective water-blocking role.

[0026] In step 4, the prepared high molecular weight hydrophobic polyionic liquid is formulated into a 0.3-0.5% solution and injected into the oil reservoir.

[0027] The objective of this invention can also be achieved through the following technical measures: a system for preparing and applying hydrophobic polyionic anti-swelling and anti-blocking agents, wherein the system uses a method for preparing and applying hydrophobic polyionic anti-swelling and anti-blocking agents to prepare cationic hydrophobic polyionic liquids of different molecular weights for injection into reservoirs and oil reservoirs.

[0028] This invention discloses a method for preparing and applying a hydrophobic polyionic anti-swelling and plugging agent. By preparing cationic hydrophobic polyionic liquids of different molecular weights, it specifically addresses the problems of low adsorption strength, poor erosion resistance, and the risk of wetting reversal in existing anti-swelling agents on clay mineral surfaces, thereby extending the anti-swelling effect. It also specifically addresses the issue that existing water-blocking systems selectively block high-permeability areas but lack selective plugging ability for oil and water in the affected areas. This method reduces the permeability of the aqueous phase without affecting the permeability of the oil phase, thus achieving water-only plugging without oil plugging. This invention, through the preparation of cationic hydrophobic polyionic liquids of different molecular weights, specifically addresses the problems of low adsorption strength, poor erosion resistance, and the risk of wetting reversal in existing anti-swelling agents on clay mineral surfaces, thereby extending the anti-swelling effect. Furthermore, it specifically addresses the issue that existing water-blocking systems selectively block high-permeability areas but lack selective plugging ability for oil and water in the affected areas. This method reduces the permeability of the aqueous phase without affecting the permeability of the oil phase, thus achieving water-only plugging without oil plugging. Attached Figure Description

[0029] Figure 1 A flowchart of a specific embodiment of the preparation and application method of the hydrophobic polyionic anti-swelling and anti-blocking agent of the present invention;

[0030] Figure 2 This is a schematic diagram of the molecular structure of the ionic liquid precursor of the present invention;

[0031] Figure 3 This is a schematic diagram of the reaction equation for the polymerization of the ionic liquid precursor of the present invention into a hydrophobic polyionic liquid.

[0032] Figure 4 This is a surface wetting angle test diagram of a rock sample after treatment with the high molecular weight hydrophobic polyionic liquid provided by this invention;

[0033] Figure 5 This is a graph showing the relative permeability of oil and water obtained by steady-state method after the rock sample was treated with a high molecular weight hydrophobic polyionic liquid.

[0034] Figure 6 This is a schematic diagram of selective water blocking using a high molecular weight hydrophobic polyionic liquid provided by the present invention. Detailed Implementation

[0035] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0036] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0037] like Figure 1 As shown, Figure 1 This is a flowchart illustrating the preparation and application method of the hydrophobic polyionic anti-swelling and anti-blocking agent of the present invention. The preparation and application method of the hydrophobic polyionic anti-swelling and anti-blocking agent includes:

[0038] Step 1. Preparation of ionic liquid precursor: 1-Methyl-2-vinylimidazolium and 1,4-dichlorobenzyl chloride were uniformly stirred and dissolved in dimethyl sulfoxide. The molar volume ratio of 1-methyl-2-vinylimidazolium, 1,4-dichlorobenzyl chloride, and dimethyl sulfoxide was 4-7 mmol:5 mmol:5-10 ml. The mixture was heated at 55-75 °C for 20-24 h under a nitrogen atmosphere. After the reaction was completed, the supernatant was filtered, and the solid was collected. The solid was rotary evaporated for 5-7 h, and then dried in a vacuum drying oven at 80-100 °C for 24-30 h to obtain the ionic liquid, which was used as the precursor for the next reaction. The ionic liquid was ground into particles and added to a mixed solution of water and dimethyl sulfoxide. The mixture was stirred continuously at room temperature until completely dissolved to obtain the ionic liquid solution.

[0039] Step 2. Preparation of hydrophobic polyionic liquid: Take the ionic liquid solution, add azobisisobutyronitrile and hydroxyethyl methacrylate, and stir at 60-70℃ for 5-6 hours under nitrogen protection to ensure complete dissolution of the reactants. Then, raise the temperature to 100-115℃ and stir for 30-35 hours to ensure sufficient reaction. Wash the resulting blocky solid three times with dimethyl sulfoxide to remove unreacted reactants, then vacuum dry for 24 hours and grind to obtain black solid particles. Centrifuge the black solid particles 3-5 times at 6000-10000 r / min using anhydrous ethanol and deionized water alternately. After centrifugation, remove the supernatant, collect the precipitate, and vacuum dry the precipitate at 70-85℃ for 20-25 hours. Grind the obtained solid particles to obtain solid powder, thus obtaining the hydrophobic polyionic liquid.

[0040] The addition ratio of ionic liquid precursor, water, and dimethyl sulfoxide was controlled at 0.35-0.62 g: 0.38-0.86 ml: 3.0-3.3 ml, the addition ratio of azobisisobutyronitrile was 1.8-2.4 wt.%, and the molar ratio of ionic liquid precursor and hydroxyethyl methacrylate was 0.85-1.05 mmol: 0.45-0.65 mmol, to prepare a hydrophobic polyionic liquid with a low molecular weight of 20,000-30,000.

[0041] A hydrophobic polyionic liquid with a molecular weight of 300,000-500,000 was prepared by controlling the addition ratio of ionic liquid precursor, water, and dimethyl sulfoxide to be 1.2-1.8 g: 0.4-0.9 ml: 3.2-3.8 ml, the addition ratio of azobisisobutyronitrile to be 1.8-2.4 wt.%, and the molar ratio of precursor to hydroxyethyl methacrylate to be 2-2.5 mmol: 1.2-1.5 mmol.

[0042] Step 3: The prepared low molecular weight hydrophobic polyionic liquid is formulated into a 0.05-0.15% solution and injected into the reservoir. The polyionic liquid can be adsorbed with high strength on the negatively charged clay minerals on the surface of the reservoir rock under electrostatic action, preventing water from entering the interlayer structure of the clay minerals, thereby avoiding clay hydration and playing an anti-swelling role. Compared with traditional inorganic salt anti-swelling agents such as ammonium chloride, the polyionic liquid has a stronger electrostatic adsorption force with clay minerals, so it is more resistant to erosion and has a longer anti-swelling effect.

[0043] Step 4: The prepared high molecular weight hydrophobic polyionic liquid is formulated into a 0.3-0.5% solution and injected into the reservoir. The polyionic liquid preferentially enters the high permeability area along with the solution and is adsorbed on the rock. A hydrophobic film is formed on the rock wall and in the pore throat, making it difficult for the water phase to pass through while the oil phase can pass through easily. That is, the water phase permeability is greatly reduced without affecting the oil phase permeability, thus playing a selective water-blocking role.

[0044] This invention can be applied to oilfield development and production. It can be injected into the reservoir as an anti-swelling agent or injected into the oil reservoir, which significantly reduces the water phase permeability without affecting the oil phase permeability, thus achieving selective water shut-off.

[0045] The following are several specific embodiments of the application of the present invention.

[0046] Example 1:

[0047] This embodiment provides a method for preparing a low molecular weight hydrophobic polyionic liquid and its application in preventing swelling, including:

[0048] S1: Preparation of the ionic liquid precursor: 1-Methyl-2-vinylimidazole and 1,4-dichlorobenzyl chloride were uniformly stirred and dissolved in dimethyl sulfoxide. The molar volume ratio of 1-methyl-2-vinylimidazole, 1,4-dichlorobenzyl chloride, and dimethyl sulfoxide was 5 mmol:5 mmol:10 ml. The mixture was heated at 70 °C for 20 h under a nitrogen atmosphere. After the reaction was complete, the supernatant was filtered, and a pale yellow solid was collected. The solid was rotary evaporated for 6 h, and then dried in a vacuum drying oven at 100 °C for 30 h to obtain the ionic liquid. Its molecular structure is as follows: Figure 2 As shown in the figure, the ionic liquid itself carries a positive charge, meaning the obtained ionic liquid is cationic.

[0049] S2: Preparation of low molecular weight hydrophobic polyionic liquid: The ionic liquid obtained in S1 was ground into particles and added to a mixed solution of water and dimethyl sulfoxide (DMSO). The ratio of ionic liquid, water, and DMSO was 0.5 g: 0.5 ml: 3.0 ml. The mixture was stirred continuously at room temperature until completely dissolved to obtain an ionic liquid solution. Azobisisobutyronitrile (AIBN) and hydroxyethyl methacrylate (HYMA) were added to the ionic liquid solution. The ratio of AIBN to IABN was 1 mmol: 0.5 mmol: 2.0 wt.%. Under nitrogen protection, the mixture was stirred at 70 °C for 6 hours, then heated to 100 °C and stirred for 30 hours to obtain a black blocky solid. The solid obtained from the reaction was washed three times with DMSO to remove unreacted reactants, then vacuum dried for 24 hours and ground to obtain black solid particles. The black solid particles were centrifuged five times at 8000 r / min using alternating cycles of anhydrous ethanol and deionized water. After centrifugation, the supernatant was removed, and the precipitate was collected and vacuum-dried at 80℃ for 24 h. Then, a Soxhlet extraction was performed using a mixture of ethanol and water to remove excess small-molecule solvent. The resulting solid was ground again to obtain a black solid powder, thus preparing the hydrophobic polyionic liquid. Its molecular weight was measured to be approximately 26000. The molecular structure of the polyionic liquid is shown below. Figure 3 As shown, each repeating monomer has two positive charges in its body portion;

[0050] S3: Indoor evaluation of the anti-swelling performance of low molecular weight hydrophobic polyionic liquid; a hydrophobic polyionic liquid solution with a mass concentration of 0.1% was prepared using oilfield reinjection wastewater; the anti-swelling rate was determined by centrifugation according to the petroleum and natural gas industry standard, and its water wash resistance and permeability retention rate were tested. The results showed an anti-swelling rate of 93.3%, a water wash resistance of 97.0%, and a permeability retention rate of 92.7%, all of which exceeded the requirements of Shengli Oilfield for anti-swelling agents;

[0051] S4: Field application evaluation of the anti-swelling performance of hydrophobic polyionic liquid; dissolving 0.15 tons of hydrophobic polyionic liquid into 150m³ 3 In a case study, an acid solution containing a hydrophobic polyionic liquid was injected into an oil well in the Shengli Oilfield for acidizing and unblocking. The results were compared with those of an acidizing and unblocking well in the same block that used potassium chloride as an anti-swelling agent. Before unblocking, the acid system using the hydrophobic polyionic liquid as an anti-swelling agent produced 3.0 tons of fluid and 0.5 tons of oil per day; after unblocking, it produced 8.3 tons of fluid and 4.7 tons of oil per day. The acid system using the hydrophobic polyionic liquid as an anti-swelling agent produced 3.2 tons of fluid and 1.5 tons of oil per day before unblocking; after unblocking, it produced 6.8 tons of fluid and 3.5 tons of oil per day. Overall, using the hydrophobic polyionic liquid as an anti-swelling agent resulted in better seepage retention and better unblocking performance.

[0052] Example 2:

[0053] This embodiment provides a method for preparing a high molecular weight hydrophobic polyionic liquid and its application in selective water plugging, including:

[0054] S1: Preparation of the ionic liquid precursor: 1-Methyl-2-vinylimidazole and 1,4-dichlorobenzyl chloride were uniformly stirred and dissolved in dimethyl sulfoxide. The molar volume ratio of 1-methyl-2-vinylimidazole, 1,4-dichlorobenzyl chloride, and dimethyl sulfoxide was 5 mmol:5 mmol:10 ml. The mixture was heated at 70 °C for 20 h under a nitrogen atmosphere. After the reaction was completed, the supernatant was filtered, and a pale yellow solid was collected. The solid was rotary evaporated for 6 h, and then dried in a vacuum drying oven at 100 °C for 30 h to obtain the ionic liquid. Its molecular structure remained as shown in the figure. Figure 2 As shown;

[0055] S2: Preparation of high molecular weight hydrophobic polyionic liquid: The ionic liquid obtained in S1 was ground into particles and added to a mixed solution of water and dimethyl sulfoxide (DMSO). The ratio of ionic liquid, water, and DMSO was 1.5 g: 0.6 ml: 3.5 ml. The mixture was stirred continuously at room temperature until completely dissolved to obtain an ionic liquid solution. Azobisisobutyronitrile (AIBN) and hydroxyethyl methacrylate (HYMA) were added to the ionic liquid solution. The ratio of ionic liquid solution, HYMA, and AIMA was 2 mmol: 1.5 mmol: 2.2 wt.%. Under nitrogen protection, the mixture was stirred at 70 °C for 6 hours, then heated to 100 °C and stirred for 30 hours to obtain a black blocky solid. The solid obtained from the reaction was washed three times with DMSO to remove unreacted reactants, then vacuum dried for 24 hours and ground to obtain black solid particles. The black solid particles were centrifuged five times at 8000 r / min using alternating cycles of anhydrous ethanol and deionized water. After centrifugation, the supernatant was removed, and the precipitate was collected and vacuum-dried at 80℃ for 24 h. Then, a Soxhlet extraction was performed using a mixture of ethanol and water to remove excess small-molecule solvent. The resulting solid was ground again to obtain a black solid powder, thus preparing the hydrophobic polyionic liquid. Its molecular weight was measured to be 390,000, and the molecular structure of the polyionic liquid remained as described above. Figure 3 As shown, however, the number of repeating monomers, n, is much greater than the number of low molecular weight hydrophobic polyions, n.

[0056] S3: Indoor evaluation of the hydrophobic properties of high molecular weight hydrophobic polyionic liquid; a hydrophobic polyionic liquid with a mass fraction of 0.5% was prepared using oilfield reinjection wastewater; firstly, the effect of the hydrophobic polyionic liquid on the wettability of rock samples was evaluated: in accordance with the petroleum and natural gas industry standards, the rock samples were treated with the prepared hydrophobic polyionic liquid, and the wettability was measured according to the contact angle method. Figure 4The wetting angles of oil and water droplets on the treated rock surface are shown. It can be seen that after treatment with the high molecular weight hydrophobic polyionic liquid, oil droplets spread completely on the rock surface, indicating a strongly oil-wet surface; water droplets are almost spherical on the rock surface, indicating a strongly hydrophobic surface. Then, the relative permeability curves of cores treated with and without the hydrophobic polyionic liquid were measured using a steady-state method. The results are as follows: Figure 5 As shown, the water phase permeability of the core treated with hydrophobic polyionic liquid is significantly reduced, indicating the hydrophobic and water-blocking effect of the hydrophobic polyionic liquid. Due to the decrease in water permeability, the crude oil outflow from the core outlet under constant injection rate conditions is significantly increased, leading to an increase in oil phase permeability. The isopermeability point of the phase permeability curve shifts to the right, indicating that the oil-water flow relationship is improved. The hydrophobic polyionic liquid exhibits the effect of regulating phase permeability and blocking water without blocking oil.

[0057] S4: Field application evaluation of hydrophobic polyionic liquids; dissolving 1.5 tons of hydrophobic polyionic liquid into 300m³ 3 A plugging agent solution was prepared from wastewater reinjected into the oilfield. A high-yield, high-water-cut oil well in the Shengli Oilfield was selected, and the plugging agent solution was injected into the well. After simmering for 3 days, the well was reopened. Before the treatment, the well produced 18 tons of fluid and 1.5 tons of oil per day, with a water cut of 91.7%. After the treatment, the well produced 12 tons of fluid and 3.5 tons of oil per day, with a water cut of 70.8%. Compared to other oil wells where daily fluid production decreased by more than 50% after gel plugging, the hydrophobic polyionic liquid did not completely block the high-permeability layer but preserved its oil-producing capacity, thus improving the fluid production retention capacity. Figure 6 The differences in mechanism between gel-based water plugging and hydrophobic polyionic liquid-based water plugging are presented: When using gel-based water plugging, after the gel forms in the pore throat of the high-permeability zone, its three-dimensional network structure occupies the entire pore throat space, preventing both oil and water from passing through, i.e., complete oil and water plugging; When using hydrophobic polyionic liquid-based water plugging, after entering the pore throat, its cationic groups are tightly connected and adsorbed to the negatively charged clay minerals by electrostatic force, and the hydrophobic chains extend into the pore throat to form a hydrophobic film. When oil flows into this space, it can easily pass through, while water cannot pass through, i.e., water plugging but not oil plugging.

[0058] The present invention relates to the preparation of hydrophobic polyionic liquid and its application in anti-swelling and selective water shut-off. By preparing an ionic liquid precursor and obtaining a polyionic liquid through a polymerization reaction, the polyionic liquid is used for clay anti-swelling and selective water shut-off in oilfield development to improve the anti-swelling and water shut-off effects.

[0059] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0060] Except for the technical features described in the specification, all other technologies are known to those skilled in the art.

Claims

1. A method for preparing and applying a hydrophobic polyionic anti-swelling and anti-blocking agent, characterized in that, The preparation and application methods of this hydrophobic polyionic anti-swelling and plugging agent include: Step 1: Prepare the ionic liquid precursor, which is made by mixing 1-methyl-2-vinylimidazolium, 1,4-dichlorobenzyl, and dimethyl sulfoxide. Step 2: Prepare low molecular weight hydrophobic polyionic liquid and high molecular weight hydrophobic polyionic liquid. Both low molecular weight hydrophobic polyionic liquid and high molecular weight hydrophobic polyionic liquid are prepared by mixing ionic liquid precursor, water and dimethyl sulfoxide. Step 3: Prepare the low molecular weight hydrophobic polyionic liquid into a solution and inject it into the reservoir; Step 4: Prepare a solution from the high molecular weight hydrophobic polyionic liquid and inject it into the oil reservoir.

2. The method for preparing and applying the hydrophobic polyionic anti-swelling and plugging agent according to claim 1, characterized in that, In step 1, 1-methyl-2-vinylimidazole and 1,4-dichlorobenzyl were uniformly stirred and dissolved in dimethyl sulfoxide, and heated at high temperature under a nitrogen atmosphere. After the reaction was completed, the supernatant was filtered, the solid was collected, the solid was rotary evaporated, and then dried in a vacuum drying oven to obtain an ionic liquid, which was used as the precursor for the reaction in step 2. The ionic liquid was ground into particles and added to a mixed solution of water and dimethyl sulfoxide, and stirred continuously at room temperature until completely dissolved to obtain the ionic liquid precursor.

3. The method for preparing and applying the hydrophobic polyionic anti-swelling and anti-blocking agent according to claim 2, characterized in that, In step 1, the molar volume ratio of 1-methyl-2-vinylimidazole, 1,4-dichlorobenzyl, and dimethyl sulfoxide is 4-7 mmol: 5 mmol: 5-10 ml.

4. The method for preparing and applying the hydrophobic polyionic anti-swelling and anti-blocking agent according to claim 1, characterized in that, In step 2, the ionic liquid precursor was taken, and azobisisobutyronitrile and hydroxyethyl methacrylate were added. Under nitrogen protection, the mixture was first stirred at high temperature to ensure complete dissolution of the reactants, and then heated and stirred to ensure sufficient reaction. The resulting blocky solid was washed multiple times with dimethyl sulfoxide to remove unreacted reactants, and then vacuum dried and ground to obtain black solid particles. The black solid particles were centrifuged multiple times with alternating anhydrous ethanol and deionized water. After centrifugation, the supernatant was removed, the precipitate was collected, and the precipitate was vacuum dried at high temperature. The obtained solid particles were then ground to obtain solid powder, thus preparing the hydrophobic polyionic liquid.

5. The method for preparing and applying the hydrophobic polyionic anti-swelling and anti-blocking agent according to claim 4, characterized in that, In step 2, the addition ratio of ionic liquid precursor, water, and dimethyl sulfoxide is controlled to be 0.35-0.62 g: 0.38-0.86 ml: 3.0-3.3 ml, the addition ratio of azobisisobutyronitrile is 1.8-2.4 wt.%, and the molar ratio of ionic liquid precursor and hydroxyethyl methacrylate is 0.85-1.05 mmol: 0.45-0.65 mmol, to obtain a hydrophobic polyionic liquid with a low molecular weight of 20,000-30,000.

6. The method for preparing and applying the hydrophobic polyionic anti-swelling and anti-blocking agent according to claim 4, characterized in that, In step 2, the addition ratio of ionic liquid precursor, water, and dimethyl sulfoxide is controlled to be 1.2-1.8 g: 0.4-0.9 ml: 3.2-3.8 ml, the addition ratio of azobisisobutyronitrile is 1.8-2.4 wt.%, and the molar ratio of ionic liquid precursor and hydroxyethyl methacrylate is 2-2.5 mmol: 1.2-1.5 mmol, to obtain a hydrophobic polyionic liquid with a high molecular weight of 300,000-500,000.

7. The method for preparing and applying the hydrophobic polyionic anti-swelling and anti-blocking agent according to claim 1, characterized in that, In step 3, the prepared low molecular weight hydrophobic polyionic liquid is formulated into a solution and injected into the reservoir. The polyionic liquid can be adsorbed on the negatively charged clay minerals on the surface of the reservoir rock under electrostatic action, preventing water from entering the interlayer structure of the clay minerals.

8. The method for preparing and applying the hydrophobic polyionic anti-swelling and anti-blocking agent according to claim 7, characterized in that, In step 3, the prepared low molecular weight hydrophobic polyionic liquid is formulated into a 0.05-0.15% solution and injected into the reservoir.

9. The method for preparing and applying the hydrophobic polyionic anti-swelling and anti-blocking agent according to claim 1, characterized in that, In step 4, the prepared high molecular weight hydrophobic polyionic liquid is formulated into a solution and injected into the reservoir. The polyionic liquid preferentially enters the high permeability area along with the solution and is adsorbed on the rock. A hydrophobic film is formed on the rock wall and in the pore throat, making it difficult for the water phase to pass through while the oil phase can pass through easily. This significantly reduces the water phase permeability without affecting the oil phase permeability, thus playing a selective water-blocking role.

10. The method for preparing and applying the hydrophobic polyionic anti-swelling and plugging agent according to claim 9, characterized in that, In step 4, the prepared high molecular weight hydrophobic polyionic liquid is formulated into a 0.3-0.5% solution and injected into the oil reservoir.

11. A system for preparing and applying hydrophobic polyionic anti-swelling and anti-blocking agents, characterized in that, The system for preparing and applying hydrophobic polyionic anti-swelling and plugging agent uses the method described in any one of claims 1-10 to prepare cationic hydrophobic polyionic liquids of different molecular weights for injection into reservoirs and oil reservoirs.

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