A microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs and its preparation method

Abstract

This invention discloses a microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs and its preparation method. The microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs comprises, by weight percentage: 10-15% micelle agent, 15-20% emulsifier, 4-6% co-surfactant, 10-15% regulator, 15-20% solubilizer, 3-5% enhancer, and the balance being deionized water. This invention solves the problems of high start-up pressure gradient, low water drive efficiency, poor oil displacement efficiency, limited pressure space of surface water injection systems, and the exacerbation of planar and vertical contradictions in ultra-low permeability reservoirs due to microfractures in some reservoirs. It achieves integrated operation of pressure reduction and injection enhancement, profile modification, oil displacement, and production enhancement in low-permeability reservoirs, maintains formation energy in the well group, reduces the natural decline rate of the reservoir, and provides a favorable approach for the efficient utilization, rapid development, and long-term management of ultra-low permeability reservoirs.

Description

Technical Field

[0001] This invention belongs to the field of oilfield development technology, and relates to the field of self-regulating oil displacement, production enhancement and stabilization technology for ultra-low permeability reservoirs. Specifically, it relates to a microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs and its preparation method. Background Technology

[0002] While waterflooding in ultra-low permeability reservoirs has achieved good production results, the tight geological conditions limit the establishment of effective pressure displacement systems in some well groups. Water wells exhibit high pressure under-injection, with formation pressure remaining below 90% of normal levels, and a significant annual decrease of 25-50% in the initial stages. Some ultra-low permeability reservoirs also suffer from poor fracture network matching, rapid water cut increases, and overall low waterflooding efficiency, resulting in a low utilization rate of water-driven oilfields. To improve the utilization rate of water-driven oil in ultra-low permeability reservoirs, domestic methods mainly include surfactant flooding, polymer microsphere flooding, air foam flooding, and carbon dioxide flooding. Surfactant flooding primarily uses sulfonate and sulfate surfactants to reduce oil-water interfacial tension and improve water recovery. However, due to the high permeability of tight reservoirs in ultra-low permeability reservoirs, the utilization of lateral residual oil is limited. Air foam flooding and carbon dioxide flooding mainly use gaseous media to increase formation energy. However, due to the influence of early fracturing and channeling, gas channeling becomes severe after a certain period of production, affecting well group productivity. Polymer microsphere-based enhanced oil recovery (EOR) utilizes high-dose, low-concentration nano- or micron-sized polymer materials to seal microfractures in the water-drive channels of ultra-low permeability reservoirs. Multiple rounds of sealing and pressure increases cause subsequent water injection to bypass these fractures, expanding the water-drive sweep area and playing a crucial role in improving oil recovery in ultra-low permeability reservoirs. However, the working fluid of polymer microsphere-based EOR suffers from increased water injection pressure and limited pressure space after multiple rounds of EOR in ultra-low permeability reservoirs. Furthermore, its ability to absorb, permeate, and wash away residual oil laterally is weak, leading to a gradual decrease in the rate of oil recovery improvement. Therefore, for water-drive EOR in ultra-low permeability oilfields, a displacement agent with strong absorption, permeation, and oil washing capabilities, capable of self-regulating fluid viscosity and particle size changes, is needed to specifically address these issues. This would enable integrated pressure reduction, profile control, oil displacement, and oil production enhancement in ultra-low permeability reservoirs, providing a favorable method for efficient utilization, rapid development, and long-term management of ultra-low permeability reservoirs.

[0003] Chinese Patent Publication No. CN113604209A, published on November 5, 2021, discloses an online-produced nanocomposite viscoelastic oil displacement agent, relating to the field of viscoelastic oil displacement agent technology. The online-produced nanocomposite oil displacement agent comprises, by weight percentage: 0.05%–0.8% surfactant and the balance water; wherein the surfactant includes erucamide propyl hydroxysulfonate, or erucamide propyl betaine, hexadecylamide propyl hydroxypropyl sulfonate, and tetradecylpropyl sulfonate. The composite oil displacement agent of this invention may further include at least one of tetradecylamide propyl hydroxypropyl sulfonate and hexadecylpropyl sulfonate, and / or, a content not exceeding 0.05% of nano-silica, and / or, a content not exceeding 0.03% of sodium dodecylbenzenesulfonate, and / or, 0.05%–0.1% of polyether diamine and 0.05%–0.1% of salicylic acid. For reservoirs with varying salinity and permeability, the viscosity and interfacial tension of the nanocomposite viscoelastic oil displacement agent of this invention are controllable within the oil layer; it fully utilizes inorganic ions in the injection water while ensuring online injection. Chinese Patent Publication (Announcement) No. CN115926204A, published on April 7, 2023, discloses a thermosensitive spherical shell with self-regulating permeability polymer microspheres and its preparation method. This relates to the technical field of polymer microspheres and their preparation methods. Specifically, it discloses a thermosensitive bidirectional shape memory nanoparticle composite within a spherical shell, acting as a "microswitch." The shrinkage / recovery effect generated by the nanoparticles in response to temperature increases / decreases increases / decreases the pore size within the shell, thereby regulating the shell's permeability. This allows for increasing the pore size of the shell without damaging its structure, thereby enhancing water vapor permeability during high-temperature drying and accelerating the escape rate of moisture from the microsphere's core. After drying, the pore size of the shell shrinks at room temperature, ensuring the mechanical and optical properties required for the application of core-shell polymer microspheres. This invention can significantly improve the drying efficiency of water-containing core-shell polymer microspheres, facilitating the high-throughput manufacturing of hollow polymer microspheres. Chinese Patent Publication (Announcement) No. CN115340857A, published on November 15, 2022, discloses an in-situ self-emulsifying nano-oil displacement agent, its preparation method, and its application. This invention relates to the field of nano-oil displacement agents, their preparation methods, and applications, and discloses an in-situ self-emulsifying nano-oil displacement agent, its preparation method, and its application. It includes hyperbranched nanomaterials, polymeric AOS, and anionic surfactants; wherein the mass fraction of the hyperbranched nanomaterials is 7–10 wt%; the mass fraction of the polymeric AOS is 20–30 wt%; the mass fraction of the anionic surfactant is 10–20 wt%; and the remainder is water.This application's in-situ emulsified nano-oil displacement agent uses a low concentration, exhibits excellent emulsification, and achieves an interfacial tension of 10⁻² mN / m. It has a wide temperature range, suitable for temperatures from 30 to 120°C, demonstrates good stability, exhibits no stratification or precipitation, and displays excellent salt resistance. After aging at 120°C for 8 hours, the emulsification solubility and interfacial tension show minimal changes, indicating excellent temperature resistance. No demulsifier is required; dehydration is achieved simply by standing, achieving the excellent effect of "emulsification upon contact and dehydration upon cessation."

[0004] The aforementioned patents represent viscoelastic and emulsified nano-displacement agents, which reduce the interfacial tension between crude oil and injected water by emulsifying crude oil with surfactants. They also introduce nano-silica or hyperbranched nanomaterials to form a nanofluid, expanding the contact area and adsorption capacity of the agent on the rock surface to extend the effective period of oil displacement. Self-regulating polymer microsphere-based displacement materials primarily use nano- or micron-sized polymer molecular clusters to slowly expand and block water-drive channels in old fractures within the formation. Depending on the expansion ratio, they self-regulate the blocking of fractures of different widths, forcing a change in water-drive flow direction and improving the recovery rate of remaining reservoir oil. These patented products and technologies play a crucial role in enhancing oil recovery and maintaining efficient development of low-permeability oilfields through water-drive. In ultra-low permeability reservoirs, the rock matrix has low permeability and is denser, with a median pore radius of only 200-300 nm. Solid-phase nanomaterial oil displacement agents are present. Although the particle size is as small as 20-50 nm, the adsorption specific surface efficiency of nanomaterials is a double-edged sword. High-efficiency nanomaterials are difficult to achieve single-layer adsorption in rock pores. Low-concentration, long-term injection of such oil displacement agents can easily lead to adsorption and aggregation, clogging of pore throats, causing under-injection of deep water wells under high pressure, which brings great difficulties to the next step of injection enhancement measures. Ultra-low permeability reservoirs have high water-drive initiation pressure gradients, making it very difficult for injected water to displace the matrix. 50nm or 100nm polymer microspheres used for water-driven oil recovery have difficulty circulating within the matrix. When these microspheres swell upon contact with water, they are almost unable to enter the pore throats of the ultra-low permeability reservoir rock, limiting their ability to drive residual oil in the wellbore's lateral matrix. This material only extends from low-permeability reservoirs to ultra-low permeability reservoirs. The ability of polymers and injected water alone to wash oil from the rock is weak, which is one of the reasons why the recovery rate of polymer microsphere-driven oil recovery in ultra-low permeability reservoirs has decreased year by year in the past. To improve the recovery rate of denser ultra-low permeability reservoirs, it is necessary to address issues such as high start-up pressure gradients, low water drive efficiency, poor oil displacement efficiency, and limited pressure space in surface water injection systems. Additionally, some reservoirs exhibit microfractures, exacerbating horizontal and vertical contradictions in ultra-low permeability reservoirs. Therefore, it is essential to develop an oil displacement working fluid that can effectively address these problems, achieving integrated pressure reduction and injection enhancement, profile modification, oil displacement, and production improvement in ultra-low permeability reservoirs, while maintaining formation energy within the well group, thus facilitating the efficient development of ultra-low permeability reservoirs. Summary of the Invention

[0005] The purpose of this invention is to address the problems of high start-up pressure gradient, low waterflooding efficiency, poor oil displacement efficiency, limited pressure space in surface water injection systems, and the exacerbation of planar and vertical contradictions in ultra-low permeability reservoirs caused by microfractures in some reservoirs. This invention aims to achieve integrated operations of depressurization and injection enhancement, profile modification, oil displacement, and production enhancement in low-permeability reservoirs, maintaining formation energy, reducing the natural decline rate of the reservoir, and providing a favorable approach for the efficient utilization, rapid development, and long-term management of ultra-low permeability reservoirs. This invention also provides a microemulsion viscoelastic self-regulating oil displacement agent formulation and preparation method for ultra-low permeability reservoirs.

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

[0007] A microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs, comprising the following components by weight percentage:

[0008] micelle agent 10-15%,

[0009] Emulsifier 15-20%,

[0010] 4-6% co-surfactant

[0011] Regulator 10-15%,

[0012] Solubilizer 15-20%,

[0013] 3-5% reinforcing agent

[0014] The remainder is deionized water.

[0015] Furthermore, the micelle agent is composed of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate and oleamidopropyl dimethylamine, wherein the weight percentage content of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate is 55-77%, and the weight percentage content of oleamidopropyl dimethylamine is 23-45%.

[0016] Furthermore, the emulsifier is composed of styrene-based phenol polyoxyethylene ether, isotridecyl alcohol polyoxyethylene ether, wherein the weight percentage content of styrene-based phenol polyoxyethylene ether is 52-70%, the weight percentage content of isotridecyl alcohol polyoxyethylene ether is 25-35%, and the weight percentage content of isotridecyl alcohol polyoxyethylene polyoxypropylene ether is 5-13%.

[0017] Furthermore, the co-surfactant is bis(dodecylmethylhydroxypropyl)sulfobetaine.

[0018] Furthermore, the regulator is one or more components of α-piperene or β-piperene.

[0019] Furthermore, the solubilizer is one or a mixture of N'N dimethylacetamide or N'N dimethylformamide.

[0020] Furthermore, the reinforcing agent is composed of potassium chloride and potassium hydroxide, wherein the potassium chloride content is 50-75% by weight and the potassium hydroxide content is 25-50% by weight.

[0021] A method for preparing a microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs includes the following steps:

[0022] First, add 15-20% by weight of solubilizer to the reactor, heat the reactor to 40-50℃, and start stirring at a speed of 50-60 r / min. Then, add 15-20% by weight of emulsifier and stir until the solid is completely dissolved. Next, add 10-15% by weight of regulator and add it over a time of 40-60 min. Then, mix 3-5% by weight of reinforcing agent with 21-41% by weight of deionized water to obtain a reinforcing agent solution. Add the reinforcing agent solution to the reactor under stirring and add it over a time of 40-60 min. Then, add 10-15% by weight of micelle agent and stir for 10-20 min. Finally, add 4-6% by weight of co-surfactant and stir for 20-30 min. Cool to room temperature and discharge to obtain the ultra-low permeability reservoir microemulsion viscoelastic self-regulating oil displacement agent product.

[0023] Furthermore, the micelle agent is composed of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate and oleamide propyl dimethylamine;

[0024] The emulsifier is composed of styrene-based phenol polyoxyethylene ether, isotridecyl alcohol polyoxyethylene ether, and others.

[0025] The co-surfactant is bis(dodecylmethylhydroxypropyl)sulfobetaine;

[0026] The regulator is α-piperene or β-piperene;

[0027] The solubilizer is one or a mixture of N'N dimethylacetamide or N'N dimethylformamide;

[0028] The reinforcing agent is composed of potassium chloride and potassium hydroxide.

[0029] Furthermore, the preparation method of the ultra-low permeability reservoir microemulsion viscoelastic self-regulating oil displacement agent includes the following steps:

[0030] S1. First, add 15-20% by weight of one or a mixture of both of N'N dimethylacetamide and N'N dimethylformamide to the reactor, heat the reactor to 40-50℃, and start stirring at a stirring speed of 50-60r / min.

[0031] S2, then add 9-12% by weight of styrene-phenol polyoxyethylene ether, 5-6% by weight of isotridecyl alcohol polyoxyethylene ether and 1-2% by weight of isodecyl alcohol polyoxyethylene polyoxypropylene ether, and stir at 100-120 r / min for 10-20 min until the solid is completely dissolved.

[0032] S3, then add 10-15% by weight of one or a mixture of α-piperene or β-piperene, and control the dropping time at 40-60 min;

[0033] S4. Mix 2-3% potassium chloride, 1-2% potassium hydroxide and 21-41% deionized water by weight to obtain a reinforcing agent solution. Add the reinforcing agent solution to the reaction vessel under stirring at 100-120 r / min, and control the dropping time at 40-60 min.

[0034] S5, under stirring conditions of 50-60 r / min, add 7-10% by weight of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate and 3-5% by weight of oleamidopropyl dimethylamine, and stir for 10-20 min;

[0035] S6, and finally add 4-6% by weight of dodecylmethylhydroxypropyl sulfobetaine, stir for 20-30 minutes, cool to room temperature and discharge to obtain the ultra-low permeability reservoir microemulsion viscoelastic self-regulating oil displacement agent product.

[0036] Compared with the prior art, the advantages of the present invention are as follows:

[0037] 1. Microemulsion viscoelastic self-regulating oil displacement agents in ultra-low permeability reservoirs utilize the viscoelastic properties of surfactants to automatically regulate the oil displacement process within the water drive channel, forcing the oil displacement agent into areas with high oil saturation or enriched residual oil, thereby improving the oil displacement efficiency. In the microemulsion viscoelastic self-regulating oil displacement agent, octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate, oleamide propyl dimethylamine, and didodecyl methyl hydroxypropyl sulfobetaine form large and small energy-compensating micelles in potassium chloride solution, exhibiting good viscoelasticity. Upon encountering high-salinity formation water (the dominant channel for early water drive), the viscosity increases accordingly, increasing water drive flow resistance and forcing the oil displacement agent solution to flow in other directions. When the microemulsion viscoelastic self-regulating oil displacement agent encounters areas with high oil saturation or enriched residual oil, the formation water and crude oil cause the viscoelastic micelles of the oil displacement agent to decrease in viscosity and break down, reducing water drive flow resistance and expanding the sweep area and oil displacement efficiency of the oil displacement agent in areas with high oil saturation or enriched residual oil.

[0038] 2. Microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs nanoscales the injected water molecules, further enhancing the penetration of the oil displacement agent in the low-porosity, narrow throats of ultra-low permeability reservoirs, thus promoting water well pressure reduction and injection enhancement. The microemulsion viscoelastic self-regulating oil displacement agent contains no solid-phase nanomaterials. It mainly consists of styrene-based phenol polyoxyethylene ether, isomeric tridecyl alcohol polyoxyethylene ether, and isomeric decayl alcohol polyoxyethylene polyoxypropylene ether, along with α-piperene (β-piperene), forming a nanoscale microemulsion under the action of N'N dimethylformamide. This improves the permeability and penetration of injected water. Furthermore, when mixed with injected water, it does not cause blockage of the pores and throats of ultra-low permeability reservoirs due to multilayer adsorption of solid-phase nanomaterials, leading to under-injection of high pressure in water wells. Instead, it utilizes the small particle size effect of the microemulsion to reduce the capillary resistance of the narrow throats in the water drive channels of ultra-low permeability reservoirs, thereby reducing injection pressure and achieving an integrated function of oil displacement, pressure reduction, and injection enhancement.

[0039] 3. Microemulsion viscoelastic self-regulating oil displacement agents in ultra-low permeability reservoirs nanoscale the injected water molecules, enhancing the oil-water permeation and displacement capacity of the injected water containing the oil displacement agent within the ultra-low permeability reservoir matrix. This promotes the aggregation and displacement of remaining oil, thus improving the overall crude oil recovery rate within the matrix. Emulsifiers such as styrene-phenol polyoxyethylene ether, combined with pendiene under the action of N'N dimethylformamide, form nanoscale microemulsions. With the support of potassium chloride and potassium hydroxide salts and surfactants, these microemulsions mutually dissolve and clean the heavy organic components on the matrix pore walls, enhancing their ability to displace crude oil. Some oil in the small pores is displaced and driven out. Through nanoemulsification, the permeated and displaced crude oil aggregates into clusters. As time increases, the oil droplets inside the ultra-low permeability reservoir core gradually increase in size and become denser; the denser the clusters, the more pronounced the oil production, forming displaceable crude oil droplets. This results in a higher crude oil recovery rate in the small pores of the ultra-low permeability reservoir matrix compared to conventional surfactants, facilitating further utilization of remaining oil.

[0040] 4. Microemulsion viscoelastic self-regulating oil displacement agents for ultra-low permeability reservoirs have integrated functions of pressure reduction and injection enhancement, profile modification, oil displacement, and production enhancement. These agents utilize the small particle size, multi-scale, and high specific surface area of ​​microemulsions to permeate and absorb within the small pores of the matrix. Micellar agents form viscoelastic surfactants that control the direction of water drive, while regulators and solubilizers dissolve high-carbon-chain organic matter. The surfactants, under the action of potassium hydroxide and micellar agents, enhance oil displacement capacity. Under the water drive pressure of the well group, these agents achieve multi-functional integration, combining water well injection enhancement, production enhancement, profile modification, and oil displacement to achieve multiple effects with a single agent. This maintains formation energy, reduces the natural decline rate of the reservoir, and ensures efficient utilization and rapid development of ultra-low permeability reservoirs. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly described below.

[0042] Figure 1Figure 1 shows the test results of permeation time and permeation amount of ultra-low permeability oil reservoirs in different media.

[0043] Figure 2 This is a schematic diagram showing the test results of the viscoelasticity index of the microemulsion viscoelastic self-regulating oil displacement agent in ultra-low permeability reservoirs. Detailed Implementation

[0044] The invention can be further understood in conjunction with the following detailed description of preferred embodiments and included examples. Unless otherwise stated, 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. If any definition of a specific term disclosed in the prior art differs from any definition provided herein, the definition provided herein shall prevail.

[0045] This invention relates to a microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs, comprising the following components by weight percentage:

[0046] micelle agent 10-15%,

[0047] Emulsifier 15-20%,

[0048] 4-6% co-surfactant

[0049] Regulator 10-15%,

[0050] Solubilizer 15-20%,

[0051] 3-5% reinforcing agent

[0052] The remainder is deionized water.

[0053] Furthermore, the micelle agent is composed of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate and oleamidopropyl dimethylamine, wherein the weight percentage content of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate is 55-77%, and the weight percentage content of oleamidopropyl dimethylamine is 23-45%.

[0054] Furthermore, the emulsifier is composed of styrene-based phenol polyoxyethylene ether, isotridecyl alcohol polyoxyethylene ether, wherein the weight percentage content of styrene-based phenol polyoxyethylene ether is 52-70%, the weight percentage content of isotridecyl alcohol polyoxyethylene ether is 25-35%, and the weight percentage content of isotridecyl alcohol polyoxyethylene polyoxypropylene ether is 5-13%.

[0055] Furthermore, the co-surfactant is bis(dodecylmethylhydroxypropyl)sulfobetaine.

[0056] Furthermore, the regulator is one or more components of α-piperene or β-piperene.

[0057] Furthermore, the solubilizer is one or a mixture of N'N dimethylacetamide or N'N dimethylformamide.

[0058] Furthermore, the reinforcing agent is composed of potassium chloride and potassium hydroxide, wherein the potassium chloride content is 50-75% by weight and the potassium hydroxide content is 25-50% by weight.

[0059] This invention also provides a method for preparing a microemulsion viscoelastic self-regulating displacement agent for ultra-low permeability reservoirs, comprising the following steps:

[0060] First, add 15-20% by weight of solubilizer to the reactor, heat the reactor to 40-50℃, and start stirring at a speed of 50-60 r / min. Then, add 15-20% by weight of emulsifier and stir until the solid is completely dissolved. Next, add 10-15% by weight of regulator and add it over a time of 40-60 min. Then, mix 3-5% by weight of reinforcing agent with 21-41% by weight of deionized water to obtain a reinforcing agent solution. Add the reinforcing agent solution to the reactor under stirring and add it over a time of 40-60 min. Then, add 10-15% by weight of micelle agent and stir for 10-20 min. Finally, add 4-6% by weight of co-surfactant and stir for 20-30 min. Cool to room temperature and discharge to obtain the ultra-low permeability reservoir microemulsion viscoelastic self-regulating oil displacement agent product.

[0061] Preferably, the micelle agent is composed of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate and oleamide propyl dimethylamine; the emulsifier is composed of styrene-based phenol polyoxyethylene ether and isomeric tridecyl alcohol polyoxyethylene ether; the co-surfactant is bis(dodecylmethyl hydroxypropyl)sulfobetaine; the regulator is one or a mixture of α-piperene and β-piperene; the solubilizer is one or a mixture of N'N dimethylacetamide and N'N dimethylformamide; and the reinforcing agent is composed of potassium chloride and potassium hydroxide.

[0062] Furthermore, the preparation method of the ultra-low permeability reservoir microemulsion viscoelastic self-regulating oil displacement agent includes the following steps:

[0063] S1. First, add 15-20% by weight of one or a mixture of both of N'N dimethylacetamide and N'N dimethylformamide to the reactor, heat the reactor to 40-50℃, and start stirring at a stirring speed of 50-60r / min.

[0064] S2, then add 9-12% by weight of styrene-phenol polyoxyethylene ether, 5-6% by weight of isotridecyl alcohol polyoxyethylene ether and 1-2% by weight of isodecyl alcohol polyoxyethylene polyoxypropylene ether, and stir at 100-120 r / min for 10-20 min until the solid is completely dissolved.

[0065] S3, then add 10-15% by weight of one or a mixture of α-piperene or β-piperene, and control the dropping time at 40-60 min;

[0066] S4. Mix 2-3% potassium chloride, 1-2% potassium hydroxide and 21-41% deionized water by weight to obtain a reinforcing agent solution. Add the reinforcing agent solution to the reaction vessel under stirring at 100-120 r / min, and control the dropping time at 40-60 min.

[0067] S5, under stirring conditions of 50-60 r / min, add 7-10% by weight of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate and 3-5% by weight of oleamidopropyl dimethylamine, and stir for 10-20 min;

[0068] S6, and finally add 4-6% by weight of dodecylmethylhydroxypropyl sulfobetaine, stir for 20-30 minutes, cool to room temperature and discharge to obtain the ultra-low permeability reservoir microemulsion viscoelastic self-regulating oil displacement agent product.

[0069] Example 1:

[0070] This invention discloses a microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs, comprising, by weight percentage:

[0071] 10% octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate, 5% oleamide propyl dimethylamine, 9% styrylphenol polyoxyethylene ether, 5% isomeric tridecyl alcohol polyoxyethylene ether, 1% isomeric decayl alcohol polyoxyethylene polyoxypropylene ether, 15% N'N dimethyl acetamide, 4% dodecylmethyl hydroxypropyl sulfobetaine, 15% α-piperene, 3% potassium chloride, 2% potassium hydroxide, and 31% deionized water.

[0072] The preparation method of the above-mentioned microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs is as follows:

[0073] First, add 15% N'N dimethylacetamide to the reactor and heat the reactor to 50°C. Start stirring at a speed of 50 rpm. Then, add 9% styrene-based phenol polyoxyethylene ether, 5% isomeric tridecyl alcohol polyoxyethylene ether, and 1% isomeric decadecyl alcohol polyoxyethylene polyoxypropylene ether, and stir for 10 minutes until all solids are completely dissolved. Adjust the stirring speed to 120 rpm and slowly and evenly add 15% α-piperene, controlling the dropwise addition time at 40 minutes, and continue stirring for 30 minutes. Dissolve 3% potassium chloride and 2% potassium hydroxide in 31... Add % deionized water until the solid is completely dissolved and stir until homogeneous to obtain an enhancing agent solution. Slowly and evenly add the enhancing agent solution to the reaction vessel, controlling the dropwise addition time at 40 min and the stirring speed at 100 r / min. Adjust the stirring speed again to 50 r / min, add 10% octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate and 5% oleamide propyl dimethylamine, and stir for 10 min. Add 4% dodecyl methyl hydroxypropyl sulfobetaine, stir for 30 min, cool to room temperature and discharge to produce the ultra-low permeability reservoir microemulsion viscoelastic self-regulating oil displacement agent product.

[0074] Example 2:

[0075] This invention discloses a microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs, comprising, by weight percentage: 10% octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate, 5% oleamide propyl dimethylamine, 12% styrene-based phenol polyoxyethylene ether, 6% isomeric tridecyl alcohol polyoxyethylene ether, 2% isomeric decayl alcohol polyoxyethylene polyoxypropylene ether; 20% solubilizer N'N dimethyl acetamide; 4% co-surfactant bis(dodecylmethyl hydroxypropyl)sulfobetaine; 10% regulator α-piperene; 3% potassium chloride, 2% potassium hydroxide, and 26% deionized water.

[0076] The preparation method of the above-mentioned microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs is as follows:

[0077] First, add 20% N'N dimethylacetamide to the reactor and heat the reactor to 40°C. Start stirring at a speed of 60 r / min. Then add 12% styrene-based phenol polyoxyethylene ether, 6% isomeric tridecyl alcohol polyoxyethylene ether, and 2% isomeric decadecyl alcohol polyoxyethylene polyoxypropylene ether, and stir for 20 min until all solids are completely dissolved. Adjust the stirring speed to 100 r / min and slowly and evenly add 10% α-piperene, controlling the dropwise addition time at 60 min, and continue stirring for 40 min. Dissolve 2% potassium chloride and 1% potassium hydroxide in 3... Add 1% deionized water until the solid is completely dissolved and stir until homogeneous to obtain an enhancer solution. Slowly and evenly add the enhancer solution to the reactor, controlling the addition time at 60 min and the stirring speed at 120 r / min. Adjust the stirring speed again to 60 r / min, add 7% octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate and 3% oleamide propyl dimethylamine, and stir for 20 min. Add 6% dodecyl methyl hydroxypropyl sulfobetaine, stir for 30 min, cool to room temperature and discharge to produce the ultra-low permeability reservoir microemulsion viscoelastic self-regulating oil displacement agent product.

[0078] Example 3:

[0079] This invention discloses a method for preparing a microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs, specifically as follows:

[0080] First, add 9% N'N dimethylacetamide and 8% N'N dimethylformamide to the reactor, heat the reactor to 45°C, and start stirring at a speed of 55 r / min. Then add 10% styrene-based phenol polyoxyethylene ether, 5.5% isomeric tridecyl alcohol polyoxyethylene ether, and 1.5% isomeric decadecyl alcohol polyoxyethylene polyoxypropylene ether, and stir for 15 min until the solids are completely dissolved. Adjust the stirring speed to 110 r / min, and slowly and evenly add 12% α-piperene, controlling the addition time at 50 min. Add 2.5% potassium chloride and 1.5% hydroxide. Potassium was dissolved in 32% deionized water. After the solid was completely dissolved, the mixture was stirred until homogeneous to obtain an enhancing agent solution. The enhancing agent solution was slowly and evenly added to the reactor, with the addition time controlled at 50 min and the stirring speed at 110 r / min. The stirring speed was then adjusted to 55 r / min, and 9% octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate and 4% oleamide propyl dimethylamine were added. The mixture was stirred for 15 min. Then, 5% didodecyl methyl hydroxypropyl sulfobetaine was added and stirred for 30 min. The mixture was cooled to room temperature and discharged to produce the ultra-low permeability reservoir microemulsion viscoelastic self-regulating oil displacement agent product.

[0081] The following tests were conducted on the ultra-low permeability reservoir microemulsion viscoelastic self-regulating displacement agent prepared in the above embodiments:

[0082] 1. First, the permeability of the core was measured using a gas permeability measuring device. After measuring the permeability, the dry weight of the core was measured. The core was then evacuated for 6 hours using a vacuum device, and then saturated with kerosene for about 10 hours. After that, its wet weight was measured. The core was then placed in a dialysis experimental apparatus, and then liquid (distilled water or standard saline for comparison) was poured into the dialysis experimental apparatus. The oil seeping around the core was observed and photographed, and the daily oil yield was recorded.

[0083] Figure 1 This represents the permeation rate of a microemulsion viscoelastic self-regulating displacement agent in an ultra-low permeability reservoir on an ultra-low permeability natural core (0.19 mD) at different permeation times. For example... Figure 1 As shown, the initial oil production from natural cores in ultra-low permeability reservoirs is relatively low. As time increases, the oil droplets on the core surface gradually increase in size and become more concentrated. At 96 hours, the self-absorption capacity of the microemulsion viscoelastic self-regulating displacement agent in ultra-low permeability reservoirs reaches saturation at 0.42 ml, which is much faster than the saturation time of distilled water and standard brine (500 hours).

[0084] 2. The variation of median particle size of microemulsion viscoelastic self-regulating displacement agent in aqueous solution under different salinities in ultra-low permeability reservoirs was tested. The test results are shown in Table 1.

[0085] The standard brine was prepared according to section 7.7.1.1 of SY / T5107-2021 "Evaluation Method for Performance of Water-Based Fracturing Fluids" regarding standard brine in flowing media.

[0086] Table 1. Test results of median particle size of microemulsion viscoelastic self-regulating displacement agent in different media for ultra-low permeability reservoirs.

[0087]

[0088] As shown in Table 1, the median particle size of the microemulsion viscoelastic self-regulating displacement agent in ultra-low permeability reservoirs in distilled water increases from 6.2 nm to 11.6 nm as the concentration decreases, and the median particle size increases by about 100% with increasing salinity.

[0089] 3. Referring to the viscoelasticity test method in Chapter 7.5 of SY / T5107-2016 "Performance Evaluation Method of Water-based Fracturing Fluids", the viscoelastic parameters of the microemulsion viscoelastic self-regulating oil displacement agent in ultra-low permeability reservoirs were tested at different frequencies.

[0090] Test results are as follows Figure 2 As shown, the storage modulus G' is greater than 6 Pa and the dissipation modulus G" is greater than 0.35 Pa. With the increase of shear frequency, the storage modulus G' increases, while the dissipation modulus G" shows a decreasing trend within the shear frequency of 0.6 Hz. When the shear frequency exceeds 0.6 Hz, the dissipation modulus gradually increases again.

[0091] 4. Referring to the test methods in Chapter 9 of YT 6424-2014 "Performance Test Methods for Composite Oil Displacement Systems", the oil displacement efficiency of microemulsion viscoelastic self-regulating oil displacement agent in ultra-low permeability reservoirs was tested for ultra-low permeability natural cores. The test results are shown in Table 2.

[0092] Table 2. Oil displacement efficiency test of microemulsion viscoelastic self-regulating oil displacement agent in ultra-low permeability reservoirs.

[0093]

[0094] As shown in Table 2, the 0.5% microemulsion viscoelastic self-regulating oil displacement agent achieved an oil displacement efficiency of 37.45% in ultra-low permeability natural core (0.21 mD), which is 25.42% higher than that of standard brine oil displacement.

[0095] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs, characterized in that, This self-regulating oil displacement agent comprises the following components by weight percentage: The micelle agent comprises 10-15% of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate and oleamide propyl dimethylamine. Emulsifier 15-20%, wherein the emulsifier is composed of styrene-phenol polyoxyethylene ether, isotridecyl alcohol polyoxyethylene ether and isodecyl alcohol polyoxyethylene polyoxypropylene ether; 4-6% of co-surfactant, wherein the co-surfactant is dodecylmethylhydroxypropylsulfobetaine; 10-15% of a regulator, wherein the regulator is one or more of α-piperene or β-piperene; The solubilizer is 15-20%, wherein the solubilizer is one or a mixture of N'N dimethylacetamide or N'N dimethylformamide; 3-5% reinforcing agent, wherein the reinforcing agent is composed of potassium chloride and potassium hydroxide; The remainder is deionized water.

2. The microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs as described in claim 1, characterized in that: The micelles contain 55-77% by weight of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate and 23-45% by weight of oleamide propyl dimethylamine.

3. The microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs as described in claim 1, characterized in that: The emulsifier contains 52-70% by weight of styrene-phenol polyoxyethylene ether, 25-35% by weight of isotridecyl alcohol polyoxyethylene ether, and 5-13% by weight of isodecyl alcohol polyoxyethylene polyoxypropylene ether.

4. The microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs as described in claim 1, characterized in that: The reinforcing agent contains 50-75% potassium chloride and 25-50% potassium hydroxide by weight.

5. A method for preparing a microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs according to any one of claims 1-4, characterized in that, Includes the following steps: First, add 15-20% by weight of solubilizer to the reactor, heat the reactor to 40-50℃, and start stirring at a speed of 50-60 r / min. Then, add 15-20% by weight of emulsifier and stir until the solid is completely dissolved. Next, add 10-15% by weight of regulator and add it over a time of 40-60 min. Then, mix 3-5% by weight of reinforcing agent with 21-41% by weight of deionized water to obtain a reinforcing agent solution. Add the reinforcing agent solution to the reactor under stirring and add it over a time of 40-60 min. Then, add 10-15% by weight of micelle agent and stir for 10-20 min. Finally, add 4-6% by weight of co-surfactant and stir for 20-30 min. Cool to room temperature and discharge to obtain the ultra-low permeability reservoir microemulsion viscoelastic self-regulating oil displacement agent product.

6. The preparation method of the microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs as described in claim 5, characterized in that: The micelle agent is composed of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate and oleamide propyl dimethylamine; The emulsifier is composed of styrene-phenol polyoxyethylene ether, isotridecyl alcohol polyoxyethylene ether and isodecyl alcohol polyoxyethylene polyoxypropylene ether. The co-surfactant is bis(dodecylmethylhydroxypropyl)sulfobetaine; The regulator is α-piperene or β-piperene; The solubilizer is one or a mixture of N'N dimethylacetamide or N'N dimethylformamide; The reinforcing agent is composed of potassium chloride and potassium hydroxide.

7. The preparation method of the microemulsion viscoelastic self-regulating oil displacement agent for ultra-low permeability reservoirs as described in claim 5, characterized in that, Includes the following steps: S1. First, add 15-20% by weight of one or a mixture of both of N'N dimethylacetamide and N'N dimethylformamide to the reactor, heat the reactor to 40-50℃, and start stirring at a stirring speed of 50-60r / min. S2, then add 9-12% by weight of styrene-phenol polyoxyethylene ether, 5-6% by weight of isotridecyl alcohol polyoxyethylene ether and 1-2% by weight of isodecyl alcohol polyoxyethylene polyoxypropylene ether, and stir at 100-120 r / min for 10-20 min until the solid is completely dissolved. S3, then add 10-15% by weight of one or a mixture of α-piperene or β-piperene, and control the dropping time at 40-60 min; S4. Mix 2-3% potassium chloride, 1-2% potassium hydroxide and 21-41% deionized water by weight to obtain a reinforcing agent solution. Add the reinforcing agent solution to the reaction vessel under stirring at 100-120 r / min, and control the dropping time at 40-60 min. S5, under stirring conditions of 50-60 r / min, add 7-10% by weight of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate and 3-5% by weight of oleamidopropyl dimethylamine, and stir for 10-20 min; S6, and finally add 4-6% by weight of dodecylmethylhydroxypropyl sulfobetaine, stir for 20-30 minutes, cool to room temperature and discharge to obtain the ultra-low permeability reservoir microemulsion viscoelastic self-regulating oil displacement agent product.

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