Nano synergistic oil washing agent for CO2 flooding of low-permeability reservoir as well as preparation method and application of nano synergistic oil washing agent

Abstract

The invention discloses a nano synergistic oil washing agent for CO2 flooding of a low-permeability reservoir. The nano synergistic oil washing agent comprises 38%-48% of a nano surfactant, 12%-22% of an anionic surfactant, 15%-20% of a nonionic surfactant, 4%-6% of low-carbon alcohol and the balance of water. The invention discloses a preparation method of a nano synergistic oil washing agent for CO2 flooding of a low-permeability reservoir, which comprises the following steps: (1) adding a non-ionic surfactant with a formula amount into a reaction container, then adding low-carbon alcohol with a formula amount into the reaction container, and uniformly stirring at a certain temperature to obtain a mixed solution; and (2) adding a formula amount of water into the reaction container, stirring, then adding a formula amount of anionic surfactant and a formula amount of nano surfactant into the reaction container, and fully and uniformly stirring to obtain the nano synergistic oil washing agent for CO2 flooding of the low-permeability reservoir. The invention discloses application of a nano synergistic oil washing agent for CO2 flooding of a low-permeability reservoir in oil extraction of an oil field.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemistry, and particularly relates to a nano-enhanced oil washing agent for CO2 flooding in low-permeability reservoirs, its preparation method, and its application. Background Technology

[0002] According to the latest data, global crude oil consumption continues to grow. Without the successful development of new energy sources, oil remains the primary energy source.

[0003] With the exploitation of high-quality oil reservoirs, the proportion of low-permeability oil reservoirs is increasing year by year. The development of low-permeability oil reservoirs will be the main force of China's future oil and gas development and an important foundation for China's long-term stable production. How to develop low-permeability oil reservoirs economically and effectively is a difficult problem that has been troubling researchers. In recent years, CO2 flooding technology has also been increasingly applied to low-permeability oil reservoirs.

[0004] CO2 can dissolve not only in water but also in crude oil. Under certain temperature and pressure conditions, CO2 and crude oil can form a miscible phase. The CO2 flooding mechanism has the following eight aspects: (1) reducing the interfacial tension between oil and water and reducing the residual oil saturation; (2) reducing the viscosity of crude oil, which is conducive to the flow of crude oil in the formation; (3) causing the crude oil volume to expand; (4) dissolving gas drive effect; (5) improving the oil-water mobility ratio; (6) acidifying the formation and clearing formation blockages; (7) extracting light hydrocarbons from crude oil; (8) miscibility effect.

[0005] Chinese patent application CN 113801282 A discloses a washing agent for carbon dioxide displacement, its preparation method, and its application, belonging to the field of carbon dioxide displacement oil recovery. The preparation of this washing agent includes the following steps: in formic acid, a first monomer reacts with formaldehyde to obtain a first reactant; the first reactant reacts with borane, an oxidant is added, and the reaction proceeds under alkaline conditions to generate a second reactant; an aromatic hydrocarbon reacts with a second monomer to obtain a third reactant; the second and third reactants react under heating conditions to obtain the washing agent; wherein, the first monomer is selected from at least one of 3-phenyl-4-penten-1-amine, 4-penten-1-amine, 4-methyl-penten-1-amine, and 2-amino-4-pentenoic acid; the second monomer is selected from at least one of succinic anhydride, 2,3-dimethylsuccinic anhydride, glutaric anhydride, and adipic anhydride; and the aromatic hydrocarbon is selected from at least one of benzene, toluene, and ethylbenzene. However, the above technical solution has the following shortcomings: the synthesis process is complex, and it uses raw materials that are highly toxic and hazardous, making it unsuitable for widespread application.

[0006] Current reports on the combined use of CO2 and surfactants mostly focus on improving foam stability, enhancing CO2 solubility, and forming surfactant microemulsions to seal pores. For example, US Patent 9828815B2 reports the use of anionic sulfonate surfactants with 20-24 carbon chains containing olefin structures to stabilize foam fluids with a total salinity of 30,000 mg / L, with surfactant concentrations ranging from 1% to 50%. US Patent Application US5358046A describes a method for enhancing oil recovery using water-soluble polymers, surfactants, and CO2. By using water-soluble polymers and surfactants, the solubility of supercritical CO2 emulsions in crude oil was successfully improved, effectively reducing the viscosity of the crude oil.

[0007] The methods described above, whether using surfactants alone or in combination with CO2, all suffer from drawbacks such as poor compatibility with CO2 and low overall oil washing efficiency, which limits their practical application as oil displacement compositions. To address this issue, there is an urgent need to develop a synergistic oil washing agent suitable for CO2 flooding in low-permeability reservoirs.

[0008] Meanwhile, with the continuous development of nanotechnology, related research on nanochemical flooding technology has attracted great attention worldwide. In recent years, nanofilm flooding and nanomaterial depressurization and injection enhancement technologies have achieved certain results and gained recognition. Current indoor evaluation studies and field tests in some oil fields show that nanoparticles can improve oil washing efficiency to a certain extent by reducing interfacial tension and changing the wettability of rock surfaces.

[0009] Therefore, it is essential to further explore the organic combination of nanomaterials and CO2 flooding to ultimately achieve the goal of significantly improving crude oil recovery in low-permeability reservoirs. Summary of the Invention

[0010] Objective: To address the problems of poor compatibility with CO2 and low overall oil washing efficiency in CO2 flooding, this invention provides a nano-enhanced oil washing agent for CO2 flooding in low-permeability reservoirs, its preparation method, and its application. This oil washing agent is effectively applicable to formation water with a salinity ≤100,000 mg / L, a calcium and magnesium ion concentration ≤2,000 mg / L, and a permeability of (0.1~50)×10⁻⁶. -3 μm 2 In low-permeability reservoirs, it enhances the CO2 flooding effect, and its preparation process is simple, low-cost, and environmentally friendly.

[0011] Technical solution: Nano-enhanced oil washing agent for CO2 flooding in low-permeability reservoirs, comprising, by weight percentage:

[0012] The composition consists of 38%-48% nano-surfactants, 12%-22% anionic surfactants, 15%-20% nonionic surfactants, 4%-6% low-carbon alcohols, and the remainder is water.

[0013] As a preferred embodiment of this application, the nanosurfactant used is SD-702 nanosurfactant. The nanosurfactant exhibits good instillability, high oil washing efficiency, and resistance to temperature and salt. The nanosurfactant SD-702 was commercially available from Ningbo Fengcheng Nanotechnology Co., Ltd.

[0014] Furthermore, the particle size of the nanosurfactant is ≤200nm.

[0015] As a preferred embodiment of this application, the anionic surfactant is one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and sodium dodecyl sulfonate.

[0016] As a preferred embodiment of this application, the nonionic surfactant is polyoxyethylene alkylolamide. This nonionic surfactant possesses excellent wetting, penetrating, and emulsifying properties, high oil washing efficiency, and is resistant to temperature and salt. This polyoxyethylene alkylolamide was purchased from a petrochemical manufacturer in Hai'an, Jiangsu Province.

[0017] As a preferred embodiment of this application, the lower alcohol is one of ethanol, isopropanol, methanol, n-propanol, and butanol.

[0018] As a preferred embodiment of this application, the mineralization of the water is ≤100000 mg / L, wherein the concentration of calcium and magnesium ions is ≤2000 mg / L.

[0019] The preparation method of the above-mentioned nano-enhanced oil washing agent for CO2 flooding in low-permeability reservoirs includes the following steps:

[0020] (1) Add the amount of nonionic surfactant in the formula to the reaction vessel, then add the amount of low carbon alcohol in the formula, and stir evenly at a certain temperature to obtain a mixture.

[0021] (2) Add the prescribed amount of water to the reaction vessel, stir for a period of time, and then add the prescribed amount of anionic surfactant and the prescribed amount of nano surfactant to the reaction vessel. After stirring evenly, the nano-enhanced washing agent for CO2 flooding of low-permeability oil reservoirs is obtained.

[0022] As a preferred embodiment of this application, the stirring temperature in step (1) is 40℃~50℃.

[0023] As a preferred embodiment of this application, in step (2), the prescribed amount of water is added to the reaction vessel and stirred for at least 10 minutes, preferably 20-40 minutes, and then the prescribed amount of anionic surfactant and the prescribed amount of nano surfactant are added to it.

[0024] The above-mentioned application of nano-enhanced washing agents for CO2 flooding in low-permeability reservoirs in oilfield production.

[0025] Furthermore, the formation conditions of the oilfield are: formation temperature ≤150℃, permeability (0.1~50)×10⁻⁶. -3 μm 2 Formation water salinity ≤ 100,000 mg / L, of which:

[0026] Calcium and magnesium ion concentration ≤2000 mg / L.

[0027] As a preferred embodiment of this application, the concentration of the nano-enhanced washing agent for CO2 flooding of low-permeability reservoirs is 0.2wt% to 1wt%.

[0028] Furthermore, the concentration of the nano-enhanced washing agent for CO2 flooding of low-permeability reservoirs is 0.2wt% to 0.5wt%, preferably 0.3wt%.

[0029] This invention comprises a compound of nano-active materials and surfactants. The nano-active materials form a continuous adsorption layer on the surface of oil-wetted rocks through chemical bonding, creating a hydrophilic surface and enhancing the system's ability to alter wettability, thereby improving oil washing efficiency. The combination of nano-active materials and surfactants further enhances the hydrophilicity of the rocks, reduces the oil-water interfacial tension, overcomes the capillary forces in low-permeability reservoirs, and significantly improves crude oil recovery.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. It has good compatibility with CO2 and can work synergistically with CO2 to improve oil displacement efficiency;

[0032] 2. This product has good compatibility with oil and water in the application site, does not produce sediment, and will not cause formation blockage;

[0033] 3. The production process is simple, the raw materials are readily available and do not contain organic chlorine, and it is harmless to the environment and personnel from production to use, meeting the requirements of green environmental protection;

[0034] 4. The usage is relatively small, which saves on usage costs and is economically sound. Attached Figure Description

[0035] Figure 1 This invention discloses a method for preparing a nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs. Detailed implementation method:

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] All raw materials used in the embodiments of this application were purchased commercially. The nano surfactant SD702 was purchased from Ningbo Fengcheng Nanotechnology Co., Ltd., the nonionic surfactant polyoxyethylene alkyl alcohol amide was purchased from Jiangsu Haian Petrochemical Plant, and the others were commercially available products.

[0038] Example 1

[0039] Nano-enhanced wash oil agent for CO2 flooding of low-permeability reservoirs, comprising, by weight percentage:

[0040] The composition consists of 38% nano-surfactants, 22% anionic surfactants, 20% nonionic surfactants, 4% low-carbon alcohols, and the remainder is water.

[0041] Furthermore, the nanosurfactant is selected from SD-702 nanosurfactants.

[0042] Furthermore, the particle size of the nanosurfactant is ≤200nm.

[0043] Furthermore, the anionic surfactant is sodium dodecylbenzenesulfonate.

[0044] Furthermore, the nonionic surfactant is a polyoxyethylene alkyl alcohol amide.

[0045] Furthermore, the lower alcohol is ethanol.

[0046] Furthermore, the water has a mineralization of ≤100,000 mg / L, wherein the concentration of calcium and magnesium ions is ≤2,000 mg / L.

[0047] The preparation method of the above-mentioned nano-enhanced oil washing agent for CO2 flooding in low-permeability reservoirs includes the following steps:

[0048] 200 kg of polyoxyethylene alkanolamide was added to the reactor, followed by 40 kg of ethanol. After stirring evenly at 45°C, 160 kg of water was added and stirred for 30 min. Finally, 220 kg of sodium dodecylbenzene sulfonate and 380 kg of nano surfactant SD702 were added and stirred evenly to obtain a nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs.

[0049] The above-mentioned application of nano-enhanced washing agents for CO2 flooding in low-permeability reservoirs in oilfield production.

[0050] Furthermore, the formation conditions of the oilfield are: formation temperature ≤150℃, permeability (0.1~50)×10⁻⁶. -3 μm 2 Formation water salinity ≤ 100,000 mg / L, of which:

[0051] Calcium and magnesium ion concentration ≤2000 mg / L.

[0052] Furthermore, the concentration of the nano-enhanced washing agent used for CO2 flooding in low-permeability reservoirs is 1 wt%.

[0053] Example 2

[0054] Nano-enhanced wash oil agent for CO2 flooding of low-permeability reservoirs, comprising, by weight percentage:

[0055] The composition consists of 40% nano-surfactant, 20% anionic surfactant, 19% nonionic surfactant, 5% low-carbon alcohol, and the remainder is water.

[0056] Furthermore, the nanosurfactant is selected from SD-702 nanosurfactants.

[0057] Furthermore, the particle size of the nanosurfactant is ≤200nm.

[0058] Furthermore, the anionic surfactant is sodium dodecylbenzenesulfonate.

[0059] Furthermore, the nonionic surfactant is a polyoxyethylene alkyl alcohol amide.

[0060] Furthermore, the lower alcohol is isopropanol.

[0061] Furthermore, the water has a mineralization of ≤100,000 mg / L, wherein the concentration of calcium and magnesium ions is ≤2,000 mg / L.

[0062] The preparation method of the above-mentioned nano-enhanced oil washing agent for CO2 flooding in low-permeability reservoirs includes the following steps:

[0063] 190 kg of polyoxyethylene alkyl alcohol amide was added to the reactor, followed by 50 kg of isopropanol. After stirring evenly at 45°C, 160 kg of water was added and stirred for 30 min. Finally, 200 kg of sodium dodecylbenzene sulfonate and 400 kg of nano surfactant SD702 were added and stirred evenly to obtain a nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs.

[0064] The above-mentioned application of nano-enhanced washing agents for CO2 flooding in low-permeability reservoirs in oilfield production.

[0065] Furthermore, the formation conditions of the oilfield are: formation temperature ≤150℃, permeability (0.1~50)×10⁻⁶. -3 μm 2 Formation water salinity ≤ 100,000 mg / L, of which:

[0066] Calcium and magnesium ion concentration ≤2000 mg / L.

[0067] Furthermore, the concentration of the nano-enhanced washing agent used for CO2 flooding in low-permeability reservoirs is 0.3 wt%.

[0068] Example 3

[0069] Nano-enhanced wash oil agent for CO2 flooding of low-permeability reservoirs, comprising, by weight percentage:

[0070] The composition consists of 42% nano-surfactants, 18% anionic surfactants, 18% nonionic surfactants, 6% low-carbon alcohols, and the remainder is water.

[0071] Furthermore, the nanosurfactant is selected from SD-702 nanosurfactants.

[0072] Furthermore, the particle size of the nanosurfactant is ≤200nm.

[0073] Furthermore, the anionic surfactant is sodium dodecyl sulfonate.

[0074] Furthermore, the nonionic surfactant is a polyoxyethylene alkyl alcohol amide.

[0075] Furthermore, the lower alcohol is ethanol.

[0076] Furthermore, the water has a mineralization of ≤100,000 mg / L, wherein the concentration of calcium and magnesium ions is ≤2,000 mg / L.

[0077] The preparation method of the above-mentioned nano-enhanced oil washing agent for CO2 flooding in low-permeability reservoirs includes the following steps:

[0078] 180 kg of polyoxyethylene alkanolamide was added to the reactor, followed by 60 kg of ethanol. After stirring evenly at 45°C, 160 kg of water was added and stirred for 30 min. Finally, 180 kg of sodium dodecyl sulfonate and 420 kg of nano surfactant SD702 were added and stirred evenly to obtain a nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs.

[0079] The above-mentioned application of nano-enhanced washing agents for CO2 flooding in low-permeability reservoirs in oilfield production.

[0080] Furthermore, the formation conditions of the oilfield are: formation temperature ≤150℃, permeability (0.1~50)×10⁻⁶. -3 μm 2 Formation water salinity ≤ 100,000 mg / L, of which:

[0081] Calcium and magnesium ion concentration ≤2000 mg / L.

[0082] Furthermore, the concentration of the nano-enhanced washing agent used for CO2 flooding in low-permeability reservoirs is 0.5 wt%.

[0083] Example 4

[0084] Nano-enhanced wash oil agent for CO2 flooding of low-permeability reservoirs, comprising, by weight percentage:

[0085] The composition consists of 44% nano-surfactants, 16% anionic surfactants, 17% nonionic surfactants, 5% low-carbon alcohols, and the remainder is water.

[0086] Furthermore, the nanosurfactant is selected from SD-702 nanosurfactants.

[0087] Furthermore, the particle size of the nanosurfactant is ≤200nm.

[0088] Furthermore, the anionic surfactant is sodium dodecyl sulfonate.

[0089] Furthermore, the nonionic surfactant is a polyoxyethylene alkyl alcohol amide.

[0090] Furthermore, the lower alcohol is methanol.

[0091] Furthermore, the water has a mineralization of ≤100,000 mg / L, wherein the concentration of calcium and magnesium ions is ≤2,000 mg / L.

[0092] The preparation method of the above-mentioned nano-enhanced oil washing agent for CO2 flooding in low-permeability reservoirs includes the following steps:

[0093] 170 kg of polyoxyethylene alkanolamide was added to the reactor, followed by 50 kg of methanol. After stirring evenly at 50°C, 180 kg of water was added and stirred for 10 min. Finally, 160 kg of sodium dodecyl sulfonate and 440 kg of nano surfactant SD702 were added and stirred evenly to obtain a nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs.

[0094] The above-mentioned application of nano-enhanced washing agents for CO2 flooding in low-permeability reservoirs in oilfield production.

[0095] Furthermore, the formation conditions of the oilfield are: formation temperature ≤150℃, permeability (0.1~50)×10⁻⁶. -3 μm 2 Formation water salinity ≤ 100,000 mg / L, of which:

[0096] Calcium and magnesium ion concentration ≤2000 mg / L.

[0097] Furthermore, the concentration of the nano-enhanced washing agent used for CO2 flooding in low-permeability reservoirs is 0.4 wt%.

[0098] Example 5

[0099] Nano-enhanced wash oil agent for CO2 flooding of low-permeability reservoirs, comprising, by weight percentage:

[0100] The composition consists of 46% nano-surfactants, 14% anionic surfactants, 16% nonionic surfactants, 5% low-carbon alcohols, and the remainder is water.

[0101] Furthermore, the nanosurfactant is selected from SD-702 nanosurfactants.

[0102] Furthermore, the particle size of the nanosurfactant is ≤200nm.

[0103] Furthermore, the anionic surfactant is sodium dodecyl sulfate.

[0104] Furthermore, the nonionic surfactant is a polyoxyethylene alkyl alcohol amide.

[0105] Furthermore, the lower alcohol is n-propanol.

[0106] Furthermore, the water has a mineralization of ≤100,000 mg / L, wherein the concentration of calcium and magnesium ions is ≤2,000 mg / L.

[0107] The preparation method of the above-mentioned nano-enhanced oil washing agent for CO2 flooding in low-permeability reservoirs includes the following steps:

[0108] 160 kg of polyoxyethylene alkanolamide was added to the reactor, followed by 50 kg of n-propanol. After stirring evenly at 40-50℃, 190 kg of water was added and stirred for 20 min. Finally, 140 kg of sodium dodecyl sulfate and 460 kg of nano surfactant SD702 were added and stirred evenly to obtain a nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs.

[0109] The above-mentioned application of nano-enhanced washing agents for CO2 flooding in low-permeability reservoirs in oilfield production.

[0110] Furthermore, the formation conditions of the oilfield are: formation temperature ≤150℃, permeability (0.1~50)×10⁻⁶. -3 μm 2 Formation water salinity ≤ 100,000 mg / L, of which:

[0111] Calcium and magnesium ion concentration ≤2000 mg / L.

[0112] Furthermore, the concentration of the nano-enhanced washing agent used for CO2 flooding in low-permeability reservoirs is 0.6 wt%.

[0113] Example 6

[0114] Nano-enhanced wash oil agent for CO2 flooding of low-permeability reservoirs, comprising, by weight percentage:

[0115] The composition consists of 48% nano-surfactants, 12% anionic surfactants, 15% nonionic surfactants, 5% low-carbon alcohols, and the remainder is water.

[0116] Furthermore, the nanosurfactant is selected from SD-702 nanosurfactants.

[0117] Furthermore, the particle size of the nanosurfactant is ≤200nm.

[0118] Furthermore, the anionic surfactant is sodium dodecyl sulfate.

[0119] Furthermore, the nonionic surfactant is a polyoxyethylene alkyl alcohol amide.

[0120] Furthermore, the lower alcohol is one of butanol.

[0121] Furthermore, the water has a mineralization of ≤100,000 mg / L, wherein the concentration of calcium and magnesium ions is ≤2,000 mg / L.

[0122] The preparation method of the above-mentioned nano-enhanced oil washing agent for CO2 flooding in low-permeability reservoirs includes the following steps:

[0123] 150 kg of polyoxyethylene alkanolamide was added to the reactor, followed by 50 kg of butanol. After stirring evenly at 40°C, 200 kg of water was added and stirred for 40 min. Finally, 120 kg of sodium dodecyl sulfate and 480 kg of nano surfactant SD702 were added and stirred evenly to obtain a nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs.

[0124] The above-mentioned application of nano-enhanced washing agents for CO2 flooding in low-permeability reservoirs in oilfield production.

[0125] Furthermore, the formation conditions of the oilfield are: formation temperature ≤150℃, permeability (0.1~50)×10⁻⁶. -3 μm 2 Formation water salinity ≤ 100,000 mg / L, of which:

[0126] Calcium and magnesium ion concentration ≤2000 mg / L.

[0127] Furthermore, the concentration of the nano-enhanced washing agent used for CO2 flooding in low-permeability reservoirs is 0.4 wt%.

[0128] The nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs provided by this invention has its components and proportions determined based on a large number of experiments. Any change will cause a decrease in performance indicators.

[0129] Comparative Example 1

[0130] The method is largely the same as in Example 2, except that 190 kg of polyoxyethylene alkylolamide was not added, and the amount of polyoxyethylene alkylolamide was made up with water. Therefore, the specific preparation method for Comparative Example 1 is as follows:

[0131] 50 kg of isopropanol and 350 kg of water were added to a reactor and stirred evenly at 45°C. Then, 200 kg of sodium dodecylbenzenesulfonate and 400 kg of nano surfactant SD702 were added and stirred evenly to obtain a nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs.

[0132] Comparative Example 2

[0133] The preparation method is largely the same as in Example 2, except that the amount of sodium dodecylbenzenesulfonate in the formulation of Example 2 is removed, and the amount of sodium dodecylbenzenesulfonate removed is made up with water. That is, the preparation method of Comparative Example 2 is as follows:

[0134] 190 kg of polyoxyethylene alkyl alcohol amide was added to the reactor, followed by 50 kg of isopropanol. After stirring evenly at 45°C, 360 kg of water was added and stirred for 30 min. Finally, 400 kg of nano surfactant SD702 was added and stirred evenly to obtain a nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs.

[0135] Comparative Example 3

[0136] The preparation method for Comparative Example 3 is largely the same as that for Example 2, except that the nano-surfactant SD702 in the formulation of Example 2 is removed, and the SD702 is replaced with water. Therefore, the preparation method for Comparative Example 3 is as follows:

[0137] 190 kg of polyoxyethylene alkyl alcohol amide was added to the reactor, followed by 50 kg of isopropanol. After stirring evenly at 45°C, 560 kg of water was added and stirred for 30 min. Finally, 200 kg of sodium dodecylbenzene sulfonate was added and stirred evenly to obtain a nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs.

[0138] Comparative Example 4

[0139] Similar to Example 2, except that the amount of polyoxyethylene alkanolamide in the formulation of Example 2 deviated from the range of 15%-20%, that is, 140 kg of polyoxyethylene alkanolamide (14%) was added to obtain a low-permeability reservoir enhanced CO2 drive nano-washing agent, and the amount of polyoxyethylene alkanolamide added was made up with water.

[0140] The preparation method of Comparative Example 4 is as follows:

[0141] 140 kg of polyoxyethylene alkyl alcohol amide was added to the reactor, followed by 50 kg of isopropanol. After stirring evenly at 45°C, 210 kg of water was added and stirred for 30 min. Finally, 200 kg of sodium dodecylbenzene sulfonate and 400 kg of nano surfactant SD702 were added and stirred evenly to obtain a nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs.

[0142] Comparative Example 5

[0143] The preparation method is largely the same as in Example 2, except that the amount of polyoxyethylene alkanolamide in the formulation of Example 2 deviates from the range of 15%-20%, that is, 210 kg of polyoxyethylene alkanolamide (21%) was added, and the excess polyoxyethylene alkanolamide was removed from the water. Therefore, the preparation method of Example 5 is as follows:

[0144] 210 kg of polyoxyethylene alkyl alcohol amide was added to the reactor, followed by 50 kg of isopropanol. After stirring evenly at 45°C, 140 kg of water was added and stirred for 30 min. Finally, 200 kg of sodium dodecylbenzene sulfonate and 400 kg of nano surfactant SD702 were added and stirred evenly to obtain a nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs.

[0145] Comparative Example 6

[0146] The method is largely the same as in Example 2, except that the amount of sodium dodecylbenzenesulfonate in the formulation of Example 2 deviates from the range of 12%-22%, that is, 110 kg of sodium dodecylbenzenesulfonate (11%) was added, and the missing amount of sodium dodecylbenzenesulfonate was made up with water. Therefore, the preparation method of Comparative Example 6 is as follows:

[0147] 190 kg of polyoxyethylene alkyl alcohol amide was added to the reactor, followed by 50 kg of isopropanol. After stirring evenly at 45°C, 250 kg of water was added and stirred for 30 min. Finally, 110 kg of sodium dodecylbenzene sulfonate and 400 kg of nano surfactant SD702 were added and stirred evenly to obtain a nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs.

[0148] Comparative Example 7

[0149] The method is largely the same as in Example 2, except that the amount of sodium dodecylbenzenesulfonate in the formulation of Example 2 deviates from the range of 12%-22%, that is, 230 kg of sodium dodecylbenzenesulfonate (23%) was added, and the excess sodium dodecylbenzenesulfonate was removed from the water. Therefore, the preparation method of Comparative Example 7 is as follows:

[0150] 190 kg of polyoxyethylene alkyl alcohol amide was added to the reactor, followed by 50 kg of isopropanol. After stirring evenly at 45°C, 130 kg of water was added and stirred for 30 min. Finally, 230 kg of sodium dodecylbenzene sulfonate and 400 kg of nano surfactant SD702 were added and stirred evenly to obtain a nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs.

[0151] Comparative Example 8

[0152] The preparation method is largely the same as in Example 2, except that the amount of nano-surfactant SD702 in the formulation of Example 2 deviates from the range of 38%-48%, that is, 370 kg of nano-surfactant SD702 (37%) was added, and the amount of nano-surfactant SD702 that was added was made up with water. Therefore, the preparation method of Comparative Example 8 is as follows:

[0153] 190 kg of polyoxyethylene alkyl alcohol amide was added to the reactor, followed by 50 kg of isopropanol. After stirring evenly at 45°C, 190 kg of water was added and stirred for 30 min. Finally, 200 kg of sodium dodecylbenzene sulfonate and 370 kg of nano surfactant SD702 were added and stirred evenly to obtain a nano-enhanced oil washing agent for CO2 flooding of low-permeability reservoirs.

[0154] Comparative Example 9

[0155] The method is largely the same as in Example 2, except that the amount of nano-surfactant SD702 in the formulation of Example 2 deviates from the range of 38%-48%, that is, 490 kg of nano-surfactant SD702 (49%) was added, and the excess nano-surfactant SD702 was removed from the water. Therefore, the preparation method of Comparative Example 9 is as follows:

[0156] 190 kg of polyoxyethylene alkyl alcohol amide was added to the reactor, followed by 50 kg of isopropanol. After stirring evenly at 45°C, 70 kg of water was added and stirred for 30 min. Finally, 200 kg of sodium dodecylbenzene sulfonate and 490 kg of nano surfactant SD702 were added and stirred evenly to obtain a nano-enhanced washing agent for CO2 flooding of low-permeability reservoirs.

[0157] Performance testing:

[0158] The products prepared in the above examples and comparative examples were prepared at a concentration of 0.3% for performance testing. The test conditions and methods are as follows:

[0159] Test conditions:

[0160] 1. Testing instruments: TX500C rotating drop interfacial tensiometer, constant temperature drying oven, core displacement device.

[0161] 2. Test temperature: Block A of Shengli Oilfield, with a formation temperature of 80℃;

[0162] 3. Crude oil used for testing: Dehydrated crude oil from a certain block of Shengli Oilfield;

[0163] 4. Test water: Injection water from a block in Shengli Oilfield, with a salinity of 98,200 mg / L and a calcium and magnesium ion concentration of 1,540 mg / L.

[0164] Test method:

[0165] 1. Interface tension test

[0166] A nano-washing agent test solution (mass fraction of 0.3%) was prepared using injection water from a block in Shengli Oilfield. Then, the interfacial tension between the test solution and the target block oil sample was measured at 80℃ using a TX500C rotating drop interfacial tensiometer (rotation speed 5000 r / min, density difference calculated as 0.1). The lowest value of the interfacial tension was recorded.

[0167] 2. Wash-oil ratio test

[0168] 2.1 Mix the simulated formation sand and the experimental oil sample at a ratio of 4:1 (by mass), place them in a constant temperature drying oven, and age them at the reservoir temperature for 7 days. Stir once a day to ensure that the oil and sand are mixed evenly, and then remove them for use.

[0169] 2.2 Weigh 5g of aged oil sand (mass m, accurate to 0.001g) and place it in a 100mL conical flask (mass m1, accurate to 0.001g). Add 50.0g of 0.3% concentration nano-washing agent test solution, mix thoroughly, and let stand at the reservoir temperature for 48h.

[0170] 2.3 After the sample solution has settled, remove any floating crude oil and crude oil adhering to the bottle wall with clean cotton gauze. Pour out the sample solution and rinse the oil sand 2-3 times with distilled water until no foam remains. Carefully pour out the solution. Place the conical flask containing the washed oil sand in a 105℃ constant temperature drying oven until constant weight, and weigh it (record as m2, accurate to 0.001g).

[0171] 2.4 Use petroleum ether to wash the dried oil sands from 2.3 until the petroleum ether is colorless. Place the conical flask containing the washed formation sands after the crude oil has been washed out in an oven at 120°C for 2 hours and weigh it (recorded as m3, accurate to 0.001g).

[0172] 2.5 The wash oil rate is calculated according to formula (2):

[0173]

[0174] In the formula: σ—washing rate, expressed as a percentage;

[0175] m — mass of aged oil sand, in grams (g);

[0176] m1 — the mass of the conical flask, in grams (g);

[0177] m2 — the total mass of the conical flask and oil sand after washing, in grams (g);

[0178] m3 — The total mass of the conical flask and the washed formation sand, expressed in grams (g).

[0179] 3. Oil displacement test

[0180] A sample with a length of 30cm, a diameter of 2.5cm, and a permeability of 1.5μm was selected. 2 Oil displacement tests were conducted on the core samples. First, formation water from Shengli Oilfield was used to drive the oil to a water cut of 92%. Then, carbon dioxide or carbon dioxide washing agent (0.3 pv) was injected for displacement. Gas displacement was carried out until the cumulative gas displacement amount was greater than 1.2 pv. Then, water was used to drive the oil to a water cut of 100%. The increased recovery rate was calculated for each case.

[0181] The nano-washing agents for enhancing CO2 flooding in low-permeability reservoirs obtained in Examples 1-6 and Comparative Examples 1-9 were subjected to interfacial tension, washout rate, and oil displacement tests according to the above test methods. The test results are shown in Table 1. Referring to several relevant standards, the following parameters are defined as follows: interfacial tension ≤ 5 × 10⁻⁶. -3 mN / m, oil washing rate ≥95%, CO2 flooding recovery rate increased by ≥5%.

[0182] Table 1 Performance Test of Nano-Washing Agent for Enhancing CO2 Flooding in Low-Permeability Reservoirs

[0183]

[0184] As can be seen from Table 1 above, the formulation provided in this application, under the synergistic effect of nano-surfactant SD702, anionic surfactant, nonionic surfactant, and their component ratios, can enable the obtained low-permeability reservoir enhanced CO2 flooding nano-washing agent to have an interfacial tension ≤5×10⁻⁶. -3 With features such as mN / m, oil washing rate ≥95%, and CO2 recovery rate improvement ≥5%, it can improve CO2 recovery rate to a certain extent when applied to CO2 flooding in low-permeability reservoirs.

[0185] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A nano-synergistic oil-washing agent for CO2 flooding in low-permeability oil reservoirs, characterized in that, comprising, by mass percentage: a nano surfactant 38%-48%, an anionic surfactant 12%-22%, a nonionic surfactant 15%-20%, a low carbon alcohol 4%-6%, and the rest being water.

2. The nano-augmented oil-washing agent for CO2 flooding of low-permeability oil reservoirs according to claim 1, characterized in that, The nano surfactant is selected from SD-702 nano surfactant.

3. The nano-flooding agent for CO2 flooding in low permeability reservoirs according to claim 2, wherein, The nano surfactant has a particle size of ≤200 nm.

4. The nano-flooding wash oil for CO2 flooding of low permeability reservoirs as claimed in claim 1, wherein, The anionic surfactant is one of sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, and sodium dodecyl sulfonate.

5. The nano-flooding wash oil for CO2 flooding of low permeability reservoirs as claimed in claim 1, wherein, The nonionic surfactant is polyoxyethylene alkylolamide.

6. The nano-augmented oil-wash for CO2 flooding of low permeability reservoirs as claimed in claim 1, wherein, The low carbon alcohol is one of ethanol, isopropanol, methanol, n-propanol, and butanol.

7. The nano-flooding wash oil for CO2 flooding of low permeability reservoirs as claimed in claim 1, wherein, The water has a mineralization of ≤100000 mg / L, and a calcium and magnesium ion concentration of ≤2000 mg / L.

8. The method for preparing the nano-augmented oil-washing agent for CO2 flooding in low-permeability oil reservoirs according to any one of claims 1-7, characterized in that, comprising the following steps: (1) adding a formula amount of nonionic surfactant to a reaction container, then adding a formula amount of low carbon alcohol thereto, stirring uniformly at a certain temperature to obtain a mixture; (2) adding a formula amount of water to the reaction container, stirring for a period of time, then adding a formula amount of anionic surfactant and a formula amount of nano surfactant to the reaction container, and stirring uniformly to obtain the nano synergistic oil washing agent for CO2 flooding of low permeability oil reservoirs.

9. The method for preparing the nano-augmented oil-washing agent for CO2 flooding in low-permeability oil reservoirs according to claim 8, characterized in that, The stirring temperature in step (1) is 40-50°C.

10. The preparation method of the nano-enhanced oil washing agent for CO2 flooding in low-permeability reservoirs as described in claim 8, characterized in that, In step (2), the formula amount of water is added to the reaction container, and stirred for at least 10 minutes, preferably 20-40 minutes, then the formula amount of anionic surfactant and the formula amount of nano surfactant are added thereto.

11. The nano synergistic oil washing agent for CO2 flooding of low permeability oil reservoirs according to any one of claims 1-7 for use in oilfield oil production.

12. The use according to claim 11, wherein the compound is ###00003### or a pharmaceutically acceptable salt thereof. The formation condition of the oil field is: formation temperature ≤ 150℃, permeability is (0.1-50)×10 -3 μm 2 , formation water salinity ≤ 100000 mg / L, wherein: The calcium and magnesium ion concentration is ≤2000 mg / L.

13. The use according to claim 11, wherein the compound is ###0002### The nano synergistic oil washing agent for CO2 flooding of low permeability oil reservoirs has a use concentration of 0.2wt%-1wt%.

14. Use according to claim 13, wherein the compound is ###00010### or a pharmaceutically acceptable salt thereof. The nano synergistic oil washing agent for CO2 flooding of low permeability oil reservoirs has a use concentration of 0.2wt%-0.5wt%, preferably 0.3wt%.

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