Composite oil-displacing agent for cold production of thickened oil and preparation method of composite oil-displacing agent

Abstract

The invention provides a composite oil-displacing agent for heavy oil cold production and a preparation method thereof, and belongs to the technical field of oilfield chemistry. The composite oil displacement agent is prepared from the following components in parts by weight: 42 to 48 parts of acrylamide, 12 to 14 parts of acrylic acid, 16 to 18 parts of N, N-dimethylformamide, 9 to 10 parts of 2-acrylamido-2-methylpropanesulfonic acid, 10 to 12 parts of allyl 2-ethylbutyrate, 0.5 to 1 part of 2, 2-dimethylolbutanol, 6 to 7 parts of an interfacial tension regulator, 9 to 10 parts of a penetration enhancer, 0.35 to 0.45 part of a slow release initiator, 1 to 2 parts of a stabilizer and 180 to 200 parts of deionized water. A polymerization product obtained by adopting the components can remarkably improve the stability and viscosity of the composite oil-displacing agent, more effectively carry out heavy oil, improve the adsorption capacity of a surfactant on an oil-water interface, reduce the tension of the oil-water interface and improve the recovery ratio.

Description

Technical Field

[0001] The present invention belongs to the technical field of oilfield chemistry, and particularly relates to a composite oil displacement agent for cold production of heavy oil and a preparation method thereof, which is particularly suitable for efficient exploitation under low-temperature reservoir conditions. Background Art

[0002] As an important strategic resource, the efficient exploitation of petroleum is of great significance to economic development. With the decreasing of conventional petroleum resources, the exploitation of heavy oil has become an important development direction of the petroleum industry. Although the global heavy oil reserves are huge, it is difficult to exploit due to its high viscosity and poor fluidity.

[0003] At present, the conventional heavy oil exploitation technologies mainly include steam flooding, huff and puff, diluent injection for bottom-hole viscosity reduction and chemical viscosity reduction flooding technologies. These technologies mainly rely on physical methods to destroy the viscous force by molecular thermal motion or form water-in-oil emulsions by chemical methods. Generally, the chemical methods can be divided into three categories according to their action mechanisms: one is polymer flooding, which improves the oil displacement efficiency by increasing the viscosity of the injected water, reducing the water-oil mobility ratio and increasing the swept volume of the injected water; the second is surfactant flooding and alkaline water flooding, which improve the oil displacement efficiency of the injected water by reducing the oil-water interfacial tension; the third is the ternary composite flooding developed in recent years, which can not only increase the swept volume but also improve the oil displacement efficiency.

[0004] Composite flooding refers to an oil displacement agent composed of two or more oil displacement components combined, which has higher oil displacement efficiency. However, at present, the composite oil displacement agent has insufficient salt tolerance and low stability, and is prone to phase separation or performance attenuation during storage, making it difficult to balance multiple functions such as viscosity reduction, oil washing and displacement, resulting in low recovery rate. Based on this, the present invention provides a composite oil displacement agent with high stability, which can be used for cold production of heavy oil and improve the heavy oil recovery rate. By optimizing the formulation design and preparation process, the present invention realizes ultra-low interfacial tension and excellent salt tolerance, and has stable long-term storage performance. This technology provides an efficient and economical solution for cold production of heavy oil, is particularly suitable for the development of deep heavy oil resources, and has important industrial application value and broad market prospects. Summary of the Invention

[0005] The purpose of the present invention is to provide a composite oil displacement agent for cold production of heavy oil and a preparation method thereof. The composite oil displacement agent uses an anionic surfactant and a cationic surfactant in combination to increase the adsorption force of the surfactant at the oil-water interface to a greater extent and reduce the oil-water interfacial tension. In addition, the polymerization product can significantly increase the stability of the final composite oil displacement agent, increase the viscosity of the oil displacement agent, and can more effectively carry and displace crude oil, thereby improving the recovery rate.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a composite oil displacement agent for cold production of heavy oil. The composite oil displacement agent comprises, by weight parts:

[0008] 42 - 48 parts of acrylamide;

[0009] 12 - 14 parts of acrylic acid;

[0010] 16 - 18 parts of N,N - dimethylformamide;

[0011] 9 - 10 parts of 2 - acrylamido - 2 - methylpropanesulfonic acid;

[0012] 10 - 12 parts of allyl 2 - ethylbutyrate;

[0013] 0.5 - 1 part of 2,2 - bis(hydroxymethyl)butanol;

[0014] 6 - 7 parts of composite surfactant;

[0015] 9 - 10 parts of propanol;

[0016] 0.35 - 0.45 part of ammonium persulfate capsule breaker;

[0017] 1 - 2 parts of sodium benzoate;

[0018] 180 - 200 parts of deionized water.

[0019] The present invention also provides a preparation method of the composite oil displacement agent for cold production of heavy oil as described in the above technical solution, which is characterized by comprising the following steps:

[0020] (1) Under the protection of nitrogen (purity above 99.99%), dissolve acrylamide, acrylic acid, and 2 - acrylamido - 2 - methylpropanesulfonic acid in N,N - dimethylformamide and deionized water, add ammonium persulfate capsule breaker, and react at 78 ± 2 °C for 25 ± 5 min to obtain a prepolymer;

[0021] (2) Add allyl 2 - ethylbutyrate and 2,2 - bis(hydroxymethyl)butanol to the prepolymer, and react at 45 ± 2 °C for 25 ± 5 min to obtain a graft - crosslinked composite polymer;

[0022] (3) Prepare a 15% NaOH solution with deionized water, slowly add it to the product of step (2), adjust the pH to 9.5 - 10.5, and simultaneously add the composite surfactant and sodium benzoate;

[0023] (4) Finally, add propanol, shear and emulsify at 2000 - 2500 rpm for 10 - 15 min, and after shear emulsification, filter through a microporous membrane to obtain a transparent microemulsion, which is the composite oil displacement agent.

[0024] In the preparation method of a composite oil displacement agent for heavy oil cold production according to the present invention, in step (1), at 78 ± 2 °C, the ammonium persulfate capsule breaker slowly releases ammonium persulfate and decomposes to generate ·SO4 - radicals, initiating the copolymerization of acrylamide, acrylic acid, and 2-acrylamido-2-methylpropanesulfonic acid. The resulting prepolymer is a terpolymer and contains unreacted allyl groups and tertiary carbon radicals generated by chain transfer at the ends. The structural schematic is:

[0025]

[0026] In step (2), since the ammonium persulfate capsule breaker in step (1) has slowly released ammonium persulfate and decomposed to generate ·SO4 - radicals, at 45 ± 2 °C, the radicals generated by the decomposition of ammonium persulfate attack the double bond of allyl 2-ethylbutyrate to form new active centers, and two reactions occur with the prepolymer:

[0027] One is chain transfer grafting:

[0028]

[0029] The other is double bond addition:

[0030]

[0031] The 2,2-dimethylolbutanol added in step (2) participates in the reaction as a chain terminator. The hydroxyl group captures radicals to form a stable structure; it also participates in the reaction as a crosslinking node, mainly esterifying with acrylic acid units to form reversible crosslinks.

[0032] In the present invention, the ammonium persulfate capsule breaker is used as an initiator, which is more conducive to controlling the reaction process, greatly improving the controllability and stability of the reaction, providing a strong guarantee for large-scale industrial production, and having broad application prospects and significant economic benefits.

[0033] In the present invention, propanol is used as a penetration enhancer. Through its unique amphiphilic molecular structure, it can significantly improve the performance of the composite oil displacement agent in heavy oil cold production. The small molecule characteristics of propanol can quickly penetrate into the heavy oil colloid-asphaltene network, reduce the viscosity of heavy oil by destroying the intermolecular forces; at the same time, it can also act synergistically with surfactants to reduce the oil-water interfacial tension, thereby greatly reducing the flow resistance of crude oil. In addition, propanol can also form a dynamic hydrogen bond network with 2,2-dimethylolbutanol in the system, which not only ensures the oil-carrying capacity during displacement but also ensures the injection performance, providing an efficient solution for heavy oil cold production.

[0034] In the present invention, N,N-dimethylformamide serves as a multifunctional reaction medium. On the one hand, through its unique solvation effect, it can significantly improve the polymerization reaction efficiency. At the same time, the hydrophobic methyl groups in its molecules can effectively shield high-valent metal ions, enhancing the salt tolerance of the composite oil displacement agent, which is a key component to ensure the efficient synthesis of the product. On the other hand, by using N,N-dimethylformamide as the reaction medium, it can also ingeniously solve the technical problem of viscosity out-of-control in the traditional aqueous-phase polymerization process. Since the polymerization product is insoluble in N,N-dimethylformamide, a stable dispersion system can be formed, effectively avoiding the common instantaneous viscosity increase phenomenon in aqueous-phase reactions. This unique solvent selection enables the reaction system to always maintain an appropriate operating viscosity, creating conditions for subsequent precise control. After polymerization, through the synergistic effect of high-speed shear emulsification at 2000 - 2500 rpm and microfiltration through microporous membranes, the polymerization product is successfully transformed into a transparent microemulsion system with a uniform particle size distribution and excellent stability, ultimately obtaining a composite oil displacement agent product with excellent performance. This process design not only ensures the full progress of the polymerization reaction but also realizes the precise control of the product morphology, which is one of the key technical breakthroughs of the present invention.

[0035] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0036] (1) Ultra-low interfacial tension system, significantly improving oil displacement efficiency

[0037] The present invention adopts an anionic-cationic-nonionic composite surfactant system. Through electrostatic attraction-hydrophobic synergy, the oil-water interfacial tension is reduced to within the range of 10 -3 mN / m. The anionic (sodium dodecyl sulfate) adsorbs on the oil phase, reducing the coalescence tendency of oil droplets; the cationic (cetyltrimethylammonium bromide) anchors in the aqueous phase, enhancing the interfacial film strength; the nonionic (alkanolamide) acts as a bridging molecule to form a three-dimensional supramolecular structure and fills the interfacial voids, improving the emulsion stability. This system can significantly reduce the flow resistance of heavy oil in pores, increasing the core oil displacement efficiency by more than 22%.

[0038] (2) High-performance polymer backbone, enhancing displacement and oil-carrying capabilities

[0039] The present invention copolymerizes acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and allyl 2-ethylbutyrate, and introduces 2,2-dimethylolbutanol to construct a dynamic cross-linked network, enabling the oil displacement agent to have: ① high thickening property, which can reduce the oil-water mobility ratio and effectively carry heavy oil; ② salt and shear resistance: in formation water with a salinity ≤ 80000 mg / L, the viscosity retention rate ≥ 90%; ③ temperature adaptability: at 55 °C, hydrogen bonds reversibly break, the viscosity decreases for easy injection, and it returns to a high-viscosity state after cooling, achieving intelligent profile control.

[0040] (3) Nano - level microemulsion to enhance oil washing and emulsifying ability

[0041] Through high - shear emulsification at 2000 - 2500 rpm, the present invention obtains: ① Microemulsion with particle size D90 ≤ 200 nm, which can drive oil in tiny pores; ② Zeta potential of - 35 to - 40 mV to ensure the long - term stability of the emulsion; ③ Temperature and salt tolerance: no stratification within 60 days under the conditions of 50 °C and high salinity. This microemulsion can significantly improve the oil - washing efficiency (> 80%) and reduce the formation residual oil saturation.

[0042] (4) Slow - release initiation technology to optimize the polymerization reaction

[0043] The present invention uses ammonium persulfate capsule breaker as an initiator, which has significant advantages compared with the traditional method of directly using ammonium persulfate. This ammonium persulfate capsule breaker can achieve the slow release of the initiator, effectively avoiding the occurrence of explosive polymerization, thus preventing the problem of too wide molecular weight distribution. And it can accurately control the degree of polymerization, making the performance of the final product far superior to that prepared by conventional initiators. This unique initiator is more conducive to controlling the reaction process, greatly improving the controllability and stability of the reaction, and thus providing a strong guarantee for large - scale industrial production, with broad application prospects and significant economic benefits.

[0044] In addition, sodium benzoate in the composite oil displacement agent acts as a stabilizer, which can capture free radicals to prevent secondary polymerization during storage, ensuring that the product stability ≥ 6 months. At the same time, - COO - of sodium benzoate can form hydrogen bonds with alcohol hydroxyl groups to enhance the stability of the molecular network. Detailed implementation methods

[0045] The present invention provides a composite oil displacement agent for cold production of heavy oil. The composite oil displacement agent includes, by weight:

[0046] 42 - 48 parts (preferably 45 parts) of acrylamide;

[0047] 12 - 14 parts (preferably 13 parts) of acrylic acid;

[0048] 16 - 18 parts (preferably 17 parts) of N,N - dimethylformamide;

[0049] 9 - 10 parts (preferably 9.5 parts) of 2 - acrylamido - 2 - methylpropanesulfonic acid;

[0050] 10 - 12 parts (preferably 11 parts) of allyl 2 - ethylbutyrate;

[0051] 0.5 - 1 part of 2,2 - dimethylolbutanol (forming a hydrogen - bond network with propanol);

[0052] 6 - 7 parts of composite surfactant (as an interfacial tension regulator, composed of sodium dodecyl sulfate, cetyltrimethylammonium bromide and alkanolamide in a mass ratio of 4:1:1.5, where the alkanolamide is purchased from Xingtai Xinlanxing Technology Co., Ltd.);

[0053] 9 - 10 parts of propanol (as a penetration enhancer);

[0054] 0.35 - 0.45 parts of ammonium persulfate capsule breaker (as a slow - release initiator, purchased from Beijing Shida Aode Technology Co., Ltd.);

[0055] 1 - 2 parts of sodium benzoate (as a stabilizer);

[0056] 180 - 200 parts of deionized water.

[0057] The present invention adopts an anionic - cationic - nonionic composite surfactant system. Through electrostatic attraction - hydrophobic synergy, the oil - water interfacial tension is reduced to below 5×10 -3 mN / m. The anionic adsorbs on the oil phase, reducing the coalescence tendency of oil droplets; the cationic anchors in the water phase, enhancing the interfacial film strength; the nonionic fills the interfacial voids, improving the emulsion stability. This system can significantly reduce the work required for interfacial deformation when oil beads move through narrow pores, greatly reduce the flow resistance of heavy oil in pores, and improve the oil recovery rate.

[0058] The present invention also provides a preparation method of the composite oil displacement agent for cold production of heavy oil described in the above technical solution, including the following steps:

[0059] (1) Under the protection of nitrogen (purity above 99.99%), acrylamide, acrylic acid, and 2 - acrylamido - 2 - methylpropanesulfonic acid are dissolved in N,N - dimethylformamide and deionized water, and ammonium persulfate capsule breaker is added, and the reaction is carried out at 78 ± 2°C for 25 ± 5 min to obtain a prepolymer;

[0060] (2) 2 - allyl butyrate and 2,2 - dimethylolbutanol are added to the prepolymer, and the reaction is carried out at 45 ± 2°C for 25 ± 5 min to obtain a graft - crosslinked composite polymer;

[0061] (3) A 15% NaOH solution is prepared with deionized water and slowly added to the product of step (2), the pH is adjusted to 9.5 - 10.5, and at the same time, the composite surfactant and sodium benzoate are added;

[0062] (4) Finally, propanol is added, and shear emulsification is carried out at 2000 - 2500 rpm for 10 - 15 min. After shear emulsification, it is filtered through a microporous membrane to obtain a transparent microemulsion, which is the composite oil displacement agent.

[0063] The present invention copolymerizes acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid and allyl 2-ethylbutyrate, and introduces 2,2-dimethylolbutanol to construct a dynamic cross-linked network. That is, the present invention uses specific components to prepare a polymerization product, and the obtained polymerization product can significantly increase the stability of the final composite oil displacement agent, increase the viscosity of the oil displacement agent, and can more effectively carry and displace crude oil, especially those heavy residual crude oils that are difficult to be displaced by water flooding. In addition, the polymerization product can also improve the stability of the oil-in-water emulsion formed by the alkali and surfactant in the present invention, further enhance the oil washing effect, and thus improve the oil recovery rate.

[0064] In the present invention, ammonium persulfate capsule breaker is used as an initiator, which can realize the slow release of the initiator, avoid explosive polymerization resulting in too wide a molecular weight distribution, and can accurately control the degree of polymerization, and its performance is far superior to that of conventional initiators.

[0065] The technical solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0066] Example 1

[0067] (1) Dissolve 45 parts of acrylamide, 13 parts of acrylic acid, and 9.5 parts of 2-acrylamido-2-methylpropanesulfonic acid in 17 parts of N,N-dimethylformamide and 110 parts of deionized water, and then mix with 0.4 part of ammonium persulfate capsule breaker, and heat at a temperature of 78±2°C for 25±5 minutes to obtain a prepolymer.

[0068] (2) Add 11 parts of allyl 2-ethylbutyrate and 0.7 part of 2,2-dimethylolbutanol to the prepolymer, and react at 45±2°C for 25±5 minutes to obtain a graft-crosslinked composite polymer.

[0069] (3) Prepare a 15% NaOH solution with 80 parts of deionized water, slowly add it to the product of step (2), adjust the pH to 10, and at the same time add 6.5 parts of a composite surfactant (composed of sodium dodecyl sulfate, cetyltrimethylammonium bromide and alkanolamide in a mass ratio of 4:1:1.5) and 1.5 parts of sodium benzoate.

[0070] (4) Finally, add 9.5 parts of propanol, shear and emulsify at 2500 rpm for 10 minutes, and after shear emulsification, filter through a microporous membrane to obtain a transparent microemulsion, which is the composite oil displacement agent.

[0071] Test method: Take the composite oil displacement agent prepared in this example, prepare an aqueous solution with a concentration of 0.3%, and use a TX-500C full-range rotary drop interfacial tension meter to measure the interfacial tension, and use a Zetasizer Nano ZS nanoparticle size and Zeta potential analyzer to measure the Zeta potential and particle size distribution.

[0072] The Zeta potential of the composite oil displacement agent prepared in this example is -38.4 mV, and the particle size distribution D90 is 118.03 nm; in clear water, the interfacial tension is lower than 4.54×10 -3 mN / m; in 8×10 4 mg / L mineralized water, the interfacial tension is within 10 -3 mN / m. After storage for 6 months, the composite oil displacement agent is stable, without stratification, the Zeta potential is -39.7 mV, the particle size distribution D90 is 122.14 nm, and the interfacial tension in clear water and 8×10 4 mg / L mineralized water is still within 10 -3 mN / m.

[0073] Example 2

[0074] (1) Dissolve 42 parts of acrylamide, 12 parts of acrylic acid, and 9 parts of 2-acrylamido-2-methylpropanesulfonic acid in 16 parts of N,N-dimethylformamide and 100 parts of deionized water, then mix with 0.35 parts of ammonium persulfate capsule breaker, and heat at a temperature of 78±2 °C for 25±5 min to obtain a prepolymer;

[0075] (2) Add 10 parts of allyl 2-ethylbutyrate and 0.5 parts of 2,2-dimethylolbutanol to the prepolymer, and react at 45±2 °C for 25±5 min to obtain a graft-crosslinked composite polymer;

[0076] (3) Prepare a 15% NaOH solution with 80 parts of deionized water, slowly add it to the product of step (2), adjust the pH to 10, and at the same time add 6 parts of a composite surfactant (composed of sodium dodecyl sulfate, cetyltrimethylammonium bromide, and alkanolamide in a mass ratio of 4:1:1.5) and 1 part of sodium benzoate;

[0077] (4) Finally, add 9 parts of propanol, shear and emulsify at 2000 rpm for 15 min, and after shear emulsification, filter through a microporous membrane to obtain a transparent microemulsion, which is the composite oil displacement agent.

[0078] The test method is the same as that in Example 1. The Zeta potential of the composite oil displacement agent prepared in this example is -35.3 mV, the particle size distribution D90 is 132.08 nm, and the interfacial tension in clear water is lower than 3.55×10 -3 mN / m, in 8×10 4The interfacial tension in mg / L mineralized water is within 10 -3 mN / m. After storage for 6 months, the composite oil displacement agent is stable and does not delaminate. The Zeta potential is -38.2 mV, and the particle size distribution D90 is 135.33 nm. The interfacial tension in fresh water and 8×10 4 mg / L mineralized water is still within 10 -3 mN / m.

[0079] Example 3

[0080] (1) Dissolve 48 parts of acrylamide, 14 parts of acrylic acid, and 10 parts of 2-acrylamido-2-methylpropanesulfonic acid in 18 parts of N,N-dimethylformamide and 120 parts of deionized water. Then mix with 0.45 parts of ammonium persulfate capsule breaker, and heat at a temperature of 78 ± 2 °C for 25 ± 5 min to obtain a prepolymer;

[0081] (2) Add 12 parts of allyl 2-ethylbutyrate and 1 part of 2,2-dimethylolbutanol to the prepolymer, and react at 45 ± 2 °C for 25 ± 5 min to obtain a graft-crosslinked composite polymer;

[0082] (3) Prepare a 15% NaOH solution with 80 parts of deionized water, slowly add it to the product of step (2), adjust the pH to 10, and at the same time add 7 parts of a composite surfactant (composed of sodium dodecyl sulfate, cetyltrimethylammonium bromide, and alkanolamide in a mass ratio of 4:1:1.5) and 2 parts of sodium benzoate;

[0083] (4) Finally, add 9 parts of propanol, shear and emulsify at 2500 rpm for 10 min, and after shear emulsification, filter through a microporous membrane to obtain a transparent microemulsion, which is the composite oil displacement agent.

[0084] The testing method is the same as that in Example 1. The Zeta potential of the composite oil displacement agent prepared in this example is -37.1 mV, the particle size distribution D90 is 168.12 nm, the interfacial tension in fresh water is lower than 3.71×10 -3 mN / m, and the interfacial tension in 8×10 4 mg / L mineralized water is within 10 -3 mN / m. After storage for 6 months, the composite oil displacement agent is stable and does not delaminate. The Zeta potential is -38.6 mV, the particle size distribution D90 is 171.06 nm, and the interfacial tension in fresh water and 8×10 4 mg / L mineralized water is still within 10 -3 mN / m.

[0085] Comparative Example 1

[0086] Refer to Example 1, the difference is that the composite surfactant is not added.

[0087] Compared with Example 1, during the interfacial tension test of the composite oil displacement agent prepared in this comparative example, the oil droplet height-to-length ratio was stable at 1:1 to 1.2:1, and an ultra-low interfacial tension could not be achieved.

[0088] Comparative Example 2

[0089] Referring to Example 1, the difference is that the ammonium persulfate capsule breaker is replaced by ammonium persulfate.

[0090] During the preparation process of this comparative example, explosive polymerization occurred in step (1), and a stable composite oil displacement agent could not be prepared.

[0091] Comparative Example 3

[0092] Referring to Example 1, the difference is that sodium benzoate was not added.

[0093] After the composite oil displacement agent prepared in this comparative example was stored for 1 month, gel lumps appeared at the bottom.

[0094] Comparative Example 4

[0095] Referring to Example 1, the difference is that step (4) was changed to "Finally, add 9.5 parts of propanol and stir to obtain the composite oil displacement agent.

[0096] Since the composite oil displacement agent prepared in this comparative example was not subjected to high-speed shear emulsification and microfiltration through a microporous membrane, stratification occurred within 24 hours.

[0097] Comparative Example 5

[0098] Referring to Example 1, the difference is that N,N-dimethylformamide was not added.

[0099] During the preparation process of this comparative example, a stable composite oil displacement agent could not be prepared.

[0100] This is because the polymerization product can dissolve in water and rapidly increase in viscosity, finally resulting in too high a solution viscosity. The polymerization product is insoluble in N,N-dimethylformamide and can form a stable dispersion system, effectively avoiding the instantaneous viscosity increase phenomenon common in aqueous phase reactions. Finally, through high-speed shear emulsification and microfiltration through a microporous membrane, a transparent microemulsion, that is, the composite oil displacement agent, can be obtained.

[0101] Comparative Example 6

[0102] Referring to Example 1, the difference is that 2,2-dimethylolbutanol was not added.

[0103] The oil displacement performance of the composite oil displacement agent prepared in this comparative example was evaluated.

[0104] Comparative Example 7

[0105] Referring to Example 1, the difference is that allyl 2-ethylbutyrate is not added.

[0106] The displacement performance of the composite oil displacement agent prepared in this comparative example was evaluated.

[0107] Comparative Example 8

[0108] Referring to Example 1, the difference is that propanol is not added.

[0109] The displacement performance of the composite oil displacement agent prepared in this comparative example was evaluated.

[0110] Displacement performance evaluation

[0111] Heavy oil from a certain block in Shengli Oilfield was selected. At a reservoir temperature of 50 °C, the ground crude oil viscosity was 10250 mPa·s, the emulsified water cut was 38.4%, the salinity of the injected water was 72943 mg / L, and the calcium and magnesium ion concentration was 836 mg / L. A core displacement experiment was carried out using a sand-packed tube. First, a water flooding experiment was carried out until the water cut reached 98%, and then the composite oil displacement agent prepared in Example 1 of the present invention was used to continue the oil displacement experiment until the water cut reached 98%. During the experiment, 75 mL of water was saturated, the permeability was 2717 mD, and 61.37 mL of oil was saturated.

[0112] The results of the oil displacement experiment showed that: the oil production by water flooding was 19.41 mL, and the displacement efficiency was 31.63%. When the composite oil displacement agent was used for displacement, the additional oil production was 15.15 mL, and the displacement efficiency at this stage was 56.32%. The oil displacement efficiency of the composite oil displacement agent increased by 24.69%.

[0113] According to the above oil displacement performance evaluation method, the composite oil displacement agent prepared in Example 1 was replaced with the composite oil displacement agents prepared in Comparative Example 6, Comparative Example 7, and Comparative Example 8 respectively, and the oil displacement efficiency increased only by 8.20%, 7.66%, and 9.71% respectively.

[0114] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A composite oil displacement agent for cold production of heavy oil, characterized in that, Comprising by weight parts: 42 - 48 parts of acrylamide; 12 - 14 parts of acrylic acid; 16 - 18 parts of N,N - dimethylformamide; 9 - 10 parts of 2 - acrylamido - 2 - methylpropanesulfonic acid; 10 - 12 parts of allyl 2 - ethylbutyrate; 0.5 - 1 part of 2,2 - bis(hydroxymethyl)butanol; 6 - 7 parts of interfacial tension regulator; 9 - 10 parts of penetration enhancer; 0.35 - 0.45 part of slow - release initiator; 1 - 2 parts of stabilizer; 180 - 200 parts of deionized water.

2. The composite oil displacement agent for heavy oil cold production according to claim 1, characterized in that, The interfacial tension regulator is a composite surfactant, composed of sodium dodecyl sulfate, cetyltrimethylammonium bromide and alkanolamide in a mass ratio of 4:1:1.

5.

3. A composite oil displacement agent for heavy oil cold production according to claim 1, characterized in that, The slow - release initiator is an ammonium persulfate capsule breaker.

4. A composite oil displacement agent for heavy oil cold production according to claim 1, characterized in that The penetration enhancer is propanol.

5. A composite oil displacement agent for heavy oil cold production according to claim 1, characterized in that, The stabilizer is sodium benzoate.

6. A preparation method of the composite oil displacement agent according to any one of claims 1 to 5, characterized in that, Comprising: (1) Under the protection of nitrogen (purity above 99.99%), dissolve acrylamide, acrylic acid and 2 - acrylamido - 2 - methylpropanesulfonic acid in N,N - dimethylformamide and deionized water, add ammonium persulfate capsule breaker, and react at 78 ± 2 °C for 25 ± 5 min to obtain a prepolymer; (2) Add allyl 2 - ethylbutyrate and 2,2 - bis(hydroxymethyl)butanol to the prepolymer, and react at 45 ± 2 °C for 25 ± 5 min to obtain a graft - crosslinked composite polymer; (3) Prepare a 15% NaOH solution with deionized water, slowly add it to the product of step (2), adjust the pH to 9.5 - 10.5, and simultaneously add the composite surfactant and sodium benzoate as the stabilizer; (4) Finally, add propanol, shear - emulsify at 2000 - 2500 rpm for 10 - 15 min, and after shear - emulsification, filter through a microporous membrane to obtain a transparent microemulsion, which is the composite oil - displacement agent.

7. The method according to claim 6, characterized in that, The Zeta potential of the obtained composite oil - displacement agent is - 35 to - 40 mV, and the particle size distribution D90 ≤ 200 nm.

8. The method according to claim 6, wherein After the obtained composite oil - displacement agent is stored at 50 °C for 60 days, the absolute value of the Zeta potential decreases by ≤ 10%, and the particle size growth rate ≤ 5%.

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