Polymer type surfactant as well as preparation method and application thereof

Abstract

The invention relates to the technical field of surfactants for oil extraction, and provides a polymer type surfactant as well as a preparation method and application thereof. The polymer type surfactant comprises an interfacial activity repetitive unit and a branched cross-linking unit, the interfacial activity repetitive unit comprises a structure with interfacial activity, and the branched cross-linking unit comprises an ester group structure. The polymer type surfactant provided by the invention is of a cross-linked network structure at normal temperature, and can be decrosslinked in a high-temperature aqueous solution to form linear polymer molecules with interfacial activity. When being applied to oil extraction, the surfactant can be consumed less at the initial stage of being injected into a stratum, and can effectively play a role of a surfactant after entering the deep part of the stratum to be in contact with crude oil; and meanwhile, the problem of chromatographic elution of a micromolecular surfactant and a macromolecular polymer for oil displacement in migration can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of surfactants for oil production, and more specifically, to a polymer-type surfactant, its preparation method and application. Background Art

[0002] Petroleum is an important energy source and chemical raw material source in the current industrial field, and its importance is self-evident. With the development of the economy, the demand for petroleum is increasing, but continuous exploitation makes it more and more difficult to produce crude oil, and ensuring the supply of crude oil has become a prerequisite for the stable development of the economy.

[0003] In order to obtain a high crude oil recovery rate, a large number of chemical agents have been developed for oil displacement. Among them, surfactants are one of the important auxiliaries that can effectively reduce the oil-water interfacial tension, increase the capillary number, emulsify crude oil, and improve the recovery rate. Most of the commonly used surfactants are small molecule surfactants. As the injected water enters the formation, due to the adsorption of the formation itself and degradation caused by various impurities, the proportion of the actual surfactant contacting and taking effect with the crude oil is small. And only after the surfactant migrates to effectively contact the crude oil can it effectively improve the recovery rate. How to reduce the consumption of surfactants in the initial stage of entering the formation will be beneficial to improving the efficiency and effectiveness of surfactants in oil production, and is of great significance for improving the crude oil recovery rate.

[0004] At the same time, displacement is a complex process. In the commonly used composite flooding, macromolecular polymers and small molecule surfactants are used in combination. However, due to the difference in the order of magnitude of the molecular weights of small molecules and macromolecular polymers, they cannot be effectively synergistically promoted, and chromatographic separation will occur in the formation, and each will take effect, and the synergistic effect cannot be achieved. Therefore, developing a surfactant with a molecular size similar to that of macromolecular polymers and capable of migrating synchronously in the formation is also of great significance for improving the efficiency of composite flooding. Summary of the Invention

[0005] The purpose of the present invention is to provide a polymer-type surfactant to solve the technical problems of excessive consumption of surfactants in the initial stage of entering the formation and chromatographic elution of small molecule surfactants and macromolecular polymers for oil displacement in the prior art.

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

[0007] In the first aspect, the present invention provides a polymer-type surfactant, which includes an interfacial activity repeating unit and a branched cross-linking unit. The interfacial activity repeating unit includes a structure with interfacial activity, and the branched cross-linking unit includes an ester group structure.

[0008] The interfacial active repeating units in the polymeric surfactant provided by the present invention endow it with surface activity, and the branched crosslinking units enable it to form a hyperbranched weak crosslinked network. The polymeric surfactant is in a flowable gel state at room temperature. After entering the formation with the injected water, initially, the interfacial active repeating units are all wrapped in the hyperbranched weak crosslinked network, and the molecular size of the polymeric surfactant is relatively large, so it can migrate synchronously with the polymer flooding agent. The entanglement between the molecular chains of the polymer flooding agent and the molecular chains of the polymeric surfactant can also promote synchronous migration and reduce chromatographic elution. When migrating to the deep part of the formation, the ester groups in the polymeric surfactant are hydrolyzed and inactivated under the high-temperature formation conditions, and then the crosslinking points are broken. The polymeric surfactant is converted from a crosslinked polymer to a chain polymer with interfacial activity, achieving the purpose of emulsifying crude oil with a surfactant and reducing the oil-water interfacial tension.

[0009] According to some embodiments of the present invention, the polymeric surfactant includes an interfacial active repeating unit molecular chain and a branched crosslinking unit connecting the interfacial active repeating unit molecular chains.

[0010] According to some embodiments of the present invention, the polymeric surfactant can generally remain as a crosslinked polymer for a long time below 45°C; above 45°C, the ester groups often undergo hydrolysis, the crosslinked network breaks, and it transforms into a chain polymer.

[0011] According to some embodiments of the present invention, the number of interfacial active repeating units in the polymeric surfactant is 10 - 100,000.

[0012] According to some embodiments of the present invention, the structure with interfacial activity includes a hydrophobic group and a hydrophilic group. The hydrophobic group includes an alkyl group with no less than 6 carbon atoms, and the hydrophilic group includes at least one of an amide group, an ether group, and an ammonium ion.

[0013] According to some embodiments of the present invention, the interfacial active repeating unit includes any three or more of the structural units represented by the following formulas (1)-(5);

[0014]

[0015]

[0016] Wherein, R 2 、R 3 、R 4 、R 6 、R 7 、R 8 are all alkyl groups with 6 - 24 carbon atoms, and R 5 is a polyethoxy or polypropoxy group with a polymerization degree of 1 - 200.

[0017] According to some embodiments of the present invention, the alkyl group includes a straight-chain alkyl group or a branched-chain alkyl group.

[0018] According to some embodiments of the present invention, the alkyl chain lengths in more than three surfactant repeating units are different from each other.

[0019] According to some embodiments of the present invention, the proportion of the surfactant repeating unit in the polymeric surfactant is 75-95 wt%.

[0020] According to some embodiments of the present invention, the branched crosslinking unit includes four or more covalent bonds connecting to other units (surfactant repeating units or other branched crosslinking units).

[0021] According to some embodiments of the present invention, the branched crosslinking unit is obtained by participating in a polymerization reaction with at least one of polyethylene glycol diacrylate, glycerol triacrylate, and pentaerythritol tetraacrylate.

[0022] Specifically, when the branched crosslinking unit is obtained by participating in a polymerization reaction with polyethylene glycol diacrylate, the branched crosslinking unit includes four covalent bonds connecting to other units, and the polymeric surfactant may have a structure as described in the following formula (I):

[0023]

[0024] When the branched crosslinking unit is obtained by participating in a polymerization reaction with glycerol triacrylate, the branched crosslinking unit includes six covalent bonds connecting to other units, and the polymeric surfactant may have a structure as described in the following formula (II):

[0025]

[0026] When the branched crosslinking unit is obtained by participating in a polymerization reaction with pentaerythritol tetraacrylate, the branched crosslinking unit includes eight covalent bonds connecting to other units, and the polymeric surfactant may have a structure as described in the following formula (III):

[0027]

[0028] Wherein, R 1 is a surfactant structural unit, n is 10-100000, and m is 1-600.

[0029] In a second aspect, the present invention provides a method for preparing a polymeric surfactant, comprising: subjecting an interfacial active monomer and a branched crosslinking monomer to a free radical polymerization reaction to obtain the polymeric surfactant; the interfacial active monomer comprising a structure having interfacial activity and a polymerizable double bond, the branched crosslinking monomer comprising an ester group and at least two alkenyl groups, the ester group being located between the two alkenyl groups.

[0030] In the present invention, the branched crosslinking monomer includes at least two alkenyl groups, which can enable the product obtained from the polymerization reaction to have a crosslinked structure; and the ester group located between the two alkenyl groups can undergo hydrolysis when the temperature of the aqueous solution rises during use, disconnecting the crosslinked network and converting the crosslinked polymer into a chain polymer.

[0031] According to some embodiments of the present invention, the structure having interfacial activity includes a hydrophobic group and a hydrophilic group, the hydrophobic group includes an alkyl group having at least 6 carbon atoms, and the hydrophilic group includes at least one of an amide group, an ether group, and an ammonium ion.

[0032] According to some embodiments of the present invention, the alkyl group has 6 to 24 carbon atoms.

[0033] According to some embodiments of the present invention, the interfacial active monomer includes at least one of alkyl acrylamide, dialkyl acrylamide, 2-acrylamido-alkyl sulfonic acid and its sodium salt, allyloxyalkyl polyethylene glycol, and alkyl dimethyl allyl ammonium chloride.

[0034] According to some embodiments of the present invention, the interfacial active monomer includes at least one of didodecyl acrylamide, dihexadecyl acrylamide, hexadecyl acrylamide, octadecyl acrylamide, 2-acrylamido-dodecyl sulfonic acid, 2-acrylamido-tetradecyl sulfonic acid, allyloxydodecyl polyethylene glycol, allyloxytetradecyl polyethylene glycol, and octadecyl dimethyl allyl ammonium chloride.

[0035] According to some embodiments of the present invention, the interfacial active monomer includes at least three of alkyl acrylamide, dialkyl acrylamide, 2-acrylamido-alkyl sulfonic acid and its sodium salt, allyloxyalkyl polyethylene glycol, and alkyl dimethyl allyl ammonium chloride, and the alkyl groups in the at least three interfacial active monomers have different carbon atom numbers.

[0036] In the present invention, by using three interfacial active monomers having different alkyl carbon atom numbers in combination, it is possible to better adapt to the wide distribution characteristics of the carbon chain lengths in crude oil, making the performance of the polymeric surfactant more adaptable to crude oil and having better interfacial activity.

[0037] According to some embodiments of the present invention, the branched crosslinking monomer includes at least one of polyethylene glycol diacrylate, glycerol triacrylate, and pentaerythritol tetraacrylate.

[0038] According to some embodiments of the present invention, the surfactant monomer accounts for 75-95 wt% of the total amount of the polymerization monomers.

[0039] According to some embodiments of the present invention, the polymerization reaction system further includes an initiator, water, and an antifoaming agent, and the initiator includes an oxidizing agent and a reducing agent.

[0040] In the present invention, adding an antifoaming agent to the polymerization reaction system can avoid a large amount of foam generated by the surfactant monomer and enable the reaction to proceed smoothly.

[0041] The antifoaming agent used in the present invention can adopt various common types of aqueous solution antifoaming agents, such as silane-based aqueous solution antifoaming agents, etc.

[0042] According to some embodiments of the present invention, the oxidizing agent is selected from at least one of potassium persulfate, sodium persulfate, and ammonium persulfate.

[0043] According to some embodiments of the present invention, the reducing agent is selected from at least one of sodium thiosulfate, sodium sulfite, sodium bisulfite, sodium metabisulfite, and sodium dithionite.

[0044] According to some embodiments of the present invention, based on 100 parts of the total amount of the polymerization monomers, the amounts of each component are as follows:

[0045] Oxidizing agent: 0.075-0.04 parts, preferably 0.01-0.02 parts;

[0046] Reducing agent: 0.075-0.05 parts, preferably 0.01-0.025 parts;

[0047] Water: 100-200 parts, preferably 150-175 parts;

[0048] Antifoaming agent: 0.015-0.09 parts, preferably 0.02-0.075 parts.

[0049] According to some embodiments of the present invention, the preparation method includes:

[0050] 1) Prepare a uniform aqueous solution of the surfactant monomer, the branched crosslinking monomer, and the antifoaming agent, adjust the pH value to between 7 and 8 with sodium hydroxide, and transfer it to a reaction kettle;

[0051] 2) Purge with nitrogen to remove oxygen for 30-60 min, add the aqueous solutions of the oxidizing agent and the reducing agent, continuously purge with nitrogen to remove oxygen, and ensure the temperature of the reaction system is above 20 °C by water bath;

[0052] 3) React for 4 to 6 hours continuously. After the temperature of the reaction system stabilizes, stop the reaction to obtain the polymer surfactant.

[0053] In a third aspect, the present invention provides a polymer surfactant prepared by the preparation method described in the second aspect.

[0054] In a fourth aspect, the present invention provides the application of the polymer surfactant described in the first aspect or the polymer surfactant described in the third aspect in the development of oil and gas reservoirs.

[0055] The beneficial effects of the present invention are at least as follows:

[0056] The polymer surfactant provided by the present invention has a cross-linked network structure at room temperature and can be de-cross-linked in a high-temperature aqueous solution to form linear polymer molecules with interfacial activity. When it is applied to oil production, it can consume less at the initial stage of injection into the formation, and can effectively play the role of a surfactant after contacting with crude oil in the deep part of the formation; at the same time, it can effectively solve the chromatographic elution problem of small molecule surfactants and macromolecular polymers for oil displacement during migration. Specific Embodiments

[0057] In order to make the technical problems to be solved, technical solutions and beneficial effects of the present invention clearer and more understandable, the present invention will be further described in detail below in combination with specific embodiments. It should be understood that the specific embodiments described here are only used to explain this patent in detail and do not limit the protection scope of the present invention in any way.

[0058] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which the present invention belongs. The reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the raw materials, instruments and equipment used in the following embodiments can all be obtained through market purchase or can be obtained by existing methods; the reagent dosages are all the reagent dosages in conventional experimental operations unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0059] The synthesis methods of the polymer surfactants in each example and comparative example are as follows:

[0060] Add the branched cross-linking monomer and the interfacial active monomer into water to prepare a uniform solution, add an antifoaming agent, adjust the pH value to 7.5 with sodium hydroxide, stir evenly and transfer it to a reaction kettle, and pass nitrogen to remove oxygen for 30 minutes. Keep the temperature of the reaction system at 20 °C in a water bath. Prepare aqueous solutions with a concentration of 1 wt% of the oxidant and the reductant respectively, add them to the reaction system, continuously stir and pass nitrogen to remove oxygen. After reacting for 4 hours, take out the viscous product as the product.

[0061] The specific formulations and proportions of each example and comparative example are shown in Table 1. The defoamer is a commercially available aqueous silane defoamer (Evonik Industries, AROSURF FC 2805).

[0062] Table 1 Synthesis Formulations and Dosages of Samples in Each Example and Comparative Example (in parts by weight)

[0063]

[0064]

[0065] Prepare a solution with a product concentration of 2000 ppm in water with a salinity of 30000 mg / L, where the calcium ion content is 1000 mg / L, the magnesium ion content is 800 mg / L, and the rest are chloride ions and sodium ions. Seal the solution and store it in an aging oven at 90 °C. After different times, take the aged solution and measure its interfacial tension with the crude oil from Block Ming 15 in Zhongyuan Oilfield. See Table 2 for details.

[0066] Take polyacrylamide with a molecular weight of 10 - 12 million (hydrolysis degree 15%) and configure it into a solution with the product at a concentration of 2000 ppm each. At room temperature, inject it into a 1 m long sand-packed tube (permeability 1500 mD, diameter 38 mm), and take the produced liquid and repeat the injection. Let it flow through the sand-packed tube 10 times in total, and measure the concentration ratio of the polymer to the product at the outlet. See Table 2 for details.

[0067] Wherein:

[0068] Interfacial tension: Use the SDT interfacial tensiometer of KRUSS company to measure the interfacial tension between the solution and the crude oil.

[0069] The concentration is measured as follows: Take a small amount of the produced liquid and measure the total carbon element content through the TOC-L instrument of Shimadzu, Japan. Take a certain amount of the produced liquid and precipitate it in ethanol, take the supernatant and measure the carbon element content, and calculate the active substance concentration after deducting ethanol. Calculate the polymer content through the difference between the total carbon element content and the active substance concentration.

[0070] Table 2 Interfacial Tension of Samples in Each Example and Comparative Example after Different Aging Times and Concentration Ratio after 10 m Migration

[0071]

[0072] Compared with the samples of Comparative Examples 1-3, the difference in Examples 1-3 is whether the branched crosslinking monomer as a crosslinking agent is added. It can be seen from the test results in Table 2 that the interfacial activity of the samples in Examples 1-3 has the characteristic of delayed appearance. In the initial stage of entering the solution, due to the molecular chains being bound by the crosslinking network, they cannot effectively arrange at the interface, so the oil-water interfacial tension cannot be effectively reduced. As the crosslinking points degrade, the interfacial tension can be effectively reduced. However, the samples of Comparative Examples 1-3 can reduce the interfacial tension initially and do not have the characteristic of delayed release. This also enables the composite system of the polymer and the samples in Examples 1-3 to effectively migrate synchronously to the deep formation during migration. Therefore, after a migration of 10 m, the concentration ratio of the two is still close to 1:1. For the samples of Comparative Examples 1-3, due to the absence of a crosslinked structure and the molecular weight of the linear component being much smaller than that of the polymer flooding agent, severe chromatographic separation occurs and synchronous migration cannot be effectively achieved, so the synergistic effect of the composite flooding cannot be fully demonstrated.

[0073] Another reason why the samples in Examples 1-3 can effectively migrate synchronously with the polymer is that the interfacial active molecular chains are initially bound in the crosslinking network, so the adsorption is less and the degradation caused by various impurities is also less, thus effectively improving their utilization efficiency.

[0074] The difference between Example 4 and Example 3 is only the amount of each monomer used. The content of the branched crosslinking monomer in Example 4 is higher than that in Example 3, being 30 wt%, resulting in too low content of the interfacial active repeating units in the prepared polymer surfactant, insufficient interfacial activity of the polymer surfactant, and obvious reduction in oil displacement efficiency.

[0075] The difference between Example 5 and Example 1 is only that didodecylacrylamide in the interfacial active monomer is replaced by octadecylacrylamide, and the difference between Example 6 and Example 1 is only that 2-acrylamido-tetradecanesulfonic acid in the interfacial active monomer is replaced by 2-acrylamido-dodecanesulfonic acid. It can be seen from Table 2 that the interfacial activity of Example 5 and Example 6 is slightly worse than that of Example 1. This is mainly because the carbon chains in crude oil have a relatively wide distribution. Therefore, when the carbon chain number distribution in the polymer surfactant broadens, it can more effectively adapt to the characteristics of the wide carbon chain distribution of crude oil, with higher activity and higher oil displacement efficiency. It should be noted that the above rules only apply to this type of polymer surfactant and cannot be simply inferred to all surfactant products.

[0076] For the same reason, when only one or two interfacial active monomers are used, the adaptability of the prepared product to the wide carbon chain distribution characteristics of crude oil decreases, and the activity relatively decreases, as shown in Example 7. However, it still has the characteristic of synchronous migration of polymer and active substances, so the change in concentration ratio is not significant after 10m migration. The product prepared in Comparative Example 4 without adding branched cross-linking monomers has serious chromatographic separation, cannot effectively migrate synchronously, and cannot fully reflect the synergistic effect of composite flooding.

[0077] Evaluation of oil recovery effect

[0078] Take the mixed system of monomers with the same ratio as in Examples 1-3 but not polymerized as Comparative Examples 5-7. The samples of Examples 1-7 and Comparative Examples 1-7 were respectively configured into solutions with a concentration of 2000 ppm with polyacrylamide (hydrolysis degree 15%) with a molecular weight of 10 million to 12 million. First, water flooding was carried out in a sand-packed tube with a permeability of 1500 mD (1m long and 38mm thick) until the water cut reached 98%, then 0.3PV of the above solution was injected, and then subsequent water flooding was carried out until the water cut reached 100%. Then, an oil displacement experiment was carried out. The crude oil used was the crude oil from Block Ming 15 in Zhongyuan Oilfield, and the displacement results are shown in Table 3.

[0079] Table 3 Oil displacement performance of samples in each example and comparative example

[0080] Group Enhanced oil recovery after water flooding (%) Example 1 27.1 Example 2 29.3 Example 3 28.8 Example 4 21.3 Example 5 24.3 Example 6 24.9 Example 7 21.1 Comparative Example 1 20.6 Comparative Example 2 19.8 Comparative Example 3 17.8 Comparative Example 4 17.2 Comparative Example 5 18.3 Comparative Example 6 15.2 Comparative Example 7 16.1

[0081] As can be seen from Table 3, using the polymer surfactant provided by the present invention can effectively improve the oil recovery rate.

[0082] It should be noted that the above-described embodiments are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described by referring to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words rather than limiting words. Modifications can be made to the present invention within the scope of the claims of the present invention, and the present invention can be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A polymer surfactant, characterized in that it comprises surfactant repeating units and branched crosslinking units, the surfactant repeating units comprise a surfactant structure, and the branched crosslinking units comprise an ester group structure.

2. The polymer surfactant according to claim 1, characterized in that the surfactant structure comprises a hydrophobic group and a hydrophilic group, the hydrophobic group comprises an alkyl group with no less than 6 carbon atoms, and the hydrophilic group comprises at least one of an amide group, an ether group, and an ammonium ion; Preferably, the surfactant repeating units comprise any three or more of the structural units represented by the following formulas (1)-(5); Among them, R 2 , R 3 , R 4 , R 6 , R 7 , R 8 are all alkyl groups with 6 to 24 carbon atoms, and R 5 is a polyethoxy or polypropoxy group with a degree of polymerization of 1 to 200; and / or, the branched crosslinking units are obtained by polymerization reaction of at least one of polyethylene glycol diacrylate, glycerol triacrylate, and pentaerythritol tetraacrylate.

3. The polymer surfactant according to claim 1 or 2, characterized in that the proportion of the surfactant repeating units in the polymer surfactant is 75-95 wt%.

4. A preparation method of a polymer surfactant, characterized in that it comprises: a free radical polymerization reaction occurs between a surfactant monomer and a branched crosslinking monomer to obtain the polymer surfactant; the surfactant monomer comprises a surfactant structure and a polymerizable double bond, and the branched crosslinking monomer comprises an ester group and at least two alkenyl groups, and the ester group is located between the two alkenyl groups.

5. The preparation method according to claim 4, characterized in that the surfactant structure comprises a hydrophobic group and a hydrophilic group, the hydrophobic group comprises an alkyl group with no less than 6 carbon atoms, and the hydrophilic group comprises at least one of an amide group, an ether group, and an ammonium ion; Preferably, the alkyl group has 6-24 carbon atoms; More preferably, the surfactant monomer comprises at least one of alkyl acrylamide, dialkyl acrylamide, 2-acrylamido-alkyl sulfonic acid and its sodium salt, allyloxyalkyl polyethylene glycol, and alkyl dimethyl allyl ammonium chloride; Even more preferably, the surfactant monomer comprises at least three of alkyl acrylamide, dialkyl acrylamide, 2-acrylamido-alkyl sulfonic acid and its sodium salt, allyloxyalkyl polyethylene glycol, and alkyl dimethyl allyl ammonium chloride, and the alkyl groups in the at least three surfactant monomers have different carbon atom numbers; and / or, the branched crosslinking monomer comprises at least one of polyethylene glycol diacrylate, glycerol triacrylate, and pentaerythritol tetraacrylate.

6. The preparation method according to claim 4 or 5, characterized in that the surfactant monomer accounts for 75-95 wt% of the total amount of polymerization monomers.

7. The preparation method according to any one of claims 4-6, characterized in that the polymerization reaction system further comprises an initiator, water, and an antifoaming agent, and the initiator comprises an oxidizing agent and a reducing agent; Preferably, the oxidizing agent is selected from at least one of potassium persulfate, sodium persulfate, and ammonium persulfate; and / or, the reducing agent is selected from at least one of sodium thiosulfate, sodium sulfite, sodium bisulfite, sodium metabisulfite, and sodium dithionite.

8. The preparation method according to claim 7, characterized in that based on the total amount of polymerization monomers being 100 parts, the dosages of each component are respectively: oxidizing agent: 0.075 - 0.04 parts, preferably 0.01 - 0.02 parts; reducing agent: 0.075 - 0.05 parts, preferably 0.01 - 0.025 parts; water: 100 - 200 parts, preferably 150 - 175 parts; defoaming agent: 0.015 - 0.09 parts, preferably 0.02 - 0.075 parts.

9. A polymer surfactant prepared by the preparation method according to any one of claims 4 - 8.

10. The application of the polymer surfactant according to any one of claims 1 - 3 or the polymer surfactant according to claim 9 in the development of oil and gas reservoirs.

Images