A foam stabilizer based on graded modification of enteromorpha and a preparation method and application thereof

Abstract

The application belongs to the technical field of oilfield exploitation, and particularly relates to a foam stabilizer based on graded modification of Enteromorpha, and a preparation method and application thereof. The foam stabilizer comprises a foam stabilizer or a chelated foam stabilizer. The preparation method of the foam stabilizer comprises the following steps: step one, Enteromorpha pretreatment: washing and drying Enteromorpha, and then crushing; step two, hot water leaching separation: adding deionized water according to a solid-liquid ratio of 1:25-35, stirring and leaching at 85-95 DEG C for 4 h, and filtering to obtain filtrate and residue; and step three, preparation of the foam stabilizer or the chelated foam stabilizer: drying the residue at 80 DEG C for 24 h, and sieving through a 200-mesh sieve to obtain the foam stabilizer; and alkali-activating the foam stabilizer and then performing a carboxylation reaction to obtain the chelated foam stabilizer. The application realizes high-value utilization of waste, and has the advantages of mild process, low cost, excellent foam stabilization under high temperature and high salinity, and effectively makes up for the defects of the prior art.

Description

Technical Field

[0001] This invention belongs to the field of oilfield development technology, specifically relating to a foam stabilizer based on the graded modification of seaweed, its preparation method and application. Background Technology

[0002] Foam possesses characteristics such as blocking large areas but not small ones, blocking water but not oil, low frictional resistance, low density, low filtration loss, and minimal damage to the formation. Therefore, it is widely used in oil and gas development fields such as enhanced oil and gas recovery, oil and gas field development, drilling, cementing, reservoir protection, and reservoir stimulation. However, foam is a thermodynamically unstable system, highly susceptible to disproportionation and aggregation; furthermore, oil and gas reservoirs generally exhibit high-temperature and high-salinity conditions, rich in Ca. 2+ Mg 2+ Metal ions readily combine with traditional foam stabilizers (such as surfactants), disrupting the stability of the foam liquid film, leading to a shortened foam half-life, reduced plugging ability, and severely limiting the foam displacement effect. To improve foam stability, salt-resistant surfactants (such as betaines) are typically used, or additives such as nanoparticles and polymers are added to the surfactant solution to enhance foam liquid film strength, inhibit foam drainage and aggregation, thereby improving foam stability.

[0003] Currently, relevant technicians have developed various foam stabilizer systems, obtaining foam stabilizers with excellent foam stabilizing performance. For example, patent CN119371951A discloses a nano-shell powder foam stabilizer and its preparation method. Nano-shell powder is obtained by grinding shells after high-temperature calcination. The prepared nano-shell powder exhibits good foam stabilizing performance, realizing the high-value utilization of shell resources. Patent CN119823743A discloses an amphiphilic graphene oxide temperature-resistant foam stabilizer and its preparation method. Graphene is modified with a silane coupling agent to obtain an amphiphilic graphene oxide foam stabilizer. This foam stabilizer can increase the strength of the foam liquid film, prolong the drainage time, and improve foam stability under high temperature and wide pH conditions. It has a synergistic effect with foaming agents and shows good application prospects in high-temperature acidic oil and gas reservoir fracturing and chemical flooding. Patent CN119219865A discloses a nano-foam stabilizer. This nano-foam stabilizer not only possesses hydrophobic groups, enabling hydrophobic interactions with the tail of the foaming agent, but also has electrically neutral hydrophilic polymer groups on its particles. On the one hand, this provides temperature and salt resistance; on the other hand, compared to some anionic polymers, it helps reduce or avoid charge repulsion with surfactant head groups, promoting the adsorption of nanoparticles at the gas-liquid interface, thereby improving foam stability. Patent CN118931559A discloses a modified fly ash foam stabilizer, its preparation method, and its application. This method mainly involves ultrasonically treating ultrafine fly ash with acetic acid to obtain the modified fly ash foam stabilizer. The preparation process is simple, and the resulting foam stabilizer exhibits uniform bubbles and stable performance, effectively achieving the clean and efficient conversion and utilization of solid waste. Patent CN115701437A discloses a microgel temperature-sensitive foam stabilizer and its preparation method. The poly(acrylamide-acrylic acid-N,N-methylenebisacrylamide) monodisperse random copolymer microgel particles prepared by this invention can stabilize foam at high temperatures (40-80℃) and defoam at low temperatures (below 40℃) when used as a foam stabilizer. The aforementioned foam stabilizers are mainly prepared using the principle of enhancing the viscoelasticity of foam liquid films through nanoparticles or polymers. They generally rely on non-renewable, high-value materials or regionally specific waste, have a single foam stabilization mechanism (physical adsorption or enhancement of liquid film viscoelasticity only), weak shear dehydration resistance, and are difficult to adapt to high temperatures (≥100℃) and high mineralization (≥20×10⁻⁶). 4 Oil reservoirs with a concentration of mg / L may also have problems such as high process energy consumption and significant environmental risks.

[0004] Therefore, there is an urgent need for a foam stabilizer and its preparation method that is mild in process, low in cost, has excellent foam stabilization under high temperature and high salt conditions, and can realize the high-value utilization of waste. Summary of the Invention

[0005] To address the problems of poor temperature and salt resistance and insufficient foam stability of existing foam stabilizers in high-salinity oil reservoirs, this invention provides a foam stabilizer based on graded modification of Ulva prolifera. This stabilizer is prepared by grading Ulva prolifera to form "water-insoluble powder or modified water-insoluble powder + water-soluble polysaccharide thickener". The water-insoluble powder or modified water-insoluble Ulva prolifera powder acts as a foam stabilizer, while the modified water-insoluble Ulva prolifera powder can also chelate metal ions. The Ulva prolifera polysaccharide acts as a thickener. The interaction between the two enhances the stability of the foam under high-salinity conditions. Furthermore, the foam stabilizer alone can withstand 130℃, and the addition of polysaccharide shows excellent performance at 80℃ and high salinity, reducing oilfield extraction costs and simultaneously achieving resource utilization of Ulva prolifera waste.

[0006] The specific technical solution adopted in this invention is as follows:

[0007] A method for preparing a foam stabilizer based on the graded modification of *Ulva prolifera*, wherein the foam stabilizer comprises a foam stabilizer or a chelating foam stabilizer, and the method for preparing the foam stabilizer comprises the following steps:

[0008] Step 1: Pretreatment of seaweed: Take seaweed, wash it, dry it at 80℃, and then pulverize it into coarse powder;

[0009] Step 2, hot water extraction and separation: Add deionized water at a solid-liquid ratio of 1:25~35, and extract by stirring in a constant temperature water bath at 85~95℃ for 4h~6h. Filter through a 1000-mesh filter cloth to obtain filtrate and filter residue. In Step 2 and Step 3, solids are expressed in g and liquids in mL.

[0010] The purpose of hot water extraction is to separate soluble and insoluble substances. The soluble substances are processed into polysaccharide thickeners, while the insoluble substances are prepared into foam stabilizers or chelated foam stabilizers.

[0011] Step 3: Preparation of foam stabilizer or chelated foam stabilizer: The filter residue is dried, pulverized, and passed through a 200-mesh sieve to obtain *Ulva prolifera* powder. The *Ulva prolifera* powder is then modified to obtain a chelated foam stabilizer. The specific steps are as follows:

[0012] ① Dry the filter residue at 80℃ for 24 hours, and pass it through a 200-mesh sieve to obtain the foam stabilizer;

[0013] ②The foam stabilizer is activated by alkali and then carboxylated to obtain a chelated foam stabilizer.

[0014] More preferably, the foam stabilizer further includes a polysaccharide thickener, and the preparation method of the foam stabilizer further includes the following steps:

[0015] Step 4: Preparation of polysaccharide thickener: The filtrate is concentrated, precipitated with ethanol, deproteinized, and dried to obtain the polysaccharide thickener. Specific steps are as follows:

[0016] ① Concentrate the filtrate to 1 / 4 of its original volume at 45-55℃; specifically: pour the filtrate into a rotary evaporator (water bath temperature is 45-55℃) and concentrate the volume to 1 / 4 of the original volume.

[0017] ② Add 3 times the amount of anhydrous ethanol and let stand at 4℃ for 12-24h. Centrifuge at 3500-4500r / min to collect the precipitate. Specifically, while stirring, add anhydrous ethanol to the concentrate, place it in a refrigerator at 4℃ and let it stand for 12-24h to precipitate. Then centrifuge at 3500-4500r / min for 15min and collect the precipitate at the bottom of the tube.

[0018] ③ Remove protein 2-3 times with Sevag reagent, freeze-dry and sieve; specifically: prepare Sevag reagent with chloroform: n-butanol = 4:1 (volume ratio), dissolve the precipitate collected in step ② in water, add 1 / 5 volume of Sevag reagent, mechanically stir at 300 r / min for 30 min, centrifuge at 3000 r / min for 20 min, after the solution separates into layers, take the upper polysaccharide aqueous solution, and repeat the operation 2-3 times; freeze-dry to obtain polysaccharide thickener, then pulverize and sieve (200 mesh).

[0019] In a further preferred embodiment, the preparation method of the chelated foam stabilizer in step three is as follows:

[0020] ① Add 5-10wt% NaOH to the foam stabilizer at a solid-liquid ratio of 1:5-1:10, pre-disperse ultrasonically for 15 min, and then alkalize at 40-60℃ for 1-2 h. The preferred method is to add a small amount of 2-3wt% NaOH solution to the foam stabilizer at a solid-liquid ratio of 1:5-1:10 (g:mL), pre-disperse ultrasonically for 15 min at an ultrasonic power of 300-500W and a frequency of 20-40kHz, and then add the remaining NaOH solution, totaling 5-10wt%, preferably 8wt% sodium hydroxide solution. Stir in a constant temperature water bath at 40-60℃ for 1-2 h (300-500r / min) to fully activate the alcohol hydroxyl groups.

[0021] ② Add 10-20wt% chloroacetic acid solution and react for 2-4 hours at 60-80℃. Preferably, the pH is controlled at 8-10 by adding a 0.1mol / L Na2CO3-NaHCO3 buffer system to avoid excessive acidity that could lead to product hydrolysis.

[0022] ③ After the reaction is complete, adjust the pH to 6-7 with hydrochloric acid (1 mol / L), centrifuge (3000 r / min, 10 min) to collect the solid, wash with deionized water until chlorine-free, vacuum dry at 60℃ to constant weight, pulverize and pass through a 200-mesh sieve to obtain carboxyl-modified powder, which is the chelating foam stabilizer.

[0023] The present invention also discloses a foam stabilizer based on the graded modification of seaweed, which is prepared by any of the preparation methods described above.

[0024] This invention also discloses the application of a foam stabilizer based on the graded modification of *Ulva prolifera*, used to prepare a foam flooding system suitable for high-salinity oil reservoirs, wherein high salinity refers to a salinity ≥ 20 × 10⁻⁶. 4 mg / L.

[0025] Furthermore, the preparation method of the foam flooding system is as follows: the foam stabilizer is fully dissolved in mineralized water containing surfactant, and foaming is achieved by stirring; the foam stabilizer includes a foam stabilizer or a chelated foam stabilizer, and the mass percentage of the foam stabilizer or chelated foam stabilizer in the foam flooding system is 2%-10%;

[0026] Preferably, it is applied at a temperature of 125-135℃ and a mineralization of 20×10⁻⁶. 4 -25×10 4 When applied to reservoirs with a salinity of mg / L, especially at a temperature of 130℃ and a salinity of 22×10, it is particularly suitable for use in oil reservoirs with a salinity of mg / L. 4 For oil reservoirs with a concentration of mg / L, a foam flooding system with a chelated foam stabilizer comprising 10% by mass is preferred. This system has a liquid half-life of 42 min under this application environment.

[0027] Furthermore, the foam stabilizer also includes a polysaccharide thickener, wherein the polysaccharide thickener accounts for 0.2%-1.0% of the mass of the foam flooding system.

[0028] Preferably, it is applied at a temperature of 75-85℃ and a mineralization degree of 3×10. 4 -8×10 4 This is particularly suitable for oil reservoirs with a salinity of 5×10 mg / L, especially at temperatures of 80℃. 4 For oil reservoirs with a concentration of mg / L, a foam flooding system with a chelating foam stabilizer of 10% by mass and a polysaccharide thickener of 0.6% by mass is preferred, and the liquid half-life of this system is ≥52 min.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] This invention uses graded modification of seaweed waste to produce foam stabilizers, which not only realizes the high-value utilization of waste, but also has the advantages of mild process, low cost, and excellent foam stabilization under high temperature and high salt conditions, effectively making up for the defects of existing technologies.

[0031] For the first time, *Ulva prostrata* was classified into insoluble powder and soluble polysaccharide, and the insoluble powder could be further modified into a chelating foam stabilizer to achieve a synergistic foam stabilizing effect of "chelating metal ions + liquid film thickening"; at 130℃ and 22×10 4At a salinity of mg / L, compared to a simple surfactant system, the addition of a foam stabilizer or a chelated foam stabilizer significantly improves the half-life of the liquid and enhances foam stability, effectively addressing the problem of insufficient high-temperature stability in existing technologies.

[0032] The foam stabilizer, chelating foam stabilizer, and polysaccharide thickener provided in this application use marine waste *Ulva prolifera* as raw material, which reduces costs compared to traditional salt-resistant surfactants. Furthermore, the raw materials and products exhibit good biodegradability, avoiding pollution to oil reservoirs and the environment. The modified *Ulva prolifera* powder itself can adsorb at the gas-liquid interface, enhancing the viscoelasticity and foam strength of the foam film. Moreover, the modified *Ulva prolifera* powder foam stabilizer with polycarboxylic acid functional groups can effectively chelate high-valence calcium and magnesium ions (such as...) in formation water. Figure 7 As shown, Figure 7 In this invention, M represents high-valence metal ions and R represents insoluble components of *Ulva prolifera*, mitigating the negative impact of high-valence metal ions on foam performance. Simultaneously, *Ulva prolifera* polysaccharides increase the viscosity of the foam liquid film through thickening, and synergistically with the chelating effect of the modified powder, significantly improving the half-life of the foam under high mineralization conditions, which is superior to single surfactant systems. This invention uses *Ulva prolifera* as a modified raw material, realizing the high-value utilization of *Ulva prolifera*-related materials, which is beneficial to environmental protection and conforms to the concept of green and sustainable development. Attached Figure Description

[0033] Figure 1(a) shows the 25℃ 22×10 Ω·cm configuration provided in the embodiment of this application. 4 Foaming performance of water with a mineral content of mg / L after the addition of foam stabilizer and chelated foam stabilizer;

[0034] Figure 1(b) shows the 25℃ 22×10 Ω·cm configuration provided in the embodiment of this application. 4 The half-life performance of the precipitate after adding foam stabilizer and chelated foam stabilizer to water with a mineralization of mg / L;

[0035] Figure 2(a) shows the 25℃ 5×10 ℃ configuration provided in the embodiment of this application. 4 Foaming performance diagram of water with a mineral content of mg / L after adding chelated foam stabilizer and polysaccharide thickener;

[0036] Figure 2(b) shows the 25℃ 5×10 ℃ configuration provided in the embodiment of this application. 4 The half-life performance of the precipitate after adding chelating foam stabilizer and polysaccharide thickener to water with a mineral content of mg / L;

[0037] Figure 3(a) shows the 130℃ 22×10 ℃ achievable according to the embodiment of this application. 4 Foaming performance of water with a mineral content of mg / L after the addition of foam stabilizer and chelated foam stabilizer;

[0038] Figure 3(b) shows the 130℃ 22×10 ℃ temperature provided in the embodiment of this application. 4The half-life performance of the precipitate after adding foam stabilizer and chelated foam stabilizer to water with a mineralization of mg / L;

[0039] Figure 4(a) shows the 80℃ 5×10 ℃ 5×10 ℃ 5×10 ℃ 5×10 ℃ 5×10 ℃ 80 ... 4 Foaming performance diagram of water with a mineral content of mg / L after adding chelated foam stabilizer and polysaccharide thickener;

[0040] Figure 4(b) shows the 80℃ 5×10 ℃ 5×10 ℃ 5×10 ℃ 5×10 ℃ 5×10 ℃ 80 ... 4 The half-life performance of the precipitate after adding chelating foam stabilizer and polysaccharide thickener to water with a mineral content of mg / L;

[0041] Figure 5 This is a shear viscosity diagram of different concentrations of polysaccharide thickener in deionized aqueous solution at 25 and 80 °C according to this application.

[0042] Figure 6 For this application, at 25 and 80°C, different concentrations of polysaccharide thickener were used at 5×10 4 Shear viscosity plot of mineralized water at mg / L;

[0043] Figure 7 This is a schematic diagram illustrating the chelation of the chelating agent of this application with high-valence metal ions. Detailed Implementation

[0044] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0045] In each embodiment, lauramidopropyl betaine LAB (specifically model LAB-35) was purchased from Shanghai Yincong New Material Technology Co., Ltd., surfactant ZK25150 was purchased from Qingtian Zhongke Plant Technology Co., Ltd., and the source of Ulva prolifera was the Yellow Sea area of ​​Qingdao.

[0046] Example 1

[0047] This embodiment provides a method for preparing a foam stabilizer based on the graded modification of Ulva prolifera. The foam stabilizer includes a foam stabilizer and a polysaccharide thickener. The specific preparation method is as follows:

[0048] Step 1: Pre-treatment of seaweed: After washing the fresh seaweed, place it in an 80℃ oven and pulverize it to obtain coarse seaweed powder;

[0049] Step 2: Hot water extraction and separation: Take 100g of coarse seaweed powder, add 3000mL of deionized water, stir and extract at 95℃ for 6h, filter through 1000 mesh to obtain filtrate and residue.

[0050] Step 3: Prepare foam stabilizer and chelated foam stabilizer;

[0051] The filter residue was dried at 80℃ for 24 hours, pulverized and passed through a 200-mesh sieve to obtain 55g of insoluble seaweed powder, which is the foam stabilizer.

[0052] Take 50g of insoluble seaweed powder, add a small amount of sodium hydroxide solution for pretreatment and ultrasonic dispersion, then add 250mL of 8% sodium hydroxide solution, alkalize at 50℃ for 1.5h, and wash until neutral;

[0053] Add 500 mL of 15% chloroacetic acid solution and etherify at 70°C for 3 hours;

[0054] Adjust the pH to 6.5 with hydrochloric acid, wash until chlorine-free, dry and pulverize through a 200-mesh sieve to obtain 45g of modified powder, which is the chelated foam stabilizer.

[0055] Step 4: Preparation of polysaccharide thickener: The filtrate was concentrated under reduced pressure to 500 mL, 1500 mL of anhydrous ethanol was added, and the mixture was allowed to stand at 4 °C for 18 h. After centrifugation at 4000 r / min for 12 min, the precipitate was washed and dried under vacuum at 60 °C. Protein was removed by Sevag reagent, and 5 g of water-soluble polysaccharide was finally obtained.

[0056] Example 2

[0057] At 25°C, two surfactants (lauromamide propyl betaine LAB and ZK-25150), the foam stabilizer prepared by the method of Example 1, and the chelated foam stabilizer were dissolved in 22 × 10⁻⁶ solution according to the proportions described in Table 1. 4 Compositions 1-16 were obtained in water with a mineralization of mg / L, comparative compositions 2-3 and 5-6 were prepared, and two surfactants were dissolved in 22×10 mg / L water at 25°C. 4 Comparative composition 1 and comparative composition 4 were obtained from water with a mineralization of mg / L.

[0058] Example 3

[0059] At 25°C, two surfactants (lauramidopropyl betaine LAB and ZK-25150), the chelating foam stabilizer prepared according to the method of Example 1, and the polysaccharide thickener were dissolved in 5×10 solution according to the proportions shown in Table 2. 4 Compositions 17-32 were obtained from water with a mineralization of mg / L. Simultaneously, lauramidopropyl betaine LAB and surfactant ZK-25150 were dissolved in 5×10 mg / L water at 25°C. 4 Comparative compositions 7-8 were obtained in water with a mineralization of mg / L.

[0060] Example 4

[0061] At 130°C, surfactant ZK-25150, the foam stabilizer prepared according to the method of Example 1, and the chelated foam stabilizer were dissolved in 22×10 solution according to the proportions shown in Table 1. 4 Compositions 33-40 were obtained from water with a mineralization of mg / L, compared to composition 10-11. Simultaneously, surfactant ZK-25150 was dissolved in 22 × 10 mg / L water at 130°C. 4 Comparative composition 9 was obtained in water with a mineralization of mg / L.

[0062] Example 5

[0063] At 80°C, ZK-25150, the chelated foam stabilizer prepared according to the method of Example 1, and the polysaccharide thickener were dissolved in 5×10 solution according to the proportions shown in Table 2. 4 Compositions 41-46 were obtained by dissolving surfactant ZK-25150 in 5×10 mg / L mineralized water at 80°C. 4 Comparative composition 12 was obtained in water with a mineralization of mg / L.

[0064] Experimental Example 1

[0065] To verify the actual performance of the foam stabilizer of this application, the foaming performance of the surfactants in Examples 2 to 5 and the foam stabilizing performance of the foam stabilizers were tested in accordance with SY / T 5350-2009 "Evaluation Procedure for Foaming Agents for Drilling Fluids".

[0066] The test methods for foaming and foam stabilization performance include: foaming volume and half-life are determined by stirring. Take 100 mL of the prepared surfactant solution (compositions 1-46, control compositions 1-12) and stir it in a high-speed stirrer at 8000 r / min for 3 min. Pour the generated foam into a graduated cylinder and record the maximum foaming volume and half-life (the time required for 50 mL of solution to precipitate).

[0067] The test results are detailed in Tables 1 to 4.

[0068] Table 1 Performance results of compositions 1-12 prepared in Example 2

[0069]

[0070] Table 2 Performance results of compositions 17-32 prepared in Example 3

[0071]

[0072] Table 3 Performance results of compositions 33-40 prepared in Example 4

[0073]

[0074] Table 4 Performance results of compositions 41-46 prepared in Example 5

[0075]

[0076] According to Table 1 and Figure 1(a) , 1(b) It can be seen that 25℃, 22×10 4 At a salinity of mg / L, for both surfactants, the addition of foam stabilizers and chelating foam stabilizers significantly improved the half-life of the eluent. Although the foam volume decreased slightly compared to the levels without foam stabilizers and chelating foam stabilizers, it still remained at a high foaming level. This indicates that the addition of both foam stabilizers and chelating foam stabilizers improves foam stability, with chelating foam stabilizers showing a more significant effect. This suggests that chelating foam stabilizers combine foam stabilizing properties with the chelating effect of polycarboxylic acids on high-valence metal ions, thereby mitigating the impact of high-valence metal ions on foam stability. Among these, chelating foam stabilizers showed the most significant improvement in the foam stability of ZK-25150. Table 1, Figures 1(a) and 1(b) also show that when the addition amount of foam stabilizers and chelating foam stabilizers exceeds 10%, both the foam volume and the half-life of the eluent decrease simultaneously. Therefore, the preferred addition range is 2–10 wt%.

[0077] The increased quality of the chelating foam stabilizer allows it to better act as a "physical barrier" at the boundary, inhibiting the coalescence of small bubbles into larger ones. Simultaneously, it can adsorb moisture from the liquid film, forming "local water storage areas," slowing down the dehydration rate of the liquid film, preventing foam failure due to "dry film rupture," and extending foam life. Furthermore, the chelating foam stabilizer can also be adsorbed into the foam liquid film, increasing its thickness and slowing down liquid film drainage.

[0078] From Table 2 and Figure 2(a) , 2(b) It can be seen that 25℃, 5×10 4 At a salinity of mg / L, for both surfactants, the addition of a chelating foam stabilizer significantly improves foam stability. The addition of a polysaccharide thickener also significantly increases the foam's half-life. While the polysaccharide thickener increases foam viscosity, excessively high concentrations can negatively impact the half-life; the optimal concentration is 0.6 wt% polysaccharide thickener. These two synergistic effects result in a significant increase in the foam's half-life.

[0079] From Table 3 and Figure 3(a) , 3(b) It can be seen that 130℃ and 22×10 4 At a salinity of mg / L, adding 2-10 wt% of foam stabilizer and chelating foam stabilizer to the ZK-25150 surfactant can improve foam stability, as shown in Table 1 and... Figure 1(a), 1(b) In summary, the foam stabilizer and chelated foam stabilizer of this invention can improve foam stability at both low and high temperatures, with the chelated foam stabilizer showing a more significant effect on improving foam stability. Furthermore, at 130℃ and 22×10⁻⁶ °C, the foam stabilizer... 4 At a salinity of mg / L, its performance degradation is small, and it exhibits good foam stabilization performance at high temperature and high salinity.

[0080] From Table 4 and Figure 4(a) , 4(b) It can be seen that at 80℃, 5×10 4 At a certain salinity, for the ZK-25150 surfactant, the addition of chelating foam stabilizers and polysaccharide thickeners can improve foam stability, as shown in Table 2 and... Figure 2(a) , 2(b) In summary, the chelated foam stabilizer and polysaccharide thickener system of this invention can improve foam stability at both low and high temperatures, and the optimal addition amount of the polysaccharide thickener is 0.6 wt%. Meanwhile, at 80°C and 5 × 10⁻⁶ °C, the foam stability is improved. 4 At a salinity of mg / L, its performance degradation is relatively small, and it exhibits good foam stabilization performance under high temperature and high salinity conditions. It can withstand more complex reservoirs, thereby improving oil recovery.

[0081] Experiment Example 2

[0082] Shear viscosity test:

[0083] This application describes shear viscosity tests on polysaccharide thickener solutions of different concentrations. The test method involves using an Anton Paar rheometer to measure the shear viscosity of different concentrations of polysaccharide thickener in deionized water and 5×10⁻⁶ solutions at 25°C and 80°C. 4 mg / L mineralization, variable shear rate in water 0-100 s⁻¹ -1 The viscosity of the prepared solution was measured automatically by computer under the specified conditions. After measurement, the data was recorded and the results were saved. The results are as follows: Figure 5 , Figure 6 As shown, where, Figure 5 Polysaccharide thickeners of different concentrations at 25℃ and 80℃ ( Figure 5 The shear viscosity change of *Ulva prolifera* polysaccharide in deionized water. Figure 6 Polysaccharide thickeners of different concentrations at 25℃ and 80℃ ( Figure 6 The polysaccharide in *Ulva prolifera* (5×10) 4 Shear viscosity change in water with a salinity of mg / L.

[0084] Depend on Figure 5 It can be seen that when the shear rate is less than 30 s⁻¹, -1 At this point, as the shear rate increases, the viscosity of the solution decreases rapidly; when the shear rate exceeds 30 s⁻¹... -1Subsequently, the viscosity of the solution decreased slowly. Because it is a pseudoplastic fluid, shear dilution occurs when flowing through the formation. The viscosity of *Ulva prolifera* polysaccharide decreases slowly within 0-100 s. -1 At a shear rate of [value missing], it exhibits good viscosity retention. The shear viscosity test curve at 80℃ shows a similar pattern, indicating that the thickener of this invention has good temperature resistance. Meanwhile, [details missing]. Figure 6 It can be seen that under high salinity, the viscosity exhibits the same pattern at different shear rates as under non-salinity conditions. Figure 5 and Figure 6 It is known that the viscosity reduction of *Ulva prolifera* polysaccharide is low under high mineralization, and it can act as a polysaccharide thickener under high mineralization.

[0085] In summary, the foam stabilizer, chelated foam stabilizer, and polysaccharide thickener prepared in the embodiments of this application exhibit excellent foam stabilizing performance under high salinity and high temperature conditions, and are expected to solve the problem of poor foam stability of single foam stabilizers, playing an important role in the field of oil and gas well production enhancement. The *Ulva prolifera* graded modification system described in this invention is of great significance for ensuring the production of oil and gas wells.

[0086] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for preparing a foam stabilizer based on a fractionated modification of Enteromorpha, characterized in that, The foam stabilizer comprises a foam stabilizer or a chelated foam stabilizer, and a preparation method of the foam stabilizer comprises the following steps: Step one, Enteromorpha pretreatment: clean and dry Enteromorpha, and then crush it; Step two, hot water extraction and separation: add deionized water according to a solid-liquid ratio of 1:25-35, stir and extract at 85-95 ℃ for 4 h, and then filter to obtain filtrate and residue, wherein the solid is measured in g, and the liquid is measured in mL; Step three, preparation of the foam stabilizer or the chelated foam stabilizer: dry the residue at 80 ℃ for 24 h, and then sieve it through a 200-mesh sieve to obtain the foam stabilizer; alkali-activate the foam stabilizer, and then perform a carboxylation reaction to obtain the chelated foam stabilizer.

2. The method for preparing a foam stabilizer based on a fractionated modification of Enteromorpha according to claim 1, characterized in that, The foam stabilizer further comprises a polysaccharide thickening agent, and a preparation method of the foam stabilizer further comprises the following step: Step four, preparation of the polysaccharide thickening agent: concentrate the filtrate at 45-55 ℃ to 1 / 4 of the volume, place it at 4 ℃ for 12-24 h after adding 3 times of anhydrous ethanol, centrifuge at 3500-4500 r / min to obtain a precipitate, remove proteins by using Sevag reagent for 2-3 times, and freeze-dry and sieve the precipitate.

3. The method for preparing a foam stabilizer based on a fractionated modification of Enteromorpha according to claim 1, characterized in that, The step three is specifically as follows: dry the residue at 80 ℃ for 24 h, and then sieve it through a 200-mesh sieve to obtain the foam stabilizer; add 5-10 wt% NaOH to the foam stabilizer according to a solid-liquid ratio of 1:5-1:10, perform ultrasonic pre-dispersion for 15 min, alkalinize at 40-60 ℃ for 1-2 h, add 10-20 wt% chloroacetic acid solution, and perform a reaction at 60-80 ℃ and at pH 8-10 for 2-4 h; adjust the pH to 6-7 by using hydrochloric acid, centrifuge to collect the solid, wash until no chlorine is present, vacuum-dry the solid at 60 ℃, and then sieve the solid, to obtain the chelated foam stabilizer, wherein the solid is measured in g, and the liquid is measured in mL.

4. The method for preparing a foam stabilizer based on a fractionated modification of Enteromorpha according to claim 3, characterized in that, In the step three, add 8 wt% NaOH to the foam stabilizer, perform ultrasonic dispersion at an ultrasonic power of 300-500 W and a frequency of 20-40 kHz, and alkalinize at 50 ℃ for 1.5 h; after adding 15 wt% chloroacetic acid solution, perform a reaction at 70 ℃ for 3 h.

5. A foam stabilizer based on fractionally modified Enteromorpha, characterized in that, The preparation method is prepared by using any one of the preparation methods in claims 1-4.

6. Use of the hierarchically modified foam stabilizer based on Enteromorpha in accordance with claim 5, characterized in that, A foam flooding system suitable for use in high salinity reservoirs, where by high salinity is meant a salinity of > 20 x 10 4 mg / L.

7. Use of a foam stabilizer based on fractionally modified Enteromorpha according to claim 6, characterized in that The preparation method of the foam oil displacement system is as follows: dissolve the foam stabilizer in water containing a surfactant and having a salinity, stir and foam, the foam stabilizer comprises a foam stabilizer or a chelated foam stabilizer, and the mass ratio of the foam stabilizer or the chelated foam stabilizer in the foam oil displacement system is 2%-10%.

8. Use of a foam stabilizer based on fractionally modified Enteromorpha according to claim 7, characterized in that The foam stabilizer is a chelate foam stabilizer, and the mass ratio of the chelate foam stabilizer in the foam oil displacement system is 10%, which is applied to a reservoir with a temperature of 125-135 ℃ and a salinity of 20×10 4 -25×10 4 mg / L.

9. The use of a foam stabilizer based on a fractionated modification of Enteromorpha according to claim 7, characterized in that The foam stabilizer further comprises a polysaccharide thickening agent, and the mass ratio of the polysaccharide thickening agent in the foam oil displacement system is 0.2%-1.0%.

10. Use of the hierarchically modified foam stabilizer based on Enteromorpha in accordance with claim 5, characterized in that, A foam flooding system for preparing a reservoir suitable for a temperature of 75-85℃, a salinity of 3×10 4 -8×10 4 mg / L, the foam stabilizer comprising a chelating foam stabilizer and a polysaccharide thickening agent, the mass ratio of the chelating foam stabilizer in the foam flooding system being 10%, and the mass ratio of the polysaccharide thickening agent in the foam flooding system being 0.6%.

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