Salt-tolerant zwitterionic lignin surfactant as well as preparation method and application thereof

Abstract

The invention discloses a salt-tolerant zwitterionic lignin surfactant as well as a preparation method and application thereof. The structural formula of the surfactant is as follows: # imgabs0 #, wherein n is 4, and m is 10. The lignin ampholytic surfactant disclosed by the invention can adapt to high-salinity oil reservoirs, has a good viscosity reduction effect on thick oil emulsion, is environment-friendly, has excellent high temperature resistance, salt resistance and acid resistance, and can be widely applied to the field of oil production. The development of the surfactant is of great significance to the efficient development of heavy oil reservoirs and the gathering and transportation of heavy oil in China.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield chemistry, and particularly relates to a salt-tolerant zwitterionic lignin surfactant, a preparation method thereof, and an application thereof. Background Art

[0002] Heavy oil (viscosity > 100 mPa·s), as an important part of global unconventional oil and gas resources, accounts for more than 70% of the proven oil reserves and is an important alternative resource for energy security under the background of the depletion of conventional crude oil. A high salinity heavy oil reservoir refers to a reservoir that simultaneously has high salinity formation water and high viscosity crude oil. High salinity means that the total concentration of salts (such as NaCl, CaCl2, etc.) dissolved in the formation water is extremely high. Usually, the salinity > 100,000 mg / L (some literatures even use > 300,000 mg / L as the standard), resulting in water quality close to brine or salt brine. Heavy oil has a high viscosity (usually viscosity > 100 mPa·s at 50°C), poor fluidity, and is semi-solid or colloidal at room temperature, requiring special production technologies (such as thermal oil recovery). High salinity formation water and heavy oil may form stable oil-in-water (O / W) or water-in-oil (W / O) emulsions, further increasing the flow resistance. Its high density, high viscosity, high content of resins and asphaltenes lead to extremely poor fluidity. Traditional thermal oil recovery (such as steam flooding, SAGD) has high energy consumption and large carbon dioxide emissions. The cold production technology of ordinary heavy oil chemical flooding has become a research hotspot for the efficient development of heavy oil due to its controllable cost and wide environmental adaptability. However, conventional chemical flooding agents (such as alkylbenzene sulfonates) are prone to inactivation and precipitation in high-temperature and high-salt reservoirs; and with the increasingly strict environmental regulations, traditional flooding agents have limitations in biological toxicity. There is an urgent need to develop a new type of surfactant for oil displacement that combines high efficiency in viscosity reduction, salt resistance, and environmental friendliness.

[0003] Surfactants adsorb on the oil-water interface to form an ordered hydrophilic group-hydrophobic group arrangement structure, reducing the interfacial tension, thereby realizing the transformation of the heavy oil emulsion from W / O to O / W, effectively reducing the system viscosity, significantly improving the recovery rate, and reducing the energy consumption during the gathering and transportation process. Currently, the commonly used surfactants mainly include anionic, cationic, non-ionic, zwitterionic surfactants, and their blends.

[0004] Chinese Patent (CN202210849176) discloses an application of a boron-containing anionic-nonionic surfactant (SYW) in heavy oil emulsification and viscosity reduction. Chinese Patent (CN201610566053) discloses a lignosulfonate-based zwitterionic surfactant using lignin as a raw material, which is suitable for tertiary oil recovery in oilfields, especially as an alkali-free oil displacement agent. Chinese Patent (CN00131002) discloses a preparation method of a lignin surfactant suitable for composite oil displacement, which modifies lignin by electrooxidation, alkylation, and sulfonation and is used in tertiary oil recovery technology.

[0005] Although the above surfactants have certain emulsifying effects, they generally have some common defects: such as being prone to failure in oil reservoirs with high salinity (>100,000 mg / L); the difficult-to-degrade components in surfactants leading to ecological risks, etc. In short, the demulsifying and viscosity-reducing agents mentioned in the prior art do not well balance environmental protection and adaptability to high-salinity oil reservoirs. Summary of the Invention

[0006] The object of the present invention is to provide a salt-tolerant zwitterionic lignin surfactant and its preparation method and application, so as to solve the problem that the demulsifying and viscosity-reducing agents in the prior art cannot simultaneously balance the adaptability to high-salinity oil reservoirs and environmental friendliness.

[0007] To solve the above problems, the present invention adopts the following technical solutions:

[0008] According to the first aspect of the present invention, there is provided a salt-tolerant zwitterionic lignin surfactant for emulsifying and reducing the viscosity of heavy oil, and its structural formula is as follows:

[0009] Wherein, n is 4 and m is 10.

[0010] The present invention systematically characterized the molecular structure of the surfactant through elemental analysis and GPC. The experimental data show that when the grafting number n = 4 and the grafting chain segment length m = 10, the optimal emulsifying and viscosity-reducing effects can be achieved. Those skilled in the art should understand that different synthesis conditions (such as monomer ratio, reaction temperature, initiator concentration, etc.) may lead to different grafting numbers n and m, and the above values of n and m are the most preferred implementation modes optimized by the present invention through response surface analysis.

[0011] According to the lignin zwitterionic surfactant provided by the present invention (i.e., DMS surfactant), it not only has excellent salt tolerance and pH adaptability, but also has excellent emulsifying and viscosity-reducing properties. Moreover, the lignin surfactant is non-toxic and non-corrosive, and has good surface activity. The lignin polycyclic aromatic structure is similar to the asphaltene structure. This structural similarity can enhance the intermolecular force and effectively destroy the supramolecular interaction of heavy components. Grafting functional groups through a rigid skeleton can not only improve the molecular structure strength, but also prevent the aggregation of surfactant molecules under high-salt conditions.

[0012] According to the second aspect of the present invention, there is provided a preparation method of a salt-tolerant zwitterionic lignin surfactant for emulsifying and reducing the viscosity of heavy oil. Under alkaline conditions, MAL is mixed with aqueous solutions of SBMA and DMAPMA in a certain ratio, and under the action of an initiator, a salt-tolerant zwitterionic lignin surfactant DMS is polymerized; wherein, the synthesis molar ratio of MAL:SBMA:DMAPMA is 1:3.9:5.8.

[0013] In the present invention, lignin and maleic anhydride (mass ratio 1:5) are esterified without solvent to obtain an intermediate product, maleic acid esterified lignin (MAL). Then, using MAL, N,N-dimethylaminopropyl methacrylamide (DMAPMA), and 3-((2-(methacryloyloxy)ethyl)dimethylammonio)propane-1-sulfonate (SBMA) as raw materials, a DMS surfactant is synthesized through a polymerization reaction.

[0014] In the present invention, through a series of experiments, different molar ratios of DMAPMA and SBMA, as well as different concentrations of initiators, were studied. During the experimental process, the dosage of MAL was fixed at 1 mol, the molar amount of DMAPMA was changed within the range of 4.2–12.5 mol, the molar amount of SBMA was within the range of 2.56 - 8.33 mol, and the surfactant synthesized within the range of initiator concentration of 1 wt% - 2 wt% had the best effect. Based on this range, response surface curve analysis was carried out to obtain the optimal synthesis scheme.

[0015] Most preferably, the synthesis molar ratio of DMS is MAL:SBMA:DMAPMA = 1:3.9:5.8, and the optimal dosage of the initiator is 1.49 wt%.

[0016] According to the third aspect of the present invention, there is provided an application of the salt-tolerant zwitterionic lignin surfactant as described above in the emulsification and viscosity reduction of heavy oil.

[0017] The application includes: dissolving the salt-tolerant zwitterionic lignin surfactant in water to form an emulsion aqueous phase, mixing the heavy oil and the emulsion aqueous phase to obtain a heavy oil emulsion, and emulsifying to form an oil-in-water (O / W) emulsion to reduce the viscosity of the heavy oil.

[0018] Preferably, the concentration of the lignin-based zwitterionic surfactant DMS in the heavy oil emulsion is between 300 mg / L and 2500 mg / L.

[0019] Preferably, the emulsification temperature is between 40°C and 80°C.

[0020] Preferably, the pH value of the emulsion is between 5 and 9.

[0021] Preferably, the salinity is between 2004 mg / L and 200460 mg / L.

[0022] Preferably, the water content of the heavy oil emulsion is between 20% and 70%.

[0023] Preferably, the viscosity of the heavy oil is between 200 and 30000 mPa·s. In a preferred embodiment, the viscosity of the heavy oil is between 200 and 30000 mPa·s.

[0024] Through innovative molecular structures, the present invention proposes a salt-tolerant zwitterionic lignin surfactant to break through the performance boundaries of existing de-emulsifying and viscosity-reducing agents that cannot simultaneously balance the adaptability to high salinity reservoirs and environmental friendliness. The salt-tolerant zwitterionic lignin surfactant provided by the present invention has a good viscosity reduction rate. For example, for the Xinjiang heavy oil emulsion with a water cut of 40%, at 50 °C and an addition amount of 1000 mg / L, the viscosity reduction rate can reach 91.6%, and the de-emulsifying and viscosity-reducing effect is excellent. The salt-tolerant zwitterionic lignin surfactant provided by the present invention also has excellent salt tolerance and acid resistance. In the stability comparison test carried out under the simulated salinity gradient (Na + : 5,000 - 300,000 mg / L; Ca 2+ : 250 - 4,000 mg / L), it shows that the DMS surfactant prepared according to the present invention can maintain colloid stability under all test conditions. For the Xinjiang heavy oil emulsion with a water cut of 40%, the de-emulsifying and viscosity reduction rate exceeds 88% within the pH range of (5–9). Even under the high salinity condition of 200460 mg / L, the viscosity reduction rate still reaches 84.8%.

[0025] In summary, the salt-tolerant zwitterionic lignin surfactant provided by the present invention can adapt to high-salt and high-salinity reservoirs, has a good viscosity reduction effect on heavy oil emulsions, is environmentally friendly, and also has excellent high-temperature, salt, and acid resistance. The development of this surfactant is of great significance for the efficient development of heavy oil reservoirs and heavy oil gathering and transportation in China. Description of the Drawings <>

[0026] <> Figure 1 is the FT-IR spectrum of the DMS surfactant; <>

[0027] <> Figure 2 is the 1 H NMR spectrum of the DMS surfactant; <>

[0028] <> Figure 3 is the surface tension curve of the DMS surfactant; <>

[0029] <> Figure 4 is the comparison chart of the salt tolerance performance between DMS and SDBS. Detailed Embodiments

[0030] The following further illustrates the present invention in combination with specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional operations in the art or the experimental methods recommended by the kit and instrument manufacturers. The reagents and materials used in the embodiments can be obtained from commercial sources unless otherwise specified.

[0031] The experimental reagents used in the following examples are shown in Table 1 below.

[0032] Table 1 Experimental Reagents [[ID=⑤]] [[ID=⑥]] [[ID=⑦]] [[ID=⑧]]

[0033] [[ID=⑨]]The experimental instruments used in the following examples are shown in Table 2 below. [[ID=⑩]] [[ID=⑪]]

[0034] [[ID=⑫]]Table 2 Experimental Instruments [[ID=⑬]] [[ID=⑭]] [[ID=⑮]] [[ID=⑯]]

[0035] [[ID=⑰]]Natural alkali lignin contains impurities such as ash and polysaccharides, and has a broad molecular weight distribution. Direct reaction will lead to uncontrollable product structure. It is preferably refined by hot water dissolution and acid precipitation (pH = 2): low molecular weight components are preferentially dissolved in 60 °C hot water, and acidic precipitation captures high molecular weight lignin, while removing ash impurities synchronously. This step ensures that the raw materials for subsequent reactions have a uniform density of active hydroxyl groups and avoids the consumption of reaction reagents by impurities. [[ID=⑱]] [[ID=⑲]]

[0036] [[ID=⑳]]Under solvent-free conditions, lignin and maleic anhydride are mixed and heated to achieve an esterification reaction. This process does not use organic solvents, is green and efficient, and lays a foundation for the subsequent synthesis of surfactants by introducing double bonds into the lignin skeleton. The process is represented by Reaction Equation 1. [[ID=㉑]] [[ID=㉒]]

[0037] [[ID=㉓]]Under alkaline conditions (pH = 9), the MAL intermediate is mixed with aqueous solutions of SBMA and DMAPMA in a certain proportion, and polymerized under the action of initiator potassium persulfate or ammonium persulfate to obtain lignin amphoteric surfactant DMS. The process is represented by Reaction Equation 2. [[ID=㉔]] [[ID=㉕]]

[0038] [[ID=㉖]]The reaction equation of the preparation method according to the present invention is as follows: [[ID=㉗]] [[ID=㉘]] [[ID=㉙]] [[ID=㉚]]

[0039] [[ID=㉛]]Synthesis of DMS Surfactant [[ID=㉜]] [[ID=㉝]]

[0040] [[ID=㉞]]According to the preparation method of the present invention, alkali lignin (ALignin) is dispersed in ultrapure water at a solid-liquid ratio of 1:10 (g / mL), magnetically stirred at 60 °C for 2 h, and then centrifuged (2000 rpm, 60 min). The supernatant is collected, the pH is adjusted to 2.0 with 1M HCl, allowed to stand for 24 h, and then centrifuged to separate the precipitate. The precipitate is washed with ultrapure water until the filtrate is neutral, and finally dried in a forced-air oven at 100 °C for 24 h, ground through a 100-mesh sieve and reserved. Purified lignin is obtained. [[ID=㉟]] [[ID=㊱]]

[0041] Weigh 10 g of purified Alignin and add it to molten maleic anhydride (50 g, 70 °C). React under magnetic stirring at 120 °C for 4 h. After the reaction is completed, cool to 60 °C, add 200 mL of absolute ethanol to precipitate the product, stir magnetically for 2 h, and then centrifuge to collect the precipitate. Wash the precipitate successively three times with a mixture of ethanol:water (3:1, v / v), and dry at 60 °C for 24 h to obtain MAL, which is stored in a desiccator.

[0042] Disperse 10 g of MAL in 70 ml of ultrapure water, and adjust the pH to 9 with 1 M NaOH. Prepare 20 wt% aqueous solutions of SBMA and DMAPMA respectively, as well as a 10 wt% potassium persulfate initiator solution. Add the MAL solution, monomer mixture (MAL:SBMA:DMAPMA = 1:3.9:5.8, mol / mol), and initiator (1.49% of the total mass of the monomers) successively into a four-necked flask equipped with a stirrer, N2 protection, and a thermometer, and react at a constant temperature of 65 °C for 10 h. The reaction solution is further purified and refined by thin-film osmosis (using a dialysis bag with a molecular weight cut-off of 1000 Da (MWCO, N-buliv)), and a brown solid is obtained after drying.

[0043] Preparation of heavy oil emulsion

[0044] According to the analysis data of formation water in the oilfield field (Table 3 below), prepare simulated formation water by yourself, and its salinity reaches 10023 mg·L, which is a high-salinity calcium chloride-type water.

[0045] Table 3 Analysis data of oilfield formation water

[0046] Weigh a certain mass of DMS surfactant and dissolve it in the simulated formation water. Stir well with a glass rod and then let it stand. The solution is clear and transparent, which is the aqueous phase of the emulsion.

[0047] The oil sample is from Xinjiang Oilfield. The density of the oil sample at 20 °C is 960.1 kg·m -3 , and the viscosity at 50 °C is 1850 mPa·s. It can be seen that the experimental oil is a common heavy oil.

[0048] Place the heavy oil and the aqueous phase in a constant temperature water bath at 70 °C (emulsification temperature) and preheat for 30 min. Then pour the heavy oil into the aqueous phase according to different volume ratios, and stir with a homogenizer at a speed of 5000 r / min for 10 min to obtain a heavy oil emulsion.

[0049] Pour the prepared heavy oil emulsion into a test measuring cup. Use an NDJ-8ST viscometer to measure the viscosity of the heavy oil emulsion at the set temperature, and the viscosity reduction rate is calculated as shown in Equation (1).

[0050] In the formula, f is the viscosity reduction rate (%), μ0 is the viscosity of the heavy oil (mPa·s), and μ is the viscosity of the heavy oil emulsion (mPa·s).

[0051] Determination Method for Stability of Heavy Oil Emulsion

[0052] The "bottle test method" is used to measure the stability of the heavy oil emulsion. The prepared oil-water emulsion is poured into a graduated glass test tube at 50°C, kept at a constant temperature and left standing. The volume of the separated water is recorded at regular intervals, and the standing sedimentation time is 3 h. The water separation rate is used to represent the stability. The larger the water separation rate, the worse the stability of the emulsion. The calculation formula for the water separation rate is shown in Equation (2). In the formula is the dehydration rate (%), V t is the volume of the separated water (ml), and V0 is the volume of water in the emulsion (ml).

[0053] Optimization of Synthesis Ratio of DMS Surfactant

[0054] The inventor found that the raw material ratio and the dosage of the initiator have a great influence on the performance of the synthesized amphoteric surfactant. Therefore, factor analysis was carried out on the raw material ratio and the dosage of the initiator.

[0055] Table 4 Factors and Levels of Box-Behnken Test for Optimizing the Synthesis Ratio of DMS Surfactant

[0056] The experimental results and analysis are shown in Table 5 below.

[0057] Table 5 Experimental Results of Box-Behnken for Optimizing the Synthesis Conditions of DMS Surfactant

[0058] In the experimental study, according to the process variables of the design matrix, a second-order polynomial model equation was obtained, and the response of each factor at a given level was predicted according to the equation. The level of each factor was specified in the original unit. Based on the DesignExpert.V8.0.6.1r data analysis software, the response of the viscosity reduction rate f was predicted according to the experimental data, and Equation 3 of the quadratic polynomial equation was obtained:[[]]

[0059] Y = 68.52 + 81.71*X1 + 121.12*X2 + 4.96*X3 - 13.07*X1X2 - 11.17*X1X3 - 5.93*X2X3 - 198.27*X1 2 - 247.33*X2 2 - 1.13*X3 2 (Equation 3)

[0060] Wherein, Y is the predicted response (viscosity reduction rate f), X1 is the molar ratio of MAL / DMAPMA, X2 is the molar ratio of MAL / SBMA, and X3 is the dosage of initiator.

[0061] In the analysis of the results of variance analysis, the p-value is 0.0029, which is less than 0.05, indicating that the model terms are significant. The lack-of-fit term is 0.0573 > 0.05, which is not significant, indicating that the model can fully explain the data.

[0062] Stepwise regression was performed on the obtained regression equation, and the shape of the three-dimensional response surface diagram was examined. The optimized synthesis ratio parameters were obtained: X1 was 0.174, X2 was 0.256, and X3 was 1.49. That is, the synthesis molar ratio of MAL:SBMA:DMAPMA was 1:3.9:5.8, and the initiator dosage was 1.49 wt%. Under these conditions, the predicted value of the emulsifying viscosity reduction rate of the synthesized surfactant was 90.7%. According to these optimized conditions, we carried out three batches of parallel experiments to synthesize the DMS surfactant and conducted the heavy oil emulsifying viscosity reduction experiment on it (the results are shown in Table 6 below). The average viscosity reduction rate was 91.6%, which was relatively consistent with the model predicted value of 90.7%, verifying the reliability of the design model.

[0063] Table 6 Results of repeated parallel experiments

[0064] Elemental Analysis of DMS Surfactant

[0065] The contents of C, H, N, S, and O elements in the DMS surfactant were detected using an elemental analyzer (UNICUBE, elemental, Germany). The O content was determined using the O mode to obtain the basic element composition of C, H, O, N, and S in the DMS surfactant and the percentage of each element. The test results are shown in Table 7 below.

[0066] Table 7 Element types and contents of the DMS surfactant

[0067] Gel Permeation Chromatography (GPC) Analysis of DMS Surfactant

[0068] The average molecular weight and distribution of DMS were determined by gel chromatography (Agilent 1260, Waters, USA). The mobile phase solvent was the aqueous phase; the injection volume was 100.0 μL, and the flow rate was 1.00 mL / min. The gel permeation chromatography analysis of DMS and MAL surfactant is shown in Table 8 below. The number average molecular weight Mn of the MAL surfactant was 1031; the number average molecular weight Mn of the DMS surfactant was 3643. The contents of S and N elements in the reaction product were obtained by elemental analysis. The S content in DMS was 3.10 wt%, which was completely derived from the SBMA monomer. The N content was 9.17 wt%, and nitrogen was contained in both DMAPMA and SBMA. The grafting number of SBMA could be calculated from the S content. After subtracting the nitrogen content of SBMA, the remaining N content could be used to calculate the grafting number of DMAPMA. Combining the monomer molecular weights (SBMA = 279.35 g·mol -1 , DMAPMA = 170.25 g·mol -1 ) and the S and N contents from elemental analysis, the theoretical grafting numbers were calculated as follows: the grafting number of SBMA n = 3.5, and the grafting number of DMAPMA m = 10.2. The theoretical molecular weight increment calculated from elemental analysis was 2714 g·mol -1 , which was close to the experimentally measured increment of 2612 g·mol -1 by GPC.

[0069] Table 8 Molecular Weight and Polydispersity Index of DMS Surfactant

[0070] Fourier Transform Infrared Spectroscopy of DMS Surfactant

[0071] Fourier Transform Infrared Spectroscopy (FT-IR) Analysis of DMS Surfactant To further study the structure of the synthesized DMS surfactant, the DMS surfactant was subjected to FT-IR analysis using a Nicolet iN10 infrared spectrometer produced by Thermo Company of the United States. The experimental samples were processed by the KBr pellet method, and the test wavelength range was 400 - 4000 cm -1 . The FT-IR spectrum of DMS is shown as Figure 1 .

[0072] The Fourier transform infrared spectrum of the product DMS showed characteristic bands: the broad peak at 3446 cm -1 corresponded to the stretching vibration of phenolic -OH, while the C-H stretching modes at 2923 / 2850 cm -1 corresponded to -CH3 and -CH2 groups. After maleic anhydride modification, the MAL spectrum showed an obvious stretching vibration of ester carbonyl (C=O) at 1727 cm -1 , confirming the success of esterification. Representing 1658 cm -1(Amide I band, C=O) and 1570 cm -1 (C-N) vibration peaks confirm the introduction of DMAPMA. While 1176 cm -1 (O=S=O asymmetric stretching) and 1030 cm -1 (S-O symmetric stretching) characterize the successful grafting of SBMA.

[0073] Nuclear Magnetic Resonance Spectroscopy Analysis of DMS Surfactant

[0074] To further determine the structure of the DMS surfactant, Bruker Ascend 600 superconducting nuclear magnetic resonance spectrometer produced by Bruker Company of Germany was used to perform 1 1H NMR on DMS, and the sample solvent was D2O. 1 The 1H NMR results are as Figure 2 shown.

[0075] Figure 2 The characteristic signals in the DMS spectrum in [reference] include δ 2 ppm (b) representing the alcoholic hydroxyl group on lignin, δ 3.61 ppm (b) representing the methoxy group (-O-CH3) on lignin, and δ 4.1 ppm (f) representing the methylene group adjacent to the ester group (-CH2-O-). Meanwhile, δ 4.48 ppm (p) is for COOCH3, and δ 3.12 ppm (k) belongs to the -N + (CH3)2 group, and δ 3.45 ppm (j) and δ 3.37 ppm (j) correspond to the -CH2- near the quaternary ammonium functional group. The above characteristic peaks all come from SBMA. In addition, δ 2.1 ppm (d) corresponds to the dimethylamino group, and δ 3.2 ppm (r) corresponds to the -CH2- near the amide. The above characteristic peaks all come from DMAPMA. The remaining δ 1.52 ppm (l) is the middle -CH2- molecule in the grafted monomer; while δ 2.9 ppm (i) represents the -CH2- group near the sulfonate and dimethylamino functional groups. The characteristic signal of the double bond peak disappears after polymerization, indicating that the reaction is complete.

[0076] Surface Tension Analysis of DMS Surfactant

[0077] A series of surfactant solutions with different concentrations were prepared with ultrapure water. Using a JK99B (Shanghai Zhongchen Digital Technology Equipment Co., Ltd.) surface tension meter, a series of surface tension measurements were carried out at 25 °C by the ring method. To enable the solution to reach adsorption equilibrium at the air / water interface, the solution was left standing in a series of measurement cells at 25 °C for 30 minutes. The results are as Figure 3 shown.

[0078] The surface tension method was used to measure DMS at 25 °C. Figure 3Surface tension curve of DMS surfactant. As the concentration increases, the surface tension of DMS surfactant shows two stages: the initial linear decline stage (dominated by single-molecule interfacial adsorption) and the plateau stage (dominated by micelle formation). The critical micelle concentration CMC of DMS is determined to be 5.3×10 -4 mol·L -1 .

[0079] Salt Tolerance Performance Analysis of DMS Surfactant

[0080] The salt tolerance of surfactants is evaluated by measuring the solubility of DMS in different salt solutions containing Na + or Ca 2+ at 25°C. First, prepare 2.00 g / L DMS and DMS with ultrapure water. Then, prepare a series of NaCl and CaCl2 solutions with different concentrations. Next, take the same volume of surfactant solution and salt solution to prepare a 1.00 g / L surfactant salt solution. The solution is ultrasonically treated for one hour at 25°C to dissolve completely. The salt tolerance of the surfactant will be determined according to the salt concentration when precipitation is first observed. The results are shown in Table 9, Table 10 and Figure 4 as shown.

[0081] The salt tolerance of surfactants determines their viability in high-salinity reservoirs. Stability comparison tests conducted under simulated salinity gradients (Na + : 5,000 - 300,000 mg / L; Ca 2+ : 250 - 4,000 mg / L) show that DMS can maintain colloid stability under all test conditions, while SDBS will precipitate when Na + ≥20,000 mg / L and Ca 2+ ≥250 mg / L.

[0082] Table 9 Effect of Na + concentration on the solubility of DMS surfactant

[0083] Note: -: The solution is clear and transparent without forming a new phase; +: A new phase is formed in the solution.

[0084] Table 10 Effect of Ca 2+ concentration on the solubility of DMS surfactant

[0085] Note: -: The solution is clear and transparent without forming a new phase; +: A new phase is formed in the solution.

[0086] In summary, the structural formula of the target product DMS surfactant obtained is:

[0087] Example 1: Influence of Different Surfactants on Viscosity Reduction Rate of Emulsified Heavy Oil

[0088] Emulsification viscosity reduction means that under the action of a suitable surfactant, crude oil becomes the dispersed phase and water becomes the continuous phase, that is, a W / O emulsion is formed. The formation of the O / W oil-water emulsion significantly reduces its viscosity. Therefore, determining a suitable emulsifier is the key technology for emulsification viscosity reduction of heavy oil. The viscosity of Xinjiang heavy oil at 50 °C is 1850 Pa·s. Experiments were carried out under the conditions of an oil-water volume ratio of 6:4, a surfactant concentration of 1000 mg / L, and an emulsification temperature of 50 °C. The lignin surfactant synthesized above and its raw materials SDBS, DMAPMA, and MAL were used as emulsification viscosity reducers for research.

[0089] Different surfactants have different emulsification effects on heavy oil. The viscosity reduction rate of SDBS is 22.3%, that of ALignin is 8.1%, that of MAL is 10.8%, the viscosity reduction rates of DMAPMA and SBMA are 5.4% and 24.5% respectively, and the viscosity reduction rate of the synthesized DMS is 91.6%.

[0090] The corresponding data of the emulsification viscosity reduction effect are shown in Table 11 below.

[0091] Table 11 Emulsification viscosity reduction effect of surfactants

[0092] Example 2: Influence of Different Concentrations of Surfactants on Viscosity Reduction Rate of Emulsified Heavy Oil

[0093] The typical anionic surfactant sodium dodecylbenzene sulfonate SDBS was introduced as a control. The viscosity reduction effects of SDBS and DMS at different concentrations. As the concentration increases, the viscosities of both emulsions decrease to a certain extent. When the DMS concentration reaches 1000 mg / L, the viscosity of the emulsion decreases significantly, and the viscosity reduction rate reaches 91.6% at this time. This is because the lignin in DMS has a similar structure to asphaltene. The aromatic ring structure of lignin replaces some asphaltene and resin in heavy oil, reducing the accumulation. The hydrophilic groups are inserted into the water, making the heavy oil emulsion change from W / O to O / W, thus reducing the viscosity of the oil-water emulsion. While SDBS is an anionic surfactant, since the ions in high salinity water will destroy the double-layer electron structure of its oil-water interface film and the surface activity weakens, it does not show a good viscosity reduction effect within a certain concentration range at this salinity. The corresponding data of the viscosity reduction effect are shown in Table 12 and Table 13 below.

[0094] Table 12 Emulsification viscosity reduction effect of DMS surfactant

[0095] Table 13 Emulsification viscosity reduction effect of SDBS surfactant

[0096] Example 3: Influence of Temperature on Viscosity Reduction Rate of Heavy Oil Emulsion

[0097] Investigate the effect of DMS surfactant on the viscosity reduction of heavy oil emulsion at different emulsification temperatures. Limited by experimental conditions, the investigated temperature range is 40°C to 80°C. The emulsification viscosity reduction experiment was carried out under the conditions of an oil-water volume ratio of 6:4 and a DMS surfactant concentration of 1000 mg / L.

[0098] Viscosity is an important parameter characterizing the physical properties of oil products, especially important for heavy oil. A viscometer was used to measure the viscosity of Xinjiang heavy oil at different temperatures (see Table 14 below).

[0099] Table 14 Viscosity of heavy oil at different temperatures

[0100] Investigate the viscosity and viscosity reduction rate of heavy oil emulsion with 1000 mg / L DMS surfactant at different temperature values. The experimental data are shown in Table 15 below.

[0101] Table 15 Effect of emulsification temperature on the viscosity reduction rate of heavy oil emulsion

[0102] Example 4: Influence of Different pH Values on Emulsification of Heavy Oil

[0103] Investigate the viscosity and viscosity reduction rate of heavy oil emulsion with 1000 mg / L DMS surfactant at different pH values. The experimental data are shown in Table 16 below.

[0104] Table 16 Effect of pH on the emulsification viscosity reduction effect of surfactant

[0105] Example 5: Influence of Different Salinities on Heavy Oil Emulsion

[0106] Investigate the effect of 1000 mg / L DMS surfactant on the viscosity reduction rate of heavy oil at different salinities (the salinity concentration is 0.2 times to 20 times the original formation water salinity). With the increase of salinity, the viscosity of the heavy oil emulsion containing DMS surfactant increases to a certain extent, and the viscosity reduction rate decreases to a certain extent. However, at high salinities of 50,000 - 200,000, the viscosity reduction rate of DMS surfactant can still be maintained above 84.8%. It shows that DMS has excellent salt tolerance and can adapt to most reservoirs with extreme salinities. The experimental data are shown in Table 17 below.

[0107] Table 17 Effect of salinity on the emulsification viscosity reduction effect of surfactant

[0108] Example 6: Influence of Different Oil-Water Ratios on Viscosity Reduction Effect of Heavy Oil Emulsion

[0109] Investigate the viscosity and viscosity reduction rate of DMS surfactant at a concentration of 1000 mg / L under different water contents. As the water content increases, the viscosity of the Xinjiang heavy oil emulsion without surfactant reaches its peak at a water content of 40% - 50%; below this value, the natural W / O emulsifier in the heavy oil promotes the formation of O / W, increasing the viscosity, and above this value, the viscosity of the emulsion decreases with the increase in water content. It is observed that when the water content is greater than 30%, the viscosity reduction rate of the emulsion containing DMS increases significantly and levels off at 40%, and at this time the viscosity reduction rate has reached 91.6%. This shows that adding DMS can convert the W / O emulsion into an O / W emulsion at a lower water content, reducing the viscosity of the heavy oil emulsion from 1850 mPa·s to about 150 mPa·s. The experimental data are shown in Table 18 below.

[0110] Table 18 Influence of different oil-water ratios on the viscosity reduction rate of heavy oil emulsion

[0111] Example 7: Influence of Different Oil-Water Ratios on Water Separation Rate of Heavy Oil Emulsion

[0112] Investigate the influence of different oil-water ratios on the water separation rate of heavy oil emulsion. As the oil-water ratio increases, the water separation rate gradually decreases. When the water content is below 30%, more water in the emulsion is the internal phase and more oil is the external phase, and a certain degree of phase inversion will occur, making it difficult for water to separate through the oil phase, that is, the water separation rate is low. The static stability of the emulsion gradually increases. When the water content is higher than 30%, since the water phase gradually increases, a large amount of water accumulates and settles under the condition of gravity, and the influence of time on the water separation rate of the emulsion increases significantly. The emulsion containing DMS surfactant forms a stable O / W solution at a water content of 40% and can achieve a water separation rate of 65% within 3 h, which is beneficial for demulsification in the later stage. It is very beneficial for the chemical flooding of heavy oil. The experimental data are shown in Table 19 below.

[0113] Table 19 Water separation effect of heavy oil emulsion with surfactant

[0114] In summary, through esterification and free radical graft copolymerization reactions, an environmentally friendly lignin zwitterionic surfactant (DMS) was prepared using renewable alkali lignin as the raw material. Through 1H nuclear magnetic resonance ( 11H NMR) and infrared (FTIR) were used to verify the chemical structure of the DMS surfactant. Under the simulated heavy oil production conditions (50 °C, oil-water ratio of 6:4, surfactant concentration of 1000 mg / L), the viscosity reduction rate of DMS reached 91.6%. Even under the high salinity condition of 200460 mg / L, the viscosity reduction rate still reached 84.8%, meeting the actual requirements for heavy oil production under high salinity. In addition, the emulsifying viscosity reduction rate of DMS exceeded 88% within the pH range of (5–9), showing excellent acid-base adaptability. Under the experimental conditions, the addition of DMS converted the heavy oil emulsion from W / O to O / W, with excellent emulsifying viscosity reduction effect.

[0115] The above are only the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various changes can be made to the above embodiments of the present invention. That is, all simple, equivalent changes and modifications made according to the claims and the content of the specification of the present invention application fall within the scope of protection of the claims of the present invention patent. Those not described in detail in the present invention are all conventional technical contents.

Claims

1. A salt-tolerant zwitterionic lignin surfactant for viscosity reduction of heavy oil emulsification, characterized in that, Its structural formula is as follows: Where n is 4 and m is 10.

2. A preparation method of a salt-tolerant zwitterionic lignin surfactant for heavy oil emulsification and viscosity reduction according to claim 1, characterized in that, Under alkaline conditions, MAL is mixed with aqueous solutions of SBMA and DMAPMA in a certain ratio, and under the action of an initiator, the salt-tolerant zwitterionic lignin surfactant DMS is polymerized; among them, the synthetic molar ratio of MAL:SBMA:DMAPMA is 1:3.9:5.

8.

3. Application of the salt-tolerant zwitterionic lignin surfactant according to claim 1 in emulsifying and reducing the viscosity of heavy oil.

4. The application according to claim 1, characterized in that The said application includes: dissolving the salt-tolerant zwitterionic lignin surfactant in water to form an emulsion aqueous phase, mixing the heavy oil and the emulsion aqueous phase to obtain a heavy oil emulsion, and emulsifying to form an oil-in-water emulsion to reduce the viscosity of the heavy oil.

5. The application according to claim 4, wherein The concentration of the salt-tolerant zwitterionic lignin surfactant in the heavy oil emulsion is between 300 mg / L and 2500 mg / L.

6. The application according to claim 4, wherein The emulsification temperature is between 40 °C and 80 °C.

7. The application according to claim 4, characterized in that The pH range is between 5 and 9.

8. The application according to claim 4, characterized in that The water content of the heavy oil emulsion is between 20% and 70%.

9. The application according to claim 4, characterized in that The salinity of the heavy oil is between 2004 mg / L and 200460 mg / L.

10. The application according to claim 4, characterized in that, The viscosity of the heavy oil is between 200 and 30000 mPa·s.

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