Preparation method of novel viscosity reducer for CO2 displacement or huff and puff

Abstract

The invention discloses a preparation method of a novel viscosity reducer for CO2 displacement or huff and puff, which comprises the following steps: dispersing acidolysis waxy corn starch in a mixed solution of dimethylformamide and pyridine, activating for 1 hour in a 75 DEG C water bath and under stirring conditions, adding a certain amount of benzene sulfonyl chloride, reacting for 2 hours, reducing the temperature to 40 DEG C, continuously adding long-chain alkyl acyl chloride, reacting for 2 hours, cooling to 40 DEG C, filtering, washing, and drying to obtain the viscosity reducer for CO2 displacement or huff and puff. Raising the temperature to 75 DEG C, reacting for 2 hours, and precipitating with a large amount of water to obtain modified starch complex ester; and then adding the mixed aromatic hydrocarbon and the small molecular alcohol ether, and stirring and mixing to obtain the viscosity reducer. According to the invention, through the synergistic effect of the agents, the viscosity reduction performance of the product on thick oil is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield chemical reagents, and in particular to a method for preparing a novel viscosity reducer for CO2 displacement or throughput. Background Art

[0002] Heavy oil is an important component of petroleum resources. my country's proven reserves currently account for about 10% of the total, with great development potential. However, this type of oil contains a large amount of macromolecular substances such as colloids, asphaltene, paraffin and organic acids, which show high viscosity and poor fluidity, and there are problems of difficulty in mining. At present, CO2 displacement or huff and puff is one of the effective methods to improve oil recovery. Its advantages are: (1) supercritical CO2 fluid has very low viscosity, strong fluidity, small molecular weight, can enter small pore throats, and has a large impact range; (2) CO2 can be dissolved in crude oil, increase the volume of crude oil, reduce crude oil viscosity, increase the fluidity of residual oil, and improve oil washing efficiency; (3) CO2 can be buried. However, in reality, due to the huge viscosity difference between CO2 and crude oil, gas channeling is prone to occur during gas injection, the oil and gas contact time is short, and it is even possible that the oil will break through early before the light hydrocarbons can be extracted. In addition, since the temperature of most oil reservoirs in my country is higher than 60°C, the solubility of CO2 in crude oil is extremely limited, making it difficult to achieve a satisfactory viscosity reduction effect. Furthermore, it has been gradually discovered that the combined use of chemical agents and CO2 is beneficial to further improve the viscosity reduction efficiency and thus increase the recovery rate. Summary of the invention

[0003] The purpose of the present invention is to address the deficiencies in the above-mentioned background technology and provide a novel method for preparing a viscosity reducer for CO2 displacement or huff and puff for use in heavy oil production.

[0004] To achieve the above-mentioned purpose, the present invention provides a novel viscosity reducer for CO2 displacement or huff and puff and a preparation method thereof, which adopts the following technical scheme: A novel viscosity reducer for CO2 displacement or huff and puff, comprising the following components by weight: 1-20% of modified starch composite ester, 50-90% of mixed aromatic hydrocarbons, and 9-18% of small molecule alcohol ether. The C content in the mixed aromatic hydrocarbons is between 6 and 10.

[0005] A novel method for preparing a viscosity reducer for CO2 displacement or throughput, characterized in that it comprises the following steps: dispersing acid-decomposed waxy corn starch in a mixture of dimethylformamide and pyridine, activating it in a water bath at 75°C for 1 hour, adding a certain amount of benzenesulfonyl chloride, reacting for 2 hours, lowering the temperature to 40°C, continuing to add long-chain alkyl acyl chloride, raising the temperature to 75°C, reacting for 2 hours, and precipitating with a large amount of water to obtain a modified starch composite ester; then adding mixed aromatic hydrocarbons and small molecule alcohol ethers, stirring and mixing to obtain a viscosity reducer. The volume ratio of the mixture of dimethylformamide and pyridine is 2:1. Benzenesulfonyl chloride is an organic compound containing sulfonylbenzene and acyl chloride groups, including one or more of dodecylbenzenesulfonyl chloride, p-toluenesulfonyl chloride, 4-methylbenzenesulfonyl chloride, o-phthaldisulfonyl chloride, and o-fluorobenzenesulfonyl chloride. The length of the C chain in the long-chain alkyl acyl chloride is between 6 and 20.

[0006] Compared with the prior art, the present invention has the following beneficial effects: The present invention effectively improves the viscosity reduction performance of the product on heavy oil through the synergistic effect between the agents. By introducing CO2-philic and lipophilic groups into the starch molecular chain through chemical reaction, and adding a large number of hydrophilic groups contained in the starch itself, the starch can act on water, CO2 and crude oil at the same time, thereby effectively reducing the interfacial tension between the three phases. Dodecylbenzenesulfonyl chloride and lauroyl chloride are selected to hydrophobically modify the starch, and the hydrophilicity and hydrophobicity of the final product are adjusted by changing the dosage of the two, so that the starch can be stabilized at the oil-water interface and exhibit performance similar to that of a surfactant. In order to further improve the viscosity reduction and mixing reduction performance, a mixed aromatic compound is selected as a cosolvent; in order to improve the storage, transportation and construction safety of the product, a small molecule alcohol ether is selected as a cosolvent. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a CO2 dissolving device; Figure 2 Schematic diagram of the structure of modified starch ester and 1 H NMR spectrum; Figure 3 (A) Scanning electron micrograph of modified starch ester, (B) Laser confocal image of emulsion droplets (oil-water volume ratio 1:1), (C) Actual images of emulsions with different oil-water volume ratios (starch ball concentration is 2wt%, oil phase is kerosene), (D) Effect of oil-water volume ratio on the conductivity of emulsions; Figure 4 The viscosity-temperature curve of crude oil before and after adding chemicals; Figure 5 This is the effect of viscosity reducer on the minimum miscibility pressure of CO2 / crude oil. DETAILED DESCRIPTION

[0008] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0009] A novel viscosity reducer for CO2 displacement or huff and puff, comprising the following components by weight: 1-20% of modified starch composite ester, 50-90% of mixed aromatics, and 9-18% of small molecule alcohol ether. The C content in the mixed aromatics is between 6 and 10.

[0010] The preparation method of the novel viscosity reducer for CO2 displacement or huff-and-puff is as follows: dispersing acid-hydrolyzed waxy corn starch in a mixture of dimethylformamide and pyridine, activating it in a water bath at 75°C for 1 hour with stirring, adding a certain amount of benzenesulfonyl chloride, reacting for 2 hours, lowering the temperature to 40°C, continuing to add long-chain alkyl chloride, raising the temperature to 75°C, reacting for 2 hours, and precipitating with a large amount of water to obtain a modified starch composite ester; then adding mixed aromatic hydrocarbons and small molecule alcohol ethers and stirring and mixing to obtain a viscosity reducer. The volume ratio of the mixture of dimethylformamide and pyridine is 2:1.

[0011] Preferably, the mass of the acid-hydrolyzed waxy corn starch is 1 g, the mass of benzenesulfonyl chloride is 3.5 mmol, the mass of the long-chain alkyl acyl chloride is 12 mmol, the mass of water is 500 mL, and the mass of dimethylformamide and pyridine are 20 mL and 10 mL respectively.

[0012] The detection step of the viscosity reducer is to perform performance detection on the viscosity reducer prepared by using modified starch composite ester, mixed aromatic hydrocarbons and small molecule alcohol ether in different mass ratios.

[0013] Table 1 is the viscosity reducer formula. Viscosity reducer Modified starch complex ester Aromatic solvents Small molecule alcohol ether Recipe 1 0 90% 10% Recipe 2 20% 56% 14% Recipe 3 15% 64% 16% Recipe 4 10% 72% 18% Recipe 5 5% 85.5% 9.5% The detection method is as follows: Figure 1 As shown in Figure 1, crude oil without or with different viscosity reducers (Table 1) at a concentration of 1% was placed in a 250 mL three-necked flask, and fully exposed to CO2 for 0.5 h under high mechanical stirring rate and 70 °C water bath conditions. Then it was quickly taken out and the viscosity-temperature curve was tested by rheometer, and the constant shear rate was set to 170 s -1 , the temperature variation range is set between 20-70°C.

[0014] Note: When the test liquid is taken out, it should remain in a fully mixed state and no stratification should occur. If stratification cannot be avoided due to the influence of crude oil properties or the mechanical stirring rate is too slow, the crude oil and water should be filled with CO2 gas for 0.5h in a 70°C water bath and fully mixed with an ultra-high-speed homogenizer before the viscosity-temperature curve test. In addition, since the purpose of this test is only to determine the optimal formula of the viscosity reducer, the test conditions are simplified: (1) provide a certain shear rate; (2) provide a fixed ambient temperature; (3) do not consider the influence of formation pressure; (4) do not consider the influence of viscosity reducer and CO2 plug injection method.

[0015] Test results Characterization of modified starch complex esters Figure 2 The figure shows the chemical structure of modified starch complex ester. 1 H NRM spectrum was used to determine the chemical structure and degree of substitution of modified starch esters. As shown in the figure, the double peaks at 7.0-8.0 ppm are the H peaks on the benzene ring in p-dodecylbenzenesulfonyl chloride. The continuous peaks at 3.0-6.0 ppm are the H peaks on the starch ring. The peaks at 2.0-3.0 ppm correspond to the H peaks of -CH3 and -CH2 on the long chain of p-dodecylbenzenesulfonyl chloride. The peaks at 0.5-2.0 ppm belong to the peaks of -CH3 and -CH2 on the long chain of lauroyl chloride. Finally, we used 1 The substitution degrees of dodecylbenzenesulfonyl chloride and lauroyl chloride were calculated to be 0.46 and 1.64, respectively, from the H NRM spectrum.

[0016] Figure 3 (A) is a scanning electron microscope image of modified starch ester. Since a large number of long-chain groups are grafted onto the modified starch ester, the long chains will fold due to density differences when it sinks in water, forming starch particles. Through statistics and calculations, its average size is about 200nm. In order to understand the mechanism of action of modified starch ester, we grafted fluorescein onto the modified starch ester and tracked the distribution of the modified starch ester in the emulsion through laser confocal microscopy. The results are shown in Figure 2. Figure 3 As shown in (B), most of the modified starch esters are accumulated on the surface of the droplets, playing the role of reducing interfacial tension and stabilizing the emulsion. In order to further explore the type of emulsion formed, we prepared emulsions with a starch ester content of 1wt% with oil-water volume ratios of 3:7, 4:6, 5:5, 6:4, and 7:3 from left to right. Through a simple conductivity test experiment, it was found that when the oil phase volume fraction was 0.3, the conductivity was 6.35S / m, indicating that the emulsion formed was an oil-in-water emulsion, and when the oil phase volume ratio increased to 0.4, the conductivity dropped sharply to 0.1S / m, approaching 0, which means that the emulsion at this time has undergone a phase inversion without changing the wettability of the starch ester and has become an oil-in-water emulsion.

[0017] Best formula like Figure 4 As shown in the figure, through data analysis we can draw the following conclusions: (1) In general, the viscosity reduction effect increases with the decrease of modified starch ester content. This is because the solvent has a smaller molecular weight, stronger diffusivity, and is easier to penetrate into the crude oil to change its fluidity; (2) The formula without modified starch ester shows the worst viscosity reduction effect, which may indicate that there is a synergistic effect between starch ester and solvent; (3) Obviously, formula 4 and formula 5 have the best viscosity reduction effect, and there is no significant difference between the two. However, considering safety issues, formulas with high starch ester content should be selected as much as possible, so the best formula is formula 4, that is, the mass ratio of modified starch ester: aromatic solvent: small molecule alcohol ether solvent is 10:72:18. Its viscosity reduction rate at 20 and 70°C is 48.6% and 53.0%, respectively.

[0018] Effect of viscosity reducer on mixing of CO2 and crude oil Here, the interfacial tension elimination method is used to test the minimum miscible pressure of CO2 and oil samples. Since the interfacial tension is theoretically 0 when the phases are mixed, it cannot be tested. By observing the interface characteristics between oil droplets and carbon dioxide, when the light components in the crude oil evaporate faster, the crude oil is difficult to drop and appears smoke-like. The pressure point at this time is the minimum miscible pressure point. The interfacial tension between CO2 and oil samples at different pressures is tested at 70°C for the oil samples before and after dosing, and the result values ​​are plotted ( Figure 5 D) It can be seen that at a constant temperature, pressure and interfacial tension are linearly correlated. From this, we can deduce that the minimum miscibility pressure of crude oil and crude oil after drug addition is 20.92 and 17.49 MPa respectively, and the mixing reduction rate is 16.4%. This shows that the viscosity reducer has good mixing reduction performance.

[0019] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A novel viscosity reducer for CO2 displacement or huff and puff, characterized by: The invention comprises the following ingredients by weight: 1-20% of modified starch complex ester, 50-90% of mixed aromatic hydrocarbons and 9-18% of small molecule alcohol ether.

2. A novel viscosity reducer for CO2 displacement or huff and puff according to claim 1, characterized in that: The C content in the mixed aromatics is between 6 and 10.

3. A method for preparing a novel viscosity reducer for CO2 displacement or huff and puff, characterized in that: The method comprises the following steps: dispersing acid-hydrolyzed waxy corn starch in a mixed solution of dimethylformamide and pyridine, activating it for 1 hour in a water bath at 75°C with stirring, adding a certain amount of benzenesulfonyl chloride, reacting for 2 hours, lowering the temperature to 40°C, continuously adding long-chain alkyl acyl chloride, raising the temperature to 75°C, reacting for 2 hours, and precipitating it with a large amount of water to obtain a modified starch composite ester; and then adding mixed aromatic hydrocarbons and small molecule alcohol ethers and stirring and mixing to obtain a viscosity reducer.

4. The method for preparing a novel viscosity reducer for CO2 displacement or huff and puff according to claim 3, characterized in that: The volume ratio of the mixed solution of dimethylformamide and pyridine is 2:

1.

5. The method for preparing a novel viscosity reducer for CO2 displacement or huff and puff according to claim 3, characterized in that: The benzenesulfonyl chloride is an organic compound containing sulfonylbenzene and acyl chloride groups.

6. The method for preparing a novel viscosity reducer for CO2 displacement or huff and puff according to claim 5, characterized in that: The benzenesulfonyl chloride is one or more of dodecylbenzenesulfonyl chloride, p-toluenesulfonyl chloride, 4-methylbenzenesulfonyl chloride, o-phthaldisulfonyl chloride and o-fluorobenzenesulfonyl chloride.

7. The method for preparing a novel viscosity reducer for CO2 displacement or huff and puff according to claim 3, characterized in that: The C chain length of the long-chain alkyl acyl chloride is between 6 and 20.

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