Modified polysaccharide, preparation method and application of modified polysaccharide as oil-displacing agent in oil exploitation
Modifying polysaccharides with sodium cyanoborohydride solves the problem of poor stability of traditional polysaccharides in high-temperature and high-salt environments, significantly improves its viscosity and salt resistance, and is suitable for tertiary oil recovery in high-salt formations.
Patent Information
- Application Number
- CN202411222145.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-02
- Publication Date
- 2025-01-21
AI Technical Summary
Traditional polysaccharides have poor stability in extreme underground environments such as high temperature and high salt, resulting in a sharp drop in viscosity and affecting oil displacement efficiency.
The polysaccharide is modified by sodium cyanoborohydride to enhance its viscosity and salt tolerance to form modified galactomannan, modified welan gum or modified arabinogalactan.
The viscosity of the modified polysaccharide has increased by about 200-440%, the salt resistance has been significantly improved, and it can remain stable in high-salt environments, making it suitable for tertiary oil recovery in high-salt formations.
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Figure CN119331116A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of oilfield exploitation, and in particular relates to a modified polysaccharide, a preparation method and an application of the modified polysaccharide as an oil displacement agent in oil exploitation. Background Art
[0002] In the field of oil extraction, especially in enhanced oil recovery (EOR) technology, polysaccharides, as an important class of polymer materials, have shown great potential in the development of oil displacement agents due to their unique rheological properties. However, traditional polysaccharides have poor stability in extreme underground environments such as high temperature and high salt, which can easily lead to a sharp drop in viscosity, thus affecting their oil recovery efficiency.
[0003] In oil recovery applications, the use of modified polysaccharides can improve oil recovery efficiency. The increased viscosity after modification can effectively reduce the relative permeability between oil and water, increase the contact area between crude oil and formation rock, and promote the effective recovery of residual oil in difficult-to-recover oil layers. The thermal stability and salt resistance of modified polysaccharides help maintain reservoir pressure under complex geological conditions, reduce damage to formations, and maintain the long-term production capacity of oil wells. Compared with traditional chemical oil recovery agents, polysaccharide-based biopolymers have better biodegradability and can reduce the potential risk of pollution to groundwater resources and the ecological environment. Therefore, the development of a modified polysaccharide that can maintain or increase viscosity under high temperature and high salt conditions has become one of the key technologies to improve oil recovery efficiency. Summary of the invention
[0004] In view of the problems existing in the above-mentioned prior art, in order to solve the technical defect that the conventional polysaccharide of the present invention has poor stability in extreme underground environments such as high temperature and high salt, which easily leads to a sharp decrease in viscosity, thereby affecting its oil recovery efficiency. The purpose of the present invention is to design and provide a modified polysaccharide, a preparation method and its application as an oil recovery agent in oil production. The polysaccharide modified by sodium cyanoborohydride has a higher viscosity. With the increase of salt concentration (sodium chloride), the viscosity can remain stable and increase to a certain extent, and can be applied to tertiary oil recovery in high-salt formations.
[0005] In order to achieve the above object, the present invention adopts the following technical solutions:
[0006] A modified polysaccharide is obtained by modifying polysaccharide with sodium cyanoborohydride as the main component.
[0007] The modified polysaccharide is a modified galactomannan, a modified welan gum or a modified arabinogalactan;
[0008] The structural formula of the modified galactomannan is as follows (Formula I):
[0009]
[0010] Wherein, n is an integer greater than 50;
[0011] The structural formula of modified Weilan gum is as follows (Formula II):
[0012]
[0013] Wherein, n is an integer greater than 50;
[0014] The structural formula of the modified arabinogalactan is as follows (Formula III):
[0015]
[0016] Wherein, n is an integer greater than 50.
[0017] The method for preparing a modified polysaccharide comprises the following steps:
[0018] (1) dispersing the polysaccharide in water, heating and stirring until completely dissolved, and cooling to room temperature to obtain a polysaccharide aqueous solution;
[0019] (2) Weighing sodium cyanoborohydride, adding it to the above polysaccharide aqueous solution, carrying out a modification reaction, and obtaining a modified polysaccharide solution; performing reduction modification on the polysaccharide to enhance the rheological properties of the polysaccharide.
[0020] (3) The modified polysaccharide solution is cooled to room temperature, ethanol is added, the precipitate is collected after centrifugation, and the modified polysaccharide solid is obtained after drying.
[0021] In the preparation method, the polysaccharide in step (1) is galactomannan, welan gum or arabinogalactan.
[0022] In the preparation method, the mass ratio of the polysaccharide to water in step (1) is 1:80 to 1:100;
[0023] The heating and stirring conditions are: temperature 70-90° C., time 3-5 h.
[0024] In the preparation method, the mass volume ratio of the sodium cyanoborohydride to the modified polysaccharide solution in step (2) is 1g:10mL to 1g:20mL; when the addition amount of the sodium cyanoborohydride is 5% (w / v), the modified polysaccharide has better viscosity increasing and salt resistance effects.
[0025] The conditions of the modification reaction are: temperature 40-50° C., time 3-5 h.
[0026] In the preparation method, the content of ethanol in step (3) is 20% to 50%;
[0027] The centrifugal speed is 7000-8000 rpm, and the centrifugal time is 7-10 min;
[0028] The drying time is 12 to 24 hours.
[0029] In the preparation method, the centrifugation method in step (3) is treatment with a refrigerated centrifuge; and the drying method is freeze-drying.
[0030] The modified polysaccharide, or the modified polysaccharide prepared by any of the methods described above, is used as an oil displacement agent.
[0031] The modified polysaccharide or the modified polysaccharide prepared by any of the methods described above is used in petroleum production.
[0032] Compared with the prior art, the present invention has the following beneficial effects:
[0033] (1) The modified polysaccharide of the present invention has an excellent viscosity-increasing effect. Compared with the original polysaccharide, the viscosity of the modified polysaccharide increases by about 210%. The increased viscosity of the modified polysaccharide can effectively reduce the relative permeability between oil and water, increase the contact area between crude oil and formation rock, and promote the effective recovery of residual oil in difficult-to-recover oil layers.
[0034] (2) The modified polysaccharide of the present invention exhibits good salt resistance and good salt thickening effect. Compared with the original polysaccharide, the modified polysaccharide has an approximately 500% increased tolerance to NaCl at 50,000 mg / L, which indicates that sodium cyanoborohydride modification can significantly improve the salt resistance of the polysaccharide and exhibit an excellent salt thickening effect. The heat resistance and salt resistance of the modified polysaccharide help maintain reservoir pressure under complex geological conditions, reduce damage to the formation, and maintain the long-term production capacity of the oil well.
[0035] (3) Compared with traditional chemical oil displacement agents, polysaccharide-based biopolymers have better biodegradability, reducing the potential pollution risk to groundwater resources and the ecological environment. BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Figure 1 are the structural formulas of galactomannan before and after modification with sodium cyanoborohydride;
[0037] Figure 2 is the structural formula of Welan gum before and after modification with sodium cyanoborohydride;
[0038] Figure 3 are the structural formulas of arabinogalactan before and after modification with sodium cyanoborohydride;
[0039] Figure 4The shear rate-viscosity curves of 0.5% (w / v) galactomannan solution and modified galactomannan solution at 25°C;
[0040] Figure 5 The 0.5% (w / v) galactomannan solution before and after modification in Example 1 was subjected to a shear rate of 7.34 s -1 , 50000mg / LNaCl concentration-viscosity bar graph at 85°C;
[0041] Figure 6 The 1% (w / v) Weilan gum solution before and after modification in Example 2 at a shear rate of 7.34s -1 , 50000mg / LNaCl concentration-viscosity bar graph at 85°C;
[0042] Figure 7 The 1% (w / v) arabinogalactan solution before and after modification in Example 3 at a shear rate of 7.34 s -1 , 50000mg / LNaCl concentration-viscosity bar graph at 85°C;
[0043] Figure 8 0.5% (w / v) galactomannan solution and modified galactomannan solution of Example 1 were prepared at a shear rate of 7.34 s -1 , temperature-viscosity curve with a temperature of 25 to 85°C. DETAILED DESCRIPTION
[0044] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.
[0045] In the following examples, if no specific experimental steps or conditions are specified, the operation or conditions of the conventional experimental steps described in the literature in this area can be carried out. If the manufacturer is not specified for reagents or instruments used, they are all conventional reagent products that can be obtained commercially. In this article, unless otherwise noted, percentage refers to weight / weight percentage.
[0046] Embodiment 1:
[0047] (1) Extracting galactomannan from Leucaena leucophylla seeds, the specific extraction method is: taking Leucaena leucophylla seeds, crushing them, extracting them with hot water to obtain an extract, adding an organic solvent to the extract to obtain a precipitate A, drying and redissolving it, adding protease and centrifuging to obtain a supernatant, adding an organic solvent ethanol to obtain a precipitate B, washing and drying the precipitate B to obtain a galactomannan solid.
[0048] (2) A method for preparing a modified polysaccharide, comprising the following steps:
[0049] Step S1: preparing a polysaccharide aqueous solution;
[0050] The galactomannan solid powder obtained above was dispersed in an aqueous solution, the mass ratio of the galactomannan solid powder to distilled water was 1:100, the concentration of the prepared polysaccharide solution was 1% (w / v), the heating and stirring temperature was 70-90°C, the time was 3h, stirring was performed until completely dissolved, and then cooled to room temperature.
[0051] Step S2: sodium cyanoborohydride modification;
[0052] Sodium cyanoborohydride (5%) was added to the solution prepared in step S1, that is, the mass volume ratio of sodium cyanoborohydride to polysaccharide solution was 1 g:20 mL, the reaction temperature was 50° C., and the reaction time was 3 h, to carry out sodium cyanoborohydride modification.
[0053] Step S3: Collection of modified products;
[0054] The modified solution prepared in step S2 is cooled to room temperature, and ethanol is added, wherein the ethanol content is 50%; the alcohol precipitation product is centrifuged in a refrigerated centrifuge, and the precipitate is collected, wherein the speed of the refrigerated centrifuge is 8000 rpm, and the centrifugation time is 7 minutes, and the precipitate is the polysaccharide modified by sodium cyanoborohydride. The precipitate is freeze-dried, and the vacuum freeze-drying time is 24 hours, and finally the dried precipitate is ground to obtain the modified galactomannan powder.
[0055] The structural formula of galactomannan before and after modification with sodium cyanoborohydride is as follows Figure 1 As shown, wherein n is an integer greater than 50.
[0056] Embodiment 2:
[0057] (1) A method for preparing a modified polysaccharide, comprising the following steps:
[0058] Step S1: preparing a polysaccharide aqueous solution;
[0059] The welan gum polysaccharide solid powder is dispersed in the aqueous solution, the mass ratio of the welan gum solid powder to distilled water is 1:100, the concentration of the prepared polysaccharide solution is 1% (w / v), the heating and stirring temperature is 70-90°C, the time is 3h, stirring until completely dissolved, and cooling to room temperature.
[0060] Step S2: sodium cyanoborohydride modification;
[0061] Sodium cyanoborohydride (5%) was added to the solution prepared in step S1, that is, the mass volume ratio of sodium cyanoborohydride to polysaccharide solution was 1 g:20 mL, the reaction temperature was 50° C., and the reaction time was 3 h, to carry out sodium cyanoborohydride modification.
[0062] Step S3: Collection of modified products;
[0063] The modified solution prepared in step S2 is cooled to room temperature, and ethanol is added, the ethanol content is 50%; the alcohol precipitation product is centrifuged with a refrigerated centrifuge, and the precipitate is collected. The speed of the refrigerated centrifuge is 8000rpm, and the centrifugation time is 7min. The precipitate is the wellan gum modified with sodium cyanoborohydride. The precipitate is freeze-dried, and the vacuum freeze-drying time is 24h. Finally, the dried precipitate is ground to obtain the modified wellan gum powder. The structural formula of wellan gum before and after sodium cyanoborohydride modification is as follows: Figure 2 As shown, wherein n is an integer greater than 50.
[0064] Embodiment 3:
[0065] Based on Example 2, the only difference from Example 2 is that in step S1, the polysaccharide is arabinogalactan. The structural formula of arabinogalactan before and after sodium cyanoborohydride modification is as follows: Figure 3 As shown, wherein n is an integer greater than 50.
[0066] Comparative Example 1:
[0067] The galactomannan extracted from Leucaena leucophylla seeds in step S1 of Example 1 was used as a raw material to prepare a 0.5% (w / v) original galactomannan aqueous solution, which was used as a control group to compare product performance with the modified galactomannan.
[0068] Comparative Example 2:
[0069] A 1% (w / v) original wellan gum aqueous solution was prepared and used as a control group to compare product performance with the modified wellan gum.
[0070] Comparative Example 3:
[0071] A 1% (w / v) original arabinogalactan aqueous solution was prepared and used as a control group to compare product performance with that of the modified arabinogalactan.
[0072] The modified polysaccharides obtained in Comparative Examples (1-3) and Examples (1-3) were compared to evaluate the product performance:
[0073] 1. Evaluation of viscosity-increasing properties of modified polysaccharides
[0074] The determination method is as follows: the modified polysaccharide prepared in Example 1 is stirred at 80°C and dispersed in water to prepare 20 mL of a solution with a concentration of 0.5% (w / v), and the modified polysaccharides prepared in Examples 2 and 3 are stirred at 80°C and dispersed in water to prepare 20 mL of a solution with a concentration of 1% (w / v). A rotational rheometer (Anton Paar MCR302) is then used to measure the prepared solution at a temperature of 25°C and a shear rate of 0.01-1000s -1The apparent viscosity of the change, the results of Comparative Example 1 and Example 1 are shown in Figure 4 Then the cross equation (1) was used to fit the data to obtain the rheological properties. The viscosity data obtained by fitting is shown in Table 1 below.
[0075]
[0076] Where η α is the apparent viscosity; η0 and η ∞ are the zero shear viscosity and the limiting viscosity at infinite shear rate, respectively; τ is the time constant; γ is the shear rate; and m is a dimensionless constant.
[0077] Table 1. Parameters obtained by fitting the examples (1 to 3) and the comparative examples (1 to 3) using the cross equation
[0078]
[0079] Table 1 shows the viscosity of comparative examples (1-3) and examples (1-3) at 25°C. It can be seen that the zero shear viscosity (η0) of comparative example 1 is 1831.75±3.56 mPa·s, and the sodium cyanoborohydride modification increases the η0 of the modified polysaccharide of example 1 by 210%, increasing η0 to 5708.17±7.27 mPa·s. The zero shear viscosity (η0) of comparative example 2 is 331.48±0.32 mPa·s, and the sodium cyanoborohydride modification increases the η0 of the modified polysaccharide of example 1 by 210%. The modification increased the η0 of the modified welan gum in Example 2 by 440%, increasing η0 to 1797.86±38.73 mPa·s, the zero shear viscosity (η0) of Comparative Example 3 was 727.21±0.34 mPa·s, and the sodium cyanoborohydride modification increased the η0 of the modified arabinogalactan in Example 3 by 200%, increasing η0 to 2289.55±24.23 mPa·s, indicating that sodium cyanoborohydride modification can increase the viscosity of polysaccharides.
[0080] 2. Evaluation of salt tolerance of modified polysaccharides
[0081] The viscosity of the modified polysaccharides obtained in Examples (1-3) and the original polysaccharides in Comparative Examples (1-3) at a NaCl concentration of 50000 mg / L (the shear rate was constant at 7.34 s -1 , the temperature is kept constant at 85°C). The results are shown in Figure 5 , 6, 7. When the NaCl concentration is 50000 mg / L, the viscosity of the modified polysaccharides obtained in Examples (1-3) is 122.22 mPa·s, 215.40 mPa·s and 230.35 mPa·s, respectively, and the viscosity of the original polysaccharides in Comparative Examples (1-3) is 19.74 mPa·s, 30.20 mPa·s and 46.10 mPa·s, respectively, indicating that the salt tolerance of the modified polysaccharides is significantly improved, and there is an obvious salt thickening phenomenon. The tolerance of the modified polysaccharide obtained in Example 1 to NaCl is increased by about 5 times relative to the tolerance of the original polysaccharide in Comparative Example 1, the tolerance of the modified polysaccharide obtained in Example 2 to NaCl is increased by about 6 times relative to the tolerance of the original polysaccharide in Comparative Example 2, and the tolerance of the modified polysaccharide obtained in Example 3 to NaCl is increased by about 4 times relative to the tolerance of the original polysaccharide in Comparative Example 3, indicating that the modification helps to improve the tolerance of the polysaccharide to NaCl, showing an excellent salt thickening effect.
[0082] 3. Evaluation of heat resistance of modified polysaccharides
[0083] The modified polysaccharide obtained in Example 1 and the original polysaccharide in Comparative Example 1 were measured at a shear rate of 7.34 s -1 , viscosity at a temperature of 25 to 85°C. Figure 8 In the range of 25-85°C, the viscosity of Example 1 is greater than that of Comparative Example 1, and as the ambient temperature gradually increases, the viscosity shows a significant downward trend, but the viscosity of Example 1 always remains higher than that of Comparative Example 1. This indicates that the modified polysaccharide has better temperature resistance.
[0084] In summary, the polysaccharide was modified with sodium cyanoborohydride, and the modified polysaccharide had an excellent thickening effect. Compared with the original polysaccharide, the viscosity of the modified polysaccharide increased by about 200-440%. The salt tolerance of the modified polysaccharide was improved. Compared with the original polysaccharide, the tolerance of the modified polysaccharide to NaCl increased by about 4-6 times, which shows that sodium cyanoborohydride modification can significantly improve the salt tolerance of polysaccharides. The modified polysaccharide showed a good salt thickening effect. When the added NaCl concentration reached 50000 mg / L, the viscosity of the modified polysaccharide increased by about 4-6 times compared with the initial viscosity. It can be seen that sodium cyanoborohydride modification shows an excellent salt thickening effect and has a good resistance to sodium chloride.
Claims
1. A modified polysaccharide, characterized in that: The modified polysaccharide is mainly composed of polysaccharide and is obtained by modification with sodium cyanoborohydride.
2. A modified polysaccharide according to claim 1, characterized in that: The modified polysaccharide is modified galactomannan, modified welan gum or modified arabinogalactan; The structural formula of the modified galactomannan is as follows (Formula I): Wherein, n is an integer greater than 50; The structural formula of modified Weilan gum is as follows (Formula II): Wherein, n is an integer greater than 50; The structural formula of the modified arabinogalactan is as follows (Formula III): Wherein, n is an integer greater than 50.
3. A method for preparing a modified polysaccharide according to claim 1 or 2, characterized in that: The following steps are involved: (1) dispersing the polysaccharide in water, heating and stirring until completely dissolved, and cooling to room temperature to obtain a polysaccharide aqueous solution; (2) weighing sodium cyanoborohydride and adding it to the polysaccharide aqueous solution to carry out a modification reaction to obtain a modified polysaccharide solution; (3) The modified polysaccharide solution is cooled to room temperature, ethanol is added, the precipitate is collected after centrifugation, and the modified polysaccharide solid is obtained after drying.
4. The preparation method according to claim 3, characterized in that: The polysaccharide in step (1) is galactomannan, welan gum or arabinogalactan.
5. The preparation method according to claim 3, characterized in that: The mass ratio of the polysaccharide to water in step (1) is 1:80 to 1:100; The heating and stirring conditions are: temperature 70-90° C., time 3-5 h.
6. The preparation method according to claim 3, characterized in that: The mass volume ratio of sodium cyanoborohydride to the modified polysaccharide solution in step (2) is 1 g:10 mL to 1 g:20 mL; The conditions of the modification reaction are: temperature 40-50° C., time 3-5 h.
7. The preparation method according to claim 3, characterized in that: The content of ethanol in step (3) is 20% to 50%; The centrifugal speed is 7000-8000 rpm, and the centrifugal time is 7-10 min; The drying time is 12 to 24 hours.
8. The preparation method according to claim 3, characterized in that: The centrifugation method in step (3) is refrigerated centrifuge treatment; the drying method is freeze drying.
9. Use of the modified polysaccharide according to claim 1 or 2, or the modified polysaccharide prepared by the method according to any one of claims 3 to 8 as an oil displacement agent.
10. Use of the modified polysaccharide according to claim 1 or 2, or the modified polysaccharide prepared by the method according to any one of claims 3 to 8 in petroleum production.