A polymer type CO2 oil flooding thickener and preparation method thereof, and CO2 oil flooding system

Abstract

The present invention belongs to the technical field of oil production, and specifically relates to a polymeric CO2 oil recovery thickener and a preparation method thereof, and a CO2 oil recovery system. The structural formula of the polymeric CO2 oil recovery thickener is shown in Formula I: Formula I, wherein R1 is a perfluoroalkyl group with 6 to 12 carbon atoms, R2 is an alkyl group with 1 to 4 carbon atoms, R3 is an alkyl group with 2 to 6 carbon atoms, n is selected from an integer between 5 and 13, a is selected from an integer between 1000 and 10000, b is selected from an integer between 200 and 4000, c is selected from an integer between 200 and 4000, and d is selected from an integer between 100 and 2000. The polymeric CO2 oil recovery thickener combines solubilized perfluoroalkyl ethyl acrylate monomers and methacrylate monomers and thickened methacryloyloxypropyl trialkoxy silane monomers and olefinic acid monomers, so that it can be efficiently dissolved in carbon dioxide without using additives and solvents, and thus can achieve high-fold thickening of carbon dioxide at low concentrations.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum extraction, and in particular relates to a polymer-type CO2 oil-displacing thickener and a preparation method thereof, and a CO2 oil-displacing system. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Carbon dioxide flooding is an efficient tertiary oil recovery technology. Thanks to its excellent permeability, carbon dioxide can easily penetrate into tiny pores and effectively displace crude oil by reducing crude oil viscosity, volume expansion, and dissolved gas drive, thereby improving crude oil recovery. However, due to the low viscosity of carbon dioxide, severe heterogeneity, and the existence of natural fractures as channels, viscous fingering and crossover are prone to occur, resulting in an unfavorable mobility ratio. The crossover of carbon dioxide in the reservoir will significantly affect the effect of gas drive to improve oil recovery; in those wells with severe gas crossover, although the oil increase effect is obvious, the liquid production will drop significantly, and even stop spraying. In addition, due to the gravity overburden effect, during the carbon dioxide displacement process, the gas tends to crossflow to the upper part of the reservoir to form a crossflow channel, which not only limits the volume of gas drive, but also seriously affects the oil recovery efficiency of carbon dioxide drive, and increases the difficulty of blocking gas. In order to solve the problems existing in carbon dioxide drive, thickeners, especially polymers with higher thickening efficiency, have been widely used in carbon dioxide drive. However, most thickeners have poor solubility, which results in a large amount of thickener being used, resulting in increased costs.

[0004] CN107236091A discloses a supercritical carbon dioxide thickener and its preparation method and application, the thickener contains the following components: (a) polydimethylsiloxane; (b) acrylate compound; (c) styrene compound; (d) initiator; (e) emulsifier; wherein the component (a) is polydimethylsiloxane with a viscosity of 50-3000mPa·s. The thickener can thicken supercritical carbon dioxide by more than 100 times, and the supercritical carbon dioxide fluid thickened by the thickener can suspend 1%-10% (volume ratio) of the proppant. The thickener needs to use a supercritical carbon dioxide medium during the preparation process, which increases the preparation cost. Although the thickener can effectively thicken at 3~6 wt%, it needs to be compounded with an organic co-solvent during use, which has an adverse effect on environmental pollution and process operation.

[0005] CN115703862A discloses a high-efficiency thickener for thickening carbon dioxide oil displacement and a preparation method thereof. The high-efficiency thickener for thickening carbon dioxide oil displacement comprises the following raw material components by mass percentage: 35-54% of carbon dioxide-philic solvent, 15-20% of oil-soluble solvent, 5-10% of carbonate solubilizing monomer, 20-25% of acrylate viscosity-increasing monomer, 3-5% of perfluoroalkyl viscosity-increasing monomer, 2-3% of fluorine-containing acrylate structural monomer, 0.5-1% of oil-soluble chain transfer agent and 0.5-1% of oil-soluble initiator. The thickener introduces carbon dioxide-philic solvent and oil-soluble solvent that do not need to be removed during the preparation process to dissolve the copolymer and improve the solubility of the thickener in carbon dioxide. Although the viscosity of the thickener can reach more than 2mPa·s at a concentration of 0.1%, a solvent is still required to improve its solubility in carbon dioxide.

[0006] Based on the above analysis, the thickeners used in the prior art have significant deficiencies in intrinsic solubility, and their dissolution process in carbon dioxide still requires the intervention of auxiliary agents or solvents. This has led to a significant increase in the amount of thickeners used, the complication of the ingredients, and a significant increase in costs, and has inevitably caused pollution and potential damage to the reservoir. Summary of the invention

[0007] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a polymer-type CO2 oil recovery thickener and a preparation method thereof, and a CO2 oil recovery system. The polymer-type CO2 oil recovery thickener of the present invention can be efficiently dissolved in carbon dioxide without the need for external additives or solvents, and can achieve 2600 times the viscosity of carbon dioxide at a dosage of 0.2 wt%.

[0008] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0009] In a first aspect, the present invention provides a polymer-based CO2 oil recovery thickener, the structural formula of the polymer-based CO2 oil recovery thickener is shown in Formula I:

[0010] Formula I,

[0011] In the formula, R1 is a perfluoroalkyl group having 6 to 12 carbon atoms, R2 is an alkyl group having 1 to 4 carbon atoms, R3 is an alkyl group having 2 to 6 carbon atoms, n is selected from an integer between 5 and 13, a is selected from an integer between 1000 and 10000, b is selected from an integer between 200 and 4000, c is selected from an integer between 200 and 4000, and d is selected from an integer between 100 and 2000.

[0012] The polymer type CO2 oil displacement thickener of the present invention is a quaternary polymer with perfluoroalkyl ethyl acrylate (structural formula as shown in formula II), methacryloxypropyl trialkoxy silane (structural formula as shown in formula II), methacrylate (structural formula as shown in formula IV), and olefinic acid (structural formula as shown in formula V) as monomers. Among them, perfluoroalkyl ethyl acrylate dissolves well in CO2; methacryloxypropyl trialkoxy silane can greatly increase the viscosity of CO2; methacrylate has good solubility in CO2 and low cost; olefinic acid is a long-chain fatty acid and can increase the viscosity of CO2.

[0013] The structural formula of the perfluoroalkyl ethyl acrylate is shown in Formula II:

[0014] Formula II;

[0015] The structural formula of the methacryloxypropyl trialkoxy silicone grease is shown in III:

[0016] Formula III;

[0017] The structural formula of the methacrylate is shown in Formula IV:

[0018] Formula IV;

[0019] The structural formula of the olefinic acid is shown in Formula V:

[0020] Formula V.

[0021] Preferably, R1 is perfluorooctyl, R2 is methyl, R3 is butyl, and n is 9.

[0022] Preferably, the viscosity-average molecular weight of the polymer-type CO2 oil-displacing thickener is 2,000,000 to 5,000,000.

[0023] In a second aspect, the present invention provides a method for preparing the polymer-type CO2 oil displacement thickener as described in the first aspect, comprising the following steps:

[0024] S1, mixing perfluoroalkylethyl acrylate, methacryloyloxypropyl trialkoxy silicone grease, methacrylate, olefinic acid and toluene, replacing the air with an inert gas, adding an initiator, raising the temperature to react, and obtaining a mixed solution;

[0025] S2. Add hydroquinone to the mixed solution, distill under reduced pressure, add ethanol after stopping the distillation, and obtain a polymer-type CO2 oil-displacing thickener by heating to dissolve, cooling, crystallizing, filtering and drying.

[0026] Preferably, in step S1, the molar ratio of perfluoroalkylethyl acrylate, methacryloyloxypropyltrialkoxy silicone, methacrylate and olefinic acid is (0.2-0.4):(0.2-0.4):(0.1-0.2):1, and the weight ratio of toluene to perfluoroalkylethyl acrylate is (20-30):1.

[0027] Preferably, in step S1, the initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile and benzoyl peroxide, and the weight ratio of the initiator to perfluoroalkylethyl acrylate is (0.02~0.05):1.

[0028] Preferably, in step S1, the temperature is raised to 70°C-80°C and the reaction is maintained for 2-4 hours.

[0029] Preferably, in step S2, the weight ratio of hydroquinone to perfluoroalkyl ethyl acrylate is (0.01-0.02):1, and the weight ratio of ethanol to perfluoroalkyl ethyl acrylate is (15-20):1.

[0030] Preferably, in step S2, distillation is stopped when 20-30 wt % of toluene remains.

[0031] In a third aspect, the present invention provides a CO2 flooding system, comprising CO2 and a polymer-type CO2 flooding thickener as described in the first aspect with a mass concentration of 0.2 to 2 wt%.

[0032] The beneficial effects achieved by one or more technical solutions of the present invention are as follows:

[0033] The polymer-type CO2 oil-displacing thickener of the present invention combines solubilizing perfluoroalkylethyl acrylate monomers and methacrylate monomers with thickening methacryloxypropyltrialkoxysilane monomers and olefinic acid monomers, so that it can be efficiently dissolved in carbon dioxide without the use of additives and solvents, and thus can achieve high-multiple thickening of carbon dioxide at low concentrations.

[0034] At 50°C and 30MPa, a 0.2wt% polymer-based CO2 oil-flooding thickener concentration can increase the viscosity of carbon dioxide to more than 13mPa•s, with a viscosity increase multiple of more than 260 times. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in combination with specific embodiments and comparative examples.

[0036] Example 1

[0037] (1) Add 10 mmol perfluorooctylethyl acrylate, 2 mmol methacryloyloxypropyltrimethoxysilane, 3 mmol butyl methacrylate, 2 mmol undecylenic acid and 104 g toluene to the reactor in sequence, replace the air with nitrogen, stir to dissolve, add 0.1 g azobisisobutyronitrile, slowly raise the temperature to 70°C, and keep the temperature for 2 h to obtain a viscous mixed solution.

[0038] (2) Add 0.05 g of hydroquinone to the mixed solution, continue stirring for 10 min, and distill the mixed solution under reduced pressure. When the remaining toluene is 20 wt%, stop distilling, add 77.7 g of ethanol, heat to dissolve, cool to below 10 °C, crystallize, filter, and dry to obtain a polymer-based CO2 oil-displacing thickener.

[0039] Example 2

[0040] (1) Add 10 mmol perfluorooctylethyl acrylate, 2.3 mmol methacryloyloxypropyltrimethoxysilane, 4 mmol butyl methacrylate, 1 mmol undecylenic acid and 112 g toluene to the reactor in sequence, replace the air with nitrogen, stir to dissolve, add 0.13 g azobisisobutyronitrile, slowly raise the temperature to 80°C, and keep the temperature for 4 h to obtain a viscous mixed solution.

[0041] (2) Add 0.06 g of hydroquinone to the mixed solution, continue stirring for 20 min, and distill the mixed solution under reduced pressure. When the remaining toluene is 25 wt%, stop distilling, add 84 g of ethanol, heat to dissolve, cool to below 10 °C, crystallize, filter, and dry to obtain the product polymer-type CO2 oil-displacing thickener.

[0042] Example 3

[0043] (1) Add 10 mmol perfluorooctylethyl acrylate, 2.6 mmol methacryloyloxypropyltrimethoxysilane, 3.7 mmol butyl methacrylate, 1.2 mmol undecylenic acid and 155 g toluene to the reactor in sequence, replace the air with nitrogen, stir to dissolve, add 0.18 g azobisisoheptanenitrile, slowly raise the temperature to 75°C, and keep the temperature for 3 h to obtain a viscous mixed solution.

[0044] (2) Add 0.08 g of hydroquinone to the mixed solution, continue stirring for 20 min, and distill the mixed solution under reduced pressure. When the remaining toluene is 30 wt%, stop distilling, add 103 g of ethanol, heat to dissolve, cool to below 10 °C, crystallize, filter, and dry to obtain a polymer-based CO2 oil-displacing thickener.

[0045] Example 4

[0046] (1) Add 10 mmol perfluorooctylethyl acrylate, 3 mmol methacryloyloxypropyltrimethoxysilane, 3.5 mmol butyl methacrylate, 1.5 mmol undecylenic acid and 124 g toluene to the reactor in sequence, replace the air with nitrogen, stir to dissolve, add 0.2 g azobisisoheptanenitrile, slowly raise the temperature to 72°C, and keep the temperature for 3.5 h to obtain a viscous mixed solution.

[0047] (2) Add 0.09 g of hydroquinone to the mixed solution, continue stirring for 12 min, and distill the mixed solution under reduced pressure. When the remaining toluene is 22 wt%, stop distilling, add 88 g of ethanol, heat to dissolve, cool to below 10 °C, crystallize, filter, and dry to obtain a polymer-based CO2 oil-displacing thickener.

[0048] Example 5

[0049] (1) Add 10 mmol perfluorooctylethyl acrylate, 3.3 mmol methacryloyloxypropyltrimethoxysilane, 2.5 mmol butyl methacrylate, 1.7 mmol undecylenic acid and 133 g toluene to the reactor in sequence, replace the air with nitrogen, stir to dissolve, add 0.24 g benzoyl peroxide, slowly raise the temperature to 78°C, and keep the temperature for 2.5 h to obtain a viscous mixed solution.

[0050] (2) Add 0.1 g of hydroquinone to the mixed solution and continue stirring for 15 min. Then distill the mixed solution under reduced pressure. When the remaining toluene content is 22 wt%, stop distilling and add 91 g of ethanol. Heat to dissolve the mixture and cool it to below 10 °C. Then crystallize the mixture, filter it and dry it to obtain a polymer-based CO2 oil recovery thickener.

[0051] Example 6

[0052] (1) Add 10 mmol perfluorooctylethyl acrylate, 3.7 mmol methacryloyloxypropyltrimethoxysilane, 2 mmol butyl methacrylate, 2 mmol undecylenic acid and 124 g toluene to the reactor in sequence, replace the air with nitrogen, stir to dissolve, add 0.25 g benzoyl peroxide, slowly raise the temperature to 75°C, and keep the temperature for 3 h to obtain a viscous mixed solution.

[0053] (2) Add 0.1 g of hydroquinone to the mixed solution and continue stirring for 20 min. Then distill the mixed solution under reduced pressure. When the toluene content is 30 wt%, stop distilling and add 87 g of ethanol. Heat to dissolve the mixture and cool it to below 10 °C. Then crystallize the mixture, filter it and dry it to obtain a polymer-based CO2 oil-displacing thickener.

[0054] Example 7

[0055] (1) Add 10 mmol perfluorooctylethyl acrylate, 4 mmol methacryloyloxypropyltrimethoxysilane, 2.3 mmol butyl methacrylate, 1.2 mmol undecylenic acid and 146 g toluene to the reactor in sequence, replace the air with nitrogen, stir to dissolve, add 0.26 g benzoyl peroxide, slowly raise the temperature to 76°C, and keep the temperature for 3 h to obtain a viscous mixed solution.

[0056] (2) Add 0.1 g of hydroquinone to the mixed solution and continue stirring for 12 min. Then distill the mixed solution under reduced pressure. When the remaining toluene content is 25 wt%, stop distilling and add 100 g of ethanol. Heat to dissolve the mixture. Cool the mixture to below 10 °C, crystallize the mixture, filter it, and dry it to obtain a polymer-based CO2 oil-displacing thickener.

[0057] Comparative Example 1

[0058] (1) Add 10 mmol perfluorooctyl ethyl acrylate, 3 mmol butyl methacrylate, 2 mmol undecylenic acid and 104 g toluene to the reactor in sequence, replace the air with nitrogen, stir to dissolve, add 0.1 g azobisisobutyronitrile, slowly raise the temperature to 70°C, and keep the temperature for 2 h to obtain a viscous mixed solution.

[0059] (2) Add 0.05 g of hydroquinone to the mixed solution, continue stirring for 10 min, and distill the mixed solution under reduced pressure. When the remaining toluene is 20 wt%, stop distilling, add 77.7 g of ethanol, heat to dissolve, cool to below 10°C, crystallize, filter, and dry to obtain a thickener.

[0060] Comparative Example 2

[0061] (1) Add 10 mmol perfluorooctylethyl acrylate, 2 mmol methacryloyloxypropyltrimethoxysilane, 2 mmol undecylenic acid and 104 g toluene to the reactor in sequence, replace the air with nitrogen, stir to dissolve, add 0.1 g azobisisobutyronitrile, slowly raise the temperature to 70°C, and keep the temperature for 2 h to obtain a viscous mixed solution.

[0062] (2) Add 0.05 g of hydroquinone to the mixed solution, continue stirring for 10 min, and distill the mixed solution under reduced pressure. When the remaining toluene is 20 wt%, stop distilling, add 77.7 g of ethanol, heat to dissolve, cool to below 10°C, crystallize, filter, and dry to obtain a thickener.

[0063] Comparative Example 3

[0064] (1) Add 10 mmol perfluorooctylethyl acrylate, 2 mmol methacryloyloxypropyltrimethoxysilane, 3 mmol butyl methacrylate and 104 g toluene to the reactor in sequence, replace the air with nitrogen, stir to dissolve, add 0.1 g azobisisobutyronitrile, slowly raise the temperature to 70°C, and keep the temperature for 2 h to obtain a viscous mixed solution.

[0065] (2) Add 0.05 g of hydroquinone to the mixed solution, continue stirring for 10 min, and distill the mixed solution under reduced pressure. When the remaining toluene is 20 wt%, stop distilling, add 77.7 g of ethanol, heat to dissolve, cool to below 10°C, crystallize, filter, and dry to obtain a thickener.

[0066] Comparative Example 4

[0067] (1) Add 2 mmol of methacryloyloxypropyltrimethoxysilane, 3 mmol of butyl methacrylate, 2 mmol of undecylenic acid and 104 g of toluene to the reactor in sequence, replace the air with nitrogen, stir to dissolve, add 0.1 g of azobisisobutyronitrile, slowly raise the temperature to 70°C, and keep the temperature for 2 h to obtain a viscous mixed solution.

[0068] (2) Add 0.05 g of hydroquinone to the mixed solution, continue stirring for 10 min, and distill the mixed solution under reduced pressure. When the remaining toluene is 20 wt%, stop distilling, add 77.7 g of ethanol, heat to dissolve, cool to below 10°C, crystallize, filter, and dry to obtain a thickener.

[0069] Example 8

[0070] The polymer-type CO2 oil-flooding high-efficiency thickeners in Examples 1 to 7 and the thickeners in Comparative Examples 1 to 4 were dissolved with carbon dioxide to form a 0.2 wt% CO2 oil-flooding system, placed in a pressure-resistant, temperature-controllable closed Haake rheometer, stirred evenly, and the shear rate was adjusted to 170 s -1 The system was heated stepwise at a pressure of 30 MPa, and the viscosity of supercritical carbon dioxide (scCO2) at 50°C, 70°C, and 90°C was tested. A carbon dioxide blank was used for comparative experiments. The results are shown in Table 1.

[0071] Table 1 scCO2 viscosity test results at different temperatures

[0072]

[0073] As shown in Table 1, the polymer-type CO2 oil-flooding high-efficiency thickener prepared by the present invention can effectively thicken carbon dioxide when used alone. Under a pressure of 30 MPa, a concentration of 0.2wt% can increase the viscosity to 13.1mPa•s and above, 12.8mPa•s and above, and 12.3mPa•s and above at 50°C, 70°C, and 90°C. The viscosity of blank carbon dioxide without adding thickener is 0.05 mPa•s, 0.046 mPa•s, and 0.043 mPa•s, respectively, and the thickening effect can reach more than 260 times. At the same time, a three-monomer thickener was prepared in Comparative Example 1, and the thickening effect of the comparative example was greatly reduced due to the lack of monomers.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A polymer-type CO2 oil-displacing thickener, characterized in that: The structural formula of the polymer-type CO2 oil displacement thickener is shown in Formula I: Formula I, In the formula, R1 is a perfluoroalkyl group having 6 to 12 carbon atoms, R2 is an alkyl group having 1 to 4 carbon atoms, R3 is an alkyl group having 2 to 6 carbon atoms, n is selected from an integer between 5 and 13, a is selected from an integer between 1000 and 10000, b is selected from an integer between 200 and 4000, c is selected from an integer between 200 and 4000, and d is selected from an integer between 100 and 2000.

2. The polymer-type CO2 oil displacement thickener according to claim 1, characterized in that: R1 is perfluorooctyl, R2 is methyl, R3 is butyl, and n is 9.

3. The polymer-type CO2 oil-displacing thickener according to claim 1, characterized in that: The viscosity average molecular weight of the polymer CO2 oil displacement thickener is 2,000,000-5,000,000.

4. A method for preparing a polymeric CO2 flooding thickener as claimed in any one of claims 1 to 3, characterized in that: The following steps are involved: S1, mixing perfluoroalkylethyl acrylate, methacryloyloxypropyl trialkoxy silicone grease, methacrylate, olefinic acid and toluene, replacing the air with an inert gas, adding an initiator, raising the temperature to react, and obtaining a mixed solution; S2, adding hydroquinone to the mixed solution, distilling under reduced pressure, adding ethanol after stopping the distillation, heating to dissolve, cooling, crystallizing, filtering and drying to obtain a polymer-type CO2 oil displacement thickener; The structural formula of the perfluoroalkyl ethyl acrylate is shown in Formula II: Formula II; The structural formula of the methacryloxypropyl trialkoxy silicone grease is shown in III: Formula III; The structural formula of the methacrylate is shown in Formula IV: Formula IV; The structural formula of the olefinic acid is shown in Formula V: Formula V.

5. The preparation method according to claim 4, characterized in that: In step S1, the molar ratio of perfluoroalkyl ethyl acrylate, methacryloyloxypropyl trialkoxy silicone, methacrylate and olefinic acid is (0.2-0.4):(0.2-0.4):(0.1-0.2):1, and the weight ratio of toluene to perfluoroalkyl ethyl acrylate is (20-30):

1.

6. The preparation method according to claim 4, characterized in that: In step S1, the initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile and benzoyl peroxide, and the weight ratio of the initiator to perfluoroalkylethyl acrylate is (0.02~0.05):

1.

7. The preparation method according to claim 4, characterized in that: In step S1, the temperature is raised to 70°C-80°C and kept for reaction for 2-4 hours.

8. The preparation method according to claim 4, characterized in that: In step S2, the weight ratio of hydroquinone to perfluoroalkyl ethyl acrylate is (0.01-0.02):1, and the weight ratio of ethanol to perfluoroalkyl ethyl acrylate is (15-20):

1.

9. The preparation method according to claim 4, characterized in that: In step S2, the distillation is stopped when 20-30 wt % of toluene remains.

10. A CO2 flooding system, characterized in that: It comprises CO2 and a polymer-type CO2 oil-displacing thickener as described in any one of claims 1 to 3 with a mass concentration of 0.2 to 2 wt%.

Images