Polymer gel for CO2 flooding and channeling sealing suitable for high-temperature oil reservoir and preparation method of polymer gel

Abstract

The invention belongs to the technical field of petroleum and natural gas extraction, and discloses polymer gel for CO2 flooding and channeling sealing of a high-temperature oil reservoir and a preparation method of the polymer gel. The gel component is prepared from 0.4 wt% to 1 wt% of partially hydrolyzed polyacrylamide, 0.5 wt% to 2 wt% of phenolic resin, 0.2 wt% to 0.5 wt% of aluminum citrate, 0.2 wt% to 0.8 wt% of thiourea and the balance of water. The plugging agent has the characteristics of temperature resistance, acid resistance and the like, can effectively plug gas channeling channels such as heterogeneous high-permeability zones and natural / artificial fractures in CO2 drive oil reservoirs, and achieves the purposes of controlling gas channeling and enlarging gas drive waves and volumes.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and natural gas exploitation, and in particular relates to a polymer gel for CO2 flooding and sealing in high-temperature oil reservoirs and a preparation method thereof. Background Art

[0002] Most of my country's onshore oil fields have entered the high water content development stage. The comprehensive water content of oil well produced fluid is often above 90%, and the water injection oil recovery efficiency is very low. As a mature oil recovery technology, CO2 flooding enhanced oil recovery technology has been widely valued by major oil fields at home and abroad for its wide range of applications, high oil recovery efficiency, and low cost. As an efficient and environmentally friendly development method, CO2 flooding has more obvious technical advantages than water flooding, and is particularly suitable for the development and potential of low permeability reservoirs. Therefore, CO2 flooding enhanced oil recovery technology has also become one of the best water flooding replacement technologies.

[0003] Low permeability reservoirs have strong reservoir heterogeneity, developed microcracks, low matrix permeability, high formation water mineralization, and high original gas-oil ratio of the reservoir, which makes gas channeling inevitable during CO2 flooding development, seriously affecting the effect of gas injection development. The prevention and control of CO2 flooding gas channeling is divided into two categories: prevention before gas channeling and plugging after gas channeling. The former mainly includes water-gas alternating flooding technology (WAG), CO2 foam flooding technology, CO2 thickening technology, etc., but the applicable effect is poor for the harsh reservoir conditions of low permeability reservoirs. After gas channeling occurs, the high permeability layer is mainly plugged by injecting gel and other plugging agents. Domestic and foreign surveys and indoor experiments have shown that the current plugging agents in oil fields cannot meet the requirements of CO2 flooding and channeling in high-temperature reservoirs. It is necessary to develop plugging materials that can greatly reduce the degree of gas channeling after gas channeling, reveal its temperature, salt and acid resistance mechanisms, and study related supporting processes to provide support for large-scale promotion and application in oil fields. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a polymer gel for CO2 flooding and sealing suitable for high-temperature oil reservoirs and a preparation method thereof, which has the characteristics of temperature resistance and acid resistance, and can effectively block gas channeling channels such as heterogeneous high-permeability zones, natural / artificial fractures in CO2 flooding oil reservoirs, thereby achieving the purpose of controlling gas channeling and expanding the gas drive swept volume.

[0005] The above-mentioned purpose of the present invention is achieved through the following technical scheme: a polymer gel for CO2 flooding and sealing suitable for high-temperature oil reservoirs, comprising 0.4wt% to 1wt% of partially hydrolyzed polyacrylamide, 0.5wt% to 2wt% of phenolic resin, 0.2wt% to 0.5wt% of aluminum citrate, 0.2wt% to 0.8wt% of thiourea, and the balance is water.

[0006] Furthermore, the molecular weight of the partially hydrolyzed polyacrylamide is 12 million, and the degree of hydrolysis is 0-2%.

[0007] Furthermore, the phenolic resin is an industrial-grade water-soluble phenolic resin, and the mass percentage of phenolic resin is 35%.

[0008] Furthermore, the water is mineralized water with a concentration of more than 10,000 mg / L, wherein the content of calcium and magnesium ions is about 40 mg / L.

[0009] The method for preparing the polymer gel for CO2 flooding and sealing in high-temperature oil reservoirs comprises the following steps:

[0010] 1. Dissolve partially hydrolyzed polyacrylamide in water and stir to ripen;

[0011] 2. Add phenolic resin, aluminum citrate, and thiourea in sequence, stir to fully dissolve, and add dilute hydrochloric acid to adjust the pH to 2-3 to simulate the CO2 flooding environment;

[0012] 3. The reaction mixture in step 2 is placed in an ampoule and sealed by introducing CO2, and placed in an oven at 100°C for 1 to 3 days to polymerize, thereby obtaining a polymer gel for CO2 flooding and sealing in high-temperature oil reservoirs.

[0013] The beneficial effects of the present invention compared with the prior art are as follows: the preparation method of the polymer gel for CO2 flooding sealing suitable for high-temperature oil reservoirs provided by the present invention is simple in process, the components are environmentally friendly, and it is suitable for the low pH environment of the oil reservoir caused by CO2 flooding. It can effectively block gas channeling channels such as high permeability layers and natural / artificial fractures, expand the gas flooding swept volume, and improve the crude oil recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0015] FIG. 1 is a graph showing the change in gel strength of polymer gels of different mass fractions over time in the present invention ( Figure 1a The gel form of Example 1 at 10 days, 30 days, 60 days, and 100 days, Figure 1b The gel form of Example 2 at 10 days, 30 days, 60 days, and 100 days, Figure 1c The gel form of Example 3 at 10 days, 30 days, 60 days, and 100 days, Figure 1d The gel form of Example 4 at 10 days, 30 days, 60 days, and 100 days);

[0016] Figure 2 is the test result of viscoelastic properties of polymer gels with different mass fractions in the present invention;

[0017] Figure 3 These are the test results of thermal stability of polymer gels with different mass fractions in the present invention. DETAILED DESCRIPTION

[0018] The present invention is described in detail below by specific examples, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0019] Embodiment 1:

[0020] This embodiment provides a polymer gel for CO2 flooding and sealing in high-temperature oil reservoirs, which includes the following components by mass percentage: 0.4% partially hydrolyzed polyacrylamide, 0.5% phenolic resin, 0.2% aluminum citrate, 0.2% thiourea, and the balance is water.

[0021] (1) Gelation time and gel strength test:

[0022] The prepared polymer gel solution was placed in 100°C, the gelling time was observed and recorded, and the "visual code evaluation method" commonly used in the petroleum industry was used to evaluate and record the change in gel strength after 10 days, 30 days, 60 days, and 100 days ( Figure 1a ).

[0023] The polymer gel was gelled at 70 hours, changing from a liquid flow state to a gel, and losing its flow properties. The gel strength at 10 days, 30 days, 60 days, and 100 days after gelling was E-grade, showing a low flow gel state, and a small amount of dehydration occurred at 100 days, with a dehydration rate of 10%.

[0024] (2) Gel viscoelasticity test

[0025] The viscoelasticity (storage modulus, loss modulus) of the polymer gel of Example 1 after gelation at 100° C. and constant temperature for 10 days was measured using an Austrian MCR301 rheometer and a lamina system.

[0026] Oscillation frequency scanning, select 10% to 30% of the upper limit stress value of the linear viscoelastic region as the stress value. In order to speed up the test, the frequency range of 0.01 to 10 Hz is scanned to determine the relationship between the storage modulus G', loss modulus G" and frequency f. The test temperature is 25 ° C. The test results are shown in Figure 2 .

[0027] from Figure 2 It can be seen that the storage modulus G' of the polymer gel is higher than the loss modulus G", and the storage modulus G' is stable at around 5Pa.

[0028] (3) Gel thermal stability test

[0029] The thermal stability of the polymer gel of Example 1 after gelation at 100°C and constant temperature for 100 days was measured using a METTLER thermogravimetric analyzer (TGA).

[0030] The polymer gel of Example 1, which was gelled at 100°C and kept at a constant temperature for 100 days, was placed in a 200°C oven for 48 hours until it was completely dried and crushed. 1 to 2 mg of the sample was placed in a thermogravimetric analyzer to test the mass fraction change of the polymer gel in the range of 0 to 600°C. The test frequency was 6°C each time. The test results are shown in Figure 3 .

[0031] from Figure 3 It can be seen that the polymer gel has two obvious weight loss steps. The first weight loss step is at 200-250°C, and the weight change range is about 10%, which is mainly attributed to the heat loss of the sample polymer itself. The second weight loss step appears at 300-400°C, at which time the amide groups formed by the polymer and phenolic resin in the gel structure begin to decompose, and the weight loss is about 20%. The final residual mass of the polymer gel is 49.93%.

[0032] Embodiment 2:

[0033] This embodiment provides a polymer gel for CO2 flooding and sealing in high-temperature oil reservoirs, which includes the following components by mass percentage: 0.6% partially hydrolyzed polyacrylamide, 1.0% phenolic resin, 0.3% aluminum citrate, 0.4% thiourea, and the balance is water.

[0034] (1) Gelation time and gel strength test:

[0035] The prepared polymer gel solution was placed in 100°C, the gelling time was observed and recorded, and the "visual code evaluation method" commonly used in the petroleum industry was used to evaluate and record the change in gel strength after 10 days, 30 days, 60 days, and 100 days ( Figure 1b ).

[0036] The polymer gel was gelled at 52 hours, changing from a liquid flow state to a gel, and losing its flow properties. The gel strength at 10 days, 30 days, 60 days, and 100 days after gelling was F grade, showing a high deformation flow gel.

[0037] (2) Gel viscoelasticity test

[0038] The viscoelasticity (storage modulus, loss modulus) of the polymer gel of Example 2 after gelation at 100° C. and constant temperature for 10 days was measured using an Austrian MCR301 rheometer and a lamina system.

[0039] Oscillation frequency scanning, select 10% to 30% of the upper limit stress value of the linear viscoelastic region as the stress value. In order to speed up the test, the frequency range of 0.01 to 10 Hz is scanned to determine the relationship between the storage modulus G', loss modulus G" and frequency f. The test temperature is 25 ° C. The test results are shown in Figure 2 .

[0040] from Figure 2 It can be seen that the storage modulus G' of the polymer gel is higher than the loss modulus G", and the storage modulus G' is stable at around 10Pa.

[0041] (3) Gel thermal stability test

[0042] The thermal stability of the polymer gel of Example 2 after gelation at 100°C and constant temperature for 100 days was measured using a METTLER thermogravimetric analyzer (TGA).

[0043] After gelation at 100°C and constant temperature for 100 days, the polymer gel of Example 2 was placed in a 200°C oven for 48 hours until it was completely dried and crushed. 1 to 2 mg of the sample was placed in a thermogravimetric analyzer to test the mass fraction change of the polymer gel in the range of 0 to 600°C. The test frequency was 6°C each time. The test results are shown in Figure 3 .

[0044] from Figure 3 It can be seen that the polymer gel has two obvious weight loss steps. The first weight loss step is at 175-225°C, and the weight change range is about 10%, which is mainly attributed to the heat loss of the sample polymer itself. The second weight loss step appears at 350-400°C, at which time the amide groups formed by the polymer and phenolic resin in the gel structure begin to decompose, and the weight loss is about 15%. The final residual mass of the polymer gel is 56.74%.

[0045] Embodiment 3:

[0046] This embodiment provides a polymer gel for CO2 flooding and sealing in high-temperature oil reservoirs, which includes the following components by mass percentage: 0.8% partially hydrolyzed polyacrylamide, 1.5% phenolic resin, 0.4% aluminum citrate, 0.6% thiourea, and the balance is water.

[0047] (1) Gelation time and gel strength test:

[0048] The prepared polymer gel solution was placed in 100°C, the gelling time was observed and recorded, and the "visual code evaluation method" commonly used in the petroleum industry was used to evaluate and record the change in gel strength after 10 days, 30 days, 60 days, and 100 days ( Figure 1c ).

[0049] The polymer gel gelled at 36 hours, changing from a liquid flow state to a gel, losing its flow properties. The gel strength at 10 days, 30 days, 60 days, and 100 days after gelling was G grade, showing a medium deformation flow gel.

[0050] (2) Gel viscoelasticity test

[0051] The viscoelasticity (storage modulus, loss modulus) of the polymer gel of Example 3 after gelation at 100° C. and constant temperature for 10 days was measured using an Austrian MCR301 rheometer and a lamina system.

[0052] Oscillation frequency scanning, select 10% to 30% of the upper limit stress value of the linear viscoelastic region as the stress value. In order to speed up the test, the frequency range of 0.01 to 10 Hz is scanned to determine the relationship between the storage modulus G', loss modulus G" and frequency f. The test temperature is 25 ° C. The test results are shown in Figure 2 .

[0053] from Figure 2 It can be seen that the storage modulus G' of the polymer gel is higher than the loss modulus G", and the storage modulus G' is stable at around 50Pa.

[0054] (3) Gel thermal stability test

[0055] The thermal stability of the polymer gel of Example 3 after gelation at 100°C and constant temperature for 100 days was measured using a METTLER thermogravimetric analyzer (TGA).

[0056] After gelation at 100°C and constant temperature for 100 days, the polymer gel of Example 3 was placed in a 200°C oven for 48 hours until it was completely dried and crushed. 1 to 2 mg of the sample was placed in a thermogravimetric analyzer to test the mass fraction change of the polymer gel in the range of 0 to 600°C. The test frequency was 6°C each time. The test results are shown in Figure 3 .

[0057] from Figure 3 It can be seen that the polymer gel has two obvious weight loss steps. The first weight loss step is at 175-225°C, with a weight change range of about 5%, which is mainly attributed to the heat loss of the sample polymer itself. The second weight loss step appears at 325-400°C, when the amide groups formed by the polymer and phenolic resin in the gel structure begin to decompose, with a weight loss of about 15%. The final residual mass of the polymer gel is 58.82%.

[0058] Embodiment 4:

[0059] This embodiment provides a polymer gel for CO2 flooding and sealing in high-temperature oil reservoirs, which includes the following components by mass percentage: 1.0% partially hydrolyzed polyacrylamide, 2.0% phenolic resin, 0.5% aluminum citrate, 0.8% thiourea, and the balance is water.

[0060] (1) Gelation time and gel strength test:

[0061] The prepared polymer gel solution was placed in 100°C, the gelling time was observed and recorded, and the "visual code evaluation method" commonly used in the petroleum industry was used to evaluate and record the change in gel strength after 10 days, 30 days, 60 days, and 100 days ( Figure 1d ).

[0062] The polymer gel gelled in 24 hours, changing from a liquid flow state to a gel, and losing its flow properties. The gel strength at 10 days, 30 days, 60 days, and 100 days after gelling was H grade, showing a low deformation flow gel, basically no flow, with a tongue length, but the tongue length was short.

[0063] (2) Gel viscoelasticity test

[0064] The viscoelasticity (storage modulus, loss modulus) of the polymer gel of Example 4 after gelation at 100° C. and constant temperature for 10 days was measured using an Austrian MCR301 rheometer and a lamina system.

[0065] Oscillation frequency scanning, select 10% to 30% of the upper limit stress value of the linear viscoelastic region as the stress value. In order to speed up the test, the frequency range of 0.01 to 10 Hz is scanned to determine the relationship between the storage modulus G', loss modulus G" and frequency f. The test temperature is 25 ° C. The test results are shown in Figure 2 .

[0066] from Figure 2 It can be seen that the storage modulus G' of the polymer gel is higher than the loss modulus G", and the storage modulus G' is stable at around 60Pa.

[0067] (3) Gel thermal stability test

[0068] The thermal stability of the polymer gel of Example 4 after gelation at 100°C and constant temperature for 100 days was measured using a METTLER thermogravimetric analyzer (TGA).

[0069] The polymer gel of Example 1, which was gelled at 100°C and kept at a constant temperature for 100 days, was placed in a 200°C oven for 48 hours until it was completely dried and crushed. 1 to 2 mg of the sample was placed in a thermogravimetric analyzer to test the mass fraction change of the polymer gel in the range of 0 to 600°C. The test frequency was 6°C each time. The test results are shown in Figure 3 .

[0070] from Figure 3It can be seen that the polymer gel has two obvious weight loss steps. The first weight loss step is at 175-225°C, with a weight change range of about 5%, which is mainly attributed to the heat loss of the sample polymer itself. The second weight loss step appears at 325-400°C, when the amide groups formed by the polymer and phenolic resin in the gel structure begin to decompose, with a weight loss of about 15%. The final residual mass of the polymer gel is 60.33%.

[0071] The above-described embodiments are only preferred embodiments of the present invention, but not all feasible embodiments of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.

Claims

1. A polymer gel for CO2 flooding and sealing in high-temperature oil reservoirs, characterized in that: The components include 0.4wt%-1wt% of partially hydrolyzed polyacrylamide, 0.5wt%-2wt% of phenolic resin, 0.2wt%-0.5wt% of aluminum citrate, 0.2wt%-0.8wt% of thiourea, and the balance is water.

2. The polymer gel for CO2 flooding and sealing in high-temperature oil reservoirs according to claim 1, characterized in that: The molecular weight of the partially hydrolyzed polyacrylamide is 12 million, and the degree of hydrolysis is 0-2%.

3. The polymer gel for CO2 flooding and sealing in high-temperature oil reservoirs according to claim 1, characterized in that: The phenolic resin is an industrial-grade water-soluble phenolic resin, and the mass percentage of phenolic resin is 35%.

4. The polymer gel for CO2 flooding and sealing in high-temperature oil reservoirs according to claim 1, characterized in that: The water is mineralized water with a concentration of more than 10,000 mg / L, wherein the content of calcium and magnesium ions is about 40 mg / L.

5. The method for preparing a polymer gel for CO2 flooding and sealing in high-temperature oil reservoirs according to claim 1, characterized in that: The following steps are involved: S1. Dissolve partially hydrolyzed polyacrylamide in water and stir to ripen; S2. Add phenolic resin, aluminum citrate, and thiourea in sequence, stir to fully dissolve, and add acid dropwise to adjust the pH to 2-3 to simulate the CO2 flooding environment; S3. The reaction mixture in step S2 is placed in an ampoule and sealed by introducing CO2, and then placed in an oven to polymerize to obtain a polymer gel suitable for CO2 flooding and sealing of high-temperature oil reservoirs.

6. The method for preparing a polymer gel for CO2 flooding and sealing in high-temperature oil reservoirs according to claim 5, characterized in that: The acid added dropwise in step S2 is dilute hydrochloric acid.

7. The method for preparing a polymer gel for CO2 flooding and sealing in high-temperature oil reservoirs according to claim 5, characterized in that: The temperature of the oven in step S3 is set to 100°C.

8. The method for preparing a polymer gel for CO2 flooding and sealing in high-temperature oil reservoirs according to claim 5, characterized in that: The time of placing in the oven in step S3 is 1-3 days.

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