The present invention imposes no specific limitations on the conditions for the gelation treatment in step (3). A person skilled in the art may employ known operations and process conditions in the field, such as, by way of example, carrying it out under static conditions.

Preferably, in step (4), the conditions for the drying treatment include: a temperature of 40-90° C. and a duration of 20-72 h.

According to a particularly preferred embodiment, the method further includes, in step (2), after performing the first contact, adjusting the pH of Solution 2 to 7-8 before proceeding to step (3). The inventors of the present invention have found that, under these preferred conditions, the CO₂-responsive groups in the second monomer of the present scheme exist in a non-ionic state in this pH environment. This facilitates the shielding of crosslinking sites, avoids uncertainties in the subterranean crosslinking system, and simultaneously enhances the plugging capability under in-situ reservoir conditions.

Preferably, the method further includes, in step (4), after performing the drying treatment, subjecting the resulting dried product to a grinding treatment to obtain said gel with a particle diameter ranging from 20 nm to 10 mm. The inventors have found that, under this preferred condition, the mineralizable plugging gel provided by the scheme of the present invention exhibits superior CO₂plugging efficiency. Furthermore, the gel synthesis method described in the scheme of the present invention is a one-pot process; the bulk gel obtained after synthesis is difficult to reduce to the nanoscale through mechanical grinding alone. However, under identical synthesis conditions, employing a reverse-phase microemulsion method and optimizing the particle size by controlling the water-to-oil ratio enables the synthesis of gel particles at the nanoscale (with a minimum achievable size of 20 nm). The present invention imposes no specific requirements on the conditions for said reverse-phase microemulsion method, which can be performed, for example, by referring to the method described in Energy & Fuels, 2018, *32*(3), 3068-3076 (DOI: 10.1021/acs.energyfuels.7b03649).

As mentioned previously, a third aspect of the present invention provides a gel prepared according to the second aspect.

As mentioned previously, a fourth aspect of the present invention provides the use of the gel according to the third aspect in at least one application selected from the group consisting of the field of oilfield production, the field of subterranean CO₂conformance control, and the field of CO₂geological storage.

The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, all instruments and raw materials used are commercially available products.

First Monomer I: 2-Acrylamido-2-methylpropanesulfonic acid, purchased from Shanghai Jizhi Biochemical Technology Co., Ltd., Catalog No. TCI-A0926-100G.

First Monomer II: Sodium Styrenesulfonate (SSS), purchased from Beijing Huawei Ruike Chemical Technology Co., Ltd., Catalog No. HWG00338.

Second Monomer I: N-Vinyl Pyrrolidone, purchased from Shanghai Jizhi Biochemical Technology Co., Ltd., Catalog No. V20730.

Second Monomer II: Dimethylaminoethyl Methacrylate, purchased from Beijing Innochem Science & Technology Co., Ltd., Catalog No. R004180.

Third Monomer: N-Isopropylacrylamide, purchased from Beijing Innochem Science & Technology Co., Ltd., Catalog No. T77704.

First crosslinking agent: Poly(ethylene glycol) diacrylate (PEGDA), purchased from Shanghai Titan Technology Co., Ltd., Catalog No. P17544.

Second acid-sensitive crosslinking agent: Phenylboronic acid pinacol ester, purchased from Shanghai Titan Technology Co., Ltd., Catalog No. GC37247.

Second temperature-sensitive crosslinking agent: 2-(3,4-Epoxycyclohexyl)ethyltrimethoxysilane, purchased from Beijing XBHA Chemical Co., Ltd., Catalog No. E156231.

Initiator: Ammonium persulfate.

Enhancer I: Nano-silica, average particle diameter 20 nm, purchased from Beijing Innochem Science & Technology Co., Ltd.

Enhancer II: Nano-silica, average particle diameter 500 nm, purchased from Shanghai Macklin Biochemical Technology Co., Ltd.

Room temperature or ambient temperature mentioned in this text refers to 25±2° C.

Example 1

- (1) First, pass nitrogen gas into water for 30 minutes, then add an enhancer and perform ultrasonic dispersion treatment for 30 minutes to obtain Solution 1;
- (2) At 40° C., add a monomer material containing Monomer I-1 and Monomer I-2 to Solution 1 for the first contact, then adjust the pH value with 40% NaOH to obtain Solution 2 with a pH of 7.5; the stirring speed for the first contact is 1200 rpm, and the stirring time is 2 hours;
- (3) At 40° C., sequentially add the first crosslinking agent, the second crosslinking agent, and the initiator to Solution 2 for the second contact; the stirring speed for the second contact is 1200 rpm, and the stirring time is 2 hours; then subject the obtained Solution 3 to gel-forming treatment to obtain Intermediate 1, where the gel-forming treatment is conducted by standing at 40° C. for 12 hours; (4) Dry Intermediate 1 at 80° C. for 24 hours, then perform crushing treatment to obtain the temperature-resistant, salt-tolerant in-situ plugging enhanced gel, named Gel-1, with an average particle diameter of 100 μm.

The remaining specific process parameters of this example are shown in Table 1.

FIG. 1 is a physical photograph of the temperature-resistant, salt-tolerant in-situ plugging enhanced gel Gel-1, where 1 represents the bulk integral gel and 2 represents the crushed gel particles.

Example 2

The same process as Example 1 was adopted, with the difference that the monomer material further contained a third monomer (N-isopropylacrylamide); all other steps were the same as Example 1, and a particle gel was obtained, named Gel-2.

The remaining specific process parameters of this example are shown in Table 1.

Examples 3-7

The same process as Example 1 was adopted, with the differences in raw material types/amounts or process parameters; details are shown in Table 1, and temperature-resistant, salt-tolerant in-situ plugging enhanced gels were obtained.

Example 8

The same process as Example 1 was adopted, with the difference that the amounts of raw materials were obtained through the following method:

- Collect the formula data and performance indicators of Examples 1-7 and Comparative Example 1 (Tables 2 and 3), and extract the following features: monomer type, content, number of crosslinking agent functional groups, enhancer particle size, and process parameters (temperature, time);
- Use a random forest algorithm to train a prediction model with re-crosslinking time, CO₂breakthrough pressure, and plugging rate as output targets, and set optimization objectives: re-crosslinking time ≤5 h at 150° C., breakthrough pressure ≥6.0 MPa/m, and plugging rate ≥99%;
- Search within the component range of Claim 1 using a genetic algorithm to obtain the optimized formula.

The remaining specific process parameters of this example are shown in Table 1.

TABLE 1

case 1
case 2
case 3
case 4
case 5
case 6
case 7
case 8

enhancer

Type
Agent I
Agent I
Agent I
Agent I
Agent I
Agent I
Agent II
Agent I

Dosage/g
2.5
2.5
2.5
2.5
2.5
2.5
2.5
4

The first monomer

Type
M1 I
M1 I
M1 I +
M1I
M1I
M1I
M1I
M1I

M1II

Dosage/g
30
30
15 + 15
30
30
30
30
28

The second monomer

Type
M2 I
M2 I
M2 I
M2 II
M2 I
M2 I
M2 I
M2 I

Dosage/g
10
10
10
10
10
10
10
12

The third monomer

Type
/
NIPAM
/
/
/
/
/
/

Dosage/g
0
5
0
0
0
0
0
0

The first contact

T/° C.
40
40
40
40
40
40
40
40

RPM /rpm
1200
1200
800
1200
1200
1200
1200
1200

Time/h
2
2
2
2
2
2
2
2

the first crosslinking agent

Type
PEGDA
PEGDA
PEGDA
PEGDA
PEGDA
PEGDA
PEGDA
PEGDA

Dosage/g
0.1
0.1
0.1
0.1
0.2
0.1
0.1
0.08

The second crosslinking agent

Type
Ph-
ECETS
Ph-BPin
Ph-
Ph-
Ph-
Ph-BPin
Ph-

BPin

BPin
BPin
BPin

BPin

Dosage/g
0.2
0.2
0.2
0.2
0.1
0.2
0.2
0.15

Initiator

Type
APS
APS
APS
APS
APS
APS
APS
APS

Dosage/g
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2

Water

Dosage/g
57
52
57
57
57
57
57
55.57

The second contact

Temperature/
40
40
40
40
40
40
40
40

° C.

RPM /rpm
1200
1200
800
1200
1200
1200
1200
1200

Time/h
2
2
4
2
2
2
2
2

gel-forming treatment

T/° C.
40
40
40
40
40
60
40
40

Time/h
12
12
12
12
12
6
12
12

Drying treatment

T/° C.
80
80
80
80
80
80
80
80

Time/h
24
24
24
24
24
24
24
24

name
Gel-1
Gel-2
Gel-3
Gel-4
Gel-5
Gel-6
Gel-7
Gel-AI

Comparative Example 1

This comparative example was carried out using a method similar to that of Example 1, with the difference that in step (3), 0.3 g of the first crosslinking agent was added without adding the second crosslinking agent, and the temperature for gel-forming treatment after the second contact was increased to 80° C. All other steps were the same as in Example 1, and a granular gel was obtained, named KN-1.

Comparative Example 2

This comparative example was carried out using a method similar to that of Example 1, with the difference that in step (3), 0.3 g of the second crosslinking agent was added without adding the first crosslinking agent. All other steps were the same as in Example 1. The product prepared by this method failed to form a gel.

Test Example 1

Comparison of recrosslinking time: Using a high-precision electronic balance, 5 g of gel particles provided in Examples 1 to 7 were weighed respectively, placed in beakers containing the same volume of 10 wt % NaCl, and sealed with plastic wrap;

The beakers containing the gel samples were placed in a constant temperature incubator at 150° C., with this moment recorded as to.

The time t1 when weak crosslinking occurred between gel particles and the time t2 when the boundaries between particles disappeared were recorded. Table 2 shows the recrosslinking times of the temperature-resistant, salt-tolerant in-situ plugging reinforced gels Gel-1 to Gel-7 at 50° C., 100° C., and 150° C.

It can be seen from Table 2 that increasing temperature helps to shorten the recrosslinking time; at the same temperature, Gel-1 has the shortest recrosslinking time; when the particle diameter of the enhancer is too large, the sensitivity of the recrosslinking reaction to temperature is reduced, and the difference in recrosslinking time under different temperatures becomes smaller; the recrosslinking time of Gel-AI at 50° C. is 3.1 h, which is close to the predicted value (3 h).

TABLE 2

Temperature/

recrosslinking

° C.
t₁
t₂
time

Gel-1
50
8.8
12.2
3.4

100
7
10
3

150
6
8.5
2.5

Gel-2
50
No recrosslinking occurred

100
9.2
14.5
5.3

150
6.5
10.5
4

Gel-3
50
9.5
13.5
4

100
8.2
12
3.8

150
7.2
10.5
3.3

Gel-4
50
9.3
13.2
3.9

100
7.8
11.3
3.5

150
6.8
10
3.2

Gel-5
50
8.3
13.5
5.2

100
7.5
12.2
4.7

150
6.6
11
4.4

Gel-6
50
9
12.8
3.8

100
7.2
10.8
3.6

150
6.4
9.5
3.1

Gel-7
50
9.2
12.8
3.6

100
7
10.6
3.6

150
6.4
9.8
3.4

Test Example 2

Injectivity Test: This invention exemplarily provides the test results of the in-situ plugging reinforced gel in Example 1.

Experimental Equipment: High-temperature and high-pressure core displacement device.

Experimental Material: The in-situ plugging reinforced gel provided in Example 1 (with a particle diameter of 80-100 mesh, i.e., 150-177 μm).

Test Steps:

- 1) Using a high-precision electronic balance, weigh 10 g of gel particles, place them in a 1 L beaker filled with 10 wt % NaCl for swelling, let stand at room temperature for 24 hours, take out the swollen gel particles, and remove surface free water;
- 2) Place the treated granular gel in an intermediate container;
- 3) Prepare fractured cores with different fracture openings, including 0.1 mm, 0.3 mm, 0.5 mm, 1 mm, and 2 mm, and place the fractured cores in the core holder;