Tuff gas layer selective water shutoff agent, preparation method and application thereof, and tuff gas well water shutoff method

Abstract

The present application relates to the technical field of natural gas exploitation, and particularly relates to a tuff gas layer selective water plugging agent, a preparation method and application thereof, and a tuff gas well water plugging method. In terms of weight parts, the water plugging agent comprises: water-soluble silica gel 120-180 parts; suspending agent 0.5-5 parts; curing agent 60-100 parts; additive 5-25 parts; water 900-1100 parts; wherein the water-soluble silica gel contains silicon dioxide, sodium hydroxide, water glass and hydroxypropyl polymer, and the weight ratio of the silicon dioxide, sodium hydroxide, water glass and hydroxypropyl polymer is 1:1-2.5:0.1-1:0.001-0.01. The water plugging agent has the performance of low viscosity, high curing temperature, high strength and high temperature resistance. Meanwhile, the water plugging agent is used for gas well water plugging, has the characteristics of injection safety and accurate water plugging, and meets the selective water plugging demand of tuff gas layer.

Description

Technical Field

[0001] This invention relates to the field of natural gas extraction technology, specifically to a selective water-blocking agent for tuff gas reservoirs, its preparation method and application, and a method for water-blocking tuff gas wells. Background Technology

[0002] Tuff gas reservoirs exhibit significant permeability variations, strong heterogeneity, and well-developed fractures, typically requiring horizontal wells with screen completions. As gas well production progresses, if edge and bottom water breaches and enters the formation, it floods the well, preventing gas production. The well's water cut rises rapidly, leading to a decrease in natural gas production, ultimately resulting in well shutdown. Currently, commonly used water-blocking agents include polymer gels, cement-based agents, and precipitants. However, polymer gel solutions have high viscosity and require high injection pressure, degrading in high-temperature formations and losing their sealing effect. Cement-based agents cannot pass smoothly through precision filter pipes and cannot be transported to the water-producing zone. Precipitants, injected separately using a two-liquid method, suffer from incomplete reaction, low dosage, and low strength. Therefore, conventional water-blocking techniques are not suitable for selective water plugging in tuff gas reservoirs. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned technical problems and provide a new selective water-blocking agent for tuff gas reservoirs, its preparation method and application, and a method for water-blocking tuff gas wells. This water-blocking agent can pass smoothly through the screen pipe, effectively block the water-producing section, and improve the development efficiency of the gas well.

[0004] To achieve the above objectives, the first aspect of the present invention provides a selective water-blocking agent for tuff gas reservoirs, comprising, by weight: 120-180 parts of water-soluble silica gel; 0.5-5 parts of suspending agent; 60-100 parts of curing agent; 5-25 parts of additives; and 900-1100 parts of water.

[0005] The water-soluble silica gel contains silicon dioxide, sodium hydroxide, water glass, and hydroxypropyl polymer, and the weight ratio of silicon dioxide, sodium hydroxide, water glass, and hydroxypropyl polymer is 1:1-2.5:0.1-1:0.001-0.01.

[0006] Preferably, the water-soluble silica gel is prepared by the following method: under high temperature and high pressure conditions, silica, sodium hydroxide and water glass are first subjected to a boiling reaction; then hydroxypropyl polymer is added to carry out a hydrolysis reaction.

[0007] Preferably, the viscosity of the water-blocking agent is ≤6 mPa·s (temperature 25°C, shear rate 7 s). -1The curing temperature is preferably 3-5 mPa·s; the curing temperature is ≥80℃, preferably 100-300℃; the curing strength is ≥500kPa, preferably 500-900kPa; and the temperature resistance is ≥90℃, preferably 90-300℃.

[0008] The second aspect of the present invention provides a method for preparing a selective water-blocking agent for tuff gas reservoirs, the method comprising: mixing water-soluble silica gel, a suspending agent, a curing agent, an additive and water to obtain a water-blocking agent;

[0009] The weight ratio of the water-soluble silica gel, suspending agent, curing agent, additives and water is 120-180:0.5-5:60-100:5-25:900-1100.

[0010] The water-soluble silica gel contains silicon dioxide, sodium hydroxide, water glass, and hydroxypropyl polymer, and the weight ratio of silicon dioxide, sodium hydroxide, water glass, and hydroxypropyl polymer is 1:1-2.5:0.1-1:0.001-0.01.

[0011] Preferably, the mixing process includes:

[0012] (1) The additive and water are first mixed to obtain a mixture;

[0013] (2) The mixture, water-soluble silica gel, suspending agent and curing agent are mixed for a second time to obtain the water-blocking agent.

[0014] The third aspect of the present invention provides a water-blocking agent provided in the first aspect, or a water-blocking agent prepared by the method provided in the second aspect, for use in water plugging in gas wells.

[0015] A fourth aspect of the present invention provides a method for plugging water in a tuff gas well, the method comprising:

[0016] When the gas reservoir temperature is ≥80℃, the water-blocking agent provided in the first aspect is injected into the tuff gas well, or the water-blocking agent prepared by the method provided in the second aspect is solidified; or...

[0017] When the gas reservoir temperature is <80℃, steam is first injected into the tuff gas well; then the water-blocking agent provided in the first aspect or the water-blocking agent prepared by the method provided in the second aspect is injected; finally, steam is injected to solidify the gas.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The water-blocking agent provided by the present invention, by limiting the water-blocking agent to include a specific weight part of water-soluble silica gel, suspending agent, curing agent, additive and water, and combining the synergistic effect of each component and the specific water-soluble silica gel, makes the water-blocking agent have the properties of low viscosity, high curing temperature, high strength and high temperature resistance; in particular, by adjusting the weight part of each component and the weight ratio of each component in the water-soluble silica gel, it is more conducive to improving the performance of the water-blocking agent.

[0020] (2) The water-blocking agent preparation method provided by the present invention simplifies the process flow, is easy to operate, and is convenient for on-site preparation;

[0021] (3) The water-blocking agent provided by the present invention is used for water plugging in gas wells. It has the characteristics of safe injection and accurate water plugging, which meets the selective water plugging requirements of tuff gas layers. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] In this invention, unless otherwise specified, the terms "first" and "second" do not indicate a sequence or limit the specific materials or steps; they are merely used to distinguish that these are not the same material or step. For example, in "first mixture" and "second mixture," "first" and "second" are used only to indicate that these are not the same mixture.

[0024] The first aspect of this invention provides a selective water-blocking agent for tuff gas reservoirs, comprising, by weight: 120-180 parts of water-soluble silica gel; 0.5-5 parts of suspending agent; 60-100 parts of curing agent; 5-25 parts of additives; and 900-1100 parts of water.

[0025] The water-soluble silica gel contains silicon dioxide, sodium hydroxide, water glass, and hydroxypropyl polymer, and the weight ratio of silicon dioxide, sodium hydroxide, water glass, and hydroxypropyl polymer is 1:1-2.5:0.1-1:0.001-0.01.

[0026] In this invention, unless otherwise specified, the water-blocking agent refers to a selective water-blocking agent for tuff gas reservoirs.

[0027] In some embodiments of the present invention, preferably, the water-blocking agent comprises, by weight: 130-160 parts of water-soluble silica gel; 0.5-2 parts of suspending agent; 70-90 parts of curing agent; 10-20 parts of additives; and 950-1050 parts of water. Using these preferred conditions is beneficial for improving the performance of the water-blocking agent, namely, enabling it to possess low viscosity, high curing temperature, high strength, and high temperature resistance.

[0028] In some embodiments of the present invention, preferably, the water-blocking agent comprises, by weight: 140-150 parts of water-soluble silica gel; 1-2 parts of suspending agent; 70-80 parts of curing agent; 12-18 parts of additives; and 980-1020 parts of water. Using these preferred conditions is more conducive to improving the performance of the water-blocking agent, that is, enabling the water-blocking agent to possess low viscosity, high curing temperature, high strength, and high temperature resistance.

[0029] In some embodiments of the present invention, preferably, the weight ratio of silica, sodium hydroxide, water glass, and hydroxypropyl polymer in the water-soluble silica gel is 1:1.5-2:0.2-0.5:0.002-0.006. Using these preferred conditions, a uniform and stable water-soluble silica gel is obtained to meet the performance requirements for forming a water-blocking agent.

[0030] In this invention, the preparation method of the water-soluble silica gel has a wide range of options, as long as the weight ratio of each component in the water-soluble silica gel meets the above-mentioned limitations. Preferably, the water-soluble silica gel is prepared by the following method: under high temperature and high pressure conditions, silica, sodium hydroxide, and water glass are first subjected to a boiling reaction; then, a hydroxypropyl polymer is added for a hydrolysis reaction. This setup ensures the formation of water-soluble silica gel, and under certain conditions, the liquid-phase water-blocking agent solidifies into a solid phase.

[0031] In some embodiments of the present invention, preferably, the conditions of high temperature and high pressure include: a temperature of 180-250°C, more preferably 200-220°C; and a pressure of 1-3 MPa, more preferably 1.5-2 MPa. In the present invention, unless otherwise specified, pressure refers to gauge pressure.

[0032] In this invention, the cooking reaction ensures the complete dissolution of silicon dioxide, sodium hydroxide, and water glass. Preferably, the cooking reaction time is 1-10 hours, more preferably 1-5 hours.

[0033] In this invention, the hydrolysis reaction aims to obtain homogeneous and stable water-soluble silica gel. Preferably, the hydrolysis reaction time is 5-15 hours, more preferably 5-10 hours.

[0034] In some embodiments of the present invention, preferably, the weight-average molecular weight of the hydroxypropyl polymer is 150,000-230,000 g / mol, including but not limited to polymannose.

[0035] In some embodiments of the present invention, preferably, the suspending agent is selected from lignin sulfonate, and more preferably, the suspending agent is selected from sodium lignin sulfonate and / or calcium lignin sulfonate.

[0036] In some embodiments of the present invention, preferably, the curing agent contains trioxane and o-phenylenediamine; wherein the weight ratio of trioxane to o-phenylenediamine is 5-10:1, for example, 5:1, 6:1, 8:1, 9:1, 10:1, and any value within the range of any two values, preferably 8-10:1.

[0037] In some embodiments of the present invention, preferably, the additive is selected from alkaline oxides; wherein, the alkaline oxides include, but are not limited to, sodium hydroxide and potassium hydroxide; and the shape of the alkaline oxides includes, but is not limited to, granules, powders, etc.

[0038] According to the present invention, preferably, the viscosity of the water-blocking agent is ≤6 mPa·s (temperature 25°C, shear rate 7 s). -1 The curing temperature is preferably 3-5 mPa·s; the curing temperature is ≥80℃, preferably 100-300℃; the curing strength is ≥500kPa, preferably 500-900kPa; and the temperature resistance is ≥90℃, preferably 90-300℃.

[0039] In this invention, unless otherwise specified, the viscosity parameter is measured using a Brookfield viscometer; the curing temperature parameter is measured at different times for parallel samples. The curing temperature parameter refers to the temperature at which the water-blocking agent transforms from a liquid phase to a solid phase.

[0040] The second aspect of the present invention provides a method for preparing a selective water-blocking agent for tuff gas reservoirs, the method comprising: mixing water-soluble silica gel, a suspending agent, a curing agent, an additive and water to obtain a water-blocking agent;

[0041] The weight ratio of the water-soluble silica gel, suspending agent, curing agent, additives and water is 120-180:0.5-5:60-100:5-25:900-1100.

[0042] The water-soluble silica gel contains silicon dioxide, sodium hydroxide, water glass, and hydroxypropyl polymer, and the weight ratio of silicon dioxide, sodium hydroxide, water glass, and hydroxypropyl polymer is 1:1-2.5:0.1-1:0.001-0.01.

[0043] In this invention, unless otherwise specified, the types of water-soluble silica gel, suspending agent, curing agent and additives are all as defined above, and this invention will not elaborate further.

[0044] In this invention, the mixing process aims to uniformly mix the water-soluble silica gel, suspending agent, curing agent, additives, and water. Preferably, the mixing process includes: (1) first mixing the additives and water to obtain a mixture; (2) second mixing the mixture, water-soluble silica gel, suspending agent, and curing agent to obtain the water-blocking agent. This method ensures thorough mixing and complete dissolution, forming a uniform liquid and guaranteeing that the water-blocking agent cures into a complete cured body.

[0045] In some embodiments of the present invention, preferably, the conditions for the first mixing and the second mixing each independently include: a temperature of 15-40°C, preferably 20-30°C; and a time of 0.1-5h, preferably 0.5-2h.

[0046] In some embodiments of the present invention, preferably, the weight ratio of the water-soluble silica gel, suspending agent, curing agent, additive, and water is 130-160:0.5-2:70-90:10-20:950-1050, more preferably 140-150:1-2:70-80:12-18:980-1020. In the present invention, unless otherwise specified, the weight ratio of each material is equivalent to the feeding ratio of each material.

[0047] The third aspect of the present invention provides a water-blocking agent provided in the first aspect, or a water-blocking agent prepared by the method provided in the second aspect, for use in water plugging in gas wells.

[0048] The water-blocking agent provided by this invention has the characteristics of low viscosity and high curing temperature. It can easily enter the aqueous phase of the tuff gas layer, but it is not easy to enter the gas phase of the tuff gas layer. It can form a solidified body at a temperature ≥80℃, preferably 100-300℃, to block the water outlet channel and ensure the water-blocking effect of the solidified body.

[0049] A fourth aspect of the present invention provides a method for plugging water in a tuff gas well, the method comprising:

[0050] When the gas reservoir temperature is ≥80℃, the water-blocking agent provided in the first aspect is injected into the tuff gas well, or the water-blocking agent prepared by the method provided in the second aspect is solidified; or...

[0051] When the gas reservoir temperature is <80℃, steam is first injected into the tuff gas well; then the water-blocking agent provided in the first aspect or the water-blocking agent prepared by the method provided in the second aspect is injected; finally, steam is injected to solidify the gas.

[0052] In some embodiments of the present invention, preferably, the injection rate of the water-blocking agent is 6-10 m / s. 3 / h; Formation fracturing pressure with an injection pressure ≤80%.

[0053] According to a particularly preferred embodiment of the present invention, a selective water-blocking agent for tuff gas layers, by weight, comprises: 140-150 parts water-soluble silica gel; 1-2 parts suspending agent; 70-80 parts curing agent; 12-18 parts additives; and 980-1020 parts water.

[0054] In the water-soluble silica gel, the weight ratio of silica, sodium hydroxide, water glass and hydroxypropyl polymer is 1:1.5-2:0.2-0.5:0.002-0.006.

[0055] The viscosity of the water-blocking agent is ≤6 mPa·s (temperature 25℃, shear rate 7s). -1 Curing temperature ≥80℃; Curing strength ≥500kPa; Temperature resistance ≥90℃.

[0056] The present invention will be described in detail below through embodiments.

[0057] The physical properties of the water-blocking agents (S1-S9 and DS1-DS3) prepared in Examples 1-9 and Comparative Examples 1-3 are listed in Table 1.

[0058] Preparation Example 1

[0059] Under high temperature and high pressure conditions (temperature 200℃; pressure 1.5MPa), silica, sodium hydroxide, and water glass were first subjected to a boiling reaction for 3 hours; then, hydroxypropyl polymer (polymannose, weight average molecular weight 2×10⁻⁶) was added. 5 The water-soluble silica gel P1 was obtained by hydrolyzing the silica gel (g / mol) for 6 hours.

[0060] The weight ratio of silicon dioxide, sodium hydroxide, water glass and hydroxypropyl polymer is 1:1.8:0.25:0.004.

[0061] Preparation Example 2

[0062] Following the method of Preparation Example 1, except that the high temperature and high pressure conditions were different, namely, the temperature was 190°C and the pressure was 1 MPa; the other conditions were the same, and water-soluble silica gel P2 was obtained.

[0063] Preparation Example 3

[0064] Following the method of Preparation Example 1, except that the weight ratio of silica, sodium hydroxide, water glass and hydroxypropyl polymer was 1:1:0.1:0.001, water-soluble silica gel P3 was obtained.

[0065] Preparation Example 4

[0066] Following the method of Preparation Example 1, except that the weight ratio of silica, sodium hydroxide, water glass and hydroxypropyl polymer was 1:3:2:0.1, and the other conditions were the same, water-soluble silica gel P4 was obtained.

[0067] Example 1

[0068] (1) Mix 15 parts by weight of the auxiliary agent (granular sodium hydroxide) and 1000 parts by weight of water in the first mixing (temperature 25℃; time 1h) to obtain a mixture;

[0069] (2) The above mixture, 145 parts by weight of water-soluble silica gel P1, 1.5 parts by weight of suspending agent (sodium lignosulfonate) and 75 parts by weight of curing agent (trioxane and o-phenylenediamine, with a weight ratio of trioxane and o-phenylenediamine of 9:1) are mixed for a second time (at a temperature of 25°C for 1 hour) to obtain water-blocking agent S1.

[0070] Example 2

[0071] (1) 12 parts by weight of auxiliary agent (granular sodium hydroxide) and 980 parts by weight of water were mixed for the first time (temperature 30℃; time 0.5h) to obtain a mixture;

[0072] (2) The above mixture, 140 parts by weight of water-soluble silica gel P1, 1 part by weight of suspending agent (calcium lignosulfonate) and 70 parts by weight of curing agent (trioxane and o-phenylenediamine, with a weight ratio of trioxane and o-phenylenediamine of 8:1) are mixed for a second time (at a temperature of 30°C for 0.5 h) to obtain water-blocking agent S2.

[0073] Example 3

[0074] (1) Mix 18 parts by weight of the auxiliary agent (granular sodium hydroxide) and 1020 parts by weight of water in the first mixing (temperature 30℃; time 0.5h) to obtain a mixture;

[0075] (2) The above mixture, 150 parts by weight of water-soluble silica gel P1, 2 parts by weight of suspending agent (calcium lignosulfonate) and 80 parts by weight of curing agent (trioxane and o-phenylenediamine, with a weight ratio of trioxane and o-phenylenediamine of 10:1) are mixed for a second time (at a temperature of 30°C for 0.5 h) to obtain water-blocking agent S3.

[0076] Example 4

[0077] (1) Mix 10 parts by weight of the auxiliary agent (granular potassium hydroxide) and 1000 parts by weight of water in the first mixing (temperature 25℃; time 1h) to obtain a mixture;

[0078] (2) The above mixture, 130 parts by weight of water-soluble silica gel P1, 0.5 parts by weight of suspending agent (sodium lignosulfonate) and 85 parts by weight of curing agent (trioxane and o-phenylenediamine, with a weight ratio of trioxane and o-phenylenediamine of 9:1) are mixed for a second time (at a temperature of 25°C for 1 hour) to obtain water-blocking agent S4.

[0079] Example 5

[0080] (1) Mix 5 parts by weight of the auxiliary agent (granular potassium hydroxide) and 1000 parts by weight of water in the first mixing (temperature 25℃; time 1h) to obtain a mixture;

[0081] (2) The above mixture, 170 parts by weight of water-soluble silica gel P1, 3 parts by weight of suspending agent (sodium lignosulfonate) and 65 parts by weight of curing agent (trioxane and o-phenylenediamine, with a weight ratio of trioxane and o-phenylenediamine of 9:1) are mixed for a second time (at a temperature of 25°C for 1 hour) to obtain water-blocking agent S5.

[0082] Example 6

[0083] The method of Example 1 is followed, except that in step (2), 145 parts by weight of water-soluble silica gel P1 is replaced with 145 parts by weight of water-soluble silica gel P2, and the other conditions are the same, to obtain water-blocking agent S6.

[0084] Example 7

[0085] The method of Example 1 is followed, except that in step (2), 145 parts by weight of water-soluble silica gel P1 is replaced with 145 parts by weight of water-soluble silica gel P3, while the other conditions are the same, to obtain water-blocking agent S7.

[0086] Example 8

[0087] The method of Example 1 is followed, except that in step (2), the weight ratio of trioxane and o-phenylenediamine in 75 parts by weight of curing agent is replaced with 5:1, and the other conditions are the same, to obtain water-blocking agent S8.

[0088] Example 9

[0089] The method of Example 1 is followed, except that the components are directly mixed. Specifically, 15 parts by weight of additive (granular sodium hydroxide), 145 parts by weight of water-soluble silica gel P1, 1.5 parts by weight of suspending agent (sodium lignosulfonate), 75 parts by weight of curing agent (trioxane and o-phenylenediamine, with a weight ratio of trioxane to o-phenylenediamine of 9:1) and 1000 parts by weight of water are mixed (at a temperature of 25°C for 2 hours) to obtain water-blocking agent S9.

[0090] Comparative Example 1

[0091] Following the method of Example 1, except that 145 parts by weight of water-soluble silica gel P1 was replaced with 145 parts by weight of water-soluble silica gel P4, while the other conditions remained the same, water-blocking agent DS1 was obtained.

[0092] Comparative Example 2

[0093] Following the method of Example 1, except that 145 parts by weight of water-soluble silica gel P1 was replaced with 145 parts by weight of sodium silicate, while the other conditions remained the same, water-blocking agent DS2 was obtained.

[0094] Comparative Example 3

[0095] The method of Example 1 is different except that (1) 4 parts by weight of the auxiliary agent (granular sodium hydroxide) and 1000 parts by weight of water are first mixed (temperature is 25°C; time is 1h) to obtain a mixture;

[0096] (2) The above mixture, 115 parts by weight of water-soluble silica gel P1, 0.4 parts by weight of suspending agent (sodium lignosulfonate) and 55 parts by weight of curing agent (trioxane and o-phenylenediamine, with a weight ratio of trioxane and o-phenylenediamine of 9:1) were mixed for a second time (at a temperature of 25°C for 1 hour) to obtain water-blocking agent DS3.

[0097] Table 1

[0098]

[0099] Note: * - Weight ratio of water-soluble silica gel, suspending agent, curing agent, additives and water.

[0100] As shown in Table 1, compared to Comparative Examples 1-3, the water-blocking agents prepared in Examples 1-9 possess high curing temperature, high curing strength, high temperature resistance, and low viscosity. In other words, the selective water-blocking agent for tuff gas formations provided by this invention exhibits excellent high-temperature curing and high-strength properties.

[0101] Test case

[0102] The water-blocking agents (S1-S9 and DS1-DS3) prepared in Examples 1-9 and Comparative Examples 1-3 were tested for their precipitation effects. The test results are listed in Table 2.

[0103] Test conditions: Core tube: Φ2.5cm×40cm; stainless steel core tube; horizontal flow pump working pressure: 0-20MPa; flow rate: 0.1-20mL / min; flow rate accuracy: 0.5%; constant temperature chamber temperature ≤200℃; accuracy: 0.1℃.

[0104] Test based on actual results:

[0105] ① Fill the core tube with a certain permeability according to the design, then saturate the core tube with simulated water under vacuum, and measure the pore volume of the core.

[0106] ② Inject water at a rate of 1 mL / min. After the injection pressure stabilizes, test the water or gas phase permeability of the core tube.

[0107] ③ Inject 2.5 PV of water-blocking agent at a rate of 1 mL / min, record the injection pressure, and calculate the resistance coefficient. Seal both ends, place in a constant temperature chamber, and wait for curing at the set temperature for 48 hours.

[0108] ④ After the water has solidified, inject water at a rate of 1 ml / min. After injecting water for 5 PV, record the pressure value during the experiment and calculate the water blocking rate.

[0109] Table 2

[0110]

[0111]

[0112] As can be seen from the results in Table 2, compared with Comparative Examples 1-3, the water-blocking agent provided by the present invention has a higher water-blocking rate. In particular, by controlling the content of each component in the water-blocking agent within the preferred protection range, it is more conducive to improving the water-blocking efficiency of the water-blocking agent.

[0113] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A selective water-blocking agent for tuff gas reservoirs, characterized in that, By weight, the water-blocking agent comprises: 120-180 parts water-soluble silica gel; 0.5-5 parts suspending agent; 60-100 parts curing agent; 5-25 parts additives; and 900-1100 parts water. The curing agent contains trioxane and o-phenylenediamine; The auxiliary agent is selected from alkaline hydroxides; The water-soluble silica gel contains silica, sodium hydroxide, water glass, and hydroxypropyl polymer, and the weight ratio of silica, sodium hydroxide, water glass, and hydroxypropyl polymer is 1:1-2.5:0.1-1:0.001-0.

01. The hydroxypropyl polymer is selected from polymannose.

2. The water-blocking agent according to claim 1, wherein, By weight, the water-blocking agent comprises: 130-160 parts of water-soluble silica gel; 0.5-2 parts of suspending agent; 70-90 parts of curing agent; 10-20 parts of additives; and 950-1050 parts of water.

3. The water-blocking agent according to claim 2, wherein, By weight, the water-blocking agent comprises: 140-150 parts water-soluble silica gel; 1-2 parts suspending agent; 70-80 parts curing agent; 12-18 parts additives; and 980-1020 parts water.

4. The water-blocking agent according to claim 1, wherein, In the water-soluble silica gel, the weight ratio of silica, sodium hydroxide, water glass and hydroxypropyl polymer is 1:1.5-2:0.2-0.5:0.002-0.

006.

5. The water-blocking agent according to claim 4, wherein, The water-soluble silica gel is prepared by the following method: under high temperature and high pressure conditions, silica, sodium hydroxide and water glass are first subjected to a boiling reaction; then hydroxypropyl polymer is added to carry out a hydrolysis reaction.

6. The water-blocking agent according to claim 5, wherein, The conditions for high temperature and high pressure include: temperature of 180-250℃ and pressure of 1-3MPa.

7. The water-blocking agent according to claim 6, wherein, The conditions for high temperature and high pressure include: a temperature of 200-220℃ and a pressure of 1.5-2MPa.

8. The water-blocking agent according to claim 5, wherein, The cooking reaction time is 1-10 hours.

9. The water-blocking agent according to claim 8, wherein, The cooking reaction time is 1-5 hours.

10. The water-blocking agent according to claim 5, wherein, The hydrolysis reaction takes 5-15 hours.

11. The water-blocking agent according to claim 10, wherein, The hydrolysis reaction takes 5-10 hours.

12. The water-blocking agent according to claim 1, wherein, The weight-average molecular weight of the hydroxypropyl polymer is (1.5-2.3)×10⁻⁶. 5 g / mol.

13. The water-blocking agent according to claim 1, wherein, The suspending agent is selected from lignin sulfonate.

14. The water-blocking agent according to claim 13, wherein, The suspending agent is selected from sodium lignosulfonate and / or calcium lignosulfonate.

15. The water-blocking agent according to claim 1, wherein, The weight ratio of trioxane to o-phenylenediamine is 5-10:

1.

16. The water-blocking agent according to claim 15, wherein, The weight ratio of trioxane to o-phenylenediamine is 8-10:

1.

17. The water-blocking agent according to any one of claims 1-16, wherein, At a temperature of 25°C and a shear rate of 7 s, -1 The viscosity of the water-blocking agent is measured at 25°C and a shear rate of 7 s. -1 ≤6mPa·s; curing temperature ≥80℃; curing strength ≥500kPa; temperature resistance ≥90℃.

18. The water-blocking agent according to claim 17, wherein, At a temperature of 25°C and a shear rate of 7 s, -1 The viscosity of the water-blocking agent is 3-5 mPa·s; the curing temperature is 100-300℃; the curing strength is 500-900 kPa; and the temperature resistance is 90-300℃.

19. A method for preparing a selective water-blocking agent for tuff gas reservoirs, characterized in that, The preparation method includes: mixing water-soluble silica gel, suspending agent, curing agent, additives and water to obtain a water-blocking agent; The weight ratio of the water-soluble silica gel, suspending agent, curing agent, additives and water is 120-180:0.5-5:60-100:5-25:900-1100. The water-soluble silica gel contains silicon dioxide, sodium hydroxide, water glass, and hydroxypropyl polymer, and the weight ratio of silicon dioxide, sodium hydroxide, water glass, and hydroxypropyl polymer is 1:1-2.5:0.1-1:0.001-0.

01.

20. The preparation method according to claim 19, wherein, The mixing process includes: (1) The additive and water are mixed for the first time to obtain a mixture; (2) The mixture, water-soluble silica gel, suspending agent and curing agent are mixed for a second time to obtain the water-blocking agent.

21. The preparation method according to claim 20, wherein, The conditions for the first and second mixing independently include: a temperature of 15-40°C and a time of 0.1-5 hours.

22. The preparation method according to claim 21, wherein, The conditions for the first and second mixing independently include: a temperature of 20-30°C and a time of 0.5-2 hours.

23. The preparation method according to claim 19, wherein, The weight ratio of the water-soluble silica gel, suspending agent, curing agent, additives and water is 130-160:0.5-2:70-90:10-20:950-1050.

24. The preparation method according to claim 23, wherein, The weight ratio of the water-soluble silica gel, suspending agent, curing agent, additives and water is 140-150:1-2:70-80:12-18:980-1020.

25. The water shut-off agent according to any one of claims 1-18, or the water shut-off agent prepared by the method according to any one of claims 19-24, for use in water shut-off in gas wells.

26. The water-blocking agent according to any one of claims 1-18, or the water-blocking agent prepared by the method according to any one of claims 19-24, is used for water plugging in tuff gas wells.

27. A method for plugging water in a tuff gas well, characterized in that, The method includes: When the gas reservoir temperature is ≥80℃, the water-blocking agent according to any one of claims 1-18 is injected into the tuff gas well, or the water-blocking agent prepared by the method according to any one of claims 19-24 is solidified; or... When the gas reservoir temperature is <80℃, steam is first injected into the tuff gas well; then the water-blocking agent described in any one of claims 1-18, or the water-blocking agent prepared by the method described in any one of claims 19-24, is injected; finally, steam is injected to solidify the gas.

28. The method according to claim 27, wherein, The injection rate of the water-blocking agent is 6-10m. 3 / h; Formation fracturing pressure ≤80% of the injection pressure.

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