Reverse wetting agent

Abstract

The invention relates to a reverse wetting agent, and belongs to the technical field of oil and gas field chemicals. The wetting reversal agent is stable in performance, good in wetting improvement effect and wide in raw material source, the long-chain surfactant and the hydrophobic fumed silica in the wetting reversal agent show a good synergistic effect, the wetting improvement capability of the wetting reversal agent can be greatly enhanced, and the surface tension is further reduced. After the reverse wetting agent is injected into a stratum, a strong hydrophobic water control layer can be formed on the surface of rock, water locking formed in a gas reservoir pore throat due to invaded stratum water or injected fluid is relieved, the gas well productivity is recovered, and the reverse wetting agent has the performance characteristic more excellent than that of a fluorine-containing reverse wetting agent.

Description

Technical Field

[0001] The present invention relates to a wetting reversal agent, belonging to the technical field of oil and gas field chemicals. Background Art

[0002] During the development of gas reservoirs, the intrusion of edge and bottom water into natural gas reservoirs will cause a significant decline in the productivity of gas wells, or even lead to the shutdown of gas wells, through ways such as trapping, blocking, and water locking. The "water locking" formed by the external fluids injected during reservoir stimulation measures such as acidification and fracturing, which cannot be fully discharged, will also hinder the flow of natural gas and affect the productivity of gas wells. The occurrence of these problems is related to the change of reservoir wettability.

[0003] According to literature reports, reservoir wettability is a key factor affecting the recovery rate of oil and gas reservoirs. The crude oil recovery rate of water-wet reservoirs is significantly higher than that of oil-wet reservoirs. The currently published literature and patents related to wetting reversal agents are mainly used to improve the recovery rate of oil reservoirs. By using a solution mainly composed of surfactants or surfactant complexes, the wettability of the rock surface of oil reservoir is changed from oil-wet to water-wet, so as to reduce the seepage resistance of the water phase, improve the water flooding development effect, and increase the crude oil recovery rate.

[0004] In the field of natural gas development, Chinese patent document CN103498650B discloses a surfactant composed of perfluorooctylsulfonamide propylamine oxide and fatty alcohol polyoxyethylene ether, and a gas wetting reversal agent prepared by adding a methanol or ethanol solvent. This wetting reversal agent can effectively change the surface of the coal seam from liquid wettability to neutral gas wettability. Chinese patent document CN104449631A provides a strong gas wetting reversal agent prepared from modified nano-silica treated with perfluoroethyl acrylate, emulsifier, sodium dodecyl sulfate, ethanol and water, which can change the surface of the core to strong gas wettability (i.e., the characteristics of being hydrophobic to both oil and water), effectively relieve the water locking damage, and is applicable to low-permeability oil and gas reservoirs. Chinese patent document CN110982009B discloses a fluoropolymer emulsion wetting reversal agent prepared by emulsion polymerization of fluorine-substituted acrylate and acrylic monomers at 75-85°C, which can change the surface of the core to strong hydrophobicity. The common feature of the above patent documents is the use of fluorocarbon surfactants or fluorine-substituted monomers. However, raw materials such as fluorocarbon surfactants and fluorine-substituted monomers have poor solubility, are difficult to disperse, and are expensive. These defects result in that such wetting reversal agents must be deeply processed before use and cannot be directly prepared and used on-site in the mine. The high price leads to a high use cost of such wetting reversal agents, which limits their application in the field of gas reservoir development. In addition, the wetting reversal agents prepared solely by using surfactants have limited effects and are difficult to last. Summary of the Invention

[0005] The purpose of the present invention is to provide a wettability reversal agent, which can solve the problems of high cost, poor wettability reversal effect and short validity period of the wettability reversal agent currently used in gas reservoirs.

[0006] In order to achieve the above objectives, the technical solution adopted by the wettability reversal agent of the present invention is:

[0007] A wettability reversal agent comprises hydrophobic fumed silica, a long-chain surfactant, an organic solvent and water; the average particle size of the hydrophobic fumed silica is not greater than 40 nm; the long-chain surfactant has no less than 6 and no more than 20 carbon atoms; the organic solvent is an organic solvent miscible with water; in the wettability reversal agent, the mass fraction of the hydrophobic fumed silica is 0.1-0.3%, and the mass fraction of the long-chain surfactant is 0.025-0.1%.

[0008] The wettability reversal agent of the present invention has stable performance, good wettability improvement effect, and a wide range of raw material sources. The long-chain surfactant in the wettability reversal agent and the hydrophobic fumed silica show a good synergistic effect, which can greatly enhance the wettability improvement ability of the wettability reversal agent and further reduce the surface tension. This is because the presence of a surfactant with low surface energy characteristics reduces the surface tension of the system, making it easier to adsorb with the hydrophobic fumed silica with a high specific surface area, and the formed synergist can establish a hydrophobic layer on the surface of the core, thereby showing super-hydrophobic properties. Therefore, after the wettability reversal agent of the present invention is injected into the formation, a strong hydrophobic water-controlling layer can be formed on the surface of the rock, which can remove the water lock formed in the pore throat of the gas reservoir due to the intrusion of formation water or the injected fluid, and restore the gas well production capacity, and can show better performance characteristics than fluorine-containing wettability reversal agents. The wettability reversal agent of the present invention can convert the rock surface into super-hydrophobicity, which is beneficial to the natural gas reservoir to remove water locks and assist drainage to increase the gas well production capacity. The raw materials used in the wettability reversal agent of the present invention are widely available and inexpensive. Different types of long-chain surfactants can be selected according to the formation characteristics to achieve the effect of super-hydrophobic wettability reversal. The wettability reversal agent of the present invention has a low concentration of active ingredients and low field application cost, which greatly saves the cost of gas reservoir development.

[0009] Preferably, the average particle size of the hydrophobic fumed silica is 7 to 40 nm. If the particle size of the hydrophobic fumed silica is too large, its structure will be too loose, the surface area will be reduced, and the stability and strength of the microstructure will be reduced. If the particle size of the hydrophobic fumed silica is too small, its structure will be too tight, the surface area will increase, and the corresponding stability and strength will also increase, but it will lead to poor dispersion stability.

[0010] Preferably, the specific surface area of ​​the hydrophobic fumed silica is 140 to 200 m 2 / g. The specific surface area of the hydrophobic fumed silica is too large, the material has high activity, is prone to agglomeration, and is difficult to disperse. If the specific surface area of the hydrophobic fumed silica is too small, the effective contact area of the material is small, the number of active sites is small, and it is not easy to stably suspend and disperse in the solvent.

[0011] In the present invention, the specific surface area of the hydrophobic fumed silica refers to the specific surface area measured by the BET method, and the test standard is GB20020-2005.

[0012] It can be understood that in the present invention, the hydrophobic fumed silica is a product obtained by hydrophobic modification of nano-silica. The hydrophobic fumed silica used in the present invention can be obtained commercially. For example, the hydrophobic fumed silica is Degussa R974 fumed silica (particle size 7-40 nm, specific surface area 150-190 m 2 / g), fumed silica HB-202N produced by Hubei Huifu Nanomaterials Co., Ltd. (particle size 20-40 nm, specific surface area 150-190 m 2 / g), Wacker H20 fumed silica (particle size 7-40 nm, 140-200 m 2 / g).

[0013] Preferably, the long-chain surfactant is an anionic surfactant, a non-ionic surfactant, or a cationic surfactant.

[0014] Preferably, the long-chain surfactant has no less than 10 and no more than 16 carbon atoms.

[0015] Preferably, the long-chain surfactant is selected from one or any combination of C 10 -C 16 alkylbenzene sulfonates, C 10 -C 16 alkyl sulfates, C 10 -C 16 alkyl glycosides, C 10 -C 16 alkyl quaternary ammonium salts. Alkylbenzene sulfonates and alkyl sulfates have good solubility and good compatibility with cations; alkyl glycosides have limited surface activity but good conditioning performance, and have good detergency and good compatibility with other types of surfactants; alkyl quaternary ammonium salts are suitable for acidic systems, have good conditioning performance, and have a good effect on increasing viscosity. Compared with other surfactants, the above surfactants have better performance.

[0016] Preferably, the C 10 -C 16 alkylbenzene sulfonate is an alkali metal salt of C 10 -C 16 alkylbenzene sulfonic acid; the C 10~C 16 The alkyl sulfate is C 10 ~C 16 alkali metal alkyl sulfate; the C 10 ~C 16 The alkyl polyglycoside is C 10 ~C 16 alkyl glucoside; the C 10 ~C 16 The alkyl quaternary ammonium salt is C 10 ~C 16 alkyltrimethylammonium bromide and / or C 10 ~C 16 alkyltrimethylammonium chloride.

[0017] Preferably, the C 10 ~C 16 alkylbenzene sulfonate is sodium heavy alkylbenzene sulfonate, and the number of carbon atoms in the molecular chain of the sodium heavy alkylbenzene sulfonate is 10-13; the C 10 ~C 16 The alkyl sulfate is sodium dodecyl sulfate, sodium tridecyl sulfate, sodium tetradecyl sulfate, potassium dodecyl sulfate, potassium tridecyl sulfate, potassium tetradecyl sulfate; the C 10 ~C 16 The alkyl polyglycoside is dodecyl glucoside, tetradecyl glucoside; the C 10 ~C 16 The alkyl quaternary ammonium salt is cetyltrimethylammonium bromide, dodecyltrimethylammonium bromide, cetyltrimethylammonium chloride, dodecyltrimethylammonium chloride.

[0018] Preferably, in the wetting reversal agent, the mass fraction of the organic solvent is 10-30%. Preferably, the organic solvent is selected from one or any combination of alcohol solvents, alkanolamine solvents, and ether solvents. In the wetting reversal agent, the role of the organic solvent is a co-solvent. If the mass fraction of the organic solvent is too large, the effective molecular concentration per unit volume will be reduced, affecting the wetting improvement ability of the wetting reversal agent; if the mass fraction of the organic solvent is too small, the gas-phase silica will not be dispersed thoroughly, affecting the dispersion stability of the wetting reversal agent and further affecting the wetting reversal performance. In the wetting reversal agent, the role of water is the basic solvent for dissolving the surfactant.

[0019] Preferably, the organic solvent is selected from one or any combination of isopropanol, isobutanol, triethanolamine, and ethylene glycol monobutyl ether.

[0020] Preferably, the preparation method of the wetting reversal agent comprises the following steps: adding a formulated amount of long-chain surfactant into water, mixing evenly to obtain a long-chain surfactant solution; adding a formulated amount of hydrophobic fumed silica into an organic solvent, mixing evenly to obtain a dispersion; and finally adding the dispersion into the long-chain surfactant solution, mixing evenly to obtain the wetting reversal agent.

[0021] The preparation method of the wetting reversal agent of the present invention is simple in operation and can be prepared and used immediately at the oilfield. The prepared wetting reversal agent has the advantages of stable performance and low surface tension, and can transform the rock surface into superhydrophobicity.

[0022] Preferably, the adding speed of the dispersion into the long-chain surfactant solution is 10-100 mL / min. If the adding speed is too fast, the two solutions cannot be fully mixed evenly, affecting the final synergistic effect; if the adding speed is too slow, the volatilization of the organic solvent will be caused, affecting the base liquid concentration.

[0023] If the long-chain surfactant, water, organic solvent and hydrophobic fumed silica are directly added into a mixer and stirred evenly, the dispersion stability of the hydrophobic fumed silica will be poor, resulting in the stratification of the wetting reversal agent. Description of the Drawings

[0024] Figure 1 It is a schematic diagram of the contact angle of a water droplet on the rock surface in the experimental example of the present invention;

[0025] Figure 2 It is a schematic diagram of the contact angle of a water droplet on the rock surface treated with the wetting reversal agent of Examples 1-5 of the present invention;

[0026] Figure 3 It is a schematic diagram of the contact angle of a water droplet on the rock surface treated with the wetting reversal agent of Comparative Examples 1-5 of the present invention;

[0027] Figure 4 It is a schematic diagram of the contact angle of a water droplet on the rock surface treated with the wetting reversal agent of Comparative Examples 6-10 of the present invention. Detailed Embodiments

[0028] The technical solutions of the present invention will be further described below in conjunction with specific embodiments.

[0029] I. Specific embodiments of the wetting reversal agent of the present invention are as follows:

[0030] Example 1

[0031] The wetting reversal agent of this embodiment is composed of hydrophobic fumed silica, long-chain surfactant, organic solvent and water. The long-chain surfactant is heavy alkyl benzene sulfonate sodium, and the organic solvent is isopropanol. In the wetting reversal agent, the mass fractions of hydrophobic fumed silica, long-chain surfactant and organic solvent are 0.3%, 0.05% and 30% respectively, and the mass fraction of water is 69.65%. The hydrophobic fumed silica used in the wetting reversal agent of this embodiment is Degussa R974 type fumed silica from Germany.

[0032] Example 2

[0033] The wetting reversal agent of this embodiment is composed of hydrophobic fumed silica, long-chain surfactant, organic solvent and water. The long-chain surfactant is sodium dodecyl sulfate, and the organic solvent is triethanolamine. In the wetting reversal agent, the mass fractions of hydrophobic fumed silica, long-chain surfactant and organic solvent are 0.3%, 0.1% and 30% respectively, and the mass fraction of water is 69.6%. The hydrophobic fumed silica used in the wetting reversal agent of this embodiment is fumed silica HB-202N produced by Hubei Huifu Nanomaterials Co., Ltd.

[0034] Example 3

[0035] The wetting reversal agent of this embodiment is composed of hydrophobic fumed silica, long-chain surfactant, organic solvent and water. The long-chain surfactant is dodecyl glucoside, and the organic solvent is ethylene glycol monobutyl ether. In the wetting reversal agent, the mass fractions of hydrophobic fumed silica, long-chain surfactant and organic solvent are 0.3%, 0.025% and 10% respectively, and the mass fraction of water is 89.675%. The hydrophobic fumed silica used in the wetting reversal agent of this embodiment is Wacker H20 type fumed silica.

[0036] Example 4

[0037] The wetting reversal agent of this embodiment is composed of hydrophobic fumed silica, long-chain surfactant, organic solvent and water. The long-chain surfactant is cetyl trimethyl ammonium bromide, and the organic solvent is isopropanol. In the wetting reversal agent, the mass fractions of hydrophobic fumed silica, long-chain surfactant and organic solvent are 0.3%, 0.05% and 30% respectively, and the mass fraction of water is 69.65%. The hydrophobic fumed silica used in the wetting reversal agent of this embodiment is Wacker H20 type fumed silica.

[0038] Example 5

[0039] The wetting reversal agent of this embodiment is composed of hydrophobic fumed silica, long-chain surfactant, organic solvent and water. The long-chain surfactant is dodecyl glucoside, and the organic solvent is isopropanol. In the wetting reversal agent, the mass fractions of hydrophobic fumed silica, long-chain surfactant and organic solvent are 0.1%, 0.05% and 30% respectively, and the mass fraction of water is 69.85%. The hydrophobic fumed silica used in the wetting reversal agent of this embodiment is Degussa R974 fumed silica from Germany.

[0040] Comparative Example 1

[0041] The difference between the wetting reversal agent of this comparative example and that of Example 1 is only that the mass of the hydrophobic fumed silica used in the wetting reversal agent of this comparative example is 0, and the mass fraction of the long-chain surfactant is increased from 0.05% to 0.35%.

[0042] Comparative Example 2

[0043] The difference between the wetting reversal agent of this comparative example and that of Example 2 is only that the mass of the hydrophobic fumed silica used in the wetting reversal agent of this comparative example is 0, and the mass fraction of the long-chain surfactant is increased from 0.1% to 0.4%.

[0044] Comparative Example 3

[0045] The difference between the wetting reversal agent of this comparative example and that of Example 3 is only that the mass of the hydrophobic fumed silica used in the wetting reversal agent of this comparative example is 0, and the mass fraction of the long-chain surfactant is increased from 0.3% to 0.325%.

[0046] Comparative Example 4

[0047] The difference between the wetting reversal agent of this comparative example and that of Example 4 is only that the mass of the hydrophobic fumed silica used in the wetting reversal agent of this comparative example is 0, and the mass fraction of the long-chain surfactant is increased from 0.05% to 0.35%.

[0048] Comparative Example 5

[0049] The difference between the wetting reversal agent of this comparative example and that of Example 5 is only that the mass of the hydrophobic fumed silica used in the wetting reversal agent of this comparative example is 0, and the mass fraction of the long-chain surfactant is increased from 0.05% to 0.15%.

[0050] Comparative Example 6

[0051] The difference between the wetting reversal agent of this comparative example and that of Example 1 is only that the mass of the long-chain surfactant used in the wetting reversal agent of this comparative example is 0, and the mass fraction of hydrophobic fumed silica is increased from 0.3% to 0.35%.

[0052] Comparative Example 7

[0053] The difference between the wetting reversal agent of this comparative example and that of Example 2 is only that the mass of the long-chain surfactant used in the wetting reversal agent of this comparative example is 0, and the mass fraction of hydrophobic fumed silica is increased from 0.3% to 0.4%.

[0054] Comparative Example 8

[0055] The difference between the wetting reversal agent of this comparative example and that of Example 3 is only that the mass of the long-chain surfactant used in the wetting reversal agent of this comparative example is 0, and the mass fraction of hydrophobic fumed silica is increased from 0.3% to 0.325%.

[0056] Comparative Example 9

[0057] The difference between the wetting reversal agent of this comparative example and that of Example 4 is only that the mass of the long-chain surfactant used in the wetting reversal agent of this comparative example is 0, and the mass fraction of hydrophobic fumed silica is increased from 0.3% to 0.35%.

[0058] Comparative Example 10

[0059] The difference between the wetting reversal agent of this comparative example and that of Example 5 is only that the mass of the long-chain surfactant used in the wetting reversal agent of this comparative example is 0, and the mass fraction of hydrophobic fumed silica is increased from 0.1% to 0.15%.

[0060] Comparative Example 11

[0061] The difference between the wetting reversal agent of this comparative example and that of Example 1 is only that the long-chain surfactant used in the wetting reversal agent of this comparative example is perfluorooctylsulfonamidopropyltrimethylammonium iodide.

[0062] Comparative Example 12

[0063] The difference between the wetting reversal agent of this comparative example and that of Example 1 is only that the hydrophobic fumed silica used in the wetting reversal agent of this comparative example is Hydrophobic-100 type hydrophobic fumed silica (particle size 7 - 40 nm, specific surface area 100 m 2 / g).

[0064] Comparative Example 13

[0065] The wetting reversal agent of this comparative example differs from that of Example 1 only in that the mass fraction of the long-chain surfactant used in the wetting reversal agent of this comparative example is 0.02%.

[0066] Comparative Example 14

[0067] The wetting reversal agent of this comparative example differs from that of Comparative Example 13 only in that the mass of the hydrophobic fumed silica used in the wetting reversal agent of this comparative example is 0, and the mass fraction of the long-chain surfactant is increased from 0.02% to 0.32%.

[0068] Comparative Example 15

[0069] The wetting reversal agent of this comparative example differs from that of Example 1 only in that the mass fraction of the long-chain surfactant used in the wetting reversal agent of this comparative example is 0.2%.

[0070] Comparative Example 16

[0071] The wetting reversal agent of this comparative example differs from that of Comparative Example 15 only in that the mass of the hydrophobic fumed silica used in the wetting reversal agent of this comparative example is 0, and the mass fraction of the long-chain surfactant is increased from 0.2% to 0.5%.

[0072] Comparative Example 17

[0073] The wetting reversal agent of this comparative example differs from that of Example 1 only in that the silica used in the wetting reversal agent of this comparative example is prepared by a method including the following steps: adding a silane coupling agent, a solvent, and silica particles with an average particle size of 15 nm into a reaction vessel, then heating the materials in the reaction vessel to 60°C, stirring and reacting at a rate of 1200 r / min for 6 h, standing for 48 h after the reaction, then taking the upper suspension for suction filtration, washing with an anhydrous ethanol solution and drying to obtain silane coupling agent-modified silica; wherein, the silane coupling agent is 3-methacryloyloxytrimethylsilane, the solvent consists of water and ethanol with a mass ratio of 1:1, and the mass ratio of the silane coupling agent, silica particles with an average particle size of 15 nm, and the solvent is 1:2:47.

[0074] II. Specific embodiments of the preparation method of the wetting reversal agent of the present invention are as follows:

[0075] Example 6

[0076] The preparation method of the wetting reversal agent in this example is the same as that in Example 1, and specifically includes the following steps: Add the formulated amount of long-chain surfactant to water and stir evenly to obtain a long-chain surfactant solution; Add the formulated amount of hydrophobic fumed silica to an organic solvent and stir evenly to obtain a dispersion; Finally, slowly add the dispersion to the long-chain surfactant solution under stirring (the addition rate is 10 mL / min). After the addition of the dispersion is completed, continue stirring for 3 h to obtain the wetting reversal agent.

[0077] Example 7

[0078] The preparation method of the wetting reversal agent in this example is the same as that in Example 2, and specifically includes the following steps: Add the formulated amount of long-chain surfactant to water and stir evenly to obtain a long-chain surfactant solution; Add the formulated amount of hydrophobic fumed silica to an organic solvent and stir evenly to obtain a dispersion; Finally, slowly add the dispersion to the long-chain surfactant solution under stirring (the addition rate is 100 mL / min). After the addition of the dispersion is completed, continue stirring for 4 h to obtain the wetting reversal agent.

[0079] Example 8

[0080] The preparation method of the wetting reversal agent in this example is the same as that in Example 3, and specifically includes the following steps: Add the formulated amount of long-chain surfactant to water and stir evenly to obtain a long-chain surfactant solution; Add the formulated amount of hydrophobic fumed silica to an organic solvent and stir evenly to obtain a dispersion; Finally, slowly add the dispersion to the long-chain surfactant solution under stirring (the addition rate is 50 mL / min). After the addition of the dispersion is completed, continue stirring for 3.5 h to obtain the wetting reversal agent.

[0081] Example 9

[0082] The preparation method of the wetting reversal agent in this example is the same as that in Example 4, and specifically includes the following steps: Add the formulated amount of long-chain surfactant to water and stir evenly to obtain a long-chain surfactant solution; Add the formulated amount of hydrophobic fumed silica to an organic solvent and stir evenly to obtain a dispersion; Finally, slowly add the dispersion to the long-chain surfactant solution under stirring (the addition rate is 70 mL / min). After the addition of the dispersion is completed, continue stirring for 3.5 h to obtain the wetting reversal agent.

[0083] Example 10

[0084] The preparation method of the wetting reversal agent in this example is the same as that of the wetting reversal agent in Example 5, and specifically includes the following steps: Add the formulated amount of long-chain surfactant to water and stir evenly to obtain a long-chain surfactant solution; Add the formulated amount of hydrophobic fumed silica to an organic solvent and stir evenly to obtain a dispersion; Finally, slowly add the dispersion to the long-chain surfactant solution (the addition rate is 20 mL / min) under stirring. After the addition of the dispersion is completed, continue to stir for 4 h to obtain the wetting reversal agent.

[0085] Comparative Example 18

[0086] The difference between the preparation method of the wetting reversal agent in this comparative example and that in Example 6 is only that the preparation method of the wetting reversal agent in this comparative example specifically includes the following steps: First, add the formulated amount of long-chain surfactant to the mixed liquid composed of the formulated amount of organic solvent and water and stir evenly to obtain a mixed solution, and then add the formulated amount of hydrophobic fumed silica to the mixed solution. After the addition is completed, continue to stir for 3 h to obtain the wetting reversal agent.

[0087] Experimental Example

[0088] In order to evaluate the wetting performance of the wetting reversal agents of Examples 1-5 and Comparative Examples 1-18 on rocks, the surface tensions of the respective wetting reversal agents and the contact angles between the rock surfaces treated with the respective wetting reversal agents and water were measured. The measurement method was carried out according to the regulations in the standard "Determination Method for Wettability of Reservoir Rocks SY / T 5153-2017", and the test medium was fresh water. Then, the storage stability of the respective wetting reversal agents was tested. The test method was as follows: The wetting reversal agents of Examples 1-5 and Comparative Examples 1-18 were sealed and left standing at 120 °C for 15 days. Observe whether the wetting reversal agent shows stratification or solid particle sedimentation, and record the observation results. The storage stability of the sample without stratification was determined to be excellent, the stability of the sample with slight stratification was determined to be good, and the storage stability of the sample with obvious solid particle sedimentation or floating was determined to be poor.

[0089] The test results of the surface tensions of fresh water, the wetting reversal agents of Examples 1-5 and Comparative Examples 1-18, the contact angles between the rock surfaces or the rock surfaces treated with the wetting reversal agents and water, and the test results of the storage stability of the respective wetting reversal agents are shown in Table 1. The schematic diagram of the contact angle of a water droplet on the rock surface is as Figure 1 shown; The schematic diagram of the contact angle of a water droplet on the rock surface treated with the wetting reversal agents of Examples 1-5 is as Figure 2 shown, where Figure 2Diagrams showing the contact angles of the rock surfaces treated with the wetting reversal agents in Examples 1, 2, 3, 4, and 5 are represented by a, 2b, 2c, 2d, and 2e respectively; diagrams showing the contact angles of the water droplets on the rock surfaces treated with the wetting reversal agents in Comparative Examples 1-5 are as shown in Figure 3 shown, where Figure 3 Diagrams showing the contact angles of the rock surfaces treated with the wetting reversal agents in Comparative Examples 1, 2, 3, 4, and 5 are represented by a, 3b, 3c, 3d, and 3e respectively; diagrams showing the contact angles of the water droplets on the rock surfaces treated with the wetting reversal agents in Comparative Examples 6-10 are as shown in Figure 4 shown, where Figure 4 Diagrams showing the contact angles of the rock surfaces treated with the wetting reversal agents in Comparative Examples 6, 7, 8, 9, and 10 are represented by a, 4b, 4c, 4d, and 4e respectively.

[0090] Table 1 Surface tensions of the wetting reversal agents in Examples 1-5 and Comparative Examples 1-18, contact angles of water on the rock surfaces treated with each wetting reversal agent, and storage stabilities of each wetting reversal agent

[0091]

[0092]

[0093] As can be seen from Table 1, the surfactants used in the wetting reversal agents of Examples 1-5 include anionic, cationic and non-ionic types, all of which exhibit excellent wetting reversal properties and can reverse the rock surface from strong hydrophilicity to superhydrophobicity (contact angle > 150°). After aging for 15 days at the reservoir temperature of 120 °C, good dispersion stability can still be maintained. At the same time, according to the test results of the wetting reversal agents of Comparative Examples 1-10, the wetting reversal agents prepared by simply using surfactants can effectively reduce the surface tension, but the effect of improving the wettability of the core surface is limited. At the same time, after aging for 15 days at the reservoir temperature of 120 °C, the wetting reversal agent shows stratification or solid particles are observed to settle or float. The wetting improvement effect of the wetting reversal agent prepared according to Comparative Example 18 is poor, and it can be observed that the hydrophobic fumed silica floats to the liquid surface after standing for 24 h after preparation, which is very unstable. Simply using hydrophobic fumed silica can enhance the gas wettability of the core surface to a certain extent, but the improvement degree is limited and the superhydrophobic effect cannot be achieved. In addition, the wetting reversal agent prepared with a surfactant without fluorine shows better wetting improvement ability than the wetting reversal agent prepared with a surfactant containing fluorine. Comparing the test results of the wetting reversal agents of Examples 1-5 and Comparative Examples 1-10, it can be seen that the surfactant and hydrophobic fumed silica in the wetting reversal agent show good synergistic effects, which can greatly enhance the wetting improvement ability of the wetting reversal agent and further reduce the surface tension. This is because the presence of the surfactant with low surface energy characteristics reduces the surface tension of the system, making it easier to adsorb with the hydrophobic fumed silica with a high specific surface area. The formed synergistic body can establish a hydrophobic layer on the core surface, thus showing superhydrophobic properties. In addition, this synergistic effect between the two is also beneficial to promoting the overall dispersion stability of the system and ensuring the long-term effectiveness of the strong gas wetting performance of the wetting reversal agent. However, the wetting reversal agent prepared with hydrophobic fumed silica with a relatively low specific surface area, although it can also achieve superhydrophobic performance, has relatively weak dispersion stability under reservoir conditions. This is because the smaller specific surface area of hydrophobic fumed silica is not conducive to its stable suspension and dispersion in the solvent. Therefore, the core surface treated with the wetting reversal agent shows strong hydrophobicity, which is very beneficial for relieving water lock in formation pores and assisting the backflow of injected fluids.

Claims

1. A wetting reversal agent, characterized in that, it comprises hydrophobic fumed silica, a long-chain surfactant, an organic solvent and water; the average particle size of the hydrophobic fumed silica is not more than 40 nm; the long-chain surfactant has not less than 6 and not more than 20 carbon atoms; the organic solvent is an organic solvent miscible with water; in the wetting reversal agent, the mass fraction of the hydrophobic fumed silica is 0.1 - 0.3%, and the mass fraction of the long-chain surfactant is 0.025 - 0.1%.

2. The wetting reversal agent according to claim 1, characterized in that, the average particle size of the hydrophobic fumed silica is 7 - 40 nm.

3. The wetting reversal agent according to claim 1, characterized in that, The specific surface area of the hydrophobic fumed silica is 140 to 200 m 2 / g.

4. The wetting reversal agent according to any one of claims 1 - 3, characterized in that, The long-chain surfactant has no less than 10 and no more than 16 carbon atoms; the long-chain surfactant is selected from C 10 ~C 16 alkylbenzene sulfonates, C 10 ~C 16 alkyl sulfates, C 10 ~C 16 alkyl glycosides, C 10 ~C 16 alkyl quaternary ammonium salts, or any combination thereof.

5. The wetting reversal agent according to claim 4, characterized in that, The C 10 to C 16 alkylbenzene sulfonate is an alkali metal salt of C 10 to C 16 alkylbenzene sulfonic acid; the C 10 to C 16 alkyl sulfate is an alkali metal salt of C 10 to C 16 alkyl sulfuric acid; the C 10 to C 16 alkyl glucoside is C 10 to C 16 alkyl glucoside; the C 10 to C 16 alkyl quaternary ammonium salt is C 10 to C 16 alkyl trimethyl ammonium bromide and / or C 10 to C 16 alkyl trimethyl ammonium chloride.

6. The wetting reversal agent according to claim 4, characterized in that, The C 10 ~C 16 alkylbenzene sulfonate is sodium heavy alkylbenzene sulfonate, and the number of carbon atoms in the molecular chain of the sodium heavy alkylbenzene sulfonate is 10 to 13; the C 10 ~C 16 alkyl sulfates are sodium dodecyl sulfate, sodium tridecyl sulfate, sodium tetradecyl sulfate, potassium dodecyl sulfate, potassium tridecyl sulfate, potassium tetradecyl sulfate; the C 10 ~C 16 alkyl glucosides are dodecyl glucoside, tetradecyl glucoside; the C 10 ~C 16 alkyl quaternary ammonium salts are cetyl trimethyl ammonium bromide, dodecyl trimethyl ammonium bromide, cetyl trimethyl ammonium chloride, dodecyl trimethyl ammonium chloride.

7. The wetting reversal agent according to any one of claims 1 - 3, characterized in that, in the wetting reversal agent, the mass fraction of the organic solvent is 10 - 30%.

8. The wetting reversal agent according to any one of claims 1 - 3, characterized in that, the organic solvent is selected from one or any combination of alcohol solvents, alkanolamine solvents, and ether solvents.

9. The wetting reversal agent according to claim 8, characterized in that, the organic solvent is selected from one or any combination of isopropanol, isobutanol, triethanolamine, and ethylene glycol monobutyl ether.

10. The wetting reversal agent according to any one of claims 1 - 3, characterized in that, the preparation method of the wetting reversal agent comprises the following steps: adding the formulated amount of the long-chain surfactant to water and mixing evenly to obtain a long-chain surfactant solution; adding the formulated amount of the hydrophobic fumed silica to the organic solvent and mixing evenly to obtain a dispersion; finally, adding the dispersion to the long-chain surfactant solution and mixing evenly to obtain the wetting reversal agent.

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