Working fluid capable of controlling water and increasing yield as well as preparation method and application of working fluid

Abstract

The invention provides a water-controlling and yield-increasing working solution as well as a preparation method and application thereof. The water-controlling and yield-increasing working solution is prepared from the following components in percentage by mass: 0.3 to 0.6 percent of oxidized modified graphite calculated by graphite, 0.3 to 1.8 percent of a fluorocarbon ammonium salt surfactant, 0.6 to 3 percent of a hydrophilic improver and the balance of water, wherein the mass of the oxidized modified graphite is 100 percent. The water-controlling and yield-increasing working fluid can enter a stratum, and the purposes of water blocking and gas increasing are achieved by conducting hydrophobic modification on the surface of rock, agglomerating particles when meeting saline water and blocking a water-containing layer.

Description

Technical Field

[0001] The present invention belongs to the field of oil and gas field development - oil production engineering, and particularly relates to a water control and production increase working fluid, a preparation method thereof, and an application thereof. Background Art

[0002] During the development of low - permeability gas reservoirs, the amount of water invasion has a great impact on the exploration and development of water - bearing gas reservoirs. Water invasion is the seepage process in which formation water flows along the dominant channels of the reservoir to the gas well. Locally, it shows tongue - like and finger - like shapes, and overall, it shows bottom - water coning and edge - water intrusion. The degree of water invasion depends on the size and distribution of the water body, heterogeneity characteristics, and gas well production. Water invasion may lead to serious consequences such as reduced productivity, sand production, equipment corrosion, and scaling.

[0003] With the deepening of exploration and development, the development of low - permeability and high - water - cut gas reservoirs is the current research focus. At present, the main methods for water control in gas wells include water shutoff, drainage gas production, and production allocation. Currently, the development effects of processes such as gel water shutoff and relative permeability control are not ideal, the direction of water control technology is unclear, and the research difficulty is great.

[0004] Chemical water shutoff is applicable to anisotropic multi - layers and also to heterogeneous thick layers. In this method, a chemical water shutoff agent is pumped into the high - permeability water layer or bottom - water layer, and the water shutoff agent or its physical and chemical reaction products form a barrier layer to inhibit water production. CN104929568A discloses a construction method for water control in gas reservoirs, in which gas is injected into the gas reservoir to push the invaded water in the gas layer to a distance from the well; a gel with delayed cross - linking ability is prepared and atomized to form a gas - phase dispersed gel; the gas - phase dispersed gel is co - injected into the gas reservoir with the gas; gas injection is continued to achieve the migration and dispersion of the gel in the gas layer; and a soaking - well treatment is carried out. However, the temperature of the gas well is high, the gel system has high temperature requirements, and there are certain safety problems. CN101086210A discloses a profile control and water shutoff technology for coalbed methane. This technology designs the water shutoff agent and its dosage according to the principles of sectional plug design of the water shutoff gel system, gradually increasing strength, moderate gel viscosity, and reasonable cross - linking time for each slug to achieve selective water shutoff, blocking the channel between the coalbed methane wellbore and the water storage area without blocking the cleats, fractures, and fracturing - reformed fractures of the coal reservoir, thereby effectively draining water and reducing pressure to ensure the normal production of coalbed methane wells. This technology has been verified for sandstone and limestone gas reservoirs. CN108410442A discloses a hydrophobic nano - silica emulsion for water control in low - permeability oil and gas reservoirs. The mass percentages of each component are as follows: hydrophobic nano - silica 0.1% - 3%, organic solvent 25% - 30%, emulsifier 5% - 15%, co - emulsifier 0% - 15%, and the rest is water. When the hydrophobic nano - silica emulsion is injected into the formation, as the temperature rises, nano - silica will be released and adsorbed on the rock surface to form one or more nano - films, thereby changing the wettability of the rock surface. In this technical method, nano - silica belongs to solid particles and causes plugging damage to the formation.

[0005] Therefore, in view of the problem of reducing the water content in gas wells and improving rock wettability, it is necessary to develop a water control and production-increasing working fluid formula and construction method for low-permeability and high-water-saturation gas reservoirs that can improve gas permeability, self-aggregate and block the aquifer, and reduce the permeability of the water layer, so as to achieve the purpose of water blocking and gas increasing. Summary of the Invention

[0006] In order to solve the above problems, the purpose of the present invention is to provide a water control and production-increasing working fluid, its preparation method and application. The water control and production-increasing working fluid can enter the formation, hydrophobically modify the rock surface, and the particles agglomerate in the presence of brine to block the aquifer, so as to achieve the purpose of water blocking and gas increasing.

[0007] In order to achieve the above purpose, the present invention provides a water control and production-increasing working fluid. Calculated based on the mass of the water control and production-increasing working fluid being 100%, its composition includes 0.3-0.6% of oxidized modified graphite calculated as graphite, 0.3-1.8% of fluorocarbon ammonium salt surfactant, 0.6-3% of hydrophilic improver, and the balance is water.

[0008] According to a specific embodiment of the present invention, preferably, the oxidized modified graphite is prepared by oxidizing natural flake graphite.

[0009] According to a specific embodiment of the present invention, preferably, the mesh number of the natural flake graphite is ≥80 mesh, and the carbon content is 90-98%.

[0010] According to a specific embodiment of the present invention, preferably, the fluorocarbon ammonium salt surfactant includes perfluorooctyl quaternary ammonium iodide and / or perfluorooctyl carboxylic acid quaternary ammonium salt iodide.

[0011] According to a specific embodiment of the present invention, preferably, the hydrophilic improver includes polyvinylpyrrolidone and / or polyvinyl alcohol.

[0012] According to a specific embodiment of the present invention, preferably, the number-average relative molecular mass of the polyvinylpyrrolidone is 10,000-40,000, more preferably 10,000-20,000.

[0013] According to a specific embodiment of the present invention, preferably, the degree of polymerization of the polyvinyl alcohol is 500-1000, the degree of hydrolysis is 78-99%, more preferably 99%.

[0014] The present invention also provides a preparation method of the above water control and production-increasing working fluid, which includes the following steps:

[0015] (1) Oxidize graphite successively with concentrated sulfuric acid, sodium nitrate and potassium permanganate, and then disperse it by ultrasonic wave with hydrogen peroxide to obtain the oxidized modified graphite;

[0016] (2) Mix the oxidized modified graphite, fluorocarbon ammonium salt surfactant and water at 40 - 80 °C;

[0017] (3) Add a hydrophilic improver to the mixed solution obtained in step (2), and after mixing, obtain the water control and production enhancement working fluid.

[0018] According to a specific embodiment of the present invention, preferably, in step (1), the mass ratio of graphite, concentrated sulfuric acid, sodium nitrate, and potassium permanganate is (1 - 5) : 50 : (1 - 5) : (3 - 10).

[0019] According to a specific embodiment of the present invention, preferably, oxidize graphite with concentrated sulfuric acid, sodium nitrate, and potassium permanganate successively in an ice - water bath for 1 - 4 h respectively, then react at 30 - 40 °C for 2 - 4 h (stop the reaction after the color of the reaction system changes from brown to bright yellow), and obtain the oxidized modified graphite after ultrasonic dispersion with hydrogen peroxide.

[0020] According to a specific embodiment of the present invention, preferably, the frequency of ultrasonic treatment with hydrogen peroxide is 80 - 100 KHZ, the power is 200 - 400 KW, and the time is 120 - 360 min.

[0021] According to a specific embodiment of the present invention, preferably, the mass concentration of hydrogen peroxide is 30 wt%.

[0022] According to a specific embodiment of the present invention, preferably, the mass ratio of hydrogen peroxide to graphite is 10:1 - 30:1.

[0023] According to a specific embodiment of the present invention, preferably, in step (2), the mixing and stirring rate is 100 - 300 r / min, and the stirring time is 1 - 3 h.

[0024] According to a specific embodiment of the present invention, preferably, the addition amount of the fluorocarbon ammonium salt surfactant is 1 - 3 times the mass of graphite.

[0025] According to a specific embodiment of the present invention, preferably, the fluorocarbon ammonium salt surfactant is a mixture of perfluorooctyl quaternary ammonium iodide and perfluorooctyl carboxylic acid quaternary ammonium salt iodide with a weight ratio of 1 : 2 - 8.

[0026] According to a specific embodiment of the present invention, preferably, in step (3), the addition amount of the hydrophilic improver is 2 - 5 times the mass of graphite.

[0027] According to a specific embodiment of the present invention, preferably, the hydrophilic improver is a mixture of polyvinylpyrrolidone and polyvinyl alcohol with a weight ratio of 1 : 2 - 5.

[0028] According to a specific embodiment of the present invention, the above - mentioned preparation method includes the following specific steps:

[0029] (1) Graphite is successively oxidized in an ice-water bath with concentrated sulfuric acid, sodium nitrate, and potassium permanganate, then subjected to a water bath reaction, followed by ultrasonic dispersion with hydrogen peroxide, filtered and washed with water until neutral, and then vacuum dried;

[0030] (2) Take the above dried sample, mix it in water, add a fluorocarbon ammonium salt surfactant and stir well to dissolve, heat and stir for reaction, and set aside after the reaction;

[0031] (3) Add a hydrophilic improver to the mixture obtained in step (2), and stir well to dissolve to obtain a water control and production enhancement working fluid.

[0032] The present invention also provides a construction method for water control and production enhancement in a low-permeability and high-water-saturation gas reservoir, which uses the above water control and production enhancement working fluid.

[0033] According to a specific implementation scheme of the present invention, preferably, the water control and production enhancement working fluid is used as one or a combination of two or more of the main slug, pre-slug, and post-slug.

[0034] According to a specific implementation scheme of the present invention, preferably, the water control and production enhancement working fluid is injected below the formation fracture pressure, and the injection volume of the water control and production enhancement working fluid is calculated according to the following formula:

[0035] V = π×(R 2 2 -R 1 2 )×h×Φ×S w Formula Ⅰ,

[0036] In Formula Ⅰ: V - injection volume of the water control and production enhancement working fluid, m 3 ; R 2 - outer radius of the water control and production enhancement working fluid, m; R 1 - inner radius of the water control and production enhancement working fluid, m; h - thickness of the perforated layer, m; Φ - formation porosity, %; S w - water saturation, %;

[0037] Or, the water control and production enhancement working fluid is injected above the formation fracture pressure, and the injection volume of the water control and production enhancement working fluid is calculated according to the following formula:

[0038] V = [π×(R 2 2 -R 1 2 )×h×Φ + 4×H×L×W]×S w Formula Ⅱ,

[0039] In Formula Ⅱ: V - injection volume of the water control and production enhancement working fluid, m 3 ; R 2 - outer radius of the water control and production enhancement working fluid, m; R 1- Inner radius of the water control and production enhancement working fluid, m; h - Thickness of the perforated layer, m; Φ - Formation porosity, %; L - Half-length of the fracture, m; H - Height of the fracture, m; W - Width of the fracture, m; S w - Water saturation, %.

[0040] According to the specific implementation scheme of the present invention, preferably, the injection displacement of the water control and production enhancement working fluid is 0.8 - 10 m 3 / min, more preferably 0.8 - 5 m 3 / min.

[0041] According to the specific implementation scheme of the present invention, preferably, the injection method of the water control and production enhancement working fluid is a multi - slug alternating method, and it is injected through a bare casing or a tubing.

[0042] According to the specific implementation scheme of the present invention, preferably, water with PH = 7 is used for displacement, and the water consumption is the volume required to completely displace the wellhead into the formation.

[0043] According to the specific implementation scheme of the present invention, preferably, the shut - in time is 2 - 10 hours, more preferably 5 - 8 hours.

[0044] The present invention has the following beneficial effects:

[0045] 1. Excellent water - soluble dispersibility

[0046] Through graphite oxidation modification, a large number of water - soluble functional groups such as hydroxyl, carboxyl, and epoxy groups are contained on the surface, which improves the disadvantage of graphite agglomeration and non - dispersion in water, enabling it to disperse better in water; further, a fluorocarbon cationic surfactant is used to modify graphite, increasing the graphite layer spacing, effectively improving its dispersibility and surface activity, etc., and enhancing its dispersion stability in water; water - soluble polyvinylpyrrolidone and polyvinyl alcohol are used to suspend and carry graphite, and under high - temperature conditions in the wellbore, graphene is further modified, realizing the avoidance of rapid agglomeration of graphene in high - temperature and high - salinity environments, enabling it to migrate deep into the reservoir;

[0047] 2. High - temperature instability and coalescence

[0048] After entering the formation, since the graphite modification is not completely through grafting functional groups, the modified fluorocarbon cationic surfactant, polyvinylpyrrolidone, and polyvinyl alcohol compete for adsorption on the formation core, and at the same time, the dilution effect of high - temperature and high - salinity formation water reduces the concentrations of the fluorocarbon cationic surfactant, polyvinylpyrrolidone, and polyvinyl alcohol. Eventually, the strong van der Waals force makes graphite extremely easy to agglomerate, resulting in an increase in particle size;

[0049] 3. Wetting inversion to reduce the water - phase permeability

[0050] The characteristics of the graphite nano - distribution, adsorbed on the core, have the effect of core wettability reversal. At the same time, the free fluorocarbon cationic surfactant has a long - chain hydrophobic property, lower - concentration surface activity, and excellent oil - wet characteristics. After adsorption with the negatively - charged reservoir, it reduces the water wettability of the surface rock, reduces the relative permeability of the water phase, and extends the effective period of the measure;

[0051] 4. Convenient and scientific optimization of construction parameters

[0052] The construction method of the water - control and production - increasing working fluid for low - permeability and high - water - saturation gas reservoirs in the present invention effectively guides the optimization of construction parameters for on - site personnel. Calculation methods are given for the total injection volume below and above the fracture pressure, scientifically guiding on - site construction. At the same time, appropriate injection displacement, injection method, and shut - in time are given for this system, enabling on - site workers to quickly carry out construction design. Description of the drawings

[0053] Figure 1 It is a contact - angle picture of the water - control and production - increasing working fluid and a quartz wafer. Detailed implementation manners

[0054] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the implementable scope of the present invention.

[0055] Example 1

[0056] This example provides a water - control and production - increasing working fluid, which is prepared by the following steps:

[0057] (1) Add natural flake graphite (mesh number 100, carbon content 98%) and concentrated sulfuric acid into a flask, stir continuously, and then add sodium nitrate and potassium permanganate in turn. Stir magnetically for 2 h respectively. The temperature of the whole process is controlled in an ice - water bath at 0 - 5 °C, then keep the temperature at 35 °C and stir magnetically for 2 h. Then add 2 - 3 times the volume of water, keep reacting for 2 h, then add 30 wt% hydrogen peroxide for ultrasonic dispersion. Stop the reaction after the color of the reaction system turns from brown to bright yellow; filter and wash with water until neutral, and dry in vacuum; among them, the mass ratio of graphite to concentrated sulfuric acid, sodium nitrate, and potassium permanganate is 5:50:2:3, and the mass ratio of hydrogen peroxide to graphite is 20:1; the ultrasonic frequency is 100 KHZ, the power is 400 KW, and the time is 360 min;

[0058] (2) Take the above - dried sample, dissolve it in water with a mass 90 times that of the sample, and add the surfactants perfluorooctyl quaternary ammonium iodide and perfluorooctyl carboxylic acid quaternary ammonium iodide (mass ratio 1:2, total mass is 2 times the mass of graphite) in turn and stir well to dissolve, and heat and stir for reaction; among them, the stirring rate is 300 r / min, the reaction time is 3 h, and the reaction temperature is 80 °C;

[0059] (3) After cooling the mixture obtained in step (2) to room temperature, a hydrophilic improver (the weight ratio of polyvinylpyrrolidone to polyvinyl alcohol is 1:2, and the total mass is 2 times the mass of graphite) is added, and after fully stirring and dissolving, a water-control material is obtained; the number-average relative molecular mass of polyvinylpyrrolidone is 10,000; for polyvinyl alcohol, the degree of polymerization is 500 and the degree of hydrolysis is 99%. The remaining water is supplemented to obtain a water-control and yield-increasing working fluid, so that the effective content of graphite is 0.6% (calculated based on the mass of the final water-control and yield-increasing working fluid being 100%, the same below).

[0060] Example 2

[0061] This example provides a water-control and yield-increasing working fluid, which is prepared by the following steps:

[0062] (1) Add natural flake graphite (mesh number 80, carbon content 90%) and concentrated sulfuric acid to a flask, stir continuously, and then add sodium nitrate and potassium permanganate in turn, and magnetically stir and react for 2 h respectively. The temperature of the whole process is controlled in an ice-water bath at 0-5 °C, then keep the temperature at 35 °C, magnetically stir and react for 2 h, then add 2-3 times the volume of water, keep reacting for 2 h, then add 30 wt% hydrogen peroxide for ultrasonic dispersion, and stop the reaction after the color of the reaction system turns from brown to bright yellow; filter and wash with water until neutral, and dry in vacuum; among them, the mass ratio of graphite to concentrated sulfuric acid, sodium nitrate and potassium permanganate is 3:50:5:3, and the mass ratio of hydrogen peroxide to graphite is 10:1; the ultrasonic frequency is 80 KHZ, the power is 400 KW, and the time is 300 min;

[0063] (2) Take the above dried sample, dissolve it in water with a mass 80 times that of the sample, and add the surfactants perfluorooctyl quaternary ammonium iodide and perfluorooctyl carboxylic acid quaternary ammonium iodide (mass ratio 1:2, total mass 1 times the mass of graphite) in turn, and fully stir and dissolve, and heat and stir to react; among them, the stirring rate is 200 r / min, the reaction time is 3 h, and the reaction temperature is 70 °C;

[0064] (3) After cooling the mixture obtained in step (2) to room temperature, a hydrophilic improver (the weight ratio of polyvinylpyrrolidone to polyvinyl alcohol is 1:3, and the total mass is 2.5 times the mass of graphite) is added, and after fully stirring and dissolving, a water-control material is obtained; for polyvinylpyrrolidone, the number-average relative molecular mass is 20,000; for polyvinyl alcohol, the degree of polymerization is 500 and the degree of hydrolysis is 99%. The remaining water is supplemented to obtain a water-control and yield-increasing working fluid, so that the effective content of graphite is 0.5%.

[0065] Example 3

[0066] This example provides a water-control and yield-increasing working fluid, which is prepared by the following steps:

[0067] (1) Add natural flake graphite (mesh size 100, carbon content 98%) and concentrated sulfuric acid into a flask, stir continuously, and then add sodium nitrate and potassium permanganate in turn. Stir magnetically for 2 h respectively. Control the temperature of the whole process in an ice-water bath at 0 - 5 °C, then keep the temperature at 35 °C and stir magnetically for 2 h. Then add water with a volume 2 - 3 times that of the reaction mixture, keep reacting for 2 h, then add 30 wt% hydrogen peroxide for ultrasonic dispersion, and stop the reaction after the color of the reaction system changes from dark brown to bright yellow; filter, wash with water until neutral, and dry in vacuum; among them, the mass ratio of graphite to concentrated sulfuric acid, sodium nitrate and potassium permanganate is 2:50:3:5, and the mass ratio of hydrogen peroxide to graphite is 15:1; the ultrasonic frequency is 100 KHZ, the power is 300 KW, and the time is 300 min;

[0068] (2) Take the above dried sample, dissolve it in water with a mass 80 times that of the sample, and add the surfactants perfluorooctyl quaternary ammonium iodide and perfluorooctyl carboxylate quaternary ammonium iodide (mass ratio 1:5, total mass 3 times that of the graphite mass) in turn, and stir and dissolve them fully, then heat and stir for reaction; among them, the stirring rate is 200 r / min, the reaction time is 3 h, and the reaction temperature is 70 °C;

[0069] (3) After cooling the mixture obtained in step (2) to room temperature, add the hydrophilic improver (the weight ratio of polyvinylpyrrolidone to polyvinyl alcohol is 1:2, total mass 2 times that of the graphite mass), and stir and dissolve it fully to obtain a water-control material; for polyvinylpyrrolidone, the number-average relative molecular mass is 20,000. For polyvinyl alcohol, the degree of polymerization is 600 and the degree of hydrolysis is 99%; add the remaining water to obtain a water-control and production-increasing working fluid, so that the effective content of graphite is 0.3%.

[0070] Application Example 1

[0071] In a certain gas reservoir, under the condition of lower than the fracturing breakdown pressure, it is injected as a pre-slug, and the main slug is a fracturing fluid. The total injection volume of the water-control and production-increasing working fluid is calculated according to the following formula:

[0072] V = π × (R 2 2 - R 1 2 ) × h × Φ × S w

[0073] In the formula: V - the injection volume of the water-control and production-increasing working fluid, m 3 ; R 2 - the outer radius of the water-control and production-increasing working fluid, m; R 1 - the inner radius of the water-control and production-increasing working fluid, m; h - the thickness of the perforated layer, m; Φ - the formation porosity, %; S w - the water saturation, %.

[0074] The outer radius of the designed water control and production increase working fluid is 10 m, the inner radius is 2 m, the reservoir thickness is 3.5 m (i.e., the perforated layer thickness), the water saturation is 45%, and the porosity is 11.3%. The total injection volume of the water control and production increase working fluid is 53 m 3 . The injection rate is 0.8 m 3 / min. The injection method is tubing injection. Fresh water with PH = 7 is used for displacement. The shut-in time is 5 hours.

[0075] Application Example 2

[0076] In a certain gas reservoir under formation fracturing conditions, it is injected as the main slug. The total injection volume of the water control and production increase working fluid is calculated according to the following formula:

[0077] V = [π×(R 2 2 -R 1 2 )×h×Φ + 4×H×L×W]×S w

[0078] In the formula: V - the injection volume of the water control and production increase working fluid, m 3 ; R 2 - the outer radius of the water control and production increase working fluid, m; R 1 - the inner radius of the water control and production increase working fluid, m; h - the perforated layer thickness, m; Φ - the formation porosity, %; L - the half-length of the fracture, m; H - the fracture height, m; W - the fracture width, m; S w - the water saturation, %.

[0079] The outer radius of the designed water control and production increase working fluid is 5 m, the inner radius is 0.3 m, the reservoir thickness is 10 m (i.e., the perforated layer thickness), the height of the propped fracture after closure is 13 m, the fracture width is 2 mm, the half-length of the fracture is 200 m, the water saturation is 45%, and the porosity is 11.3%. The total injection volume of the water control and production increase working fluid is 49 m 3 . The injection rate is 2.5 m 3 / min. The injection method is tubing injection. Fresh water with PH = 7 is used for displacement. The shut-in time is 6 hours.

[0080] Test Example 1

[0081] 1. Contact Angle Test

[0082] The low-permeability and high-water-saturation gas reservoir water control and production-increasing working fluid is formulated according to the method of Example 1, with the differences being: the effective content of graphite is 0.3%, the mesh number is 100 mesh, and the carbon content is 92%; the mass ratio of graphite to concentrated sulfuric acid, sodium nitrate and potassium permanganate is 5:50:2:4; the hydrophilic improver is polyvinylpyrrolidone (number-average relative molecular mass is 10,000), polyvinyl alcohol (degree of polymerization is 1000, degree of hydrolysis is 99%); the addition amount of the surfactant is 3 times the mass of graphite, and the weight ratio of perfluorooctyl quaternary ammonium iodide to perfluorooctyl carboxylate quaternary ammonium iodide is 1:2; the addition amount of the hydrophilic improver is 2 times the mass of graphite; the weight ratio of polyvinylpyrrolidone to polyvinyl alcohol is 1:3; the contact angle of the tested water control and production-increasing working fluid with the quartz sheet is 107°, as Figure 1 shown.

[0083] 2. Initial and final particle size tests

[0084] Test the particle size of the above water control and production-increasing working fluid. Add salt (NaCl:CaCl 2 :MgCl 2 ·6H 2 O = 7.0:6.0:0.4, mass ratio) to the above-prepared water control and production-increasing working fluid to simulate formation water, heat it in a water bath to 95°C, and use a nano latex stabilizer to measure the particle size of the test system. It can be seen that the system undergoes coalescence under high-temperature brine conditions, and the results are shown in Table 1.

[0085] Table 1 Particle size changes of the water control and production-increasing working fluid before and after brine

[0086]

[0087] 3. Gas permeability improvement effect

[0088] Using the above water control and production-increasing working fluid, keeping the confining pressure and driving pressure basically unchanged, test the changes in the gas and water permeability of the core before and after the injection of the water control and production-increasing working fluid according to SY / T 6385-2016 "Determination Method of Core Porosity and Permeability under Overburden Pressure", and the results are shown in Table 2 and Table 3.

[0089] Table 2 Core parameters

[0090]

[0091] Table 3 Influence of the water control and production-increasing working fluid on the core permeability

[0092]

[0093] It is found that the water control and production-increasing working fluid reduces the water drive permeability of the core by 20.49% and increases the gas-measured permeability by 6.55%, showing a water control effect.

Claims

1. A water control and production increase working fluid, which comprises 0.3-0.6% of oxidized modified graphite calculated as graphite, 0.3-1.8% of fluorocarbon ammonium salt surfactant, 0.6-3% of hydrophilic improver, and the balance is water, based on the mass of the water control and production increase working fluid being 100%.

2. The water control and production increase working fluid according to claim 1, wherein: The oxidized modified graphite is prepared by oxidizing and modifying natural flake graphite; Preferably, the mesh number of the natural flake graphite is ≥80 meshes, and the carbon content is 90-98%.

3. The water control and production increase working fluid according to claim 1, wherein: The fluorocarbon ammonium salt surfactant includes perfluorooctyl quaternary ammonium iodide and / or perfluorooctyl carboxylic acid quaternary ammonium salt iodide.

4. The water control and production increase working fluid according to claim 1, wherein: The hydrophilic improver includes polyvinyl pyrrolidone and / or polyvinyl alcohol; Preferably, the number average relative molecular mass of the polyvinyl pyrrolidone is 10000-40000, more preferably 10000-20000; Preferably, the degree of polymerization of the polyvinyl alcohol is 500-1000, and the degree of hydrolysis is 78-99%.

5. The method for preparing the water control and production increase working fluid according to any one of claims 1 to 4, comprising the following steps: (1) subjecting graphite to oxidation reaction with concentrated sulfuric acid, sodium nitrate and potassium permanganate in sequence, and then ultrasonically dispersing the graphite with hydrogen peroxide to obtain the oxidized modified graphite; (2) mixing the oxidized modified graphite, the fluorocarbon ammonium salt surfactant and water at 40-80° C.; (3) adding a hydrophilic improver to the mixed solution obtained in step (2), and mixing to obtain the water control and production increase working solution.

6. The preparation method according to claim 5, wherein: In step (1), the mass ratio of graphite, concentrated sulfuric acid, sodium nitrate and potassium permanganate is (1-5):50:(1-5):(3-10); Preferably, the graphite is oxidized with concentrated sulfuric acid, sodium nitrate and potassium permanganate in an ice-water bath for 1-4 hours respectively, then reacted at 30-40° C. for 2-4 hours, and then ultrasonically dispersed with hydrogen peroxide to obtain the oxidized modified graphite; Preferably, the frequency of hydrogen peroxide ultrasound is 80-100KHZ, the power is 200-400KW, and the time is 120-360min; Preferably, the mass concentration of hydrogen peroxide is 30wt%; Preferably, the mass ratio of hydrogen peroxide to graphite is 10:1-30:

1.

7. The preparation method according to claim 5, wherein: In step (2), the mixing stirring rate is 100-300 r / min, and the stirring time is 1-3 h; Preferably, the amount of the fluorocarbon ammonium salt surfactant added is 1-3 times the mass of graphite; Preferably, the fluorocarbon ammonium salt surfactant is a mixture of perfluorooctyl quaternary ammonium iodide and perfluorooctyl carboxylic acid quaternary ammonium salt iodide in a weight ratio of 1:2-8.

8. The preparation method according to claim 5, wherein: In step (3), the amount of the hydrophilic improver added is 2-5 times the mass of graphite; Preferably, the hydrophilic improver is a mixture of polyvinyl pyrrolidone and polyvinyl alcohol in a weight ratio of 1:2-5.

9. A construction method for controlling water and increasing production in a low-permeability, high-water-saturated gas reservoir, which is carried out using the water-controlling and increasing production working fluid according to any one of claims 1 to 4; Preferably, the water control and production increase working fluid is used as one or a combination of two or more of a main slug, a front slug, and a rear slug.

10. The construction method for controlling water and increasing production in a low-permeability, high-water-saturated gas reservoir according to claim 9, wherein: The water control and production increase working fluid is injected below the formation fracture pressure, and the injection amount of the water control and production increase working fluid is calculated according to the following formula: V=π×(R2 2 -R1 2 )×h×Φ×S w Formula I, In formula I: V-injection volume of water control and production increase working fluid, m 3 ; R2- the outer radius of the water control and production increase working fluid, m; R1- the inner radius of the water control and production increase working fluid, m; h-thickness of the perforated layer, m; Φ-formation porosity, %; S w - water saturation, %; Alternatively, the water control and production increase working fluid is injected above the formation fracture pressure, and the injection amount of the water control and production increase working fluid is calculated according to the following formula: V=[π×(R2 2 -R1 2 )×h×Φ+4×H×L×W]×S w Formula II, In formula II: V-injection volume of water control and production increase working fluid, m 3 ; R2- the outer radius of the water control and production increase working fluid, m; R1- the inner radius of the water control and production increase working fluid, m; h-thickness of perforated layer, m; Φ-formation porosity, %; L-fracture half-length, m; H-fracture height, m; W-fracture width, m; S w - Water saturation, %.

11. The construction method for controlling water and increasing production in a low-permeability, high-water-saturated gas reservoir according to claim 9, wherein: The injection rate of the water control and production increase working fluid is 0.8-10m 3 / min, preferably 0.8-5m 3 / min; Preferably, the water control and production increase working fluid is injected in a multi-stage plug alternating manner through a bare casing or a tubing; Preferably, water displacement with a pH of 7 is adopted, and the amount of water used is the volume required to completely displace the wellhead into the formation; Preferably, the shut-in time is 2-10 hours, preferably 5-8 hours.

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