CN111978944A - Application of modified nano graphene oxide as chemical agent for improving recovery ratio of low-permeability reservoir - Google Patents
Application of modified nano graphene oxide as chemical agent for improving recovery ratio of low-permeability reservoir Download PDFInfo
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Abstract
The application discloses application of modified nano graphene oxide as a chemical agent for improving the recovery ratio of a low-permeability reservoir. The modified nano graphene oxide is prepared by oxidizing and stripping microcrystalline graphite to obtain microcrystalline graphene oxide and modifying the microcrystalline graphene oxide by a modifier. The modified nano graphene oxide is mixed with water to form fluid which is injected into a low-permeability oil reservoir stratum, so that the oil recovery rate can be effectively improved. The modified nano graphene oxide material is of a flexible lamellar structure, the size of the modified nano graphene oxide material is smaller than 300nm, the modified nano graphene oxide material is suitable for the pore throat size of a low-permeability reservoir, the damage such as blockage of a stratum can not be caused, and the modified nano graphene oxide material is small in adsorption loss of the stratum, excellent in temperature resistance and salt tolerance and beneficial to overcoming the problems faced in the development process of the low-permeability reservoir at present.
Description
Technical Field
The application relates to application of modified nano graphene oxide as a chemical agent for improving the recovery ratio of a low-permeability reservoir, belonging to the field of chemical materials.
Background
Petroleum has irreplaceable effect in national economy, and along with the rapid growth of national economy in China, the demand for petroleum is also continuously and rapidly improved. According to data in blue book of oil and gas industry development analysis and prospect reports in China (2018-2019), the yield of crude oil in China in 2018 is 1.89 hundred million tons, the import quantity of crude oil is 4.62 hundred million tons, and the dependence on the outside is increased to nearly 70%. After primary oil recovery and secondary oil recovery, the underground still has abundant oil reserves, but the difficulty of exploitation is gradually increased, and particularly, the huge oil reserves are difficult to use for the low-permeability oil reservoir with the permeability lower than 50 mD. Therefore, the technology for efficiently improving the recovery efficiency aiming at the development of the low-permeability oil reservoir is a strategic demand for realizing national energy safety.
The low-permeability oil reservoir is widely distributed in more than 20 oil areas in China, and a plurality of low-permeability oil reservoirs are successively discovered in main oil fields of Daqing, Jilin, Liaohe, Shengli, Changqing and the like since the 90 s of the last century. According to statistics, the low-permeability reservoir reserves account for 60-70% of newly-explored petroleum geological reserves, and the low-permeability reservoir is the main basis for increasing production and storage for a long time in the future in China.
The current enhanced recovery techniques for low-permeability reservoirs include water flooding, surfactant flooding, polymer flooding, microbial flooding, complex flooding and other technical systems. The application of the prior art to low-permeability oil reservoirs has various problems. The low-permeability reservoir water flooding has small swept area, is easy to cause water channeling and flooding, has low oil displacement efficiency, the water flooding recovery ratio is only about 20 percent, and most of crude oil is retained in the reservoir and cannot be produced. The surfactant flooding technology has the problems of high stratum adsorption loss, intolerance to divalent salt, difficulty in treatment of oil-water emulsification of produced liquid and the like when applied on site. Due to the fact that the throat of the low-permeability reservoir is fine and the pore structure is complex, when the polymer flooding agent is applied to the low-permeability reservoir, the problems of stratum blockage and high temperature and salt resistance are caused, and the recovery efficiency cannot be effectively improved. The microbial oil displacement technology has the problems of short effective time, cross flow of an activating agent, unsatisfactory oil displacement efficiency and the like. The binary and ternary combination flooding technology has the problems, and a large amount of chemicals are not easily biodegraded after being injected into a stratum, so that underground water resource pollution and reservoir ecological environment damage can be caused.
At present, the research reports of applying the nano material oil displacement technology to a low-permeability oil reservoir are few, and the nano material is mainly a modified nano silicon dioxide material. Patent application No. CN201810838339.7 discloses a nanoparticle suspension comprising rhamnolipid surfactant, nanosilica and its application in enhanced recovery of low permeability oil reservoir. However, when the nano-silica material is applied to a low-permeability oil reservoir, the limitations of large stratum adsorption, no high temperature resistance, high salinity resistance and the like still exist.
Disclosure of Invention
According to the first aspect of the application, modified nano graphene oxide is provided to be applied as a chemical agent for improving the recovery ratio of a low-permeability reservoir, and the modified nano graphene oxide is smaller than 300nm in size and has a flexible lamellar structure, so that the modified nano graphene oxide can adapt to the pore throat size of the low-permeability reservoir through deformation, the stratum adsorption loss is small, the high-temperature and high-salt conditions can be resisted, and the problem faced in the development process of the low-permeability reservoir at present can be overcome.
The modified nano graphene oxide is applied as a chemical agent for improving the recovery ratio of an oil reservoir, the modified nano graphene oxide is formed by modifying microcrystalline graphene oxide through a modifier, the particle size of the modified nano graphene oxide is less than or equal to 300nm, and the modified nano graphene oxide is mixed with mineralized water to form fluid which is injected into an oil reservoir stratum.
Optionally, the modified nano graphene oxide is mixed with mineralized water to form a fluid with the mass concentration of 0.05-0.2% and the fluid is injected into an oil reservoir stratum.
Optionally, the reservoir refers to a low permeability reservoir having a permeability of less than 50 mD.
Optionally, the microcrystalline graphene oxide is microcrystalline graphene oxide with a particle size of 200nm or less, optionally, the upper limit of the particle size of the microcrystalline graphene oxide can be selected from 150nm and 100nm, and preferably, the particle size of the microcrystalline graphene oxide is 50-100 nm.
Optionally, the preparation method of the microcrystalline graphene oxide comprises the following steps:
oxidizing the microlite ink powder to obtain microcrystalline graphite oxide, wherein the carbon content of the microlite ink powder can be 75-100 wt%;
and stripping and removing impurities from the microcrystalline graphite oxide to obtain microcrystalline graphene oxide with the particle size of less than or equal to 200 nm.
By adopting the microcrystalline graphite powder as the raw material, on one hand, the raw material source is wide, the production cost of the modified nano graphene can be effectively reduced, and the popularization and the application of the chemical agent for improving the recovery ratio are facilitated; on the other hand, the particle size of graphite in the microcrystalline graphite is far smaller than that of graphite in the crystalline flake graphite, and the modified nano graphene oxide material with smaller size can be obtained by taking the microcrystalline graphite as a raw material.
Optionally, the particle size of the microcrystalline graphite powder is less than or equal to 5 μm.
Optionally, the particle size of the microcrystalline graphite powder is 100 nm-5 μm; the upper limit of the grain size of the microcrystalline graphite powder can be selected from 5 μm, 1.6 μm, 1.3 μm, 1 μm, 900nm, 800nm, 700nm, 600nm, 500nm, 400nm, 300nm or 200nm, and the lower limit can be selected from 1.6 μm, 1.3 μm, 1 μm, 900nm, 800nm, 700nm, 600nm, 500nm, 400nm, 300nm, 200nm or 100 nm.
Preferably, the grain diameter of the microcrystalline graphite powder is less than or equal to 1.6 mu m. When the grain size of the microcrystalline graphite powder is less than or equal to 1.6 mu m, the recovery ratio can be improved, so that the oil displacement performance is excellent, the absorption of the core is low, and the loss is less.
The microcrystalline graphene oxide with the particle size of less than or equal to 200nm can be obtained by adopting the microcrystalline graphite powder with the particle size range through oxidation, stripping and impurity removal.
Optionally, the conditions for oxidizing the microcrystalline graphite powder include:
adopting a chemical oxidation method, and taking concentrated sulfuric acid, potassium permanganate and hydrogen peroxide as oxidants; the dosage of concentrated sulfuric acid corresponding to each gram of microcrystalline graphite powder is 20-100 grams;
the dosage of potassium permanganate corresponding to each gram of microlite ink powder is 1-5 grams;
the concentration of the hydrogen peroxide is 25-40%, and the dosage of the hydrogen peroxide corresponding to every gram of the microcrystalline graphite powder is 0.1-1.2 g.
Other reaction conditions such as stirring conditions, reaction temperature, reaction time, separation conditions, washing conditions, etc. are the same as those of the conventional Hummers chemical oxidation method.
Optionally, the conditions for exfoliating the microcrystalline graphite oxide include:
peeling by ultrasound;
the ultrasonic power is 700-750W; preferably 720 w;
the ultrasonic frequency is 10-30 Hz; preferably 20 Hz;
the ultrasonic time is 0.5-2 h.
By carrying out ultrasonic stripping under the condition, the preparation time of the microcrystalline graphene oxide with small particle size is greatly shortened, and the production efficiency is improved.
Further, after the oxidizing and stripping of the microcrystalline graphite powder, the method further comprises the following steps:
removing impurities by a centrifugal mode;
the centrifugal rotating speed is 100-1000 rpm;
the centrifugation time is 5-20 min.
Alternatively, the upper limit of the centrifugation rotation speed may be selected from 1000rpm, 800rpm, 700rpm, 600rpm, 500rpm, 400rpm, 300rpm or 200rpm, and the lower limit may be selected from 800rpm, 700rpm, 600rpm, 500rpm, 400rpm, 300rpm, 200rpm or 100 rpm. The upper limit of the centrifugation time can be selected from 20min, 15min or 10min, and the lower limit can be selected from 15min, 10min or 5 min.
The preparation method belongs to normal temperature and pressure, the operation is safe and simple, and the prepared nano-grade modified graphene oxide chemical agent for improving the recovery ratio has good dispersibility in water
Optionally, the modifier comprises at least one of fatty alcohol-polyoxyethylene ether, lauric acid diethanolamide, N-vinyl pyrrolidone, polyethyleneimine, polyethylene glycol, oleic acid, sodium alpha-olefin sulfonate, acrylic acid and acrylamide,
the preparation method of the modified nano graphene oxide comprises the following steps:
and reacting the mixture containing the microcrystalline graphene oxide dispersion liquid and the modifier under the action of a catalyst to obtain the modified nano graphene oxide.
The modifying agent reacts with carboxyl, hydroxyl and epoxy groups on the microcrystalline graphene oxide by using a catalyst, and the modifying group is grafted to the microcrystalline graphene oxide, so that the microcrystalline graphene oxide is changed from hydrophilic to hydrophilic and oleophilic. When the material is applied to oil exploitation, the interfacial tension between oil and water can be effectively reduced, so that the oil recovery rate is improved, the temperature resistance and salt tolerance of the material are improved after modification, and the adsorbability of the material in a stratum environment is reduced.
Optionally, in the microcrystalline graphene oxide dispersion liquid, the concentration of the microcrystalline graphene oxide is 0.01-30 mg/ml.
Optionally, the mass ratio of the microcrystalline graphene oxide to the modifier is 1:1 to 1: 100.
Optionally, the catalyst is at least one of dicyclohexylcarbodiimide, N-diisopropylcarbodiimide, 1-ethyl- (3-dimethylaminopropyl) carbodiimide hydrochloride, N-hydroxysuccinimide, azobisisobutyronitrile, potassium persulfate, ammonium persulfate, hydrogen peroxide, 4-dimethylaminopyridine, sodium hydroxide and hydrochloric acid.
Optionally, the ratio of the amount of the catalyst to the mass of the modifier is 1:1 to 1: 100.
Optionally, the conditions of the reaction include:
reacting under stirring;
the stirring speed is 100-800 rpm;
the stirring time is 1 to 8 hours;
optionally, the mass concentration of the modified nano graphene oxide in the fluid is 0.001-0.02%.
The upper limit of the mass concentration of the modified nano graphene oxide in the fluid can be selected from 0.02%, 0.015%, 0.01% or 0.005%, and the lower limit can be selected from 0.015%, 0.01%, 0.005%, 0.001%.
Optionally, the degree of mineralization of the water is 2000-50000 mg/L. The upper limit of the degree of mineralization of the water can be selected from 50000mg/L, 45000mg/L, 40000mg/L, 35000 mg/L30000 mg/L, 25000mg/L, 20000mg/L, 15000mg/L, 10000mg/L, 5000mg/L, 4000mg/L or 3000mg/L, and the lower limit can be selected from 45000mg/L, 40000mg/L, 35000 mg/L30000 mg/L, 25000mg/L, 20000mg/L, 15000mg/L, 10000mg/L, 5000mg/L, 4000mg/L, 3000mg/L or 2000 mg/L.
In an alternative specific embodiment, the preparation method of the modified nano graphene oxide includes:
step (1), purchasing microcrystalline graphite powder meeting the requirement of particle size, and oxidizing the microcrystalline graphite powder by using a chemical oxidation method to obtain microcrystalline graphite oxide;
step (2) removing large-particle impurities at the bottom layer of the microcrystalline graphite oxide obtained in the step (1) by low-speed centrifugation, standing filtration and other modes, and washing the microcrystalline graphite oxide by deionized water to obtain relatively pure microcrystalline graphite oxide gel;
step (3) carrying out ultrasonic stripping on the microcrystalline graphite oxide obtained in the step (2), and removing impurities from the ultrasonically stripped microcrystalline graphene oxide gel to obtain a microcrystalline graphene oxide dispersion liquid with the average particle size of 100-200 nm;
and (4) modifying the microcrystalline graphene oxide dispersion liquid obtained in the step (3) to obtain a modified nano graphene oxide chemical agent for improving the recovery ratio, which is suitable for the low-permeability oil reservoir.
Optionally, screening out a microcrystalline graphite sample with the particle size of less than or equal to 1.3 mu m in the step (1);
optionally, the oxidant used in the step (1) is concentrated sulfuric acid, potassium permanganate and hydrogen peroxide, the use amount of the concentrated sulfuric acid is 20-100 times of that of the graphite, the use amount of the potassium permanganate is 1-5 times of that of the graphite, and the use amount of the hydrogen peroxide is 0.1-1.0 time of that of the graphite;
optionally, the centrifugation rotating speed in the step (2) is 100-;
optionally, the ultrasonic time in the step (3) is 0.5-2h, the ultrasonic power is 720w, and the frequency is 20 Hz.
The beneficial effects that this application can produce include:
(1) the modified nano graphene oxide material is of a flexible lamellar structure, has a size smaller than 300nm, and is suitable for the pore throat size of a low-permeability reservoir;
(2) the modified nano graphene oxide material can resist the high temperature of 80-120 ℃, can resist 50000-200000 ppm of high salinity brine, and can adapt to more harsh oil reservoir conditions;
(3) compared with materials such as polyacrylamide, surfactant and the like commonly used in oil fields, the modified nano graphene oxide material has little absorption loss in stratum;
(4) the preparation process of the modified nano graphene oxide provided by the application belongs to normal temperature and normal pressure, the operation is safe and simple, and the prepared nano modified graphene oxide chemical agent for improving the recovery ratio has good dispersibility in water and various oily solvents;
(5) the microcrystalline graphite is selected as a raw material, and compared with a crystalline flake graphite raw material with the same mesh number, the modified nano graphene oxide material with smaller size can be prepared.
Drawings
Fig. 1 is an infrared spectrum of microcrystalline graphene oxide before modification and modified nano graphene oxide after modification in example 1;
FIG. 2 is a particle size distribution diagram of modified nano-graphene oxide obtained by oxidation exfoliation and graft modification based on microcrystalline graphite in example 1;
FIG. 3 is a particle size distribution diagram of modified nano graphene oxide obtained by oxidation stripping and graft modification of crystalline flake graphite in comparative example 1;
fig. 4 is a scanning electron microscope photograph of modified nano graphene oxide obtained by oxidation exfoliation and graft modification based on microcrystalline graphite in example 1.
Detailed Description
The present application will be described in detail with reference to examples, but the present application is not limited to these examples.
The raw materials in the examples of the present application were all purchased commercially, unless otherwise specified.
Wherein the microlite ink powder is purchased from southern graphite Limited and has a size of 3000 mesh (primary particle size of 5 μm), 8000 mesh (primary particle size of 1.6 μm) and 15000 mesh (primary particle size of 1 μm);
flake graphite powder was purchased from Qingdao Virgi graphite GmbH, model 15000 mesh (primary particle size 1 μm);
concentrated sulfuric acid, potassium permanganate, hydrogen peroxide, polyethyleneimine, polyoxyethylene lauryl ether, polyethylene glycol, N-vinyl pyrrolidone, dichloromethane, azodiisobutyronitrile, N-diisopropyl carbodiimide, 1-ethyl- (3-dimethylaminopropyl) carbodiimide hydrochloride, N-hydroxysuccinimide, 4-dimethylaminopyridine, nano silicon dioxide, rhamnolipid and other reagents are purchased from Shanghai Arlatin Biotechnology GmbH.
Unless otherwise specified, the reactions in the examples were all carried out at room temperature.
The analysis method in the examples of the present application is as follows:
particle size testing was performed using a malvern laser particle sizer (available from shanghai thinking instruments systems limited);
scanning electron microscope SEM tests were performed using a Carl Zeiss EVO 18 type scanning electron microscope (from Call Zeiss, Germany);
infrared testing was performed using a Nicolet iS50 fourier transform infrared spectrometer (available from seimer feishell science ltd);
carrying out indoor petroleum displacement experiments by adopting DNQP type indoor petroleum displacement equipment (purchased from Nantong Huaxing petroleum instruments Co., Ltd.);
the rock core used in the indoor petroleum displacement experiment is an American Bailey sandstone natural rock core which is purchased from Beijing Oriental Zhisheng Petroleum science and technology Limited and has the permeability of 20-50 mD;
the concentration of the sample in the effluent was measured using a high performance liquid chromatograph model 1260 (available from Agilent, usa).
The method for calculating the enhanced oil recovery in the embodiment of the application comprises the following steps:
example 1
1. Weighing 250mL of 98 mass percent concentrated sulfuric acid, pouring the concentrated sulfuric acid into a 500mL glass beaker with a stirrer for stirring, slowly adding weighed 5.00g of 15000-mesh microcrystalline graphite powder into the beaker, carrying out magnetic stirring in an ice water bath for 30min, slowly adding 25g of ground potassium permanganate powder while stirring, continuously keeping stirring in the ice water bath for 120min, removing the ice water bath, raising the temperature to 37 ℃, continuously keeping stirring for 120min, slowly adding deionized water, controlling the temperature to be lower than 60 ℃, adding water until the temperature of a reaction system does not rise any more, and dropwise adding 5mL of H with the concentration of 30%2O2；
2. Placing the solution in a centrifuge, setting the rotation speed to 800 revolutions for 5 minutes, standing, filtering to remove large-particle impurities, transferring into a 1000mL beaker, adding deionized water, and washing until the pH value is more than or equal to 6 to obtain microcrystalline graphite oxide gel;
3. placing the microcrystalline graphite oxide gel into an ultrasonic dispersion machine, ultrasonically dispersing for 60min at the power of 720w and the frequency of 20Hz, peeling, transferring to a centrifuge, centrifuging for 5min at the rotating speed of 3000rpm, removing impurities to obtain microcrystalline graphene oxide dispersion liquid, and testing the average particle size by using a Malvern laser particle sizer;
4. sequentially adding 50 g of polyethyleneimine, 10 g of 1-ethyl- (3-dimethylaminopropyl) carbodiimide hydrochloride and 6 g of N-hydroxysuccinimide into the microcrystalline graphene oxide dispersion liquid, adjusting the pH value of the mixture to 6-7, keeping stirring for reaction for 24 hours, filtering and centrifuging, and redispersing in deionized water to obtain polyethyleneimine modified nano graphene oxide serving as a chemical agent for improving the recovery ratio, wherein the chemical agent is marked as C1;
5. using a Malvern laser particle size analyzer to test the average particle size as shown in figure 2, using an SEM to observe the morphology of the nano material as shown in figure 4, using an infrared spectrometer to detect the grafting degree of the modifier as shown in figure 1, using mineralized water to dilute the modified nano graphene oxide dispersion liquid to a specified concentration, and putting the diluted nano graphene oxide dispersion liquid into an oven with a set temperature to perform temperature resistance and salt tolerance stability investigation.
6. And (3) diluting the modified nano graphene oxide dispersion liquid to a specified concentration by using mineralized water, performing an indoor petroleum displacement experiment, evaluating the performance of improving the recovery rate, detecting the concentration of the modified nano graphene oxide in the displacement liquid, and evaluating the degree of adsorption loss.
Example 2
In this example, 8000-mesh microcrystalline graphite was used instead of 15000-mesh microcrystalline graphite powder in example 1, and the same method and procedure as in example 1 were used to obtain a polyethyleneimine-modified nano graphene oxide chemical agent for improving recovery, which is denoted as C2.
Example 3
This example was prepared essentially the same as example 1 except that 3000 mesh microcrystalline graphite powder was used in step 1 and the final product was designated C3.
Example 4
The preparation method of the embodiment is basically the same as that of embodiment 1, except that in step 1, the amount of concentrated sulfuric acid is 100mL, and the amount of potassium permanganate is 5g, so as to finally obtain the polyethyleneimine-modified nano graphene oxide chemical agent for improving the recovery ratio, which is recorded as C4.
Example 5
4. sequentially adding 50 g of N-vinyl pyrrolidone and 5g of azodiisobutyronitrile into the microcrystalline graphene oxide dispersion liquid, introducing nitrogen to remove oxygen, heating to 70 ℃, keeping stirring at 500 revolutions per minute, and reacting for 5 hours to obtain polyvinylpyrrolidone modified nano graphene oxide serving as a chemical agent for improving the recovery ratio, which is marked as C5;
Example 6
4. drying the microcrystalline graphene oxide water dispersion, dissolving the microcrystalline graphene oxide water dispersion by using dichloromethane, adding 50 g of lauryl alcohol polyoxyethylene ether, 1 g of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride and 1 g of 4-dimethylaminopyridine, stirring at room temperature for 24 hours, then carrying out dilute hydrochloric acid washing, water washing and filtering to obtain lauryl alcohol polyoxyethylene ether modified nano graphene oxide water dispersion serving as a chemical agent for improving the recovery ratio, which is marked as C6;
Example 7
The preparation method of the embodiment is basically the same as that of embodiment 6, except that polyethylene glycol is used to replace lauryl alcohol polyoxyethylene ether in step 4, and finally the polyethylene glycol modified nano graphene oxide enhanced recovery chemical agent, which is recorded as C7, is obtained.
Example 8
The preparation method of the embodiment is basically the same as that of embodiment 6, except that oleic acid is used to replace lauryl alcohol polyoxyethylene ether to obtain the oleic acid modified nano graphene oxide enhanced recovery chemical agent, which is marked as C8.
Comparative example 1
In the comparative example, 15000-mesh crystalline flake graphite is used to replace microcrystalline graphite in example 1, and the preparation method and the steps which are the same as those in example 1 are adopted to obtain the polyethyleneimine modified nano graphene oxide chemical agent for improving the recovery ratio, which is recorded as D1.
Comparative example 2
Mixing nano silicon dioxide particles with the average particle size of 15nm and rhamnolipid according to the mass ratio of 25:1 to obtain the chemical agent for improving the recovery ratio, which is recorded as D2.
Analysis of the product
The results of the infrared spectroscopy measurements of the microcrystalline graphene oxide before modification and the modified nano graphene oxide after modification with polyethyleneimine in example 1 are shown in fig. 1. As can be seen from FIG. 1, the microcrystalline graphene oxide before modification was at 1720cm-1And 1612cm-1The characteristic absorption peaks at (a) are respectively attributed to the carbon-oxygen double bond of the carboxylic acid group on the graphene oxide and the carbon-carbon double bond on the graphene oxide. The infrared spectrogram of the modified nano graphene oxide has strong amido bond (3337 cm)-1、3182cm-1、1646cm-1，1596cm-1) The infrared characteristic absorption peak proves that the grafting of the polyethyleneimine on the microcrystalline graphene oxide is successful.
Examples 2, 3, 4 also exhibited the same or similar characteristics as example 1, demonstrating the success of polyethyleneimine-modified grafting.
Comparison of infrared spectra of graphene oxide before and after modification in examples 5, 6, 7, and 8 shows that ester bonds appear, which proves successful grafting of the modifier.
The particle size of the product is shown in table 1:
TABLE 1 particle size table of the products
The results of the particle size tests of C1 and D1 show that compared with crystalline flake graphite, the size of the product can be effectively reduced by selecting microcrystalline graphite, and the results of C1-C8 show that the preferable dosage of the oxidant, the type of the modifier and the dosage of the catalyst can ensure that the size of the modified nano graphene oxide chemical agent for improving the recovery ratio is smaller. The comparative product D2 based on nano-silica shows the smallest particle size, but the subsequent temperature resistance, salt tolerance and adsorption performance tests show the defects.
Taking C1 as a representative example, fig. 2 is a particle size distribution diagram of the modified nano graphene oxide, and as can be seen from fig. 2, the average particle size of the modified nano graphene oxide C1 is 143.2 nm.
Taking C1 as a typical representative, FIG. 4 is a scanning electron micrograph of the modified graphene oxide, and it can be seen from the scanning electron micrograph that the modified nano graphene oxide is a multi-fold flexible lamellar nano material.
Example 9
Carrying out temperature resistance and salt tolerance tests on the products provided in examples 1-8 and comparative examples 1-2:
preparing a test sample:
mixing products C1, C2, C3, C4, C5, C6, C7, C8, D1 and D2 with water with the mineralization degree of 50000ppm respectively to obtain dispersion liquid samples with the mass fraction of 0.1%, which are respectively marked as H1, H2, H3, H4, H5, H6, H7, H8, H9 and H10;
mixing products C1, C2, C3, C4, C5, C6, C7, C8, D1 and D2 with water with the mineralization degree of 100000ppm respectively to obtain dispersion liquid samples with the mass fraction of 0.1 percent, which are respectively marked as G1, G2, G3, G4, G5, G6, G7, G8, G9 and G10;
mixing products C1, C2, C3, C4, C5, C6, C7, C8, D1 and D2 with water with the mineralization degree of 200000ppm respectively to obtain dispersion liquid samples with the mass fraction of 0.1%, which are respectively marked as L1, L2, L3, L4, L5, L6, L7, L8, L9 and L10;
the method for testing the temperature resistance and salt tolerance comprises the following steps:
the dispersion sample was placed in a precision incubator at 80 ℃, 100 ℃ and 120 ℃. And (5) observing the appearance of the diluent after the diluent is placed for 7 days at constant temperature, and observing whether precipitates and suspended particles exist in an environment with sufficient light.
The test results of the temperature resistance and salt tolerance of the product are shown in the table 2:
TABLE 2 test results of temperature and salt resistance stability of the product
The temperature resistance and salt tolerance test results in table 2 show that the modified graphene oxide enhanced recovery chemical agent in examples 1 to 8 can tolerate higher temperature and mineralization degree compared with the chemical agent products in comparative examples 1 to 2. The products C1-C8 can simultaneously resist the high temperature of 120 ℃ and the salinity of 20 ten thousand brine to keep stable dispersion without precipitation, while the comparative product D1 can only resist the temperature of 80 ℃ and the comparative product D2 can only resist the salinity of 5 ten thousand brine.
In the tables, "√" indicates that no sediment or suspended particles have occurred, and "×" indicates that sediment or suspended particles have occurred
Example 10
Oil displacement performance and adsorption performance tests were performed on dispersion samples H1, H2, H3, H4, H5, H6, H7, H8, H9, and H10:
the oil displacement performance test method comprises the following steps:
firstly, drying a rock core at 110 ℃ for 12 hours, vacuumizing, injecting mineralized water for water saturation, obtaining pore volume PV by a weighing method, then injecting crude oil for oil saturation, recording saturated oil quantity V1, aging at 70 ℃ for 48 hours, injecting mineralized water for water flooding until no oil is expelled (injection volume 2PV), and then sequentially performing enhanced recovery chemical flooding (enhanced recovery chemical injected in volume 2PV) and subsequent water flooding (injection volume 2 PV). The injection rate was maintained at 0.2mL/min and the oil volume from the water flooding stage, V2, the oil volume from the enhanced recovery chemical flooding stage, V3, and the oil volume from the subsequent water flooding stage, V4, were recorded.
And (V3+ V4)/V1 multiplied by 100 percent is calculated to be the rate-increasing value.
The results of the sample oil displacement performance test are shown in table 3:
TABLE 3 oil displacement Performance test results of the product
| Sample (I) | H1 | H2 | H3 | H4 | H5 | H6 | H7 | H8 | H9 | H10 |
| Enhanced recovery ratio% | 24.1 | 22.3 | 21.5 | 20.4 | 21.3 | 20.9 | 20.2 | 20.8 | 10.3 | 9.8 |
And (4) analyzing results:
as can be seen from table 3, the enhanced recovery results of H1-H8 all exceed 20%, and it can be seen that the enhanced recovery results can enter the core and displace the residual oil after the first water flooding, thereby achieving the enhancement of the recovery efficiency; the enhanced oil recovery results of H9 and H10 are less than 11%, so that the oil displacement performance of the enhanced oil recovery system is obviously lower than that of the enhanced oil recovery system provided by the embodiment of the application;
particularly, the product C1 in example 1, at a concentration of 0.1% by mass (mineralization degree in dispersion is5 ten thousand ppm), the recovery ratio is improved by as high as 22.1%, and the excellent oil displacement performance is shown; in contrast, the product D2 in comparative example 2, at a concentration of 0.1% by mass (mineralization degree in dispersion is5 ten thousand ppm), the enhanced recovery ratio is only 9.8%, and the oil displacement effect is not good.
And (3) testing the adsorption performance:
the concentrations of samples H1, H2, H3, H4, H5, H6, H7, H8, H9 and H10 in the flooding liquid in the oil displacement performance experiment are detected by a high performance liquid chromatograph, and the adsorption loss degree is evaluated.
The concentration of the sample in the displacement fluid is cDriving deviceThe volume of the displacement liquid is VDriving deviceThe concentration of the injected sample is 0.1%, the injection volume is 2PV, and the adsorption rate calculation method comprises the following steps:
TABLE 4 test results of adsorption properties of the products
| Sample (I) | H1 | H2 | H3 | H4 | H5 | H6 | H7 | H8 | H9 | H10 |
| Adsorption rate% | 8.2 | 9.4 | 9.7 | 10.2 | 11.6 | 10.8 | 11.1 | 11.7 | 30.2 | 59.4 |
And (4) analyzing results:
as can be seen from Table 4, the adsorption rate results of H1-H8 are all lower than 12%, and it can be seen that the adsorption on the rock core is lower and the loss is less; the adsorption rate results of H9 and H10 are both more than 30%, and the adsorption loss of the H9 and H10 in the core is very large.
Although the present application has been described with reference to a few embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application as defined by the appended claims.
Claims (10)
1. The application of the modified nano graphene oxide as a chemical agent for improving the recovery ratio of a low-permeability reservoir is characterized in that the modified nano graphene oxide is prepared by oxidizing, stripping and removing impurities from microcrystalline graphite to obtain microcrystalline graphene oxide and modifying the microcrystalline graphene oxide with a modifier;
the particle size of the modified nano graphene oxide is less than or equal to 300 nm;
and mixing the modified nano graphene oxide with mineralized water to form fluid to be injected into an oil reservoir stratum.
2. The application of claim 1, wherein the mass concentration of the modified nano graphene oxide in the fluid is 0.05-0.2%;
preferably, the grain size of the microcrystalline graphene oxide is less than or equal to 200 nm.
3. The use according to claim 2, wherein the preparation method of the microcrystalline graphene oxide comprises:
oxidizing the microlite ink powder to obtain microcrystalline graphite oxide;
and stripping and removing impurities from the microcrystalline graphite oxide to obtain microcrystalline graphene oxide.
4. The use according to claim 3, characterized in that the particle size of the microcrystalline graphite powder is ≤ 5 μm; stripping the microcrystalline graphite oxide, and removing impurities to obtain microcrystalline graphene oxide with the particle size of no more than 200 nm;
preferably, the grain diameter of the microcrystalline graphite powder is less than or equal to 1.6 mu m.
5. Use according to claim 3, wherein the conditions for oxidation of the microcrystalline graphite powder comprise:
adopting a chemical oxidation method, and taking concentrated sulfuric acid, potassium permanganate and hydrogen peroxide as oxidants;
the dosage of concentrated sulfuric acid corresponding to each gram of microcrystalline graphite powder is 20-100 grams;
the dosage of potassium permanganate corresponding to each gram of microlite ink powder is 1-5 grams;
the concentration of the hydrogen peroxide is 25-40%, and the dosage of the hydrogen peroxide corresponding to every gram of the microcrystalline graphite powder is 0.1-1.2 g.
6. The use according to claim 3, wherein the conditions for exfoliating the microcrystalline graphite oxide comprise:
peeling by ultrasound;
the ultrasonic power is 700-750W;
the ultrasonic frequency is 10-30 Hz;
the ultrasonic time is 0.5-2 h.
7. The use according to claim 3, wherein after the oxidizing and stripping of the microcrystalline graphite powder, the method further comprises:
removing impurities by a centrifugal mode;
the centrifugal rotating speed is 100-1000 rpm;
the centrifugation time is 5-20 min.
8. The use of claim 1, wherein the modifier comprises at least one of fatty alcohol-polyoxyethylene ether, lauric diethanolamide, N-vinylpyrrolidone, polyethyleneimine, polyethylene glycol, oleic acid, sodium alpha-olefin sulfonate, acrylic acid, acrylamide.
9. The application of the modified nano graphene oxide as claimed in claim 8, wherein the preparation method of the modified nano graphene oxide is as follows:
reacting a mixture containing microcrystalline graphene oxide dispersion liquid and a modifier under the action of a catalyst to obtain modified nano graphene oxide;
preferably, the catalyst is selected from at least one of dicyclohexylcarbodiimide, N-diisopropylcarbodiimide, 1-ethyl- (3-dimethylaminopropyl) carbodiimide hydrochloride, N-hydroxysuccinimide, azobisisobutyronitrile, potassium persulfate, ammonium persulfate, hydrogen peroxide, 4-dimethylaminopyridine, sodium hydroxide and hydrochloric acid.
10. The use according to claim 1, wherein the degree of mineralization of the mineralized water is 2000-200000 mg/L;
preferably, the reservoir is a low permeability reservoir having a permeability of less than 50 mD.
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