CN112646560B - A method for simulating oil recovery using cellulose nanocrystals - Google Patents

Abstract

The invention discloses a method for simulating oil recovery by using cellulose nanocrystals, comprising the following steps: processing crude oil, filtering the crude oil with a vacuum filter and filter paper; preparing a cellulose nanocrystal-sodium chloride mixed colloid solution, and screening fibers once The stable concentration range of the cellulose nanocrystal-sodium chloride mixed colloid solution was determined, and the concentration of the cellulose nanocrystal-sodium chloride colloid system that affected the permeability in the sandstone was screened out by detecting the interfacial tension measurement method and the contact angle measurement method. ; Inject the cellulose nanocrystal-sodium chloride mixed colloidal solution screened for the second time into the sandstone core according to the double displacement mode; yield data; the invention utilizes cellulose nanocrystal particles to block high-permeability strips to expand the sweep volume; utilizes cellulose nanocrystal-sodium chloride mixed colloidal solution to improve oil-water interface properties and increase crude oil recovery.

Description

A method for simulating oil recovery using cellulose nanocrystals

technical field

The invention relates to the technical field of oil recovery simulation experiment methods, in particular to a method for simulating oil recovery by using cellulose nanocrystals.

Background technique

The polymer flooding method is to increase the viscosity of water with water-soluble polymer, and use it as an injection agent for oilfield development to enhance oil recovery. The basic principle of polymer flooding to enhance oil recovery is to increase the viscosity of injected water and reduce the mobility of oil displacement agent, thereby reducing fingering and channeling, and increasing sweep efficiency to enhance oil recovery.

Currently, the most commonly used polymers for polymer flooding methods are partially hydrolyzed polyacrylamide (HPAM) and xanthan gum, both of which decrease the fluidity of water by increasing its viscosity. However, both substances have substantial performance limitations in enhancing oil recovery: xanthan gum is easily degraded by bacteria, debris is prone to pore clogging, and thermal stability is relatively poor; HPAM is susceptible to a variety of chemical, thermal, mechanical effect of degradation, so its viscosifying effect gradually decreases as it passes through the porous medium. Since many polymers used in polymer flooding today are toxic and environmentally harmful, polymer flooding methods require a stable, environmentally friendly polymer for enhanced oil recovery.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for simulating oil recovery by utilizing cellulose nanocrystals, so as to solve the blockage of rock pores caused by the polymer flooding method in the prior art, the thermal stability is relatively poor, and the various polymers used are toxic and technical problems that are harmful to the environment.

In order to solve the above-mentioned technical problems, the present invention specifically provides the following technical solutions:

A method for simulating oil recovery using cellulose nanocrystals, comprising the following steps:

Step 100, processing crude oil, using vacuum filter and filter paper to filter crude oil;

Step 200: Prepare a cellulose nanocrystal-sodium chloride mixed colloid solution, and screen the stable concentration range in the cellulose nanocrystal-sodium chloride mixed colloid solution by using the stability measurement method, and select all the stable concentration ranges. The cellulose nanocrystal-sodium chloride mixed colloid solution is screened for the second time by detecting the interfacial tension measurement method and the contact angle measurement method, and the concentration of the cellulose nanocrystal-sodium chloride colloid system that affects the permeability in the sandstone;

Step 300 , pretreating the sandstone core, and injecting the cellulose nanocrystal-sodium chloride mixed colloidal solution screened for the second time into the pretreated sandstone core according to the double displacement mode;

Step 400 , compare the produced fluids in the two displacement modes, and calculate and compare the recovery factor data of the two displacement modes.

As a preferred solution of this embodiment, in step 200, the steps of preparing the cellulose nanocrystal-sodium chloride mixed colloid solution are as follows:

Obtain the original concentrated solution of cellulose nanocrystals with a concentration of 12.18 wt%;

Mixing and diluting deionized water with the original cellulose nanocrystals to form colloidal solutions of different concentrations of the cellulose nanocrystals;

Mixing different concentrations of sodium chloride solution with the original colloidal solution of cellulose nanocrystals to dilute the colloidal solution of cellulose nanocrystals to different concentrations and to generate different classes of the cellulose nanocrystals-chlorinated Sodium mixed colloidal solution;

The cellulose nanocrystal-sodium chloride mixed colloidal solution of the same type was stirred evenly and divided into two groups, and the two groups of the cellulose nanocrystal-sodium chloride mixed colloidal solution were placed at 20° C. and 60° C. respectively. stored in an incubator at ℃.

As a preferred solution of the present embodiment, in step 200, the specific implementation method of screening the stable concentration range in the cellulose nanocrystal-sodium chloride mixed colloid solution at one time by the stability measurement method is as follows:

Periodically sample the cellulose nanocrystal-sodium chloride mixed colloid solution stored in the incubator at 20°C and 60°C for stability measurement experiments;

The measurement results of each stability measurement experiment were compared, and the cellulose nanocrystal-sodium chloride colloidal solution that remained stable after one month of preparation was screened out.

As a preferred solution of this embodiment, the cellulose nanocrystal-sodium chloride mixed colloid solution in the stable concentration range of the primary screening is screened for the second time by detecting the interfacial tension measurement method and the contact angle measurement method, and filtering out the cellulose nanocrystal-sodium chloride mixed colloid solution that affects the permeability. The concentration of the cellulose nanocrystal-sodium chloride mixed colloid solution is to improve the recovery factor, and the specific implementation method is as follows:

The interfacial tension measurement experiment was carried out on the crude oil and the cellulose nanocrystal-sodium chloride colloidal solution that was screened to maintain stability, as well as the measurement experiment of the contact angle between the colloidal solution and the sandstone surface, and the suitable concentration range was further screened from the stable colloidal solution. colloidal solution to improve the injectability of the colloidal system in sandstone.

As a preferred solution of this embodiment, the contact angle measurement method is specifically, the contact angle of dropping the cellulose nanocrystal-sodium chloride mixed colloid solution in the screened stable concentration range on the surface of the polished sandstone.

As a preferred solution of this embodiment, the polished sandstone is pre-soaked in the crude oil environment described in step 100 for saturation aging.

As a preferred solution of this embodiment, in step 300, the cellulose nanocrystal-sodium chloride mixed colloidal solution screened for the second time is injected into the pretreated sandstone core according to the double displacement mode, wherein The double displacement mode includes injecting 0.1wt% NaCl solution as the first displacement mode until no oil is produced and the pressure difference is stable; then injecting the screened cellulose nanocrystal-sodium chloride mixed colloid The solution is used as a secondary displacement mode until no oil is produced and the pressure difference is stable.

As a preferred solution of this embodiment, in step 300, the realization steps of establishing the model body are as follows:

cleaning the sandstone to prevent porosity plugging of the sandstone, and soaking the sandstone with a vacuum saturated NaCl solution;

The crude oil filtered in step 100 is injected into the sandstone, and the sandstone core is saturated with crude oil to simulate the storage environment of the crude oil in the sandstone.

As a preferred solution of this embodiment, in step 300, the specific implementation method of injecting the cellulose nanocrystal-sodium chloride mixed colloid solution into the model body is as follows:

Step 301, carrying out an oil recovery flooding experiment with a 0.1wt% concentration of sodium chloride solution in the order of first low flow rate 0.3mL/min and then high flow rate 3mL/min, and collecting the first produced fluid with a test tube with a scale;

Step 302: When there are no obvious oil droplets in the produced liquid and the pressure difference is stable, stop injecting the sodium chloride solution, and filter the cellulose nanocrystal-sodium chloride mixed colloid solution with a suitable concentration range, using the first low flow rate. After 0.3mL/min and high flow rate of 3mL/min, the secondary oil recovery and displacement experiment was carried out, and the second produced fluid was collected again;

Step 303: When there are no obvious oil droplets in the second produced liquid and the pressure difference is stable, stop injecting the cellulose nanocrystal-sodium chloride mixed colloidal solution.

As a preferred solution of this embodiment, in step 303, after the injection of the cellulose nanocrystal-sodium chloride mixed colloid solution is stopped, 0.1 wt% sodium chloride solution is re-injected to remove the retained water in the Berea sandstone core. Cellulose nanocrystals are punched out.

Compared with the prior art, the present invention has the following beneficial effects:

According to the injectability of the nanocellulose-sodium chloride solution colloid system in the sandstone, the present invention screens the concentration range of the colloid components, and reduces the risk of pore throat blockage caused by instability of the colloid system due to excessive concentration; Cellulose nanocrystal particles can block the high-permeability strip and expand the swept volume; the cellulose nanocrystal-sodium chloride mixed colloidal solution is used to improve the properties of the oil-water interface and improve the oil recovery.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that are required to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, other implementation drawings can also be obtained according to the extension of the drawings provided without creative efforts.

1 is a schematic flowchart of a simulation experiment method provided in an embodiment of the present invention;

Fig. 2 is the solution sample ratio of the cellulose nanocrystal-sodium chloride mixed colloidal solution provided in the embodiment of the present invention, namely the numbered diagram;

Fig. 3 is the measurement result diagram of particle size provided by the embodiment of the present invention;

Fig. 4 is the measurement result diagram of the zeta potential provided by the embodiment of the present invention;

Fig. 5 is the measurement result diagram of interfacial tension and contact angle provided by the embodiment of the present invention;

6 is a schematic diagram of a core data table for simulating oil exploitation provided by an embodiment of the present invention;

7 is a schematic diagram of the output oil amount of simulated oil exploitation provided by an embodiment of the present invention;

FIG. 8 is a schematic diagram of an operation flow of an experimental method provided by an embodiment of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

As shown in Figure 1, the present invention provides a method for simulating oil recovery using cellulose nanocrystals, comprising the following steps:

Step 100, processing crude oil, using vacuum filter and filter paper to filter crude oil;

Step 200: Prepare a cellulose nanocrystal-sodium chloride mixed colloid solution, and screen the stable concentration range in the cellulose nanocrystal-sodium chloride mixed colloid solution by using the stability measurement method, and select all the stable concentration ranges. The cellulose nanocrystal-sodium chloride mixed colloid solution is screened for the second time by detecting the interfacial tension measurement method and the contact angle measurement method to screen the concentration of the cellulose nanocrystal-sodium chloride colloid system that affects the permeability in sandstone.

In this step, the realization steps of preparing the cellulose nanocrystal-sodium chloride mixed colloidal solution are:

(1) A concentrated colloidal solution of pristine cellulose nanocrystals with a concentration of 12.18 wt% was obtained.

(2) The deionized water is mixed and diluted with the original cellulose nanocrystals to form colloidal solutions of cellulose nanocrystals with different concentrations.

(3) Mixing different concentrations of sodium chloride solution with the original cellulose nanocrystal colloid solution to dilute the cellulose nanocrystal colloid solution to different concentrations, and generate different types of cellulose nanocrystal-sodium chloride mixed colloids solution.

Specifically in step (2), the concentrated colloidal solution of the original cellulose nanocrystals with a concentration of 12.18wt% is diluted with deionized water into fibers with a concentration of 0.05wt%, 0.1wt%, 0.5wt% and 1.0wt% colloidal solution of prime nanocrystals.

In step (3), 0.1 wt %, 0.5 wt % sodium chloride solution was used to mix with the concentrated colloidal solution of the original cellulose nanocrystals with a concentration of 12.18 wt %, and 12.18 wt % of the original cellulose The concentrated colloidal solutions of nanocrystals were diluted into colloidal solutions of cellulose nanocrystals with concentrations of 0.05 wt %, 0.1 wt %, 0.5 wt % and 1.0 wt %, respectively.

(4) The same type of cellulose nanocrystal-sodium chloride mixed colloidal solution was stirred evenly and divided into two groups, and the two groups of cellulose nanocrystal-sodium chloride mixed colloidal solutions were placed at 20°C and 60°C respectively. Stored in the incubator of 2000 ℃, the proportion of the solution samples of the cellulose nanocrystal-sodium chloride mixed colloidal solution specifically prepared is shown in Figure 2, and a total of 24 kinds of colloidal solutions are obtained.

It should be added that when the sodium chloride solution of different solubility is mixed with the diluted cellulose nanocrystal colloidal solution, the colloidal solution is stirred by a disperser to make the particle distribution more uniform, so as to avoid agglomeration and sedimentation.

The above-mentioned 24 kinds of colloidal solutions are respectively measured according to the planned time point of particle size and zeta potential, and the specific realization method of the stable concentration range in the cellulose nanocrystal-sodium chloride mixed colloidal solution is screened once by the stability measurement method. for:

(1) Regularly sample the cellulose nanocrystal-sodium chloride mixed colloid solution stored in the incubator at 20°C and 60°C for stability measurement experiments. Among them, the time points for timing sampling and measurement are the day, 24 hours, one week and one month of preparing the solution.

(2) The stability measurement results of each measurement experiment were compared, and the cellulose nanocrystal-sodium chloride colloidal solution that remained stable after one month of preparation was screened out.

It should be added that the parameters for the stability measurement of the prepared cellulose nanocrystal-sodium chloride mixed colloidal solution are: the particle size of the colloidal solution measured at the above sampling time point and the colloidal solution at the sampling time point. The measured zeta potential, the specific experimental results are shown in Figure 3 and Figure 4.

In addition, the nanoscale Malvern Zetasizer Nano ZS potential analyzer was used in the particle measurement experiment for sampling the cellulose nanocrystal-sodium chloride mixed colloid solution to measure the nanoparticle size and size of the cellulose nanocrystal-sodium chloride mixed colloid solution. Measurement of Zeta Potential.

According to the experimental results, the data of particle size and zeta potential both confirm that the colloidal solution of cellulose nanocrystals (abbreviated as CNC (USDA)) of any concentration and 0.5wt% chlorinated The particle size of the colloidal system mixed with sodium (NaCl) solution is larger than that of the CNC (USDA) colloidal solution with the same concentration in the NaCl solution of less than 0.5wt%, and the absolute value of zeta potential of the former is also lower. to the latter.

In addition, the particle size of the 0.05wt% and 0.1wt% CNC (USDA) colloidal solutions in the 0.5wt% NaCl solution basically remains larger than 1000 nm, and the absolute value of the zeta potential is less than 30. Therefore, the colloidal solutions with the two concentration ratios That is, 0.05wt% and 0.1wt% CNC (USDA) colloid solution cannot be kept stable, the nanoparticles in the colloid system flocculate and settle in a short time, and other concentrations of CNC (USDA) and 0.5wt% concentration NaCl solution composition The colloidal system exhibits greater instability relative to its low concentration in salt solutions.

The experimental results of the particle size of the colloidal solution measured at the above sampling time point and the zeta potential of the colloidal solution measured at the sampling time point are shown in Figure 3 and Figure 4. According to the experimental results of the contact angle, it should be stable at In the concentration range, a colloidal solution with low salt concentration and high CNC (USDA) concentration was selected for the experiment. Since the salinity of seawater is not zero, 1.0wt% CNC+0.1wt% NaCl colloidal solution was finally selected as the enhanced oil recovery flooding experiment. displacement fluid.

As a preferred solution of this embodiment, the cellulose nanocrystal-sodium chloride mixed colloid solution in the stable concentration range of the primary screening is screened for the second time by detecting the interfacial tension measurement method and the contact angle measurement method to be conducive to improving oil recovery. The concentration of the cellulose nanocrystal-sodium chloride mixed colloid solution, the concrete realization method is:

The interfacial tension measurement experiment was carried out on the crude oil and the cellulose nanocrystal-sodium chloride colloidal solution that was screened to maintain stability, and the measurement experiment of the contact angle between the colloidal solution and the sandstone surface was further filtered from the stable colloidal solution. The solution concentration of the cellulose nanocrystal-sodium chloride colloid solution.

Among them, the interfacial tension measurement experiment between the crude oil and the screened colloidal solution, and the measurement experiment of the contact angle between the colloidal solution and the sandstone surface are analyzed from the permeability influencing factors (interfacial tension and contact angle) in the displacement fluid. The addition of CNC (USDA) colloid solution can reduce the interfacial tension and increase the contact angle between crude oil and sandstone. From these conclusions, it is inferred that the addition of cellulose nanocrystals can improve the recovery factor.

The contact angle measurement method is specifically that the polished sandstone is pre-soaked in the crude oil environment described in step 100 for saturation aging, and the cellulose nanocrystal-sodium chloride mixed colloid solution in the screened stable concentration range is dropped. Contact angle on a polished sandstone surface.

In this step, the North Sea crude oil was filtered with a vacuum filter and 5 μm filter paper, and then the interfacial tension between the 24 kinds of colloidal solutions as shown in Figure 2 and the crude oil was measured first, and then the interfacial tensions of the colloidal solutions dropped in the crude oil and the polished quartz were measured. contact angle of the surface.

The experimental results of the interfacial tension between 24 kinds of colloidal solutions and crude oil, and the contact angle of crude oil droplets with the polished quartz surface in the colloidal solution environment are shown in Fig. 5.

It can be seen from the interfacial tension data that the interfacial tension between crude oil and colloidal solution at 60°C is slightly lower than that at 20°C. Since the temperature of the reservoir environment is generally higher than room temperature, for the subsequent displacement experiments, from this part The experimental results infer that the effect under reservoir conditions will be better than the results obtained by the displacement simulation experiments at room temperature.

It can be seen from the contact angle data that under the same salt concentration, the higher the concentration of cellulose nanocrystals, the larger the contact angle; when the concentration of cellulose nanocrystals is the same, the higher the salt concentration, the smaller the contact angle; the colloidal solution at 60 °C The overall contact angle with the sandstone surface is greater than that at 20°C. The smaller the contact angle, the lower the wettability of crude oil to quartz, the higher the wettability of water, and the easier it is for crude oil to be detached from the rock surface.

Step 300 , pretreating the sandstone core, and injecting a stable concentration of cellulose nanocrystal-sodium chloride mixed colloidal solution into the pretreated sandstone core according to the twice-displacement mode. The specific experimental flow chart is shown in FIG. 8 . Show.

It should be added that the cellulose nanocrystal-sodium chloride mixed colloidal solution screened for the second time is injected into the pretreated sandstone core according to the double displacement mode, wherein the double displacement mode includes the first Inject 0.1wt% NaCl solution as the primary displacement mode until no oil is produced and the pressure difference is stable; then inject the screened cellulose nanocrystal-sodium chloride mixed colloid solution as the secondary displacement mode , until the displacement reaches no oil production and the pressure difference is stable.

In addition, it should be noted that the use of cellulose nanocrystal-sodium chloride mixed colloidal solution in this embodiment can not only be used to simulate oil production, but also can be used to simulate hydrate production. As for cellulose nanocrystal-chlorine The stability screening and permeability screening methods of sodium colloid solution remain unchanged. By changing the creation method of the model body, a storage environment (low temperature and high pressure) for simulating gas hydrate in the formation is established. By injecting cellulose nanocrystal- By collecting the sodium chloride colloidal solution and collecting the output of natural gas, the development amount of natural gas hydrate by cellulose nanocrystal-sodium chloride colloidal solution can be calculated, as well as the specific improvement range of natural gas hydrate recovery rate.

The realization principle of using cellulose nanocrystal-sodium chloride colloidal solution to enhance oil recovery is as follows: after a certain concentration of cellulose nanocrystal-sodium chloride colloidal solution that has been determined to remain stable is injected into the formation, it first flows into the throat with a larger radius. Large connected pores, with the flow of fluid, cellulose nanocrystals stay at the throat, resulting in the narrowing of the throat radius, the inflow pressure increases, and the fluid flows into the channel with its own narrow throat radius, increasing the sweep coefficient. Thereby increasing the recovery rate.

In this step, the realization method of preprocessing the sandstone core is as follows:

(a) performing a pretreatment operation on the Berea sandstone core, wherein the pretreatment operation includes cleaning, drying, and saturated immersion with brine on the Berea sandstone core to prevent the porosity of the sandstone from clogging;

(b) inject crude oil into the Berea sandstone core that has been pretreated, and saturate the Berea sandstone core with crude oil at a low flow rate of 1 mL/min and then a high flow rate of 10 mL/min during the injection process to simulate the crude oil in the sandstone storage environment.

In addition, the specific implementation steps of the pretreatment operation on the Berea sandstone core are as follows:

in,

(1) drying after utilizing 3%NaCl solution and methanol to clean the Berea sandstone core, and measuring the dry weight, porosity and air permeability of the Berea sandstone core after drying;

(II) soaking the Berea sandstone core with a vacuum and saturated 0.1wt% NaCl solution and weighing the saturated wet weight of the Berea sandstone core;

(III) utilize the filtered crude oil obtained in step 100 to inject the Berea sandstone core, and displace the NaCl solution in the Berea sandstone core to leaching until the in and out flow of crude oil is consistent, calculate the irreducible water saturation of the Berea sandstone core at this time, the calculated by the present embodiment The irreducible water saturation of the Berea sandstone core is 28.45%.

Wherein, when using the filtered crude oil obtained in step 100 to inject into the Berea sandstone core, firstly inject crude oil at a low speed of 1 mL/min, and then inject crude oil at a high speed of 10 mL/min after stabilization.

It should be added that after the filtered crude oil obtained in step 100 is used to inject the Berea sandstone core and the irreducible water saturation of the Berea sandstone core is calculated at this time, the Berea sandstone core is immersed in the crude oil obtained in step 100 and left to stand, so that the Berea sandstone core is immersed in the crude oil obtained in step 100 and left to stand. The pores of the sandstone core are fully saturated with crude oil.

As one of the innovations of this embodiment, according to the porosity and air permeability of the sandstone, an appropriate amount of oil is injected until saturation, so that the amount of oil injected into the sandstone can be calculated in real time. The effect of the displacement experiment of crystal-sodium chloride mixed colloidal solution on oil recovery and the data change of oil recovery.

In addition, the specific implementation method of injecting the cellulose nanocrystal-sodium chloride mixed colloidal solution into the model body is as follows:

Step 301, carrying out an oil recovery flooding experiment with a 0.1wt% concentration of sodium chloride solution in the order of first low flow rate 0.3mL/min and then high flow rate 3mL/min, and collecting the first produced fluid with a test tube with a scale;

Step 302: When there are no obvious oil droplets in the produced liquid and the pressure difference is stable, stop injecting the sodium chloride solution, and filter the cellulose nanocrystal-sodium chloride mixed colloid solution with a suitable concentration range, using the first low flow rate. After 0.3mL/min and high flow rate of 3mL/min, the secondary oil recovery and displacement experiment was carried out, and the second produced fluid was collected again;

Step 303: When there are no obvious oil droplets in the second produced liquid and the pressure difference is stable, stop injecting the cellulose nanocrystal-sodium chloride mixed colloidal solution.

In step 303, after the injection of the cellulose nanocrystal-sodium chloride mixed colloid solution is stopped, 0.1 wt% sodium chloride solution is injected to flush out the retained cellulose nanocrystals in the Berea sandstone core.

Step 400 , comparing the produced fluid in the two displacement modes, and calculating the recovery factor in the two displacement modes.

The specific experimental results are shown in Figures 6 and 7. The experimental results show that, on the basis of the original 0.1wt% sodium chloride solution secondary flooding, 1.0wt% CNC (USDA) + 0.1wt% NaCl colloidal solution three times flooding The enhanced oil recovery capacity is about 2.76%. The addition of CNC (USDA) reduces the interfacial tension between the water phase and the oil phase. In addition, the crude oil is light crude oil, and the emulsion is produced during the test.

Therefore, in this embodiment, according to the injectability of the nanocellulose-sodium chloride solution colloid system in sandstone, the concentration range of the colloid components is screened to reduce the risk of pore throat blockage due to instability of the colloid system due to excessive concentration ; Use cellulose nanocrystal particles to block the high-permeability strip and expand the swept volume; use cellulose nanocrystal-sodium chloride mixed colloidal solution to improve the properties of the oil-water interface and enhance the oil recovery.

The above embodiments are only exemplary embodiments of the present application, and are not intended to limit the present application. The protection scope of the present application is defined by the claims. Those skilled in the art can make various modifications or equivalent replacements to the present application within the spirit and protection scope of the present application, and such modifications or equivalent replacements should also be regarded as falling within the protection scope of the present application.

Claims (10)

1. A method for simulating oil recovery using cellulose nanocrystals, comprising the steps of:

step 100, processing crude oil, and filtering the crude oil by using a vacuum filter and filter paper;

200, preparing a cellulose nanocrystal-sodium chloride mixed colloidal solution, screening a stable concentration range in the cellulose nanocrystal-sodium chloride mixed colloidal solution by using a stability measurement mode for the first time, and screening the concentration of a cellulose nanocrystal-sodium chloride colloidal system influencing the permeability in sandstone for the second time in the cellulose nanocrystal-sodium chloride mixed colloidal solution in the stable concentration range;

step 300, pretreating the sandstone core, and injecting the secondarily screened cellulose nanocrystal-sodium chloride mixed colloidal solution into the pretreated sandstone core according to a twice displacement mode;

and step 400, comparing the produced fluids in the two displacement modes, and calculating and comparing the data of the recovery ratio in the two displacement modes.

2. The method for simulating oil recovery by using cellulose nanocrystals according to claim 1, wherein the step of preparing the cellulose nanocrystal-sodium chloride mixed colloidal solution in step 200 comprises the following steps:

obtaining a concentrated solution of cellulose nanocrystals at a concentration of 12.18 wt%;

mixing and diluting deionized water and the original cellulose nanocrystals to form cellulose nanocrystal colloidal solutions with different concentrations;

mixing sodium chloride solutions of different concentrations with the original cellulose nanocrystal colloidal solution to dilute the cellulose nanocrystal colloidal solution to different concentrations and generate different classes of the cellulose nanocrystal-sodium chloride mixed colloidal solution;

the cellulose nanocrystal-sodium chloride mixed colloidal solution of the same category is divided into two groups after being uniformly stirred, and the two groups of the cellulose nanocrystal-sodium chloride mixed colloidal solution are respectively stored in a constant temperature box at 20 ℃ and a constant temperature box at 60 ℃.

3. The method for simulating oil recovery by using cellulose nanocrystals according to claim 2, wherein the method for measuring stability of the mixed colloidal solution of cellulose nanocrystals and sodium chloride comprises the following steps:

sampling the cellulose nanocrystal-sodium chloride mixed colloidal solution stored in a constant temperature box at 20 ℃ and 60 ℃ at regular time to carry out a stability measurement experiment;

and comparing the measurement results of each stability measurement experiment, and screening out the cellulose nanocrystal-sodium chloride colloidal solution which is still stable after being prepared for one month.

4. The method for simulating oil recovery by using cellulose nanocrystals, as claimed in claim 3, wherein the cellulose nanocrystal-sodium chloride mixed colloidal solution with a stable concentration range obtained by the primary screening is secondarily screened by the interfacial tension measurement method and the contact angle measurement method, and the concentration of the cellulose nanocrystal-sodium chloride mixed colloidal solution affecting permeability is filtered to increase the recovery ratio, and the method is implemented by:

and (3) carrying out an interfacial tension measurement experiment on the crude oil and the cellulose nanocrystal-sodium chloride colloidal solution screened out to keep stability, and a measurement experiment on a contact angle between the colloidal solution and the sandstone surface, and further screening out a colloidal solution with a proper concentration range from the stable colloidal solution so as to improve the injectability of the colloidal system in the sandstone.

5. The method for simulating oil recovery by using cellulose nanocrystals according to claim 4, wherein the contact angle is measured by dropping the selected stable concentration range of the cellulose nanocrystal-sodium chloride mixed colloidal solution on the polished sandstone surface.

6. The method for simulating oil recovery by using cellulose nanocrystals according to claim 5, wherein the polished sandstone pre-soaking is subjected to saturated aging in the crude oil environment of the step 100.

7. The method for simulating oil recovery by using cellulose nanocrystals according to claim 4, wherein the method comprises the following steps: in step 300, injecting the secondarily screened cellulose nanocrystal-sodium chloride mixed colloidal solution into the pretreated sandstone core according to a twice-displacement mode, wherein the twice-displacement mode comprises a mode of injecting 0.1 wt% of NaCl solution as a first displacement mode until oil-free production and stable pressure difference are achieved; and then injecting the screened cellulose nanocrystal-sodium chloride mixed colloidal solution as a secondary displacement mode until oil-free production is achieved and the pressure difference is stable.

8. The method for simulating oil recovery by using cellulose nanocrystals according to claim 7, wherein the step 300 of establishing the model body is realized by:

cleaning the sandstone to prevent porosity blockage of the sandstone, and performing vacuum saturation on the sandstone by using a NaCl solution;

injecting the crude oil filtered in the step 100 into the sandstone, and performing crude oil saturation on a sandstone core to simulate the storage environment of the crude oil in the sandstone.

9. The method for simulating oil recovery using cellulose nanocrystals according to claim 8, wherein: in step 300, the specific implementation method for injecting the cellulose nanocrystal-sodium chloride mixed colloidal solution into the model main body is as follows:

301, performing a primary oil recovery displacement experiment on a 0.1 wt% sodium chloride solution by adopting a sequence of low flow rate of 0.3mL/min and high flow rate of 3mL/min, and collecting a first output liquid by using a test tube with scales;

step 302, stopping injecting the sodium chloride solution when no obvious oil drop is visible in the produced liquid and the pressure difference is stable, performing a secondary oil recovery displacement experiment on the screened cellulose nanocrystal-sodium chloride mixed colloidal solution with the appropriate concentration range by adopting a sequence of firstly low flow rate of 0.3mL/min and then high flow rate of 3mL/min, and collecting a second produced liquid again;

and step 303, stopping injecting the cellulose nanocrystal-sodium chloride mixed colloidal solution when no obvious oil drop is visible in the second output liquid and the pressure difference is stable.

10. The method for simulating oil recovery using cellulose nanocrystals according to claim 9, wherein: in step 303, after the injection of the cellulose nanocrystal-sodium chloride mixed colloidal solution is stopped, a 0.1 wt% sodium chloride solution is re-injected to flush out the retained cellulose nanocrystals in the core of the sandstone.

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