CN117126655A - Graphene oxide-carbon nano tube composite oil displacement agent and application thereof - Google Patents

Graphene oxide-carbon nano tube composite oil displacement agent and application thereof Download PDF

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CN117126655A
CN117126655A CN202311044720.3A CN202311044720A CN117126655A CN 117126655 A CN117126655 A CN 117126655A CN 202311044720 A CN202311044720 A CN 202311044720A CN 117126655 A CN117126655 A CN 117126655A
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oil
graphene oxide
carbon nanotubes
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displacing agent
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王沫然
鲁旭康
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Tsinghua University
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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
    • C09K8/58—Compositions for enhanced recovery methods for obtaining hydrocarbons, i.e. for improving the mobility of the oil, e.g. displacing fluids
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A20/00—Water conservation; Efficient water supply; Efficient water use
    • Y02A20/20—Controlling water pollution; Waste water treatment
    • Y02A20/204—Keeping clear the surface of open water from oil spills

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Abstract

The application provides a graphene oxide-carbon nano tube composite oil displacement agent and application thereof, wherein the oil displacement agent comprises a graphene oxide-carbon nano tube composite; the graphene oxide-carbon nanotube composite is of a sheet-fiber composite structure; the sheet diameter of the graphene oxide in the sheet-fibrous composite structure is selected from 100nm to 1000nm; the tube diameter of the carbon nanotubes in the sheet-fibrous composite structure is selected from 5nm to 10000nm, and the tube length of the carbon nanotubes in the sheet-fibrous composite structure is selected from 50nm to 50000nm. After the oil displacement agent is injected into the stratum, on one hand, interfacial tension can be greatly reduced through co-adsorption of graphene oxide and carbon nanotubes on a liquid-liquid interface, so that expansion of a sweep range and extraction of clustered residual oil are promoted; on the other hand, due to the curved shape of the carbon nanotubes, the residual oil in the dead-end holes or blind-end-like holes in the affected area is peeled off.

Description

Graphene oxide-carbon nano tube composite oil displacement agent and application thereof
The application relates to a split application of a graphene oxide-carbon nano tube composite oil displacement agent and application thereof, wherein the application date is 2022, 11 and 03, the application number is CN 202211370949.1.
Technical Field
The application relates to the fields of new energy and high efficiency and energy conservation, in particular to a nanomaterial oil displacement agent and a method for improving recovery ratio by applying the nanomaterial oil displacement agent.
Background
With the development of social economy, the problem of high external dependence of crude oil in China is increasingly highlighted, and oil gas resource development is an important guarantee of national energy safety. Therefore, the development of new technologies and new methods for enhanced recovery is of great importance. The chemical flooding can change the fluid property by adding a chemical reagent into the displacement fluid, so that the recovery ratio is greatly improved. However, the conventional chemical flooding method often has the problems of high cost, large consumption, formation damage and the like.
In recent years, the development of nanotechnology has led to an increasing interest in nanoparticle suspensions as a new displacement agent. The small size and high specific surface area of the nanomaterial allow it to have specific surface interface properties, such as modulating surface wettability, reducing interfacial tension, etc. However, the application of the existing nano oil displacement agent is only suitable for specific conditions, the action mechanism is relatively single, the action effect is limited, and the full play of the action in practical application is difficult.
Disclosure of Invention
The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.
The application provides a graphene oxide-carbon nano tube composite oil displacement agent and an application method thereof, wherein a graphene oxide-carbon nano tube composite system which can be well dispersed and is suitable for injection is prepared through pretreatment, and displacement fluid suitable for different reservoir environments is prepared; the various effects of the nano material can be fully exerted in the displacement process so as to improve the recovery ratio without modifying or modifying the nano material; the injection concentration which is gradually increased in a stepped way can reduce the cost and reduce the formation damage and simultaneously maximize the effect of the compound oil displacement agent.
The application provides an oil displacement agent, which comprises graphene oxide-carbon nano tube compound;
the graphene oxide-carbon nanotube composite is of a sheet-fiber composite structure;
the sheet-fiber composite structure, on the one hand, the carbon nanotubes can be randomly attached to the graphene oxide sheets; on the other hand, the presence of graphene oxide sheets can hinder contact and aggregation between carbon nanotubes;
the sheet diameter of the graphene oxide in the sheet-fibrous composite structure is selected from 100nm to 1000nm; the tube diameter of the carbon nanotubes in the sheet-fibrous composite structure is selected from 5nm to 10000nm, and the tube length of the carbon nanotubes in the sheet-fibrous composite structure is selected from 50nm to 50000nm.
In one embodiment provided by the application, the salinity of the oil displacement agent ranges from 100ppm to 2500ppm.
In one embodiment of the present application, the salt used to adjust the salinity range is selected from NaCl, KCl, caCl 2 、NaHCO 3 And MgSO 4 Any one or more of the following.
In one embodiment provided by the application, the pH value of the oil displacement agent is 3 to 11;
in one embodiment of the present application, the pH adjustor used for adjusting the pH is selected from HCl, naOH, KOH, NH 3 ·H 2 O、Na 2 CO 3 And CaO.
In one embodiment of the present application, the carbon nanotubes are selected from any one or more of single-walled carbon nanotubes, double-walled carbon nanotubes and multi-walled carbon nanotubes.
In one embodiment provided by the application, the carbon nanotubes are selected from multi-wall carbon nanotubes, preferably, the tube diameter of the multi-wall carbon nanotubes is selected from 30nm to 50nm, and the tube length of the multi-wall carbon nanotubes is selected from 100nm to 1000nm.
In still another aspect, the present application provides a method for preparing the oil-displacing agent, which comprises:
mixing graphene oxide powder with carbon nanotube powder, and fully stirring and grinding in a powder state to obtain mixed powder;
and uniformly mixing the mixed powder with water to obtain the oil displacement agent.
In one embodiment of the present application, the mass ratio of the graphene oxide powder to the carbon nanotubes is 20:1 to 1:1. In one embodiment of the present application, the mass ratio of the graphene oxide powder to the carbon nanotubes is 5:1 to 2:1.
In one embodiment of the application, graphene oxide powder and carbon nanotube powder are mixed, and fully stirred and ground in a powder state to obtain mixed powder; the full stirring and grinding are required to ensure the macroscopic uniformity and the microscopic uniformity at the same time;
macroscopically, ensuring that the relative difference between the mass ratio of the two nano materials in the sample and the set mass ratio is less than 20%; the specific operation flow is to take mixed powder with the mass of more than 0.1g and add water to disperse, at the moment, graphene oxide can be well dispersed in water, and carbon nano tubes are difficult to disperse; filtering, and obtaining the mass of the carbon nano tube after the filter cake is dried, so as to determine the mass ratio of the sample;
microcosmically, observing the dispersion condition of the powder by a high-magnification microscope, distinguishing the powder of two materials by the shape and color difference, ensuring that the powder presents a uniform dispersion state, and the proportion of the area presenting an aggregation state to the observation area is less than 10%.
In one embodiment of the present application, the weight ratio of the mixed powder to water is (0.005 to 5) 100; in one embodiment of the present application, the weight ratio of the mixed powder to water is (0.1 to 1): 100.
In one embodiment provided by the present application, the mixture of the mixed powder and the water is stirred at 400rpm to 2000rpm for 1 to 2 hours.
In one embodiment provided by the application, the mixture of the mixed powder and the water is sonicated at 300W to 1500W for 1 to 2 hours; in one embodiment provided by the application, the ultrasonic power is 600W to 800W, and the ultrasonic is performed under the ice water bath condition; in one embodiment provided by the application, each ultrasound is 25min later with an interval of 10min.
In one embodiment provided by the application, the preparation method of the graphene oxide powder comprises the following steps: preparing graphene oxide magma from natural graphite flakes using a modified Hummers method;
dispersing the graphene oxide primary pulp with deionized water again, and centrifuging at 5000rpm to 20000rpm to remove unreacted and unpeeled graphite residues, thereby obtaining supernatant; in one embodiment provided by the application, the centrifugal speed is 8000-10000rpm to ensure no graphite residue and maximum retention of the product;
taking the supernatant, performing water bath ultrasonic treatment for 0.5 to 2.5 hours under the condition of 50 to 200W to obtain graphene oxide dispersion liquid, and drying in a vacuum drying oven to obtain graphene oxide powder.
In yet another aspect, the present application provides an application of the oil-displacing agent described above, the application comprising:
(1) Selecting a target well, wherein the target well is a production well with water in the produced liquid of the production well, and optionally, the proportion of the water accounts for more than 10% of the produced liquid of the production well;
(2) Injecting the oil displacement agent through an injection well, wherein the initial injection concentration is 1/20 to 1/2 of the designed concentration; after no new oil is extracted, the injection concentration is increased to 1.5 to 5 times of the original concentration; and so on until the injection concentration reaches the design concentration; optionally, the design concentration is 0.0001wt.% to 0.5wt.%, preferably, the design concentration is 0.05wt.% to 0.2wt.%;
in one embodiment of the present application, when the operation of step (2) is performed, after the injection pressure is raised to 0.5MPa to 2MPa, the injection of water is restarted, i.e., steps (1) and (2) are repeated.
In one embodiment provided by the application, when the average pore diameter of the reservoir is less than 1 μm, or the water salinity of the stratum is higher than 80000ppm, and the concentration of the oil displacement agent is higher than 0.1 wt%, a surfactant is added to assist in dispersion, and the mass fraction of the surfactant is lower than the total mass fraction of the graphene oxide and the carbon nanotubes.
In one embodiment provided by the application, the surfactant is selected from any one or more of anionic surfactant, thiobetaine 12 and polyethylene glycol;
in one embodiment provided by the application, the anionic surfactant is selected from any one or more of sodium dodecyl sulfate and sodium dodecyl benzene sulfonate.
After the oil displacement agent is injected into a stratum, on one hand, interfacial tension can be greatly reduced through co-adsorption of graphene oxide and carbon nanotubes on a liquid-liquid interface, interfacial instability is induced by utilizing a dynamic adsorption effect, and a certain emulsification effect exists on crude oil, so that expansion of a sweep range and extraction of clustered residual oil are promoted; on the other hand, due to the bending shape of the carbon nano tube, the graphene oxide-carbon nano tube compound can form a multi-layer coarse structure after being adsorbed on a solid-liquid interface, and residual oil in blind end holes or blind end-like holes in the swept area is stripped. The composite system and synergistic effect of the two materials enable the two materials to effectively play roles in different types of reservoir environments, and the effects can be accumulated along with the increase of the concentration. At the same time, low concentration injection can reduce formation damage. Therefore, the injection concentration which is gradually increased stepwise can maximize the effect of the compound oil displacement agent and reduce the cost.
Additional features and advantages of the application will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the application. Other advantages of the application may be realized and attained by the structure particularly pointed out in the written description.
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The accompanying drawings are included to provide an understanding of the principles of the application, and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain, without limitation, the principles of the application.
Fig. 1 (a) shows the transmission electron microscope characterization result of the graphene oxide-carbon nanotube composite prepared in the example;
in fig. 1, (b) is a transmission electron microscope characterization result of graphene oxide sheets (the difference from the example is that no carbon nanotube powder is added in step (1.4), and other conditions are the same);
in fig. 1, (c) is a transmission electron microscope characterization result of the carbon nanotube (the difference from the example is that the graphene oxide powder is not added in the step (1.4), and other conditions are the same);
fig. 1 (d) shows a particle size distribution diagram of the graphene oxide-carbon nanotube composite and the graphene oxide dispersion (concentration of 0.2 wt.%) obtained in the example.
Fig. 2 (a) is a schematic diagram of a graphene oxide-carbon nanotube composite oil displacement agent under an optical microscope when the preparation of the example is completed;
fig. 2 (b) is a schematic diagram of a graphene oxide-carbon nanotube composite oil displacement agent under an optical microscope after the preparation of the example is completed for 8 hours;
FIG. 2 (c) is a schematic representation of the carbon nanotube dispersion (concentration 0.2 wt.%) at the completion of formulation under an optical microscope;
FIG. 2 (d) is a schematic diagram of the carbon nanotube dispersion (concentration of 0.2 wt.%) after preparation under an optical microscope for 8 hours;
in fig. 2 (e), the left graph shows a carbon nanotube dispersion liquid, and the right graph shows the graphene oxide-carbon nanotube composite oil-displacing agent prepared in the example, wherein the graphene oxide-carbon nanotube composite oil-displacing agent prepared in the example does not sediment after the graphene oxide-carbon nanotube composite oil-displacing agent and the carbon nanotube dispersion liquid are placed for 8 hours.
Fig. 3 (a) is a schematic diagram showing the measurement results of contact angles of the graphene oxide-carbon nanotube composite oil displacement agent, the graphene oxide dispersion liquid and the silica nanoparticle dispersion liquid prepared in the example at the same concentration (the concentration is 0.2 wt.%);
fig. 3 (b) is a schematic diagram showing the interfacial tension measurement results of the graphene oxide-carbon nanotube composite oil displacement agent, the graphene oxide dispersion liquid, and the silica nanoparticle dispersion liquid prepared in the example at the same concentration (concentration is 0.2 wt.%).
Fig. 4 shows the results of the emulsification test, wherein the volume ratio of the oil phase to the water phase in the test tube is 1:1, the oil phase is n-decane (transparent part at the upper part of the test tube before oscillation), the water phase in fig. 4 (a) is deionized water, the water phase in fig. 4 (b) is silica nanoparticle dispersion (concentration of 0.2 wt.%), the water phase in fig. 4 (c) is graphene oxide dispersion (concentration of 0.2 wt.%), and the water phase in fig. 4 (d) is graphene oxide-carbon nanotube composite oil displacement agent prepared in the example (concentration of 0.2 wt.%).
Fig. 5 is a measurement result of wall adsorption roughness of the graphene oxide-carbon nanotube composite (fig. 5 (a)), graphene oxide (fig. 5 (b)), and silica nanoparticles (fig. 5 (c)) prepared in the example at the same concentration (concentration of 0.2 wt.%).
Fig. 6 is a schematic diagram showing phase distribution and a comparison of a recovery curve and water flooding at the final moment in the displacement process of the graphene oxide-carbon nanotube composite oil displacement agent prepared in the embodiment.
Detailed Description
The following describes embodiments of the present application in detail for the purpose of making the objects, technical solutions and advantages of the present application more apparent. It should be noted that, without conflict, the embodiments of the present application and features of the embodiments may be arbitrarily combined with each other.
Examples
(1) Preparation and formulation of oil displacement agent
The mass ratio of the carbon nano tube to the graphene oxide, the salinity and the pH value of the composite dispersion liquid and the like in the preparation and the preparation parameters of the oil displacement agent are determined according to the conditions in the displacement experiment.
The specific values of the salinity and the pH of the oil displacement agent influence the stability of the composite dispersion system and the strength of the action of a liquid-liquid interface/solid-liquid interface, so that the specific values are also determined according to reservoir conditions;
the smaller the average pore size of the reservoir, the higher the pH of the displacement agent to facilitate dispersion; when the reservoir formation water salinity is higher, the pH of the displacement agent is higher to promote dispersion, the salinity is higher to maintain the salinity matching relationship.
Generally, higher pH and lower salinity are more beneficial to dispersion, but if the formation water salinity is higher, a corresponding increase in salinity is required to avoid a salinity mismatch.
For example, when the average pore size of the reservoir is less than 1 μm, or the formation water salinity is greater than 80000ppm, the salinity may be 2500ppm, and the pH may be 11; when the average pore size of the reservoir is greater than 20 μm, or the formation water salinity is less than 20000ppm, the salinity may be 100ppm and the ph may be 3; when the average pore size of the reservoir is between 1 μm and 20 μm, or the formation water salinity is between 20000ppm and 80000ppm, the salinity and pH can be flexibly selected between the above values.
The mass ratio of the carbon nano tube to the graphene oxide can be determined according to reservoir conditions, and the smaller the average pore diameter of the reservoir is, the higher the water salinity of the stratum is, the lower the ratio of the carbon nano tube is;
for example, when the reservoir average pore size is less than 1 μm, or the formation water salinity is greater than 80000ppm, the mass ratio may be 20:1; when the average pore diameter of the reservoir is greater than 20 μm, or the formation water salinity is less than 20000ppm, the mass ratio may be 1:1; the mass ratio can be flexibly selected between 20:1 and 1:1 when the average pore diameter of the reservoir is between 1 and 20 μm, or the water salinity of the stratum is between 20000 and 80000 ppm.
In this example, the average pore size of the reservoir chip used in the displacement experiment was about 7.5 μm and was between 1 μm and 20 μm, and the high salt environment of 20000ppm or more was not involved in the displacement experiment, so that the mass ratio was 3:1, the pH was 8 to 10, and the salinity was 1500ppm to 2000ppm.
(1.1) preparing graphene oxide magma from natural graphite flakes using a modified Hummers method;
(1.2) dispersing the graphene oxide magma obtained in the step (1.1) with deionized water again, and centrifuging at 9000rpm to remove unreacted/unpeeled graphite residues;
(1.3) taking the supernatant obtained in the step (1.2), performing water bath ultrasonic treatment for 1h at 100W to obtain graphene oxide dispersion liquid, and drying in a vacuum drying oven to obtain single-layer graphene oxide powder (the microstructure of the graphene oxide is flaky, and the diameter of the flaky graphene oxide is about 1-10 mu m);
(1.4) premixing the graphene oxide powder obtained in the step (1.3) with carbon nano tube powder, and fully stirring and grinding to ensure the contact area;
the carbon nanotubes are multi-wall carbon nanotubes, the specification of the carbon nanotubes is 30nm to 50nm, the tube length is 100nm to 1000nm, and the mass ratio of graphene oxide to the carbon nanotubes is 3:1;
the degree of mixing of carbon nanotubes and graphene oxide was tested: taking mixed powder with the mass of 0.1g, carrying out water bath ultrasonic treatment for 1h at 100W, filtering, taking a filter cake, drying, weighing, and taking three samples, wherein the mass ratio of the three samples (the mass ratio of graphene oxide to carbon nano tube) is 3.2:1,3.3:1 and 2.9:1 respectively, and the relative errors are less than 20%; the dispersion of the powder was observed by a high magnification microscope, and the area exhibiting an aggregation state was about 6% of the observed area.
(1.5) adding 0.2 part of the mixed powder in the step (1.4) into 100 parts of deionized water, stirring for 1h at 1200rpm, and then performing strong ultrasonic treatment for 2h at 750W by using an ultrasonic breaker (which can be probe type ultrasonic), wherein the interval is 10min after every 25min of ultrasonic treatment under the ice water bath condition; the total concentration of graphene oxide-carbon nanotube composite in the resulting dispersion was 0.2wt.%; the sheet diameter of the graphene oxide in the prepared graphene oxide-carbon nanotube composite is about 100nm to 1000nm.
(1.6) to the dispersion obtained in (1.5) was added 1500ppm of NaCl (i.e., the salinity of the dispersion was 1500 ppm), and the pH of the composite dispersion was adjusted to 8.5 with HCl and NaOH.
The transmission electron microscope characterization result of the graphene oxide-carbon nanotube composite obtained in fig. 1 (a) is shown, and compared with the case of the graphene oxide dispersion liquid in fig. 1 (b) (i.e., no carbon nanotube powder is added in step (1.4), and the other conditions are the same) and the case of the carbon nanotube dispersion liquid in fig. 1 (c) (i.e., no graphene oxide powder is added in step (1.4), and the other conditions are the same). The layered structure of the graphene oxide and the fibrous structure of the carbon nanotubes can be clearly observed according to the characterization result of the transmission electron microscope, and the stable dispersion of the carbon nanotubes can be effectively realized due to the existence of the graphene oxide, and the serious agglomeration phenomenon only occurs under the condition of the carbon nanotubes.
Fig. 1 (d) shows a particle size distribution diagram of a graphene oxide-carbon nanotube composite measured based on a dynamic light scattering principle, and is compared with a graphene oxide dispersion under the same conditions. From the measurement results, it can be seen that the graphene oxide-carbon nanotube composite has good uniform dispersibility; the average value of the hydraulic diameter of the graphene oxide is 303nm, so that a small-size sheet is formed; the graphene oxide-carbon nanotube composite has a relatively wider particle size distribution due to the random attachment of the carbon nanotubes.
Fig. 2 is an observation result under an optical microscope, and it can be seen from (a) and (b) in fig. 2 that the graphene oxide-carbon nanotube composite cannot observe any flocculent distribution at high resolution, and has long-term stability, so that it can be ensured to function under reservoir conditions; as shown in fig. 2 (c) and (d), carbon nanotubes are very easily agglomerated without graphene oxide; similar results are obtained in the static observation experiment shown in (e) in fig. 2, namely, the carbon nanotube dispersion liquid is settled and the graphene oxide-carbon nanotube composite oil displacement agent is kept stable.
FIG. 3 shows the contact angle and interfacial tension measurements (n-decane for the oil phase) of graphene oxide-carbon nanotube composite oil displacement agent, graphene oxide dispersion, silica nanoparticle dispersion at the same concentration; wherein, the particle diameter of the silicon dioxide nano particles is 20nm, and the preparation method can be referred to Chinese patent CN113881415B. It can be seen that the interface effect of the graphene oxide-carbon nanotube composite is most remarkable, and the contact angle and the interfacial tension can be reduced most effectively.
For the carbon nanotube dispersion, the dispersion state is extremely unstable, and the effective content in the dispersion is very low, so that the influence on the contact angle and the interfacial tension is very small.
FIG. 4 shows the results of the emulsification test, wherein the ratio of oil phase (n-decane) to water phase in the test tube is 1:1, and after sufficient shaking, the formation of an oil-in-water emulsion is compared. As can be seen from the graph, the deionized water and the silica nanoparticle dispersion liquid have no emulsification effect, the upper and lower layer interfaces are clear, the graphene oxide dispersion liquid and the graphene oxide-carbon nanotube composite oil displacement agent both have certain emulsification capacity, the upper transparent oil phase is replaced by the emulsion, wherein the emulsification effect of the graphene oxide-carbon nanotube composite oil displacement agent is the most intense, and the internal microstructure of the formed emulsion is shown in fig. 4.
For the carbon nano tube dispersion liquid, although emulsion can be formed due to the hydrophobic property, the carbon nano tube is seriously flocculated after encountering the oil phase, and the carbon nano tube dispersion liquid has no practical application value.
FIG. 5 shows wall adsorption roughness measurements for graphene oxide-carbon nanotube composites, graphene oxide, silica nanoparticles at the same concentration; it can be seen that the graphene oxide-carbon nanotube composite has remarkable liquid-liquid interface effect, and can also form a multi-level coarse structure through solid-liquid adsorption, so that more oil is obtained through displacement.
(2) Displacement experiment
The porous medium model used in the embodiment is an oil reservoir chip designed according to the core structure of the Changqing oilfield, the preparation method of the oil reservoir chip can refer to the preparation method of the oil reservoir chip in China patent CN110302853B, and the surface properties of the oil reservoir chip are hydrophilic and neutral. The experimental procedure was as follows:
(2.1) water was injected from the reservoir chip injection port at a flow rate of 1. Mu.L/min for 15min (total volume of the chip reservoir was 0.84. Mu.L (excluding external fixation structures)), at which point the outlet tubing had been exposed to water.
(2.2) injecting an oil-displacing agent with a concentration of 0.05wt.% (obtained by diluting 0.2wt.% of the oil-displacing agent with deionized water), and keeping the flow rate unchanged until no new oil is produced in the observation area;
when the volume change of the oil phase of the produced liquid after each injection of 1PV oil displacement agent is less than 0.1%, no new oil is produced, and the concentration is improved.
(2.3) injecting an oil-displacing agent (diluted with deionized water at a concentration of 0.1 wt.%) at a flow rate that remains unchanged until no new oil is produced in the observation area;
when the volume change of the oil phase of the produced liquid after each injection of 1PV oil displacement agent is less than 0.1%, no new oil is produced, and the concentration is improved.
(2.4) finally, the oil-displacing agent with a concentration of 0.2wt.% (design concentration) was injected, and the flow rate was kept unchanged until the experiment was ended after no new oil was produced.
When the volume change of the oil phase of the produced liquid is less than 0.1% after each injection of 1PV oil displacement agent, no new oil is considered to be produced, and the experiment is ended;
in order to illustrate the effect of the graphene oxide-carbon nanotube composite oil displacement agent and the advantages of the application method, the experiment is compared with the experiment effect of directly injecting 0.2wt.% of the graphene oxide-carbon nanotube composite oil displacement agent, directly injecting water, directly injecting 0.2wt.% of graphene oxide dispersion liquid and directly injecting 0.2wt.% of silica nanoparticle dispersion liquid. The injection flow rate and total time were the same for all experiments. Since the chip is very rapidly blocked when the carbon nanotube dispersion is injected, the harvesting effect cannot be counted.
Tables 1 and 2 show the final recovery under different conditions, and it can be seen from the results that, on one hand, the injection concentration which is gradually increased stepwise can achieve the recovery improvement effect similar to the direct high concentration injection, and the consumption of the oil displacement agent is greatly reduced; on the other hand, the graphene oxide-carbon nano tube composite oil displacement agent is obviously superior to any one of water, graphene oxide and silicon dioxide nano particles.
Table 1: final recovery under different conditions (hydrophilic surface)
Table 2: final recovery under different conditions (neutral surface)
Fig. 6 shows the recovery curve of the displacement process of the graphene oxide-carbon nanotube composite oil-displacing agent injected in the injection manner of the above steps (2.1) to (2.4) and the comparison of the distribution of the displacement phase at the final moment with the water flooding; as can be seen from fig. 6, the graphene oxide-carbon nanotube composite oil displacement agent can not only expand the sweep range, but also promote the enhancement of the displacement efficiency in the sweep region, thus being capable of playing a role in porous media with any surface properties, and continuously and stably realizing the extraction of residual oil even after breakthrough.
Illustratively, when steps (2.1) to (2.4) are performed, after the injection pressure rises to 0.5MPa to 2MPa, the injection of water is restarted, i.e., steps (2.1) to (2.4) are repeated.
Illustratively, when the average pore size of the reservoir is less than 1 μm, or the formation water salinity is greater than 80000ppm, and the concentration of the oil displacing agent is greater than 0.1wt.%, a surfactant is added to aid in dispersion, the mass fraction of the surfactant being less than the total mass fraction of graphene oxide and carbon nanotubes.
Illustratively, the surfactant is selected from any one or more of anionic surfactants, thiobetaines 12, and polyethylene glycols.
Illustratively, the anionic surfactant is selected from any one or more of sodium dodecyl sulfate and sodium dodecyl benzene sulfonate.

Claims (10)

1. An oil displacement agent is characterized by comprising graphene oxide-carbon nanotube composites;
the graphene oxide-carbon nanotube composite is of a sheet-fiber composite structure;
the sheet diameter of the graphene oxide in the sheet-fibrous composite structure is selected from 100nm to 1000nm; the tube diameter of the carbon nanotubes in the sheet-fibrous composite structure is selected from 5nm to 10000nm, and the tube length of the carbon nanotubes in the sheet-fibrous composite structure is selected from 50nm to 50000nm.
2. The oil-displacing agent of claim 1, wherein the oil-displacing agent has a salinity ranging from 100ppm to 2500ppm;
alternatively, the salt used to adjust the salinity range is selected from NaCl, KCl, caCl 2 、NaHCO 3 And MgSO 4 Any one or more of the following.
3. The oil-displacing agent as claimed in claim 1, wherein the pH of the oil-displacing agent is 3 to 11;
optionally, the pH regulator used for adjusting the pH value is selected from HCl, naOH, KOH, NH 3 ·H 2 O、Na 2 CO 3 And CaO.
4. The oil-displacing agent as claimed in claim 1, wherein the carbon nanotubes are selected from any one or more of single-walled carbon nanotubes, double-walled carbon nanotubes and multi-walled carbon nanotubes;
alternatively, the carbon nanotubes are selected from multi-walled carbon nanotubes, preferably, the tube diameter of the multi-walled carbon nanotubes is selected from 30nm to 50nm, and the tube length of the multi-walled carbon nanotubes is selected from 100nm to 1000nm.
5. The use of an oil-displacing agent as claimed in any one of claims 1 to 4,
(1) Selecting a target well, wherein the target well is a production well with water in produced liquid of the production well;
(2) Injecting the oil displacement agent through an injection well, wherein the initial injection concentration is 1/20 to 1/2 of the designed concentration; after no new oil is extracted, the injection concentration is increased to 1.5 to 5 times of the original concentration; and so on until the implant concentration reaches the design concentration.
6. The use of an oil displacing agent as claimed in claim 5, wherein the proportion of water in step (1) is more than 10% of the production fluid of the oil well.
7. The use of an oil-displacing agent as claimed in claim 5, wherein the design concentration in step (2) is 0.0001wt.% to 0.5wt.%, preferably the design concentration is 0.05wt.% to 0.2wt.%.
8. The use of the oil-displacing agent as claimed in claim 5, wherein the injection is restarted after the injection pressure rises to 0.5MPa to 2MPa when the operation of step (2) is performed, i.e., the steps (1) and (2) are repeated.
9. Use of an oil-displacing agent according to any one of claims 5 to 8, wherein when the average pore diameter of the reservoir is less than 1 μm, or the formation water salinity is higher than 80000ppm, and the concentration of the oil-displacing agent is higher than 0.1wt.%, a surfactant is added to assist dispersion, the mass fraction of the surfactant being lower than the total mass fraction of graphene oxide and carbon nanotubes.
10. The use of an oil-displacing agent as claimed in claim 9, wherein the surfactant is selected from any one or more of anionic surfactant, thiobetaine 12 and polyethylene glycol;
optionally, the anionic surfactant is selected from any one or more of sodium dodecyl sulfate and sodium dodecyl benzene sulfonate.
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