TEMPERATURE AND SALINITY TOLERANT MAGNETIC NANOFLUID, PREPARATION METHOD AND USE THEREOF

Abstract

The present invention belongs to the technical field of functional nanomaterials and petrochemicals, and proposes a temperature and salinity tolerant magnetic nanofluid, preparation method and use thereof, wherein the nanofluid comprises: magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2, with a content of 0.01-0.2 wt %, and water. The magnetic nanofluid is temperature and salinity resistant, and the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2 are characterized in having small particle sizes and uniform dispersion, and are recyclable and reusable, and the recycling rate by using magnet after imbibition displacement experiments is as high as 96%, and the present invention provides an efficient solution for the huge problem in high efficiency development of ultra-low permeability reservoirs.

Claims

1. A temperature and salinity tolerant magnetic nanofluid, comprising: magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2, with a content of 0.01-0.2 wt %, and water.

2. The temperature and salinity tolerant magnetic nanofluid according to claim 1, wherein the content of the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2 is 0.1 wt %.

3. The temperature and salinity tolerant magnetic nanofluid according to claim 1, wherein a preparation method of the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2 comprising: (1) dissolving nano Fe.sub.3O.sub.4 in ethanol, giving ultrasonic treatment until even dispersion, thereafter, adding slowly tetrabutyl titanate and ammonia solution, mechanical stirring for 5 h in ambient temperature; and (2) placing reaction products at 25 C. for 20 h, separating by using magnet, washing by using ultrapure water, vacuum drying at 55 C. and obtaining the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2.

4. The temperature and salinity tolerant magnetic nanofluid according to claim 3, wherein the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2 have particle sizes less than 20 nm.

5. The temperature and salinity tolerant magnetic nanofluid according to claim 4, wherein the water in the temperature and salinity tolerant nanofluid comprises water containing K.sup.+, Na.sup.+, Mg.sup.2+, Ca.sup.2+ and Cl.sup., wherein a total concentration of K.sup.+ and Na.sup.+ does not exceed 40000 mg/L, a total concentration of Ca.sup.2+ and Mg.sup.2+ does not exceed 5000 mg/L, and a salinity of the water does not go beyond 90000 mg/L.

6. The temperature and salinity tolerant magnetic nanofluid according to claim 5, wherein the water in the temperature and salinity tolerant nanofluid comprises water containing K.sup.+, Na.sup.+, Mg.sup.2+, Ca.sup.2+ and Cl.sup., wherein a total concentration of K.sup.+ and Na.sup.+ is 1000-40000 mg/L, a total concentration of Ca.sup.2+ and Mg.sup.2+, and a total salinity of the water is 2000-90000 mg/L, and when the salinity of the water goes beyond this range, aggregations in the magnetic nanofluid will increase.

7. A preparation method of the temperature and salinity tolerant magnetic nanofluid according to claim 5, wherein the preparation method comprises: (1) adding the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2 to water to be mother solution; and (2) during use, adding water to dilute the mother solution when stirring, and obtaining the temperature and salinity magnetic nanofluid with a required concentration.

8. Use of the temperature and salinity tolerant magnetic nanofluid according to any of claim 1 in imbibition displacement of ultra-low permeability reservoirs.

9. The use of the temperature and salinity tolerant magnetic nanofluid according to claim 8, wherein strata conditions of the ultra-low permeability reservoirs comprise temperature at 20-120 C.

10. The use of the temperature and salinity tolerant magnetic nanofluid according to claim 8, wherein strata conditions of the ultra-low permeability reservoirs comprise salinity at 0-90000 mg/L.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0025] FIG. 1 is an XPS spectrum diagram of magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2;

[0026] FIG. 2 is an infrared spectrum diagram of the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2 and Fe.sub.3O.sub.4;

[0027] FIG. 3 is a TEM diagram showing the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2;

[0028] FIG. 4 is a DLS diagram showing the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2 and Fe.sub.3O.sub.4;

[0029] FIG. 5 is a VSM diagram showing the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2 and Fe.sub.3O.sub.4;

[0030] FIG. 6 shows imbibition displacement experiment results of the magnetic nanofluid, SiO.sub.2 nanofluid commercially available and simulated formation water; and

[0031] FIG. 7 shows recycling experiment results by using magnet of the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2.

EMBODIMENTS

[0032] In order to help understand the purpose, features and advantages of the present invention more clearly, hereinafter a further description will be given to the technical solutions of the present invention. It shall be understood that, without conflict, embodiments of the present invention and features in the embodiments of the present invention can be combined with each other.

[0033] In the following description, a lot of details have been set forth to make it convenient to understand the present invention, however, the present invention can be implemented in other methods different from those given herein; apparently, the embodiments in the present description are only some embodiments of the present invention, rather than all.

[0034] Hereinafter, the preferred embodiments of the present invention have been described in detail. It shall be understood that, the following embodiments are given for the sake of explanation rather than limiting the protection scope of the present invention. Without departing from the spirit and essence of the present invention, those skilled in the art can make a variety of modifications and alternations to the present invention.

[0035] The experiment methods described in the following embodiments are conventional methods unless indicated otherwise.

[0036] Embodiment 1: temperature and salinity tolerant magnetic nanofluid for imbibition displacement of ultra-low permeability reservoirs

[0037] In the present embodiment, a temperature and salinity tolerant nanofluid for imbibition displacement of ultra-low permeability reservoirs is proposed, wherein the nanofluid comprises magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2, with a content of 0.05-0.2 wt %, the balance being water.

[0038] Wherein preparation of the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2 comprises: [0039] (1) Dissolving nano Fe.sub.3O.sub.4 2 g in ethanol 120 g, giving ultrasonic treatment for 30 min until uniform dispersion, adding slowly tetrabutyl titanate 4 g and ammonium solution 3 g, mechanical stirring for 5 h in ambient temperature; and [0040] (2) Placing a reaction product at 25 C. for 20 h, separating by using magnet, washing by using ultrapure water, vacuum drying at 55 C. for 12 h and obtaining the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2, wherein diameters of the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2 are less than 20 nm.

[0041] The water in the temperature and salinity tolerant magnetic nanofluid comprises water containing K.sup.+, Na.sup.+, Mg.sup.2+, Ca.sup.2+, and Cl.sup., wherein a total concentration of K.sup.+ and Na.sup.+ is 1000-40000 mg/L, a total concentration of Ca.sup.2+ and Mg.sup.2+ is 100-5000 mg/L, and a salinity of the water is 2000-90000 mg/L.

[0042] Embodiment 2: characterization of the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2

[0043] From the XPS of the solid powder test of the magnetic core-shell structured nanoparticle Fe.sub.3O.sub.4@TiO.sub.2, the element composition of the Fe.sub.3O.sub.4@TiO.sub.2 was analyzed, as shown in FIG. 1; from the infrared spectrum of the solid powder test of the magnetic core-shell structured nanoparticle Fe.sub.3O.sub.4@TiO.sub.2 and Fe.sub.3O.sub.4, surface group compositions of the Fe.sub.3O.sub.4@TiO.sub.2 and Fe.sub.3O.sub.4 were analyzed, as shown in FIG. 2; solutions with 0.1 wt % of Fe.sub.3O.sub.4@TiO.sub.2 and Fe.sub.3O.sub.4 were prepared, to test TEM and DLS, to analyze microscopic morphology, shell thickness and diameter distribution of the Fe.sub.3O.sub.4@TiO.sub.2, as shown in FIGS. 3 and 4, wherein the actual diameter sizes were less than 20 nm, the shell thickness is close to 3 nm and the particles are ball-like; solutions with 0.1 wt % of Fe.sub.3O.sub.4@TiO.sub.2 and Fe.sub.3O.sub.4 were prepared, to test VSM, and analyze the magnetization intensity of Fe.sub.3O.sub.4@TiO.sub.2 and Fe.sub.3O.sub.4, as shown in FIG. 5.

[0044] Embodiment 3: temperature and salinity tolerance test of the temperature and salinity tolerant magnetic nanofluid

[0045] 0.1 wt % magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2 fluids with salinity of respectively 0, 10000, 30000, 50000, 70000, 90000, and 110000 mg/L were prepared, after placing in ambient temperature for 7 days, the DLS and Zeta potential was tested to evaluate the salinity resistance performance of the fluids, and the test results were as shown in Table 1, and the salinity resistance ability is as high as 90000 mg/L.

TABLE-US-00001 TABLE 1 Salinity/mg .Math. L.sup.1 Particle size/nm Zeta potential/mV 0 17.7 44.6 10000 18.0 42.3 30000 17.8 41.7 50000 18.4 38.9 70000 18.8 35.1 90000 19.5 30.3 110000 31.4 22.7

[0046] 0.1 wt % magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2 fluids, after placing for 7 days at 20, 40, 60, 80, 100, 120, 140 C., the DLS and Zeta potential was tested to evaluate the temperature resistance performance, and the test results were as shown in Table 2, and the temperature resistance ability was as high as 120 C.

TABLE-US-00002 TABLE 2 Temperature/ C. Particle size/nm Zeta potential/mV 20 17.7 44.6 40 18.5 44.3 60 17.6 43.8 80 18.2 40.2 100 18.8 36.3 120 19.1 31.2 140 29.8 18.9

[0047] Embodiment 4: imbibition displacement abilities of the temperature and salinity tolerant magnetic nanofluid

[0048] The imbibition displacement ability was evaluated by spontaneous imbibition methods defined in the literature, wherein the experiment steps were: {circle around (1)} measuring the density of the simulated oil; {circle around (2)} cutting rocky outcrops to be sections with length around 3 cm with a core splitter, cleaning and drying, measuring dry weight, diameter, length, porosity and permeability measured by air; {circle around (3)} giving oil saturation treatment by using a high pressure core vacuum saturation device, wiping the simulated oil attached on the surface of the core and measuring the quality of the core after oil saturation; and {circle around (4)} placing an imbibition flask with the core and the temperature and salinity tolerant magnetic nanofluid in a 80 C. constant temperature water bath, reading the scale difference of the oil column in the scaled glass pipe of the imbibition flask in every some time and calculating the imbibition recovery rate. The test results were shown in FIG. 6, and it turned out that, the magnetic nanofluid exhibited good imbibition recovery abilities, and can improve significantly the recovery rate of the ultra-low permeability reservoirs.

[0049] Embodiment 5: recyclability of the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2

[0050] The recyclability was assessed by methods defined in the literature, wherein the experiment steps were: weighing a certain amount of the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2 for preparing the magnetic nanofluid for imbibition displacement experiments, and after the experiments, adding a piece of magnet, placing for 30 mins and taking the piece of magnet out, drying the nanoparticles attached to a surface of the piece of magnet and calculating the recycling rate. The experiments results were shown in FIG. 7, and it turned out that, after adding the magnet for 30 mins, a large amount of the magnetic core-shell structured nanoparticles Fe.sub.3O.sub.4@TiO.sub.2 were absorbed on the surface of the magnet, and upon calculation, it is found that the recycling rate is 96%.

Comparative Example 1

[0051] With reference to the experiment steps described in the embodiment 4, the recovery rate of the SiO.sub.2 nanofluid commercially available and that of the temperature and salinity tolerant magnetic nanofluid in the present invention were compared.

[0052] The maximum recovery rate that the SiO.sub.2 nanofluid commercially available can achieve was 28.6%, and when the content of the magnetic core-shell structured nanoparticle Fe.sub.3O.sub.4@TiO.sub.2 in the temperature and salinity tolerant magnetic nanofluid was 0.1 wt %, the recovery rate was as high as 32.2%.

[0053] The reason lies in that, common nano oil flooding agents cannot enter efficiently the ultra-low permeability cores, and the temperature and salinity tolerant nanofluid provided in the present invention is highly adaptive to the pore throats of the ultra-low permeability reservoirs, and can enter easily the micro-nano pore throats and enhance recovery of the ultra-low permeability reservoirs.

[0054] The foregoing are some embodiments of the present invention, to have those skilled in the art to understand or implement the present invention. Modifications to the embodiments are obvious to those skilled in the art, the general principles defined in the present invention can be realized in other embodiments without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the embodiments listed in the present invention and covers the widest scope that complies with the principles disclosed in the present invention and is consistent with novel features of the present invention.