An efficient nano-silica tackifier and its preparation method and application

Abstract

The present invention discloses an efficient nano-silica tackifier and its preparation method and application, which relates to the field of oilfield chemistry. The preparation method includes the following steps: taking nano-silica and ultrasonically dispersing it in a first solvent, then adding a small amount of a second solvent and a certain amount of a silane coupling agent to obtain preliminarily modified nano-silica; again, stirring and dispersing acrylic acid and ammonium persulfate in the second solvent to obtain polymer-modified silica; finally, dispersing it with glucosamine sulfate, NMI (N-methylimidazole), and TCFH (N,N,N,N-tetramethylchlorourea hexafluorophosphate) in a third solvent for reaction to obtain the product. The present invention can effectively increase the viscosity of crude oil under the conditions of high-salt and high-water-cut reservoirs, improve the oil displacement efficiency, the viscosity of the formed emulsion increases with the increase of the water cut, and the flow resistance can adapt to the change of the water cut, thereby increasing the swept volume and meeting the requirements of improving the recovery rate of high-salt and high-water-cut reservoirs.

Description

Technical Field

[0001] The present invention belongs to the field of oilfield chemistry, and particularly relates to a high-efficiency nano-silica thickening agent, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the exploitation of oilfields, some oilfields have entered the late stage of high water cut exploitation, and the oilfield production has gradually decreased. Chemical flooding is an effective method to increase crude oil production, which mainly includes surfactant flooding, polymer flooding, alkaline water flooding, etc. Although surfactants can effectively reduce the interfacial tension between oil and water, it is difficult to improve the preferential channels and thus increase the swept volume. Polymers are not resistant to high salinity. Under high salinity conditions, the polymer long chains are prone to curl and thus lose their functions. Although alkaline water flooding is simple to operate and low in cost, the environmental problems brought about cannot be ignored. Therefore, aiming at the problem that it is difficult to simultaneously achieve mobility control and reduce the interfacial tension between oil and water during the process of improving the recovery rate of high-salinity and high-water-cut oil reservoirs, water-in-oil emulsion flooding is a relatively suitable method at present.

[0003] Water-in-oil emulsion thickening refers to adding an emulsifier to contact with crude oil in the formation environment to form a water-in-oil (W / O) emulsion with controllable viscosity, thereby improving the mobility control ability during the displacement process, increasing the swept volume of the displacement fluid, and starting the crude oil in the low-permeability area to improve the recovery rate. The current main emulsifiers are surfactants. Under high water cut conditions, due to the fact that a single surfactant cannot form a stable high-viscosity emulsion, it is difficult to achieve the task of improving the recovery rate. According to existing research, nanofluids can utilize their own characteristics during the formation displacement process to strip the crude oil attached to the formation rock, form an emulsion under the formation shear action, and some nanomaterials can adsorb on the rock surface to improve the wettability, thereby better improving the crude oil recovery rate. At the same time, nanomaterials can also adsorb on the formed oil-water interface, increase the liquid film thickness, and enhance the stability of the emulsion during migration.

[0004] It can be seen that currently, aiming at the problem of low recovery rate of high-salinity and high-water-cut oil reservoirs, designing high-efficiency thickening nanomaterials is the key to improving the displacement efficiency of high-salinity and high-water-cut oil reservoirs. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-efficiency nano-silica thickening agent for emulsion thickening in high-salinity and high-water-cut oil reservoirs. The specific preparation method is as follows:

[0006] S1. In proportion, add nano-silica to the first solvent, stir ultrasonically to obtain surface-hydroxylated silica; add 3-(trimethoxysilyl)propyl-2-methylacrylate silane coupling agent to the nano-silica suspension, under the action of the first catalyst, heat and stir, and then filter, wash and dry to obtain nano-silica modified with a silane coupling agent;

[0007] S2. Add the nanosilica modified with silane coupling agent obtained in S1 to the second solvent in proportion, heat and stir under the action of the second catalyst and in an N2 atmosphere, and then filter and wash to obtain polymer-modified nanosilica;

[0008] S3. Add the polymer-modified nanosilica obtained in S2 to the third solvent in proportion, react with the modifier at room temperature under the action of the third catalyst and N2, wash and filter to obtain highly efficient tackifying nanosilica.

[0009] Preferably, in S1, the mass-to-volume ratio of the hydroxylated silica to the first solvent is 1 g: 30 - 40 ml; the first solvent is a mixed solution of ethanol and water, and the volume ratio of ethanol to water is 9:1; the volume ratio of 3-(trimethoxysilyl)propyl-2-methylacrylate silane coupling agent to the first catalyst is 10 - 12 ml: 1.5 ml - 3 ml;

[0010] The first catalyst is glacial acetic acid.

[0011] Preferably, S1 is specifically:

[0012] Add the nanosilica to the ethanol aqueous solution, place it in an ultrasonic disperser and ultrasonicate for 20 - 30 min at 20 - 30 °C, add 3-(trimethoxysilyl)propyl-2-methylacrylate silane coupling agent and stir for 20 - 30 min to fully hydrolyze the coupling agent to generate silanol; adjust the pH of the mixture to 5 with the first catalyst and stir and react at 65 - 70 °C for 20 - 26 h; after the reaction, separate the product by filtration, wash it with anhydrous ethanol multiple times to remove the unreacted silane coupling agent and by-products, and dry to obtain the nanosilica modified with silane coupling agent.

[0013] Preferably, in S2, the mass-to-volume ratio of the nanosilica modified with silane coupling agent, the second solvent and the second catalyst is 1 - 1.2 g: 40 - 50 ml: 2 - 4 ml;

[0014] The second solvent is a mixed solution of acrylic acid, ethanol and water, and the mass ratio of acrylic acid, ethanol and water is 50 - 60: 85: 3;

[0015] The second catalyst is a mixed solution of ammonium persulfate and dilute sulfuric acid, and the mass ratio is 3 - 3.5: 10 - 13.

[0016] Preferably, S2 is specifically:

[0017] Disperse the silane coupling agent - modified nano - silica obtained in S1 in the second solvent, ultrasonically disperse for 15 min, adjust the pH to 3 using the second catalyst, and heat to 75 °C under a N2 atmosphere for 6 h. After the reaction, obtain the polymer - modified nano - silica by suction filtration and washing with ethanol multiple times (to remove unreacted acrylic monomers and by - products).

[0018] Preferably, in S3, the addition amount of the third catalyst is 1.8 - 2% of the addition amount of the third solvent;

[0019] The third solvent is acetonitrile;

[0020] The third catalyst is NMI (N - methylimidazole) and TCFH (N,N,N,N - tetramethylchlorourea hexafluorophosphate), and the volume - mass ratio is 3.5 - 4 ml:0.45 - 0.6 g;

[0021] The modifier is glucosamine sulfate, and the addition amount of the modifier is 8 - 10% of the addition amount of the third solvent.

[0022] Preferably, S3 is specifically as follows:

[0023] Dissolve the polymer - modified nano - silica obtained in S2 in the third solvent, ultrasonically disperse for 10 min and transfer it to a three - necked flask, then add the third catalyst, and then introduce N2 for 25 - 30 min. Under the conditions of 25 - 30 °C, ultrasonically stir and react with the modifier for 20 - 26 h under the action of the third catalyst. Filter and collect the solid, ultrasonically wash it three times with ethanol, filter and dry to obtain the nano - silica viscosifier.

[0024] The technical effects of the present invention are as follows:

[0025] (1) The W / O emulsion formed by the high - efficiency nano - silica viscosifier of the present invention and crude oil can increase the viscosity of crude oil to more than 15 times the original in high - salt and high - water - cut reservoirs, and can better improve the oil washing efficiency and reach the displacement balance.

[0026] (2) In the indoor core displacement experiment of the present invention, the enhanced oil recovery rate for high - salt and high - water - cut reservoirs is more than 15%, and it has excellent ability to enhance oil recovery.

[0027] (3) Based on the viscosifier in the present invention having a viscosity - increasing effect with low concentration and high efficiency, it can meet the requirements of enhancing oil recovery for high - salt and high - water - cut crude oil.

[0028] The technical solutions of the present invention will be further described in detail below through the drawings and specific examples. Brief Description of the Drawings

[0029] Figure 1It is a schematic diagram of the synthesis of an efficient nano-silica tackifier of the present invention;

[0030] Figure 2 It is the FT-IR spectrum of an efficient nano-silica tackifier of the present invention;

[0031] Figure 3 It is the tackifying performance diagram of an efficient nano-silica tackifier of the present invention at different concentrations and salinities;

[0032] Figure 4 It is the tackifying performance diagram of an efficient nano-silica tackifier of the present invention at different water-oil volume ratios and salinities;

[0033] Figure 5 It is the experimental result diagram of enhanced oil recovery of an efficient nano-silica tackifier of the present invention. Detailed implementation manners

[0034] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs.

[0036] Example 1

[0037] As Figure 1 shown, an efficient nano-silica tackifier, the structural formula of its modifying group is as follows:

[0038]

[0039] Its preparation method is as follows:

[0040] (1) Add 1 g of nano-silica to an ethanol aqueous solution, place it in an ultrasonic disperser and ultrasonicate for 20 min. Take 5 g of 3-(trimethoxysilyl)propyl-2-methylacrylate (KH570) and dissolve it in the nano-silica suspension, and add 5 ml of deionized water. Stir for 30 min to fully hydrolyze KH570 to form silanol, adjust the pH to 5 with glacial acetic acid, and stir and react at 65 °C for 24 h.

[0041] (2) Filter, wash and dry to obtain nano-silica modified with a silane coupling agent (abbreviation: MS).

[0042] (3) Place MS in a beaker, add 30 ml of deionized water, ultrasonically disperse for 15 min, add 5 g of acrylic acid and 0.3 g of ammonium persulfate to the treated MS solution, adjust the pH to 3 with dilute sulfuric acid, and heat to 75 °C and react for 6 h under a N2 atmosphere.

[0043] (4) Obtain polymer-modified nano-silica (abbreviated as PS) by suction filtration, washing and drying.

[0044] (5) Transfer PS to a three-necked flask, use 25 mL of acetonitrile as the solvent, and sequentially add 1.2 g of glucosamine sulfate, 1.2 g of NMI (N-methylimidazole) as an organic base, and 1.5 g of TCFH (tetramethylchlorourea hexafluorophosphate) as a coupling agent, and stir and react at 25 °C for 24 h.

[0045] (6) Obtain a nano-silica tackifier (abbreviated as PSD) by filtration, washing and drying.

[0046] Test

[0047] (1) FT-IR test

[0048] Use FT-IR to analyze nano-silica and MS, PS, PSD prepared in Example 1, and the results are as Figure 2 shown.

[0049] It can be Figure 2 seen that in the spectrum of ordinary nano-silica, 471.44 cm -1 corresponds to the bending vibration absorption peak of Si-O, and 802.79 cm -1 , 953.27 cm -1 , 1104.62 cm -1 correspond to the stretching vibrations of the Si-O bond in different environments; MS has characteristic peaks similar to those of nano-silica, and also has a characteristic peak at 1720.50 cm -1 , and this peak may correspond to the stretching vibration of C=C or C=O. Combining with the experimental reagents, it should be the carbon-carbon double bond in the silane coupling agent; compared with MS, the peaks corresponding to PS have an additional 3231.62 cm -1 and the peak area of 1720.50 cm -1 is larger. These two characteristic peaks may correspond to the stretching vibrations of -OH and C=O respectively, which may be caused by the carboxyl group of polyacrylic acid; the additional 617.92 cm -1 , 1034.84 cm -1 of PSD may be caused by the stretching vibrations of S=O and S-O, while 3292.27 cm -1 may be caused by the stretching vibration of -CO-NH, and 1542.04 cm -1 may be caused by the bending vibration of the methylene carbon skeleton in glucosamine sulfate, and 1730.37 cm -1 , 3231.62 cm -1The characteristic peak did not completely disappear, which proved that the carboxyl groups in the modified groups did not completely react. In summary, the synthesis of the nano-silica tackifier was successful.

[0050] (2) Viscosity increasing performance tests under different tackifier concentrations and salinities

[0051] Using simulated formation water with different salinities (0 g / L, 50 g / L, 220 g / L NaCl), nano-silica tackifiers with different concentrations (50, 100, 150, 200, 250 ppm) were prepared. 100 ppm of the dispersant alkylphenol polyoxyethylene ether (OP-10) was added to them to obtain a highly efficient nano-tackifier. Under the conditions of 65 °C and a water-oil volume ratio of 3:7, it was placed in a water bath with a magnetic stirrer and stirred for 1.5 h. After that, the viscosity of the emulsion was measured using a Brookifield DV-Ⅲ viscometer. The experimental results are as Figure 3 shown. The calculation method of the emulsion viscosity increasing rate is shown in Equation 1. (The viscosity of the crude oil at 65 °C is 9.71 mPa·s)

[0052]

[0053] In the formula, η is the viscosity reduction rate of the crude oil, %, μoil is the viscosity of the crude oil, mPa·s, and μe is the viscosity of the emulsion, mPa·s.

[0054] It can be seen from Figure 3 that as the concentration of the nano-tackifier increases, the viscosity increasing rate also increases. When the concentration of the tackifier is 250 ppm, the viscosity increasing effect is the best. When the salinity is 0 g / L, 50 g / L, and 220 g / L, the viscosity increasing rates are 389.52%, 372.19%, and 337.28% respectively, and the viscosity increasing effects all reach more than 3 times, showing a good viscosity increasing effect in a high-salt environment. This may be because the structural characteristics of the nano-materials and the carboxyl polymers grafted on the surface enable the nano-tackifier to form a stable three-dimensional network structure with the crude oil, making it also show a good viscosity increasing effect in a high-salt environment. Compared with the pure water environment, the reason for the decrease in the viscosity increasing rate under high-salt conditions may be that high salt can cause salting-out, the concentration of anions and cations in the solution increases, competing with the dispersant for water molecules, weakening the hydration effect of the dispersant, reducing the solubility and dispersibility of the tackifier, and causing the viscosity increasing effect to show a downward trend.

[0055] (3) Viscosity increasing performance tests under different water-oil volume ratios and salinities

[0056] Simulated formation water with different salinities (0 g / L, 50 g / L, 220 g / L NaCl) was formulated with 250 ppm of highly efficient nano-silica viscosifier and 100 ppm of OP-10 into a nano-fluid viscosifier. Under the conditions of 65 °C and different water-oil volume ratios (1:9, 3:7, 4:6, 5:5, 6:4, 7:3), it was placed in a water bath with a magnetic stirrer and stirred for 1.5 h. After that, the viscosity of the emulsion was measured using a Brookifield DV-Ⅲ viscometer. The experimental results are as Figure 4 shown.

[0057] It can be seen from Figure 4 that within the experimental range, the viscosity increase rate of the highly efficient nano-silica viscosifier for crude oil increases with the increase of the water-oil volume ratio. And at high water cut (water-oil ratio of 7:3), salinities of 0 g / L, 50 g / L, and 220 g / L, the viscosity increase effect of crude oil is the best, and the viscosity of crude oil increases by more than 15 times, showing good mobility control ability.

[0058] (4) Enhanced oil recovery test

[0059] 1000 ppm of highly efficient nano-silica and 400 ppm of OP-10 were used to prepare a highly efficient nano-viscosifying fluid, and the enhanced oil recovery ability of the highly efficient nano-silica viscosifying fluid was measured through a core flooding experiment. A core with a water permeability of 1500 mD was selected for the core flooding experiment. The specific steps are as follows: First, the core was evacuated and saturated with simulated formation water. At 65 °C, crude oil was used to saturate the water-saturated core at a rate of 0.1 ml / min until no water came out at the end of the core holder. Then, the front and rear valves of the core holder were closed, and it was placed in an oven at 65 °C for aging for 24 h. Then, simulated formation water was injected at a rate of 0.5 ml / min. After injecting 1 PV, the water injection was stopped. Then, 0.6 PV of nano-silica thickener was injected at a rate of 0.5 ml / min, and then water was injected at a flow rate of 0.5 ml / min until the pressure at the outlet end of the core holder no longer changed and the injection was stopped.

[0060] During the whole process, the injection pressure, water cut, and cumulative oil recovery were recorded every 0.05 PV injection volume, and the water cut, oil recovery, and injection pressure curves were plotted. The oil recovery calculation formula is shown in Equation (2).

[0061]

[0062] In the formula, E is the oil recovery; V c is the cumulative volume of produced oil, ml; V n is the volume of oil in the rock pores, ml.

[0063] The experimental results of enhanced oil recovery are as Figure 5As shown, due to the two-phase flow of oil and water during the initial water flooding, the water cut of the core is relatively low at this time. As the injection volume increases, the displacement pressure and recovery rate also increase. The recovery rate after 1PV of the initial water flooding is 21.40%. Subsequently, 0.6PV of the highly efficient nano-silica viscosity-increasing fluid is injected. During the injection process, as the injection volume increases, the injection pressure significantly rises again, and W / O emulsions are observed at the outlet of the core holder. After injecting 0.6PV of the nano-viscosity-increasing agent, the recovery rate increases slightly. This may be because the nano-viscosity-increasing agent forms W / O emulsions with the crude oil in some high-water-cut areas, increasing the displacement resistance in the high-water-cut areas and carrying out some crude oil. During the subsequent water flooding, simulated formation water is continuously injected until the pressure no longer changes. It can be seen that during the subsequent water flooding, the displacement pressure continues to rise, indicating that the nano-viscosity-increasing agent is still shearing and emulsifying with the remaining crude oil in the core to form W / O emulsions, resulting in a continuous increase in the crude oil recovery rate. The final recovery rate is 38.21%, and the enhanced recovery rate is 16.81%. This shows that the highly efficient nano-silica has excellent ability to enhance oil recovery.

[0064] Therefore, the present invention adopts the above-mentioned highly efficient nano-silica viscosity-increasing agent, its preparation method and application. Under high-salt and high-water-cut conditions, the viscosity of the emulsion can reach more than 15 times that of the crude oil. The enhanced recovery rate by 0.6PV of the highly efficient nano-silica viscosity-increasing agent exceeds 15%, and the enhanced recovery effect is remarkable.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A preparation method of an efficient nano-silica tackifier, characterized in that, It includes the following steps: S1. Add nano-silica into the mixed solution of the first solvent ethanol and water, stir with ultrasonic waves to obtain surface-hydroxylated silica, then add 3-(trimethoxysilyl)propyl-2-methylacrylate silane coupling agent, under the action of the first catalyst glacial acetic acid, heat and stir, and then filter, wash and dry to obtain nano-silica modified by silane coupling agent; S2. Add the nano-silica modified by silane coupling agent obtained in S1 into the mixed solution of the second solvent acrylic acid, ethanol and water, heat and stir under the action of the second catalyst ammonium persulfate and dilute sulfuric acid mixture and N2 atmosphere, and then filter and wash to obtain nano-silica modified by polymer; S3. Add the nano-silica modified by polymer obtained in S2 into the third solvent acetonitrile, react with the modifier glucosamine sulfate under the conditions of the third catalyst NMI (N-methylimidazole) and TCFH (N,N,N,N-tetramethylchlorourea hexafluorophosphate), N2 atmosphere and 25-30 °C, wash and filter to obtain highly efficient tackifying nano-silica.

2. The preparation method of the high-efficiency nano-silica tackifier according to claim 1, characterized in that, In S1, the mass-volume ratio of the nano-silica to the first solvent is 1-1.2 g: 30-40 ml; the volume ratio of ethanol to water in the first solvent is 9:1; the volume ratio of 3-(trimethoxysilyl)propyl-2-methylacrylate silane coupling agent to the first catalyst is 10-12 ml: 1.5 ml-3 ml.

3. The preparation method of the high-efficiency nano-silica tackifier according to claim 1, characterized in that, S1 specifically is: Add nano-silica into the ethanol aqueous solution, place it in an ultrasonic disperser and ultrasonicate for 20-30 min at 20-30 °C, add 3-(trimethoxysilyl)propyl-2-methylacrylate silane coupling agent and the first catalyst at 65-70 °C, and then wash with ethanol, filter and dry to obtain nano-silica modified by silane coupling agent.

4. The preparation method of the high-efficiency nano-silica tackifier according to claim 1, characterized in that, In S2, the mass-volume ratio of the nano-silica modified by silane coupling agent, the second solvent and the second catalyst is 1-1.2 g: 40-50 ml: 2-4 ml; The mass ratio of acrylic acid, ethanol and water in the second solvent is 50-60:85:3; The mass ratio of ammonium persulfate to dilute sulfuric acid in the second catalyst is 3-3.5:10-13.

5. The preparation method of the high-efficiency nano-silica tackifier according to claim 1, characterized in that, S2 specifically: Disperse the nano-silica modified by silane coupling agent obtained in S1 in the second solvent, ultrasonically disperse for 15 min, adjust the pH with the second catalyst, and under the N2 atmosphere, heat to 70-75 °C and react for 4-8 h, filter with suction and wash to obtain nano-silica modified by polymer.

6. The preparation method of the high-efficiency nano-silica tackifier according to claim 1, characterized in that, In S3, the addition amount of the third catalyst is 1.8-2% of the addition amount of the third solvent; The volume-mass ratio of the third catalyst NMI and TCFH is 3.5-4 ml: 0.45-0.6 g; The addition amount of the modifier is 8-10% of the addition amount of the third solvent.

7. The preparation method of an efficient nano-silica tackifier according to claim 1, characterized in that, S3 specifically is: The polymer-modified silica obtained in S2 is added to a third solvent, then a third catalyst is added, and then N2 is introduced for 25 - 30 min. It is ultrasonically stirred at 25 - 30 °C and reacts with a modifier for 20 - 26 h under the action of the third catalyst. After washing and filtering, highly efficient viscosity-increasing nano-silica is obtained.

8. An efficient nano-silica tackifier prepared by the preparation method of the efficient nano-silica tackifier described in any one of claims 1-7, characterized in that, Water, alkylphenol polyoxyethylene ether and the viscosity-increasing nano-silica are mixed evenly to obtain a highly efficient viscosity-increasing agent.

9. Application of the highly efficient nano-silica viscosity-increasing agent as described in Claim 8 in high-salt and high-water-cut oil reservoirs.

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