Supercritical CO2 thickener for shale gas reservoirs based on hollow mesoporous silica nanoparticles and preparation method thereof

Abstract

The invention discloses a supercritical CO2 thickener for shale gas reservoirs based on hollow mesoporous silica nanoparticles and a preparation method thereof, and relates to the technical field of oil and gas field development. The preparation method of the thickener comprises the following steps: monomers composed of fluoroacrylate, styrene, and vinyl acetate in a molar ratio of 3-5:1-2:1-2, and hollow mesoporous silica nanoparticles with carbon-carbon double bonds accounting for 2%-5% of the total weight of the monomers are reacted under the action of an initiator to obtain the thickener. The preparation method of the invention does not add an organic solvent during the reaction process, and will not cause harm to the human body; the thickener of the invention has a good CO2 viscosity-increasing effect, a good sand-carrying performance, and can effectively improve the fracturing effect.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field development, and in particular to a supercritical CO2 thickener for shale gas reservoirs based on hollow mesoporous silica nanoparticles and a preparation method thereof. Background Art

[0002] Supercritical CO2 has high diffusivity similar to that of gas and high density and solubility of liquid, and has low viscosity and low interfacial tension. Supercritical CO2 can reduce the fracturing pressure of shale, which is about 50% lower than water and about 15% lower than liquid CO2 under the same conditions, and is easier to form a complex fracture network; it has strong solvation ability and can dissolve some organic matter in the shale layer, increase porosity and improve permeability; it has low seepage friction and can achieve effective gas displacement of nanopores in shale reservoirs; CO2's competitive adsorption capacity and adsorption orderliness in shale are much higher than CH4, and it can efficiently replace adsorbed CH4; supercritical CO2 is used to replace slick water fracturing to transform shale gas reservoirs, while replacing adsorbed gas (after replacement, it becomes free gas, and CO2 is adsorbed and buried in situ), and unadsorbed CO2 displaces free gas, which can synergistically increase the production and recovery rate of shale gas wells. However, the viscosity of supercritical CO2 is low, only 0.02 mPa·s~0.16 mPa·s under construction. It is easy to settle during the sand carrying process in the wellbore and fractures, and accumulate at the bottom of the well or the root of the fracture, forming sand plugging. Therefore, it is necessary to add a thickener to increase the viscosity of supercritical CO2.

[0003] At present, the commonly used supercritical CO2 thickeners are siloxane polymers, hydrocarbon polymers, surfactants and fluorine-containing polymers. Polysiloxane derivatives have good thickening properties, but need to add cosolvents; low molecular weight hydrocarbon polymers have poor thickening ability, and high molecular weight hydrocarbon polymers have poor solubility; surfactant thickeners are used in large quantities and can only thicken supercritical CO2 3 to 5 times; fluorine-containing polymers have the best thickening effect due to their low cohesive energy, easy solubility in CO2, and molecular chains that cross-entangle with each other to form a network structure that has a thickening effect. However, perfluorinated compounds are toxic and cannot be metabolized by organisms after entering the water circulation system in the form of wastewater, causing varying degrees of damage. Therefore, it is necessary to prepare a new type of supercritical CO2 thickener to solve the above shortcomings. Nanomaterials have small-scale strong interface effects and large specific surface areas, and have high fluidity in porous media, reduce interfacial tension, and improve rock wettability. Hollow mesoporous silica nanomaterials also have the characteristics of adjustable pore size, low density and high permeability, and have great application prospects. Summary of the invention

[0004] In order to solve at least one of the above problems, the present invention provides a supercritical CO2 thickener for shale gas reservoirs based on hollow mesoporous silica nanoparticles and a preparation method thereof.

[0005] A method for preparing a supercritical CO2 thickener for shale gas reservoirs based on hollow mesoporous silica nanoparticles comprises the following steps: monomers consisting of fluoroacrylate, styrene and vinyl acetate in a molar ratio of 3-5:1-2:1-2 and 2%-5% of the total weight of hollow mesoporous silica nanoparticles with carbon-carbon double bonds are reacted under the action of an initiator to obtain the thickener.

[0006] One embodiment of the present invention is that the initiator is one or a mixture of azobisisobutyronitrile and dicumyl peroxide, and the concentration of the initiator is 30-100 ppm.

[0007] One embodiment of the present invention is that the hollow mesoporous silica nanoparticles with carbon-carbon double bonds are obtained by grafting a monomer containing a carbon-carbon double bond onto the hollow mesoporous silica nanoparticles.

[0008] Furthermore, the monomer containing a carbon-carbon double bond is a silane coupling agent containing a carbon-carbon double bond, and the amount of the silane coupling agent used is 15% to 25% of the mass of the hollow mesoporous silica nanoparticles.

[0009] Furthermore, the silane coupling agent is one of γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane and vinyltrimethoxysilane.

[0010] Furthermore, the method specifically includes the following steps: mixing fluoroacrylate, styrene, vinyl acetate and an initiator evenly under stirring conditions, adding hollow mesoporous silica nanoparticles with carbon-carbon double bonds, and then heating to 50°C to 120°C and keeping the temperature for 3h to 6h.

[0011] In one embodiment of the present invention, the fluoroacrylate is one of heptadecafluorodecyl acrylate, hexadecadecafluorononyl acrylate, heptadecafluoroundecyl acrylate, and octadecadecafluorodecyl acrylate.

[0012] A supercritical CO2 thickener for shale gas reservoirs based on hollow mesoporous silica nanoparticles is prepared by any of the above methods and has a good viscosity-increasing effect on supercritical carbon dioxide.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: the preparation method of the present invention does not add organic solvents during the reaction process and will not cause harm to the human body; the thickener of the present invention has a good CO2 viscosity-increasing effect and good sand-carrying performance, and can effectively improve the fracturing effect. At the same time, the thickener of the present invention uses low-density hollow mesoporous silica nanoparticles. Adding this thickener to supercritical CO2 to prepare fracturing fluid is beneficial to improving the uniformity of the fracturing system. In addition, the thickener of the present invention is nano-scale and has little damage to shale reservoirs. DETAILED DESCRIPTION

[0014] The present invention will be further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0015] In the following embodiments, unless otherwise specified, the items described are conventional commercial products in the art.

[0016] In the following embodiments, unless otherwise specified, the operations described are all routine operations in the art.

[0017] In the following examples, hollow mesoporous silica nanoparticles with carbon-carbon double bonds were prepared by the following method:

[0018] 150 mL of ethanol, 6.3 mL of ammonia water and 20 mL of deionized water were added to a beaker in sequence, and stirred at 25°C for 1 h; then the temperature was raised to 50°C, 12 mL of ethyl orthosilicate was added, and stirring was continued for 3 h; then centrifuged and washed with ethanol to obtain silica nanospheres.

[0019] 400 mg of silica nanospheres were weighed and dispersed in 60 mL of ethanol / deionized water with a volume ratio of 1:2. 600 mg of hexadecyltrimethylammonium bromide was weighed and dissolved in 60 mL of ethanol / deionized water with a volume ratio of 1:2. The hexadecyltrimethylammonium bromide solution was then added to the silica nanosphere dispersion. After stirring for 30 minutes, 1 mL of ethyl orthosilicate and 2.4 mL of ammonia water were added in sequence. Stirring was continued for 12 hours, and then centrifuged. The centrifuged product was dispersed in 80 mL of deionized water. 40 mL of the dispersion was taken, 930 mg of anhydrous sodium carbonate was added to the dispersion, and then stirred at 50°C for 11 hours. After the end, the dispersion was centrifuged and washed alternately with deionized water and ethanol for 3 times, dried at 50°C for 24 hours, and then the dried product was calcined in a muffle furnace at 550°C for 6 hours to obtain hollow mesoporous silica nanospheres.

[0020] 3 g of hollow mesoporous silica nanospheres were ultrasonically dispersed into 200 mL of anhydrous ethanol / deionized water mixed solution with a pH of 4 and a volume ratio of 3:1, followed by dropwise addition of 0.6 g of γ-methacryloxypropyltrimethoxysilane, and then the temperature was raised to 70 ° C for reaction for 2 h. After centrifugation, the mixture was washed three times with anhydrous ethanol and dried at 60 ° C for 12 h to obtain hollow mesoporous silica nanoparticles with carbon-carbon double bonds.

[0021] Example 1

[0022] Under stirring conditions, 155.4 g (0.3 mol) of heptadecafluorodecyl acrylate, 10.4 g (0.1 mol) of styrene, 7.2 g (0.1 mol) of vinyl acetate and 40 ppm of azobisisobutyronitrile were mixed evenly, and then 3.5 g of hollow mesoporous silica nanoparticles with carbon-carbon double bonds were added. After stirring evenly, the temperature was raised to 60°C and kept warm for 4 hours to obtain a viscous product, which was the target product.

[0023] Example 2

[0024] Under stirring conditions, 259 g (0.5 mol) of heptadecafluorodecyl acrylate, 10.4 g (0.1 mol) of styrene, 7.2 g (0.1 mol) of vinyl acetate and 40 ppm of azobisisobutyronitrile were mixed evenly, and then 5.5 g of hollow mesoporous silica nanoparticles with carbon-carbon double bonds were added. After stirring evenly, the temperature was raised to 60°C and kept warm for 4 hours to obtain a viscous product, which was the target product.

[0025] Example 3

[0026] Under stirring conditions, 155.4 g (0.3 mol) of heptadecafluorodecyl acrylate, 20.8 g (0.2 mol) of styrene, 7.2 g (0.1 mol) of vinyl acetate and 40 ppm of azobisisobutyronitrile were mixed evenly, and then 3.7 g of hollow mesoporous silica nanoparticles with carbon-carbon double bonds were added. After stirring evenly, the temperature was raised to 60°C and kept warm for 4 hours to obtain a viscous product, which was the target product.

[0027] Example 4

[0028] Under stirring conditions, 155.4 g (0.3 mol) of heptadecafluorodecyl acrylate, 10.4 g (0.1 mol) of styrene, 14.4 g (0.2 mol) of vinyl acetate and 40 ppm of azobisisobutyronitrile were mixed evenly, and then 3.6 g of hollow mesoporous silica nanoparticles with carbon-carbon double bonds were added. After stirring evenly, the temperature was raised to 60°C and kept warm for 4 hours to obtain a viscous product, which was the target product.

[0029] Example 5

[0030] Under stirring conditions, 155.4 g (0.3 mol) of heptadecafluorodecyl acrylate, 10.4 g (0.1 mol) of styrene, 14.4 g (0.2 mol) of vinyl acetate and 40 ppm of diisopropylbenzene peroxide were mixed evenly, and then 3.6 g of hollow mesoporous silica nanoparticles with carbon-carbon double bonds were added. After stirring evenly, the temperature was raised to 110°C and kept warm for 4 hours to obtain a viscous product, which was the target product.

[0031] Comparative Example 1

[0032] Compared with Example 1, the difference is that the hollow mesoporous silica nanoparticles with carbon-carbon double bonds are not added, and the other experimental conditions are the same.

[0033] Comparative Example 2

[0034] Compared with Example 1, the difference is that the added nano material is unmodified nano silicon dioxide.

[0035] In order to further illustrate the effect of the supercritical CO2 thickener for shale gas reservoirs based on hollow mesoporous silica nanoparticles prepared in the embodiment of the present invention, it is tested as follows.

[0036] A supercritical CO2 fracturing fluid with a mass concentration of 5% was prepared using the thickeners prepared in Examples 1 to 5 and Comparative Examples 1 to 2. The thickened dissolution pressure and viscosity of the fracturing fluid at 40°C were measured using a high-temperature and high-pressure visual dissolution kettle and a JS-ND rotational viscometer. The final results are shown in Table 1.

[0037] Table 1 Solubility and viscosity of various thickeners

[0038] serial number Dissolution pressure (MPa) Viscosity (mPa·s) Example 1 8.1 6.9 Example 2 8.1 7.2 Example 3 8.4 7.4 Example 4 7.9 7.1 Example 5 8.1 7.1 Comparative Example 1 8.8 4.9 Comparative Example 2 8.6 5.4

[0039] As can be seen from Table 1, the supercritical CO2 thickener for shale gas reservoirs based on hollow mesoporous silica nanoparticles prepared in the embodiment of the present invention has a high thickening performance for supercritical carbon dioxide. At the same time, referring to Comparative Examples 1 and 2, it can be seen that after adding hollow mesoporous silica nanoparticles, the dissolution pressure of the thickener product is not only reduced, but also the viscosity of supercritical carbon dioxide can be increased, indicating that the hollow mesoporous silica nanoparticles play a key role in the thickener of the embodiment of the present invention.

[0040] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a supercritical CO2 thickener for shale gas reservoirs based on hollow mesoporous silica nanoparticles, characterized in that: The invention comprises the following steps: monomers consisting of fluoroacrylate, styrene and vinyl acetate in a molar ratio of 3-5:1-2:1-2 and hollow mesoporous silica nanoparticles with carbon-carbon double bonds accounting for 2%-5% of the total weight of the monomers are reacted under the action of an initiator to obtain the obtained hollow mesoporous silica nanoparticles; the hollow mesoporous silica nanoparticles with carbon-carbon double bonds are obtained by grafting a monomer containing a carbon-carbon double bond onto the hollow mesoporous silica nanoparticles, wherein the monomer containing a carbon-carbon double bond is a silane coupling agent containing a carbon-carbon double bond, and the amount of the silane coupling agent is 15%-25% of the weight of the hollow mesoporous silica nanoparticles, and the silane coupling agent is one of γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane and vinyltrimethoxysilane.

2. The method according to claim 1, characterized in that The initiator is one of azobisisobutyronitrile and dicumyl peroxide or a mixture of the two, and the concentration of the initiator is 30-100 ppm.

3. The method according to claim 2, characterized in that The method specifically comprises the following steps: uniformly mixing fluoroacrylate, styrene, vinyl acetate and an initiator under stirring conditions, adding hollow mesoporous silica nanoparticles with carbon-carbon double bonds, and then heating to 50° C. to 120° C. and keeping the temperature for 3 h to 6 h.

4. The method according to claim 1, characterized in that: The fluoroacrylate is one of heptadecafluorodecyl acrylate, hexadecadecafluorononyl acrylate, heptadecafluoroundecyl acrylate, and octadecadecafluorodecyl acrylate.

5. A supercritical CO2 thickener for shale gas reservoirs based on hollow mesoporous silica nanoparticles, prepared by the method described in any one of claims 1 to 4.