CN112266434A

CN112266434A - Nano cross-linked viscoelastic gel and preparation method and application thereof

Info

Publication number: CN112266434A
Application number: CN202011092468.XA
Authority: CN
Inventors: 刘艳华; 史建民; 王耀国
Original assignee: Ningbo Fengcheng Advanced Energy Materials Research Institute Co Ltd
Current assignee: Ningbo Fengcheng Advanced Energy Materials Research Institute Co Ltd
Priority date: 2020-10-13
Filing date: 2020-10-13
Publication date: 2021-01-26

Abstract

The application discloses a nano cross-linked viscoelastic gel, a preparation method and application thereof, wherein the nano cross-linked viscoelastic gel comprises a polymer and a nano material; physical cross-linking between the polymer and the nanomaterial; the polymer contains at least one of the structural units shown in the formula I. According to the invention, the strength of the viscoelastic particles is improved by introducing the nano material and the rigid particles, so that the viscoelastic particles are not easy to break. Meanwhile, physical crosslinking sites are provided, so that the expansion speed is delayed, the expansion is slow, the water absorption rate is improved, the problem of injectability is solved, and effective plugging is realized.

Description

Nano cross-linked viscoelastic gel and preparation method and application thereof

Technical Field

The application relates to a nano cross-linked viscoelastic gel and a preparation method and application thereof, belonging to the technical field of gel materials.

Background

At present, most oil fields in China enter a high water content development stage through water injection development for many years and chemical flooding development mainly based on polymer flooding, and the problems of high temperature, high salt content, large pore canals, low residual oil content, aggravation of longitudinal and plane heterogeneity of an oil layer and the like are highlighted, so that the difficulty in improving the recovery ratio is increased more and more. Researches find that the viscoelastic gel particles can effectively solve the problem of strong heterogeneity of the oil reservoir, and are particularly suitable for adjusting and improving the water absorption profile of a fractured oil reservoir and a large-pore passage stratum. The viscoelastic gel particles are mainly composed of cross-linked high polymers with strong hydrophilic groups, can absorb water to swell, and the swelled particles have elasticity and can be deformed to pass through a porous medium so as to change the flow direction of the deep part of an oil reservoir and expand the swept volume, thereby increasing the yield of crude oil and improving the recovery ratio. However, through recent research and field application, the conventional viscoelastic gel particles have high expansion times, high expansion speed, poor suspension performance in water, easy breakage under a certain shearing force, and contradiction between injectability and plugging strength, so that the conventional viscoelastic gel particles have certain problems in large-scale use.

The viscoelastic particles are prepared by polymerizing and crosslinking monomers, a crosslinking agent and other additives on the ground, and then performing processes such as granulation, drying, crushing, screening and the like. The commonly used monomers are acrylamide and acrylic acid, and some studies have introduced a small amount of salt-resistant or hydrophobic monomers to improve the salt resistance and strength of the viscoelastic particles. By adjusting the monomer ratio, the type and the amount of the cross-linking agent, the type of the additive and the like, viscoelastic gel particles with different properties are synthesized, and generally, the concentrations of the cross-linking agent, the additive and the reinforcing agent have large influence on the water absorption and the strength of the viscoelastic particles, and the concentrations of the main agent and the initiator have small influence.

Many years of research has led to improvements in the temperature resistance and salt tolerance of viscoelastic particles, particle strength enhancement, stability improvement, and slow swelling, but many disadvantages still remain. Firstly, the expansion speed and expansion multiple of the viscoelastic particles used at present are generally higher, the water absorption speed is high, the viscoelastic particles absorb water and expand without being injected, and the problem of difficult field injection exists; meanwhile, the strength of the viscoelastic particles with high expansion times is greatly reduced after the particles absorb water and expand, the particles are very easy to break, and particularly, the viscoelastic particles blocked in large channels or large cracks have a general validity period of no more than half a year due to long-term washing by strong water flow; in addition, the expanded bulked particles have insufficient stability and poor suspensibility, and also cause injectability problems, and further research on the improvement of the properties of the bulked particles is needed.

Disclosure of Invention

According to one aspect of the application, a nano cross-linked viscoelastic gel is provided, and the invention introduces rigid particles by introducing nano materials so as to improve the strength of viscoelastic particles and make the viscoelastic particles not easy to break. Meanwhile, physical crosslinking sites are provided, so that the expansion speed is delayed, the expansion is slow, the water absorption rate is improved, the problem of injectability is solved, and effective plugging is realized. Meanwhile, a branched chain functional monomer is added in the synthesis process, so that the suspension property of the modified polyvinyl chloride is improved.

According to a first aspect of the present application, there is provided a nano-crosslinked viscoelastic gel comprising a polymer and a nanomaterial; physical cross-linking between the polymer and the nanomaterial;

the polymer contains at least one of structural units shown as a formula I:

wherein R is at least one selected from hydroxyl, amino, alkoxy and substituted alkoxy.

Optionally, the nano material is selected from at least one of montmorillonite, bentonite, calcium carbonate, graphene oxide, titanium dioxide and silicon dioxide;

the polymerized monomer of the polymer is at least one of acrylic acid, acrylamide, dimethylaminoethyl methacrylate, methyl methacrylate, diallyl dimethyl ammonium chloride and N-vinyl pyrrolidone;

preferably, the substituents in the substituted alkoxy group include substituted amino;

preferably, the substituent in the substituted amino group includes C₁-C₄Alkyl group of (1).

Optionally, the maximum water absorption rate of the nano cross-linked viscoelastic gel is 30-100 g/g.

Optionally, the maximum water absorption capacity upper limit of the nano-crosslinked viscoelastic gel is independently selected from 100g/g, 82g/g, 76g/g, 68g/g and 43g/g, and the lower limit is independently selected from 30g/g, 82g/g, 76g/g, 68g/g and 43 g/g.

According to a second aspect of the present application, there is provided a method for preparing the above nanocrosslinked viscoelastic gel, the method comprising:

carrying out polymerization reaction on a material containing a polymerization monomer and a nano material in the presence of pH of 3-10 to obtain the nano cross-linked viscoelastic gel;

the polymerized monomer contains at least one of groups with a structural formula shown in a formula I.

Alternatively, the conditions of the polymerization reaction are: the temperature is 50-60 ℃; the time is 3-5 h.

Optionally, the material also contains an initiator and a cross-linking agent;

the initiator is selected from inorganic peroxide initiators;

the addition amount of the initiator is 0.1-1% of the total mass of the polymerization monomers;

the cross-linking agent is selected from at least one of N, N-methylene-bis-acrylamide, tetra allyl ammonium chloride, polyvinyl alcohol diacrylate and aluminum nitrate;

the addition amount of the cross-linking agent is 0.1-0.5% of the total mass of the polymerized monomers;

preferably, the inorganic peroxide initiator is selected from at least one of potassium persulfate, ammonium persulfate, and sodium persulfate.

Optionally, water is also included in the material; the mass fraction of the nano material in the material is 1-5%.

Optionally, the method comprises:

(1) obtaining an aqueous solution containing a polymeric monomer A, and adjusting the pH of the aqueous solution to 3-10 to obtain a solution I;

(2) adding an aqueous solution containing an initiator into a material containing the solution I, the nano material, the polymerized monomer B, the polymerized monomer C and the crosslinking agent, and carrying out polymerization reaction to obtain the nano crosslinked viscoelastic gel;

the polymerized monomer A comprises acrylic acid;

the polymerized monomer C comprises at least one of dimethylaminoethyl methacrylate, methyl methacrylate, diallyl dimethyl ammonium chloride and N-vinyl pyrrolidone;

the polymerized monomer B comprises acrylamide.

Optionally, the method comprises:

step (1): and adding a NaOH solution into the aqueous solution containing the polymerized monomer A, stirring in an ice-water bath, and adjusting the pH to 3-10.

And (2) weighing a polymerized monomer B, a polymerized monomer C, a nano material and a cross-linking agent, sequentially adding the weighed polymerized monomer B, the polymerized monomer C, the nano material and the cross-linking agent into the solution obtained in the step (1), and heating and stirring the mixture.

And (3) weighing an initiator, dissolving the initiator in deionized water, adding the solution into the solution, and preserving the temperature for a certain time at a certain temperature to obtain the nano cross-linked viscoelastic gel.

Optionally, in the solution I, the mass content of the polymerized monomer A is 10-40%.

Optionally, the adjusting the pH of the aqueous solution to 3-10 comprises: adjusting the pH of the aqueous solution to 3-10 by using a pH regulator;

the pH regulator is at least one selected from sodium hydroxide, potassium hydroxide and ammonia water.

Optionally, the mass ratio of the polymerized monomer A to the polymerized monomer B is 1: 4-4: 1;

the addition amount of the polymerized monomer C is 0.25-0.5% of the total mass of the polymerized monomer A and the polymerized monomer B.

Optionally, the mass of the initiator is 0.1-1% of the total mass of the polymerized monomers.

Specifically, the total mass of the polymerized monomers refers to the sum of the masses of the polymerized monomer a, the polymerized monomer B and the polymerized monomer C.

According to a final aspect of the application, there is provided an application of at least one of the nano-crosslinked viscoelastic gel and the nano-crosslinked viscoelastic gel prepared by the method in oil field development.

Specifically, the polymerized monomer C is a branched chain functional monomer and is used for improving the suspension property of the nano cross-linked viscoelastic gel, and the nano material used in the application is a rigid particle, so that the strength of the nano cross-linked viscoelastic gel can be improved, a physical cross-linking site is provided, and the expansion speed is delayed.

Specifically, the water absorption capacity in the present application refers to the ratio of the water that can be absorbed per unit mass of gel particles to the mass thereof, and is referred to as the water absorption capacity.

The complete swelling time refers to the time when the gel is soaked in water and does not separate out water, and the quality of the gel does not change.

The invention can produce the beneficial effects that:

according to the invention, the strength of the viscoelastic particles is improved by adding the nano material and introducing the rigid particles, so that the viscoelastic particles are not easy to break. Meanwhile, physical crosslinking sites are provided, so that the expansion speed is delayed, the expansion is slow, the water absorption rate is improved, the problem of injectability is solved, and effective plugging is realized. Meanwhile, a branched chain functional monomer is added in the synthesis process, so that the suspension property of the modified polyvinyl chloride is improved.

Detailed Description

The present application will be described in detail with reference to examples, but the present application is not limited to these examples.

The raw materials in the examples of the present application were all purchased commercially, unless otherwise specified.

Aiming at the defects of viscoelastic gel particles synthesized by the prior art, the invention develops the nano cross-linked viscoelastic gel particles with low water absorption expansion speed, high strength and good suspension property by introducing nano particles and branched chain monomers in the conventional process of synthesizing viscoelastic gel, and the specific steps are as follows:

weighing a polymerization monomer A, adding the polymerization monomer A into a plastic beaker, diluting the mixture to a certain proportion by using deionized water, then adding a NaOH solution, stirring the mixture in an ice-water bath, and adjusting the pH to about 7.

And (2) weighing the polymerized monomer B, the nano material and the cross-linking agent, sequentially adding the weighed polymerized monomer B, the nano material and the cross-linking agent into the solution obtained in the step (1), and heating and stirring the mixture.

And (3) weighing a certain amount of initiator, dissolving the initiator by using deionized water, adding the initiator into the solution, and preserving heat for a certain time at a certain temperature.

And (4) shearing the synthesized nano cross-linked viscoelastic gel, drying, crushing, screening and then testing the water absorption rate, strength and suspension performance.

The relevant content in the technical scheme of the preparation method is explained as follows:

1. in the scheme, the mass fraction of the polymerized monomer A in the step (1) is 10-40% (mass fraction in the solution I), and the concentration of NaOH is 10%.

2. In the above scheme, the mass ratio of the amount of acrylamide to acrylic acid in the step (2) is 1: 4-4: 1. the dosage of the dimethylaminoethyl methacrylate accounts for 0.25-0.5 percent of the total mass of the monomers (acrylic acid and acrylamide), the dosage of the nano material accounts for 0.01-1 percent of the mass of the water added in the step (1), the dosage of the cross-linking agent accounts for 0.1-0.5 percent of the total mass of the monomers, the heating temperature is 50-60 ℃, and the stirring speed is 250 rpm.

3. In the scheme, the nano materials used in the step (2) are nano montmorillonite, nano calcium carbonate, nano graphene oxide and the like, and the cross-linking agent is N-N methylene bisacrylamide.

4. In the scheme, the initiator used in the step (3) is potassium persulfate, ammonium persulfate and the like, the amount of deionized water is 5-10ml, the usage amount is 0.1% -1% of the total amount of the monomers (the total amount of the monomers refers to the sum of the mass of the monomer A, the mass of the monomer B and the mass of the monomer C), the heat preservation temperature is 50-60 ℃, and the reaction time is 3-5 h.

5. The nano cross-linked viscoelastic particles synthesized in the scheme have a low water absorption rate of less than 10g/g within 24h, a complete expansion time of more than 72h, a water absorption rate of 30-100g/g and a slow expansion performance. The viscoelastic particles synthesized by adding the nano material have higher strength than that of the particles without adding the nano material, and are not easy to break when being pinched and pressed by hands. The suspension properties were also improved, and the suspension was formulated such that 1 wt% of the suspension did not settle significantly after 1 day.

Example 1

Step (1): 40g of acrylic acid monomer was weighed into a plastic beaker, diluted with 60mL of deionized water, and then added with 40mL of a NaOH solution (10% by mass), stirred in an ice-water bath, and the pH was adjusted to 7.

Step (2): weighing 10g of acrylamide monomer, 0.125g of dimethylaminoethyl methacrylate, 1g of nano material montmorillonite and 0.25g of cross-linking agent N, N-methylene bisacrylamide, and sequentially adding the acrylamide monomer, the dimethylaminoethyl methacrylate, the nano material montmorillonite and the cross-linking agent N, N-methylene bisacrylamide into the solution obtained in the step (1), heating and stirring.

And (3): 0.25g of initiator potassium persulfate is weighed, dissolved by 5mL of deionized water and added into the solution, and the solution is kept at 60 ℃ for 5 hours to obtain the nano cross-linked viscoelastic gel A.

Example 2

Step (1): 25g of acrylic acid monomer was weighed into a plastic beaker, diluted with 70mL of deionized water, and then 30mL of a NaOH solution (10% by mass) was added thereto, and the mixture was stirred in an ice-water bath to adjust the pH to 7.

Step (2): 25g of acrylamide monomer, 1g of nano material bentonite and 0.1g of cross-linking agent N, N-methylene bisacrylamide are weighed and sequentially added into the solution in the step (1), and the solution is heated and stirred.

And (3): 0.1g of initiator potassium persulfate is weighed, dissolved by 5mL of deionized water and added into the solution, and the solution is kept at 60 ℃ for 3 hours to obtain the nano cross-linked viscoelastic gel B.

Example 3

Step (1): 10g of acrylic acid monomer was weighed into a plastic beaker, diluted with 80mL of deionized water, and then 20mL of a NaOH solution (10% by mass) was added thereto, and the mixture was stirred in an ice-water bath to adjust the pH to 8.

Step (2): weighing 40g of acrylamide monomer, 0.25g of N-vinyl pyrrolidone, 0.01g of nano material graphene oxide and 0.25g of cross-linking agent aluminum nitrate, sequentially adding the materials into the solution in the step (1), and heating and stirring the materials.

And (3): 0.2g of initiator potassium persulfate is weighed, dissolved by 10mL of deionized water and added into the solution, and the solution is kept at 50 ℃ for 5 hours to obtain the nano cross-linked viscoelastic gel C.

Comparative example

Step (1): 10g of acrylic acid monomer was weighed into a plastic beaker, diluted with 90mL of deionized water, and then 10mL of a NaOH solution (10% by mass) was added thereto, and the mixture was stirred in an ice-water bath to adjust the pH to 5.

Step (2): 40g of acrylamide monomer, 0.25g of dimethylaminoethyl methacrylate and 0.05g of crosslinking agent tetraallylammonium chloride are weighed and sequentially added into the solution in the step (1), and the solution is heated and stirred.

And (3): 0.05g of initiator potassium persulfate is weighed, dissolved by 5mL of deionized water and added into the solution, and the solution is kept at 60 ℃ for 5 hours to obtain the nano cross-linked viscoelastic gel D.

Example 5 Performance testing

Water absorption Rate test

The method comprises the following specific steps: putting the gel particles into a nylon net, swelling the gel particles in simulated saline, taking out the gel particles at intervals (2h 6h 24h 48h), sucking the water on the surface by using filter paper, weighing the gel particles until the mass of the gel particles is not changed any more, and calculating the water absorption rate of 2h and the maximum water absorption rate;

the water absorption capacity is (m1-m0)/m 0;

as can be seen from Table 1, the water absorption rate of the viscoelastic particles introduced into the nanomaterial is low within 2 hours, which indicates that the nanomaterial can slow down the expansion speed of the viscoelastic particles. And the maximum water absorption rate is also improved to a certain extent compared with the maximum water absorption rate without the nano material.

TABLE 1

Sample (I)	Water absorption capacity of 2h	Maximum water absorption rate
			A	14g/g	82g/g
B	11g/g	76g/g
			C	5g/g	68g/g
D	23g/g	43g/g

Strength test

The method comprises the following specific steps: after a sample after water absorption is filtered by a screen mesh, the sample is extruded by force to deform without being crushed, and the shape of the sample can be recovered after the sample is loosened, so that the profile control agent has good strength and toughness;

TABLE 2

Sample (I)	Strength of
		A	Is not easy to break
B	Is not easy to break
		C	Is not easy to break
D	Is easy to break

Although the present application has been described with reference to a few embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application as defined by the appended claims.

Claims

1. A nano-crosslinked viscoelastic gel comprising a polymer and a nanomaterial; physical cross-linking between the polymer and the nanomaterial;

the polymer contains at least one of structural units shown as a formula I:

2. The nano-crosslinked viscoelastic gel according to claim 1, wherein the nano-material is selected from at least one of montmorillonite, bentonite, calcium carbonate, graphene oxide, titanium dioxide, silica;

preferably, said substitutionSubstituents in the amino group include C₁-C₄Alkyl group of (1).

3. The nano-crosslinked viscoelastic gel according to claim 1, wherein the maximum water absorption capacity of the nano-crosslinked viscoelastic gel is 30 to 100 g/g.

4. A process for the preparation of a nanocrosslinked viscoelastic gel according to any one of claims 1 to 3, characterised in that it comprises:

5. The method according to claim 4, wherein the polymerization conditions are: the temperature is 50-60 ℃; the time is 3-5 h.

6. The method according to claim 4, wherein the material further comprises an initiator and a crosslinking agent;

the initiator is selected from inorganic peroxide initiators;

7. The method of claim 4, further comprising water in the material; the mass fraction of the nano material in the material is 1-5%.

8. The method of manufacturing according to claim 4, wherein the method comprises:

the polymerized monomer A comprises acrylic acid;

the polymerized monomer B comprises acrylamide.

9. The preparation method according to claim 8, wherein in the solution I, the mass content of the polymerized monomer A is 10-40%;

preferably, the adjusting the pH of the aqueous solution to 3-10 comprises: adjusting the pH of the aqueous solution to 3-10 by using a pH regulator;

the pH regulator is at least one selected from sodium hydroxide, potassium hydroxide and ammonia water;

preferably, the mass ratio of the polymerized monomer a to the polymerized monomer B is 1: 4-4: 1;

the addition amount of the polymerized monomer C is 0.25-0.5% of the total mass of the polymerized monomer A and the polymerized monomer B;

preferably, the mass of the initiator is 0.1-1% of the total mass of the polymerization monomers;

the total mass of the polymerized monomers is the sum of the mass of the polymerized monomer A, the mass of the polymerized monomer B and the mass of the polymerized monomer C.

10. Use of at least one of the nano-crosslinked viscoelastic gel according to any one of claims 1 to 3, the nano-crosslinked viscoelastic gel prepared according to the process of any one of claims 4 to 9, in the development of oil fields.