Partially crosslinked copolymer oil-displacing agent as well as preparation method and application thereof

Abstract

The invention provides a partially crosslinked copolymer oil-displacing agent as well as a preparation method and application thereof. The partially crosslinked copolymer oil-displacing agent is characterized by being prepared from the following raw materials in percentage by mass: 15 to 25 percent of water-soluble monomers, 5 to 10 percent of temperature-resistant monomers, 1 to 2 percent of pH (Potential of Hydrogen) regulators, 0.025 to 0.05 percent of aldehyde crosslinking agents, 0.015 to 0.03 percent of oxidation initiators, 0.008 to 0.015 percent of reduction initiators and the balance of water. The copolymer disclosed by the invention is a copolymerization type partially-crosslinked copolymer, and can be used as an oil-displacing agent to effectively improve the use performance, the ageing resistance, the temperature resistance and the salt tolerance. The partial cross-linked copolymer oil-displacing agent disclosed by the invention is adjustable in initial viscosity and elastic modulus, the viscosity rate reaches 61% or above, the construction requirements of a field profile control technology are met, and the partial cross-linked copolymer oil-displacing agent has injection and wide adaptability.

Description

Technical Field

[0001] The invention relates to a partially cross-linked copolymer oil displacement agent and a preparation method and application thereof, belonging to the technical field of oil field production. Background Art

[0002] In the three-recovery technology, water-soluble polymers used in chemical oil recovery can improve the oil-water mobility ratio, reduce the probability of injected water fingering along the high permeability layer, and improve the vertical sweep efficiency, thereby increasing the crude oil recovery rate. At present, linear acrylamide polymers are commonly used in water-soluble polymers for chemical oil recovery. Most of my country's oil fields are continental sedimentary oil fields with serious heterogeneity. After primary and secondary oil recovery, the water content in the oil layer is high, and the injected displacement fluid can easily enter the production well from the high permeability layer, reducing the oil recovery efficiency. Due to some performance defects of linear acrylamide polymers themselves, they cannot be used in high-temperature, high-salinity and highly heterogeneous reservoirs. Cross-linked polyacrylamide can effectively block high permeability layers and large pores, adjust the injected water profile, make the flow resistance of the porous medium of the reservoir uniform, expand the swept volume of the displacement fluid, and improve the recovery rate of oil. However, when used as an oil displacement agent, the polymer suspension is required to have good migration ability, be able to deform and pass through the pores, and have excellent viscoelastic properties, which can effectively increase the viscosity of the displacement phase and improve its mobility ratio, which is exactly what cross-linked polyacrylamide lacks.

[0003] Therefore, it is of great significance to develop a polyacrylamide polymer oil displacement agent that can be used in high-temperature, high-salinity and highly heterogeneous oil reservoirs. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a partially cross-linked copolymer oil-displacing agent and its preparation method and application. The copolymer of the present invention is a copolymerized partially cross-linked copolymer, which can effectively improve the performance and anti-aging, temperature resistance and salt resistance of the oil-displacing agent.

[0005] The technical solution of the present invention is as follows:

[0006] A partially cross-linked copolymer oil displacement agent comprises the following raw materials in percentage by mass: 15-25% water-soluble monomer, 5-10% temperature-resistant monomer, 1-2% pH regulator, 0.025-0.05% aldehyde cross-linking agent, 0.015-0.03% oxidation initiator, 0.008-0.015% reduction initiator, and the balance is water.

[0007] Preferably, according to the present invention, the partially cross-linked copolymer oil-displacing agent comprises the following raw materials in percentage by mass: 18-20% water-soluble monomer, 6-8% temperature-resistant monomer, 1.2-1.6% pH adjuster, 0.03-0.04% aldehyde cross-linking agent, 0.02-0.025% oxidation initiator, 0.01-0.015% reduction initiator, and the balance is water.

[0008] Preferably according to the present invention, the water-soluble monomer is acrylamide.

[0009] Preferably according to the present invention, the temperature-resistant monomer is 2-acrylamide-2-methylpropane sulfonic acid.

[0010] Preferably according to the present invention, the pH regulator is sodium hydroxide.

[0011] Preferably according to the present invention, the aldehyde cross-linking agent is hexamethylenetetramine and / or formaldehyde.

[0012] Preferably according to the present invention, the oxidation initiator is potassium persulfate.

[0013] Preferably according to the present invention, the reduction initiator is sodium bisulfite.

[0014] According to the present invention, the method for preparing the above-mentioned partially cross-linked copolymer oil-displacing agent comprises the following steps:

[0015] A water-soluble monomer, a temperature-resistant monomer, a pH regulator, an aldehyde crosslinking agent, an oxidation initiator, and a reduction initiator are sequentially added to water, mixed evenly, and then a crosslinking reaction is carried out; after the reaction is completed, the gel obtained by the reaction is dried and crushed to obtain a partially crosslinked copolymer oil displacement agent.

[0016] Preferably according to the present invention, the temperature of the cross-linking reaction is 5-10°C, more preferably 5°C; the time of the cross-linking reaction is 3-6h, more preferably 5h.

[0017] Preferably according to the present invention, the drying is performed at 60-80° C. to a constant weight.

[0018] According to the present invention, the partially cross-linked copolymer oil displacing agent is used as an oil displacing agent for oil field production; preferably, the specific application method is: using formation water to prepare a solution with a mass concentration of 0.3-0.5wt%, and injecting the solution into the formation.

[0019] The technical features and effects of the present invention are as follows:

[0020] 1. The partially cross-linked copolymer oil-displacing agent prepared by the present invention has the advantages of both cross-linked polyacrylamide and linear polyacrylamide. Its linear structure gives its aqueous solution good suspension ability and high viscosity, and its cross-linked structure provides good elasticity and shear resistance, and has a high storage modulus.

[0021] 2. In the preparation of the copolymer oil-displacing agent of the present invention, the temperature-resistant monomer 2-acrylamide-2-methylpropanesulfonic acid is added to copolymerize with acrylamide, which can improve the stability of the product at high temperature, thereby effectively improving the aging resistance of the product in aqueous solution. After the product is aged for three months, the storage modulus retention rate can be as high as 74% or more; and the amount of temperature-resistant monomer added needs to be controlled within the scope of the present invention. If the amount of temperature-resistant monomer added is too high, the viscosity is too high, it is not easy to inject, and the storage modulus is reduced; and if the amount of temperature-resistant monomer added is too low, the temperature resistance and stability are reduced.

[0022] 3. In the preparation of the copolymer oil-displacing agent of the present invention, a special type of cross-linking group is introduced to make the branching performance of the gel after cross-linking more stable. The synthesized product exhibits both the viscosity characteristics of the polymer and the elastic characteristics of PPG. The product has a high viscosity after dissolution, which can greatly improve the suspension and stability time of PPG. In addition, too high or too low a proportion of the cross-linking agent, as well as changing the type of the cross-linking agent, will reduce the performance of the copolymer oil-displacing agent.

[0023] 4. The oil displacing agent of the present invention is a copolymerized partially cross-linked copolymer, which has excellent performance, anti-aging, temperature resistance and salt resistance, and can effectively improve the crude oil recovery rate; the partially cross-linked copolymer oil displacing agent of the present invention has adjustable initial viscosity and elastic modulus, and the viscosity rate can reach more than 74%, which meets the construction requirements of on-site profile control technology and has injection and wider adaptability. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0025] The formaldehyde used in the examples is provided by a formaldehyde aqueous solution with a mass concentration of 37%.

[0026] Example 1

[0027] A partially cross-linked copolymer oil-displacing agent, comprising the following raw materials in percentage by weight: 18% acrylamide, 6% 2-acrylamido-2-methylpropanesulfonic acid, 1.2% sodium hydroxide, 0.03% aldehyde cross-linking agent, 0.02% potassium persulfate, 0.01% sodium bisulfite, and the balance being water;

[0028] The aldehyde cross-linking agent is hexamethylenetetramine.

[0029] The preparation method of the partially cross-linked copolymer oil-displacing agent comprises the following steps:

[0030] Add acrylamide and water to a reaction kettle and stir evenly; then add 2-acrylamido-2-methylpropanesulfonic acid, sodium hydroxide, and an aldehyde cross-linking agent in sequence to obtain a monomer mixed aqueous solution with a pH of 7, introduce nitrogen to drive out oxygen until the oxygen content is less than 0.1 mg / L, add potassium persulfate and sodium bisulfite, mix evenly, react at 5°C for 5 hours, and obtain an elastic gel; dry the obtained gel at 80°C to constant weight, crush it, obtain a partially cross-linked copolymer oil displacement agent, and sieve it for later use.

[0031] Example 2

[0032] A partially cross-linked copolymer oil-displacing agent is as described in Example 1, except that the aldehyde cross-linking agent is formaldehyde.

[0033] The preparation method of the partially cross-linked copolymer oil-displacing agent is as described in Example 1.

[0034] Example 3

[0035] A partially cross-linked copolymer oil-displacing agent is as described in Example 1, except that the aldehyde cross-linking agent is a combination of formaldehyde and urotropine, wherein the mass ratio of formaldehyde to urotropine is 1:1.

[0036] The preparation method of the partially cross-linked copolymer oil-displacing agent is as described in Example 1.

[0037] Example 4

[0038] A partially cross-linked copolymer oil-displacing agent is as described in Example 1, except that the amount of 2-acrylamide-2-methylpropanesulfonic acid used is 8%, the amount of sodium hydroxide used is 1.6%, and the rest is the same as Example 1.

[0039] The preparation method of the partially cross-linked copolymer oil-displacing agent is as described in Example 1.

[0040] Example 5

[0041] A partially cross-linked copolymer oil-displacing agent is as described in Example 1, except that the amount of 2-acrylamide-2-methylpropanesulfonic acid used is 10%, the amount of sodium hydroxide used is 1.9%, and the rest is the same as Example 1.

[0042] The preparation method of the partially cross-linked copolymer oil-displacing agent is as described in Example 1.

[0043] Comparative Example 1

[0044] A partially cross-linked copolymer oil-displacing agent is as described in Example 1, except that no sodium hydroxide is added, and the rest is the same as Example 1.

[0045] The preparation method of the partially cross-linked copolymer oil-displacing agent is as described in Example 1, except that the step of adding sodium hydroxide is omitted.

[0046] Comparative Example 2

[0047] A partially cross-linked copolymer oil-displacing agent is as described in Example 1, except that 2-acrylamido-2-methylpropanesulfonic acid and sodium hydroxide are not added, and the rest is the same as Example 1.

[0048] The preparation method of the partially cross-linked copolymer oil-displacing agent is as described in Example 1, except that the step of adding 2-acrylamido-2-methylpropanesulfonic acid and sodium hydroxide is omitted.

[0049] Comparative Example 3

[0050] A partially cross-linked copolymer oil-displacing agent is as described in Example 1, except that the aldehyde cross-linking agent is paraformaldehyde.

[0051] The preparation method of the partially cross-linked copolymer oil-displacing agent is as described in Example 1.

[0052] Test example

[0053] The formula of the simulated saline used in the test is: 6.191 g of sodium chloride, 0.2414 g of calcium chloride, 0.3514 g of magnesium chloride, and 0.0696 g of sodium sulfate per 1 L of solution.

[0054] (I) Storage modulus test method:

[0055] 1. Accurately weigh 5g of oil displacement agent sample, accurate to 0.0001g, weigh 1L of simulated brine into a wide-mouth bottle, turn on the constant speed stirrer at 400r / min and slowly add the sample along the vortex wall within 30s, then stir at a stirring rate of 500r / min for 2h. The resulting solution concentration is 5000mg / L.

[0056] 2. Take an appropriate amount of the solution to be tested in step 1, turn on the instrument and set the conditions according to the rheometer operating instructions, set the measurement temperature to 25°C, select the plate mode, rotor model PP50, take an appropriate amount of test liquid on the plate, set the gap to 200μm, lower the head to the set gap, wipe off the excess test liquid, and measure the storage modulus of the product according to the rheometer operating instructions.

[0057] 3. Each sample should be made into 3 parallel samples, and the relative error between each measured value and the arithmetic mean value should not exceed 10%. The arithmetic mean value shall be taken as the measurement result.

[0058] (II) Viscosity test method:

[0059] 1. Accurately weigh 5g of oil displacement agent sample, accurate to 0.0001g, weigh 1L of simulated brine into a wide-mouth bottle, turn on the constant speed stirrer at 400r / min and slowly add the sample along the vortex wall within 30s, then stir at a stirring rate of 500r / min for 2h. The resulting solution concentration is 5000mg / L.

[0060] 2. Set the startup conditions according to the rheometer operating instructions, set the measurement temperature to 30°C, move the solution to be tested into the measuring cylinder, keep the temperature constant for 3 minutes, select the coaxial cylinder mode, and set the shear rate to 7.34s -1 , measure the viscosity of the dispersion system within 1 minute according to the rheometer operating instructions, and take the average value of the viscosity, which is the viscosity of the dispersion system.

[0061] 3. Each sample should be made into 3 parallel samples, and the relative error between each measured value and the arithmetic mean value should not exceed 10%. The arithmetic mean value shall be taken as the measurement result.

[0062] (III) Test method for stability time of dispersed system

[0063] 1. Accurately weigh 5g of oil displacement agent sample, accurate to 0.0001g, weigh 1L of simulated brine into a wide-mouth bottle, turn on the constant speed stirrer at 400r / min and slowly add the sample along the vortex wall within 30s, then stir at a stirring rate of 500r / min for 2h, then stop stirring and seal the wide-mouth bottle with a bottle cap.

[0064] 2. Start timing when the stirring of the sample in step 1 stops, let it stand and observe the liquid surface, and record the time it takes for the dispersion system to change from a uniform dispersion to a clear interface. This is the stabilization time of the dispersion system.

[0065] Table 1 Performance of oil displacement agents of Examples 1-5 and Comparative Examples 1-3

[0066]

[0067] As can be seen from Table 1, the specific crosslinking agent of the present invention can play a role in branching the molecular chain. The synthesized product exhibits both the viscosity characteristics of the polymer and the elastic characteristics of PPG. Among them, increasing the amount of 2-acrylamide-2-methylpropane sulfonic acid, the viscosity of the synthesized product increases significantly, and the more 2-acrylamide-2-methylpropane sulfonic acid is used, the higher the viscosity. The maximum can be increased from 505mPa·s to 706mPa·s.

[0068] From the comparative results, it can be seen that in the case where 2-acrylamide-2-methylpropanesulfonic acid and sodium hydroxide are not added, the viscosity of the synthesized sample is greatly reduced, and the stability time is also greatly reduced. The amount of 2-acrylamide-2-methylpropanesulfonic acid added plays a crucial role in the viscosity of the synthesized product; while changing the type of crosslinking agent, the performance of the obtained polymer is greatly reduced.

Claims

1. A partially cross-linked copolymer oil-displacing agent, characterized in that: The invention comprises the following raw materials in percentage by weight: 15-25% of water-soluble monomer, 5-10% of temperature-resistant monomer, 1-2% of pH regulator, 0.025-0.05% of aldehyde cross-linking agent, 0.015-0.03% of oxidation initiator, 0.008-0.015% of reduction initiator, and the balance is water.

2. The partially cross-linked copolymer oil-displacing agent according to claim 1, characterized in that: The partially cross-linked copolymer oil displacement agent comprises the following raw materials in percentage by weight: 18-20% water-soluble monomer, 6-8% temperature-resistant monomer, 1.2-1.6% pH regulator, 0.03-0.04% aldehyde cross-linking agent, 0.02-0.025% oxidation initiator, 0.01-0.015% reduction initiator, and the balance is water.

3. The partially cross-linked copolymer oil-displacing agent according to claim 1, characterized in that: The water-soluble monomer is acrylamide.

4. The partially cross-linked copolymer oil-displacing agent according to claim 1, characterized in that: The temperature-resistant monomer is 2-acrylamide-2-methylpropane sulfonic acid.

5. The partially cross-linked copolymer oil-displacing agent according to claim 1, characterized in that: The pH regulator is sodium hydroxide.

6. The partially cross-linked copolymer oil-displacing agent according to claim 1, characterized in that: The aldehyde cross-linking agent is hexamethylenetetramine and / or formaldehyde.

7. The partially cross-linked copolymer oil-displacing agent according to claim 1, characterized in that: The oxidation initiator is potassium persulfate; the reduction initiator is sodium bisulfite.

8. The method for preparing the partially cross-linked copolymer oil-displacing agent according to claim 1, comprising the following steps: A water-soluble monomer, a temperature-resistant monomer, a pH regulator, an aldehyde crosslinking agent, an oxidation initiator, and a reduction initiator are sequentially added to water, mixed evenly, and then a crosslinking reaction is carried out; after the reaction is completed, the gel obtained by the reaction is dried and crushed to obtain a partially crosslinked copolymer oil displacement agent.

9. The method for preparing the partially cross-linked copolymer oil-displacing agent according to claim 8, characterized in that: The temperature of the cross-linking reaction is 5-10°C, preferably 5°C; the time of the cross-linking reaction is 3-6h, preferably 5h; The drying is performed at 60-80° C. to a constant weight.

10. The use of the partially cross-linked copolymer oil-displacing agent according to claim 1, characterized in that: It is used as an oil displacement agent for oil field production; preferably, the specific application method is: using formation water to prepare a solution with a mass concentration of 0.3-0.5wt%, and injecting the solution into the formation.

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