Active oil displacement polymer with interfacial activity and biodegradability

Abstract

The invention relates to an active oil displacement polymer with interfacial activity and biodegradability. The preparation method of the oil-displacing polymer comprises the following steps: mixing a water-soluble monomer with water; adding calcium lignosulphonate, adjusting the pH value of the mixture to 7, putting the mixture into a constant-temperature water bath kettle, introducing nitrogen for a period of time, heating to a preset temperature, slowly adding azobis (isobutylamidine) hydrochloride into the mixed system with the adjusted pH value, reacting under a sealed condition, drying and crushing. According to the invention, lignin biodegradability and certain surface activity of calcium lignosulphonate are utilized. The polymer is synthesized by copolymerizing with other monomers, so that the oil-water interfacial tension of the polymer is reduced, and the biodegradability is improved. And the polymer is endowed with excellent interfacial activity and biodegradability.

Description

Technical Field

[0001] This invention relates to an active oil displacement polymer that combines interfacial activity and biodegradability, belonging to the field of oilfield chemical technology. Background Technology

[0002] Currently, research on chemical flooding to improve the recovery rate of offshore heavy oil reservoirs has made some progress. For reservoirs with crude oil viscosity exceeding 350 mPa·s, the application potential of chemical flooding urgently needs to be explored. These heavy oils are rich in aromatic hydrocarbons, gums, and asphaltenes, resulting in high viscosity and high flow resistance, making them difficult to develop economically and effectively. For such oilfields, chemical flooding mainly has the following limitations: conventional polymers have poor viscosity-reducing effects, making it difficult to effectively drive crude oil flow; although surfactants can effectively reduce the interfacial tension between oil and water, their dispersion ability in heavy oil is poor, resulting in low sweep efficiency.

[0003] Both domestically and internationally, the main approach is to introduce monomers with active groups onto the polymer molecular chain, giving it both thickening properties and interfacial activity. This overcomes problems such as phase separation and chromatographic separation that occur during the migration of traditional composite oil displacement systems in porous media, thereby improving the recovery rate of heavy oil.

[0004] In addition, during the development of oil and gas fields, a large amount of polymers are used, resulting in high levels of polymer residues in the produced fluids, which are difficult to degrade.

[0005] Both domestically and internationally, the main approach is to enhance the biodegradability of polymers through the development of bio-based and biodegradable polymer technologies. Among these, biodegradable polymer technology modifies biodegradable natural compounds to give them excellent emulsifying, dispersing, and wetting properties. The modified natural compounds are then combined with other monomers to form highly efficient oil displacement polymers, further enhancing the polymer's ability to reduce oil-water interfacial tension. At the same time, the excellent degradability of the oil displacement polymers prevents the separation of oil displacement agents from failing to degrade and causing secondary pollution, thus achieving an environmentally friendly effect.

[0006] Therefore, by modifying natural compounds to give them surface-active properties and biodegradability, we can make the oil displacement polymers with the modified products have higher viscosity, lower interfacial tension, and degradability. Summary of the Invention

[0007] The purpose of this invention is to provide an active oil displacement polymer that combines interfacial activity and biodegradability, so as to enable the polymer to have excellent interfacial activity and biodegradability and thus improve the recovery rate of ordinary heavy oil at sea.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: the oil-displacing polymer is copolymerized from three structural monomers: acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, and calcium lignin sulfonate. Its structural formula is as follows: An active oil displacement polymer possessing both interfacial activity and biodegradability is synthesized as follows: The target agent molecule is synthesized using an aqueous free radical copolymerization method. Acrylamide and 2-acrylamido-2-methylpropanesulfonic acid are weighed and placed in a beaker, dissolved in water, and stirred thoroughly to obtain solution A; LSCa is added to solution A, stirred until completely dissolved, and the pH is adjusted to 7 to obtain solution B; solution B is transferred to a three-necked flask, placed in a constant temperature water bath, and nitrogen gas is introduced, followed by heating to the preset temperature; after reaching the preset temperature, the initiator is slowly added, and the reaction is carried out under sealed conditions at a constant temperature to generate a brown viscous liquid; after drying, it is pulverized.

[0009] The mass ratio of acrylamide to 2-acrylamide-2-methylpropanesulfonic acid in the oil displacement polymer is 1:0.176~0.385, accounting for about 65~74% of the total mass fraction of the monomers.

[0010] The amount of the functional monomer (calcium lignosulfonate) added to the oil displacement polymer accounts for 6-8% of the polymer system.

[0011] The solution used to adjust the pH was a 30 wt% sodium hydroxide solution, and the pH of the mixture was adjusted to 7.

[0012] During the nitrogen purging step, nitrogen is continuously purged for 30 minutes to ensure an oxygen-free environment.

[0013] The initiator is azobisisobutylamidine hydrochloride; the amount of azobisisobutylamidine hydrochloride added accounts for 0.4~0.6% of the polymer system.

[0014] After reacting at a constant temperature of 58-62℃ for 5 hours under sealed conditions, a brown viscous liquid is generated; the reaction product is repeatedly washed with anhydrous ethanol and sheared to remove unreacted monomers.

[0015] The reaction formula of this invention is as follows: The application of this oil displacement polymer is as follows: The prepared ternary polymer is mixed with simulated formation water to form a solution with a concentration of 1500 ppm. The total salinity of the simulated formation water is 11734.64 ppm. The solution is applied at a temperature of 54℃ and a rotation speed of 7.34 s. -1At the time of simulation, the apparent viscosity was 31.15 mPa·s, the simulated reservoir temperature was 54℃, and the simulated oil viscosity was 523.7 mPa·s. Crude oil was injected into the core at a rate of 0.5 mL / min until the oil saturation was about 75%. Then, simulated formation water was injected at a rate of 1 mL / min until the water cut reached 98%. Polymer flooding was then carried out at a flow rate of 0.5 mL / min, with 0.6 PV of polymer injected. Subsequent water flooding was then carried out at a flow rate of 0.5 mL / min until the water cut reached 98%. The polymer simulation improved the oil recovery rate (polymer flooding + subsequent water flooding) by more than 15.33%.

[0016] The beneficial effects of this invention are as follows: Introducing the functional monomer calcium lignin sulfonate into the acrylamide molecular chain, due to the presence of the sulfonic acid group (-SO3-) in the 2-acrylamido-2-methylpropanesulfonic acid molecule, effectively improves the water solubility and dispersibility of lignin; calcium lignin sulfonate not only retains the biodegradability of lignin, but also possesses certain surface activity due to its unique molecular structure, effectively reducing the oil-water interfacial tension, promoting the stripping of crude oil from the rock surface, thereby improving oil recovery, and further reducing the surface activity of high-valence salt ions (Ca) in offshore oil fields. 2+ Mg 2+ It has a high content and calcium lignosulfonate has good compatibility. Attached Figure Description

[0017] Figure 1 The relationship between apparent viscosity and shear rate is given for AM / AMPS binary polymers and AM / AMPS / LSCa ternary polymers.

[0018] Figure 2 The infrared spectra of the AM / AMPS binary polymer and the AM / AMPS / LSCa ternary polymer are shown.

[0019] Figure 3 The NMR spectra of the AM / AMPS binary polymer and the AM / AMPS / LSCa ternary polymer are shown.

[0020] Figure 4 shows scanning electron micrographs of the AM / AMPS / LSCa ternary polymer at 1500 ppm. (a) shows the microstructure of AM / AMPS / LSCa in pure water, and (b) shows the microstructure of AM / AMPS / LSCa in simulated formation water.

[0021] Figure 5 The interfacial tension changes of AM / AMPS binary polymer and AM / AMPS / LSCa ternary polymer at different concentrations are shown.

[0022] Figure 6 The results of the oil displacement experiment are based on 1500 ppm of AM / AMPS / LSCa ternary polymer. Detailed Implementation

[0023] Example 1: Synthesis of AM / AMPS / LSCa ternary polymer Weigh AM and AMPS monomers in a 7.5:2.5 ratio and add deionized water to prepare a mixed solution. Then add 6.5% LSCa to prepare an aqueous solution with a total monomer mass fraction of 26%. Adjust the pH to 7 with 30wt% sodium hydroxide solution. Then add 0.55wt% of the initiator azobisisobutylamidine hydrochloride. Transfer the solution to a three-necked flask, purge with nitrogen for 30 min, place in a constant temperature water bath, heat the reaction system to 60℃, and carry out the polymerization reaction under nitrogen protection for 5 h. After the reaction, wash and shear the reaction product with anhydrous ethanol several times to remove unreacted monomers. After drying, pulverize.

[0024] Example 2: Synthesis of AM / AMPS binary polymer As described in Example 1, except that calcium lignosulfonate was not added.

[0025] Example 3: Investigation of the shear properties of the polymer The oil displacement polymer prepared above was mixed with simulated formation water to form a solution with a mass concentration of 1500 ppm. The solution was then subjected to a shear rate range of 0.1–1000 s⁻¹ at 54 °C. -1 The viscosity as a function of shear rate was tested using a HAAKE MARS 40 rheometer; Figure 1 It can be seen that the viscosity of both polymer solutions decreases with increasing shear rate, and both exhibit shear dilution properties, which is consistent with the characteristics of pseudoplastic fluids.

[0026] Example 4: Infrared characterization of polymers The infrared spectra of the AM / AMPS / LSCa ternary polymer synthesized in Example 1 and the AM / AMPS binary polymer synthesized in Example 2 are shown below. Figure 2 As shown.

[0027] For the AM / AMPS / LSCa ternary polymer, as shown in the figure, the stretching vibration peak of the NH bond in the -CONH- group is located at 3430 cm⁻¹. -1 The stretching vibration peaks of the CH bonds in the -CH3 and -CH2- groups are located at 2950 cm⁻¹, respectively. -1 and 2830cm -1 Location; at 1625cm -1 An absorption peak for the C=O bond appears at 1577 cm⁻¹; the stretching vibration peak of the benzene ring skeleton is at 1577 cm⁻¹. -1 1463cm -1 The stretching vibration peak of the S=O bond in the -SO3H group is located at 1105 cm⁻¹ and its vicinity. -1 Location; at 777cm-1 At this point, an out-of-plane bending vibration peak of the CH bond on the aromatic ring appears; the stretching vibration peak of the CS bond is located at 617 cm⁻¹. -1 Place.

[0028] For the AM / AMPS binary polymer, as shown in the figure, the stretching vibration peak of the NH bond in the -CONH- group is located at 3438 cm⁻¹. -1 The stretching vibration peaks of the CH bonds in the -CH3 and -CH2- groups are located at 2946 cm⁻¹, respectively. -1 and 2829cm -1 Location; at 1614cm -1 An absorption peak for the C=O bond appeared at 1106 cm⁻¹; at 1106 cm⁻¹... -1 At 617 cm⁻¹, a stretching vibration peak appeared in the S=O bond of the -SO₃H group; at 617 cm⁻¹... -1 At that point, the peak corresponds to the stretching vibration of the CS bond.

[0029] Example 5: Nuclear Magnetic Resonance Characterization of Polymers The 1H NMR spectra of the AM / AMPS / LSCa ternary polymer synthesized in Example 1 and the AM / AMPS binary polymer synthesized in Example 2 are shown below. Figure 3 As shown.

[0030] For the AM / AMPS / LSCa ternary polymer, as shown in the figure, the -CH group in the benzene ring of LSCa... - The absorption peak of H on -SO3-O- is located at δ=6.7~6.88ppm(1); the absorption peak of H on CH3-O- in LSCa is located at δ=3.58~3.52ppm(2); the absorption peak of H on -CH2- connected to -SO3H is located at δ=3.34ppm(3); the absorption peak of H on -SO3-O- in LSCa is located at δ=3.58~3.52ppm(2); the absorption peak of H on -CH2- connected to -SO3H is located at δ=3.34ppm(3); - Connected -CH2 - The absorption peak of H on the main chain is located at δ=3.09ppm(4); the absorption peak of -CH- on the main chain is located at δ=2.24~2.11ppm(5); the absorption peak of H on -CH2- connected to alkyl carbons in the main chain and side chains is located at δ=1.66~1.38ppm(6).

[0031] For the AM / AMPS binary polymer, as shown in the figure, the absorption peak of H on -CH2- connected to -SO3H is located at δ=3.33ppm(1); the absorption peak of -CH- on the main chain is located at δ=2.26~2.11ppm(2); and the absorption peak of H on -CH2- connected to alkyl carbon in the main chain and side chain is located at δ=1.67~1.39ppm(3).

[0032] Example 6: Gel permeation chromatography test of polymers The molecular weights of the AM / AMPS / LSCa ternary polymer synthesized in Example 1 and the AM / AMPS binary polymer synthesized in Example 2 were determined using a Shimadzu Rid-20A gel permeation chromatography (GPC) instrument. Pure water was used as the solvent, and the flow rate of the mobile phase was 1 mL / min. The results of the GPC test are shown in Table 1.

[0033] Table 1. Molecular weight test data for AM / AMPS / LSCa The number-average molecular weight (Mn) of the AM / AMPS / LSCa ternary polymer is 24,719, and the weight-average molecular weight (Mw) is 56,182. The Mw of the AM / AMPS binary polymer is 47,218, and the Mn is 21,437. The higher weight-average molecular weight indicates the presence of some high-molecular-weight polymer chains, which may form a more complex network structure. The molecular weight distribution (PDI) of AM / AMPS / LSCa is 2.27283, which is greater than that of AM / AMPS (2.20264), indicating that AM / AMPS / LSCa has a wider molecular weight distribution range.

[0034] Example 7: Scanning electron microscopy test of polymer The AM / AMPS / LSCa ternary polymer synthesized in Example 1 was dissolved in pure water and simulated water to prepare a 1500 ppm solution. After freeze-drying, a solid sample was obtained. The microstructure of the sample was observed using a Phenmo Pro X scanning electron microscope, and the scanning electron microscope image is shown in Figure 4.

[0035] In pure water, the polymer exhibits a network structure formed by interwoven filaments, with a smooth and uniformly distributed surface. In simulated water, the polymer surface shows rough and densely packed small particles. This is due to the electrostatic interaction between salt ions and -SO3- on the polymer chains, causing the salt ions to adsorb onto the polymer chains. Since the adsorption of salt ions on the polymer surface shields the charge and compresses its electric double layer, the polymer molecular chains curl up, but still maintain a relatively complex network structure, indicating that it has a certain degree of salt resistance.

[0036] Example 8: Investigation of polymer interfacial activity In Examples 1 and 2, stock solutions with a concentration of 5000 ppm were prepared using simulated formation water with a salinity of 11734.64 ppm. These stock solutions were then diluted to different concentrations. The interfacial tension of the polymer solution on the oil droplets was measured using an SDT interfacial tension instrument. The results are as follows: Figure 5 As shown.

[0037] Example 9: Investigation of polymer biodegradability The five-day biochemical oxygen demand (BOD5) of the polymer was determined using an AER-208 microbial degradation respiration analyzer. The specific steps are as follows: AM / AMPS / LSCa and AM / AMPS stock solution were diluted to 100 ppm. The diluted polymer solution was transferred to the test bottle of the microbial degradation respiration apparatus. A certain amount of bacterial wastewater was added. The polymer solution prepared with simulated formation water was used as a blank control group. A small amount of KOH solution was added to each test tube to absorb the CO2 generated during the degradation process. After tightening the cap, the water bath temperature was adjusted to 54°C, and oxygen was continuously introduced into the bottle. The pressure change in the test bottle was monitored and recorded in real time. The experiment ended after five days.

[0038] The chemical oxygen demand (COD) of the polymer solution was determined using the method specified in the national environmental protection standard HJ 828-2017. The specific experimental steps are as follows: AM / AMPS / LSCa and AM / AMPS mother liquor were diluted to 100 ppm, and a certain amount of bacterial wastewater was added. A polymer solution prepared to simulate formation water was used as a blank control group. A certain amount of HgSO4 and zeolite were added sequentially, followed by an excess of K2Cr2O7 solution. After thorough mixing, the mixture was connected to a reflux device, and a constant-temperature magnetic stirrer was started. Ag2SO4-H2SO4 catalyst solution was slowly added from the top of the condenser. The reaction was maintained under reflux for 2 hours, and then heating was stopped. After the reaction system cooled to room temperature, 2-3 drops of ferriin indicator were added to the resulting solution. Quantitative analysis was performed using (NH4)2Fe(SO4)2 standard titrant. The titration endpoint was determined when the solution turned reddish-brown. The COD value was calculated based on the amount of potassium dichromate solution consumed.

[0039] Biodegradability refers to the ratio of BOD5 to COD of a polymer. The higher the ratio, the easier the polymer is to degrade, and the better its biodegradability. The BOD5 / COD data are shown in Table 2.

[0040] Table 2. BOD5 / COD values ​​of polymers under different water quality conditions Example 10: Investigation of Oil Displacement Performance The prepared ternary polymer was mixed with simulated formation water to form a solution with a concentration of 1500 ppm. The total salinity of the simulated formation water was 11734.64 ppm. The solution was then tested at a temperature of 54℃ and a rotation speed of 7.34 s. -1At the simulated reservoir temperature of 54℃ and an apparent viscosity of 31.15 mPa·s, the simulated oil viscosity was 523.7 mPa·s. Crude oil was injected into the core at a rate of 0.5 mL / min until the oil saturation reached approximately 75%. Simulated formation water was then injected at a rate of 1 mL / min until the water cut reached 98%. Polymer flooding was then performed at a flow rate of 0.5 mL / min, injecting 0.6 PV of polymer. Subsequent water flooding was then performed at a rate of 0.5 mL / min until the water cut reached 98%. This polymer-simulated enhanced oil recovery (polymer flooding + subsequent water flooding) achieved an improvement of over 15.33%. The oil displacement effect is shown in the figure below. Figure 6 As shown.

Claims

1. An active oil displacement polymer having interfacial activity and biodegradability, characterized in that The oil displacement polymer is copolymerized by acrylamide (AM), 2-acrylamide-2-methylpropanesulfonic acid (AMPS) and calcium lignosulfonate (LSCa); The active oil displacement polymer has interfacial activity and biodegradability, and has the following chemical structural formula: The active oil displacement polymer has interfacial activity and biodegradability, and has the following synthesis method: a water solution free radical copolymerization method is used to synthesize the target drug agent molecule; acrylamide and 2-acrylamide-2-methylpropanesulfonic acid are weighed and placed in a beaker, dissolved in water, and fully stirred to obtain solution A; The LSCa is added into the solution A, stirred until completely dissolved, and the pH is adjusted to 7 to obtain solution B; The solution B is transferred into a three-necked flask, placed in a constant temperature water bath, and nitrogen is introduced, and then the temperature is increased to a preset temperature; after reaching the predetermined temperature, the initiator is slowly added, and the reaction is carried out under sealed conditions at constant temperature to generate a brown viscous liquid; after drying, the brown viscous liquid is crushed to obtain the active oil displacement polymer.

2. The surfactant and biodegradable active oil displacement polymer according to claim 1, characterized in that The mass ratio of acrylamide to 2-acrylamide-2-methylpropanesulfonic acid is 1:0.176-0.385, and the total mass fraction of the monomers is about 65-74%.

3. The surfactant and biodegradable active oil displacement polymer according to claim 1, characterized in that The addition amount of the functional monomer (calcium lignosulfonate) accounts for 6-8% of the polymer system.

4. The surfactant and biodegradable active oil displacement polymer according to claim 1, characterized in that The solution for adjusting the pH is a 30wt% sodium hydroxide solution, and the pH of the mixture system is adjusted to 7.

5. The surfactant and biodegradable active oil displacement polymer according to claim 1, characterized in that Nitrogen is introduced for 30 minutes to ensure an oxygen-free environment.

6. The surfactant and biodegradable active oil displacement polymer according to claim 1, characterized in that The initiator is azobisdimethylaminoformamidine hydrochloride, and the addition amount of azobisdimethylaminoformamidine hydrochloride accounts for 0.4-0.6% of the polymer system.

7. The surfactant and biodegradable active oil displacement polymer according to claim 1, characterized in that After the reaction under sealed conditions at constant temperature of 58-62℃ for 5 hours, a brown viscous liquid is generated; the reaction product is repeatedly washed with anhydrous ethanol and sheared to remove unreacted monomers.

8. The surfactant and biodegradable active oil displacement polymer of claim 1, wherein The prepared ternary polymer was prepared into a solution with a concentration of 1500 ppm with simulated formation water, the total salinity of the simulated formation water was 11734.64 ppm, the apparent viscosity was 31.15 mPa·s at a temperature of 54 ℃ and a rotation speed of 7.34 s -1 The simulated reservoir temperature was 54 ℃, the simulated oil viscosity was 523.7 mPa·s, the crude oil was injected into the core at a rate of 0.5 mL / min until the oil saturation was about 75%; then the simulated formation water was injected at a rate of 1 mL / min until the water content reached 98%; then the polymer flooding was carried out at a flow rate of 0.5 mL / min, and 0.6 PV of the polymer was injected; then the subsequent water flooding was carried out at a flow rate of 0.5 mL / min until the water content reached 98%, and the simulated enhanced oil recovery (polymer flooding + subsequent water flooding) of the crude oil could reach 15.33% or more.

Images