A ternary compound flooding system based on nanofluid and polymer synergistic effect

Abstract

This invention discloses a ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers, belonging to the field of petroleum extraction technology. It includes a pretreatment unit, a nanofluid supply unit, a temperature- and salt-resistant polymer supply unit, a composite mixing unit, an online synergistic injection unit, and a formation synergistic displacement unit. The outlet of the pretreatment unit is connected to the composite mixing unit, and the nanofluid supply unit and the temperature- and salt-resistant polymer supply unit are connected in parallel to the composite mixing unit. Through the synergistic effect of nanofluids and temperature- and salt-resistant polymers, multiple synergistic effects of "dispersion stabilization, viscosity enhancement, seepage control, and residual oil stripping" are achieved. The modified nanoparticles and temperature- and salt-resistant polymer molecules form hydrogen bonds and electrostatic adsorption complexes, which not only significantly improve the solubility and viscosity stability of the polymer in high-temperature, high-salinity formation water environments but also prevent polymer molecular chain degradation.

Description

Technical Field

[0001] This invention belongs to the field of petroleum extraction technology, specifically relating to a ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers. Background Technology

[0002] With the continuous exploitation of oil resources, conventional crude oil extraction technologies (primary and secondary oil recovery) are no longer sufficient to meet the needs of industrial production. A large amount of residual oil remains in the reservoir strata. Therefore, tertiary oil recovery technology has become a key technical means to improve crude oil recovery rate and ensure oil and gas production. As one of the core technologies of tertiary oil recovery, composite oil displacement technology improves the reservoir seepage environment, reduces oil-water interfacial tension, and controls the mobility ratio through the synergistic effect of multiple oil displacement agents, thereby achieving efficient stripping and displacement of residual oil.

[0003] Currently, the most widely used composite flooding systems in industry mainly include polymer flooding and ternary composite flooding (alkali-surfactant-polymer). Among them, polymer flooding forms a high-viscosity system through the entanglement of polymer molecular chains to achieve flow control. However, under high temperature and high salinity reservoir conditions, polymer molecules are prone to thermal degradation and salt-sensitive degradation, resulting in a sharp drop in viscosity and a significant reduction in the flooding effect. Although traditional ternary composite flooding can improve the flooding efficiency through the synergistic effect of alkali, surfactant and polymer, the addition of strong alkali can easily cause the dispersion and migration of formation clay, resulting in a decrease in formation permeability. At the same time, it will also cause scaling in the reservoir and well bottom, increasing the difficulty of on-site construction and production costs. In addition, there are serious problems with surfactant adsorption and retention and poor stability of the flooding system. Summary of the Invention

[0004] The purpose of this invention is to provide a ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers, in order to solve the problem that under high temperature and high salinity reservoir conditions, polymer molecules are prone to thermal degradation and salt-sensitive degradation, resulting in a sharp drop in viscosity and a significant reduction in oil displacement effect; although traditional ternary composite flooding can improve oil displacement efficiency through the synergistic effect of alkali, surfactants and polymers, the addition of strong alkali can easily cause the dispersion and migration of formation clay, leading to a decrease in formation permeability.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers, comprising a pretreatment unit, a nanofluid supply unit, a temperature-resistant and salt-resistant polymer supply unit, a composite mixing unit, an online synergistic injection unit, and a formation synergistic displacement unit. The outlet of the pretreatment unit is connected to the composite mixing unit, the nanofluid supply unit and the temperature-resistant and salt-resistant polymer supply unit are connected in parallel to the composite mixing unit, and the outlet of the composite mixing unit is connected to the formation synergistic displacement unit through the online enhancement injection unit. The modified nanoparticles output from the nanofluid supply unit form hydrogen bonds and electrostatic adsorption complexes with temperature-resistant and salt-resistant polymer molecules in the composite mixing unit. The complexes are used to improve the solubility and viscosity stability of the temperature-resistant and salt-resistant polymer in high-mineralization formation water environments. The modified nanoparticles adsorb onto the pore walls of rocks, achieving small-pore sealing and seepage guidance through adsorption bridging. The temperature-resistant and salt-resistant polymer molecular chains form a three-dimensional network structure within the pore channels, constructing a high-viscosity continuous phase and achieving flow control.

[0006] In a preferred embodiment, the nanofluid supply unit includes a nano-preparation tank, a first stirrer, an ultrasonic disperser, a constant temperature heating jacket, and a first metering pump. An ultrasonic disperser is installed inside the nano-preparation tank, and a constant temperature heating jacket is wrapped around the outer wall of the nano-preparation tank. The outlet of the first metering pump is connected to the composite mixing unit to continuously supply the composite mixing unit with a stable and dispersed modified nanofluid.

[0007] In a preferred embodiment, the nanofluid is a silica / graphene oxide composite nanofluid, with hydroxyl, carboxyl, or sulfonic acid hydrophilic modification groups grafted onto the surface of the nanoparticles, and the particle size is 30–150 nm with a mass fraction of 0.05%–0.5%.

[0008] In a preferred embodiment, the temperature-resistant and salt-resistant polymer supply unit includes a polymer curing tank, a low-speed shear stirrer, an anti-settling filter, and a second metering pump; The anti-settling filter is located in the lower middle part of the polymer maturation tank, and the second metering pump delivers the fully matured polymer mother liquor into the compound mixing unit in proportion.

[0009] In a preferred embodiment, the polymer is a temperature-resistant, salt-resistant, hydrophobic associative polyacrylamide with a molecular weight of 12 million to 25 million and a mass concentration of 0.08% to 0.3%, maintaining stable viscosity under conditions of 60 to 95°C and a mineralization of 5000 to 20000 mg / L.

[0010] In a preferred embodiment, the composite mixing unit includes a multi-stage static mixer, an online concentration sensor, an online viscosity sensor, and a flow regulating valve. The multi-stage static mixer is equipped with spiral baffles, and the online concentration sensor and online viscosity sensor provide real-time feedback and adjust the mixing ratio.

[0011] In a preferred embodiment, the formation synergistic displacement unit includes a low-permeability oil reservoir formation, rock pore channels, crude oil emulsion carrying channels, and residual oil stripping interfaces; In a preferred embodiment, the online enhancement injection unit includes an injection pump, a pressure sensor, a check valve, an injection pipeline, and a wellhead distributor. The injection pump outputs a pressure of 10–35 MPa, the check valve prevents formation fluid backflow, and the wellhead distributor evenly distributes the ternary composite system to each injection well.

[0012] In a preferred embodiment, the pretreatment unit includes a buffer tank, a booster pump, and a pretreatment injection line, wherein the buffer tank stores a low concentration of clay stabilizer and wetting modifier.

[0013] In a preferred embodiment, the online enhancement injection unit is further equipped with a frequency converter, the control terminal of which is electrically connected to the injection pump.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This ternary composite oil displacement system, based on the synergistic effect of nanofluids and polymers, achieves multiple synergistic effects of "dispersion stabilization, viscosity enhancement, flow regulation, and residual oil stripping" through the synergistic interaction of nanofluids and temperature- and salt-resistant polymers. The modified nanoparticles form hydrogen bonds and electrostatic adsorption complexes with the temperature- and salt-resistant polymer molecules, which not only significantly improves the solubility and viscosity stability of the polymer in high-temperature and high-saltification formation water environments and avoids polymer molecular chain degradation, but also blocks small-diameter pores through adsorption bridging, guiding the oil displacement system to flow into medium and large-diameter pores and expanding the oil displacement range.

[0015] This ternary composite oil displacement system, based on the synergistic effect of nanofluids and polymers, utilizes a three-dimensional network structure formed by polymer molecular chains to construct a high-viscosity continuous phase, effectively controlling the mobility ratio and reducing fingering in the oil displacement system. Meanwhile, the nanofluids reduce the oil-water interfacial tension, promoting the stripping of residual oil from the rock surface. The synergistic effect of the two significantly improves the oil displacement efficiency. Experimental verification shows that, compared with traditional polymer flooding, the oil displacement system of this invention can improve the oil recovery rate. Furthermore, the invention uses silica / graphene oxide composite nanofluids and temperature-resistant, salt-resistant, hydrophobic associating polyacrylamide, both of which possess excellent temperature and salt resistance properties.

[0016] This ternary composite oil displacement system, based on the synergistic effect of nanofluids and polymers, can effectively suppress the dispersion and migration of clay particles and protect reservoir permeability through a pretreatment unit. The nanofluids adsorb onto the pore walls of rocks to form a protective film, reducing the corrosion and damage of the oil displacement agent to the rocks, while sealing small-diameter pores to prevent formation sand production. The oil displacement system does not contain strong alkalis and will not cause formation scaling and clay expansion, effectively protecting the reservoir geological environment and extending the service life of the reservoir.

[0017] This ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers can further optimize the reservoir environment, inhibit clay migration, and improve rock wettability by using clay stabilizers and wetting modifiers in the pretreatment unit. This enables the oil displacement system to adapt to various complex reservoir environments such as high temperature, high salinity, and low permeability, thus broadening the application range of the oil displacement system. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers of the present invention. Detailed Implementation

[0019] The present invention will be further described below with reference to embodiments.

[0020] The following embodiments are used to illustrate the present invention, but should not be used to limit the scope of protection of the present invention. The conditions in the embodiments can be further adjusted according to specific conditions, and simple improvements to the method of the present invention under the premise of the concept of the present invention are all within the scope of protection claimed by the present invention.

[0021] Please see Figure 1 This invention provides a ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers, including a pretreatment unit, a nanofluid supply unit, a temperature-resistant and salt-resistant polymer supply unit, a composite mixing unit, an online synergistic injection unit, and a formation synergistic displacement unit; the outlet of the pretreatment unit is connected to the composite mixing unit, the nanofluid supply unit and the temperature-resistant and salt-resistant polymer supply unit are connected in parallel to the composite mixing unit, and the outlet of the composite mixing unit is connected to the formation synergistic displacement unit through the online synergistic injection unit; The modified nanoparticles output from the nanofluid supply unit form hydrogen bonds and electrostatic adsorption complexes with temperature-resistant and salt-resistant polymer molecules in the composite mixing unit. The complexes are used to improve the solubility and viscosity stability of the temperature-resistant and salt-resistant polymer in high-saltification formation water environments. The modified nanoparticles adsorb onto the pore walls of rocks, achieving small-pore sealing and seepage guidance through adsorption bridging. The temperature-resistant and salt-resistant polymer molecular chains form a three-dimensional network structure in the pore channels, constructing a high-viscosity continuous phase and achieving flow control.

[0022] The pretreatment unit includes a buffer solution tank, a booster pump, and a pretreatment injection pipeline. The buffer solution stores a low concentration of clay stabilizer and wetting modifier. The buffer solution tank is made of corrosion-resistant and high-temperature-resistant materials, and its volume is designed according to the scale of oil reservoir development and pretreatment requirements. The inner wall of the tank is coated with an anti-corrosion coating to prevent the buffer solution from corroding the tank. The booster pump is a variable frequency booster pump, which can flexibly adjust the output pressure according to the formation pressure requirements to ensure that the buffer solution can be stably injected into the compound mixing unit, while avoiding damage to the pipeline due to excessive pressure. The pretreatment injection pipeline is made of high-strength pressure-resistant pipeline with a smooth inner wall to reduce the flow resistance of the buffer solution. The pipeline is also equipped with an external insulation layer to prevent the temperature change of the buffer solution from affecting the pretreatment effect. The core function of the pretreatment unit is to pretreat the subsequently injected oil displacement system. Low-concentration clay stabilizers can effectively inhibit the dispersion and migration of formation clay particles, prevent clay particles from clogging rock pore channels, and protect reservoir permeability. Wetting modifiers can change the wettability of the rock surface, changing the rock surface from oil-wet to water-wet, reducing the adsorption of crude oil on the rock surface, laying the foundation for the displacement of the subsequent oil displacement system, while reducing the adsorption and retention of the oil displacement agent on the rock surface and improving the utilization rate of the oil displacement agent.

[0023] The nanofluid supply unit includes a nano-preparation tank, a first stirrer, an ultrasonic disperser, a constant-temperature heating jacket, and a first metering pump. The ultrasonic disperser is installed inside the nano-preparation tank, and the constant-temperature heating jacket surrounds the outer wall of the nano-preparation tank. The outlet of the first metering pump is connected to a composite mixing unit, used to continuously supply the composite mixing unit with stably dispersed modified nanofluid. The nano-preparation tank has a sealed structure, and the inner wall of the tank is equipped with a stirring paddle mounting base and an ultrasonic disperser mounting groove to ensure uniform stirring and dispersion. The first agitator is a low-speed shear agitator with adjustable stirring speed to avoid nanoparticle agglomeration caused by high-speed stirring. The agitator blade is made of corrosion-resistant material and fits tightly against the inner wall of the tank to ensure uniform mixing of materials inside the tank. The ultrasonic disperser uses a high-frequency ultrasonic generator with an ultrasonic frequency of 20-80kHz, which can effectively break up nanoparticle agglomerates and make nanoparticles uniformly dispersed in the base liquid, thereby improving the stability of the nanofluid. The constant temperature heating jacket uses electric heating, with a temperature adjustment range of 20-100℃. It can precisely control the temperature inside the tank according to the preparation requirements of the nanofluid, ensuring the dispersion effect and stability of the nanoparticles. The first metering pump is a high-precision metering pump with a metering accuracy error of no more than ±1%. It can precisely control the supply of nanofluid according to the needs of the composite mixing unit, realize the precise ratio of nanofluid and polymer, and ensure synergistic effect.

[0024] The nanofluid is a silica / graphene oxide composite nanofluid. Hydrophilic modification groups, including hydroxyl, carboxyl, or sulfonic acid groups, are grafted onto the surface of the nanoparticles. The particle size ranges from 30 to 150 nm, with a mass fraction of 0.05% to 0.5%. The silica / graphene oxide composite nanoparticles are prepared using the sol-gel method, combining the high stability of silica with the high specific surface area and high adsorption capacity of graphene. By grafting hydrophilic modification groups onto the surface, the hydrophilicity and dispersibility of the nanoparticles are significantly improved, preventing agglomeration in water and enhancing the interaction between the nanoparticles and polymer molecules. The particle size is controlled between 30-150 nm, ensuring sufficient specific surface area and surface activity while preventing excessively large particles from clogging rock pores, thus guaranteeing the injectability of the nanofluid. The mass fraction is controlled between 0.05%-0.5%, reducing the preparation cost of the nanofluid while maintaining synergistic effects and preventing abnormal viscosity of the oil displacement system due to excessively high nanoparticle concentration, which could affect injection performance. Experimental results show that the composite nanofluid exhibits good dispersion stability under conditions of 60-95℃ and a salinity of 5000-20000 mg / L, with no significant agglomeration observed after 72 hours.

[0025] The temperature-resistant and salt-resistant polymer supply unit includes a polymer maturation tank, a low-speed shear stirrer, an anti-settling filter, and a second metering pump. The anti-settling filter is located in the lower middle part of the polymer maturation tank. The second metering pump delivers the fully matured polymer mother liquor into the compounding unit in proportion. The polymer maturation tank adopts an insulated structure, with an anti-corrosion coating on the inner wall to prevent corrosion from the polymer mother liquor, and an insulation layer on the outer wall to ensure temperature stability during the maturation process. The low-speed shear stirrer operates at a speed of 50-150 r / min, ensuring thorough dissolution and maturation of the polymer while preventing polymer molecular chain breakage caused by high-speed shearing, which would affect the polymer's viscosity and oil displacement performance. The anti-settling filter uses a high-precision stainless steel mesh with a pore size of 100-200 mesh, effectively filtering undissolved particulate impurities in the polymer mother liquor and preventing polymer sedimentation, ensuring a uniform and stable polymer mother liquor entering the compound mixing unit. The second metering pump is identical in specifications to the first metering pump, ensuring precise and controllable proportions of the polymer mother liquor and nanofluid, achieving synergistic effects between the two.

[0026] The polymer is a temperature- and salt-resistant hydrophobic associative polyacrylamide with a molecular weight of 12 million to 25 million and a mass concentration of 0.08% to 0.3%. It maintains stable viscosity under conditions of 60–95℃ and a mineralization of 5000–20000 mg / L. This hydrophobic associative polyacrylamide, through molecular structure design, introduces hydrophobic groups into the polyacrylamide molecular chain, forming a hydrophobic association effect. This effectively improves the polymer's temperature and salt resistance, preventing molecular chain degradation under high temperature and high mineralization conditions, and ensuring the viscosity stability of the polymer system. The molecular weight is controlled between 12 million and 25 million to ensure sufficient entanglement of the polymer molecular chains, forming a stable three-dimensional network structure and achieving good flowability control. The mass concentration is controlled between 0.08% and 0.3%, which ensures the viscosity requirements of the polymer system while reducing the amount of polymer used and controlling production costs. Experimental verification shows that under conditions of 95℃ and a mineralization of 20000 mg / L, the polymer retains no less than 85% of its viscosity after 72 hours, exhibiting excellent temperature and salt resistance.

[0027] The composite mixing unit includes a multi-stage static mixer, an online concentration sensor, an online viscosity sensor, and a flow control valve. The multi-stage static mixer is equipped with helical baffles. The online concentration and viscosity sensors provide real-time feedback and adjust the mixing ratio. The multi-stage static mixer adopts a 2-4 stage series structure. Each stage of the mixer is equipped with helical baffles, which allow the nanofluid and polymer mother liquor to fully contact and mix during flow, achieving uniform compounding and avoiding weakened synergistic effects due to localized concentration unevenness. The online concentration sensor can detect the concentration of nanoparticles and polymers in the blended oil displacement system in real time, with a detection accuracy error of no more than ±0.01%. The online viscosity sensor can detect the viscosity of the oil displacement system in real time, with a detection range of 10-1000 mPa·s and a detection accuracy error of no more than ±5%. The flow regulating valve is linked with the online concentration and online viscosity sensors, and automatically adjusts the output flow of the nanofluid supply unit and the temperature-resistant and salt-resistant polymer supply unit based on the real-time detection data, ensuring that the concentration and viscosity of the blended oil displacement system meet the design requirements and maximizing the synergistic effect. The core function of the composite blending unit is to achieve precise and uniform blending of nanofluids and temperature-resistant and salt-resistant polymers, providing a stable oil displacement system for subsequent injection and displacement.

[0028] The formation-assisted displacement unit includes low-permeability oil reservoirs, rock pore channels, crude oil emulsion carrying channels, and residual oil stripping interfaces. Low-permeability oil reservoirs are the target of the oil displacement system, with porosity of 5%-15% and permeability of 1-50 mD, and are typical low-permeability oil reservoirs. Rock pore channels serve as flow channels for crude oil and the oil displacement system. Their pore size distribution is uneven, including small pores (less than 100 nm), medium pores (100 nm-1 μm), and large pores (greater than 1 μm). Modified nanoparticles can block small pore channels through adsorption bridging, guiding the oil displacement system to flow into medium and large pore channels, thereby increasing the sweep range of the oil displacement system. Crude oil emulsion carrying channels are formed by the emulsification of crude oil and the oil displacement system. The three-dimensional network structure formed by the temperature-resistant and salt-resistant polymer molecular chains can encapsulate the crude oil emulsion, achieving efficient crude oil carrying. The residual oil stripping interface is the contact interface between the oil displacement system and the residual oil on the rock surface. Nanofluids can reduce the interfacial tension between oil and water, promote the stripping of residual oil from the rock surface, and the high-viscosity continuous phase formed by polymers can drive the stripped residual oil to flow to the production well, thereby achieving efficient displacement of residual oil.

[0029] The online enhancement injection unit includes an injection pump, pressure sensor, check valve, injection pipeline, and wellhead distributor. The injection pump outputs pressure from 10 to 35 MPa. The check valve prevents backflow of formation fluids, and the wellhead distributor evenly distributes the ternary composite system to each injection well. The injection pump is a high-pressure plunger pump, which can flexibly adjust the output pressure according to formation pressure requirements to ensure that the oil displacement system can be smoothly injected into the reservoir formation. The output pressure is controlled between 10 and 35 MPa to adapt to the needs of reservoirs with different depths and permeabilities. The pressure sensor monitors the injection pressure in real time. When the pressure exceeds the set threshold, it automatically issues an alarm signal to prevent excessive pressure from causing formation rupture or pipeline damage. The check valve is a high-pressure check valve, installed at the end of the injection pipeline close to the formation. It can effectively prevent formation fluids (crude oil, formation water) from flowing back into the injection pipeline, avoiding contamination of the oil displacement system and damage to the injection equipment. The injection pipeline is made of high-strength pressure-resistant pipeline with a diameter designed according to the injection flow rate. The inner wall is smooth to reduce the flow resistance of the oil displacement system, and the pipeline is equipped with an external insulation layer to prevent temperature changes in the oil displacement system from affecting its performance. The wellhead distributor adopts a multi-channel distribution structure, which can evenly distribute the mixed oil displacement system to each injection well, ensuring that the injection volume of each injection well is consistent and achieving uniform displacement of the reservoir.

[0030] The online efficiency enhancement injection unit is also equipped with a frequency converter, whose control terminal is electrically connected to the injection pump. The frequency converter can automatically adjust the speed of the injection pump according to the injection pressure detected by the pressure sensor and the formation requirements, thereby adjusting the injection flow rate and injection pressure to achieve precise control of injection parameters. At the same time, the frequency converter has an energy-saving function, which can adjust the motor power according to the changes in injection load, reduce energy consumption, and reduce production costs. In addition, the frequency converter is equipped with overload protection and short circuit protection functions, which can effectively protect the injection pump equipment and extend its service life. Example 1 A ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers is suitable for low-permeability reservoirs with a temperature of 60℃ and a salinity of 5000 mg / L (permeability 10 mD, porosity 10%).

[0031] Pretreatment unit: Buffer storage tank with a volume of 10m³ 3 The internal storage contains 0.1% clay stabilizer (polyquaternary ammonium salt) and 0.05% wetting and modifying liquid (sodium dodecylbenzene sulfonate); the booster pump is a variable frequency booster pump with an output pressure adjustment range of 5-10 MPa; the pretreatment injection pipeline has a diameter of 100 mm and is equipped with an external insulation layer.

[0032] Nanofluid supply unit: The nano-preparation tank has a volume of 5m³. 3 The stirring speed of the first stirrer is 80 r / min, the ultrasonic frequency of the ultrasonic disperser is 40 kHz, and the temperature of the constant temperature heating jacket is controlled at 40℃; the metering accuracy of the first metering pump is ±0.5%; the nanofluid is a silica / graphene oxide composite nanofluid with hydroxyl groups grafted on the surface, a particle size of 30-80 nm, and a mass fraction of 0.05%.

[0033] Temperature- and salt-resistant polymer supply unit: Polymer curing tank with a volume of 8m³ 3 The low-speed shear mixer has a stirring speed of 100 r / min and an anti-settling filter screen with a mesh size of 150 mesh; the second metering pump has the same specifications as the first metering pump; the polymer is a temperature-resistant, salt-resistant, hydrophobic associative polyacrylamide with a molecular weight of 12 million and a mass concentration of 0.08%.

[0034] Composite mixing unit: adopts a 2-stage static mixer with internal spiral baffles; the online concentration sensor has a detection accuracy of ±0.01%, and the online viscosity sensor has a detection range of 10-500 mPa·s; the flow regulating valve is linked with the sensor to automatically adjust the mixing ratio.

[0035] Online enhancement injection unit: The injection pump output pressure is 10-20MPa, and the pressure sensor detection accuracy is ±0.1MPa; the check valve is a high-pressure check valve, and the injection pipe diameter is 80mm; the wellhead distributor is a 4-channel distribution structure; the frequency converter is electrically connected to the injection pump and can adjust the injection pump speed.

[0036] Formation synergistic displacement unit: The low-permeability oil reservoir formation has a porosity of 10% and a permeability of 10mD. The rock pore channel diameter distribution is 30nm-5μm. The crude oil emulsion carrying channel is formed by the oil displacement system and crude oil emulsification. The residual oil stripping interface achieves residual oil stripping through the synergistic effect of nanofluids and polymers.

[0037] In this embodiment, the operation of the oil displacement system is as follows: First, the buffer solution from the pretreatment unit is injected into the composite mixing unit via a booster pump to pretreatment the subsequent oil displacement system; simultaneously, in the nanofluid supply unit, the composite nanoparticles in the nano-preparation tank form a stable nanofluid under stirring and ultrasonic dispersion, which is then injected into the composite mixing unit at a set flow rate via a first metering pump; in the temperature-resistant and salt-resistant polymer supply unit, the polymer is fully cured and dissolved in the curing tank, filtered through an anti-settling filter, and then injected into the composite mixing unit at a set flow rate via a second metering pump; the nanofluid and polymer mother liquor are fully mixed in the multi-stage static mixer of the composite mixing unit, achieving an online concentration... Sensors and online viscosity sensors monitor the concentration and viscosity of the blended oil displacement system in real time. The supply of both is adjusted via flow control valves to ensure the system meets design requirements. The blended system, after being pressurized by the injection pump in the online enhancement injection unit, is uniformly injected into the reservoir formation through injection pipes and wellhead distributors. Check valves prevent backflow of formation fluids, and a frequency converter adjusts the injection pump parameters based on pressure sensor data. In the reservoir formation, modified nanoparticles and polymer molecules work synergistically to achieve small-aperture sealing, flow control, and residual oil stripping. The stripped residual oil is displaced to the production well through the crude oil emulsification carry-over channel, completing crude oil extraction. Experimental verification shows that this oil displacement system can increase crude oil recovery by more than 8%.

[0038] Example 2 A ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers is suitable for low-permeability reservoirs with a temperature of 95℃ and a salinity of 20000mg / L (permeability 5mD, porosity 8%).

[0039] Pretreatment unit: Buffer storage tank volume is 15m³ 3 The internal storage contains 0.2% clay stabilizer (polyoxypropylene trimethylammonium chloride) and 0.1% wetting and modifying liquid (fatty alcohol polyoxyethylene ether); the booster pump is a variable frequency booster pump with an output pressure adjustment range of 8-15MPa; the pretreatment injection pipeline has a diameter of 120mm and is equipped with an external insulation layer.

[0040] Nanofluid supply unit: The nano-preparation tank has a volume of 8m³. 3 The stirring speed of the first stirrer is 120 r / min, the ultrasonic frequency of the ultrasonic disperser is 60 kHz, and the temperature of the constant temperature heating jacket is controlled at 60 ℃; the metering accuracy of the first metering pump is ±0.5%; the nanofluid is a silica / graphene oxide composite nanofluid with sulfonic acid groups grafted on the surface, a particle size of 100-150 nm, and a mass fraction of 0.5%.

[0041] Temperature- and salt-resistant polymer supply unit: Polymer curing tank with a volume of 12m³ 3The low-speed shear mixer has a stirring speed of 150 r / min and an anti-settling filter screen with a mesh size of 200 mesh; the second metering pump has the same specifications as the first metering pump; the polymer is a temperature-resistant, salt-resistant, hydrophobic associative polyacrylamide with a molecular weight of 25 million and a mass concentration of 0.3%.

[0042] Composite mixing unit: adopts a 4-stage static mixer with internal spiral baffles; the online concentration sensor has a detection accuracy of ±0.01%, and the online viscosity sensor has a detection range of 200-1000 mPa·s; the flow regulating valve is linked with the sensor to automatically adjust the mixing ratio.

[0043] Online enhancement injection unit: The injection pump output pressure is 25-35MPa, and the pressure sensor detection accuracy is ±0.1MPa; the check valve is a high-pressure check valve, and the injection pipe diameter is 100mm; the wellhead distributor is a 6-channel distribution structure; the frequency converter is electrically connected to the injection pump and can adjust the injection pump speed.

[0044] Formation synergistic displacement unit: The low-permeability reservoir formation has a porosity of 8% and a permeability of 5mD. The rock pore channel diameter distribution is 50nm-3μm. The crude oil emulsion carrying channel is formed by the oil displacement system and crude oil emulsification. The residual oil stripping interface achieves residual oil stripping through the synergistic effect of nanofluids and polymers.

[0045] The working process of this embodiment is basically the same as that of Embodiment 1. Experimental verification shows that the oil displacement system of this embodiment achieves a polymer viscosity retention rate of 88% in high-temperature, high-salinity, and low-permeability oil reservoirs, good nanofluid dispersion stability, and an oil recovery rate increase of more than 15%, demonstrating excellent temperature and salt resistance and oil displacement effect.

[0046] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art can make various modifications and adjustments without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention is determined by the claims.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers, characterized in that, It includes a pretreatment unit, a nanofluid supply unit, a temperature- and salt-resistant polymer supply unit, a composite mixing unit, an online synergistic injection unit, and a formation synergistic displacement unit; The outlet of the pretreatment unit is connected to the composite mixing unit, the nanofluid supply unit and the temperature-resistant and salt-resistant polymer supply unit are connected in parallel to the composite mixing unit, and the outlet of the composite mixing unit is connected to the formation synergistic displacement unit through the online enhancement injection unit. The modified nanoparticles output from the nanofluid supply unit form hydrogen bonds and electrostatic adsorption complexes with temperature-resistant and salt-resistant polymer molecules in the composite mixing unit. The complexes are used to improve the solubility and viscosity stability of the temperature-resistant and salt-resistant polymer in high-mineralization formation water environments. The modified nanoparticles adsorb onto the pore walls of rocks, achieving small-pore sealing and seepage guidance through adsorption bridging. The temperature-resistant and salt-resistant polymer molecular chains form a three-dimensional network structure within the pore channels, constructing a high-viscosity continuous phase and achieving flow control.

2. The ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers according to claim 1, characterized in that: The nanofluid supply unit includes a nano-preparation tank, a first stirrer, an ultrasonic disperser, a constant temperature heating jacket, and a first metering pump. An ultrasonic disperser is installed inside the nano-preparation tank, and a constant temperature heating jacket is wrapped around the outer wall of the nano-preparation tank. The outlet of the first metering pump is connected to the composite mixing unit to continuously supply the composite mixing unit with a stable and dispersed modified nanofluid.

3. The ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers according to claim 2, characterized in that: The nanofluid is a silica / graphene oxide composite nanofluid, with hydroxyl, carboxyl or sulfonic acid hydrophilic modification groups grafted onto the surface of the nanoparticles. The particle size is 30-150 nm and the mass fraction is 0.05%-0.5%.

4. The ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers according to claim 1, characterized in that: The temperature-resistant and salt-resistant polymer supply unit includes a polymer curing tank, a low-speed shear stirrer, an anti-settling filter, and a second metering pump. The anti-settling filter is located in the lower middle part of the polymer maturation tank, and the second metering pump delivers the fully matured polymer mother liquor into the compound mixing unit in proportion.

5. A ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers according to claim 4, characterized in that: The polymer is a temperature-resistant, salt-resistant, hydrophobic associative polyacrylamide with a molecular weight of 12 million to 25 million and a mass concentration of 0.08% to 0.3%. It maintains stable viscosity under conditions of 60 to 95°C and a mineralization of 5000 to 20000 mg / L.

6. The ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers according to claim 1, characterized in that: The composite mixing unit includes a multi-stage static mixer, an online concentration sensor, an online viscosity sensor, and a flow regulating valve. The multi-stage static mixer is equipped with spiral baffles inside, and the online concentration sensor and online viscosity sensor provide real-time feedback and adjust the mixing ratio.

7. A ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers according to claim 6, characterized in that: The formation synergistic displacement unit includes low-permeability oil reservoir formations, rock pore channels, crude oil emulsion carrying channels, and residual oil stripping interfaces.

8. The ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers according to claim 1, characterized in that: The online enhancement injection unit includes an injection pump, a pressure sensor, a check valve, an injection pipeline, and a wellhead distributor. The injection pump outputs a pressure of 10–35 MPa, the check valve prevents formation fluid backflow, and the wellhead distributor evenly distributes the ternary composite system to each injection well.

9. A ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers according to claim 1, characterized in that: The pretreatment unit includes a buffer tank, a booster pump, and a pretreatment injection pipeline. The buffer tank stores a low concentration of clay stabilizer and wetting modifier.

10. A ternary composite oil displacement system based on the synergistic effect of nanofluids and polymers according to claim 1, characterized in that: The online efficiency enhancement injection unit is also equipped with a frequency converter, and the control terminal of the frequency converter is electrically connected to the injection pump.

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