Carbon capture and oil displacement integrated method and system based on synthesis and decomposition of carbon dioxide hydrate

Abstract

The invention relates to the cross technical field of combination of environmental protection and oilfield development, in particular to a carbon capture and oil displacement integrated method and system based on carbon dioxide hydrate synthesis and decomposition. Comprising the following steps: collecting industrial tail gas, pretreating, and introducing into a gas storage tank for storage; the method comprises the following steps: sequentially filling water and gas into multi-stage series hydrate reactors 1, 2 and 3 through a water tank and a gas storage tank, and inducing to generate carbon dioxide hydrate by adjusting the temperature and pressure of the reactors; detecting the carbon dioxide concentration of the residual gas generating the carbon dioxide hydrate, and discharging if the carbon dioxide concentration is less than 5%; and if the content of the decomposition liquid is larger than 5%, the decomposition liquid is injected back into the gas storage tank again, and the decomposition liquid containing the carbon dioxide nanobubbles in the injection pump is sequentially injected into the target oil reservoir for oil displacement. Through the integrated design, carbon capture and the oil displacement process are directly coupled, intermediate treatment and transportation of carbon dioxide are avoided, and energy consumption and operation cost are reduced.

Description

Technical Field

[0001] This invention relates to the interdisciplinary field of environmental protection and oilfield development, and in particular to an integrated method and system for carbon capture and oil displacement based on the synthesis and decomposition of carbon dioxide hydrates. Background Technology

[0002] Carbon dioxide enhanced oil recovery (CEC) is a technology that collects carbon dioxide emitted from industrial sources and injects it into exploited oil reservoirs, thereby enhancing oil recovery and simultaneously sequestering carbon dioxide underground. Essentially, it is an enhanced oil recovery technology that also incorporates carbon capture, utilization, and storage (CES). However, this technology faces challenges in two areas: first, the cost of capturing and storing industrial-source carbon dioxide is high, lacking economic incentive; second, existing enhanced oil recovery technologies suffer from high energy consumption in generating micro-nano bubbles, high costs of purchased gases (such as commercial CO2), and significant risks of gas channeling.

[0003] There are currently two main carbon dioxide flooding schemes: (1) Carbon capture and storage (CCS): The captured CO2 is compressed and transported to a specific location for geological storage. This scheme lacks direct economic benefits, and the high cost of capture, transportation and storage restricts its large-scale application. (2) CO2 flooding (CO2-EOR): Commercial CO2 is usually required, which is costly. Moreover, the injected CO2 is a free gas phase, which is prone to gas channeling in heterogeneous reservoirs, resulting in low sweep efficiency. In addition, some CO2 will be discharged with the associated gas produced, which may cause additional carbon emissions and exacerbate the greenhouse effect. If micro-nano bubble flooding is used, the energy consumption of prefabricating micro-nano bubbles on the ground is high.

[0004] Conventional methods for generating micro- and nano-bubbles include: (1) Mechanical generation method: such as high-speed shearing method, jet cavitation method, etc. These methods require the establishment of high-pressure and high-speed circulation systems on the ground, which consumes a lot of energy. The generated bubble spectrum is wide and contains a large number of large bubbles that are visible to the naked eye. These large bubbles have poor stability when moving in porous media and are easy to aggregate, which affects the oil displacement effect. (2) Chemical precipitation method: by adding chemical agents to the system, a chemical reaction occurs to release gas. This method depends on and consumes chemical agents, which increases the cost and operational complexity. At the same time, the introduced chemical substances may change the wettability of the reservoir, cause pore blockage, or lead to subsequent environmental pollution. (3) Pressure dissolved gas release method: the gas is dissolved in water under high pressure and injected into the reservoir. The gas is released by depressurization. This method has strict requirements for pressure control. The gas release process is difficult to control precisely and is prone to forming unstable gas flow channels (gas channeling) instead of uniform micro- and nano-bubbles, resulting in low sweep efficiency.

[0005] It is evident that existing solutions treat "carbon capture" and "oil displacement" as two separate chains, resulting in the need for transportation, compression, and storage of captured carbon dioxide, which increases overall costs and energy consumption. At the same time, the carbon dioxide used in oil displacement often needs to be purchased externally, lacking direct coupling with carbon capture, resulting in low resource utilization efficiency and failing to achieve synergistic optimization of energy, materials, and economic benefits. Therefore, an integrated solution that can deeply integrate the two is needed to reduce costs and improve overall efficiency. Summary of the Invention

[0006] This invention provides an integrated method and system for carbon capture and oil displacement based on the synthesis and decomposition of carbon dioxide hydrates. The purpose is to combine carbon dioxide capture and oil displacement processes in an integrated manner, achieve efficient carbon capture by synthesizing carbon dioxide hydrates, and drive oil through micro-nano bubbles generated by hydrate decomposition, thereby reducing energy consumption, reducing equipment investment, and improving crude oil recovery.

[0007] To achieve the above objectives, this invention provides an integrated method for carbon capture and oil displacement based on carbon dioxide hydrate synthesis and decomposition, comprising the following steps:

[0008] S1. Collect industrial exhaust gas, pre-treat it, and then store it in a gas storage tank.

[0009] S2. Water and gas are successively supplied to the multi-stage series hydrate reactor 1 through water tank and gas storage tank. Carbon dioxide hydrate is induced to be generated by adjusting the temperature and pressure of the multi-stage series hydrate reactor 1.

[0010] S3. The residual gas from the carbon dioxide hydrate generated in the multi-stage series hydrate reactor 1 is introduced into reactor 2. By adjusting the temperature and pressure of the multi-stage series hydrate reactor 2, it continues to react with water to induce the generation of carbon dioxide hydrate. At this time, the hydrate in the multi-stage series hydrate reactor 1 decomposes due to the decrease in gas pressure, producing a decomposition liquid containing carbon dioxide nanobubbles. The diameter of the carbon dioxide micro-nanobubbles is 50-200nm, which is transported to the injection pump through a pipeline.

[0011] S4. The residual gas from the generation of carbon dioxide hydrate in the multi-stage series hydrate reactor 2 is discharged into the multi-stage series hydrate reactor 3. At this time, the hydrate in the multi-stage series hydrate reactor 2 decomposes due to the decrease in gas pressure, generating a decomposition liquid containing carbon dioxide nanobubbles, which is transported to the injection pump through the pipeline. The temperature and pressure of the multi-stage series hydrate reactor 3 are adjusted to induce the generation of carbon dioxide hydrate.

[0012] S5. Detect the carbon dioxide concentration of the residual gas generated by carbon dioxide hydrate. If it is <5%, return it to the factory for treatment and discharge in compliance with standards. If it is >5%, reinject it back into the storage tank. After the residual gas generated by the multi-stage series hydrate reactor 3 is discharged, the decomposition liquid containing carbon dioxide nanobubbles generated by the depressurization decomposition of hydrate is transported to the injection pump through the pipeline.

[0013] S6. The decomposition liquid containing carbon dioxide nanobubbles in the injection pump is sequentially injected into the target oil reservoir for oil displacement.

[0014] The core of this invention lies in using carbon dioxide hydrate as a key intermediate carrier connecting the carbon capture and oil displacement processes. This integrated design, through the synthesis and decomposition process of hydrate, achieves a transformation in material form, transport method, and mechanism of action. Its necessity is reflected in:

[0015] ① Fixed form and stable transportation: Converting gaseous CO2 into solid hydrates achieves CO2 immobilization, which greatly facilitates safe, stable and high-density transportation from the collection point to the injection point, avoiding the high risks and high costs of high-pressure gas pipeline transportation.

[0016] ② In-situ generation of micro / nanobubbles: Hydrates are controlled to decompose through heating or depressurization, generating uniformly distributed, size-stable micro / nanobubbles. This method requires less energy and produces more stable bubbles compared to ground-based mechanical production methods or pressure dissolution and release methods.

[0017] ③ Process coupling and energy integration: The hydrate generation can utilize industrial exhaust gas generated by the plant, and the decomposition process can also utilize the geothermal temperature or waste heat of the oil field. This achieves the cascade utilization of energy and greatly reduces the energy consumption of the entire process, which is something that discrete technology cannot achieve.

[0018] Preferably, the industrial exhaust gas in S1 contains one or more of C1-C5 hydrocarbons, hydrogen sulfide, moisture, and fine particles;

[0019] The pretreatment described in S1 is dust removal and filtration to remove impurities such as dust and droplets that may interfere with hydrate synthesis. The purified exhaust gas is then introduced into the hydrate reactor, where temperature and pressure conditions are controlled.

[0020] The solution of this invention can be adapted to better suit the waste gas by adjusting the size of carbon dioxide gas micro-nano bubbles.

[0021] Preferably, the multi-stage series hydrate reactor 1, multi-stage series hydrate reactor 2 and multi-stage series hydrate reactor 3 in S1 are connected in series sequentially, and the industrial exhaust gas passes through each stage of the reactor in sequence. The carbon dioxide gas in the industrial exhaust gas that has not reacted with water enters the next stage from the previous stage to continue the reaction.

[0022] Preferably, in the multi-stage series hydrate reactor 1 described in S3, 4, and 5, the temperature at which carbon dioxide hydrate is generated is 4-6°C and the pressure is 8-10 MPa; in the multi-stage series hydrate reactor 2, the temperature at which carbon dioxide hydrate is generated is 2-4°C and the pressure is 6-8 MPa; and in the multi-stage series hydrate reactor 3, the temperature at which carbon dioxide hydrate is generated is 0-2°C and the pressure is 4-6 MPa, with each stage having a reaction time of 1-2 hours. Furthermore, a promoter is added to the multi-stage series hydrate reactor 1, multi-stage series hydrate reactor 2, and multi-stage series hydrate reactor 3, and the promoter contains at least one of tetrahydrofuran, cyclopentane, or sodium dodecyl sulfate.

[0023] Because carbon dioxide has high solubility in water and the conditions for carbon dioxide hydrate formation are relatively mild, carbon dioxide in waste gas preferentially combines with water to form hydrates. To achieve deep carbon capture, this invention employs a multi-stage series hydrate reactor with progressively decreasing reaction conditions. Higher initial conditions are suitable for treating gases with high carbon dioxide concentrations from industrial sources or at the beginning of the cycle, while lower final conditions are thermodynamically more favorable for continued carbon dioxide extraction. Although the circulating tail gas undergoes multiple reactions, it still contains a certain concentration of carbon dioxide (5-15%). If the carbon dioxide concentration monitoring device shows a concentration higher than 5%, it is recovered and mixed with a storage tank to increase the average carbon dioxide concentration in the mixed gas before continuing the reaction. If the concentration is lower than 5%, deep carbon capture is considered complete, and the remaining tail gas is treated at the factory to meet emission standards. Through multi-stage stepped reactions, waste gas with progressively decreasing carbon dioxide concentrations can be efficiently treated, ultimately reducing the carbon dioxide concentration in the outlet gas to below 5%, exceeding the efficiency of a single-stage reactor.

[0024] Preferably, the substances described in S3, 4, and 5 decompose due to the decrease in gas pressure. During decomposition, the temperature is increased at a rate of 0.2-0.6℃ / min and the pressure is at atmospheric pressure, generating carbon dioxide gas micro-nano bubbles with a diameter of 60-100 nm.

[0025] When decomposition occurs, no heating is required; the pressure is reduced to atmospheric pressure, generating carbon dioxide micro-nano bubbles with a diameter of 80-120 nm.

[0026] For high-viscosity crude oil (> 50 mPa·s), it is preferable to generate 80-120 nm bubbles to enhance permeability and emulsification. For waste gas containing light hydrocarbons, by adjusting the hydrate synthesis pressure (increasing it to 8-12 MPa) and adding tetrahydrofuran promoter, 60-100 nm bubbles can be generated to improve the dispersibility of bubbles in the oil phase. For waste gas containing solid impurities, the system has a pre-dust removal and filtration unit to ensure the purity of hydrates and avoid affecting the concentration and size of nanobubbles.

[0027] Preferably, after the gas is re-injected into the storage tank as described in S5, a new cycle is started;

[0028] As the system enters different cycle stages, the carbon dioxide concentration gradually decreases. To maintain optimal reaction efficiency, a step-by-step control strategy is adopted. During the first three initial cycle stages, each stage of the system operates under baseline conditions. During the fourth and fifth intermediate cycle stages, due to a slight decrease in carbon dioxide concentration, the reaction pressure is increased by 0.5-1 MPa, and the promoter concentration is increased by 50%-100%. After the fifth cycle, fine adjustments are made based on the real-time monitored carbon dioxide concentration.

[0029] Preferably, in step S6, the injection pressure into the target reservoir is 5-20 MPa, and the injection rate is 0.1-1.0 m / s. 3 / min.

[0030] Under the same technical concept, the present invention also provides an integrated carbon capture and oil displacement system based on carbon dioxide hydrate synthesis and decomposition, the integrated system comprising a recovery device, a multi-stage hydrate reactor, a hydrate reaction device, an injection device and a production device.

[0031] The hydrate reaction device includes a gas storage tank, a water tank, and a hydrate reaction vessel. The gas storage tank and the water tank are respectively connected to the hydrate reaction vessel, and the recovery device is connected to the gas storage tank.

[0032] The injection device includes a delivery pipeline and an injection pump. One end of the delivery pipeline is connected to a multi-stage hydrate reactor, and the other end is connected to the oil reservoir. The injection pump is located at the inlet of the delivery pipeline.

[0033] The multi-stage hydrate reactor comprises a multi-stage series hydrate reactor 1, a multi-stage series hydrate reactor 2, and a multi-stage series hydrate reactor 3. Each of the multi-stage series hydrate reactors 1, 2, and 3 is connected at one end to a conveying pipeline and at the other end to a tail gas recovery device, and the multi-stage series hydrate reactors 1, 2, and 3 are connected in sequence. The pressure and cooling rate of each series hydrate reactor can be independently adjusted.

[0034] The exhaust gas recovery device includes a gas collection and buffer tank, a recirculating gas compressor, a dust collector, and a filter.

[0035] Preferably, the production device includes a production pump, a three-phase separator, and a crude oil downstream processing system connected in sequence.

[0036] The above-described solution of the present invention has the following beneficial effects:

[0037] (1) High efficiency in resource utilization: Through integrated design, carbon capture and oil recovery processes are directly coupled, avoiding intermediate processing and transportation of carbon dioxide, and reducing energy consumption and operating costs.

[0038] (2) Significantly reduced cost: Traditional carbon capture methods (such as amine absorption) have a high cost per ton of carbon dioxide capture, while this method can effectively control costs by using hydrate synthesis; at the same time, the use of self-produced micro-nano bubbles in the oil displacement stage reduces the cost of purchasing external gas sources.

[0039] (3) Environmentally friendly: This method realizes the resource utilization of carbon dioxide, reduces greenhouse gas emissions, and improves crude oil recovery rate through micro-nano bubble oil displacement (expected to increase recovery rate by 5-15%), thus achieving the dual benefits of carbon emission reduction and energy production increase.

[0040] (4) Strong technical adaptability: The method can be applied to various reservoir conditions, and the conditions for hydrate synthesis and decomposition are easy to control. The equipment investment is low and it is easy to promote industrialization. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the structure of an integrated carbon capture and oil displacement system based on carbon dioxide hydrate synthesis and decomposition according to the present invention.

[0042] Figure 2 The particle size distribution of carbon dioxide gas micro-nano bubbles generated by different methods; Detailed Implementation

[0043] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0044] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0045] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a locking connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0046] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0047] Example 1:

[0048] The industrial exhaust gas processed in this embodiment is a simulated oil reservoir model: a sand-filled pipe (30 cm in length and 2.5 cm in diameter) filled with standard quartz sand (300 mesh) and saturated simulated crude oil (viscosity 50 mPa·s).

[0049] This embodiment provides an integrated method for carbon capture and oil displacement based on carbon dioxide hydrate synthesis and decomposition, which includes the following steps:

[0050] S1. Carbon dioxide hydrate synthesis (carbon capture stage):

[0051] The exhaust gas from industrial emissions, containing C1-C5 hydrocarbons, hydrogen sulfide, moisture, and fine particles, undergoes pretreatment such as dust removal and filtration. The exhaust gas first passes through a cyclone separator to remove large particles, and a precision filter with an accuracy of 0.5 μm is installed at the outlet to intercept entrained trace solid impurities. The dust-removed gas is then introduced into a hydrate reactor, where it reacts with water under specific conditions to generate carbon dioxide hydrate.

[0052] S2. To improve carbon capture efficiency and system economy, this invention further proposes a gradient recovery process based on a multi-stage reactor, the specific implementation of which is as follows:

[0053] Three multi-stage hydrate reactors, namely multi-stage hydrate reactor 1, multi-stage hydrate reactor 2, and multi-stage hydrate reactor 3, are set in series, with different temperature and pressure gradients for each stage of the reactor:

[0054] Level 1: Temperature 5°C, Pressure 9 MPa;

[0055] Level 2: Temperature 3°C, Pressure 6 MPa;

[0056] Level 3: Temperature 0°C, Pressure 4 MPa.

[0057] Water and gas were successively supplied to the multi-stage series hydrate reactor 1 through water tanks and gas storage tanks. Carbon dioxide hydrate was induced to be generated by adjusting the temperature and pressure of reactor 1.

[0058] The residual gas from the generation of carbon dioxide hydrate in reactor 1 is introduced into a multi-stage series hydrate reactor 2. By adjusting the temperature and pressure of the multi-stage series hydrate reactor 2, the gas continues to react with water to induce the generation of carbon dioxide hydrate. At this time, the hydrate in the multi-stage series hydrate reactor 1 decomposes due to the decrease in gas pressure, producing a decomposition liquid containing carbon dioxide nanobubbles. The diameter of the carbon dioxide micro-nanobubbles is 50-200 nm, which is transported to the injection pump through a pipeline.

[0059] The residual gas from the generation of carbon dioxide hydrate in the multi-stage series hydrate reactor 2 is discharged into the multi-stage series hydrate reactor 3. At this time, the hydrate in the multi-stage series hydrate reactor 2 decomposes due to the decrease in gas pressure, generating a decomposition liquid containing carbon dioxide nanobubbles, which is transported to the injection pump through the pipeline. The temperature and pressure of the multi-stage series hydrate reactor 3 are adjusted to induce the generation of carbon dioxide hydrate.

[0060] The concentration of carbon dioxide in the residual gas generated by carbon dioxide hydrate is detected. If it is less than 5%, it is returned to the factory for treatment and then discharged in compliance with standards. If it is greater than 5%, it is reinjected into the gas storage tank. After the residual gas generated by carbon dioxide hydrate in reactor 3 is discharged, the decomposition liquid containing carbon dioxide nanobubbles generated by the depressurization decomposition of hydrate is transported to the injection pump through the pipeline.

[0061] In the above process, the hydrate decomposes due to the decrease in gas pressure: the synthesized carbon dioxide hydrate is decomposed in a controlled manner by depressurization or heating. The saturated simulated crude oil viscosity is 50 mPa·s, which is relatively high. Smaller bubbles have a larger specific surface area and stronger deep migration ability, making it suitable for viscosity reduction in low-permeability reservoirs. Using bubbles of 80-120 nm can achieve good results. The decomposition conditions are: the temperature is increased to 10 °C at a rate of 0.6-1 °C / min, and the pressure is reduced to atmospheric pressure, causing the hydrate to release carbon dioxide gas. The decomposition produces bubbles with a diameter of 80-120 nm.

[0062] Micro- and nanobubbles have the characteristics of large specific surface area, long residence time, and high interfacial activity, which can effectively reduce crude oil viscosity, improve mobility ratio, and enhance sweep efficiency.

[0063] The system supports continuous cyclic operation, and the pressure and cooling rate of each reactor stage can be adjusted independently; as the number of cycles increases, the reaction efficiency can be maintained by fine-tuning the pressure and adding promoter concentration.

[0064] The reaction conditions and results of Example 1 are shown in Table 1 below:

[0065] Table 1

[0066]

[0067] This embodiment employs an integrated carbon capture and oil displacement system based on carbon dioxide hydrate synthesis and decomposition, as shown in the schematic diagram below. Figure 1 As shown, the integrated system includes a recovery unit, a multi-stage hydrate reactor, a hydrate reaction unit, an injection unit, and a production unit.

[0068] The hydrate reaction apparatus includes a gas storage tank, a water tank, and a hydrate reaction vessel. The gas storage tank and the water tank are respectively connected to the hydrate reaction vessel, and the recovery device is connected to the gas storage tank.

[0069] The injection device includes a delivery pipeline and an injection pump. One end of the delivery pipeline is connected to the hydrate reaction vessel, and the other end leads into the oil reservoir. The injection pump is a constant-speed displacement pump and is located at the inlet of the delivery pipeline. The production device includes a production pump, a three-phase separator, and a crude oil downstream processing system.

[0070] The multi-stage hydrate reactor comprises a multi-stage series hydrate reactor 1, a multi-stage series hydrate reactor 2, and a multi-stage series hydrate reactor 3. Each of the three reactors is connected at one end to a conveying pipeline and at the other end to a tail gas recovery device, and they are connected sequentially. The pressure and cooling rate of each reactor can be independently adjusted.

[0071] The recovery unit includes a gas collection and buffer tank, a recirculating gas compressor, a dust collector, and a filter.

[0072] S3, Micro-nano bubble enhanced oil recovery (crude oil recovery stage):

[0073] A fluid rich in micro / nanobubbles is injected into the target reservoir to displace crude oil. The displacement process employs a combined approach of "micro / nanobubble slug + subsequent water flooding": the displacement fluid rich in micro / nanobubbles, generated from hydrate decomposition, is continuously injected into the simulated reservoir model at a pressure of 5 MPa and a rate of 0.5 m³ / min. The injection volume is typically 0.1 times the reservoir pore volume (PV). Calculations show that continuous injection for 25 minutes is required in this embodiment to form a highly efficient oil displacement slug. After the slug injection is complete, water is immediately injected at the same pressure and rate. The role of water flooding is to propel the slug forward, maintain formation pressure, and wash away residual oil behind the slug. Water flooding continues until the water cut of the quartz sand increases sharply. Micro / nanobubbles migrate within the reservoir, interacting with the crude oil to form foam oil or emulsions, improving wash-out efficiency and oil recovery. Micro / nanobubbles effectively expand the swept volume and reduce gas channeling through mechanisms such as the Jamin effect, reduced interfacial tension, and flowability control, thereby enhancing oil recovery.

[0074] This method integrates carbon capture and oil displacement processes into the same system. The hydrate decomposition liquid generated during the carbon capture stage is directly used for oil displacement, avoiding the transportation and storage of carbon dioxide, significantly reducing costs and energy consumption, and adapting to industrial applications of different scales.

[0075] Comparative Example 1:

[0076] This comparative example uses micro-nano bubble generator technology to generate micro-nano bubbles.

[0077] Figure 2 The results show that the peak particle size distribution of bubbles in the micro / nano bubble generator is larger, while the peak particle size distribution of bubbles generated by hydrate decomposition is smaller. The hydrate decomposition method tends to produce smaller bubbles, which have a larger specific surface area and volume ratio, and therefore can exhibit higher efficiency in gas mass transfer processes.

[0078] Comparative experiment on oil recovery rate of micro / nanobubbles generated by different methods:

[0079] ①Experimental objective:

[0080] The difference in oil displacement efficiency between hydrate decomposition fluid and micro-nano bubble liquid generated by conventional micro-nano bubble generators under simulated reservoir conditions was compared.

[0081] ②Experimental materials and apparatus:

[0082] Simulated oil reservoir model: Sand-filled pipe (30 cm in length, 2.5 cm in diameter), filled with standard quartz sand (300 mesh), saturated with simulated crude oil (viscosity 25 mPa·s).

[0083] Displacement system: constant speed displacement pump, pressure sensor, fluid collection system.

[0084] Experimental liquid:

[0085] (a) Hydrate decomposition liquid: The liquid containing micro- and nano-bubbles collected after carbon dioxide hydrate is synthesized at 3.5 MPa and 0°C and decomposed at atmospheric pressure;

[0086] (b) Control group liquid: Liquid containing micro-nano bubbles prepared using a micro-nano bubble generator (jet cavitation type) at the same gas-water ratio.

[0087] ③ Experimental steps:

[0088] (a) Saturate the sand-filled pipe with simulated crude oil to the original oil saturation and record the original oil content.

[0089] (b) Perform water flooding until the water cut reaches 98%, and record the water flooding recovery rate.

[0090] (c) The hydrate decomposition liquid and the micro / nano bubble generator liquid were injected into the sand-filled tube at the same injection rate (0.5 mL / min) to conduct an oil displacement experiment.

[0091] (d) Record the recovery increment and final recovery rate at different injection pore volume multiples (0.5 PV, 1.0 PV, 1.5 PV).

[0092] (e) Each experiment was repeated three times, and the average value was taken. The experimental results are shown in Table 2 below.

[0093] ④ Experimental results: Table 2

[0094]

[0095] ⑤ Results Analysis:

[0096] The total oil recovery rate after hydrate decomposition fluid displacement reached 62.8%, which is 17.6% higher than that of waterflooding; while the micro-nano bubble generator fluid only improved by 11.2%. The hydrate decomposition fluid showed higher oil displacement efficiency at the same injection volume, especially after 1.0 PV, the recovery rate growth remained stable, indicating that its micro-nano bubbles have better mobility and longer residence time in the porous medium.

[0097] ⑥ Conclusion:

[0098] Experiments have shown that using micro-nano bubbles generated by hydrate decomposition for oil displacement can significantly improve oil recovery compared to micro-nano bubbles generated by conventional mechanical methods. Furthermore, the bubbles are more stable and the oil displacement process is more stable, further verifying the technical advantages of this integrated method in improving oil displacement efficiency.

Claims

1. A method for integrated carbon capture and oil displacement based on carbon dioxide hydrate synthesis and decomposition, characterized in that, Includes the following steps: S1. Collect industrial exhaust gas, pre-treat it, and then store it in a gas storage tank. S2. Water and gas are successively supplied to the multi-stage series hydrate reactor 1 through water tank and gas storage tank. Carbon dioxide hydrate is induced to be generated by adjusting the temperature and pressure of the multi-stage series hydrate reactor 1. S3. The residual gas from the generation of carbon dioxide hydrate in the multi-stage series hydrate reactor 1 is introduced into the multi-stage series hydrate reactor 2. By adjusting the temperature and pressure of the multi-stage series hydrate reactor 2, the gas continues to react with water to induce the generation of carbon dioxide hydrate. At this time, the hydrate in the multi-stage series hydrate reactor 1 decomposes due to the decrease in gas pressure, producing a decomposition liquid containing carbon dioxide nanobubbles. The diameter of the carbon dioxide micro-nanobubbles is 50-200nm, which is transported to the injection pump through a pipeline. S4. The residual gas from the generation of carbon dioxide hydrate in the multi-stage series hydrate reactor 2 is discharged into the multi-stage series hydrate reactor 3. At this time, the hydrate in the multi-stage series hydrate reactor 2 decomposes due to the decrease in gas pressure, generating a decomposition liquid containing carbon dioxide nanobubbles, which is transported to the injection pump through the pipeline. The temperature and pressure of the multi-stage series hydrate reactor 3 are adjusted to induce the generation of carbon dioxide hydrate. S5. Detect the carbon dioxide concentration of the residual gas generated by carbon dioxide hydrate. If it is <5%, return it to the factory for treatment and discharge in compliance with standards. If it is >5%, reinject it back into the storage tank. After the residual gas generated by carbon dioxide hydrate in reactor 3 is discharged, the decomposition liquid containing carbon dioxide nanobubbles generated by the depressurization decomposition of hydrate is transported to the injection pump through the pipeline. S6. The decomposition liquid containing carbon dioxide nanobubbles in the injection pump is sequentially injected into the target oil reservoir for oil displacement.

2. The integrated method as described in claim 1, characterized in that, The industrial exhaust gas described in S1 contains one or more of C1-C5 hydrocarbons, hydrogen sulfide, moisture, and fine particles. The pretreatment includes dust removal and filtration.

3. The integrated method as described in claim 1, characterized in that, The multi-stage series hydrate reactor 1, multi-stage series hydrate reactor 2, and multi-stage series hydrate reactor 3 described in S1 are connected in series sequentially. Industrial exhaust gas passes through each stage of reactor sequentially, and carbon dioxide gas in the industrial exhaust gas that has not reacted with water enters the next stage from the previous stage to continue the reaction.

4. The integrated method as described in claim 3, characterized in that, The temperature at which carbon dioxide hydrate is generated in the multi-stage series hydrate reactor 1 described in S3, 4, and 5 is 4-6℃ and the pressure is 8-10 MPa; the temperature at which carbon dioxide hydrate is generated in the multi-stage series hydrate reactor 2 is 2-4℃ and the pressure is 6-8 MPa; and the temperature at which carbon dioxide hydrate is generated in the multi-stage series hydrate reactor 3 is 0-2℃ and the pressure is 4-6 MPa. The reaction time for each stage is 1-2 hours. An accelerator is also added to the multi-stage series hydrate reactor 1, multi-stage series hydrate reactor 2, and multi-stage series hydrate reactor 3. The accelerator contains at least one of tetrahydrofuran, cyclopentane, or sodium dodecyl sulfate.

5. The integrated method as described in claim 1, characterized in that, The substances described in S3, 4, and 5 decompose due to the decrease in gas pressure. During decomposition, the temperature is increased at a rate of 0.2-0.6℃ / min and the pressure is at atmospheric pressure, generating carbon dioxide gas micro-nano bubbles with a diameter of 60-100 nm. When decomposition occurs, no heating is required; the pressure is reduced to atmospheric pressure, generating carbon dioxide micro-nano bubbles with a diameter of 80-120 nm.

6. The integrated oil displacement method as described in claim 4, characterized in that, Once the gas is re-injected into the storage tank as described in S5, a new cycle begins. A step-by-step control strategy is adopted. During the first three initial cycles, each system operates under baseline conditions. During the fourth and fifth intermediate cycles, the reaction pressure is increased by 0.5-1 MPa due to a slight decrease in carbon dioxide concentration, while the accelerator concentration is increased by 50%-100%. After the fifth cycle, fine adjustments are made based on the real-time monitored carbon dioxide concentration.

7. The integrated oil displacement method as described in claim 1, characterized in that, The injection pressure in the target reservoir described in S6 is 5-20 MPa, and the injection rate is 0.1-1.0 m / s. 3 / min.

8. An integrated carbon capture and oil displacement system based on carbon dioxide hydrate synthesis and decomposition, characterized in that, The integrated system includes a multi-stage hydrate reactor, a hydrate reaction device, a carbon dioxide concentration monitoring device, a tail gas recovery device, an injection device, and a production device. The hydrate reaction device includes a gas storage tank, a water tank, and a hydrate reaction vessel. The gas storage tank and the water tank are respectively connected to the hydrate reaction vessel, and the recovery device is connected to the gas storage tank. The injection device includes a delivery pipeline and an injection pump. One end of the delivery pipeline is connected to a multi-stage hydrate reactor, and the other end is connected to the oil reservoir. The injection pump is located at the inlet of the delivery pipeline. The multi-stage hydrate reactor comprises a multi-stage series hydrate reactor 1, a multi-stage series hydrate reactor 2, and a multi-stage series hydrate reactor 3. Each of the multi-stage series hydrate reactors 1, 2, and 3 is connected at one end to a conveying pipeline and at the other end to a tail gas recovery device, and the multi-stage series hydrate reactors 1, 2, and 3 are connected in sequence. The pressure and cooling rate of each series hydrate reactor can be independently adjusted. The exhaust gas recovery device includes a gas collection and buffer tank, a recirculating gas compressor, a dust collector, and a filter.

9. The integrated system as described in claim 8, characterized in that, The production unit includes a production pump, a three-phase separator, and a crude oil downstream processing system connected in sequence.

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