A high-efficiency carbon dioxide reinjection system and method based on dual-phase mixed injection

Abstract

This invention belongs to the field of CO2 reinjection technology, and specifically relates to a high-efficiency carbon dioxide reinjection system and method based on two-phase mixed injection. The technical solution is as follows: a high-efficiency carbon dioxide reinjection system and method based on two-phase mixed injection, which, based on the basic process of liquid-phase CO2 and supercritical CO2 wellhead reinjection, also incorporates a high-efficiency media mixing system, a liquid-phase flow rate regulation system, and a liquid-phase bypass temperature regulation system, etc., to achieve efficient and safe wellhead reinjection of mixed liquid-phase CO2 and supercritical CO2, effectively mitigating problems such as temperature fluctuations after mixing low-temperature liquid-phase CO2 and supercritical CO2, back pressure fluctuations after changes in injection flow rate, and flow rate and temperature compensation when the supercritical CO2 flow rate is lower than the basic reinjection volume.

Description

Technical Field

[0001] This invention belongs to the field of CO2 reinjection technology, and specifically relates to a high-efficiency carbon dioxide reinjection system and method based on biphasic hybrid injection. Background Technology

[0002] Against the backdrop of ever-increasing demands for energy conservation, emission reduction, and environmental protection in the energy and chemical industry, large-scale capture and utilization of carbon dioxide is a preferred approach to effectively reduce carbon emissions. Among these methods, carbon dioxide sequestration is an effective means of achieving carbon emission reduction. Its basic concept involves capturing and pressurizing carbon dioxide, then injecting it into reinjection wells through reinjection pipelines, and finally storing it in depleted oil and gas reservoirs or saline aquifers. A relatively pure carbon dioxide medium has a critical temperature of approximately 31.1℃ and a critical pressure of approximately 7.38 MPa. However, carbon dioxide used for reinjection and sequestration generally also contains impurities such as nitrogen and hydrogen sulfide, which affect the critical pressure and critical temperature.

[0003] Carbon dioxide reinjection can be used in oilfield flooding (EOR) or geological storage, achieved through methods such as wellhead reinjection after long-distance pipeline transport and liquid-phase reinjection after wellhead storage. Compared to oilfield flooding, geological storage has relatively lower requirements for injection temperature and injection rate, while oilfield flooding requires maintaining a supercritical injection phase to improve the oil displacement effect. Therefore, for reinjection and storage scenarios, energy saving and economic efficiency should be the primary considerations. Furthermore, reinjection methods include wellhead cryogenic liquid-phase reinjection and pressurized pipeline transport reinjection, the main difference being the reinjection phase. To match the carbon source, construction, and dual-carbon target schedules, a hybrid injection mode combining pipeline reinjection and wellhead liquid-phase reinjection can be used simultaneously to achieve CO2 reinjection, enhancing the carbon source adaptability of the reinjection system.

[0004] However, the mixed injection mode exhibits significant characteristics: similar reinjection pressure but markedly different reinjection temperatures. Due to the influence of the pressurization process, pipeline reinjection primarily involves supercritical transport, resulting in reinjection medium temperatures generally above 20°C. In contrast, the CO2 temperature in liquid-phase reinjection is affected by the tank operating temperature, typically around -20°C. Therefore, the medium temperature during mixed injection is significantly affected by the mixing volume, directly impacting the density of the injected medium. Furthermore, in storage scenarios, lower reinjection temperatures lead to lower wellhead reinjection pressures, primarily due to the higher pressure of the hydrostatic column in the wellbore. Simultaneously, because the horizontal distance between the reinjection point and the wellhead is relatively short, changes in reinjection temperature contribute more significantly to the wellhead reinjection pressure than variations in reinjection flow rate. Therefore, it is necessary to fully consider temperature control during mixed reinjection.

[0005] Currently, while there are relatively many cases of single-phase CO2 reinjection, such as liquid-phase CO2 reinjection and supercritical CO2 reinjection, there are few reported cases of mixed injection of liquid-phase and supercritical CO2. The key technical aspects of mixed injection have not yet been thoroughly explored and revealed. Therefore, it is necessary to conduct comprehensive and systematic research, integrating the surface reinjection process with the wellbore hydrostatic column problem, and from the perspective of efficient and energy-saving reinjection, to carry out research on efficient CO2 reinjection systems and methods using two-phase mixed injection, and to formulate feasible, reasonable, and efficient reinjection strategies. Summary of the Invention

[0006] In order to solve the above-mentioned problems in the prior art, the purpose of this invention is to provide a high-efficiency carbon dioxide reinjection system and method based on biphasic hybrid injection.

[0007] The technical solution adopted in this invention is as follows:

[0008] A high-efficiency carbon dioxide reinjection system based on two-phase mixed injection includes a static mixer. The inlet end of the static mixer is connected to a supercritical CO2 reinjection pipeline and a liquid CO2 mixing pipeline. The other end of the liquid CO2 mixing pipeline is connected to a liquid CO2 reinjection pipeline and a liquid CO2 storage tank. The outlet end of the static mixer is connected to a wellhead reinjection pipeline, and the other end of the wellhead reinjection pipeline is connected to the reinjection wellhead.

[0009] The supercritical CO2 reinjection pipeline is sequentially connected to a supercritical CO2 inlet temperature transmitter, a supercritical CO2 inlet flow transmitter, and a supercritical CO2 pipeline end pressure transmitter; the liquid phase CO2 reinjection pipeline is sequentially connected to a storage tank outlet temperature transmitter, a primary booster pump, a primary booster pressure transmitter, a secondary booster pump, a secondary booster pressure transmitter, a liquid phase CO2 inlet temperature transmitter, and a liquid CO2 inlet flow transmitter; the wellhead reinjection pipeline is sequentially connected to a blended temperature transmitter, a blended pressure transmitter, and a blended flow transmitter.

[0010] A liquid phase CO2 bypass is connected in parallel on the liquid phase CO2 reinjection pipeline. One end of the liquid phase CO2 bypass is connected between the primary booster pump and the primary booster pressure transmitter, and the other end of the liquid phase CO2 bypass is connected between the secondary booster pump and the secondary booster pressure transmitter. A bypass primary booster pump, a bypass air bath heat exchanger, and a bypass secondary booster pump are connected in sequence on the liquid phase CO2 bypass.

[0011] As a preferred embodiment of the present invention, a supercritical reinjection pipeline shut-off valve is connected to the supercritical CO2 reinjection pipeline, and the supercritical reinjection pipeline shut-off valve is located on the side of the supercritical CO2 inlet temperature transmitter away from the supercritical CO2 inlet flow transmitter.

[0012] As a preferred embodiment of the present invention, a liquid phase CO2 reinjection pipeline is connected to a liquid phase storage tank outlet shut-off valve, which is located between the liquid phase CO2 storage tank and the storage tank outlet temperature transmitter.

[0013] As a preferred embodiment of the present invention, a wellhead reinjection shut-off valve is connected to the wellhead reinjection pipeline, and the wellhead reinjection shut-off valve is located on the side of the mixed flow transmitter near the reinjection wellhead.

[0014] As a preferred embodiment of the present invention, a spare supercritical CO2 mixing valve is connected to a section of the supercritical CO2 reinjection pipeline near the static mixer, a spare liquid CO2 mixing valve is connected to a section of the liquid phase CO2 mixing pipeline near the static mixer, and a spare mixing-off valve is connected to a section of the wellhead reinjection pipeline near the static mixer.

[0015] As a preferred embodiment of the present invention, the liquid phase CO2 bypass is further connected to a first liquid phase bypass valve and a second liquid phase bypass valve. The first liquid phase bypass valve is located on the side of the bypass primary booster pump away from the bypass air bath heat exchanger, and the second liquid phase bypass valve is located on the side of the bypass secondary booster pump away from the bypass air bath heat exchanger.

[0016] A highly efficient carbon dioxide reinjection method based on biphasic hybrid injection includes the following steps:

[0017] S1: During normal operation, the supercritical CO2 reinjection pipeline is connected to the supercritical CO2 of the upstream reinjection booster station; the reinjection well site pressurizes the low-temperature liquid CO2; the supercritical CO2 and the pressurized liquid CO2 are mixed in a static mixer according to the designed injection ratio; the injection volume is detected in real time by the supercritical CO2 inlet flow transmitter and the liquid CO2 inlet flow transmitter; the temperature change of the injected mixed medium is detected in real time by the temperature transmitter after mixing; a standard value for temperature control is set to stabilize the temperature of the injected medium after mixing.

[0018] S2: During normal reinjection, the amount of liquid CO2 reinjected is adjusted and controlled according to the set reinjection temperature control value;

[0019] S3: By configuring the supercritical CO2 inlet flow transmitter and the blended temperature transmitter, the liquid phase CO2 flow rate regulation function based on the supercritical CO2 reinjection flow rate as the basic variable is met.

[0020] S4: When the supercritical CO2 inlet flow transmitter is lower than the minimum reinjection volume specified in the project, start the bypass primary booster pump, bypass air bath heat exchanger, and bypass secondary booster pump.

[0021] As a preferred embodiment of the present invention, step S2 specifically involves: when the actual temperature detected by the temperature transmitter after mixing is 2°C higher than the reinjection temperature setpoint, increasing the discharge rate of the first-stage booster pump and the second-stage booster pump to increase the liquid phase CO2 reinjection amount and reduce the temperature of the mixed medium; when the actual temperature detected by the temperature transmitter after mixing is 2°C lower than the reinjection temperature setpoint, decreasing the discharge rate of the first-stage booster pump and the second-stage booster pump to reduce the liquid phase CO2 reinjection amount and increase the temperature of the mixed medium.

[0022] As a preferred embodiment of the present invention, step S3 specifically involves: when the supercritical CO2 inlet flow transmitter exceeds the set value, and the actual temperature detected by the temperature transmitter after mixing is 2°C higher than the reinjection temperature set value, increasing the discharge capacity of the first-stage booster pump and the second-stage booster pump to increase the liquid phase CO2 reinjection amount and reduce the temperature of the mixed medium; when the supercritical CO2 inlet flow transmitter is lower than the set value, and the actual temperature detected by the temperature transmitter after mixing is 2°C lower than the reinjection temperature set value, decreasing the discharge capacity of the first-stage booster pump and the second-stage booster pump to reduce the liquid phase CO2 reinjection amount and increase the temperature of the mixed medium.

[0023] As a preferred embodiment of the present invention, in step S4, when the supercritical CO2 reinjection volume remains at a low level, the liquid CO2 flow rate through the bypass primary booster pump, bypass air bath heat exchanger, and bypass secondary booster pump is gradually reduced within 24 hours, while the liquid CO2 flow rate through the primary booster pump and secondary booster pump is gradually increased to maintain a stable total liquid CO2 flow rate. The temperature of the reinjected CO2 after overall blending is gradually reduced, and the reinjection pressure is reduced.

[0024] The beneficial effects of this invention are as follows:

[0025] Based on the fundamental physical properties of CO2, the basic process of liquid phase wellhead reinjection, the basic process of supercritical phase wellhead reinjection, factors affecting wellhead reinjection pressure, and the mixing law of the medium, this invention addresses the engineering requirements of liquid phase and supercritical phase CO2 wellhead mixed reinjection by setting up a high-efficiency mixing system, a liquid phase flow rate regulation system, and a liquid phase bypass temperature regulation system. From the perspective of high-efficiency and stable reinjection, based on the basic processes of liquid phase CO2 reinjection and supercritical CO2 reinjection, this invention effectively overcomes the problems of the influence of mixed medium temperature differences on the mechanical properties of mixed reinjection pipelines, wellhead back pressure rise and its fluctuation, etc. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the present invention.

[0027] In the diagram: 1-Supercritical reinjection pipeline shut-off valve; 2-Wellhead reinjection shut-off valve; 3-Reinjection wellhead; 4-Reinjection wellbore; 5-Liquid CO2 storage tank; 6-Liquid storage tank outlet shut-off valve; 7-First-stage booster pump; 8-Liquid CO2 reinjection pipeline; 9-Second-stage booster pump; 10-Storage tank outlet temperature transmitter; 11-Pressure transmitter after first-stage booster; 12-Pressure transmitter after second-stage booster; 13-Pressure transmitter at the end of the supercritical CO2 pipeline; 14-Wellhead reinjection pipeline; 21-Liquid CO2 mixing pipeline; 22-Static mixer; 23-Backup supercritical CO2 pipeline. 2 - Blending valve; 24 - Standby liquid phase CO2 blending valve; 25 - Standby post-blending shut-off valve; 31 - Supercritical CO2 inlet temperature transmitter; 32 - Supercritical CO2 inlet flow transmitter; 33 - Liquid phase CO2 inlet temperature transmitter; 34 - Liquid CO2 inlet flow transmitter; 35 - Post-blending temperature transmitter; 36 - Post-blending pressure transmitter; 37 - Post-blending flow transmitter; 41 - Liquid phase bypass first shut-off valve; 42 - Bypass first-stage booster pump; 43 - Bypass air bath heat exchanger; 44 - Bypass second-stage booster pump; 45 - Liquid phase bypass second shut-off valve. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the invention can be combined with each other.

[0030] Based on the fundamental physical properties of CO2, the basic process of liquid phase wellhead reinjection, the basic process of supercritical phase wellhead reinjection, the factors affecting wellhead reinjection pressure, and the mixing law of the medium, this invention addresses the engineering requirements of liquid phase and supercritical phase CO2 wellhead mixed reinjection. From the perspective of efficient and stable reinjection, based on the basic processes of liquid phase CO2 reinjection and supercritical CO2 reinjection, it fully considers the influence of the temperature difference of the mixed medium on the mechanical properties of the mixed reinjection pipeline, wellhead back pressure and its fluctuations, and sets up a high-efficiency mixing system, a liquid phase flow rate regulation system, and a liquid phase bypass temperature regulation system. The system comprises several components: a high-efficiency mixing system, a high-efficiency mixer, and a liquid CO2 / supercritical CO2 mixing system. The high-efficiency mixer promotes rapid and uniform mixing of liquid CO2 and supercritical CO2, ensuring uniform CO2 temperature after mixing. The system also monitors the stress and strain of the mixer to provide basic deformation parameters for subsequent engineering. A liquid CO2 flow rate control system, based on supercritical CO2 flow rate, controls the liquid CO2 flow rate to achieve a stable temperature after mixing, preventing a rapid increase in wellhead back pressure when the supercritical CO2 injection rate increases alone. A liquid bypass temperature control system, equipped with a low supercritical CO2 flow rate alarm and a liquid CO2 bypass heat exchange function, actively increases the liquid CO2 temperature to prevent further decreases in liquid CO2 injection rate when the supercritical CO2 injection rate falls below the basic injection rate. This ensures minimum injection capacity while maintaining stable temperature and pressure of the reinjected medium. This system achieves efficient and safe liquid CO2 and supercritical CO2 mixed reinjection.

[0031] The invention incorporates a high-efficiency media mixing system, a liquid phase flow rate regulation system, and a liquid phase bypass temperature regulation system to achieve efficient and safe wellhead reinjection of mixed liquid-phase CO2 and supercritical CO2. This effectively mitigates issues such as temperature fluctuations after mixing low-temperature liquid-phase CO2 and supercritical CO2, back pressure fluctuations due to changes in injection flow rate, and flow and temperature compensation when the supercritical CO2 flow rate falls below the basic reinjection volume. Furthermore, this invention is based on the basic process of liquid-phase CO2 and supercritical CO2 wellhead reinjection; this process serves only as the foundation of the invention and is not considered as innovative content.

[0032] The wellhead reinjection infrastructure system includes a supercritical reinjection pipeline shut-off valve 1 located near the reinjection wellhead 3, a wellhead reinjection shut-off valve 2, a reinjection wellhead 3, a reinjection wellbore 4, a liquid CO2 storage tank 5, a liquid storage tank outlet shut-off valve 6, a primary booster pump 7, a liquid CO2 reinjection pipeline 8, a secondary booster pump 9, a storage tank outlet temperature transmitter 10, a primary booster pressure transmitter 11, a secondary booster pressure transmitter 12, a supercritical CO2 pipeline end pressure transmitter 13, and a wellhead reinjection pipeline, etc., used to provide wellhead reinjection channels for liquid CO2 and supercritical CO2. This wellhead reinjection infrastructure system process is only used as the basis of this invention and is not considered as innovative content.

[0033] The high-efficiency blending system includes a liquid-phase CO2 blending pipeline 21, a static mixer 22, a backup supercritical CO2 blending valve 23, a backup liquid-phase CO2 blending valve 24, and a backup shut-off valve 25 after blending. It is used to provide efficient and uniform blending of the liquid-phase CO2 and supercritical CO2 to be blended, achieving rapid temperature mixing of the liquid-phase CO2 and supercritical CO2 media. Simultaneously, the static mixer 22 is equipped with stress-strain monitoring plates to characterize the temperature field distribution and stress-strain distribution after blending. The backup valve provides online access functionality for the backup static mixer 22, avoiding the impact of replacing the static mixer 22 on production.

[0034] The liquid phase flow regulation system includes a supercritical CO2 inlet temperature transmitter 31, a supercritical CO2 inlet flow transmitter 32, a liquid phase CO2 inlet temperature transmitter 33, a liquid CO2 inlet flow transmitter 34, a mixed temperature transmitter 35, a mixed pressure transmitter 36, and a mixed flow transmitter 37, etc., which are used to establish coordinated control of the flow rate after mixing liquid phase CO2 and supercritical CO2, and prevent the temperature fluctuation value after mixing from deviating from the set value by 2℃.

[0035] The liquid phase bypass temperature control system includes a liquid phase bypass first shut-off valve 41, a bypass first-stage booster pump 42, a bypass air bath heat exchanger 43, a bypass second-stage booster pump 44, and a liquid phase bypass second shut-off valve 45, etc. It is used to actively increase the liquid phase CO2 injection volume to supplement the supercritical CO2 injection volume when it is lower than the basic injection volume, and to actively adjust (raise) the liquid phase CO2 reinjection temperature to keep the temperature as stable as possible after mixing, and avoid excessive temperature changes in the reinjection system and the resulting excessive changes in reinjection pressure.

[0036] Example 1:

[0037] like Figure 1As shown, the efficient carbon dioxide reinjection system based on dual-phase mixed injection in this embodiment includes a static mixer 22. The inlet end of the static mixer 22 is connected to a supercritical CO2 reinjection pipeline and a liquid phase CO2 mixing pipeline 21. The other end of the liquid phase CO2 mixing pipeline 21 is connected to a liquid phase CO2 reinjection pipeline 8. The other end of the liquid phase CO2 reinjection pipeline 8 is connected to a liquid phase CO2 storage tank 5. The outlet end of the static mixer 22 is connected to a wellhead reinjection pipeline 14. The other end of the wellhead reinjection pipeline 14 is connected to the reinjection wellhead 3.

[0038] The supercritical CO2 reinjection pipeline is sequentially connected to a supercritical CO2 inlet temperature transmitter 31, a supercritical CO2 inlet flow transmitter 32, and a supercritical CO2 pipeline end pressure transmitter 13; the liquid phase CO2 reinjection pipeline 8 is sequentially connected to a storage tank outlet temperature transmitter 10, a primary booster pump 7, a primary booster pressure transmitter 11, a secondary booster pump 9, a secondary booster pressure transmitter 12, a liquid phase CO2 inlet temperature transmitter 33, and a liquid CO2 inlet flow transmitter 34; the wellhead reinjection pipeline 14 is sequentially connected to a blended temperature transmitter 35, a blended pressure transmitter 36, and a blended flow transmitter 37.

[0039] A liquid phase CO2 bypass is connected in parallel to the liquid phase CO2 reinjection pipeline 8. One end of the liquid phase CO2 bypass is connected between the primary booster pump 7 and the primary booster pressure transmitter 11, and the other end of the liquid phase CO2 bypass is connected between the secondary booster pump 9 and the secondary booster pressure transmitter 12. A bypass primary booster pump 42, a bypass air bath heat exchanger 43, and a bypass secondary booster pump 44 are connected in sequence on the liquid phase CO2 bypass.

[0040] The supercritical CO2 reinjection pipeline is connected to a supercritical reinjection pipeline shut-off valve 1, which is located on the side of the supercritical CO2 inlet temperature transmitter 31 away from the supercritical CO2 inlet flow transmitter 32.

[0041] The liquid phase CO2 reinjection pipeline 8 is connected to a liquid phase storage tank outlet shut-off valve 6, which is located between the liquid phase CO2 storage tank 5 and the storage tank outlet temperature transmitter 10.

[0042] The wellhead reinjection pipeline 14 is connected to a wellhead reinjection shut-off valve 2, which is located on the side of the mixed flow transmitter 37 near the reinjection wellhead 3.

[0043] A spare supercritical CO2 mixing valve 23 is connected to a section of the supercritical CO2 reinjection pipeline near the static mixer 22; a spare liquid CO2 mixing valve 24 is connected to a section of the liquid phase CO2 mixing pipeline 21 near the static mixer 22; and a spare post-mixing shut-off valve 25 is connected to a section of the wellhead reinjection pipeline 14 near the static mixer 22.

[0044] The liquid phase CO2 bypass is also connected to a first liquid phase bypass valve 41 and a second liquid phase bypass valve 45. The first liquid phase bypass valve 41 is located on the side of the bypass first-stage booster pump 42 away from the bypass air bath heat exchanger 43, and the second liquid phase bypass valve 45 is located on the side of the bypass second-stage booster pump 44 away from the bypass air bath heat exchanger 43.

[0045] The wellhead reinjection basic system comprises the following components: supercritical reinjection pipeline shut-off valve 1, wellhead reinjection shut-off valve 2, reinjection wellhead 3, reinjection wellbore 4, liquid CO2 storage tank 5, liquid storage tank outlet shut-off valve 6, primary booster pump 7, liquid CO2 reinjection pipeline 8, secondary booster pump 9, storage tank outlet temperature transmitter 10, primary booster pressure transmitter 11, secondary booster pressure transmitter 12, supercritical CO2 pipeline end pressure transmitter 13, and wellhead reinjection pipeline 14. This system provides wellhead reinjection channels for both liquid CO2 and supercritical CO2. This wellhead reinjection basic system process is only used as the basis of this invention and is not considered part of the invention's innovation.

[0046] The system comprises a liquid-phase CO2 blending pipeline 21, a static mixer 22, a backup supercritical CO2 blending valve 23, a backup liquid-phase CO2 blending valve 24, and a backup shut-off valve 25, forming a high-efficiency media blending system. This system provides efficient and uniform blending of the liquid-phase CO2 and supercritical CO2 to be blended, achieving rapid temperature mixing of the two media. Simultaneously, the static mixer 22 is equipped with stress-strain monitoring plates to characterize the temperature field distribution and stress-strain distribution after blending. The backup valves provide online access to the backup static mixer 22, avoiding any impact on production during static mixer 22 replacement.

[0047] Specifically, in the system shown, the liquid CO2 blending pipeline 21 connects the secondary booster pump 9 and the static mixer 22, providing pressurized liquid CO2 to the static mixer 22. The material is preferably carbon steel. The static mixer 22 is also made of carbon steel, preferably with a horizontal structure. The mixing unit structure is optimized through CFD simulation to provide rapid and efficient mixing of supercritical CO2 and liquid CO2, improving the temperature stability of the outlet fluid. Stress strain gauges are installed on the external surface of the static mixer 22, located upstream, in the mixing unit area, and downstream of the mixing unit, to detect stress and strain data on the surface of the static mixer 22 during long-term operation. The standby supercritical CO2 blending valve 23, the standby liquid CO2 blending valve 24, and the standby post-blending shut-off valve 25 are all made of carbon steel and are located at the end of the supercritical reinjection pipeline, the end of the liquid CO2 blending pipeline 21, and the beginning of the wellhead reinjection pipeline 14, respectively, to provide online access to the standby static mixer 22, improving the reliability of the reinjection system.

[0048] The system comprises a supercritical CO2 inlet temperature transmitter 31, a supercritical CO2 inlet flow transmitter 32, a liquid CO2 inlet temperature transmitter 33, a liquid CO2 inlet flow transmitter 34, a mixed temperature transmitter 35, a mixed pressure transmitter 36, and a mixed flow transmitter 37, which together form a liquid phase flow regulation system. This system is used to establish coordinated flow control of liquid CO2 and supercritical CO2 after mixing, and to prevent the temperature fluctuation value after mixing from deviating from the set value by 2℃.

[0049] Specifically, the supercritical CO2 inlet temperature transmitter 31 is installed at the end of the supercritical reinjection pipeline to detect the real-time temperature of the supercritical CO2 medium entering the static mixer 22. The supercritical CO2 inlet flow transmitter 32 is installed at the end of the supercritical reinjection pipeline to detect the real-time flow rate of the supercritical CO2 medium entering the static mixer 2222, and alarms when it deviates from the set flow rate by 1%. The liquid phase CO2 inlet temperature transmitter 33 is installed in the liquid phase CO2 blending pipeline 21 to detect the real-time temperature of the liquid phase CO2 medium entering the static mixer 2222. The liquid CO2 inlet flow transmitter 34 is installed in the liquid phase CO2 blending pipeline 21 to detect the real-time flow rate of the liquid phase CO2 medium entering the static mixer 22. The post-blending temperature transmitter 35 is installed at the beginning of the wellhead reinjection pipeline 14 to detect the temperature of the mixed medium, and sends a flow rate adjustment signal to the liquid phase CO2 reinjection pump when the detected temperature deviates from the reinjection temperature set value by 2℃. The pressure transmitter 36 after mixing is installed at the beginning of the wellhead reinjection line 14 to detect the wellhead back pressure value. The flow transmitter 37 after mixing is installed at the beginning of the wellhead reinjection line 14 to detect the real-time flow rate of the mixed medium.

[0050] The liquid phase bypass first shut-off valve 41, bypass first-stage booster pump 42, bypass air bath heat exchanger 43, bypass second-stage booster pump 44, and liquid phase bypass second shut-off valve 45 constitute the liquid phase bypass temperature regulation system. This system is used to actively increase the liquid phase CO2 injection volume to supplement the supercritical CO2 injection volume when it is lower than the basic injection volume, and to actively regulate (raise) the liquid phase CO2 reinjection temperature to keep the temperature as stable as possible after mixing, thereby avoiding excessive temperature changes in the reinjection system and the resulting excessive changes in reinjection pressure.

[0051] Specifically, the first shut-off valve 41 of the liquid phase bypass is located in the liquid phase CO2 bypass, is normally closed, and is a ball valve, used to control the opening and closing of the liquid phase CO2 bypass pressurization and temperature control channels. The first-stage bypass booster pump 42 is located downstream of the first shut-off valve 41 of the liquid phase bypass, used to provide the first-stage bypass booster function for liquid phase CO2, preferably with a booster pressure between 5 and 6 MPa, to ensure that the temperature of the liquid phase CO2 after heat exchange in the bypass air-bath heat exchanger 43 does not exceed its bubble point temperature. The bypass air-bath heat exchanger 43 is preferably an air-bath heat exchanger made of carbon steel, used to heat and raise the temperature of the liquid phase CO2 at the outlet of the first-stage bypass booster pump 42, appropriately increasing the medium temperature to compensate for the temperature drop of the medium after mixing with supercritical CO2 after increasing the liquid phase CO2 flow rate. The second-stage bypass booster pump 44 is located downstream of the bypass air-bath heat exchanger 43, used to pressurize the heat-exchanged liquid phase CO2 to the reinjection pressure. The second shut-off valve 45 for the liquid phase bypass is located in the liquid phase CO2 bypass. It is normally closed, a ball valve, and is used to control the opening and closing of the liquid phase CO2 bypass pressurization and temperature control channels. The bypass primary booster pump 42 and the bypass secondary booster pump 44 have a linear flow regulation function, realizing the flexibility of bypass liquid phase CO2 compensation and regulation.

[0052] The working principle of this invention is as follows:

[0053] First, based on the basic physical properties of CO2 and the engineering requirements of supercritical CO2 and liquid CO2 mixed injection, this invention has identified problems such as uneven temperature distribution and excessive temperature change in the mixed medium, and identified potential impacts and hazards. Because the injection temperature of supercritical CO2 is relatively high, while the reinjection temperature of liquid CO2 is approximately -20℃, there is a significant temperature difference between the two. Using conventional blending methods results in uneven temperature distribution at the blending point and in downstream pipelines and wellbore, primarily manifested as uneven temperature field distribution and periodic variations in the temperature field distribution. This causes high-period, large-amplitude stress changes in some pipelines and equipment. Therefore, the proposed high-efficiency media blending system uses a static mixer 22 as its core, with blending temperature as the control indicator, to minimize the uniform mixing time and achieve rapid "cold-hot" mixing. Furthermore, to monitor stress changes in the static mixer 22, stress-strain monitoring plates are installed to characterize the temperature field distribution and stress-strain distribution after blending. Additionally, to ensure continuous production, a backup valve is provided to allow online access to a backup static mixer 22, avoiding the impact of static mixer 22 replacement on production.

[0054] Secondly, due to the higher CO2 reinjection pressure and the significantly higher density of the reinjection medium compared to conventional natural gas storage reinjection, the main influencing factor on the reinjection pressure is the medium temperature, which directly affects the wellbore hydrostatic pressure. Efficiently controlling the reinjection temperature and preventing excessive temperatures directly optimizes the wellhead reinjection pressure. To address this, a liquid phase flow rate regulation system was implemented. This system effectively controls the reinjection medium temperature by adjusting the liquid phase CO2 injection rate proportionally to the supercritical CO2 reinjection rate. This addresses the issue of increased reinjection temperature caused by increased supercritical CO2 flow rate, achieving the effect of minimal pressure change despite increased flow rate. Furthermore, during normal operation, a refined reinjection pressure calculation cycle is set, comprehensively considering the influence of seasons and time of day on the supercritical CO2 medium temperature. By setting a reinjection temperature setpoint and establishing a reinjection temperature detection mechanism, the liquid phase CO2 injection rate is effectively controlled, achieving relative stability in the reinjection temperature and thus ensuring economical and stable reinjection pressure.

[0055] Third, to address the issue of excessively low supercritical CO2 flow rate, this invention incorporates a liquid-phase bypass temperature control system. This system, equipped with a bypass CO2 pressurization-heat exchanger 43, moderately increases the liquid-phase CO2 temperature while simultaneously increasing the liquid-phase CO2 injection rate. This maintains a stable overall mixing temperature and prevents significant short-term temperature fluctuations in the reinjection temperature, which could affect the stability of the reinjection pressurization system. Furthermore, to address the potentially persistent problem of low supercritical CO2 reinjection flow rate, the overall mixing temperature can be gradually reduced by decreasing the flow rate of the liquid-phase bypass temperature control system and increasing the original liquid-phase CO2 flow rate. This increases the density of the mixed medium and reduces the reinjection pressure. In summary, to address the issue of low supercritical CO2 flow rate, a strategy of short-term maintenance and long-term adjustment has been established, balancing system stability and economy.

[0056] This led to the development of a working principle for a high-efficiency CO2 storage and reinjection system based on liquid phase injection.

[0057] Example 2:

[0058] This invention also discloses a highly efficient carbon dioxide reinjection method based on biphasic hybrid injection, comprising the following main contents:

[0059] S1: During normal operation, the supercritical CO2 pipeline connects to the upstream reinjection booster station's supercritical CO2; the reinjection well site pressurizes the low-temperature liquid CO2. The connected supercritical CO2 and the pressurized liquid CO2 are mixed in the static mixer 22 according to the designed injection ratio; the injection volume is monitored in real time by the supercritical CO2 inlet flow transmitter 32 and the liquid CO2 inlet flow transmitter 34; the temperature change of the injected mixed medium is monitored in real time by the mixed temperature transmitter 35. A standard value for temperature control is set by using the designed supercritical CO2 injection volume, the pre-injection temperature of supercritical CO2 (preferably the monthly average temperature), the designed liquid CO2 injection volume, and the liquid CO2 injection temperature to obtain the standard value for temperature control, which is used to stabilize the temperature of the injected medium after mixing. The preferred standard value for temperature control is adjusted monthly. Since the pressure at the reinjection wellhead 3 is mainly affected by the hydrostatic pressure in the wellbore, and the medium density has a significant impact on the hydrostatic pressure, controlling the stability of the reinjection temperature can effectively prevent large changes in the hydrostatic pressure.

[0060] S2: During normal reinjection, the amount of liquid CO2 reinjected is adjusted and controlled according to the set reinjection temperature control value; when the actual temperature detected by the temperature transmitter 35 after mixing is 2°C higher than the set reinjection temperature value, the amount of liquid CO2 reinjected is increased by increasing the discharge of the first-stage booster pump 7 and the second-stage booster pump 9, thereby reducing the temperature of the mixed medium; when the actual temperature detected by the temperature transmitter 35 after mixing is 2°C lower than the set reinjection temperature value, the amount of liquid CO2 reinjected is decreased by reducing the discharge of the first-stage booster pump 7 and the second-stage booster pump 9, thereby increasing the temperature of the mixed medium.

[0061] S3: Since supercritical CO2 is continuously pressurized and supplied after being captured by the upstream treatment plant, its reinjection flow rate may fluctuate. Therefore, the configured liquid phase flow regulation system satisfies the function of liquid phase CO2 flow regulation based on the supercritical CO2 reinjection flow rate as the fundamental variable. When the supercritical CO2 inlet flow transmitter 32 exceeds the set value, and the actual temperature detected by the mixed temperature transmitter 35 is higher than the reinjection temperature set value by 2°C, the discharge of the first-stage booster pump 7 and the second-stage booster pump 9 is increased to increase the liquid phase CO2 reinjection amount and reduce the temperature of the mixed medium. When the supercritical CO2 inlet flow transmitter 32 is lower than the set value, and the actual temperature detected by the mixed temperature transmitter 35 is lower than the reinjection temperature set value by 2°C, the discharge of the first-stage booster pump 7 and the second-stage booster pump 9 is reduced to decrease the liquid phase CO2 reinjection amount and increase the temperature of the mixed medium.

[0062] S4: Further, when the supercritical CO2 reinjection rate is lower than the minimum reinjection rate specified in the project, the liquid phase bypass temperature control system is activated. Specifically, if step S3 is continued when the supercritical CO2 inlet flow transmitter 32 is lower than the minimum reinjection rate specified in the project, the reinjection rate of the mixed medium will not meet the reinjection rate requirements specified in the project. Therefore, the first shut-off valve 41 of the liquid phase bypass, the first-stage bypass booster pump 42, the bypass air bath heat exchanger 43, the second-stage bypass booster pump 44, and the second shut-off valve 45 of the liquid phase bypass are opened. The bypass air bath heat exchanger 43 is used to increase the injection temperature of the liquid phase CO2 to match the mixing temperature downstream of the static mixer 22 and meet the reinjection temperature requirements. At the same time, the reinjection rate of the mixed medium is increased to avoid drastic fluctuations in the reinjection pressure due to the large-scale replenishment of low-temperature liquid phase CO2. Furthermore, when the supercritical CO2 reinjection rate remains at a low level, it is preferable to gradually reduce the flow rate of the liquid phase bypass temperature control system (i.e., the liquid phase CO2 flow rate passing through the bypass first-stage booster pump 42, bypass air bath heat exchanger 43, and bypass second-stage booster pump 44) and gradually increase the liquid phase CO2 flow rate passing through the first-stage booster pump 7, liquid phase CO2 reinjection pipeline 8, and second-stage booster pump 9 within 24 hours to maintain a stable total liquid phase CO2 flow rate, gradually reduce the temperature of the reinjected CO2 after overall blending, and reduce the reinjection pressure.

[0063] Thus, by controlling multiple key issues, efficient and safe mixing and injection of biphasic CO2 can be achieved.

[0064] Compared with the prior art, the present invention has the following positive effects:

[0065] First, scientific setup

[0066] This invention addresses the engineering requirements of supercritical CO2 and liquid CO2 co-injection. It analyzes the potential impact of temperature mixing on pipeline material properties, wellhead back pressure, and operational efficiency. A high-efficiency media mixing system is implemented to achieve rapid and uniform mixing of low-temperature liquid CO2 and high-temperature supercritical CO2, avoiding excessively large non-uniform temperature ranges and protecting downstream pipelines and equipment. A liquid phase flow regulation system is also included. Considering that the main factor affecting wellhead reinjection pressure is media density, a process of dynamically mixing supercritical CO2 with liquid CO2 is adopted, effectively ensuring temperature stability of the mixed media during specific injection periods, thereby achieving density stability and wellhead back pressure stability. Finally, a liquid phase bypass temperature regulation system is implemented to ensure overall reinjection temperature stability when the supercritical CO2 flow rate is too low by actively increasing the liquid CO2 temperature.

[0067] Second, it is economical.

[0068] This invention offers significant economic benefits. Regarding the uniformity of mixing temperature, the use of a high-efficiency mixer enables rapid mixing of low-temperature and medium-to-high-temperature media, avoiding stress fluctuations and uneven deformation in downstream pipelines and accessories caused by uneven medium temperature. This ensures the structural safety of the pipeline system and offers substantial potential economic advantages. Furthermore, by setting a relatively stable reinjection temperature, the reinjection pressure during the reinjection cycle is effectively controlled, preventing a sharp increase in reinjection pressure due to increased mixing temperature when the supercritical CO2 reinjection volume is too high, resulting in significant energy savings. Simultaneously, the inclusion of a liquid phase bypass temperature control system not only prevents drastic changes in wellhead back pressure caused by excessively low supercritical CO2 flow rates but also reduces wellhead back pressure later, achieving similar energy-saving effects.

[0069] Third, promote technological development

[0070] Currently, my country has not yet carried out practical work on the mixed injection and reinjection of supercritical CO2 and liquid CO2 for storage. The scheme proposed in this system plays an important role in engineering guidance and reference. The key process system configurations proposed, such as the efficient media mixing system, liquid phase flow regulation system, and liquid phase bypass temperature regulation system, can effectively promote the development of technical concepts and technological progress in this field, and ensure efficient and safe production.

[0071] This invention is not limited to the above-described optional embodiments. Anyone can derive other various forms of products under the guidance of this invention. However, regardless of any changes made in their shape or structure, any technical solution that falls within the scope of the claims of this invention shall be protected by this invention.

Claims

1. A high-efficiency carbon dioxide reinjection system based on two-phase hybrid injection, characterized in that: Includes a static mixer (22), the inlet end of which is connected to a supercritical CO2 reinjection pipeline and a liquid phase CO2 mixing pipeline (21), the other end of which is connected to a liquid phase CO2 reinjection pipeline (8), the other end of which is connected to a liquid phase CO2 storage tank (5), the outlet end of the static mixer (22) is connected to a wellhead reinjection pipeline (14), and the other end of which is connected to the reinjection wellhead (3); The supercritical CO2 reinjection pipeline is sequentially connected to a supercritical CO2 inlet temperature transmitter (31), a supercritical CO2 inlet flow transmitter (32), and a supercritical CO2 pipeline end pressure transmitter (13); the liquid phase CO2 reinjection pipeline (8) is sequentially connected to a storage tank outlet temperature transmitter (10), a first-stage booster pump (7), a first-stage booster pressure transmitter (11), a second-stage booster pump (9), a second-stage booster pressure transmitter (12), a liquid phase CO2 inlet temperature transmitter (33), and a liquid CO2 inlet flow transmitter (34); the wellhead reinjection pipeline (14) is sequentially connected to a blended temperature transmitter (35), a blended pressure transmitter (36), and a blended flow transmitter (37); A liquid phase CO2 bypass is connected in parallel to the liquid phase CO2 reinjection pipeline (8). One end of the liquid phase CO2 bypass is connected between the first-stage booster pump (7) and the first-stage booster pressure transmitter (11), and the other end of the liquid phase CO2 bypass is connected between the second-stage booster pump (9) and the second-stage booster pressure transmitter (12). A bypass first-stage booster pump (42), a bypass air bath heat exchanger (43), and a bypass second-stage booster pump (44) are connected in sequence on the liquid phase CO2 bypass.

2. The efficient carbon dioxide reinjection system based on dual-phase hybrid injection according to claim 1, characterized in that: The supercritical CO2 reinjection pipeline is connected to a supercritical reinjection pipeline shut-off valve (1), which is located on the side of the supercritical CO2 inlet temperature transmitter (31) away from the supercritical CO2 inlet flow transmitter (32).

3. The efficient carbon dioxide reinjection system based on dual-phase hybrid injection according to claim 1, characterized in that: The liquid phase CO2 reinjection pipeline (8) is connected to a liquid phase storage tank outlet shut-off valve (6), which is located between the liquid phase CO2 storage tank (5) and the storage tank outlet temperature transmitter (10).

4. A high-efficiency carbon dioxide reinjection system based on dual-phase hybrid injection according to claim 1, characterized in that: The wellhead reinjection pipeline (14) is connected to a wellhead reinjection shut-off valve (2), which is located on the side of the mixed flow transmitter (37) near the reinjection wellhead (3).

5. A high-efficiency carbon dioxide reinjection system based on dual-phase hybrid injection according to claim 1, characterized in that: A spare supercritical CO2 mixing valve (23) is connected to a section of the supercritical CO2 reinjection pipeline near the static mixer (22), a spare liquid CO2 mixing valve (24) is connected to a section of the liquid phase CO2 mixing pipeline (21) near the static mixer (22), and a spare post-mixing shut-off valve (25) is connected to a section of the wellhead reinjection pipeline (14) near the static mixer (22).

6. A high-efficiency carbon dioxide reinjection system based on dual-phase hybrid injection according to claim 1, characterized in that: The liquid phase CO2 bypass is also connected to a first liquid phase bypass valve (41) and a second liquid phase bypass valve (45). The first liquid phase bypass valve (41) is located on the side of the bypass first-stage booster pump (42) away from the bypass air bath heat exchanger (43), and the second liquid phase bypass valve (45) is located on the side of the bypass second-stage booster pump (44) away from the bypass air bath heat exchanger (43).

7. A highly efficient carbon dioxide reinjection method based on biphasic hybrid injection, characterized in that: Using the high-efficiency carbon dioxide reinjection system based on biphasic hybrid injection as described in any one of claims 1 to 6; comprising the following steps: S1: During normal operation, the supercritical CO2 reinjection pipeline is connected to the supercritical CO2 of the upstream reinjection booster station; the reinjection well site pressurizes the low-temperature liquid CO2; the supercritical CO2 and the pressurized liquid CO2 are mixed in the static mixer (22) according to the designed injection ratio; the injection volume is detected in real time by the supercritical CO2 inlet flow transmitter (32) and the liquid CO2 inlet flow transmitter (34); the temperature change of the injected mixed medium is detected in real time by the temperature transmitter (35) after mixing; the standard value of temperature control is set to stabilize the temperature of the injected medium after mixing. S2: During normal reinjection, the amount of liquid CO2 reinjected is adjusted and controlled according to the set reinjection temperature control value; S3: By configuring the supercritical CO2 inlet flow transmitter (32) and the mixed temperature transmitter (35), the liquid phase CO2 flow rate regulation function based on the supercritical CO2 reinjection flow rate as the basic variable is satisfied. S4: When the supercritical CO2 inlet flow transmitter (32) is lower than the minimum reinjection volume specified in the project, start the bypass first-stage booster pump (42), bypass air bath heat exchanger (43), and bypass second-stage booster pump (44).

8. The efficient carbon dioxide reinjection method based on biphasic hybrid injection according to claim 7, characterized in that: Step S2 is as follows: When the actual temperature detected by the temperature transmitter (35) after mixing is 2°C higher than the set value of the reinjection temperature, the liquid phase CO2 reinjection amount is increased by increasing the discharge of the first-stage booster pump (7) and the second-stage booster pump (9), thereby reducing the temperature of the mixed medium; when the actual temperature detected by the temperature transmitter (35) after mixing is 2°C lower than the set value of the reinjection temperature, the liquid phase CO2 reinjection amount is reduced by decreasing the discharge of the first-stage booster pump (7) and the second-stage booster pump (9), thereby increasing the temperature of the mixed medium.

9. A method for efficient carbon dioxide reinjection based on biphasic hybrid injection according to claim 7, characterized in that: Step S3 is as follows: When the supercritical CO2 inlet flow transmitter (32) exceeds the set value, and the actual temperature detected by the mixed temperature transmitter (35) is higher than the reinjection temperature set value by 2°C, the discharge of the first-stage booster pump (7) and the second-stage booster pump (9) is increased to increase the liquid phase CO2 reinjection amount and reduce the temperature of the mixed medium; when the supercritical CO2 inlet flow transmitter (32) is lower than the set value, and the actual temperature detected by the mixed temperature transmitter (35) is lower than the reinjection temperature set value by 2°C, the discharge of the first-stage booster pump (7) and the second-stage booster pump (9) is reduced to decrease the liquid phase CO2 reinjection amount and increase the temperature of the mixed medium.

10. A method for efficient carbon dioxide reinjection based on biphasic hybrid injection according to claim 7, characterized in that: In step S4, when the supercritical CO2 reinjection rate remains at a low level, the flow rate of liquid CO2 passing through the bypass primary booster pump (42), bypass air bath heat exchanger (43), and bypass secondary booster pump (44) is gradually reduced within 24 hours, while the flow rate of liquid CO2 passing through the primary booster pump (7) and secondary booster pump (9) is gradually increased to maintain a stable total flow rate of liquid CO2, and the temperature of the reinjected CO2 after overall blending is gradually reduced to lower the reinjection pressure.

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