A high-efficiency CO2 storage and injection system and method based on liquid phase injection

Abstract

The application discloses a CO2 high-efficiency burying and reinjection system and method based on liquid phase injection, and belongs to the technical field of liquid phase CO2 reinjection, which comprises a pipe tank precooling system, a first-stage injection pipeline supercooling system, a pipeline overpressure bypass pressure relief system, a pressurizing medium backflow pressure compensation system and a downhole plug removing and injecting system. The application can effectively relieve problems such as vaporization of the first-stage injection pipeline, direct discharge of overpressure during shutdown, excessively low pressure of the storage tank in the middle and later stages of reinjection, downhole plugging during reinjection and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of liquid-phase CO2 reinjection, and particularly relates to a CO2 high-efficiency storage and reinjection system and method based on liquid-phase injection. BACKGROUND

[0002] Carbon dioxide storage is an effective way to achieve carbon emission reduction. The basic concept is to capture carbon dioxide, increase the pressure, inject it into a reinjection well through a reinjection pipeline, and then store it in a depleted oil and gas reservoir or a saline layer. The critical temperature of relatively pure carbon dioxide medium is about 31.1℃, and the critical pressure is about 7.38MPa. The carbon dioxide used for reinjection and storage generally also includes impurities such as nitrogen and hydrogen sulfide, which affect the critical pressure and critical temperature.

[0003] Carbon dioxide reinjection can be used for oil field oil displacement (EOR) or geological storage. The implementation modes include wellhead reinjection after long-distance pipeline transportation and liquid-phase reinjection after wellhead storage. Compared with oil field oil displacement, the requirement for injection temperature is relatively low, which provides an opportunity for efficient and energy-saving injection. The advantage of relatively large density of low-temperature CO2 can be fully utilized, the reinjection pressure can be reduced as much as possible through the contribution of wellbore static pressure, and further, compared with long-distance pipeline transportation and injection (the pipeline end point temperature is close to the ground temperature, and a compressor is needed for re-pressurization to reach the required reinjection pressure, and the reinjection temperature is relatively high), the low-temperature liquid-phase injection of CO2 can fully utilize the upstream CO2 liquefaction cold energy (the storage temperature is generally about -20℃), and has the potential to achieve energy-saving injection under the condition of greatly optimizing external cold energy input. Overall, for the low-temperature liquid-phase injection mode, the low-temperature liquefied CO2 is transported to the injection well site for storage, and then injected into the reinjection well through multiple pressurizations to achieve CO2 geological storage. However, there are still problems such as reinjection pipeline medium vaporization, reinjection temperature control, pressure protection after shutdown, and abnormal downhole reinjection pressure, and further refinement of the key injection process is still needed.

[0004] However, there are relatively few public cases of liquid-phase CO2 injection, and most of them focus on the ground process flow. There is no detailed report on vaporization prevention and control, energy-saving injection, safety protection, and dynamic injection during the reinjection process. Therefore, it is necessary to fully carry out systematic research, integrate the ground reinjection system and the wellbore reinjection system, pay attention to the temperature control of the reinjection system, the overpressure protection of the reinjection system during shutdown, and the pressure anomaly of the reinjection system, and achieve the synergistic goal of energy-saving reinjection and safe reinjection. SUMMARY

[0005] The application aims at providing a CO2 high-efficiency storage and reinjection system and method based on liquid phase injection to overcome the defects of the prior art.

[0006] The application aims at providing a CO2 high-efficiency storage and reinjection system and method based on liquid phase injection to overcome the defects of the prior art.

[0007] The CO2 high-efficiency storage and reinjection system based on liquid phase injection comprises a wellhead reinjection basic system, wherein the wellhead reinjection basic system comprises a liquid phase CO2 storage device, an outlet of the liquid phase CO2 storage device is sequentially connected with a first injection pipeline, a second injection pipeline and a third injection pipeline, a storage device outlet shut-off valve is arranged between the liquid phase CO2 storage device and the first injection pipeline, a first shielding pump is arranged between the first injection pipeline and the second injection pipeline, a second pressurizing pump and a third injection pipeline starting point shut-off valve are arranged between the second injection pipeline and the third injection pipeline, a third injection pipeline end point shut-off valve is arranged at an end of the third injection pipeline and connected with a reinjection wellhead, and the reinjection wellhead is communicated with a reinjection wellbore.

[0008] The pipe tank precooling system comprises a precooling adjusting device arranged at an inlet of the liquid phase CO2 storage device and a precooling venting shut-off valve arranged at an end of the third injection pipeline.

[0009] The first injection pipeline supercooling system comprises a supercooling heat exchange device arranged between the first injection pipeline and the second injection pipeline, and the supercooling heat exchange device is used for performing supercooling heat exchange on a medium in the first injection pipeline.

[0010] The pipeline overpressure bypass pressure relief system comprises an overpressure protection device arranged at the end of the third injection pipeline.

[0011] The pressurizing medium backflow pressure compensation system is arranged between an outlet of the first shielding pump and the liquid phase CO2 storage device and is used for introducing backflow medium into the liquid phase CO2 storage device.

[0012] The downhole blockage removal injection system comprises a blockage removal pipeline arranged upstream of the reinjection wellhead.

[0013] A data monitoring system, which comprises a storage device pressure monitoring device and a storage device temperature monitoring device arranged in the liquid-phase CO2 storage device, a primary injection pipeline temperature monitoring device arranged in the primary injection pipeline, a secondary injection pipeline pressure monitoring device arranged in the secondary injection pipeline, a subcooling system temperature monitoring device arranged in the primary injection pipeline subcooling system, and a backflow flow monitoring device arranged in the pressurizing medium backflow pressure compensation system.

[0014] Further, the precooling conditioning device comprises an air-bath heat exchanger, the air-bath heat exchanger input port is provided with a precooling conditioning valve, and the air-bath heat exchanger output port is provided with a precooling cut-off valve and is communicated with the liquid-phase CO2 storage device.

[0015] Further, the subcooling heat exchange device comprises a heat exchanger arranged in the primary injection pipeline, the heat exchanger is communicated with the secondary injection pipeline through a heat exchange pipeline, and a liquid taking conditioning valve and a liquid taking conditioning valve temperature monitoring device are further arranged at the heat exchange pipeline entering the secondary injection pipeline.

[0016] Further, the overpressure protection device comprises a bypass pressure relief pipeline, the bypass pressure relief pipeline is provided with a bypass cut-off valve and a bypass thermal safety valve, and the inlet end of the bypass cut-off valve is located on the inlet side of the tertiary injection pipeline end-point cut-off valve.

[0017] Further, the outlet end of the bypass thermal safety valve is located on the outlet side of the tertiary injection pipeline end-point cut-off valve, and the overpressure medium is guided into the injection wellbore.

[0018] Further, the overpressure protection device further comprises a venting thermal safety valve and a wellhead venting riser, one end of the venting thermal safety valve is connected to the tertiary injection pipeline end, and the other end is connected to the wellhead venting riser.

[0019] Further, the pressurizing medium backflow pressure compensation system comprises a backflow pipeline communicated between the primary shielding pump outlet and the liquid-phase CO2 storage device, and the backflow pipeline is further provided with a backflow conditioning valve and a backflow flow monitoring device.

[0020] Further, the plug-removing pipeline is provided with an injection cut-off valve, and the end of the plug-removing pipeline is provided with a movable injection device.

[0021] In another aspect, the application further provides a high-efficiency CO2 burial injection method based on liquid-phase injection, which is realized based on any one of the foregoing injection systems, and the method comprises the following steps:

[0022] Before the system is put into operation, a system pipe tank precooling operation is performed using the pipe tank precooling system;

[0023] When the liquid CO2 is reinjected, the liquid CO2 in the liquid CO2 storage device is injected into the wellhead through the first injection pipeline, the first shielding pump, the second injection pipeline, the second booster pump and the third injection pipeline; during the reinjection process, when the pressure fluctuation of the second injection pipeline exceeds the preset fluctuation amplitude and / or the vibration amplitude of the first shielding pump exceeds the preset amplitude, a part of the pressurized liquid CO2 is pressure-regulated to normal pressure by the supercooling heat exchange device, and the medium in the first injection pipeline is supercooled by the low temperature caused by the pressure reduction;

[0024] After the reinjection system stops, the outlet cutoff valve of the storage device, the start point cutoff valve of the third injection pipeline and the end point cutoff valve of the third injection pipeline are closed, the pipeline of the pressurized medium backflow pressure compensation system is connected to the liquid CO2 storage device, the first injection pipeline and the second injection pipeline, and the pipeline of the pipeline overpressure bypass pressure relief system is opened;

[0025] After the pressure monitoring device of the storage device is lower than the preset threshold, the pressurized medium backflow pressure compensation system is opened, and part of the liquefied CO2 reinjection amount is depressurized and vaporized and then introduced back into the liquid CO2 storage device;

[0026] When the wellhead reinjection pressure continuously rises during the reinjection process, the downhole plug removal injection system is used to inject a plug removal agent, and the injection is stopped when the wellhead reinjection pressure returns to normal.

[0027] Further, the plug removal agent comprises ethylene glycol.

[0028] The beneficial effects of the present application are:

[0029] (1) The present application optimizes and improves the conventional injection process from multiple angles such as pre-cooling before production, supercooling control of the first injection pipeline, pipeline overpressure bypass pressure relief, pressurized medium backflow pressure compensation and downhole plug removal prevention, etc., to ensure that the system operates at a relatively low temperature, improve the reinjection efficiency, ensure that the pump inlet medium does not vaporize, improve the operation efficiency and safety, fully utilize the receiving capacity of the wellbore and downhole to the overpressure medium, avoid direct discharge of the overpressure low-temperature medium caused by shutdown, actively introduce the backflow medium to compensate the liquid CO2 storage tank when the medium pressure in the liquid CO2 storage tank is low, to improve the inlet pressure of the first shielding pump, and provide wellhead agent injection function for potential downhole plugging problems.

[0030] (2) The application optimizes the density of the injection medium by controlling the reinjection flow temperature of the liquid-phase CO2 medium, fully utilizes the influence of the wellbore hydrostatic pressure, and reduces the ground reinjection pressure; the low temperature is obtained by regulating the pressure of the pressurized CO2 through the setting of the liquid taking regulating valve, the supercooling of the medium in the primary injection pipeline is realized, the additional refrigerant circulation system is avoided, and the long-term stable operation of the pressurizing equipment is ensured; the bypass pressure relief system is set, the potential direct venting amount of CO2 after the shutdown of the injection pipeline is minimized, and the safety of the pipeline system is ensured; the backflow pressure compensation system can effectively ensure the pressure in the liquid-phase CO2 storage tank, stabilize the inlet pressure of the primary shield pump, and reduce the operation energy consumption; the downhole plug removal injection system is set, the downhole reservoir plugging problem can be quickly responded, and the recommissioning time is shortened. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a schematic diagram of the CO2 high-efficiency storage reinjection system based on liquid-phase injection provided by the embodiment of the application.

[0032] The drawings show that: 1 is a liquid-phase CO2 storage tank, 2 is a storage tank pressure transmitter, 3 is a storage tank temperature transmitter, 4 is a storage tank inlet shut-off valve, 5 is a storage tank outlet shut-off valve, 6 is a primary injection pipeline, 7 is a primary shield pump, 8 is a secondary injection pipeline, 9 is a secondary pressurizing pump, 10 is a tertiary injection pipeline starting point shut-off valve, 11 is a tertiary injection pipeline, 12 is a tertiary injection pipeline end point shut-off valve, 13 is a reinjection wellhead, 14 is a reinjection wellbore, 15 is a primary injection pipeline temperature transmitter, 16 is a secondary injection pipeline pressure transmitter, 17 is a storage tank safety valve, 18 is a storage tank area venting vertical pipe, 21 is a precooling regulating valve, 22 is an air bath type heat exchanger, 23 is a precooling shut-off valve, 24 is a precooling venting shut-off valve, 31 is a liquid taking regulating valve, 32 is a heat exchange pipeline, 33 is a heat exchanger, 34 is a temperature transmitter after the regulating valve, 41 is a bypass shut-off valve, 42 is a bypass thermal safety valve, 43 is a venting thermal safety valve, 44 is a wellhead venting vertical pipe, 51 is a backflow regulating valve, 52 is a backflow pipeline, 53 is a backflow flow transmitter, 61 is a movable reinjection device, and 62 is a reinjection shut-off valve. DETAILED DESCRIPTION

[0033] The embodiments of the application are described below through specific specific examples, and other advantages and effects of the application can be easily understood by those skilled in the art from the disclosure of the specification. The application can also be implemented or applied through other different specific embodiments, and various modifications or changes can be made to the details in the specification based on different views and applications without departing from the spirit of the application. It should be noted that the following examples and features in the examples can be combined with each other without conflict.

[0034] All other embodiments obtained by those of ordinary skill in the art without creative labor based on the embodiments of the present application fall within the scope of protection of the present application.

[0035] Currently, there are relatively few disclosed cases of liquid CO2 injection, and most of them focus on surface process flow, and there are no detailed reports on vaporization prevention and control during reinjection, energy-saving injection, safety protection, dynamic injection, etc. Therefore, it is necessary to fully carry out systematic research, comprehensively consider the surface reinjection system, the wellbore reinjection system, pay attention to the temperature control of the reinjection system, the overpressure protection of the shutdown of the reinjection system, and the pressure anomaly of the reinjection system, and realize the synergistic goal of energy-saving reinjection and safe reinjection.

[0036] To solve the above technical problems, the following embodiments of a CO2 high-efficiency storage and reinjection system and method based on liquid phase injection are provided.

[0037] Reference Figure 1 As Figure 1 shown is a schematic diagram of a CO2 high-efficiency storage and reinjection system based on liquid phase injection provided by the present embodiment.

[0038] Specifically, the wellhead reinjection basic system includes a liquid CO2 storage tank 1, a storage tank pressure transmitter 2, a storage tank temperature transmitter 3, a storage tank inlet shut-off valve 4, a storage tank outlet shut-off valve 5, a first-stage injection pipeline 6, a first-stage shield pump 7, a second-stage injection pipeline 8, a second-stage booster pump 9, a third-stage injection pipeline starting point shut-off valve 10, a third-stage injection pipeline 11, a third-stage injection pipeline end point shut-off valve 12, a reinjection wellhead 13, a reinjection wellbore 14, a first-stage injection pipeline temperature transmitter 15, a second-stage injection pipeline pressure transmitter 16, a storage tank safety valve 17, a storage tank area venting vertical pipe 18, etc., which are used to provide basic functions such as liquid CO2 storage, pressurization and reinjection, and serve as the basic flow of the CO2 high-efficiency storage and reinjection system based on liquid phase injection of the present embodiment.

[0039] It should be noted that the first-stage injection pipeline 6, the first-stage shield pump 7, the second-stage injection pipeline 8, the second-stage booster pump 9, the third-stage injection pipeline 11, etc. are insulated to sufficiently maintain the low temperature of the liquid CO2, improve the medium density of the injection wellbore, and reduce the wellhead reinjection pressure.

[0040] The tank and pipeline precooling system includes a precooling regulating valve 21, an air bath heat exchanger 22, a precooling shut-off valve 23 arranged at the inlet of the liquid CO2 storage tank 1, and a precooling venting shut-off valve 24 arranged at the end of the third-stage injection pipeline 11, which is used to precool the ground storage tank, pipeline, pipe fitting, etc. by introducing liquefied CO2 as a displacement and precooling medium before the reinjection system is put into production or restarted, so as to avoid the boiling or vaporization of liquid CO2 due to excessive temperature of the tank and pipeline during normal injection operation.

[0041] Specifically, the pre-cooling regulating valve 21 is arranged at the inlet of the liquid-phase CO2 storage tank 1, preferably an electric regulating valve made of stainless steel, for regulating the pressure of the liquid-phase CO2 to normal pressure to obtain a lower pre-cooling temperature; the air-bath heat exchanger 22 is arranged downstream of the pre-cooling regulating valve 21 and made of stainless steel, being a movable module, for air-bath heat exchange of the low-temperature CO2 obtained by the pre-cooling regulating valve 21 (as low as -80℃) to obtain CO2 with a temperature ranging from -35℃ to -40℃ for low-temperature purging and pre-cooling of the downstream pipe-tank system; the pre-cooling cut-off valve 23 is a manual ball valve made of low-temperature carbon steel, for cutting off or connecting the pipe-tank pre-cooling system; and the pre-cooling venting cut-off valve 24 is a manual cut-off valve made of low-temperature carbon steel, for discharging the upstream introduced low-temperature CO2 to the venting vertical pipe.

[0042] The primary injection pipeline subcooling system is arranged on the secondary injection pipeline 8 and includes a liquid-taking regulating valve 31, a heat exchange pipeline 32, a heat exchanger 33, a temperature transmitter 34 behind the regulating valve, etc., for subcooling heat exchange of the medium in the primary injection pipeline 6 when the primary shield pump 7 is blocked by gas or the outlet pressure is abnormal, actively reducing the temperature of the liquid-phase CO2 in the primary injection pipeline 6 to avoid gas-liquid two-phase flow before entering the primary shield pump 7 and when passing through the primary shield pump 7.

[0043] Specifically, the liquid-taking regulating valve 31 is arranged on the secondary injection pipeline 8 and is an electric regulating valve made of stainless steel, for taking the liquid-phase CO2 pressurized by the primary injection pipeline 6 from the secondary injection pipeline 8 to obtain low-temperature gas by throttling for supply to the heat exchanger 33 to reduce the temperature of the medium in the primary injection pipeline 6 to realize medium subcooling; the heat exchange pipeline 32 is connected to the liquid-taking regulating valve 31 and the heat exchanger 33 and is made of stainless steel; and the heat exchanger 33 is preferably a multi-tube heat exchanger, for subcooling heat exchange of the low-temperature CO2 obtained by the liquid-taking regulating valve 31 and the medium in the primary injection pipeline 6, with the temperature after heat exchange being 5℃ lower than the bubble point temperature of the CO2 medium corresponding to the operating pressure at this time.

[0044] The pipeline overpressure bypass pressure relief system is arranged at the end of the tertiary injection pipeline 11 and includes a bypass cut-off valve 41, a bypass thermal safety valve 42, a venting thermal safety valve 43, a wellhead venting vertical pipe 44, etc., for overpressure protection of the tertiary injection pipeline 11 blocked between the start point cut-off valve 10 and the end point cut-off valve 12 of the tertiary injection pipeline, and fully utilizing the pressure receiving capacity of the wellbore and the reservoir to preferably guide the overpressure medium in the ground sealing pipeline due to the increase of ambient temperature into the wellbore to avoid direct discharge, while providing the second layer pressure protection of the ground sealing pipeline overpressure medium to the wellhead venting vertical pipe.

[0045] Specifically, the bypass cut-off valve 41 is arranged on the bypass of the three-stage injection pipeline terminal cut-off valve 12, is a manual cut-off valve, is made of low-temperature carbon steel, is normally closed, and is opened after the reinjection system is shut down; the bypass thermal safety valve 42 is a thermal safety valve, is opened when the internal medium pressure of the three-stage injection pipeline 11 is increased due to environmental warming and exceeds the set value, and then the overpressure medium is discharged into the downstream wellhead and wellbore to avoid the overpressure medium directly entering the venting system, and the set pressure is 95% of the design pressure of the three-stage injection pipeline 11; the venting thermal safety valve 43 is a thermal safety valve arranged on the three-stage injection pipeline 11, is the second protection for thermal overpressure, is started when the bypass thermal safety valve 42 cannot effectively reduce the thermal overpressure of the three-stage injection pipeline 11, and the set pressure is 105% of the design pressure of the three-stage injection pipeline 11; the wellhead venting vertical pipe 44 is arranged on the wellhead, is used for safely discharging the thermal overpressure medium, and simultaneously supports the pre-cooling medium diffusion of the pre-cooling system of the tank.

[0046] The pressurized medium backflow pressure compensation system is arranged at the outlet of the primary shield pump 7, includes a backflow regulating valve 51, a backflow pipeline 52, a backflow flow transmitter 53, and the like, is used for actively introducing backflow medium to compensate the pressure of the liquid-phase CO2 storage tank 1 when the pressure of the medium in the liquid-phase CO2 storage tank 1 is low, and improves the inlet pressure of the primary shield pump 7.

[0047] Specifically, the backflow regulating valve 51 is arranged at the outlet of the primary shield pump 7, is an electric regulating valve, is made of low-temperature carbon steel, is used for throttling vaporization of part of CO2 from the secondary injection pipeline 8, and is backflowed to the gas-phase region of the liquid-phase CO2 storage tank 1 to compensate the pressure of the storage tank; the backflow pipeline 52 is connected with the backflow regulating valve 51 and the liquid-phase CO2 storage tank 1, is made of low-temperature carbon steel, is not heat-insulated, is used for fully utilizing the ambient temperature to slightly heat the medium in the pipeline, and is injected into the liquid-phase CO2 storage tank 1; and the backflow flow transmitter 53 is used for monitoring the flow of the backflow CO2.

[0048] The downhole plugging removal injection system is arranged upstream of the reinjection wellhead 13, includes a movable reinjection device 61, a reinjection cut-off valve 62, and the like, is used for relieving the injection plugging removal agent for the potential downhole reservoir plugging problem caused by CO2 injection, and relieves the problem that the reinjection pressure is long-term excessively high due to the influence of the downhole reservoir plugging.

[0049] Specifically, the movable reinjection device 61 is preferably a movable skid-mounted equipment with ethylene glycol (MEG) storage, metering and pressurization, is used for providing the ethylene glycol (MEG) reinjection function, and relieving the potential reservoir plugging problem existing in the downhole due to CO2 reinjection; and the reinjection cut-off valve 62 is a manual ball valve, is used for connecting or isolating the movable reinjection device 61.

[0050] The pipe tank precooling system in the embodiment is arranged in the ground storage tank, and includes a regulating valve, a vaporizer and the like, and is used for precooling before the ground pipe tank system is put into production or use; the first injection pipeline supercooling system is installed on the first injection pipeline connecting the storage tank outlet and the first shield pump, and includes a shield pump post regulating valve, a low temperature pipeline, a heat exchanger, a venting pipeline and the like, and is used for supercooling the first injection pipeline in case of vibration of the first shield pump, abnormality of the outlet pressure and the like, and guaranteeing the pressure increasing performance of the first shield pump; the pipeline overpressure bypass pressure relief system is arranged at the end of the third injection pipeline, and includes a bypass cutoff valve, an overpressure bypass relief valve, an overpressure venting valve and the like, and is used for protecting the overpressure of the pipeline medium due to the expansion of the medium in the pipeline after the third injection pipeline is shut down, preferentially guiding the overpressure medium into the wellbore through the bypass, and providing a secondary protection function of the pipeline overpressure medium for the venting system; the pressurized medium backflow pressure compensation system is arranged downstream of the first shield pump, and includes a bypass pipeline, a pressure regulating valve, a backflow pipeline and the like, and is used for guiding the vaporized CO2 through backflow to increase the pressure of the storage tank and compensate the suction pressure of the first shield pump when the liquid level of the storage tank is low; the downhole plug removal injection system is arranged at the end of the third injection pipeline, and includes a reserved injection cutoff valve and a movable injection pry, and is used for injecting plug removal reagents from the wellhead when potential flow channel plugging occurs in the downhole due to CO2 injection. Thus, the efficient and safe liquid phase CO2 reinjection is realized.

[0051] The working principle of the CO2 efficient burial reinjection system based on liquid phase injection in the embodiment is as follows:

[0052] The system is based on the basic physical properties of CO2, the gasification and liquefaction law, the basic process of wellhead reinjection, the basic influencing factors of wellhead reinjection pressure, etc. For the engineering needs of liquid phase CO2 wellhead reinjection, from the perspective of safe reinjection and efficient reinjection, a tank pre-cooling system, a primary injection pipeline supercooling system, a pipeline overpressure bypass pressure relief system, a pressurized medium backflow pressure compensation system and a downhole plugging injection system are set up, so as to fully based on the basic reinjection process of the wellhead, form a system with the functions of tank pre-cooling before production, CO2 supercooling control in the primary injection pipeline, optimized discharge of overpressure CO2 after the ground pipeline stops, active pressure compensation of the pressurized reinjection tank in the later stage, and prevention of potential plugging in the wellbore. Among them, the tank pre-cooling system is set in the ground tank, including regulating valve, vaporizer, etc., which is used for pre-cooling before the ground tank system is put into production or use; the primary injection pipeline supercooling system is installed on the primary injection pipeline connecting the tank outlet and the primary shield pump, including the shield pump post-regulating valve, low-temperature pipeline, heat exchanger, vent pipeline, etc., which is used for supercooling the primary injection pipeline in case of vibration of the primary shield pump, abnormal outlet pressure and other conditions, to ensure the pressure compensation performance of the primary shield pump; the pipeline overpressure bypass pressure relief system is set at the end of the tertiary injection pipeline, including bypass cut-off valve, bypass overpressure relief valve, overpressure vent valve, etc., which is used for protecting the overpressure of the pipeline medium due to the expansion of the medium caused by the increase of the ambient temperature after the tertiary injection pipeline stops, and preferentially guiding the overpressure medium into the wellbore through the bypass, and providing a secondary protection function of the overpressure medium in the pipeline for the standby introduction into the vent system; the pressurized medium backflow pressure compensation system is set downstream of the primary shield pump, including bypass pipeline, pressure regulating valve, backflow pipeline, etc., which is used for introducing the vaporized CO2 through backflow to improve the tank pressure and compensate the suction pressure of the primary shield pump when the tank liquid level is low; the downhole plugging injection system is set at the end of the tertiary injection pipeline, including a reserved injection cut-off valve and a movable injection pry, which is used for injecting plugging agents from the wellhead when potential flow passage plugging occurs in the wellbore due to CO2 injection. Thus, efficient and safe liquid phase CO2 reinjection is realized.

[0053] In the normal reinjection process, the liquid phase CO2 pulled by the tank car is injected into the liquid phase CO2 tank 1, and the stable pressurization pressure is provided by the primary shield pump 7, and the CO2 is pressurized to the wellhead reinjection pressure by the secondary pressurization pump 9, and then reinjected.

[0054] In order to improve the density of the injection medium, the primary injection pipeline 6, the primary shield pump 7, the secondary injection pipeline 8, the secondary pressurization pump 9, the tertiary injection pipeline 11 and the like are insulated in this embodiment, so as to fully maintain the low temperature of the liquid phase CO2, improve the medium density of the injection wellbore, and reduce the wellhead reinjection pressure.

[0055] Because the initial temperature of the pipe-tank system is high (not pre-cooled) and the pressure is low (not pressurized), the externally introduced liquid-phase CO2 (temperature at -25℃ to -20℃, pressure at about 2.0 MPa) can be violently vaporized, so the embodiment proposes to set a pipe-tank pre-cooling system to obtain low-temperature gaseous CO2 through throttling and heat exchange to pre-cool and pressurize the pipe-tank system.

[0056] The primary shield pump 7 can be affected by the vaporization of the inlet medium, the vaporization of the medium in the pump, and the vibration of the primary shield pump 7, and the outlet gas resistance problem, so the embodiment sets a primary injection pipeline supercooling system to supercool and heat exchange the medium of the primary injection pipeline 6, actively reduces the temperature of the liquid-phase CO2 in the primary injection pipeline 6, and avoids the occurrence of gas-liquid two-phase before entering the primary shield pump 7 and after passing through the primary shield pump 7.

[0057] Because the injection system is all low-temperature CO2, after the system stops injection, the pipe system will be affected by the external environment, and the temperature will rise, causing the pressure of the medium in the pipe to rise. To this end, the embodiment sets a pipe overpressure bypass pressure relief system for overpressure protection of the third injection pipeline 11 between the start point shut-off valve 10 of the third injection pipeline and the end point shut-off valve 12 of the third injection pipeline, and makes full use of the pressure receiving capacity of the wellbore and the reservoir to preferentially guide the overpressure medium in the ground sealing pipe caused by the increase of the ambient temperature into the wellbore to avoid direct discharge, while providing a second layer of pressure protection for the ground sealing pipe overpressure medium to be discharged to the wellhead venting riser.

[0058] After the liquid-phase CO2 storage tank 1 continuously outputs CO2, the medium in the tank gradually decreases, causing the pressure in the tank to decrease and increasing the pressurization load of the primary shield pump 7. To this end, the embodiment sets a pressurization medium backflow pressure supplementing system for actively introducing backflow medium to supplement the pressure of the liquid-phase CO2 storage tank 1 when the pressure of the medium in the liquid-phase CO2 storage tank 1 is low, so as to increase the inlet pressure of the primary shield pump 7. By partially throttling, heat exchanging, and reinjecting the pressurized liquid-phase CO2 into the liquid-phase CO2 storage tank, the gas-phase temperature and volume of the liquid-phase CO2 storage tank are increased, which actively improves the operating pressure of the liquid-phase CO2 storage tank.

[0059] Potential CO2 injection can cause solid-phase precipitation and plugging in the downhole reservoir, mainly because the dehydrated CO2 can absorb the moisture of the downhole salt water layer, causing salt precipitation and plugging the flow channel. To this end, the embodiment sets a downhole plugging removal injection system to alleviate the problem of long-term high reinjection pressure caused by the plugging of the downhole reservoir by injecting plugging removal agents (preferably MEG).

[0060] The embodiment of the present application provides a CO2 efficient storage and reinjection method based on liquid-phase injection according to the foregoing system, which comprises the following contents.

[0061] Step one: After the overall drying and replacement of the tank system, the system needs to be pre-cooled before operation. The low temperature of the vaporized liquid CO2 provides cold energy, and at the same time, the replacement of the tank system is completed. Specifically, close the storage tank inlet cutoff valve 4 and the last point of the three-stage injection pipeline cutoff valve 12, open the storage tank outlet cutoff valve 5, the beginning point of the three-stage injection pipeline cutoff valve 10 and the pre-cooling venting cutoff valve 24; input-20℃ to-25℃ liquid CO2 upstream of the pre-cooling regulating valve 21, open the pre-cooling regulating valve 21, the air bath heat exchanger 22 and the pre-cooling cutoff valve 23, adjust the temperature of the air bath heat exchanger 22 to-35℃ to-40℃, continuously provide low-temperature CO2 gas to the storage tank and the downstream pipeline, and monitor the temperature through the temperature transducer of the system multi-point position. When the temperature of the system point transducer is lower than-25℃ for 10 minutes, close the pre-cooling venting cutoff valve 24, keep the CO2 input of the storage tank, gradually pressurize the system, and stop pressurizing when the pressure of the liquid CO2 storage tank 1, the first-stage injection pipeline 6, the second-stage injection pipeline 8 and the third-stage injection pipeline 11 is not lower than 1.5MPa, to provide sufficient back pressure for the later injection operation and avoid causing too low injection throttle temperature.

[0062] Step two: When the liquid CO2 is injected, the liquid CO2 in the liquid CO2 storage tank 1 is injected into the wellhead through the first-stage injection pipeline 6, the first-stage shield pump 7, the second-stage injection pipeline 8, the second-stage booster pump 9, the third-stage injection pipeline 11, etc. During this process, the pressure change of the second-stage injection pipeline pressure transducer 16 and the vibration of the first-stage shield pump 7 are continuously monitored. When there is a significant pressure fluctuation or outlet pressure or first-stage shield pump vibration, it indicates that the medium in the first-stage injection pipeline 6 is vaporized due to flow temperature rise, or the fluid in the first-stage shield pump 7 is vaporized due to internal temperature rise. In this case, open the liquid taking regulating valve 31 to regulate a part of the liquid CO2 under pressure to normal pressure, use the low temperature caused by pressure reduction to supercool the medium in the first-stage injection pipeline 6 in the heat exchanger 33, and control the temperature after heat exchange to be 5℃ lower than the bubble point temperature of the CO2 medium under the current operating pressure. The low-temperature CO2 after heat exchange is discharged into the storage tank area venting standpipe 18.

[0063] Step three: after the injection system stops, the storage tank outlet cutoff valve 5, the third injection pipeline starting point cutoff valve 10, and the third injection pipeline end point cutoff valve 12 are closed to isolate the storage tank from the pump system, the ground injection pipeline system (the third injection pipeline 11), and the wellhead. The backflow regulating valve 51 is actively opened to connect the liquid CO2 storage tank 1, the first injection pipeline 6, and the second injection pipeline 8 to prevent the pipeline from being heated by external heat and expanding due to the heat.

[0064] Step four: after the liquid level of the liquid CO2 storage tank 1 continuously decreases, the pressure in the tank may continuously decrease, causing the inlet pressure of the first shield pump 7 to be too low, which increases energy consumption. Therefore, when the pressure of the storage tank pressure transmitter 2 is lower than 1.2 MPag, the backflow regulating valve 51 is opened to direct 5% of the liquefied CO2 back to the liquid CO2 storage tank 1 after being depressurized and vaporized. Since the backflow pipeline 52 is not insulated, the medium entering the liquid CO2 storage tank 1 must be in the gas phase, which can significantly increase the pressure in the liquid CO2 storage tank 1.

[0065] Step five: during the injection process, if the wellhead injection pressure continuously and significantly increases, it may be due to the salt blockage caused by the absorption of water in the brine by CO2. Therefore, the movable injection device 61 can be connected to the injection cutoff valve 62, and the injection medium is preferably ethylene glycol, which can reduce the water absorption of injected CO2 and improve the water release of the underground water-containing CO2. When the wellhead injection pressure returns to normal, the injection is stopped.

[0066] Thus, through the control of multiple key issues, efficient and safe injection of liquid CO2 is achieved.

[0067] The positive effects of the present embodiment compared to the prior art are based on the basic physical properties of CO2, the gasification and liquefaction rules, the basic process of wellhead injection, and the basic influencing factors of wellhead injection pressure. In view of the engineering requirements of liquid CO2 wellhead injection and safe injection and efficient injection, the pipe tank pre-cooling system, the first injection pipeline supercooling system, the pipeline overpressure bypass pressure relief system, the pressurizing medium backflow pressure supplementing system, and the downhole deblocking injection system are set up to form an efficient storage injection system with the functions of pipe tank pre-cooling, CO2 supercooling control in the first injection pipeline, optimized discharge of overpressure CO2 after the ground pipeline stops, active pressure supplementing of the storage tank in the later pressurizing injection period, and prevention of potential blockage in the well.

[0068] Specifically embodied as:

[0069] (1) For the potential key issues of liquid CO2 injection, the conventional injection process is optimized and improved from the aspects of pre-production subcooling, primary injection pipeline subcooling control, pipeline overpressure bypass pressure relief, pressurized medium backflow pressure compensation and downhole plug removal prevention, etc., to ensure low system operating temperature, improve injection efficiency, ensure non-vaporization of pump inlet medium, improve operating efficiency and safety, fully utilize the receiving capacity of wellbore and downhole for overpressure medium, avoid direct discharge of low-temperature medium after overpressure caused by shutdown, actively introduce backflow medium to compensate the pressure of liquid CO2 storage tank 1 when the medium pressure is low, to improve the inlet pressure of primary shield pump 7, and provide wellhead agent injection function for potential downhole plugging problems.

[0070] (2) By controlling the injection flow temperature of liquid CO2 medium, optimizing the density of injection medium, fully utilizing the influence of wellbore static pressure, the ground injection pressure is reduced; by setting the liquid taking regulating valve 31, the low temperature is obtained after pressure regulation of pressurized CO2, the primary injection pipeline medium is subcooled, the additional refrigerant circulation system is avoided, and the long-term stable operation of the pressurizing equipment is ensured; by setting the bypass pressure relief system, the potential direct venting amount of CO2 after the shutdown of the injection pipeline is minimized, the safety of the pipeline system is ensured; through the backflow pressure compensation system, the pressure in the liquid CO2 storage tank can be effectively guaranteed, the inlet pressure of the primary shield pump 7 is stabilized, and the operating energy consumption is reduced; by setting the downhole plug removal injection system, the downhole reservoir plugging problem can be quickly responded, and the re-production time is shortened.

[0071] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A high-efficiency CO2 storage and injection system based on liquid phase injection, the system comprising a wellhead injection base system, the wellhead injection base system comprising a liquid phase CO2 storage device, the liquid phase CO2 storage device being connected in turn with a first injection pipeline, a second injection pipeline and a third injection pipeline, a storage device outlet shut-off valve being provided between the liquid phase CO2 storage device and the first injection pipeline, a first shielding pump being provided between the first injection pipeline and the second injection pipeline, a second pressurizing pump and a third injection pipeline starting point shut-off valve being provided between the second injection pipeline and the third injection pipeline, a third injection pipeline end point shut-off valve being provided at the end of the third injection pipeline and being connected with a wellhead, the wellhead being connected with an injection wellbore, characterized in that, The system further comprises: a pipe tank pre-cooling system, which comprises a pre-cooling regulating device arranged at the inlet of the liquid CO2 storage device and a pre-cooling venting cut-off valve arranged at the end of the tertiary injection pipeline; a primary injection pipeline sub-cooling system, which comprises a sub-cooling heat exchange device arranged at the primary injection pipeline and the secondary injection pipeline, and the sub-cooling heat exchange device is used for sub-cooling heat exchange of the medium in the primary injection pipeline; a pipeline overpressure bypass pressure relief system, which comprises an overpressure protection device arranged at the end of the tertiary injection pipeline; a pressurized medium backflow pressure compensation system, which is arranged between the outlet of the primary shield pump and the liquid CO2 storage device, and is used for introducing backflow medium into the liquid CO2 storage device; a downhole plug removal injection system, which comprises a plug removal pipeline arranged upstream of the injection wellhead; a data monitoring system, which comprises a storage device pressure monitoring device and a storage device temperature monitoring device arranged at the liquid CO2 storage device, a primary injection pipeline temperature monitoring device arranged at the primary injection pipeline, a secondary injection pipeline pressure monitoring device arranged at the secondary injection pipeline, a sub-cooling system temperature monitoring device arranged at the primary injection pipeline sub-cooling system, and a backflow flow monitoring device arranged at the pressurized medium backflow pressure compensation system; the overpressure protection device comprises a bypass pressure relief pipeline, which is provided with a bypass cut-off valve and a bypass thermal safety valve, and the inlet end of the bypass cut-off valve is located on the inlet side of the end point cut-off valve of the tertiary injection pipeline; the outlet end of the bypass thermal safety valve is located on the outlet side of the end point cut-off valve of the tertiary injection pipeline, and the overpressure medium is introduced into the injection wellbore; the overpressure protection device further comprises a venting thermal safety valve and a wellhead venting riser, one end of the venting thermal safety valve is connected to the end of the tertiary injection pipeline, and the other end is connected to the wellhead venting riser.

2. The liquid phase injection based CO2 efficient sequestration and reinjection system of claim 1, wherein, the pre-cooling regulating device comprises an air bath heat exchanger, the input port of the air bath heat exchanger is provided with a pre-cooling regulating valve, and the output port of the air bath heat exchanger is provided with a pre-cooling cut-off valve and is communicated with the liquid CO2 storage device.

3. The liquid phase injection based CO2 efficient sequestration and reinjection system of claim 1, wherein, the sub-cooling heat exchange device comprises a heat exchanger arranged at the primary injection pipeline, the heat exchanger is communicated with the secondary injection pipeline through a heat exchange pipeline, and a liquid taking regulating valve and a liquid taking regulating valve temperature monitoring device are further arranged at the heat exchange pipeline entering the secondary injection pipeline.

4. The liquid phase injection based CO2 efficient sequestration and reinjection system of claim 1, wherein, the pressurized medium backflow pressure compensation system comprises a backflow pipeline communicated between the outlet of the primary shield pump and the liquid CO2 storage device, and a backflow regulating valve and a backflow flow monitoring device are further arranged on the backflow pipeline.

5. The liquid phase injection based CO2 efficient sequestration and reinjection system of claim 1, wherein, the plug removal pipeline is provided with an injection cut-off valve, and a movable injection device is arranged at the end of the plug removal pipeline.

6. A high-efficiency CO2 sequestration and reinjection method based on liquid phase injection, characterized in that, The method is realized based on the injection system according to any one of claims 1-5, and the method comprises: performing a system pipe tank pre-cooling operation using the pipe tank pre-cooling system before the system is put into operation; When the liquid CO2 is reinjected in liquid phase, the liquid CO2 in the liquid CO2 storage device is injected into the reinjection wellhead through the first injection pipeline, the first shielding pump, the second injection pipeline, the second booster pump and the third injection pipeline. During the reinjection process, when the pressure fluctuation of the second injection pipeline exceeds the preset fluctuation amplitude and / or the vibration amplitude of the first shielding pump exceeds the preset amplitude, a part of the pressurized liquid CO2 is pressure-regulated to normal pressure by the subcooling heat exchange device, and the medium in the first injection pipeline is subcooled by the low temperature caused by the pressure reduction; After the reinjection system stops, the outlet shut-off valve of the storage device, the start point shut-off valve of the third injection pipeline and the end point shut-off valve of the third injection pipeline are closed, the pipeline of the pressurized medium backflow pressure compensation system is connected to the liquid CO2 storage device, the first injection pipeline and the second injection pipeline, and the pipeline of the pipeline overpressure bypass pressure relief system is opened; After the pressure monitoring device of the storage device is lower than the preset threshold, the pressurized medium backflow pressure compensation system is opened, and part of the reinjected liquid CO2 is depressurized and vaporized and then introduced back into the liquid CO2 storage device; When the wellhead reinjection pressure continuously rises during the reinjection process, the plugging removal injection system is used to inject a plugging removal agent, and the injection is stopped when the wellhead reinjection pressure returns to normal.

7. The liquid phase injection-based CO2 efficient sequestration and re-injection method according to claim 6, wherein, The plugging removal agent comprises ethylene glycol.

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