CO2 Storage System

Abstract

The present invention is 2 The storage system (100) relates to CO 2 The storage system (100) stores liquid CO 2 and at least one outlet (116, 118) connected to at least one injection well (126) in a subsurface reservoir (124). 2 The subsea storage unit (102) includes at least one pipeline (104), and the subsea storage unit (102) is configured to store CO 2 and extracting the CO2 from the surrounding seawater. 2 The present invention also relates to a system configured to transfer heat to a CO 2 Regarding storage methods.

Description

[Technical field]

[0001] The present invention relates to the field of CO2 storage, and more particularly to a CO2 storage system. The system includes a subsea CO2 storage unit having at least one inlet for receiving liquid CO2 and at least one outlet connected to at least one injection well in an underground reservoir. The subsea CO2 storage unit includes at least one pipeline. The subsea CO2 storage unit is configured to contain and store CO2 and transfer heat from the surrounding seawater to the contained CO2. The present invention also relates to a CO2 storage method. [Background technology]

[0002] Carbon storage projects often utilize underground formations to deposit the CO2. Such underground formations are often offshore and therefore have offshore oil platforms, cargo systems, and / or pipelines connected to mainland CO2 sources that transport and deliver the CO2 to the underground reservoir. The logistics of the transportation and delivery steps are highly dependent on offshore weather conditions and can often be hindered when such conditions are severe or unstable. Also, CO2 storage facilities are often onshore, which can be unaesthetic and take up a lot of space. Furthermore, the condition of the reservoir itself can also be counterproductive to the conditioning of such steps. Also, when the CO2 arrives at the underground reservoir wellhead on a shuttle vessel, it is generally too cold (e.g., around -26°C) for successful injection of CO2 into the underground reservoir, especially from an equipment design perspective. Therefore, additional equipment is required to condition the CO2 before it is ready for injection.

[0003] Aspects of these issues are addressed in the following documents:

[0004] UK Patent Application No. 2470122A relates to a subsea high-pressure liquid carbon dioxide storage device including a carrier vessel for holding and carrying high-pressure liquid carbon dioxide, a surface power supply device arranged on the water surface for supplying power, a subsea storage device in which high-pressure liquid carbon dioxide is stored, a relay float tank in which high-pressure liquid carbon dioxide is stored, and a subsea injection pump fixedly provided on the seabed and configured to inject high-pressure liquid carbon dioxide into the subsea storage base. The storage device may include a buoyancy controller that uses a seawater inlet pump and an outlet pump to adjust the buoyancy of the storage tank. The storage facility may include a measurement unit or sensor for measuring the amount of liquid CO2 and non-condensable gas in the storage space.

[0005] Korean Patent No. 101915855B1 relates to a system and method for injecting and treating carbon dioxide using a seawater heat source and a compression array source. Using a seawater heat source and a compressor as a thermal energy source available on an offshore platform, carbon dioxide is treated according to an injection condition and injected into the sea. The system is characterized by comprising: a supply unit for injecting carbon dioxide that reaches the upper surface of the offshore platform through a predetermined treatment and supplying carbon dioxide, a separator for separating the supplied carbon dioxide into liquid carbon dioxide and gaseous carbon dioxide, a pump for pressurizing the liquid carbon dioxide supplied from the separator, a compressor for pressurizing the gaseous carbon dioxide supplied from the separator, a seawater heat exchanger for exchanging heat with the liquid carbon dioxide pressurized by the pump using the seawater heat source, and a compressor array heat exchanger for exchanging heat between the gaseous carbon dioxide that has passed through the compressor and the liquid carbon dioxide that has passed through the seawater heat exchanger.

[0006] JP 07-96888A relates to storing liquid CO2 in the ocean without diffusing or dissolving it in seawater by filling and sealing liquid CO2 in a liquid-tight bag to obtain filled liquid CO2, and sinking the filled liquid CO2 to the deep seabed through a long pipe in a vertical direction under the pressure of exhaust air. The liquid CO2 in a tank on a filling station is pressurized to about 40 atmospheres by a pressure pump, and then fed to a heat exchanger and heated to 0°C. The CO2 is then introduced into a lock hopper and filled into an impermeable bag. The filled liquid CO2 is transferred to a filling pipe that has been pressurized to 40 atmospheres in advance, and is suspended by hooks from weights attached to both ends of a long wire. The filled liquid CO2 and the weights are then lowered about 400m to reach the seawater surface in the filling pipe. Furthermore, after reaching a depth of 300m from the sea surface, where the relationship between the specific gravity of seawater and the specific gravity of liquid CO2 is reversed, the filled liquid CO2 is sunk to the seabed and stored.

[0007] Korean Patent Application No. 20110123056A relates to a liquefied carbon dioxide transport vessel having an underground storage device. The liquefied carbon dioxide transport vessel having an underground storage device includes a liquefied carbon dioxide storage tank and the underground storage device. The liquefied carbon dioxide storage tank stores liquefied carbon dioxide. The underground storage device secures an underground storage location for storing the liquefied carbon dioxide. The underground storage device includes a pressure pump. The pressure pump pressurizes the liquefied carbon dioxide discharged from the liquefied carbon dioxide storage tank.

[0008] In this context, there remains a need for improved systems for efficient and optimized CO2 storage. Summary of the Invention

[0009] It is therefore an object of the present invention to provide a CO2 storage system including a subsea CO2 storage unit having at least one inlet for receiving liquid CO2 and at least one outlet connected to at least one injection well in a subsurface reservoir, wherein the subsea storage unit includes at least one pipeline, and wherein the subsea storage unit is configured to contain and store CO2 and to transfer heat from surrounding seawater to the contained CO2.

[0010] According to some embodiments, the subsea CO2 storage unit includes a pipe rack that includes a manifold connected to multiple pipeline branches.

[0011] According to some embodiments, the pipe rack has a length of 10m to 250m, preferably 50m to 200m, a rack height of 1m to 30m, preferably 10m to 20m, and / or a rack width of 10m to 100m, preferably 30m to 60m.

[0012] According to some embodiments, the plurality of branches includes 10-500 branches, preferably 50-300 branches.

[0013] According to some embodiments, the subsea CO2 storage unit includes spacers along the pipe rack.

[0014] According to some embodiments, the total pipe length of the subsea CO2 storage unit is between 10km and 90km, preferably between 30km and 70km, more preferably between 40km and 60km.

[0015] According to some embodiments, the diameter of at least one pipeline is between 50 cm and 150 cm, preferably between 70 cm and 115 cm, more preferably between 75 cm and 110 cm.

[0016] According to some embodiments, the subsea CO2 storage unit includes a bundle pipeline, the bundle pipeline including at least one inner pipeline within an outer pipeline and fluidly connected to the outer pipeline.

[0017] According to some embodiments, the total expanded pipe length of the subsea CO2 storage unit is between 1 km and 50 km.

[0018] According to some embodiments, the subsea CO2 storage unit includes a single pipeline.

[0019] According to some embodiments, the total pipe length of the subsea CO2 storage unit is between 1 km and 30 km, preferably between 1 km and 25 km, more preferably between 5 km and 7 km.

[0020] According to some embodiments, the subsea storage unit is on the ocean floor.

[0021] According to some embodiments, the subsea CO2 storage unit is not positioned horizontally.

[0022] According to some embodiments, the subsea CO2 storage unit includes multiple inlets and / or multiple outlets.

[0023] According to some embodiments, the multiple outlets are connected to multiple injection wells.

[0024] According to some embodiments, the pressure in the subsea CO2 storage unit is between 3 MPa and 7 MPa, preferably between 4 MPa and 5 MPa.

[0025] According to some embodiments, the subsea CO2 storage unit stores CO2 in both liquid and gas phases.

[0026] According to some embodiments the seabed CO2 storage unit is at a depth of between 10m and 3000m, preferably between 30m and 300m.

[0027] According to some embodiments, the system includes at least one CO2 transfer line connected at one end to an inlet of the subsea CO2 storage unit and at the other end to a CO2 source, such as a storage unit on a shuttle vessel, an onshore CO2 storage unit, or an offshore platform.

[0028] According to some embodiments, the system includes a liquid CO2 injection line connected at one end to a liquid CO2 outlet of the subsea CO2 storage unit and at the other end to at least one injection well.

[0029] According to some embodiments, the system includes a steam CO2 injection line connected at one end to a steam CO2 outlet of the subsea CO2 storage unit and at the other end to at least one injection well.

[0030] According to some embodiments, the system includes a pump disposed along the liquid CO2 injection line.

[0031] According to some embodiments, the system includes an expansion unit along the liquid CO2 injection line configured to convert the liquid CO2 to vapor CO2.

[0032] According to some embodiments, the system includes a pipeline end module connected to an inlet to the subsea CO2 storage unit and / or an outlet to the subsea CO2 storage unit.

[0033] According to some embodiments, the system includes a number of subsea CO2 storage units.

[0034] Another object of the present invention is to provide a method for CO2 storage, the method comprising: supplying liquid CO2 to at least one inlet of a subsea CO2 storage unit of a CO2 storage system, the subsea CO2 storage unit including at least one pipeline; Capturing and storing the CO2 in an undersea CO2 storage unit; Transferring heat from the surrounding seawater to the contained CO2; injecting CO2 from at least one outlet of the subsea CO2 storage unit into at least one injection well in the subsurface reservoir; Includes.

[0035] According to some embodiments, the steps of providing liquid CO2 and injecting CO2 are performed simultaneously.

[0036] According to some embodiments, the steps of providing liquid CO2 and injecting CO2 are performed sequentially.

[0037] According to some embodiments, the pressure in the subsea CO2 storage unit is between 3 MPa and 7 MPa, preferably between 4 MPa and 5 MPa.

[0038] According to some embodiments, a portion of the liquid CO2 provided to the subsea CO2 storage unit transitions to a gas phase within the subsea storage unit.

[0039] According to some embodiments, liquid CO2 is supplied from a CO2 source to at least one inlet of the subsea CO2 storage unit, where the CO2 source is in the form of a pipeline connected to the onshore storage unit. The pressure of the liquid CO2 supplied to the subsea CO2 storage unit is between 4 MPa and 20 MPa, preferably between 4 MPa and 15 MPa, upon entering the subsea storage unit.

[0040] According to some embodiments, liquid CO2 is supplied from a CO2 source to at least one inlet of a subsea CO2 storage unit. The CO2 source is in the form of a shuttle vessel CO2 storage unit. The pressure of the liquid CO2 supplied to the subsea CO2 storage unit is between 0.5 MPa and 3 MPa, preferably between 1.5 MPa and 2.5 MPa, more preferably about 2 MPa, upon entering the subsea CO2 storage unit, and the temperature of the liquid CO2 supplied to the subsea CO2 storage unit is between -20°C and -30°C, preferably between -24°C and -28°C, upon entering the subsea CO2 storage unit.

[0041] According to some embodiments, CO2 is injected into at least one injection well from a subsea CO2 storage unit as a liquid CO2 stream, a vapor CO2 stream, or a combination of liquid and vapor CO2 streams.

[0042] According to some embodiments, liquid CO2 is captured from an undersea CO2 storage unit and converted to steam CO2 before being injected into at least one injection well.

[0043] According to some embodiments, the system for CO2 storage is according to any of the embodiments described above.

[0044] The present invention makes it possible to address the above-mentioned needs, in particular the method provides an efficient and optimized CO2 storage system with respect to the prior art.

[0045] This is accomplished by a subsea CO2 storage unit, which is configured to contain and store the CO2 prior to injection into the underground reservoir. This allows for a reduction in the amount of CO2 stored on land. It also provides a reserve or buffer system for CO2 in cases where the reservoir is not yet ready for CO2 injection when the shuttle vessel arrives to deliver the CO2, or where direct injection from the shuttle vessel or other delivery means (e.g., a pipeline connected to the mainland or offshore platform) into the underground reservoir wellhead is not desirable.

[0046] The subsea CO2 storage unit is also configured to transfer heat from the surrounding seawater to the contained CO2. This can heat the CO2 to a temperature high enough to facilitate injection into the underground reservoir. The heat transfer can also result in the formation of vaporized CO2 toward the top surface of the subsea CO2 storage unit (the term "top surface" refers to the surface closest to the water surface) in addition to the liquid CO2 present in the remainder of the subsea CO2 storage unit. This can allow the vaporized CO2 to be discharged from the subsea CO2 storage unit and injected into the underground reservoir, in addition to the heated liquid CO2.

[0047] The system therefore allows for the storage and conditioning of liquid CO2, eliminating the need for an additional heater in the system, simplifying the system and reducing energy costs.

[0048] Advantageously, according to some embodiments, the subsea CO2 storage unit comprises a pipe rack, bundled pipelines, or a single pipeline, which provides sufficient containment and storage of the CO2 and improves heat transfer between the CO2 and seawater. [Brief description of the drawings]

[0049] Non-limiting examples of the present invention will now be described with reference to the accompanying drawings. [Figure 1] FIG. 1 is a diagram of a system according to one embodiment. [Diagram 2] FIG. 1 is a diagram of a system according to one embodiment. [Diagram 3] FIG. 1 is a diagram of a system according to one embodiment. [Figure 4] FIG. 1 illustrates the phase transitions of CO2 in an offshore CO2 storage unit according to one embodiment. [Figure 5a] FIG. 1 is a diagram of a system having multiple subsea CO2 storage units including pipe racks, according to one embodiment. [Figure 5b] FIG. 1 is a diagram of a system having multiple subsea CO2 storage units including bundle pipelines, according to one embodiment. [Figure 5c] FIG. 1 is a diagram of a system having multiple subsea CO2 storage units including a single pipeline, according to one embodiment. [Figure 6] FIG. 1 is a schematic diagram illustrating countercurrent flow in an undersea CO2 storage unit according to one embodiment. [Figure 7] FIG. 1 is a schematic diagram of a system according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] The invention will now be described in more detail without, however, being limited thereto.

[0051] The system of the present invention includes a subsea CO2 storage unit including at least one pipeline. The subsea CO2 storage unit has at least one inlet for receiving liquid CO2 and at least one outlet connected to at least one injection well in the underground reservoir. A "subsea" CO2 storage unit refers to a CO2 storage unit that is submerged in water, more specifically submerged in the waters of the sea or ocean. In other words, the entire CO2 storage unit is below the water surface. A "CO2 storage unit" refers to a device used to contain and / or store CO2 for a period of time. Such period is equal to or greater than the period of time that the CO2 needs to be heated to a desired temperature by the surrounding seawater. A subsea CO2 storage unit configured to "contain" CO2 refers to the CO2 being held within the subsea CO2 storage unit. A subsea CO2 storage unit configured to "store" CO2 refers to the CO2 being held within the subsea CO2 storage unit for future use. A subsea CO2 storage unit configured to "transfer heat from the surrounding seawater to the contained CO2" refers to the transfer of heat from the surrounding seawater through one or more walls of the subsea CO2 storage unit to the contained CO2 by convection and conduction. The storage of CO2 in the CO2 storage unit is said to be ephemeral, as the CO2 will eventually be injected into a subsurface reservoir.

[0052] "Subsurface reservoir" refers to a hydrocarbon reservoir within a subsurface formation. The reservoir is located offshore, e.g., at a depth of more than 1 km below sea level, e.g., 2 km to 4 km. The hydrocarbon reservoir may be partially, substantially, or completely depleted. That is, the hydrocarbons within the reservoir may have been produced prior to the time the system of the present invention is realized. A reservoir is a subsurface portion in which fluids, such as CO2 and hydrocarbons, may be contained without substantial diffusion to adjacent portions. In this regard, a reservoir may be considered a geological enclosure within a subsurface formation. For example, the adjacent portions may be formed from rock material having a lower porosity than the rock material of the reservoir itself. In some variations, a clay layer may exist above the reservoir. In some variations, a water-bearing layer may exist below the reservoir. In some variations, the reservoir may be partially bounded by cracks that form discontinuous voids through which fluids are less likely to flow. The reservoir may have an elongated shape, for example with a height of 20m to 300m and / or a lateral dimension of 2km to 15km, for example 3km to 10km.

[0053] "Injection well" refers to a well for injecting CO2 into an underground reservoir. The well may be a dry well, e.g., a well located on a platform. Alternatively, the well may be a wet well, i.e., a well located on a seafloor template.

[0054] Various embodiments of the present invention are described below. Some embodiments provide a system having an undersea CO2 storage unit that includes a pipe rack.

[0055] Another embodiment provides a system having a subsea CO2 storage unit including a bundle pipeline.

[0056] Another embodiment provides a system having an undersea CO2 storage unit that includes a single pipeline.

[0057] [General principle] FIG. 1 is a general view of a CO2 storage system 100 according to one embodiment. Here, the CO2 storage system 100 includes a subsea CO2 storage unit 102 including at least one pipeline 104. The subsea CO2 storage unit 102 may be supplied with liquid via an inlet 106. The inlet 106 may be connected to one end of a transfer line 108. The one end of the transfer line 108 may be supplied with liquid CO2 from a CO2 source 110, such as, for example, a shuttle vessel or a CO2 storage unit on an offshore platform, to which the other end of the transfer line 108 is connected. The transfer line 108 may be connected to the storage unit on the offshore platform via a connection unit, such as, for example, a loading buoy. The transfer line 108 may be in the form of, for example, a flexible riser. Additionally or alternatively, the CO2 transfer line 108 may be connected to another CO2 source 110, such as, for example, an onshore storage unit, from which liquid CO2 may be supplied to the inlet 106. The transfer line 108 may be connected to the storage unit of the onshore storage unit via a connection unit, such as, for example, an onshore terminal.

[0058] As shown in FIG. 2, the pipeline 129 connected to the onshore storage unit may be directly connected at one end to the transfer line 108. Alternatively, the pipeline 129 connected to the onshore storage unit may be tapped at one point along its length for connection to the transfer line 108. Here, the end of the pipeline 129 bypasses the subsea CO2 storage unit and continues to supply CO2 to at least one injection well 126 in the subsurface reservoir 124a, 124b. According to some embodiments, the liquid CO2 may be supplied from the shuttle vessel via an offshore platform located above the at least one injection well 126 or via a dedicated riser. The shuttle vessel may supply the liquid CO2 to the offshore platform or riser via the transfer line 108 (e.g., a cryogenic flexible line, etc.) with the assistance of a tower loading unit. In other words, the offshore platform or riser may be used as an intermediate point between the shuttle vessel and the subsea storage unit 102. Some or all of the supplied CO2 may then be directed through transfer line 108 to the offshore platform and to the subsea storage unit 102. After the CO2 is directed to the riser with the assistance of the tower loading unit, the CO2 may be delivered through transfer line 108 to the subsea storage unit 102.

[0059] Alternatively, multiple transfer lines 108 connected to the same or different CO2 sources 110 may be simultaneously connected to multiple inlets 106 of the subsea CO2 storage unit 102 to supply different CO2 streams to the subsea CO2 storage unit 102. For example, liquid CO2 may be supplied from a shuttle vessel via a transfer line 108 connected to the inlet 106 while simultaneously being supplied to the inlet 106 from another pipeline 129 connected to an onshore storage unit.

[0060] Referring again to FIG. 1, the subsea CO2 storage unit 102 may contain and store CO2 within the subsea CO2 storage unit 102. The subsea CO2 storage unit 102 is preferably in a fixed position relative to the seabed. The subsea CO2 storage unit 102 may be positioned horizontally. According to some embodiments, the subsea CO2 storage unit 102 may be positioned on the seabed. Alternatively, the subsea CO2 storage unit may be such that seawater completely surrounds the subsea CO2 storage unit 102, where the subsea CO2 storage unit 102 floats at a certain depth below the water surface.

[0061] The transfer line 108 delivers liquid CO2 to the subsea CO2 storage unit 102 at a temperature dependent on the pressure in the CO2 source 110. For example, this temperature may be between -20°C and -30°C, preferably between -24°C and -28°C, such as about -26°C upon entering the subsea CO2 storage unit 102.

[0062] The temperature of the surrounding seawater may be between 0°C and 30°C, for example between 5°C and 20°C, and heat may be transferred to the liquid CO2 contained within the subsea CO2 storage unit 102 so that it is at approximately the same temperature.

[0063] The subsea CO2 storage unit 102 includes one or more pipelines 104. Each pipeline 104 has an internal surface area of, for example, 5 m 2 Less than or equal to 2 m per cubic metre of internal volume, preferably 2 ~5m 2 If the pipeline 104 has a cylindrical shape with a circular cross section, the inner diameter of the pipeline 104 may be in the range of, for example, 50 cm to 2 m. The internal volume of the subsea CO2 storage unit 102 available for CO2 storage may be in the range of 1000 m 3 ~100000m 3 , preferably 2500m 3 ~75000m 3 , more preferably 5000m 3 ~50000m 3The pipeline 104 may include or be formed from steel, such as, for example, carbon steel or alloy steel.

[0064] Preferably, the subsea CO2 storage unit 102, once in use, contains substantially only CO2 and no other substances (such as, in particular, seawater).

[0065] According to some embodiments, the pressure of the CO2 in the CO2 storage unit of the shuttle vessel may be 0.5MPa to 3MPa, preferably 1.5MPa to 2.5MPa, more preferably about 2MPa when entering the subsea CO2 storage unit 102, and the temperature when entering the subsea CO2 storage unit 102 may be -20°C to -30°C, preferably -24°C to -28°C when the transfer line 108 supplies liquid CO2 to the subsea CO2 storage unit 102. According to other embodiments, the pressure of the CO2 in the pipeline 129 connected to the onshore storage unit may be 4MPa to 20MPa, preferably 4MPa to 15MPa when entering the subsea CO2 storage unit 102. In some variations, a pressure reducing valve may be provided at or upstream of the inlet of the CO2 storage unit 102. The pressure of the CO2 in the subsea CO2 storage unit 102 may be increased by the static pressure in the subsea CO2 storage unit 102.

[0066] As a result, the CO2 may not only undergo a heat transfer conditioning step of increasing temperature, but also a pressure conditioning step in preparation for injection into the underground reservoir 124.

[0067] The subsea CO2 storage unit 102 may contain CO2 in both the liquid phase 114 and the gas phase 112, as some of the liquid CO2 may transition to the gas phase within the subsea CO2 storage unit 102 as a result of heat transfer and pressure regulation of the subsea CO2 storage unit 102.

[0068] The pressure in the subsea CO2 storage unit 102 (especially after a certain storage period) may be, for example, 3 MPa to 7 MPa, preferably 4 MPa to 5 MPa, and more preferably about 4 MPa. After a certain storage period, the liquid CO2 may be in equilibrium with the vapor CO2 in the subsea CO2 storage unit 102. The pressure in the subsea CO2 storage unit 102 then depends on the temperature in the unit, which itself is preferably approximately equal to the surrounding seawater temperature.

[0069] The steam CO2 112 may be in the upper portion of the subsea CO2 storage unit 102 (i.e., closer to the water surface than the rest of the unit). According to some embodiments, the subsea CO2 unit may not be positioned horizontally, especially if positioned on a sloping portion of the seabed. In this case, the steam CO2 may occupy an upper portion of the subsea CO2 storage unit 102 that is elevated relative to the rest of the subsea CO2 storage unit 102.

[0070] The subsea CO2 storage unit 102 may include at least one outlet. The subsea CO2 storage unit 102 may actually include multiple outlets. The multiple outlets may be connected to one injection well. Additionally or alternatively, the multiple outlets may be connected to multiple injection wells. The subsea CO2 storage unit 102 may inject liquid CO2 from at least one liquid outlet 116 of the subsea CO2 storage unit 102 (preferably located at the bottom of the subsea CO2 storage unit 102) to at least one injection well 126 of the underground reservoir 124 via a liquid CO2 injection line 120 connected at one end to the liquid CO2 outlet 116 of the subsea CO2 storage unit 102 and at the other end to at least one injection well 126. The pump 103 may be disposed along the liquid injection line 120 to facilitate injection into the underground reservoir 124. An expansion unit (not shown) may be disposed along the liquid CO2 injection line 120. This may convert some or all of the liquid CO2 to vapor CO2 upon collection of the liquid CO2 by the liquid CO2 injection line 120 prior to injection into the at least one injection well 126. To facilitate connections between the transfer line 108 and / or the injection lines 120, 122, the CO2 storage system 100 may include a pipeline end module (not shown) connected to an inlet to the subsea CO2 storage unit and / or an outlet to the subsea CO2 storage unit.

[0071] The subsea CO2 storage unit 102 may inject steam CO2 from at least one steam outlet 118 of the subsea CO2 storage unit 102 (preferably located at the top of the subsea CO2 storage unit 102) to at least one injection well 126 of the underground reservoir 124 via a steam CO2 injection line 122 connected at one end to the steam CO2 outlet 118 of the subsea CO2 storage unit 102 and at the other end to at least one injection well 126. In an advantageous embodiment, no compressor is provided in the steam CO2 injection line 122 since the pressure in the CO2 storage unit 102 is sufficient for injection of steam CO2.

[0072] 2, the liquid CO2 injection line 120 and / or the vapor CO2 injection line 122 may be fully underwater and directly connected to a subsea wellhead 121 of the underground reservoir 124a. Additionally or alternatively, the liquid CO2 injection line 120 and / or the vapor CO2 injection line 122 may be connected to an injection well 126 via a rigid riser 128 on an offshore platform above the water surface. Injection into the underground reservoir 124b may be performed via the rigid riser 128.

[0073] Each CO2 injection line, particularly the liquid CO2 injection line 120 and / or the vapor CO2 injection line 122 (if present), may be provided with at least one closeable valve 127 to control whether CO2 is injected and, optionally, to control the flow rate of CO2 in the respective injection line.

[0074] According to some embodiments, the steps of supplying liquid CO2 to the CO2 storage system 100 and injecting CO2 from the subsea CO2 storage unit 102 into the subsurface reservoirs 124a, 124b may be performed simultaneously. In other words, while liquid CO2 is being supplied to the subsea CO2 storage unit 102, liquid CO2 and / or vapor CO2 may be injected from one or more outlets 116, 118 of the subsea CO2 storage unit 102. During the simultaneous supply and injection, the average residence time of CO2 in the subsea CO2 storage unit 102 may range, for example, from 3 hours to 12 hours.

[0075] The subsea CO2 storage unit 102 may experience pressure fluctuations of, for example, 100 kPa to 200 kPa or so during the course of CO2 supply and injection.

[0076] Alternatively, the steps of supplying liquid CO2 to the CO2 storage system 100 and injecting CO2 from the subsea CO2 storage unit 102 into the underground reservoirs 124a, 124b may be performed consecutively. In other words, the reservoirs 124a, 124b may remain filled or partially filled for a period of time after supplying liquid CO2 to the subsea CO2 storage unit 102 until injection into the underground reservoirs 124a, 124b begins. Such a period may be a short pause, for example, from 1 day to 7 days, or from 24 hours to 72 hours, or from 1 hour to 24 hours. Alternatively, such a period may be several weeks, for example, less than 2 weeks, or from 2 weeks to 1 month. Alternatively, such a period may be several months, for example, from 1 month to 6 months, or from 6 months to 12 months, or from 12 months to 18 months. In practice, such a period may be several years, such as less than 5 years, or more than 5 years, or less than 10 years, or more than 10 years, in which case the subsea CO2 storage unit 102 acts as a buffer between supply and injection.

[0077] These sequential steps are advantageous, for example, to ensure that the CO2 is properly conditioned to the desired temperature within the subsea CO2 storage unit 102.

[0078] Alternatively, the simultaneous feeding and injection steps may alternate with feeding-only or injection-only steps. Additionally or alternatively, the simultaneous feeding and injection steps may include pauses during which no feeding or injection takes place. For example, the CO2 injection into the subsurface reservoirs 124a, 124b may be performed substantially continuously, while the CO2 supply to the subsea CO2 storage unit 102 may be performed intermittently. In this case, the flow rate of the CO2 injection is lower than the flow rate of the CO2 supply to the subsea CO2 storage unit 102. This is particularly advantageous when the CO2 is supplied to the subsea CO2 storage unit 102 by a shuttle vessel and is necessarily supplied discontinuously.

[0079] The pressure within the subsea CO2 storage unit 102 may remain constant or relatively constant throughout the course of supplying the subsea CO2 storage unit 102 and injecting CO2 from the subsea CO2 storage unit 102 into the underground reservoirs 124a, 124b. The depth at which the subsea CO2 storage unit 102 is located is between 10m and 3000m, preferably between 30m and 300m.

[0080] According to some embodiments, CO2 may be injected from the subsea CO2 storage unit 102 into at least one injection well 126 as a liquid CO2 stream, a vapor CO2 stream, or a combination of liquid and vapor CO2 streams. Thus, the CO2 injected into the subsurface reservoirs 124a, 124b may be a single-phase or two-phase mixture.

[0081] According to some embodiments, the subsea CO2 storage unit 102 may include a pipe rack. Alternatively, according to some embodiments, the subsea CO2 storage unit 102 may include a bundle pipeline including at least one internal pipeline within an external pipeline and fluidly connected to the external pipeline. Alternatively, according to some embodiments, the subsea CO2 storage unit 102 may include a single pipeline.

[0082] [Pipe rack] 3-5a relate to an example of a subsea CO2 storage unit including a pipe rack 130. Referring to FIG. 3, the pipe rack 130 includes a manifold 132 connected to a plurality of pipeline branches 138. The pipeline branches 138 may run substantially parallel to one another and may form a two-dimensional, or as shown, a three-dimensional array. In this example, the manifold 132 includes (e.g., eight) prongs 134 horizontally spaced apart from one another. Each prong 134 is connected to (e.g., eight) branches 138 vertically spaced apart from one another. The plurality of branches 138 may include a total of 10-500 branches 138, preferably 50-300 branches 138. The spacing between the branches 138 may be selected to optimize heat transfer across the pipe rack, such as a fixed dimension, e.g., 0.1 m to 1 m.

[0083] Optionally, the pipe rack 130 may be provided with an external and / or internal frame (not shown) to hold the bifurcations 138. The subsea CO2 storage unit 102 may include spacers (not shown) along the pipe rack 130 to allow for thermal expansion of the bifurcations 138. The spacers may be positioned perpendicular to the bifurcations 138.

[0084] Each pipeline branch 138 may be closed at its end opposite the manifold 132. Alternatively, the pipe rack 130 may include a second manifold connected to the pipeline branch at its end opposite the manifold 132. In this case, the pipeline branch 138 extends between the two manifolds. The pipe rack 130 may have a length of 10m to 250m, preferably 50m to 200m, a rack height of 1m to 30m, preferably 10m to 20m, and / or a rack width of 10m to 100m, preferably 30m to 60m. The length of the pipe rack 130 may correspond to the length of the branches 138 extending from the manifold 132 (because the pipe rack 130 may include multiple pipeline branches, the total pipe length in the pipe rack 130 may be greater, for example a subsea CO2 storage unit may have a total pipe length of 10km to 90km, preferably 30km to 70km, more preferably 40km to 60km).

[0085] Given the relatively short length of the pipe rack 130 (compared to the other embodiments described below), the slope of the seabed can be neglected, so the pipe rack can often be considered to be positioned substantially horizontally relative to the seabed.

[0086] The diameter of the pipeline branch may be 50 cm to 150 cm, preferably 70 cm to 115 cm, and more preferably 75 cm to 110 cm. 3 ~10000m 3 , preferably 2500m 3 ~75000m 3 , more preferably 5000m 3 ~50000m 3The ratio of vapor CO2 to liquid CO2 in the subsea CO2 storage unit 102 may vary over time. The subsea CO2 storage unit may have a liquid fraction of 00% to 100% by weight, for example 70% to 80% by weight, or for example about 75% by weight, at the start of the injection step, for example when the steps of supplying liquid CO2 to the CO2 storage system and injecting CO2 from the subsea CO2 storage unit 102 into the underground reservoir 124 are performed consecutively. According to such an embodiment, the liquid fraction in the subsea CO2 storage device may decrease during the injection.

[0087] The pipe rack 130 may include an upper branch 138 that contains vapor CO2 and a lower branch 138 that contains liquid CO2. The boundary between the vapor CO2 and liquid CO2 may move over time as the weight ratio of vapor to liquid CO2 in the pipe rack 130 changes. The vapor CO2 may be injected into the wellhead of the underground reservoir 124 via a vapor CO2 outlet in one or more of the upper branches 138. Similarly, liquid CO2 may be injected into the wellhead of the underground reservoir 124 via a liquid CO2 outlet in one or more of the lower branches 138. In FIG. 4, both liquid CO2 and vapor CO2 are injected into the wellhead via the rigid riser 128.

[0088] [Bundle Pipeline] Figures 4, 5b, 6 and 7 relate to an example of a subsea storage unit comprising at least one bundle pipeline 137. The bundle pipeline 137 may comprise at least one internal pipeline concentrically arranged within and fluidly connected to an external pipeline. This allows optimizing the heat transfer by internal heat exchange of the CO2 against itself. In particular, the CO2 may flow in countercurrent through the internal and external pipelines.

[0089] Two or more bundle pipelines 137 may be connected in series or in parallel.

[0090] The subsea CO2 storage unit 102 may also include one or more fluidly connected (unbundled) pipelines in addition to the bundle pipeline 137.

[0091] As shown in FIG. 4, the subsea CO2 storage unit 102 may include an inlet 106 connected to a lower bundle pipeline 137, which itself extends substantially horizontally above the lower bundle pipeline and is fluidly connected to a number of pipeline branches 138, e.g., vertically spaced apart from one another. The CO2 may flow first in the bundle pipeline 137 (e.g., first the inner pipeline 139 and then the outer pipeline 136) and then in the pipeline branch 138. The pipeline branch 138 may include a lower portion that contains liquid CO2 and an upper portion that contains vapor CO2. A flow path may continue from the bundle pipeline 137 to the lower portion and then to the upper portion. A liquid outlet 116 may be connected to the lower portion and a vapor outlet 118 may be connected to the upper portion.

[0092] As the CO2 moves through the subsea CO2 storage unit 102, the surrounding seawater (e.g., at a temperature of about 5°C) heats the CO2 through the walls of the bundle pipeline 137 and the pipeline branch 138. During feeding, the temperature of the CO2 in the subsea CO2 storage unit 102 may not be uniform. For example, the temperature of the CO2 may increase to about 0°C along the inner pipeline 139 of the bundle pipeline 137, and then increase to about 2°C-4°C along the outer pipeline 136 of the bundle pipeline 137. The temperature of the CO2 may reach about 5°C, for example, at one or more pipeline branches 138 downstream of the bundle pipeline 137. The temperature in the subsea CO2 storage unit 102 may be uniform in the absence of a feeding step. Additionally (i.e., at another time) or alternatively, the temperature in the subsea CO2 storage unit 102 may not be uniform in the absence of a feeding step, for example, during the period immediately after the feeding is completed.

[0093] 7, in some variations, the outer pipeline 136 of the bundle pipeline may be connected to at least two pipeline branches 138, one below the bundle pipeline 137 and the other above the bundle pipeline 137. The liquid outlet 116 may be connected to the lower pipeline branch 138 of the bundle pipeline 137, and the vapor outlet 118 may be connected to the upper pipeline branch of the bundle pipeline 137.

[0094] As shown in Figure 6, the subsea CO2 storage unit 102 may include at least two bundle pipelines 137. The at least two bundle pipelines 137 may be fluidly connected and arranged in parallel, possibly with a vertical gap between them. CO2 may be supplied to an inner pipeline 139 of the bundle pipelines 137, and the outer pipelines 136 may be fluidly connected to each other as shown.

[0095] According to some embodiments, the total extended pipe length of the bundle pipeline (inner and outer pipes) may be preferably 1 km to 15 km, preferably 5 km to 10 km, more preferably 5 km to 7 km. If one or more unbundled pipelines are connected to the bundle pipeline, the total extended pipe length of the subsea CO2 storage unit 102 may be, for example, 1 km to 50 km.

[0096] [Single Pipeline] Referring to FIG. 5c, the subsea CO2 storage unit 102 may include a single pipeline 160. As with the bundled pipeline, according to some embodiments, the total length of the subsea CO2 storage unit 102 may be between 1 km and 30 km, preferably between 1 km and 25 km, more preferably between 5 km and 7 km. An outlet located at one end of the single pipeline 160 may inject only one-phase liquid CO2. This liquid may expand to vapor CO2 as it exits the outlet.

[0097] [Multiple Pipelines] The system may include multiple subsea CO2 storage units 102 using any combination of the above-mentioned embodiments. With reference to Figures 5a-5c, the CO2 storage system includes multiple subsea storage units including a pipe rack 130 (Figure 5a) or multiple bundle pipelines 137 (Figure 5b) or multiple single pipes 160 (Figure 5c). Liquid CO2 may be sent to dedicated individual transfer lines 108a, 108b, 108c of the multiple subsea storage units via a common transfer line 108. Liquid CO2 may flow through the outlet of each pipe rack 130 / bundle pipeline 137 / single pipeline 160, and each pipe rack 130 / bundle pipeline 137 / single pipeline 160 is connected to its own liquid CO2 injection line and / or its own steam CO2 injection line 140a, 140b, 140c. Each steam CO2 injection line or liquid CO2 injection line 140a, 140b, 140c may be used independently. Alternatively, at least two injection lines may feed CO2 into one common injection line 120 before the CO2 is injected into at least one injection well 126 in the underground reservoir 124.

[0098] Additionally, independently, the subsea CO2 storage unit 102 may include a pipe rack 130 and a bundle pipeline 137, or a pipe rack 130 and a single pipeline 160, or a bundle pipeline 137 and a single pipeline 160, which may be fluidly connected in series.

[0099] Additionally, the pipe rack 130 may include one or more bundle pipelines 137 as part or all of the branch 138 described above.

Claims

1. CO ２ A storage system (100) comprising: ２ and at least one outlet (116, 118) connected to at least one injection well (126) in a subsurface reservoir (124). ２ The subsea CO storage unit (102) ２ The storage unit (102) includes at least one pipeline (104), and the subsea CO ２ The storage unit (102) is ２ and extracting the CO from the surrounding seawater. ２ a system configured to transfer heat to the

2. The seabed CO ２ The system of claim 1 , wherein the storage unit includes a pipe rack (130) including a manifold (132) connected to a plurality of pipeline branches (138).

3. 3. The system of claim 2, wherein the pipe rack (130) has a length of 10m to 250m, preferably 50m to 200m, a rack height of 1m to 30m, preferably 10m to 20m, and / or a rack width of 10m to 100m, preferably 30m to 60m.

4. The system according to claim 2 or 3, wherein the plurality of pipeline branches comprises between 10 and 500 branches, preferably between 50 and 300 branches.

5. The seabed CO ２ The system of any one of claims 2 to 4, wherein the storage unit includes spacers along the pipe rack (130).

6. The seabed CO ２ The system according to any one of claims 1 to 5, wherein the total pipe length of the storage unit is between 10km and 90km, preferably between 30km and 70km, more preferably between 40km and 60km.

7. The system according to any one of claims 1 to 6, wherein the diameter of the at least one pipeline is between 50cm and 150cm, preferably between 70cm and 115cm, more preferably between 75cm and 110cm.

8. The seabed CO ２ 2. The system of claim 1, wherein the storage unit includes a bundle pipeline (137) including at least one internal pipeline (139) within an external pipeline (136) and fluidly connected to the external pipeline.

9. The seabed CO ２ The system of claim 8, wherein the total extended pipe length of the storage unit is between 1 km and 50 km.

10. The seabed CO ２ The system of claim 1 , wherein the storage unit comprises a single pipeline (160).

11. The seabed CO ２ The system according to claim 10, wherein the total pipe length of the storage unit is between 1 km and 30 km, preferably between 1 km and 25 km, more preferably between 5 km and 7 km.

12. The seabed CO ２ The system of any one of claims 1 to 11, wherein the storage unit is on the seabed.

13. The seabed CO ２ 12. The system of claim 10 or 11, wherein the storage units are not arranged horizontally.

14. The seabed CO ２ The system according to any one of claims 1 to 13, wherein the storage unit comprises multiple inlets and / or multiple outlets.

15. The system of claim 14 , wherein the multiple outlets are connected to multiple of the injection wells.

16. The seabed CO ２ The system according to any one of claims 1 to 15, wherein the pressure in the reservoir unit is between 3 MPa and 7 MPa, preferably between 4 MPa and 5 MPa.

17. The seabed CO ２ The storage unit stores CO in both the liquid phase (114) and the gas phase (112). ２ The system according to any one of claims 1 to 16, comprising:

18. The seabed CO ２ A system according to any one of claims 1 to 17, wherein the storage unit is at a depth of between 10m and 3000m, preferably between 30m and 300m.

19. One end of the seabed CO ２ It is connected to the inlet of the storage unit, and the other end is CO ２ At least one CO ２ A transfer line (108) is included, ２ The source (110) may be, for example, a storage unit on a shuttle ship, an onshore CO ２ The system of any one of claims 1 to 18, which is a storage unit or an offshore platform.

20. One end of the seabed CO ２ Liquid CO in storage unit ２ a liquid CO2 outlet (116) connected at one end to at least one of said injection wells; ２ The system of any one of claims 1 to 19, comprising an infusion line (120).

21. One end of the seabed CO ２ Storage unit steam CO ２ an outlet (118) and a steam CO2 having the other end connected to at least one of said injection wells; ２ The system of any one of claims 1 to 20, comprising an infusion line (122).

22. The liquid CO ２ 22. The system of claim 20 or 21, comprising a pump (103) disposed along the infusion line.

23. liquid CO ２ Steam CO ２ The liquid CO2 is configured to convert ２ A system according to any one of claims 20 to 22, comprising an expansion unit along the injection line.

24. The seabed CO ２ an inlet to a storage unit, and / or ２ A system according to any one of claims 1 to 23, comprising a pipeline end module connected to an outlet to a storage unit.

25. The seabed CO ２ The system according to any one of claims 1 to 24, comprising a plurality of storage units.

26. CO ２ A method of storage comprising the steps of: ・Liquid CO ２ CO ２ Seabed CO storage system (100) ２ supplying at least one inlet (106) of a storage unit (102) with said subsea CO ２ The storage unit (102) includes at least one pipeline (104); ・CO ２ The subsea CO ２ storing and storing in a storage unit (102); The collected CO from the surrounding seawater ２ and transferring heat to the The CO ２ The seabed CO ２ injecting from at least one outlet (116, 118) of the storage unit (102) into at least one injection well (126) of a subterranean reservoir (124); A method comprising:

27. liquid CO ２ and supplying CO ２ 27. The method of claim 26, wherein the steps of injecting are performed simultaneously.

28. liquid CO ２ and supplying CO ２ 27. The method of claim 26, wherein the steps of injecting are performed continuously.

29. The seabed CO ２ The method according to any one of claims 26 to 28, wherein the pressure in the storage unit is between 3 MPa and 7 MPa, preferably between 4 MPa and 5 MPa.

30. The seabed CO ２ The liquid CO supplied to the storage unit ２ A part of the seabed CO ２ The method according to any one of claims 26 to 29, wherein the transition to the gas phase occurs in a storage unit.

31. The liquid CO ２ CO ２ The subsea CO ２ The CO is supplied to the at least one inlet of a storage unit. ２ The source is in the form of a pipeline (129) connected to an onshore storage unit, said subsea CO ２ The liquid CO supplied to a storage unit. ２ The pressure of the subsea CO ２ A method according to any one of claims 26 to 30, wherein the pressure upon entering the storage unit is between 4 MPa and 20 MPa, preferably between 4 MPa and 15 MPa.

32. The liquid CO ２ CO ２ The subsea CO ２ The CO is supplied to the at least one inlet of a storage unit. ２ The source is the shuttle ship's CO ２ The subsea CO storage unit is in the form of ２ The liquid CO supplied to a storage unit. ２ The pressure of the subsea CO ２ Upon entering the storage unit, the seabed CO is at a pressure of 0.5 MPa to 3 MPa, preferably 1.5 MPa to 2.5 MPa, more preferably about 2 MPa. ２ The liquid CO supplied to a storage unit. ２ The temperature of the seabed CO ２ A method according to any one of claims 26 to 30, wherein the temperature upon entry into the storage unit is between -20°C and -30°C, preferably between -24°C and -28°C.

33. CO ２ is liquid CO ２ Flow of steam CO ２ or liquid CO ２ Flow of CO and steam ２ The subsea CO ２ 33. The method of any one of claims 26 to 32, wherein the water is injected into at least one injection well from a storage unit.

34. liquid CO ２ The subsea CO ２ and recovering the steam CO from the storage unit prior to injection into at least one of said injection wells. ２ The method according to any one of claims 26 to 33, wherein

35. The CO ２ The method of any one of claims 26 to 34, wherein the reservoir system is made according to any one of claims 1 to 25.

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