A method of offshore carbon sequestration

Abstract

A kind of offshore carbon sequestration method, there is steel frame, steel frame is carried on the deck of FPSO or FLNG, FPSO or FLNG's exploitation pipeline sends crude oil or natural gas to carbon dioxide separation unit, carbon dioxide separation unit sends separated carbon dioxide to booster unit, receiving metering unit receives liquid carbon dioxide sent by carbon dioxide transport ship, and sends received liquid carbon dioxide to booster unit, after booster unit is boosted to 10MPa to received liquid carbon dioxide, it is sent into carbon dioxide storage tank and is stored, sequestration metering unit sends liquid carbon dioxide to booster heating unit, liquid carbon dioxide is converted into supercritical carbon dioxide after being heated and pressurized, is sent into supercritical carbon dioxide injection unit, and is sent into seabed wellhead via pipeline.The present application is strong in adaptability, wide in application, flexible in installation, utilizes seabed oil well and related pipeline to maximum, improves the economy and safety of offshore carbon sequestration operation.

Description

Technical Field

[0001] This invention belongs to the field of marine vessel design and construction, and specifically relates to a method for marine carbon sequestration. Background Technology

[0002] Compared to terrestrial carbon sequestration, offshore carbon sequestration has the following advantages: seawater pressure and rock caps provide greater sealing and security; seabed reservoirs suitable for carbon sequestration are widely distributed, with great application potential and easy selection of sequestration sites; offshore storage is not only far from freshwater aquifers but also far from residential areas, resulting in lower local risks and greater environmental friendliness; utilizing abandoned offshore oil fields for carbon sequestration can significantly reduce the overall costs of geological exploration and drilling.

[0003] The first offshore carbon sequestration project collects and stores the associated carbon dioxide produced during natural gas extraction, which only solves the problem of its own carbon emissions and cannot carry out additional carbon sequestration work.

[0004] Currently, research on offshore CCUS focuses more on carbon sequestration processes and methods. Patent CN219655826U discloses a co-injection and extraction system for carbon dioxide sequestration in seabed saline water layers; patent CN114278257A discloses a device and method for synchronizing offshore oilfield development and supercritical carbon dioxide sequestration, both of which are innovations in CCUS technology.

[0005] Research on offshore CCUS equipment is still in its early stages. Patent CN116480934A discloses an offshore floating carbon dioxide storage and methanol production equipment, which mentions storing carbon dioxide in old oil fields, but does not mention how to open up old oil fields that have been abandoned and sealed.

[0006] Offshore carbon dioxide sequestration in aging oil fields requires re-drilling wells in these already sealed areas, significantly increasing the cost of carbon sequestration. Furthermore, aging oil fields exhibit instability in terms of pressure, composition, and geology; reopening these wells could trigger accidents such as wellhead collapse or well fluid (gas) eruptions.

[0007] The safest and most ideal method for offshore carbon dioxide sequestration is to simultaneously extract and store carbon dioxide in offshore oil and gas fields, with offshore oil and gas extraction and carbon dioxide sequestration complementing and proceeding synchronously. Currently, there are no patents disclosing floating devices with this type of operation mode. Summary of the Invention

[0008] To address the above problems, this invention provides a method for marine carbon sequestration, the technical solution of which is as follows:

[0009] A method for offshore carbon sequestration includes a steel frame mounted on the deck of an FPSO or FLNG. The steel frame has three layers: upper, middle, and lower. The lower layer has no equipment and its safety height is D. The middle layer contains carbon dioxide storage tanks. The upper layer contains a carbon dioxide separation unit, a receiving and metering unit, a pressurization unit, a sequestration and metering unit, a pressurization and heating unit, and a supercritical carbon dioxide injection unit.

[0010] The production pipeline of FPSO or FLNG delivers crude oil or natural gas to the carbon dioxide separation unit. The carbon dioxide separation unit sends the separated carbon dioxide to the pressurization unit. The receiving and metering unit receives liquid carbon dioxide transported by carbon dioxide carriers and sends the received liquid carbon dioxide to the pressurization unit. The pressurization unit pressurizes the received liquid carbon dioxide to 10 MPa and then sends it to the carbon dioxide storage tank for storage. The carbon dioxide storage tank sends gaseous carbon dioxide back to the pressurization unit.

[0011] The sealing and metering unit is connected to the carbon dioxide storage tank. The sealing and metering unit sends liquid carbon dioxide to the pressurization and heating unit. After being heated and pressurized, the liquid carbon dioxide is converted into supercritical carbon dioxide and sent to the supercritical carbon dioxide injection unit. The supercritical carbon dioxide injection unit sends the supercritical carbon dioxide into the seabed wellhead through pipelines.

[0012] Furthermore, in the aforementioned method for offshore carbon sequestration, one end of the carbon dioxide separation unit is connected to the extraction pipeline of the FPSO or FLNG, and the other end is connected to the pressurization unit via a pipeline. One end of the receiving and metering unit is connected to the carbon dioxide transport vessel, and the other end is connected to the pressurization unit. The pressurization unit is connected in sequence via pipelines to the carbon dioxide storage tank, the sequestration and metering unit, the pressurization and heating unit, and the supercritical carbon dioxide injection unit. The carbon dioxide storage tank is equipped with a loop leading to the pressurization unit.

[0013] Furthermore, in the above-mentioned method of marine carbon sequestration, when the steel frame is mounted on the FPSO deck, the safety height D is not less than 3 meters, and when the steel frame is mounted on the FLNG deck, the safety height is not less than 6 meters.

[0014] Furthermore, in the aforementioned method of marine carbon sequestration, the carbon dioxide storage tank is connected to the modular structure via a semi-circular saddle, with the saddle angle being 120° ≤ 180°.

[0015] Furthermore, in the aforementioned method of marine carbon sequestration, a dedicated pump is installed inside the carbon dioxide storage tank to pump liquid carbon dioxide from the carbon dioxide storage tank to the sequestration metering unit.

[0016] Furthermore, in the aforementioned method of marine carbon sequestration, the pressure of the carbon dioxide storage tank is greater than 7.3 MPa.

[0017] Furthermore, in the aforementioned method for marine carbon sequestration, the heating temperature of the pressurization heating unit is 60°C, and the pressurization pressure is 20 MPa.

[0018] Furthermore, in the aforementioned method for offshore carbon sequestration, a carbon dioxide separation unit is equipped with monoethanolamine and diethanolamine, which act as chemical absorbents to absorb carbon dioxide from crude oil or natural gas.

[0019] Furthermore, in the above-mentioned marine carbon sequestration method, the inlet temperature of the carbon dioxide separation unit is 38°C, and the outlet temperature is 100°C.

[0020] The beneficial effects of this invention are:

[0021] 1. It can be mounted on FPSO and FLNG, with strong adaptability, wide application range, and flexible installation.

[0022] 2. It enables the simultaneous development of crude oil extraction and carbon dioxide sequestration, maximizing the utilization of subsea oil wells and related pipelines, and improving the economic efficiency of offshore carbon sequestration operations.

[0023] 3. It avoids the risks associated with re-drilling abandoned oil wells and improves the safety of offshore carbon sequestration operations.

[0024] 4. During the crude oil (natural gas) extraction process, carbon dioxide can be injected into the oil field to pressurize it, thereby assisting crude oil (natural gas) extraction while simultaneously injecting carbon dioxide. This allows crude oil (natural gas) extraction and carbon dioxide injection operations to complement each other, further improving the overall economic efficiency of the unit. Attached Figure Description

[0025] Figure 1 This is a side view of the present invention;

[0026] Figure 2 This is a top view of the present invention;

[0027] Figure 3 This is a front view of the present invention;

[0028] Figure 4 This is a flowchart of the operation process of this invention;

[0029] Figure 5 This is a side view of the module structure of the present invention.

[0030] Among them: 1-Module structure, 2-Carbon dioxide storage tank, 3-Carbon dioxide separation unit, 4-Receiving and metering unit, 5-Pressure boosting unit, 6-Storage and metering unit, 7-Pressure boosting and heating unit, 8-Supercritical carbon dioxide injection unit, A-FPSO / FLNG, B-Carbon dioxide transport ship, C-Carbon dioxide storage well, D-Safety height, L_CO2-Liquid carbon dioxide, G_CO2-Gaseous carbon dioxide, S_CO2-Supercritical carbon dioxide. Detailed Implementation

[0031] The invention will be further described with reference to the accompanying drawings.

[0032] This invention provides a marine carbon sequestration module, such as... Figure 1 , Figure 2 , Figure 3 As shown, the device of the present invention is installed on an FPSO / FLNG and, while extracting crude oil / natural gas, utilizes existing oil and gas wells to perform carbon sequestration operations on carbon dioxide associated with oil and gas fields and carbon dioxide transported by carbon dioxide carriers.

[0033] The carbon sequestration operation process on the FPSO / FLNG of this unit is as follows: Figure 4 As shown, the process can be divided into two main steps: collecting carbon dioxide and storing carbon dioxide, as detailed below:

[0034] Collecting carbon dioxide:

[0035] The carbon dioxide in this invention module comes from two sources: one is the associated carbon dioxide from crude oil / natural gas in oil and gas fields; the other is the carbon dioxide delivered by external carbon dioxide transport ships.

[0036] 1.1 Collection of associated carbon dioxide:

[0037] FPSO / FLNG separates carbon dioxide from crude oil / natural gas extracted from oil and gas fields in a carbon dioxide separation unit, separating and storing the carbon dioxide contained in the crude oil / natural gas, thus achieving zero carbon emissions for the FPSO / FLNG itself during the crude oil / natural gas extraction process.

[0038] The specific process involves connecting crude oil or natural gas pipelines to a carbon dioxide separation unit during FPSO / FLNG extraction. The crude oil or natural gas extracted from the oil and gas field passes through the carbon dioxide separation unit, thereby separating the carbon dioxide contained therein.

[0039] The carbon dioxide separation unit uses chemical absorption to separate carbon dioxide from crude oil or natural gas. Monoethanolamine and diethanolamine are used as chemical absorbents. The temperature at the inlet of the carbon dioxide separation unit is controlled at 38°C, and the chemical absorbents absorb carbon dioxide from the crude oil or natural gas. The temperature at the outlet of the carbon dioxide separation unit is controlled at 100°C, and the chemical absorbents release the absorbed carbon dioxide and send it into the pressurization unit.

[0040] The transfer rate of crude oil or natural gas in the pipeline is the same as the transfer rate of associated carbon dioxide. This technical parameter is matched with the capacity of the chemical absorbent in the carbon dioxide separation unit. A rate that is too high will result in insufficient carbon dioxide separation, while a rate that is too low will affect efficiency. In this example, the carbon dioxide transfer rate is 10 m / min. However, the transfer rate should not exceed 20 m / min.

[0041] 1.2 Carbon dioxide transport ships deliver carbon dioxide

[0042] The carbon dioxide carrier is moored alongside the FPSO / FLNG vessel via a side-by-side mooring method. Liquid carbon dioxide from its hold is transferred to the module of this invention via a transfer pump and hose. The receiving and metering unit on this invention receives the liquid carbon dioxide and simultaneously measures it, which serves as the basis for carbon dioxide storage fees. The received liquid carbon dioxide is then sent to the pressurization unit and pressurized to 10 MPa.

[0043] 1.3 Carbon Dioxide Storage

[0044] Associated carbon dioxide and carbon dioxide transported by carbon dioxide carriers enter the pressurization unit. Located in the upper layer of the modular structure of this invention, the pressurization unit receives gaseous carbon dioxide (at atmospheric pressure) from the carbon dioxide separation unit and liquid carbon dioxide (typically at a pressure of 7.3 MPa) from the receiving and metering unit. The pressurization unit pressurizes the received carbon dioxide to 10 MPa, thereby liquefying the gaseous carbon dioxide and increasing the pressure of the liquid carbon dioxide to provide sufficient reserve pressure, preventing vaporization or even explosion of the liquid carbon dioxide in the pipeline due to pressure drop. The pressurized liquid carbon dioxide (initial pressure 10 MPa) is then sent to a carbon dioxide storage tank located in the middle layer for storage.

[0045] The pressure inside the carbon dioxide storage tank must never be less than 7.3 MPa, and should be maintained at around 10 MPa under normal conditions. A temperature sensor is installed inside the tank; when the internal temperature reaches 30°C, an audible and visual alarm is triggered, and the pressurization system is activated to increase the pressure inside the tank, thereby maintaining the carbon dioxide in a liquid state. A small amount of carbon dioxide vaporized into gaseous form is collected in the carbon dioxide storage tank and injected into the pressurization unit. The pressurization unit then pressurizes it to 10 MPa, converting it back into liquid form before returning it to the carbon dioxide storage tank.

[0046] At this point, the carbon dioxide collection operation of the module of this invention is complete.

[0047] Carbon dioxide sequestration:

[0048] Carbon dioxide sequestration requires that the subsea oil and gas field possess the necessary conditions for carbon dioxide sequestration. Carbon dioxide sequestration operations can be carried out at subsea wellheads in two situations: first, when carbon dioxide is needed as an extraction aid during the extraction process; and second, when the wellhead has been completed and can be used as a carbon dioxide sequestration well.

[0049] The two carbon dioxide sequestration conditions described above correspond to two operating scenarios of this invention: one is carbon dioxide sequestration during crude oil or natural gas extraction, achieving the goal of zero carbon emissions from FPSOs or FLNGs during crude oil or natural gas extraction; the other is storing carbon dioxide transported by carbon dioxide carriers using offshore wells.

[0050] When the conditions for carbon dioxide sequestration operations are met in the subsea oil and gas field, a special pump in the carbon dioxide storage tank pumps the liquid carbon dioxide stored inside to the sequestration metering unit.

[0051] The carbon dioxide storage and metering unit receives and measures liquid carbon dioxide from the carbon dioxide storage tank, which serves as a statistical measure of the carbon dioxide storage capacity of this invention. Simultaneously, the difference in pressure between the carbon dioxide stored and metered units after being converted to the same pressure represents the carbon dioxide content in the oil and gas field over a given period. These data can serve as a basis for theoretical research and characterize the carbon dioxide storage capacity of this invention. The metered liquid carbon dioxide then enters the pressurization and heating unit.

[0052] The pressurization and heating unit receives liquid carbon dioxide from the storage and metering unit and pressurizes and heats the liquid carbon dioxide at 10 MPa. The pressure is increased to 20 MPa and the temperature is heated to 60°C. After pressurization and heating, the liquid carbon dioxide is converted into supercritical carbon dioxide, which is in a state between gas and liquid, and then sent to the supercritical carbon dioxide injection unit.

[0053] After receiving supercritical carbon dioxide, the supercritical carbon dioxide injection unit controls the delivery path of the supercritical carbon dioxide through pipelines and valves, and uses a special pump to send the supercritical carbon dioxide into the designated wellhead on the seabed to complete the carbon dioxide sequestration operation.

[0054] At this point, the carbon dioxide storage operation of the module of this invention is completed.

[0055] The above describes the entire operation of a marine carbon sequestration module according to the present invention.

Claims

1. A method for marine carbon sequestration, characterized in that, It has a steel frame, which is mounted on the deck of FPSO or FLNG. The steel frame has three layers: upper, middle and lower. The lower layer is equipped with a safety height D. The middle layer contains a carbon dioxide storage tank. The upper layer is equipped with a carbon dioxide separation unit, a receiving and metering unit, a pressurization unit, a sealing and metering unit, a pressurization and heating unit, and a supercritical carbon dioxide injection unit. The production pipeline of FPSO or FLNG delivers crude oil or natural gas to the carbon dioxide separation unit. The carbon dioxide separation unit sends the separated carbon dioxide to the pressurization unit. The receiving and metering unit receives liquid carbon dioxide transported by carbon dioxide carriers and sends the received liquid carbon dioxide to the pressurization unit. The pressurization unit pressurizes the received liquid carbon dioxide to 10MPa and then sends it to the carbon dioxide storage tank for storage. The carbon dioxide storage tank sends gaseous carbon dioxide back to the pressurization unit. The sealing and metering unit is connected to the carbon dioxide storage tank. The sealing and metering unit sends liquid carbon dioxide to the pressurization and heating unit. After being heated and pressurized, the liquid carbon dioxide is converted into supercritical carbon dioxide and sent to the supercritical carbon dioxide injection unit. The supercritical carbon dioxide injection unit sends the supercritical carbon dioxide into the seabed wellhead through pipelines. One end of the carbon dioxide separation unit is connected to the extraction pipeline of FPSO or FLNG, and the other end is connected to the pressurization unit through a pipeline. One end of the receiving and metering unit is connected to the carbon dioxide transport ship, and the other end is connected to the pressurization unit. The pressurization unit is connected to the carbon dioxide storage tank, the sealing and metering unit, the pressurization and heating unit, and the supercritical carbon dioxide injection unit in sequence through pipelines. The carbon dioxide storage tank is equipped with a loop leading to the pressurization unit. The carbon dioxide separation unit is equipped with monoethanolamine and diethanolamine, which act as chemical absorbents to absorb carbon dioxide from crude oil or natural gas. The inlet temperature of the carbon dioxide separation unit is 38℃, and the outlet temperature is 100℃.

2. The method for marine carbon sequestration according to claim 1, characterized in that, The carbon dioxide storage tank is connected to the modular structure via a semi-circular saddle, with the saddle angle between 120° and 180°.

3. The method for marine carbon sequestration according to claim 1, characterized in that, The carbon dioxide storage tank is equipped with a dedicated pump to pump liquid carbon dioxide from the storage tank to the sealing and metering unit.

4. A method for marine carbon sequestration according to claim 1, characterized in that, The carbon dioxide storage tank has a pressure greater than 7.3 MPa and will issue an audible and visual alarm when the internal temperature reaches 30°C, while simultaneously activating the pressurization system to increase the internal pressure.

5. A method for marine carbon sequestration according to claim 1, characterized in that, The heating temperature of the pressurized heating unit is 60℃, and the pressurization pressure is 20MPa.

6. A method for marine carbon sequestration according to claim 1, characterized in that, When the steel frame is mounted on the FPSO deck, the safety height D shall not be less than 3 meters; when the steel frame is mounted on the FLNG deck, the safety height shall not be less than 6 meters.

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