Offshore carbon sequestration method

Abstract

An offshore carbon sequestration method comprises the steps that a steel frame is arranged and carried on a deck of an FPSO or FLNG, a production pipeline of the FPSO or FLNG conveys crude oil or natural gas to a carbon dioxide separation unit, the carbon dioxide separation unit conveys separated carbon dioxide to a pressurization unit, and a receiving and metering unit receives liquid carbon dioxide conveyed by a carbon dioxide conveying ship and conveys the liquid carbon dioxide to a carbon dioxide storage unit; the receiving unit receives liquid carbon dioxide and sends the received liquid carbon dioxide to the pressurizing unit, the pressurizing unit pressurizes the received liquid carbon dioxide to 10MPa and then sends the liquid carbon dioxide into a carbon dioxide storage tank for storage, the sealing and metering unit sends the liquid carbon dioxide to the pressurizing and heating unit, and the liquid carbon dioxide is converted into supercritical carbon dioxide after being heated and pressurized. And the supercritical carbon dioxide is fed into a subsea wellhead through a pipeline. The device is high in adaptability, wide in application range and flexible to install, seabed oil wells and related pipelines are utilized to the maximum degree, and the economical efficiency and safety of offshore carbon sequestration operation are improved.

Description

Technical Field

[0001] The present invention belongs to the field of offshore ship design and construction, and specifically relates to an offshore carbon sequestration method. Background Art

[0002] Compared with terrestrial carbon storage, offshore carbon storage has the following advantages: the barrier of seawater pressure and rock cover makes it more sealed and safer; the seabed reservoirs that can be used for carbon storage are widely distributed, have great application potential, and are easy to select storage sites; seabed storage is not only far away from freshwater aquifers, but also far away from human settlements, with less local risks and greater environmental friendliness; using abandoned offshore oil fields for carbon storage can significantly reduce the comprehensive cost of corresponding geological surveys and drilling and mining.

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

[0004] At present, the research on offshore CCUS focuses more on the process methods of carbon sequestration. Patent CN219655826U discloses a same-well injection and extraction system for storing carbon dioxide in seabed saline layers; Patent CN114278257A discloses a synchronous device and method for offshore oil field exploitation 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, mentioning the storage of carbon dioxide in old oil fields, but the patent does not mention how to open old oil fields that have been abandoned and sealed.

[0006] To store CO2 offshore in old oil fields, it is necessary to drill new wells in old offshore oil fields that have been sealed, which greatly increases the cost of carbon storage. At the same time, the pressure, composition, geology, etc. in old oil fields are all unstable to a certain extent. Reopening old oil wells may cause accidents such as wellhead collapse or liquid (gas) eruption in the well.

[0007] The safest and most ideal way to store offshore carbon dioxide is to exploit offshore oil and gas fields while storing carbon dioxide. Offshore oil and gas exploitation and carbon dioxide storage complement each other and are carried out simultaneously. Currently, there is no patent disclosing a floating device for this type of operation mode. Summary of the invention

[0008] In order to solve the above problems, the present invention provides an offshore carbon storage method, the technical solution adopted by the present invention is: A method for offshore carbon storage comprises a steel frame which is mounted on the deck of an FPSO or FLNG. The steel frame comprises three layers: an upper layer, a middle layer and a lower layer. The lower layer is not provided with any equipment, and the safety height of the lower layer space is D. A carbon dioxide storage tank is arranged in the middle layer space; a carbon dioxide separation unit, a receiving and metering unit, a pressurizing unit, a storage and metering unit, a pressurizing and heating unit, and a supercritical carbon dioxide injection unit are arranged in the upper layer space.

[0009] The production pipeline of FPSO or FLNG delivers crude oil or natural gas to the carbon dioxide separation unit, the carbon dioxide separation unit delivers the separated carbon dioxide to the pressurizing unit, the receiving and metering unit receives the liquid carbon dioxide delivered by the carbon dioxide transport ship, and delivers the received liquid carbon dioxide to the pressurizing unit. The pressurizing 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 the gaseous carbon dioxide back to the pressurizing unit.

[0010] The sealing and metering unit is connected to the carbon dioxide storage tank. The sealing and metering unit sends the liquid carbon dioxide to the pressurization and heating unit. The liquid carbon dioxide is converted into supercritical carbon dioxide after heating and pressurization, 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 a pipeline.

[0011] The above-mentioned offshore carbon storage method, further, one end of the carbon dioxide separation unit is connected to the production pipeline of FPSO or FLNG, and the other end is connected to the pressurization unit through the pipeline, one end of the receiving 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 storage metering unit, the pressurization heating unit, and the supercritical carbon dioxide injection unit in sequence through the pipeline, and the carbon dioxide storage tank is provided with a loop leading to the pressurization unit.

[0012] The above-mentioned offshore carbon storage method, further, 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.

[0013] In the above-mentioned offshore carbon sequestration method, further, the carbon dioxide storage tank is connected to the module structure through a semicircular saddle, and the saddle angle is 120°≤≤180°.

[0014] In the above-mentioned offshore carbon sequestration method, further, a special pump is provided in the carbon dioxide storage tank for pumping liquid carbon dioxide out of the carbon dioxide storage tank to the sequestration metering unit.

[0015] In the above-mentioned offshore carbon sequestration method, further, the pressure of the carbon dioxide storage tank is greater than 7.3MPa.

[0016] In the above-mentioned offshore carbon storage method, further, the heating temperature of the pressurization heating unit is 60° C. and the pressurization pressure is 20 MPa.

[0017] In the above-mentioned offshore carbon sequestration method, further, monoethanolamine and diethanolamine are arranged in the carbon dioxide separation unit, and the monoethanolamine and diethanolamine are used as chemical absorbents to absorb carbon dioxide in crude oil or natural gas.

[0018] In the above-mentioned offshore carbon sequestration method, further, the temperature at the inlet of the carbon dioxide separation unit is 38°C, and the temperature at the outlet is 100°C.

[0019] The beneficial effects of the present invention are: 1. It can be carried on FPSO and FLNG, with strong adaptability, wide application and flexible installation.

[0020] 2. It has achieved the simultaneous development of crude oil production and carbon dioxide storage, maximizing the utilization of submarine oil wells and related pipelines, and improving the economic efficiency of offshore carbon storage operations.

[0021] 3. It avoids the risks brought by secondary drilling of abandoned oil wells and improves the safety of offshore carbon storage operations.

[0022] 4. During the crude oil (natural gas) extraction process, carbon dioxide can be injected into the oil field to increase the pressure of the oil field (gas field), so that the carbon dioxide injection can assist the crude oil (natural gas) extraction at the same time, so that the crude oil (natural gas) extraction operation and the carbon dioxide injection operation complement each other, further improving the economy of the entire device. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a side view of the present invention; Figure 2 is a top view of the present invention; Figure 3 It is a front view of the present invention; Figure 4 It is the operation flow chart of the present invention; Figure 5 It is a side view of the module structure of the present invention.

[0024] Among them: 1-module structure, 2-carbon dioxide storage tank, 3-carbon dioxide separation unit, 4-receiving metering unit, 5-pressurization unit, 6-storage metering unit, 7-pressurization 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 DESCRIPTION

[0025] The present invention will be further described in conjunction with the accompanying drawings.

[0026] The present invention provides an offshore carbon storage module, such as Figure 1 , Figure 2 , Figure 3 As shown, the device of the present invention is installed on FPSO / FLNG. While exploiting crude oil / natural gas, it utilizes existing oil and gas wells to perform carbon sequestration operations on carbon dioxide associated with the oil and gas fields and carbon dioxide transported by carbon dioxide transport ships.

[0027] The carbon storage operation process of this device on FPSO / FLNG is as follows Figure 4 As shown, it can be divided into two major steps: collecting carbon dioxide and storing carbon dioxide, as follows: Collecting Carbon Dioxide: The carbon dioxide in the module of the present invention comes from two sources: one is the associated carbon dioxide of crude oil / natural gas in the oil and gas field; the other is the carbon dioxide delivered by external carbon dioxide transport ships.

[0028] 1.1 Collection of associated carbon dioxide: FPSO / FLNG performs carbon dioxide separation operations in the carbon dioxide separation unit on the crude oil / natural gas extracted from the oil and gas fields, separates the carbon dioxide contained in the crude oil / natural gas and seals it, thus achieving zero carbon emissions from the FPSO / FLNG itself during the crude oil / natural gas extraction process.

[0029] The specific process is that during the FPSO / FLNG exploitation process, the crude oil or natural gas pipeline is connected to the carbon dioxide separation unit, and the crude oil or natural gas extracted from the oil and gas field passes through the carbon dioxide separation unit to separate the carbon dioxide contained therein.

[0030] 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 absorbent absorbs carbon dioxide in crude oil or natural gas; the temperature at the outlet of the carbon dioxide separation unit is controlled at 100°C, and the chemical absorbent releases the absorbed carbon dioxide and sends it to the booster unit.

[0031] The transmission rate of crude oil or natural gas in the crude oil or natural gas pipeline is the transmission rate of associated carbon dioxide. This technical parameter matches the capacity of the chemical absorbent in the carbon dioxide separation unit. Too fast a rate will cause insufficient separation of carbon dioxide, and too slow a rate will affect efficiency. In this example, the carbon dioxide transmission rate is 10m / min. In any case, the transmission rate should not exceed 20m / min.

[0032] 1.2 CO2 transport by CO2 carrier The carbon dioxide transport ship is moored to the side of the FPSO / FLNG by berthing, and the liquid carbon dioxide in its cabin is transported to the module of the present invention by a transfer pump and a hose. The receiving and metering unit of the present invention receives the liquid carbon dioxide and measures the liquid carbon dioxide as the basis for charging for carbon dioxide storage. The received liquid carbon dioxide will be sent to the increasing unit and pressurized to 10Mpa.

[0033] 1.3 Carbon dioxide storage The associated carbon dioxide and the carbon dioxide transported by the carbon dioxide transport ship enter the boosting unit. The boosting unit is located in the upper layer of the modular structure of the present invention, and receives gaseous carbon dioxide (normal pressure) from the carbon dioxide separation unit and liquid carbon dioxide (usually with a pressure value of 7.3MPa) from the receiving metering unit. The boosting unit boosts the received carbon dioxide to 10MPa, thereby liquefying the gaseous carbon dioxide and increasing the pressure of the liquid carbon dioxide so that it has sufficient reserve pressure to prevent the liquid carbon dioxide from gasifying due to pressure drop in the pipeline, or even exploding. The pressurized liquid carbon dioxide (initial pressure 10MPa) is sent to the carbon dioxide storage tank located in the middle layer for storage.

[0034] The pressure in the carbon dioxide storage tank shall not be less than 7.3MPa at any time, and should be maintained at about 10MPa under normal conditions. A temperature sensor is installed in the tank. When the temperature in the tank reaches 30°C, an audible and visual alarm is issued, and the pressurization system is started to increase the pressure in the tank, thereby keeping the carbon dioxide in a liquid state. A small amount of carbon dioxide that is vaporized into gas is collected in the carbon dioxide storage tank and injected into the booster unit. After being pressurized to 10MPa by the booster unit and converted into liquid, it returns to the carbon dioxide storage tank.

[0035] At this point, the module of the present invention completes the collection of carbon dioxide.

[0036] Storing CO2: The storage of carbon dioxide requires that the subsea oil and gas fields meet the conditions for carbon dioxide storage. There are two situations in which the subsea wellhead can be used for carbon dioxide storage: one is when carbon dioxide is needed as a production aid during the production process at the subsea wellhead; the other is when the subsea wellhead is used as a carbon dioxide storage well after the production is completed.

[0037] The above two carbon dioxide storage conditions correspond to two working conditions of the present invention, namely: one is the carbon dioxide storage in the process of crude oil or natural gas extraction, which realizes the goal of zero carbon emission in the process of crude oil or natural gas extraction by FPSO or FLNG; the other is to use the empty seabed well to store the carbon dioxide transported by the carbon dioxide transport ship.

[0038] When the subsea oil and gas field is ready for carbon dioxide storage operations, a dedicated pump in the carbon dioxide storage tank pumps the liquid carbon dioxide stored in it out to the storage metering unit.

[0039] The storage metering unit receives liquid carbon dioxide from the carbon dioxide storage cabin and measures it as the statistics of the carbon dioxide storage amount of the module of the present invention. At the same time, the difference between the carbon dioxide after pressure conversion between the storage metering unit and the receiving metering unit is the content of carbon dioxide in the oil and gas field over a period of time. These data can be used as the basis for theoretical research and the characterization of the carbon dioxide storage capacity of the present invention. The measured liquid carbon dioxide enters the pressurization heating unit.

[0040] The pressurization and heating unit receives liquid carbon dioxide from the storage and metering unit and performs pressurization and heating operations on 10Mpa liquid carbon dioxide. The pressure is increased to 20MPa and the temperature is heated to 60°C. After pressurization and heating, the liquid carbon dioxide is converted into supercritical carbon dioxide between gas and liquid and sent to the supercritical carbon dioxide injection unit.

[0041] After receiving the 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 deliver the supercritical carbon dioxide to the designated wellhead on the seabed to complete the carbon dioxide storage operation.

[0042] At this point, the module of the present invention completes the storage operation of carbon dioxide.

[0043] The above is the entire operation of an offshore carbon storage module of the present invention.

Claims

1. An offshore carbon storage method, characterized in that: There is a steel frame, which is carried on the deck of FPSO or FLNG. The steel frame has three layers: upper, middle and lower. The lower layer is provided with a safety height D, and the middle layer is provided with a carbon dioxide storage tank; the upper layer is provided with a carbon dioxide separation unit, a receiving and metering unit, a pressurizing unit, a sealing and metering unit, a pressurizing 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, and the carbon dioxide separation unit delivers the separated carbon dioxide to the boosting unit. The receiving and metering unit receives the liquid carbon dioxide delivered by the carbon dioxide transport ship and delivers the received liquid carbon dioxide to the boosting unit. The boosting unit pressurizes the received liquid carbon dioxide to 10MPa and then delivers it to the carbon dioxide storage tank for storage. The carbon dioxide storage tank delivers the gaseous carbon dioxide back to the boosting unit. The sealing and metering unit is connected to the carbon dioxide storage tank. The sealing and metering unit sends the liquid carbon dioxide to the pressurization and heating unit. The liquid carbon dioxide is converted into supercritical carbon dioxide after heating and pressurization, 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 a pipeline.

2. The offshore carbon storage method according to claim 1, characterized in that: One end of the carbon dioxide separation unit is connected to the production pipeline of FPSO or FLNG, and the other end is connected to the boosting unit through a pipeline. One end of the receiving metering unit is connected to the carbon dioxide transport ship, and the other end is connected to the boosting unit. The boosting unit is connected to the carbon dioxide storage tank, the sealing metering unit, the boosting heating unit, and the supercritical carbon dioxide injection unit in sequence through pipelines. The carbon dioxide storage tank is provided with a loop leading to the boosting unit.

3. The offshore carbon sequestration method according to claim 1, characterized in that: The carbon dioxide storage tank is connected to the module structure through a semicircular saddle, and the saddle angle is 120°≤≤180°.

4. The offshore carbon storage method according to claim 1, characterized in that: A special pump is provided in the carbon dioxide storage tank to pump liquid carbon dioxide out of the carbon dioxide storage tank to the sealing and metering unit.

5. The offshore carbon storage method according to claim 1, characterized in that: The pressure of the carbon dioxide storage tank is greater than 7.3MPa, and when the temperature inside the tank reaches 30℃, an audible and visual alarm will be issued, and the pressurization system will be started to increase the pressure inside the tank.

6. The offshore carbon storage method according to claim 1, characterized in that: The heating temperature of the pressurizing and heating unit was 60°C, and the pressurizing pressure was 20 MPa.

7. The offshore carbon storage method according to claim 1, characterized in that: Monoethanolamine and diethanolamine are arranged in the carbon dioxide separation unit, and the monoethanolamine and diethanolamine are used as chemical absorbents to absorb carbon dioxide in crude oil or natural gas.

8. The offshore carbon storage method according to claim 1, characterized in that: The temperature at the inlet of the carbon dioxide separation unit was 38°C and the temperature at the outlet was 100°C.

9. The offshore carbon sequestration method 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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