Carbon dioxide injection

Abstract

A method of injecting carbon dioxide into an offshore injection well (4), the method comprising: storing carbon dioxide within a plurality of storage conduits (103) of an offshore storage facility (1); and injecting the stored carbon dioxide into the injection well (4).

Description

TECHNICAL FIELD

[0001] The present invention relates to a method of injecting carbon dioxide into an offshore or subsea injection well, and to an offshore storage facility configured to store carbon dioxide and subsequently inject it into an offshore or subsea injection well. BACKGROUND ART

[0002] Injection is a process that can be used to maintain or increase the pressure within a hydrocarbon-producing reservoir, thereby allowing or improving the production of hydrocarbons from the reservoir. A known form of injection relies on injecting carbon dioxide (CO 2 ) into the reservoir via one or more injection wells. Carbon dioxide is an injection agent with significant advantages, as it is readily available and thus inexpensive, and it also has the additional effect of reducing the viscosity of oil, which makes it easier to produce hydrocarbons.

[0003] The injection of carbon dioxide can also be a useful climate solution, as carbon dioxide that might otherwise be emitted into the environment can be stored long-term in the reservoir or other subsea geological formations into which it has been injected. Thus, the well-known harmful effects that might result from the emission of carbon dioxide into the environment can be avoided.

[0004] A known method of injecting carbon dioxide into an offshore injection well involves a vessel (i.e., a tanker) loaded with carbon dioxide traveling to the site of the injection well. The carbon dioxide is then unloaded from the vessel and injected into the well. Once the carbon dioxide is depleted, the vessel leaves the injection site to continue bringing in carbon dioxide.

[0005] The problem with this known method is that the injection is discontinuous (i.e., it only occurs when the vessel is located at the site of the offshore injection well). Since the unloading of carbon dioxide from the vessel occurs over a relatively short period of time, it also involves a high flow rate of carbon dioxide, which in turn means that the process involves high pressures and thus requires high design pressures, which is not ideal.

[0006] For example, an alternative method of injecting into an offshore injection well is known from the applicant's own "Northern Lights" project (https: / / www.equinor.com / energy / northern-lights). Instead of a vessel traveling to the offshore site of the injection well, an onshore (i.e., land-based) storage facility is connected to the offshore injection well via a subsea pipeline. The pipeline enables carbon dioxide to flow from the storage facility to the offshore injection well for injection there. The storage facility stores carbon dioxide in large containers (storage tanks) under ambient pressure conditions and at a temperature significantly lower than ambient temperature. Compared to those methods based on transport vessels, the advantage of this method is that the injection does not have to be discontinuous because the pipeline can continuously transport carbon dioxide to the injection well while the storage facility provides a continuous feed of carbon dioxide. Additionally, given the continuous presence of the pipeline, the high flow rates and pressures associated with methods relying on transport vessels can be avoided.

[0007] There is still a need for further alternative methods and devices for injecting carbon dioxide into an offshore injection well. Summary of the Invention

[0008] According to a first aspect of the present invention, there is provided a method of injecting carbon dioxide into an offshore injection well, the method comprising: storing carbon dioxide in a plurality of storage pipelines of an offshore storage facility; and injecting the stored carbon dioxide into the injection well.

[0009] The method of the first aspect provides advantages over known prior art methods that rely on transport vessels to transport carbon dioxide and directly unload it into the injection well. Notably, this is because the problems associated with discontinuous injection and the high flow rate / pressure associated with such prior art methods can be avoided using the method of the first aspect. Since the offshore storage facility is effectively permanently connected to the injection well, it can supply carbon dioxide continuously to the injection well, thereby avoiding the high pressures associated with discontinuous supply.

[0010] Furthermore, compared to these known prior art methods that rely on transport vessels, the method of the first aspect has advantages in reducing operational and infrastructure requirements, which in turn reduces the costs of operation and infrastructure. Importantly, the method of the first aspect does not require transport vessels to frequently travel to the site of the injection well (or at least significantly reduces the frequency with which transport vessels must travel to the site of the injection well / offshore storage facility), thereby avoiding or reducing the significant operational costs associated therewith. Similarly, the method of the first aspect avoids the need for high design pressures as discussed above, thereby avoiding the significant infrastructure requirements associated with such high design pressures.

[0011] The method of the first aspect also has advantages over the injection schemes known from the applicant's own "Aurora Borealis" project, especially for scenarios where the injection well is located in a remote location, in a "hard-to-reach" location or at a relatively long distance from an established onshore carbon dioxide storage facility. In such scenarios, given the "remoteness" of the injection well described above, it may be technically and / or commercially infeasible to provide pipelines connected to the injection well, but a marine storage facility of the type defined in the first aspect of the present invention can feasibly be used to allow injection at the well described above.

[0012] The carbon dioxide to be stored and subsequently injected can have been captured from a carbon dioxide production source (such as a chemical plant or other industrial plant, a gas-fired power plant or power source, a coal-fired power plant or power source, etc.) before it is emitted into the environment / atmosphere. Alternatively, the carbon dioxide can have been captured directly from the atmosphere. Thus, the method of the first aspect can include, optionally, capturing carbon dioxide from a carbon dioxide production source or the environment before the step of storing the carbon dioxide. This step of capturing carbon dioxide can be carried out at a carbon capture facility, which can be onshore (land-based) or offshore. These optional features of the present invention have significant environmental benefits.

[0013] From the above discussion, it can be seen that a marine storage facility can be provided at the site of the injection well. That is to say, a marine storage facility can be provided near the injection well (i.e., in a position very close to the injection well). Thus, the marine storage facility can be considered to be combined with and / or paired with the injection well. Referring to the lateral direction (i.e., the direction aligned with the sea level and / or the seabed), the marine storage facility can be located within 2 km of the injection well. Optionally, referring to the lateral direction (i.e., the direction aligned with the sea level and / or the seabed), the marine storage facility can be located within 1 km, 500 m, 400 m, 300 m, 200 m or 100 m of the injection well. The marine storage facility can effectively be located above the injection well.

[0014] As described above, a marine storage facility can provide an effectively continuous supply of carbon dioxide to an offshore injection well. Thus, the total storage capacity of the marine storage facility (i.e., the total storage capacity provided by the storage pipeline) can be able to meet the injection requirements of the offshore injection well over a relatively long period of time (such as at least 1 week, 1 month, 6 months, 1 year, 5 years or optionally even longer). The total storage capacity of the marine storage facility (i.e., the total storage capacity provided by the storage pipeline) can be, for example, 10,000 m 3 、30,000 m 3 、100,000 m 3 , or optionally even larger.

[0015] An offshore injection well can also be referred to as a subsea injection well or an offshore / subsea injection well.

[0016] As mentioned above, the offshore injection well may be located in a remote location and / or at a relatively long distance from land and / or at a relatively long distance from any established carbon dioxide storage infrastructure other than the offshore storage facility of the present invention (such as an onshore carbon dioxide storage facility). The relatively long distance may refer to a distance at which it would be technically and / or commercially infeasible to provide a pipeline from the land / established infrastructure to the offshore injection well. In a particular context, those skilled in the art will readily understand what distance constitutes such a distance. For example, the injection well may be located at a distance of more than 60 km from the land and / or the established infrastructure, optionally more than 100 km, and further optionally more than 200 km.

[0017] The injection well may communicate with a hydrocarbon reservoir. The hydrocarbon reservoir may be a hydrocarbon-producing reservoir, i.e., a hydrocarbon-producing reservoir from which hydrocarbons are being or will be produced. Injection into the well may maintain or increase the pressure within the hydrocarbon reservoir. This may allow or improve the production of hydrocarbons from the hydrocarbon reservoir via, for example, a hydrocarbon production system.

[0018] This combination of features is considered to be particularly advantageous. Thus, according to a second aspect of the present invention, there is provided a method of operating a hydrocarbon production system, the method comprising: injecting carbon dioxide into an offshore injection well according to the first aspect of the present invention, wherein the offshore injection well is connected to a hydrocarbon reservoir; and producing hydrocarbons from the hydrocarbon reservoir using the hydrocarbon production system.

[0019] Using carbon dioxide as an injectant in the second aspect of the present invention has a synergistic effect of supporting hydrocarbon production and avoiding carbon dioxide emissions into the environment.

[0020] Producing hydrocarbons from the hydrocarbon reservoir may be carried out in a conventional manner and may use conventional production equipment and / or devices.

[0021] An optional hydrocarbon production system may include a hydrocarbon production facility. The hydrocarbon production facility may include a hydrocarbon production platform, such as an unmanned hydrocarbon production platform or a floating production, storage and offloading unit (FPSO).

[0022] The injection well may form part of the hydrocarbon production system or the hydrocarbon production facility. Thus, the hydrocarbon production system or the hydrocarbon production facility may include the injection well. The hydrocarbon production system or the hydrocarbon production facility may include one or more additional injection wells, such as the additional injection wells described below.

[0023] A hydrocarbon production system is a system specifically configured for producing and / or processing hydrocarbons (such as oil, natural gas, etc.). Thus, a hydrocarbon production system (such as a hydrocarbon production facility) may include a certain degree of production equipment and / or a certain degree of processing equipment, the processing equipment being configured for processing or partially processing the produced hydrocarbons.

[0024] A hydrocarbon production system and / or hydrocarbon production facility may be provided at the site of an injection well and / or a marine storage facility. That is, a hydrocarbon production system and / or hydrocarbon production facility may be provided near the injection well and / or the marine storage facility (i.e., at a location very close to the injection well and / or the marine storage facility). Thus, the hydrocarbon production system and / or hydrocarbon production facility may be considered to be combined and / or paired with the injection well and / or the marine storage facility. Referring to the lateral direction (i.e., the direction aligned with the sea level and / or the seabed), the hydrocarbon production system and / or hydrocarbon production facility may be located within a range of 2 km of the injection well and / or the marine storage facility. Optionally, referring to the lateral direction (i.e., the direction aligned with the sea level or the seabed), the hydrocarbon production system and / or hydrocarbon production facility may be located within a range of 1 km, 500 m, 400 m, 300 m, 200 m, or 100 m of the injection well and / or the marine storage facility. The hydrocarbon production system and / or hydrocarbon production facility may be effectively located above the injection well.

[0025] However, it is not required that the injection well be connected to a hydrocarbon reservoir. Instead of a hydrocarbon reservoir, the injection well may communicate with an alternative geological formation (i.e., not a hydrocarbon reservoir or at least not a hydrocarbon-producing reservoir, such as a hydrocarbon storage reservoir whose hydrocarbons have been depleted previously). Thus, the injection of carbon dioxide may not be used to support hydrocarbon production, but only as a way to store carbon dioxide underground.

[0026] The method of the first aspect may include injecting carbon dioxide into a plurality of offshore injection wells. Thus, the method may include storing carbon dioxide in a plurality of storage pipelines of a marine storage facility; and injecting the stored carbon dioxide into the plurality of injection wells. Each of the plurality of injection wells may be consistent with the injection well described above.

[0027] The step of storing carbon dioxide in a plurality of storage pipelines of a marine storage facility may include storing carbon dioxide as a liquid (i.e., liquefied carbon dioxide). Thus, the method may include the step of liquefying carbon dioxide before storing it in the plurality of storage pipelines of the marine storage facility. This liquefaction step may be carried out at the marine storage facility before the step of storing carbon dioxide in the plurality of storage pipelines of the marine storage facility (i.e., as a pre-step of the step of storing carbon dioxide in the plurality of storage pipelines of the marine storage facility). Alternatively, carbon dioxide may be liquefied before it reaches the marine storage facility. That is, carbon dioxide may have been transported to the marine storage facility as a liquid, for example, via a transport ship (this alternative feature will be introduced in detail below).

[0028] The step of injecting stored carbon dioxide may include (optionally using a pump) injecting carbon dioxide as a liquid. Injecting liquid carbon dioxide using a pump has advantages in terms of efficiency because using a pump is more efficient than using a compressor, which is typically used to inject gaseous carbon dioxide.

[0029] Optionally, the method may include storing carbon dioxide as a liquid in a plurality of storage pipes of an offshore storage facility under ambient temperature conditions. Accordingly, the method may also include liquefying carbon dioxide under ambient temperature conditions prior to storage. Those skilled in the art will understand that storing liquefied carbon dioxide under ambient temperature conditions requires pressurizing carbon dioxide at a pressure far above ambient pressure conditions, and the exact pressure conditions are determined by the specific ambient temperature at which the carbon dioxide is stored.

[0030] Conventionally, the liquefaction and storage of carbon dioxide as a liquid is carried out under ambient pressure conditions and thus, as those skilled in the art will understand, at very cold temperature conditions significantly below ambient temperature conditions. However, in the context of the present invention, while possible, storing carbon dioxide at temperature conditions significantly below ambient temperature conditions is less advantageous. This is because at such temperature and ambient pressure conditions, producing and maintaining liquid carbon dioxide has considerable complexity as well as operational and capital expenditures associated with the required equipment, personnel, and processes. In an offshore scenario, limited space also means that providing the necessary infrastructure for storing liquefied carbon dioxide under ambient pressure conditions may not be feasible.

[0031] Accordingly, in the context of the present invention in the above aspects, storing liquid carbon dioxide under ambient temperature conditions is considered particularly advantageous (although optional). As described above, this requires carbon dioxide to be pressurized at pressure conditions far above ambient conditions; however, the required pressurization is associated with significantly reduced complexity as well as operational and capital expenditures in terms of the equipment, personnel, and processes involved, and is thus particularly suitable for an offshore scenario.

[0032] The ambient temperature conditions may be a temperature between 0 - 25 °C. Accordingly, the pressure required to store liquefied carbon dioxide may be between 34 barg - 45 barg, and the exact pressure required is determined by the ambient temperature.

[0033] The term "storage pipe" refers to a storage container formed by a length of pipe that has been closed at each end, optionally by, for example, a hemispherical cap or dome that has been welded to the ends of the pipe. Accordingly, the storage pipe is highly elongated and typically has a length - diameter ratio of at least 20.

[0034] Using storage pipelines as the basis for storage in an offshore storage facility is advantageous compared to, for example, traditional tank storage (i.e., container storage), as it is associated with significantly reduced capital and operating expenditures, particularly in the alternative context of storing liquid carbon dioxide at high pressures and ambient temperature conditions.

[0035] Typical "tank" - type storage solutions require tanks with thick steel walls. The provision cost of these tanks is very high (considering the large amount of material usually required), and given their weight (again considering the large amount of material required), the transportation cost to their location of use is also high. The required wall thickness (and thus the weight of the tank) also limits the size of the tanks that can be used, meaning the volume of carbon dioxide stored therein is limited.

[0036] In contrast, providing pipeline storage is relatively inexpensive because standard "off - the - shelf" pipelines can be used to fabricate them. Additionally, for a given storage volume, pipeline storage can have a relatively small wall thickness. Thus, with pipeline storage, a relatively lower total weight of storage tank material can be used to store a given volume of carbon dioxide, which can thus be achieved with lower capital expenditure. Therefore, pipeline storage is a more feasible solution.

[0037] Each of the storage pipelines can have a nominal diameter between 40 - 60 inches (1.0m - 1.5m). Preferably, each pipeline can have a nominal size of 42 inches (1.1m) or 56 inches (1.4m), or can have any nominal size within the range of 42 inches (1.1m) to 56 inches (1.4m).

[0038] Vessels with a nominal diameter greater than approximately 56 - 60 inches (1.4m - 1.5m) are generally regarded by those skilled in the art as conventional storage tanks (or pressure vessels) distinct from pipelines. This consideration also holds in the context of the present application, and thus any vessel with a nominal diameter greater than approximately 56 - 60 inches (1.4m - 1.5m) will not be regarded as a pipeline.

[0039] According to the API SPEC 5L specification, the storage pipelines can be or have X52, X56, X60, X65, X70, or X80 pipes.

[0040] As described above, the storage pipelines are highly slender. Thus, each storage pipeline can have a length between 10m and 30m, such as 12m, 24m, or 26m.

[0041] The storage pipelines can be formed from rolled tubes (optionally having a single longitudinal seam). Such pipelines are typically "off - the - shelf" type components and are generally inexpensive.

[0042] The storage pipeline can be configured to store carbon dioxide at high pressure, such as storing liquefied carbon dioxide under ambient temperature conditions. The storage pipeline can be configured to store carbon dioxide between 34 barg and 45 barg. The exact pressurization conditions at which the storage pipeline is configured to store carbon dioxide can be selected based on the ambient temperature at which the carbon dioxide (optionally as a liquid) is to be stored, the tolerances of the storage pipeline, and / or the tolerances of the equipment used to load and unload carbon dioxide into and out of the storage pipeline.

[0043] Each of the storage pipelines can be arranged vertically (i.e., the main axis of the storage pipeline can be arranged vertically or substantially vertically) or horizontally (i.e., the main axis of the storage pipeline can be arranged horizontally or substantially horizontally). The storage pipelines can include a combination of horizontally arranged storage pipelines and vertically arranged storage pipelines. Each or some of the storage pipelines can be arranged in any other orientation between horizontal and vertical.

[0044] A particularly advantageous but optional combination of features consists of using the storage pipeline to store liquefied carbon dioxide under the ambient temperature conditions of an offshore storage facility. This combination of features provides a cheap, simple, and technically non-challenging method for storing liquid carbon dioxide under ambient temperature conditions, which is superior to other storage options.

[0045] The method can include transporting carbon dioxide to the site of an offshore storage facility. The method can subsequently include the step of transferring the carbon dioxide to the offshore storage facility.

[0046] The step of transporting carbon dioxide to the site of an offshore storage facility can include transporting carbon dioxide from a carbon capture facility. The carbon capture facility can be located on land (i.e., land-based) or offshore.

[0047] The step of transporting carbon dioxide to the site of an offshore storage facility can include transporting the carbon dioxide as a liquid (i.e., liquefied carbon dioxide), optionally as a liquid under ambient temperature conditions. The step of transferring the carbon dioxide to the offshore storage facility can include transferring the carbon dioxide as a liquid (i.e., liquefied carbon dioxide), optionally as a liquid under ambient temperature conditions. Thus, the (optional) step of liquefying the carbon dioxide, optionally under ambient temperature conditions, can be carried out before transporting the carbon dioxide to the site of the offshore storage facility.

[0048] The transportation step can be achieved using a transportation vessel (such as a ship) that includes a storage device for carbon dioxide.

[0049] The storage device of the transportation vessel can be, for example, a second plurality of storage pipelines. The second plurality of storage pipelines can correspond to the storage pipelines provided at the offshore storage facility as described above, and optionally can be consistent with any compatible optional features of the storage pipelines provided at the offshore storage facility as described above.

[0050] The step of transferring carbon dioxide to the offshore storage facility can include transferring carbon dioxide from the transportation vessel to the offshore storage facility. This can include the use of unloading equipment (e.g., including conduits, pumps, compressors, etc.), which can be configured to keep carbon dioxide in a liquid state under ambient temperature conditions by maintaining carbon dioxide at the necessary pressure.

[0051] The offshore storage facility can be regarded as an intermediate storage facility and / or a buffer storage facility. That is, the offshore storage facility can serve as a temporary storage / buffer for supplying carbon dioxide to the injection well, optionally after the carbon dioxide has been transferred from the transportation vessel to the offshore storage facility.

[0052] The offshore storage facility can be a single, independent unit, such as a single modular unit. The offshore storage facility can be independent, separate, and separable from, for example, the injection well, an optional hydrocarbon production system, an optional hydrocarbon facility, an optional transportation vessel, etc.

[0053] The offshore storage facility can be an offshore floating storage facility. For example, the offshore storage facility can take the form of a floating platform, such as a spar platform, a tension leg platform, a semi-submersible platform, etc. Alternatively, the offshore storage facility can also take the form of a spar buoy or a vessel (e.g., a ship or a barge). The offshore storage facility can include a ship-shaped hull, such as a modified hull.

[0054] Alternatively, the offshore storage facility can be a fixed offshore storage facility (i.e., non-floating). For example, the offshore storage facility can take the form of a fixed platform, a jack-up platform, a jacket platform, a gravity-based platform, etc. The storage pipelines of the fixed offshore storage facility can be located at sea level, above sea level, below sea level, or partially above sea level and partially below sea level.

[0055] The offshore storage facility can include a pump. The pump can be configured to pump carbon dioxide out of the storage pipeline and into the injection well. Therefore, the step of injecting the stored carbon dioxide into the injection well of the hydrocarbon production system can include using the pump to pump carbon dioxide out of the storage pipeline and into the injection well. The pump can additionally or alternatively be configured to pump carbon dioxide into the storage pipeline. Therefore, before the step of storing carbon dioxide in the plurality of storage pipelines of the offshore storage facility, the method can include pumping carbon dioxide into the plurality of storage pipelines.

[0056] An offshore storage facility may include a receiving device. The receiving device may be arranged to receive carbon dioxide transferred to the offshore storage facility, for example, carbon dioxide transferred from a transport vessel to the offshore storage facility. Accordingly, the method may include receiving, at the receiving device, carbon dioxide transferred to the offshore storage facility. The receiving device may be arranged to supply carbon dioxide to a storage pipeline for subsequent storage therein, optionally with the aid of a pump. Accordingly, the method may include supplying carbon dioxide from the receiving device to the storage pipeline. In embodiments where the carbon dioxide is in liquid form, the receiving device may be arranged to ensure that only liquid carbon dioxide is supplied to the storage pipeline.

[0057] The offshore storage facility may be unmanned, such as an unmanned platform or an unmanned vessel. That is, the offshore storage facility may not have permanent personnel and may only have personnel present for specific operations such as maintenance and / or installation of equipment. The unmanned offshore storage facility may not require personnel of the offshore storage facility to perform its normal functions, such as the daily functions associated with the steps of storing carbon dioxide and injecting carbon dioxide.

[0058] The unmanned offshore storage facility may not include facilities provided for the stay of personnel. For example, it may not have a personnel shelter, no toilet facilities, no potable water, and / or no communication equipment operated by personnel. The unmanned offshore storage facility may also not include a helicopter deck and / or a lifeboat.

[0059] The unmanned offshore storage facility may alternatively or additionally be defined based on the relative amount of time during operation that personnel presence is required. The relative amount of time may be defined as the number of maintenance hours required per year. For example, the unmanned offshore storage facility may require less than 10,000 hours of maintenance per year, optionally less than 5,000 hours of maintenance per year, and possibly less than 3,000 hours of maintenance per year.

[0060] According to a third aspect of the present invention, there is provided an offshore storage facility comprising a plurality of storage pipelines configured to store carbon dioxide therein, wherein the offshore storage facility is configured to inject the stored carbon dioxide into an injection well.

[0061] The offshore storage facility of the third aspect may be consistent with the offshore storage facility discussed in connection with the above aspects of the present invention and may be consistent with any optional form thereof.

[0062] According to a fourth aspect of the present invention, there is provided a combination comprising a subsea injection well and an offshore storage facility according to the third aspect of the present invention, optionally an offshore storage facility in any optional form according to the third aspect. The offshore storage facility is connected to the injection well via a conduit, wherein the conduit allows carbon dioxide to be injected from the offshore storage facility into the injection well.

[0063] The injection well of the fourth aspect of the present invention may be consistent with the injection wells discussed in connection with the above aspects of the present invention and may be consistent with any optional form thereof. Similarly, the offshore storage facility of the fourth aspect may be consistent with the offshore storage facilities discussed in connection with the above aspects of the present invention and may be consistent with any optional form thereof.

[0064] According to a fifth aspect of the present invention, there is provided a combination comprising a hydrocarbon production system for producing hydrocarbons from a hydrocarbon reservoir and an offshore storage facility according to the third aspect of the present invention, optionally an offshore storage facility in any optional form according to the third aspect of the invention. The hydrocarbon production system includes a subsea injection well in communication with the hydrocarbon reservoir, wherein the subsea injection well is connected to the offshore storage facility via a conduit that permits injection of carbon dioxide from the offshore storage facility into the injection well.

[0065] The hydrocarbon production system of the fifth aspect of the present invention may be consistent with the hydrocarbon production systems discussed in connection with the above aspects of the present invention and may be consistent with any optional form thereof. Similarly, the injection well of the fifth aspect of the present invention may be consistent with the injection wells discussed in connection with the above aspects of the present invention and may be consistent with any optional form thereof. The offshore storage facility of the fifth aspect may also be consistent with the offshore storage facilities discussed in connection with the above aspects of the present invention and may be consistent with any optional form thereof. The hydrocarbon reservoir of the fifth aspect may be consistent with the hydrocarbon reservoirs described in connection with the above aspects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Certain embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

[0067] Figure 1 An offshore storage facility connected to a subsea injection well of a hydrocarbon production system is schematically depicted;

[0068] Figure 2 is Figure 1 a perspective view of the offshore storage facility;

[0069] Figure 3 is Figure 1 and Figure 2 a sectional view of the offshore storage facility; and

[0070] Figure 4 is Figure 1 a partially cut-away side view and a cut-away plan view of a ship. DETAILED DESCRIPTION

[0071] Figure 1Shows a marine storage facility 1, more specifically, a floating marine storage facility 1 located on-site of a subsea injection well 4 and connected to the subsea injection well 4 via a conduit 4a. The subsea injection well 4 communicates with a hydrocarbon-producing reservoir 6 and forms part of a hydrocarbon production system 3. The hydrocarbon production system additionally includes a hydrocarbon production platform 5 which itself includes production and processing equipment capable of producing hydrocarbons from the hydrocarbon reservoir 6 and processing them.

[0072] A ship 2 is also connected to the floating marine storage facility 1. The ship 2 is connected to the floating marine facility 1 via two separate conduits 2a, 2b, each conduit being arranged to convey fluid, in particular liquid carbon dioxide, as will be described in more detail below, between the ship 2 and the floating marine storage facility 1. The conduits 2a and 2b are reversibly connected to the ship 2, also as will be described in further detail below.

[0073] Reference Figure 2 and Figure 3 More particularly visible, the floating marine storage facility 1 has a hull 101 which is mainly ship-shaped, and a landing pad 102 for helicopters located at the top of the hull 101 to allow personnel to enter the facility 1 for maintenance or other operations. Accommodated within the hull 101 are a plurality of vertically oriented storage pipes 103. The storage pipes 103 are arranged to store liquid carbon dioxide therein at ambient temperature conditions and thus at a pressure between 34 barg - 45 barg (the exact storage pressure depending on ambient temperature conditions). Each storage pipe 103 is formed by pipe sections having an X45 specification and is sealed at both ends via suitable hemispherical caps. As shown, hundreds of storage pipes 103 are accommodated within the hull 101 of the floating marine facility 1.

[0074] The hull 101 also includes a plurality of pumps 105 which are configured to pump liquid carbon dioxide into the storage pipes 103 when the floating marine storage facility 1 receives carbon dioxide from the ship 2 (more will be introduced below). The pumps 105 are also configured to pump liquid carbon dioxide out of the storage pipes and pump it to the injection well 4 for injection purposes.

[0075] Figure 4 More details of the ship 2 are shown. The ship 2 includes a plurality of storage pipes 23 (likewise hundreds of storage pipes 23), distributed among several cargo holds 25 on the ship 2. The storage pipes 23 are similar to the storage pipes 103 located on the floating marine facility 1, they are vertically oriented on the ship 2 and are arranged to store liquid carbon dioxide therein at ambient temperature conditions and thus at a pressure between 34 barg - 45 barg (the exact storage pressure depending on ambient temperature conditions). Each storage pipe 23 is formed by pipe sections having an X45 specification and is sealed at both ends via suitable hemispherical caps.

[0076] In use, the storage pipe 23 on the ship 2 is loaded with ambient temperature liquid carbon dioxide at a carbon capture facility remote from the offshore floating storage facility 1 and the hydrocarbon production system 3. Then, the ship 2 sails to the site of the offshore floating storage facility 1 and the hydrocarbon production system 3 (such as as Figure 1 shown), while the liquid, ambient temperature carbon dioxide is kept unchanged within the storage pipe 23. This is achieved by ensuring that the storage pipe 23 maintains an appropriate pressure during the transportation by the ship 2. Once at the site of the offshore floating facility 1, the conduits 2a, 2b are connected to the ship 2. Then, the liquid carbon dioxide is unloaded from the storage pipe 23 on the ship 2 to the offshore floating facility 1 via the conduit 2a and with the support provided by the pump 105.

[0077] The transfer between the storage pipe 23 and the storage pipe 103 and subsequent storage in the storage pipe 103 are carried out with the carbon dioxide kept in the liquid state at ambient temperature conditions as much as possible. This requires the transfer and subsequent storage in the pipe 103 to be carried out under appropriately pressurized conditions, and the maintenance of these pressurized conditions is supported by the pump 105. However, even with the support of the pump 105, it is generally not possible to keep all the carbon dioxide in the liquid state during such transfer. For example, before introducing the liquid carbon dioxide into the storage pipe 103, the interior of the storage pipe 103 can be under ambient pressure conditions and filled with air and / or gaseous carbon dioxide, which are residues of previously stored carbon dioxide. Therefore, initially introducing the pressurized liquid carbon dioxide into the storage pipe 103 at ambient temperature conditions will cause some initial decompression of the liquid carbon dioxide, such that it vaporizes into the gaseous form. However, shortly thereafter, the storage pipe 103 will be sufficiently pressurized such that further introduced carbon dioxide remains in the liquid state at ambient temperature conditions.

[0078] During the transfer of carbon dioxide between the ship 2 and the offshore floating facility 1 (for example, after the initial introduction into the storage pipe 103 discussed above), if any part of the carbon dioxide vaporizes, the vaporized part of the carbon dioxide is separated from the liquid carbon dioxide at the offshore floating facility 1 and transferred back to the ship 2 via the conduit 2b. Then, this gaseous carbon dioxide can be re - condensed on the ship 2 at ambient temperature conditions and subsequently transferred back to the offshore facility 1 via the conduit 2a for storage thereon. Alternatively, the gaseous carbon dioxide can be stored on the ship 2 for transportation back to, for example, the carbon capture facility.

[0079] Once all the liquid carbon dioxide has been unloaded from the ship 2, the conduits 2a, 2b are disconnected. Then, the ship 2 sails away from the offshore floating facility 1 and optionally returns to the carbon capture facility to further load and transport carbon dioxide.

[0080] The liquid carbon dioxide stored in the storage pipeline 103 on the offshore floating facility 1 is used as the injection agent for the subsea injection well 4. This is achieved by pumping the liquid carbon dioxide out of the storage pipeline 103 using the pump 105 and transferring the carbon dioxide to the subsea injection well 4 via the conduit 4a under the power provided by the pump 105.

[0081] The carbon dioxide injected into the subsea injection well 4 is introduced into the hydrocarbon reservoir 6. This maintains (i.e., compensates for any pressure drop caused by hydrocarbon production) or increases the pressure within the hydrocarbon production reservoir 6, thereby maintaining, allowing, or improving the production of hydrocarbons from the hydrocarbon production reservoir through the hydrocarbon production platform 5.

[0082] Thus, the offshore storage facility 1 provides buffer storage for the injection agent (i.e., carbon dioxide) of the subsea injection well 4. Through this buffer storage, an effective and continuous supply of carbon dioxide can be supplied to the injection well 4 for injection. The offshore storage facility 1 will have a total carbon dioxide storage capacity capable of meeting the injection requirements at the subsea injection well 4 for a relatively long period of time, and when the volume of carbon dioxide at the offshore storage facility 1 is insufficient, the ship 2 can transport additional carbon dioxide to the offshore storage facility 1 to ensure that the injection of carbon dioxide at the subsea injection well 4 can be maintained at the desired and optimal rate.

Claims

1. A method of injecting carbon dioxide into an offshore injection well, the method comprises: storing carbon dioxide in a plurality of storage pipelines of an offshore storage facility; and injecting the stored carbon dioxide into the injection well.

2. The method according to claim 1, wherein, the carbon dioxide is stored as a liquid in the storage pipeline under ambient temperature conditions.

3. The method according to claim 2, wherein, the ambient temperature conditions are between 0°C and 25°C.

4. The method according to any one of the preceding claims, wherein, the offshore storage facility is provided on-site of the injection well.

5. The method according to any one of the preceding claims, wherein, the offshore storage facility is an offshore floating storage facility.

6. The method according to any one of the preceding claims, wherein, the injection well is in communication with a geological formation capable of storing the carbon dioxide.

7. The method according to any one of the preceding claims, wherein, each of the plurality of storage pipelines is formed of a pipe of a certain length, and the pipe of the certain length is closed at each end.

8. The method according to any one of the preceding claims, wherein, each of the storage pipelines has a nominal diameter between 40 - 60 inches (1.0 m - 1.5 m), optionally, a nominal diameter in the range of 42 inches (1.1 m) to 56 inches (1.4 m).

9. The method according to any one of the preceding claims, wherein, each of the plurality of storage pipelines is an X52, X56, X60, X65, X70 or X80 pipe according to API SPEC 5L specification.

10. The method according to any one of the preceding claims, wherein, each of the storage pipelines has a length between 10 m and 30 m.

11. The method according to any one of the preceding claims, including transporting the carbon dioxide to the offshore storage facility.

12. The method according to claim 11, wherein, the transporting step includes using a transport vessel, and the transport vessel includes a second plurality of storage pipelines for storing the carbon dioxide therein during transportation.

13. The method according to claim 12, wherein, the carbon dioxide is stored as a liquid in the second plurality of storage pipelines under ambient temperature conditions.

14. A method of operating a hydrocarbon production system, the method comprises: injecting carbon dioxide into an offshore injection well according to any one of the preceding claims, wherein the offshore injection well is connected to a hydrocarbon reservoir; and producing hydrocarbons from the hydrocarbon reservoir using the hydrocarbon production system.

15. An offshore storage facility, comprising a plurality of storage pipelines configured to store carbon dioxide therein, wherein, the offshore storage facility is configured to inject the stored carbon dioxide into an injection well.

16. An assembly comprising a subsea injection well and the offshore storage facility according to claim 15, wherein, the offshore storage facility is connected to the injection well via a conduit, and wherein the conduit allows carbon dioxide to be injected from the offshore storage facility into the injection well.

17. An assembly comprising a hydrocarbon production system for producing hydrocarbons and an offshore storage facility according to claim 15, wherein, the hydrocarbon production system comprises an offshore injection well in communication with a hydrocarbon reservoir, and wherein the offshore injection well is connected to the offshore storage facility via a conduit that permits injection of carbon dioxide from the offshore storage facility into the injection well.

Images