carbon dioxide injection

Abstract

A method for injecting carbon dioxide into an offshore injection well (4), comprising the steps of storing carbon dioxide in a plurality of storage pipes (103) in 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 subsea injection well and to an offshore storage facility configured to store and subsequently inject carbon dioxide into an offshore subsea injection well. [Background technology]

[0002] Injection is a process that can be used to maintain or increase pressure within a hydrocarbon-producing reservoir, thereby enabling or improving hydrocarbon production from the reservoir. One known form of injection relies on the injection of carbon dioxide (CO2) into the reservoir through one or more injection wells. Carbon dioxide is readily available, therefore inexpensive, and has the added effect of reducing the viscosity of the oil. This makes it a particularly advantageous injection material because it allows for easier hydrocarbon production.

[0003] Carbon dioxide injection can also be used as a useful climate solution, as it allows carbon dioxide that would otherwise be released into the environment to be stored for long periods within the injected reservoir or other seabed geological structures, thus avoiding the well-known adverse effects that releasing carbon dioxide into the environment can have.

[0004] One known method of injecting carbon dioxide into offshore injection wells involves a vessel (i.e., tanker) loaded with carbon dioxide traveling to the injection well site. The carbon dioxide is then offloaded from the vessel and injected into the injection well. Once the carbon dioxide is depleted, the vessel leaves the injection site for further capture of the carbon dioxide.

[0005] A problem with this known method is that the injection is discontinuous (i.e., injection only occurs while the vessel is at the site of the offshore injection well). Because the shipment of carbon dioxide from the vessel occurs over a relatively short time frame, it also results in a high flow rate of carbon dioxide. This therefore means that the process involves high pressures and therefore requires undesirably high design pressures.

[0006] An alternative method for injection at offshore injection wells is known, for example, 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 by a subsea pipeline. The pipeline allows carbon dioxide to flow from the storage facility to the offshore injection well and be injected at the injection well. The storage facility stores the carbon dioxide in large vessels (tanks) at ambient pressure and at temperatures significantly lower than ambient. Compared to methods based on transport vessels, this method offers the advantage that the pipeline can continuously transport the carbon dioxide to the injection well, while the injection does not need to be discontinuous, assuming the storage facility provides a continuous supply of carbon dioxide. Furthermore, assuming the continuous presence of the pipeline, the high flow rates and high pressures associated with methods relying on transport vessels can be avoided. Summary of the Invention [Problem to be solved by the invention]

[0007] Further alternative methods and apparatus for injecting carbon dioxide in offshore injection wells are desired. [Means for solving the problem]

[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 the carbon dioxide in a plurality of storage pipes in an offshore storage facility, and injecting the stored carbon dioxide into the injection well.

[0009] The method of the first aspect offers advantages over known prior art methods that rely on transfer vessels to transport carbon dioxide and ship it directly to an injection well. Among other things, this is because the problems associated with discontinuous injection and the associated high flow rates / high pressures associated with such prior art methods may be avoided using the method of the first aspect. Because the offshore storage facility is substantially permanently connected to the injection well, it may allow for a continuous supply of carbon dioxide to the injection well, thus avoiding the high pressures associated with discontinuous supply.

[0010] Additionally, the method of the first aspect offers advantages over these known prior art methods that rely on transport vessels in that it requires less operational and infrastructural demands, and therefore lower operational and infrastructure costs. Importantly, the method of the first aspect eliminates the need for transport vessels to travel to injection well sites (or at least significantly reduces the frequency with which transport vessels must travel to injection well / offshore storage facility sites), 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 infrastructural demands associated with such high design pressures.

[0011] The method of the first aspect also offers advantages over injection solutions known from the Applicant's own "Northern Lights" project, particularly in scenarios where injection wells are located in remote, "hard to reach" locations or at great distances from established onshore carbon dioxide storage facilities. In such scenarios, depending on how "remote" it may not be technically and / or commercially feasible to provide a pipeline in communication with said injection well, although an offshore storage facility of the type defined in the first aspect of the invention may feasibly be used to enable injection at said injection well.

[0012] The carbon dioxide to be stored and later injected may have been previously captured from the carbon dioxide producing source (e.g., a chemical or other industrial plant, a gas-fired power plant or power source, a coal-fired power plant or power source, etc.) before being released into the environment / atmosphere. Alternatively, the carbon dioxide may be captured directly from the atmosphere. Thus, the method of the first aspect may optionally include capturing carbon dioxide from the carbon dioxide producing source or the environment before the step of storing the carbon dioxide. This step of capturing carbon dioxide may take place in a carbon capture facility which may be onshore (land-based) or offshore. These optional features of the invention have clear environmental advantages.

[0013] As suggested by the above discussion, the offshore storage facility may be provided at the site of the injection well. That is, the offshore storage facility may be provided near (i.e., in close proximity to) the injection well. Thus, the offshore storage facility may be considered to be combined with and / or paired with the injection well. The offshore storage facility may be located within 2 km of the injection well in a lateral direction (i.e., in a direction consistent with the sea surface and / or seabed). Optionally, the offshore storage facility may be located within 1 km, 500 m, 400 m, 300 m, 200 m, or 100 m of the injection well in a lateral direction (i.e., in a direction consistent with the sea surface and / or seabed). The offshore storage facility may be located substantially above the injection well.

[0014] As noted above, the offshore storage facility may provide a substantially continuous supply of carbon dioxide to the offshore injection well. Thus, the total storage volume in the offshore storage facility (i.e., the total storage volume provided by the storage pipes) may be capable of meeting the injection needs at the offshore injection well for a significant period of time, for example, at least one week, one month, six months, one year, five years, or optionally even longer. The total storage volume in the offshore storage facility (i.e., the total storage volume provided by the storage pipes) may be, for example, 10,000 m 3 , 30,000m 3 , 100,000m 3 Or optionally even larger.

[0015] Offshore injection wells may also be referred to as subsea injection wells or offshore / subsea injection wells.

[0016] As alluded to above, the offshore injection well may be located remotely and / or at a great distance from land and / or from any established infrastructure (e.g., onshore carbon dioxide storage facilities) that enables carbon dioxide storage other than the offshore storage facility of the present invention. A great distance may be a distance where it is not technically and / or commercially feasible to provide a pipeline from land / established infrastructure to the offshore injection well. Those skilled in the art will readily understand what such distances are given the particular circumstances. For example, the injection well may be located more than 60 km from land and / or from existing infrastructure, optionally more than 100 km, and even optionally more than 200 km.

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

[0018] This combination of features is considered to be particularly advantageous and therefore according to a second aspect of the present invention there is provided a method of operating a hydrocarbon production system comprising the steps of 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 with the hydrocarbon production system.

[0019] The use of carbon dioxide as an injectant in the second aspect of the present invention has the synergistic effect of supporting hydrocarbon production while avoiding the emission of carbon dioxide into the environment.

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

[0021] The optional hydrocarbon production system may include a hydrocarbon refinery 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 subsea injection well may form part of a hydrocarbon production system or facility. Thus, the hydrocarbon production system or facility may include the injection well. The hydrocarbon production system or 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 the production and / or processing of hydrocarbons (e.g., oil, natural gas, etc.). Thus, a hydrocarbon production system (e.g., a hydrocarbon production facility) may include some production equipment and / or some processing equipment configured to process or partially process the produced hydrocarbons.

[0024] The hydrocarbon production system and / or hydrocarbon production facility may be provided at the site of the injection well and / or offshore storage facility. That is, the hydrocarbon production system and / or hydrocarbon production facility may be provided near (i.e., in close proximity to) the injection well and / or offshore storage facility. Accordingly, the hydrocarbon production system and / or hydrocarbon production facility may be considered to be in combination with and / or paired with the injection well and / or offshore storage facility. The hydrocarbon production system and / or hydrocarbon production facility may be located within 2 km of the injection well and / or offshore storage facility in a lateral direction (i.e., in a direction consistent with the sea surface and / or seabed). Optionally, the hydrocarbon production system and / or hydrocarbon production facility may be located within 1 km, 500 m, 400 m, 300 m, 200 m, or 100 m of the injection well and / or offshore storage facility in a lateral direction (i.e., in a direction consistent with the sea surface and / or seabed). The hydrocarbon production system and / or hydrocarbon production facility may be located substantially above the injection well.

[0025] However, the injection well need not be connected to a hydrocarbon reservoir. Instead of a hydrocarbon reservoir, the injection well may be in communication with an alternative geological structure (i.e., not a hydrocarbon reservoir, or at least not a hydrocarbon-producing reservoir, e.g., a hydrocarbon reservoir that is already depleted of hydrocarbons). Thus, carbon dioxide injection may not be used to support hydrocarbon production, but instead simply as a means 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 pipes at an offshore storage facility, and injecting the stored carbon dioxide into a plurality of injection wells. Each of the plurality of injection wells may conform to the injection wells described above.

[0027] Storing the carbon dioxide in the plurality of storage pipes at the offshore storage facility may include storing the carbon dioxide as a liquid (i.e., liquefied carbon dioxide). Thus, the method may include liquefying the carbon dioxide before storing it in the plurality of storage pipes at the offshore storage facility. This liquefaction step may occur at the offshore storage facility prior to (i.e., as a precursor to) storing the carbon dioxide in the plurality of storage pipes at the offshore storage facility. Alternatively, the carbon dioxide may be liquefied before arriving at the offshore storage facility. That is, the carbon dioxide may have been transported to the offshore storage facility as a liquid, for example, by a transport vessel (this optional feature is described in more detail below).

[0028] The step of injecting the stored carbon dioxide may optionally include injecting the carbon dioxide as a liquid using a pump. Injecting liquid carbon dioxide using a pump has efficiency advantages as 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 the carbon dioxide as a liquid at ambient temperature conditions in a plurality of storage pipes at the offshore storage facility. Accordingly, the method may also include liquefying the carbon dioxide at ambient temperature conditions prior to storage. Those skilled in the art will appreciate that storing liquefied carbon dioxide at ambient temperature conditions requires the carbon dioxide to be pressurized to a pressure much higher than ambient pressure conditions, with the exact pressure conditions depending on the particular ambient temperature at which the carbon dioxide is stored.

[0030] Traditionally, liquefaction of carbon dioxide and storage as a liquid is performed at ambient pressure conditions and, therefore, at very low temperature conditions that are significantly lower than ambient temperature conditions, as will be understood by those skilled in the art. However, in the context of the present invention, storing carbon dioxide at temperature conditions that are significantly lower than ambient temperature conditions, while possible, is less advantageous. This is because there are significant complexities and expenditures, both operational and capital, associated with the equipment, personnel, and processes required to produce and maintain carbon dioxide as a liquid at such temperature and ambient pressure conditions. In offshore scenarios, limited space also means that it may not be feasible to provide the infrastructure necessary to store liquefied carbon dioxide at ambient pressure conditions.

[0031] Therefore, in connection with the above aspects of the present invention, it is believed to be particularly advantageous (although optional) to store liquid carbon dioxide at ambient temperature conditions. As noted above, this requires the carbon dioxide to be pressurized at pressures significantly higher than ambient conditions. However, the required pressurization leads to significant reductions in complexity and expenditure, both operational and capital, in terms of the equipment, personnel and processes involved, and is therefore particularly suitable for offshore scenarios.

[0032] Ambient temperature conditions may be temperatures between 0 and 25°C. The pressure required to store liquefied carbon dioxide may therefore be between 34 barg and 45 barg. The exact pressure required will depend on the ambient temperature.

[0033] The term "storage pipe" refers to a storage vessel formed from a length of pipe, optionally closed at both ends, for example by hemispherical caps or domes welded to the ends of the pipe. Storage pipes are therefore very elongated, typically having a length to diameter ratio of at least 20.

[0034] The use of storage pipes as the basis for storage at offshore storage facilities, for example as compared to conventional tank storage (i.e., ship storage), is advantageous as it is associated with significantly lower expenditures, both capital and operational, particularly in connection with optionally storing liquid carbon dioxide at high pressure and ambient temperature conditions.

[0035] Typical "tank" type storage solutions require thick-walled tanks made from steel. These tanks are expensive to provide (given the large amounts of material typically required), and due to the weight of the tanks, they are also expensive to transport to the point of use (also assuming the large amounts of material required). The required wall thickness (and therefore the weight of the tank) also limits the size of the tank that can be used, which means that the volume of carbon dioxide that can be stored in the tank is limited.

[0036] In contrast, pipe storage can be provided relatively inexpensively because it can be manufactured using standard, off-the-shelf pipes. Furthermore, for a given storage volume, pipe storage can have a relatively thin wall thickness. Thus, pipe storage can be used to store a given volume of carbon dioxide using a relatively low total weight of storage tank material, and as a result, this can be achieved with a lower capital expenditure. Therefore, pipe storage is a more feasible solution.

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

[0038] Vessels having a nominal diameter greater than about 56-60 inches (1.4 m-1.5 m) are typically considered by those skilled in the art to be conventional tanks (or pressure vessels) as distinct from pipes. This consideration also applies in the context of the present application. Vessels having a nominal diameter greater than about 56-60 inches (1.4 m-1.5 m) are not considered pipes.

[0039] The storage pipe may be or have an X52, X56, X60, X65, X70 or X80 pipe conforming to API SPEC5L specifications.

[0040] As mentioned above, the storage pipes are very elongated, so each storage pipe may have a length of between 10m and 30m, for example 12m, 24m or 26m.

[0041] The storage pipe may optionally be formed from rolled pipe having a single longitudinal seam. Such pipe is commonly available as an "off-the-shelf" type component and is typically inexpensive.

[0042] The storage pipe may be configured to store carbon dioxide at elevated pressure, for example to store liquefied carbon dioxide at ambient temperature conditions. The storage pipe may be configured to store carbon dioxide at 34 barg to 45 barg. The exact pressurization conditions at which the storage pipe is configured to store carbon dioxide may be selected depending on the ambient temperature of the carbon dioxide (optionally as a liquid) to be stored in the storage pipe, the tolerances of the storage pipe and / or the tolerances of the equipment used to load and unload the carbon dioxide from the storage pipe.

[0043] Each storage pipe may be oriented vertically (i.e., the major axis of the storage pipe may be oriented vertically or substantially vertically) or horizontally (i.e., the major axis of the storage pipe may be oriented horizontally or substantially horizontally). The storage pipes may include a combination of horizontally and vertically oriented storage pipes. Each storage pipe, or some of the storage pipes, may be oriented in any other orientation between horizontal and vertical.

[0044] A particularly advantageous, but optional, combination of features is the use of storage pipes to store liquefied carbon dioxide at ambient temperature conditions in an offshore storage facility. This combination of features provides a cheap, simple and technically less challenging means for storing liquid carbon dioxide at ambient temperature conditions that is superior to other storage solutions.

[0045] The method may include transporting the carbon dioxide to an offshore storage facility site. The method may then include transferring the carbon dioxide to the offshore storage facility.

[0046] The step of transporting the carbon dioxide to the offshore storage facility site may include transporting the carbon dioxide from a carbon capture facility, which may be located onshore (land-based) or offshore.

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

[0048] The transporting step may be accomplished using a transport vessel (eg, a tanker) that includes storage for the carbon dioxide.

[0049] The storage portion of the transport vessel may be, for example, a second plurality of storage pipes, which may correspond to the storage pipes provided at the offshore storage facility, as described above, and optionally conform to any optional features thereof that are compatible therewith, also as discussed above.

[0050] Transferring the carbon dioxide to the offshore storage facility may include transferring the carbon dioxide from a transport vessel to the offshore storage facility, which may include use of offloading equipment (e.g., including conduits, pumps, compressors, etc.), which may be configured to maintain the carbon dioxide at the required pressure to maintain the carbon dioxide as a liquid at ambient temperature conditions.

[0051] The offshore storage facility may be considered an interim and / or buffer storage facility, i.e., it may act as a temporary reservoir / buffer for supplying carbon dioxide to injection wells, optionally after it has been transferred from the transport vessel to the offshore storage facility.

[0052] The offshore storage facility may be a single, self-contained unit, e.g., a single modular unit. The offshore storage facility may be self-contained, e.g., separate and separable from the injection well, optional hydrocarbon production system, optional hydrocarbon facility, optional carrier vessel, etc.

[0053] The offshore storage facility may be an offshore floating storage facility. For example, the offshore storage facility may 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 may take the form of a spar buoy or a vessel (e.g., a tanker or barge). The offshore storage facility may include a ship-shaped hull, for example a converted hull.

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

[0055] The offshore storage facility may include a pump. The pump may be configured to pump the carbon dioxide from the storage pipe to the injection well. Thus, injecting the stored carbon dioxide into an injection well of the hydrocarbon production system may include pumping the carbon dioxide from the storage pipe to the injection well using the pump. The pump may additionally or alternatively be configured to pump the carbon dioxide into the storage pipe. Thus, the method may include pumping the carbon dioxide into a plurality of storage pipes prior to storing the carbon dioxide in the plurality of storage pipes at the offshore storage facility.

[0056] The offshore storage facility may include a receiver. The receiver 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. The method may therefore include receiving at the receiver the carbon dioxide transferred to the offshore storage facility. The receiver may be arranged to supply the carbon dioxide, optionally with the aid of a pump, to a storage pipe for subsequent storage in the storage pipe. The method may therefore include supplying the carbon dioxide from the receiver to the storage pipe. In embodiments where the carbon dioxide is in liquid form, the receiver may be arranged to ensure that only liquid carbon dioxide is supplied to the storage pipe.

[0057] The offshore storage facility may be unmanned, e.g., an unmanned platform or vessel. That is, there may be no permanent personnel on-site at the offshore storage facility, and personnel may be deployed only for specific tasks, such as equipment maintenance and / or installation. An unmanned offshore storage facility may not require personnel for the offshore storage facility to perform its normal functions, such as the routine functions associated with storing and injecting carbon dioxide.

[0058] Unmanned offshore storage facilities may not include facilities for personnel accommodation, such as personnel shelters, toilet facilities, potable water, and / or personnel-operated communications equipment. Unmanned offshore storage facilities may also not include helidecks and / or lifeboats.

[0059] An unmanned offshore storage facility may alternatively or additionally be defined based on the relative amount of time personnel are required to be present during operation. This relative amount of time may be defined as the maintenance hours required per year. For example, an unmanned offshore storage facility may require less than 10,000 maintenance hours per year, optionally less than 5000 maintenance hours per year, and perhaps less than 3000 maintenance hours per year.

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

[0061] The offshore storage facility of the third aspect may be in accordance with the offshore storage facilities discussed with respect to the above aspects of the invention, and may be in accordance 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, optionally, an offshore storage facility according to the third aspect of the present invention in any optional form thereof, the offshore storage facility being connected to the injection well via a conduit which allows injection of carbon dioxide from the offshore storage facility into the injection well.

[0063] The injection well of the fourth aspect of the invention may be in accordance with the injection wells discussed with respect to the previous aspects of the invention, and may be in accordance with any optional form thereof. Similarly, the offshore storage facility of the fourth aspect of the invention may be in accordance with the offshore storage facility discussed with respect to the previous aspects of the invention, and may be in accordance 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 optionally an offshore storage facility according to the third aspect of the present invention in any optional form, the hydrocarbon production system comprising a subsea injection well in communication with the hydrocarbon reservoir, the subsea injection well being connected to the offshore storage facility via a conduit allowing 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 in accordance with the hydrocarbon production system discussed with respect to the previous aspects of the present invention, and may be in accordance with any optional form thereof. Similarly, the injection well of the fifth aspect of the present invention may be in accordance with the injection well discussed with respect to the previous aspects of the present invention, and may be in accordance with any optional form thereof. The offshore storage facility of the fifth aspect may also be in accordance with the offshore storage facility discussed with respect to the previous aspects of the present invention, and may be in accordance with any optional form thereof. The hydrocarbon reservoir of the fifth aspect may be in accordance with the hydrocarbon reservoir described with respect to the previous aspects of the present invention.

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

[0067] [Figure 1] 1 is a schematic diagram of an offshore storage facility connected to a subsea injection well of a hydrocarbon production system. [Figure 2] FIG. 2 is a perspective view of the offshore storage facility of FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view of the offshore storage facility of FIGS. 1 and 2. [Figure 4] 2 is a partially cutaway side view and a cutaway plan view of the tanker of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0068] Figure 1 shows an offshore storage facility 1, more specifically an offshore floating storage facility 1 that is on-site with a subsea injection well 4 and connected to the subsea injection well 4 via a conduit 4a. The subsea injection well 4 is in communication with a hydrocarbon production reservoir 6 and forms part of a hydrocarbon production system 3. The hydrocarbon production system further includes a hydrocarbon production platform 5, which itself includes production and processing equipment that enables the production of hydrocarbons from the hydrocarbon reservoir 6 and the processing thereof.

[0069] Also connected to the offshore floating storage facility 1 is a tanker 2. The tanker 2 is connected to the offshore floating storage facility 1 via two separate conduits 2a, 2b, which are each arranged to transport a fluid, in particular liquid carbon dioxide, between the tanker 2 and the offshore floating storage facility 1, as will be described in more detail below. The conduits 2a and 2b are reversibly connected to the tanker 2, also as will be described in more detail below.

[0070] As can be seen in more detail with reference to Figures 2 and 3, the offshore floating storage facility 1 has a primarily ship-shaped hull 101 and a helicopter landing pad 102 located on the hull 101 to allow personnel access to the facility 1 for maintenance and the like. Housed 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 therefore at a pressure of 34 barg to 45 barg (the exact storage pressure depends on the ambient temperature conditions). Each storage pipe 103 is formed from a section of pipe having an X45 specification and is sealed at both ends by appropriate hemispherical caps. As shown, several hundred storage pipes 103 are housed within the hull 101 of the offshore floating facility 1.

[0071] The hull 101 also includes a plurality of pumps 105. The pumps 105 are configured to pump liquid carbon dioxide into storage pipes 103 at the time the carbon dioxide is received at the offshore floating storage facility 1 from the tanker 2 (as will be described in more detail below). The pumps 105 are further configured to pump the liquid carbon dioxide from the storage pipes to injection wells 4 for injection.

[0072] Figure 4 shows further details of the tanker 2. The tanker 2 comprises a plurality of storage pipes 23 (again, several hundred storage pipes 23) divided into a plurality of cargo holds 25 on the tanker 2. The storage pipes 23 are similar to the storage pipes 103 located on the offshore floating facility 1 in that they are oriented vertically on the tanker 2 and arranged to store liquid carbon dioxide therein at ambient temperature conditions and therefore at a pressure of 34 barg to 45 barg (the exact pressure of storage will depend on the ambient temperature conditions). Each storage pipe 23 is formed from a section of pipe having an X45 specification and is sealed at both ends by suitable hemispherical caps.

[0073] In use, the storage pipe 23 on the tanker 2 is loaded with ambient temperature liquid carbon dioxide at a carbon capture facility remote from the offshore floating storage facility 1 and hydrocarbon production system 3. The tanker 2 is then moved to the offshore floating storage facility 1 and hydrocarbon production system 3 site (e.g., as shown in Figure 1) with the liquid ambient temperature carbon dioxide maintained intact within the storage pipe 23. This is achieved by ensuring that the storage pipe 23 remains appropriately pressurized during the transfer of the tanker 2. On arrival at the offshore floating facility 1 site, conduits 2a, 2b are connected to the tanker 2. The liquid carbon dioxide is then unloaded from the storage pipe 23 of the tanker 2 to the offshore floating facility 1 through conduit 2a and with assistance provided by pump 105.

[0074] The transfer between storage pipe 23 and storage pipe 103, and subsequent storage in storage pipe 103, is performed while maintaining the carbon dioxide as a liquid at ambient temperature conditions as much as possible. This requires that the transfer to and subsequent storage in pipe 103 be performed under appropriate pressurized conditions, and maintaining these pressurized conditions is assisted by pump 105. However, even with the assistance of pump 105, it is typically not possible to maintain all of the carbon dioxide in a liquid state during this transfer. For example, prior to the introduction of liquid carbon dioxide into storage pipe 103, the interior of storage pipe 103 may be under ambient pressure conditions and filled with air and / or gaseous carbon dioxide remaining as a residue from previous carbon dioxide storage. Thus, the initial introduction of pressurized liquid carbon dioxide into storage pipe 103 at ambient temperature conditions results in an initial decompression of some of the liquid carbon dioxide, which then vaporizes into gaseous form. However, shortly thereafter, storage pipe 103 sufficiently pressurizes, such that any additional carbon dioxide introduced remains in a liquid state at ambient temperature conditions.

[0075] If some of the carbon dioxide is vaporized during transfer between tanker 2 and offshore floating facility 1 (e.g., after initial introduction into storage pipe 103 as discussed above), the vaporized portion of the carbon dioxide is separated from the liquid carbon dioxide at offshore floating facility 1 and transferred back to tanker 2 via conduit 1b. This gaseous carbon dioxide may then be re-condensed on tanker 2 at ambient temperature conditions and then transferred back to offshore facility 1 via conduit 2a for storage therein. Alternatively, the gaseous carbon dioxide may be stored on board tanker 2 and transferred back, for example, to a carbon capture facility.

[0076] Once all the liquid carbon dioxide has been unloaded from the tanker 2, the conduits 2a, 2b are disconnected. The tanker 2 then moves away from the offshore floating facility 1, optionally returning to the carbon capture facility for further loading and transport of carbon dioxide.

[0077] Liquid carbon dioxide stored in storage pipe 103 on offshore floating facility 1 is used as an injection material into subsea injection well 4. This is achieved by pumping the liquid carbon dioxide from storage pipe 103 using pump 105 and transporting the carbon dioxide through conduit 4a to subsea injection well 4 under the impulsive force provided by pump 105.

[0078] The carbon dioxide injected into the subsea injection well 4 is further introduced into the hydrocarbon reservoir 6. This maintains (i.e., corrects pressure drops due to hydrocarbon production) or increases the pressure within the hydrocarbon producing reservoir 6, thereby maintaining, permitting or improving the production of hydrocarbons from the hydrocarbon producing reservoir by the hydrocarbon production platform 5.

[0079] In this manner, offshore storage facility 1 provides buffer storage for the injection material, i.e., carbon dioxide, for subsea injection well 4. This buffer storage allows a substantially continuous supply of carbon dioxide to be supplied for injection to injection well 4. Offshore storage facility 1 has a total carbon dioxide storage volume capable of meeting the injection demands at subsea injection well 4 over a significant period of time, and as the amount of carbon dioxide at offshore storage facility 1 becomes low, tanker 2 can transport additional carbon dioxide to offshore storage facility 1, thereby maintaining the injection of carbon dioxide at subsea injection well 4 at a desired optimum rate.

Claims

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

2. 10. The method of claim 1, wherein the carbon dioxide is stored in the storage pipe as a liquid at ambient temperature conditions.

3. 3. The method of claim 2, wherein the ambient temperature condition is between 0°C and 25°C.

4. The method of any one of claims 1 to 3, wherein the offshore storage facility is provided at the site of the injection well.

5. The method according to any one of claims 1 to 4, wherein the offshore storage facility is an offshore floating storage facility.

6. The method of any one of claims 1 to 5, wherein the injection well is in communication with a geological formation capable of storing the carbon dioxide.

7. A method according to any preceding claim, wherein each of said plurality of storage pipes is formed from a length of pipe that is closed at each end.

8. 8. The method of any one of claims 1 to 7, wherein each of the storage pipes has a nominal diameter of 40 to 60 inches (1.0 m to 1.5 m), optionally within the range of 42 inches (1.1 m) to 56 inches (1.4 m).

9. 9. The method of any one of claims 1 to 8, wherein each of the plurality of storage pipes is an X52, X56, X60, X65, X70 or X80 pipe conforming to API SPEC 5L specifications.

10. The method according to any one of claims 1 to 9, wherein each of the storage pipes has a length of between 10m and 30m.

11. The method of any one of claims 1 to 10, comprising transporting the carbon dioxide to the offshore storage facility.

12. 12. The method of claim 11, wherein the transporting step includes using a transport vessel, the transport vessel including a second plurality of storage pipes for storing the carbon dioxide therein during transport.

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

14. 14. A method of operating a hydrocarbon production system, comprising the steps of injecting carbon dioxide into an offshore injection well according to any one of claims 1 to 13, wherein the offshore injection well is connected to a hydrocarbon reservoir; and producing hydrocarbons from the hydrocarbon reservoir with the hydrocarbon production system.

15. An offshore storage facility including a plurality of storage pipes configured to store carbon dioxide therein, the offshore storage facility configured to inject the stored carbon dioxide into an injection well.

16. 16. A combination comprising a subsea injection well and the offshore storage facility of claim 15, wherein the offshore storage facility is connected to the injection well via a conduit, the conduit enabling injection of carbon dioxide from the offshore storage facility into the injection well.

17. 16. A combination comprising: a hydrocarbon production system for producing hydrocarbons; and the offshore storage facility of claim 15, wherein the hydrocarbon production system comprises an offshore injection well in communication with a hydrocarbon reservoir, the offshore injection well being connected to the offshore storage facility via a conduit that enables injection of carbon dioxide from the offshore storage facility into the injection well.

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