The present invention relates to a method of operating a hydrocarbon production system, with reduced carbon dioxide (CO2) emission. The invention further extends to a corresponding hydrocarbon production system, to a method of forming such a hydrocarbon production system and to a method of retrofitting an existing hydrocarbon production system for conformity with the hydrocarbon production system of the invention.

Hydrocarbon production systems, and in particular offshore hydrocarbon production facilities, often comprise one or more gas turbine engines (GTE) for local power generation at the production system. Typically, a portion of the hydrocarbon gases produced may be combusted in the GTE to produce power for the operation of the production system. The exhaust gases produced from the combustion, comprising a significant portion of carbon dioxide, are vented to the atmosphere.

The significant detrimental impacts that carbon dioxide emission has on the environment are notoriously well-known. There is therefore a general desire, where possible, to reduce carbon dioxide emission to the environment and, as time goes on, this desire only grows. The regulations surrounding operation of hydrocarbon production systems reflects this growing desire, with mandates on the reduction of the ‘carbon footprint’ for such systems being introduced by the various regulatory bodies.

KR 20210007791 A discloses a structure including a fuel cell capable of producing power from hydrogen, which may optionally be mixed with other fuels.

US 2017/0218727 A1 discloses a fracking system powered by gas turbine engines fuelled by a combustible liquid fuel source.

In accordance with a first aspect of the invention, there is provided a method of operating a hydrocarbon production system, the hydrocarbon production system comprising a power source configured to provide power to the hydrocarbon production system and a plurality of storage pipes, the method comprising: storing ammonia as a liquid at ambient temperature conditions in the plurality of storage pipes; and using the ammonia as an energy source for the power source in order to provide power to the hydrocarbon production system.

For the production of power, the method of the first aspect is reliant on ammonia (NH3) as an energy source. As the skilled person will appreciate, the byproducts of using ammonia as an energy source (e.g. as fuel in a combustion engine or as fuel for a fuel cell) are nitrogen (N2) and water (H2O). No carbon dioxide (CO2) is produced and vented to the atmosphere as in the prior art scenarios where hydrocarbon gas is combusted for power production. As such, emission of carbon dioxide to the atmosphere (and the detrimental environmental impacts associated therewith) through operation of the hydrocarbon production system in accordance with the first aspect of the invention is reduced and may in fact be totally avoided (i.e. the method of the first aspect of the invention can result in operation of the hydrocarbon production system with net-zero carbon dioxide emissions). The method of the first aspect thus provides a far less environmentally harmful method of operation of a hydrocarbon production system as compared to known methods of operation because the nitrogen and water produced as byproducts have little to no detrimental environmental impact, at least when compared with carbon dioxide.

The power source may be a combustion engine. The combustion engine may be a gas turbine engine. Alternatively, the combustion engine may be a gas engine (i.e. gaseous-fuelled engine), e.g. a two-stroke, four-stroke, six-stroke or wankel rotary engine. The gas engine may be a V-type engine, e.g. a V18 engine. The combustion engine may be specifically configured to combust ammonia or hydrogen (i.e. the design, operation and performance of the combustion may be specifically selected, tuned, designed etc. for optimal combustion of ammonia/hydrogen). The use of hydrogen or ammonia as a fuel for the combustion engine is described in greater detail below.

The step of using the ammonia as an energy source for the power source may comprise fuelling the combustion engine with ammonia and/or combusting the ammonia in the combustion engine.

The step of using the ammonia as an energy source for the power source may comprise: cracking the ammonia to form hydrogen; and fuelling the power source with the hydrogen (e.g. combusting the hydrogen in the combustion engine). It will be appreciated that in a scenario where the ammonia is first cracked and the resultant hydrogen is as a fuel, the by-products from this overall process (i.e. nitrogen from the step of cracking and water from the use of hydrogen as a fuel) remain the same as when the ammonia is directly combusted in the combustion engine. As such, the method remains less environmentally harmful than prior art methods as discussed above. The power source may be a fuel cell. For example, the power source may be an ammonia powered fuel cell. As such, the step of using the ammonia as an energy source for the power source may comprise fuelling the ammonia powered fuel cell with the ammonia.

Alternatively, the fuel cell may be a hydrogen powered fuel cell. In such a scenario, using the ammonia as an energy source for the power source may comprise: cracking the ammonia to form hydrogen; and fuelling the hydrogen powered fuel cell with the hydrogen.

It will be noted that even in scenarios of the first aspect of the invention where a hydrogen fuel cell is used to power the hydrocarbon production system (rather than using the ammonia as a fuel directly for a combustion engine or an ammonia powered fuel cell) the by-products from the overall process (i.e. nitrogen and water) remain the same and hence the first aspect of the invention remains less environmentally harmful than prior art methods. Nitrogen is output as a byproduct at the cracking stage whilst water is output as a by-product from the hydrogen fuel cell.

The hydrocarbon production system may be offshore, e.g. it may be or comprise an offshore hydrocarbon production facility. The hydrocarbon production facility may be a hydrocarbon production platform, e.g. an unmanned hydrocarbon production platform, or a floating, production, storage and offloading vessel (FPSO).

The hydrocarbon production system may be a land based (i.e. onshore) hydrocarbon production system.

It will be understood by the skilled person that a hydrocarbon production system is a system that is specifically configured for the production and/or processing of hydrocarbons (e.g. oil, natural gas, etc.). As such, the hydrocarbon production system will comprise a degree of production equipment and/or a degree of processing equipment configured for processing or part-processing the produced hydrocarbons.

The power source may provide electrical power for the hydrocarbon production system. If the power source is a combustion engine, this may entail use of an electrical generator connected to the engine or which the combustion engine forms part of. The optional combustion engine may additionally and/or alternatively be configured to provide motive power for the hydrocarbon production system. For example, the combustion engine may be configured to directly power components of the hydrocarbon production system, e.g. to provide a direct drive to a compressor of the hydrocarbon production system and/or other rotating components of the hydrocarbon production system.

The hydrocarbon production system may comprise a plurality of power sources. Each power source may be configured to provide power for the hydrocarbon production system. The method may comprise: using the ammonia as an energy source for some or all of the plurality of the power sources to provide power for the hydrocarbon production system.

The term ‘storage pipe’ as used herein refers to a storage container formed from (i.e. comprising) a length of pipe, which has been closed at each end, optionally by a hemispherical cap or dome that has, for example, been welded to the end of the pipe. Accordingly, the storage pipes are highly elongate, typically having a length-to-diameter ratio of at least 20.

The use of storage pipes as compared to, e.g., conventional tank storage (i.e. vessel storage) as the basis for storage of ammonia at the hydrocarbon production system is advantageous since it is associated with a significantly lower capital and operational expenditure, particularly in the context of storing ammonia at the elevated pressures required to store the ammonia as a liquid at ambient temperature conditions

Typical ‘tank’ type storage solutions require thick steel walled tanks. These tanks are expensive to provide (given the large amount of material typically required), and are also expensive to transport given their weight (again, given the large amount of material required). The requisite wall thickness (and hence weight of the tank) also limits the size of the tank that can be used, meaning that the volume of ammonia stored therein is limited. The large wall thickness also occupies a large volume of space, which in turn results in tank type storage utilising available space for storage inefficiently.

In contrast, pipe storage is relatively inexpensive to provide because standard, ‘off-the-shelf’ pipes may be used to manufacture them. Moreover, for a given volume of storage, pipe storage can have a comparatively smaller wall thickness. Thus, a given volume of ammonia can be stored using a comparatively lower total weight of storage tank material using pipe storage and can be achieved at a lower capital expenditure. The relatively smaller wall thickness of pipe storage means that, for a given volume of ammonia, the total space occupied using the pipe storage solution is smaller. Thus, pipe storage is a more viable solution. Each of the storage pipes may have a nominal diameter of between 40-60 inches (1.0m - 1.5m). Preferably, the pipe may have a nominal size of 42 inches (1.1m) or 56 inches (1 ,4m), or may have any nominal size in the range of 42 inches (1.1m) to 56 inches (1.4m).

A vessel having a nominal diameter greater than about 56-60 inches (1.4 m -1.5m) would typically be considered by the skilled person as a conventional tank (or pressure vessel) that is distinct from a pipe. This consideration is also true in the context of the invention, whereby any vessel having a nominal diameter of greater than about 56-60 inches (1.4m -1.5m) would not be considered as a pipe.

Each storage pipe may comprise or be formed from a pipe that is an X42, X52, X56, X60, X65, X70 or X80 pipe in accordance with the API SPEC 5L specification.

As noted above, the storage pipes are highly elongate. Accordingly, each storage pipe may have a length of between 10 m to 30 m, for example 12 m, 24 m or 26 m.

Each of the storage pipes may be formed from rolled pipes with, optionally, a single longitudinal seam. Such pipes are commonly available as ‘off-the-shelf’ type components and are typically inexpensive.

The storage pipes are implicitly configured for storing ammonia at an elevated pressure given that liquefied ammonia is being stored at ambient temperature conditions (e.g. between 0°C and 40 °C). The storage pipes may be configured to store the ammonia at between 5 barg - 20 barg, for example at 5 barg, 10 barg, 15 barg or 20 barg. The exact pressurised conditions that the storage pipes are configured to store the ammonia at may be selected dependent on the ambient temperature of the liquid ammonia to be stored therein, the tolerances of the storage pipe and/or the tolerance of the equipment used for loading and unloading the ammonia into the storage pipes.

The method may comprise the step of liquefying ammonia at ambient temperature conditions prior to storing the ammonia.

The skilled person will appreciate that storing and/or liquefying ammonia at ambient temperature conditions requires the ammonia to be pressurised at pressures far above ambient pressure conditions with the exact pressure conditions being determined by the specific ambient temperature of the ammonia. Ambient temperature conditions may be any temperature between 0°C - 40 °C. As such, the pressure required in order to liquefy the ammonia and/or store the ammonia as a liquid may be between, for example, 5 barg - 20 barg, with the exact pressure required being determined by the ambient temperature selected.

Conventionally, liquefaction of ammonia and/or storage of ammonia as a liquid is carried out at ambient pressure conditions and hence, as will be understood by the skilled person, at low temperature conditions that are significantly below ambient temperature conditions. In the context of the invention however, in particular in the optional context of offshore hydrocarbon production systems, it is less viable and less advantageous to liquefy and store ammonia at temperature conditions significantly below ambient temperature conditions. This is because there is significant complexity and expenditure, both operational and capital, associated with the equipment, personnel and processes required to produce and maintain ammonia as a liquid at such temperature conditions and at ambient pressure conditions. In an offshore scenario, limited space also means that it may not be viable to provide the necessary infrastructure to produce liquefied ammonia at ambient pressure conditions.

Thus, it is particularly advantageous in the context of the invention of the first aspect to store liquid ammonia at ambient temperature conditions within a plurality of storage pipes. As noted above, this requires the ammonia to be pressurised at pressure conditions above ambient conditions; however, the pressurisation required is associated with significantly reduced complexity and expenditure, both operational and capital, in terms of the equipment, personnel and processes involved and hence is particularly suited to offshore scenarios.

The use of storage pipes offers a cheap, simple and technically nonchallenging means for handling liquid ammonia at ambient temperature conditions that is superior to other storage solutions.

The step of using the ammonia as an energy source for the power source may take place on/at a single, modular unit of the hydrocarbon production system. For example, combusting ammonia in the combustion engine may take place on/at a single, modular unit of the hydrocarbon production system. The step of storing the ammonia may take place on/at the single, modular unit of the hydrocarbon production system. If present, the generator may be provided on the single, modular unit.

The modular unit may be self-contained, separate and separable from the remainder of the hydrocarbon production system. By modular it is meant that the separate unit may be considered to constitute a module that is self-contained and that can be readily conjoined with and split apart from the remainder of the hydrocarbon production system. That is to say, a modular unit is not integral with the remainder of the hydrocarbon production system. Any connections between the modular unit and the remainder of the hydrocarbon production system may hence be readily reversible (i.e. they are designed to be reversible) such that the modular unit is readily disconnected from the remainder of the hydrocarbon production system (e.g. through electrical/power connections, utilities connections, walkways, etc.).

The method may comprise supplying the power produced at the power source from the modular unit to the remainder of the hydrocarbon production system (e.g. via a cable - more on this feature below).

As above, the single modular unit may be separate from the remainder of the hydrocarbon production system. For instance, this unit may be a separate facility from the portion of the hydrocarbon production system where hydrocarbon producing operations are carried out. In an offshore scenario, the separate modular unit may be a separate floating unit/facility situated adjacent, e.g., a production platform or a floating, production storage and offloading (FPSO) vessel that constitutes the remainder of the hydrocarbon production system.

Having a separate, modular unit is advantageous since it can be easily installed/retrofitted in combination with an already existing hydrocarbon production system (i.e. a brownfield facility) in order that the invention of the first aspect can be implemented without significant downtime in production at the already existent hydrocarbon production system. This also means that minimal modification is required to the already existing hydrocarbon production system for the invention to be employed other than maybe the decommissioning and/or removal of an already existent power source (e.g. gas turbine engine). Such modification/replacement may not be necessary however. It furthermore means the separate modular unit can be moved and used in combination with other already existing hydrocarbon production systems, e.g. after hydrocarbon reserves have been depleted at a first system.

The single, modular unit may form part of a plurality of hydrocarbon production systems. That is to say, a plurality of different hydrocarbon production systems (including the hydrocarbon production system to which the method of the first aspect relates) may comprise a common single, modular unit. The common, single modular unit may provide power to each of the plurality of hydrocarbon production systems. For example, in an offshore scenario, the single modular unit may take the form of a floating unit/facility situated adjacent and connected to a plurality of production platforms, production facilities and/or FPSOs and may provide power for each of the connected production platforms, production facilities and/or FPSOs. In such a scenario, the single, modular unit may be termed an energy hub given that it acts as an energy source for a plurality of systems.

The single modular unit may be connected to the remainder of the/each hydrocarbon production system via appropriate cabling. The cabling may be configured to supply electrical AC power of 50 Hz -60 Hz frequency from the single modular unit to the remainder of the/each hydrocarbon production system.

The single modular unit is not essential however, and the step of using the ammonia as an energy source for the power source and the step of storing ammonia may be carried out at the same facility as the remainder of the hydrocarbon production system. This may be the situation for, e.g., a greenfield production facility where the facility is initially built to operate in accordance with the method of the first aspect.

The method of the first aspect may be employed at a brownfield production facility or at a greenfield production facility.

The ammonia may be grey ammonia, green ammonia and/or blue ammonia.

The method may comprise, prior to the step of using the ammonia as an energy source for the power source and prior to the step of storing, transporting the ammonia to the hydrocarbon production system. The step of transporting may make use of a tanker/vessel in an offshore scenario.

In scenarios where the hydrocarbon system comprises a combustion engine, the hydrocarbon production system may also comprise a steam engine configured to provide power to the hydrocarbon production system. The steam engine may be configured to run in a combined cycled with the combustion engine. That is, the exhaust gases from combustion of the ammonia at the engine may be used to heat water which drives the steam engine to produce power for the hydrocarbon production system. As such, the method may comprise running the steam engine in a combined cycle with the combustion engine to provide power for the hydrocarbon production system. This step of running the steam engine in a combined cycle may comprise using the exhaust gases from the combustion of ammonia at the combustion engine to heat water into steam; and driving a steam engine to produce power for the hydrocarbon production system. The steam engine may be situated on/at the (optional) modular unit.

In a second aspect of the invention, there is provided a hydrocarbon production system, the hydrocarbon production system comprising: a plurality of storage pipes; and a power source configured to provide power for the hydrocarbon production system; wherein the plurality of storage pipes are configured to store liquid ammonia at ambient temperature conditions therein; and wherein the hydrocarbon production system is arranged to use ammonia as an energy source for the power source in order to provide power for the hydrocarbon production system.

The method of the first aspect of the invention, including any optional features thereof, may be a method of operating the hydrocarbon production system of the second aspect of the invention.

The hydrocarbon production system of the second aspect may be in accordance with the hydrocarbon production system discussed above in relation to the first aspect of the invention and may comprise any optional features thereof.

The storage pipes of the second aspect of the invention may comprise liquid ammonia at ambient temperature conditions.

In a third aspect of the invention, there is provided a method of retrofitting an existing hydrocarbon production system, the method comprising: decommissioning and/or removing an existent power source at the hydrocarbon production system: installing a plurality of storage pipes at the hydrocarbon production system; installing at the hydrocarbon production system a new power source configured to provide power for the hydrocarbon production system; and configuring the hydrocarbon production system to use ammonia as an energy source for the power source; wherein the plurality of storage pipes are configured to store liquid ammonia at ambient temperature conditions therein.

The existing hydrocarbon production system may be a brownfield production system.

The hydrocarbon production system resulting from the method of the third aspect may be a hydrocarbon production system in accordance with the second aspect, optionally inclusive of any optional feature thereof.

In a fourth aspect, there is provided a method of assembling a hydrocarbon production system, the method comprising providing equipment and infrastructure configured for the production and/or processing of hydrocarbons; providing a plurality of storage pipes; providing a power source configured to provide power for the hydrocarbon production system; and configuring the hydrocarbon production system to use ammonia as an energy source for the power source; wherein the plurality of storage pipes are configured to store liquid ammonia at ambient temperature conditions therein.

The hydrocarbon production system resulting from the method of the fourth aspect may be a greenfield production system.

The hydrocarbon production system resulting from the method of the fourth aspect may be a hydrocarbon production system in accordance with the second aspect, optionally inclusive of any optional feature thereof.

In accordance with a fifth aspect, there is provided a plurality of hydrocarbon production systems that comprise a common power source and a common plurality of storage pipes; wherein the common power source and the common plurality of storage pipes are both situated on a single, modular unit; wherein the power source is configured to provide power for each of the plurality of hydrocarbon production systems; wherein the plurality of storage pipes are configured to store liquid ammonia at ambient temperature conditions therein; and wherein the plurality of hydrocarbon production systems are arranged to use ammonia as an energy source for the power source to provide power for each of the plurality hydrocarbon production systems.

One or all of the hydrocarbon production systems of the fifth aspect may be in accordance with the hydrocarbon production system of the second aspect, optionally including any optional features thereof. One or all of the hydrocarbon production systems of the fifth aspect may be operated in accordance with the first aspect, optionally including any optional features thereof.

In a sixth aspect, there is provided a method of operating a plurality of hydrocarbon production systems that comprise a common power source and a common plurality of storage pipes; wherein the common power source and the common plurality of storage pipes are both situated on a single, modular unit; wherein the power source is configured to provide power for each of the plurality of hydrocarbon production systems; the method comprising: storing liquid ammonia at ambient temperature conditions within the plurality of storage pipes; and using the ammonia as an energy source for the power source to provide power for the plurality of hydrocarbon production systems. The plurality of hydrocarbon production systems of the sixth aspect may be in accordance with the fifth aspect, optionally inclusive of any optional features thereof.

In a further aspect of the invention, there is provided a method of operating a hydrocarbon production system, the hydrocarbon production system comprising a power source (e.g. a combustion engine) configured to provide power for the hydrocarbon production system and a plurality of storage pipes, the method comprising: storing ammonia as a liquid at ambient temperature conditions in the plurality of storage pipes; and fuelling the power source with the ammonia (e.g. combusting the ammonia in the combustion engine) to provide power (e.g. electrical power) for the hydrocarbon production system.

Certain embodiments of the invention will now be described, by way of example only, and with reference to the figures, in which:

Figure 1 is a schematic depiction of an offshore floating facility connected to a tanker and to three separate production facilities;

Figure 2 is a perspective view of the offshore floating facility of Figure 1;

Figure 3 is a cross-sectional view of the offshore floating facility of Figures 1 and 2;

Figure 4 shows a gas engine of a generator positioned on the offshore floating facility of Figures 1 to 3;

Figure 5 is a part-cutaway side view and cutaway plan view of the tanker of Figure 1; and

Figure 6 is a pressure enthalpy chart for ammonia.

Figure 1 shows an offshore floating facility 1 that is connected by three separates cables 3a, 4a, and 5a to three separate production facilities 3, 4, 5. Production facility 3 is an offshore production platform 3, production facility 4 is another offshore production platform 4, whilst production facility 5 is a floating, production, storage and offloading (FPSO) 5. Each production facility 3, 4, 5 is situated at its own respective hydrocarbon reservoir and is arranged to permit production of hydrocarbons from its respective reservoir via suitable production and processing equipment. The cables 3a, 4a, 5a are each electrical power cables 3a, 4a, 5a that are configured for carrying electrical power from the offshore floating facility 1 to each of the production facilities 3, 4, 5 in order to provide power thereto, as will be described in further detail below. Also connected to the offshore floating facility 1 is a tanker 2. The tanker 2 is connected to the offshore floating facility 1 via two separate conduits 2a, 2b that are each arranged to carry a fluid, specifically ammonia, between the tanker 2 and the offshore floating facility 1 as will be described in greater detail below. The conduits 2a and 2b are reversibly connected to the tanker 2 as discussed in further detail below.

As can be seen in greater detail with reference to Figures 2 and 3, the offshore floating facility 1 has a predominantly ship shaped hull 101 and, situated at a top of the hull 101 , a landing pad 102 for helicopters to permit personnel access to the facility 1 for maintenance or otherwise. Housed with the hull 101 are a plurality of vertically oriented storage pipes 103. The storage pipes 103 are arranged to store liquid ammonia therein at ambient temperature conditions and, consequently, at pressures of between 5 barg - 20 barg (the exact pressure of storage being dependent on the ambient temperature conditions as discussed below with reference to Figure 6). Each storage pipe 103 is formed from a section of pipe having an X42 specification and that is sealed at either end via a suitable hemispherical cap. As shown, several hundred storage pipes 103 are housed within the hull 101 of the offshore floating facility 1.

The hull 101 also comprises a plurality of generators 105 that each comprise a gas engine 107. Each gas engine 107, further details of which can be seen in Figure 4, is a V18 engine which is specifically configured to combust gaseous ammonia therein. Motive power produced by each engine 107 drives electricity generation at each generator 105.

Each of the generators 105 are connected to the cables 3a, 4a, 5a in a manner that permits electrical power produced at the generators 105 to be passed via the cables 3a, 4a, 5a to the production facilities 3, 4, 5.

Figure 5 shows further details of the tanker 2. The tanker 2 comprises a plurality of storage pipes 23 (again, several hundred storage pipes 23) divided between several cargo holds 25 on the tanker 2. The storage pipes 23 are comparable to storage pipes 103 situated on the offshore floating facility 1 in that they are vertically oriented on-board the tanker 2 and are arranged to store liquid ammonia therein at ambient temperature conditions and, consequently, at pressures of between 5 barg - 20 barg (the exact pressure of storage being dependent on the ambient temperature conditions). Each storage pipe 23 is formed from a section of pipe having an X42 specification and that is sealed at either end via a suitable hemispherical cap.

In use, the storage pipes 23 on-board the tanker 2 are loaded with ambient temperature liquid ammonia at an onshore site remote from the offshore floating facility 1 and the production facilities 3, 4, 5. The tanker 2 then travels to a site of the offshore floating facility 1 (e.g. as shown in Figure 1) whilst the liquid, ambient temperature ammonia is maintained as such within the storage pipes 23. This is achieved by ensuring that the storage pipes 23 remain suitably pressurised during transit of the tanker 2. Once at the site of the offshore floating facility 1 , the conduits 2a, 2b are connected to the tanker 2. Liquid ammonia is then offloaded from the storage pipes 23 on the tanker 2 to the offshore floating facility 1 via the conduit 2a and is transferred into the storage pipes 103 on-board the offshore floating facility 1 for storage therein.

The transfer between the storage pipes 23 and the storage pipes 103, and the subsequent storage therein, is carried out whilst maintaining, as far as possible, the ammonia as a liquid at ambient temperature conditions. This requires the transfer and subsequent storage in the pipes 103 to be carried out at suitably pressurised conditions. It may not however be possible to maintain all ammonia in a liquid state during this transfer and subsequent storage. For example, prior to introduction of liquid ammonia from the tanker 2 to the storage pipes 103, the interior of the storage pipes 103 may be under ambient pressure conditions and be filled with air and/or gaseous ammonia left over as a remnant from a previous stock of ammonia. As such, initial introduction of the pressurised liquid ammonia at ambient temperature conditions into the storage pipes 103 will result in an initial depressurisation of some liquid ammonia such that it is vaporised into a gaseous form. Soon after however, the storage pipes 103 will pressurise sufficiently such that further introduced ammonia will remain in a liquid state at ambient temperature conditions.

In the event of vaporisation of any portion of the ammonia during its transfer between the tanker 2 and the offshore floating facility 1 (e.g. after initial introduction into the storage pipes 103 as discussed above), then the vaporised portion of the ammonia is separated off from the liquid ammonia at the offshore floating facility 1 and is transferred back to the tanker 2 via the conduit 1b. This gaseous ammonia can then be re-condensed on board the tanker 2 at ambient temperature conditions and subsequently transferred back to the offshore facility 1 via the conduit 1a for storage thereon. Alternatively, the gaseous ammonia can be stored aboard the tanker 2 for transit back to, e.g., an on shore site. Once all of the liquid ammonia has been offloaded from the tanker 2, the conduits 2a, 2b are disconnected. The tanker 2 then travels away from the offshore floating facility, optionally back to an onshore site for further loading and transport of ammonia.

The liquid ammonia stored within the storage pipes 103 aboard the offshore floating facility 1 is used as a fuel to power the gas engines 107 comprised as part of generators 105. As such, the storage pipes 103 on-board the floating facility 1 serve as a buffer storage for fuel for the generators 105.

Specifically, the liquid ammonia stored within the storage pipes 103 is sent from the storage pipes 103 to an inlet of the engines 107. During transit between the storage pipes 103 and the gas engine 107 the liquid ammonia is vaporised, either passively as a natural result of depressurisation that occurs during transit and/or actively via a suitable vaporiser, into a gaseous form. In its gaseous form, the ammonia can then be appropriately introduced into the gas engine 107 for combustion therein.

Combustion of the ammonia in the engines 107 drives electricity generation at the generators 105. The electrical power (e.g. rated at 7 MW) produced at the generators 105 is then transferred via the cables 3a, 4a, 5a from the offshore floating facility 1 to the production facilities 3, 4, 5 and is used to power operations at the production facilities 3, 4, 5, including powering the production and processing equipment situated thereat.

The offshore floating facility 1 thus acts as an energy hub for a plurality of hydrocarbon production facilities 3, 4, 5 and serves to provide power for production and other operations that occur at each facility. The floating facility 1 is thus comprised as part of a plurality of hydrocarbon production systems, wherein the remainder of each system is formed by a respective production facility 3, 4, 5.

Figure 6 shows a pressure-enthalpy chart for ammonia. Pressure is represented along the y-axis whilst enthalpy is represented along the x-axis. The region below the saturation line 61 (termed ‘saturation dome’) represents where any addition of enthalpy will cause additional liquid ammonia to vaporize instead of raising the temperature of the ammonia. The red lines on the chart indicate constant temperatures and, whilst not depicted therein, it can be deduced from the temperature values given either side of the saturation dome that the temperature lines would be at a complete horizontal through the saturation dome. The green lines on the chart each represent a constant ratio of vapour mass to total mass of the ammonia.

The region 63 shown in blue represents where ammonia is at ambient temperature conditions (i.e. 0°C - 40 °C) within the saturation dome. Within region 63 the vast majority of ammonia would be in a liquid state whilst being at ambient temperature conditions as can be deduced from the ratios of vapour mass to total mass of the ammonia in this region. The ambient temperature liquid ammonia that is stored in the storage pipes of the invention would typically fall within region 63 of the pressure-enthalpy chart.