AU2012207059B2 - Linked LNG production facility - Google Patents

Abstract

- 23 Abstract A fixed LNG production facility positioned in a body of water at a production location is described, The facility comprises a plurality of spaced-apart modules, each module 5 provided with plant equipment related to a pre-determined function associated with the production of LNG and wherein adjacent modules are linked together using one or more bridges positioned, in use, above the body of the water. co Cl NN 4%D \ I 1 ,lo 4% 4O 00 ( 0"U Nq M 0to

Description

- 1 LINKED LNG PRODUCTION FACILITY FIELD OF THE INVENTION The present invention relates to a fixed offshore or near-shore liquefied natural gas 5 ("LNG") production facility. The LNG production facility of the present invention is particularly suited for remote gas fields. The present invention relates to both a small scale and or full scale fixed LNG production facility located offshore or near shore. BACKGROUND TO THE INVENTION 10 Natural gas ("NG") is routinely transported from one location to another location in its liquid state as "Liquefied Natural Gas ("LNG"). Liquefaction of the natural gas makes it more economical to transport as LNG occupies only about 1 1 6 0 0 th of the volume that the same amount of natural gas does in its gaseous state. After liquefaction, LNG is typically 15 stored in cryogenic containers either at or slightly above atmospheric pressure. LNG is regasified before distribution to end users through a pipeline or other distribution network at a temperature and pressure that meets the delivery requirements of the end users. Conventional LNG production from offshore gas fields involves the use of upstream 20 receiving facilities which deliver treated wellhead gas through large diameter gas pipelines to shore, onshore LNG plants, onshore storage terminals and deepwater export terminal jetties. Commonly there is further treatment of the gas onshore. Typically the only offshore treatment is drying and sometimes removal of liquids, Further treatment (removal of acid gases, drying to < 1 ppm water, mercury removal and removal of LPGs to obtain 25 desired heating value) is generally done onshore. These conventional facilities are typically large and the costs associated with building and operating such facilities are significant. One of the most significant development costs associated with conventional onshore LNG production is the cost of laying and maintaining the offshore pipeline that links the offshore gas field with the onshore LNG production facility, some of which can be 30 more than 400 km in length. Various floating offshore development concepts have been considered in the past that combine upstream receiving facilities along with downstream processing facilities on a singular offshore facility to process stranded gas or associated gas, 35 -2 For example, US Publication Number 2006/0000615 describes a method for developing a sub-sea hydrocarbon field. Sub-sea flow lines convey the natural gas output from a sub sea oil/gas separator to a Floating Production Storage Shuttle Vessel (FPSSV). Natural gas is liquefied using an LNG Production Facility located aboard the FPSSV, the LNG so 5 produced being stored in storage tanks onboard the FPSSV. When the storage tanks are full, the FPSSV transports the LNG to an onshore terminal. At the onshore terminal, the LNG is re-gasified and a new batch of liquid nitrogen is produced using energy recovered during LNG regasification. 10 US Publication Number 2006/0010910 and US Publication Number 2006/0010911 A each describe methods and systems for transportation of a cryogenic fluid. The system includes a floating liquefaction unit receiving a gas from a source, a shuttle vessel for carrying liquefied gas away from the liquefaction unit, and a floating regasification unit for receiving the liquefied gas from the vessel, regassifying the liquefied gas and providing 15 the gas to a distribution system. The cryogenic fluid is preferably LNG. The floating liquefaction unit is positioned on a body of water and is moored via a connection to a source of natural gas. This source of natural gas may be a direct pipeline connection to natural gas being produced from a well (s), a mobile vessel (s), or to storage tanks. Periodic connections could also be made to land or marine transport vessels carrying 20 storage tanks of natural gas. US Publication Number 2003/0226373 A describes a process and apparatus for exploitation and liquefaction of natural gas in offshore stranded gas reserves. Two ordinary nautical vessels are used to produce, store and unload LPG and LNG. Typical 25 front end gas processing is performed on the first vessel to produce a treated inlet gas stream. The treated inlet gas is transported to the second vessel where the stream goes through liquefaction and storage until the LNG can be offloaded to a transport vessel for shipment. The liquefaction process utilizes two refrigerant cycles that utilize two expanded refrigerants, at least one of which is circulated in a gas phase refrigeration 30 cycle. The refrigerants and the inlet gas stream are transported between the two vessels by the use of piping. US Patent 6,003,603 (Breivik) teaches the use of two ships for the processing and storage of offshore natural gas. The first ship includes the field installation for gas treatment. The -3 treated gas is then transferred in compressed form to an LNG Carrier for conversion to a liquefied form, which is stored on the LNG Carrier. Breivik utilizes a single refrigerant for cooling purposes within the liquefaction process, which is either in a liquid phase or a mixed phase. Once the LNG Carrier storage vessels are full, the LNG Carrier is 5 disconnected from a buoy to which it is attached and sets sail. Another LNG Carrier takes its place to receive the treated inlet gas for liquefaction. The LNG Carrier is required to be seaworthy in order to transport the LNG product from the stranded reserves to facilities for further use. 10 International Patent Publication Number WO 1996/036529 describes a method of loading and treatment of a gaseous or liquid hydrocarbon mixture produced on an offshore production platform, a production vessel or a well installation when producing oil and gas from a reservoir, wherein the mixture is supplied to a gas treatment vessel via a buoy loading system comprising a buoy of the STL/STP type, and is treated on board the vessel 15 for producing liquefied natural gas (LNG) or an LPG mixture stored in tanks on the vessel, Simultaneously with the supply of the hydrocarbon mixture, oil is also supplied to the vessel via the same buoy, the buoy including a multi-course STP connector, the oil being transferred directly from the STP connector via a pipeline and an unloading means on the vessel to a tanker for storage and transport of the supplied oil. 20 GB Patent 1596330 relates to a process for the production of a liquefied natural gas, preferably offshore, which process comprises the steps of supplying gaseous natural gas to a sea-going vessel which is adapted to store and transport LNG, and passing the said gaseous natural gas and a liquefied gas through a heat exchanger situated on board the 25 said sea-going vessel so that the said gaseous natural gas is liquefied and the said liquefied gas is gasified, the said liquefied gas having a boiling point at atmospheric pressure which is lower than the critical temperature of methane. Liquid air or nitrogen is produced on shore and transported in a tanker to the field. The tanker is equipped with heat exchangers and other equipment for gas liquefaction. At the field are one or more 30 mooring terminals to which the tanker can be moored and connected to a supply of gas from the production facilities, most probably via a subsea flowline, buoy riser, and loading hose. After mooring, gas is admitted to the liquefaction plant on or in the tanker and liquefied by heat exchange with the liquid air/nitrogen. Before its liquefaction each gas has to be pre-treated to remove therefrom impurities, such as water and carbon dioxide, to an -4 extent which is sufficient to avoid blockages, The liquefied gas is then stored in the cryogenic tanks on the tanker until a full or substantial load is achieved. The tanker unmoors and returns to port. Here, LNG is discharged, liquid air/nitrogen reloaded, and the cycle re-commenced. By the use of more than one tanker and mooring terminal, 5 continuous gas liquefaction can be achieved by the field. International Patent Publication Number W02002/021060 describes a floating plant for liquefying natural gas comprising a barge which is provided with a liquefaction plant, means for receiving natural gas, means for storing LNG and means for discharging LNG. 10 The liquefaction plant includes a heat exchanger in which heat removed when liquefying natural gas is transferred to water. The liquefied natural gas is stored in the barge and it can be discharged into a vessel suitable for transporting the liquefied natural gas to shore, European Patent Publication Number EP130066 relates generally to a method and system 15 for producing natural gas from wells located offshore, and making it available to a terminal installation. This patent describes transporting pressure vessel means mounted on watercraft, which are utilized to recover raw natural gas from shut-in offshore wells. After a discrete batch of raw gas is contained within the transporting pressure vessel means, the watercraft is moved to a processing station, also preferably located on a platform 2 0 offshore. At the processing station, liquids are separated from the natural gas, and then the natural gas is passed through a dehydrator and compressor before entering a pipeline. In all of these prior art offshore concepts, the LNG production facilities are floating, with the plant equipment for liquefaction located onboard the same barge or vessel within 25 which the LNG is stored. The power generation facilities, the vents, the flares, and the crew accommodation facilities are all located on the same barge or vessel which results in an unacceptable risk in the event of an incident, accident or mishap at sea. Another drawback with these prior art offshore concepts is the limited space which requires that the LNG production facility is designed to fit within the compact footprint of a barge or 30 vessel and is restricted to a particular fixed size. The layout issues are further complicated by some of the equipment being sensitive to motion during different sea states. There are also large loads placed on plant equipment on such barges as a consequence of wave motion upon these floating structures and the overall stability of the structure is dependent upon maintaining a low centre of gravity.

- 5 There remains a need to explore alternative designs for LNG production facilities. SUMMARY OF THE INVENTION According to a first aspect of the present invention there is provided a fixed LNG 5 production facility positioned in a body of water at a production location, the facility comprising a plurality of spaced-apart modules, each module provided with plant equipment related to a pre-determined function associated with the production of LNG wherein at least a portion of the body of water is a body of shallow water such that the base of at least one of the spaced-apart modules rests on a bottom of the body of shallow 10 water to secure the position of said module, and wherein the production facility comprises a variable number of modules for tailoring the production capacity of the LNG production facility for the production location. In one form, the body of shallow water has a depth in the range of 2 to 50 meters or 10 to 15 35 meters or 15 to 30 meters or 2 to 20 meters. In one form, one or more of the plurality of modules is transportable from a construction location to an assembly location by towing or on floating barges. 20 In one form, one or more of the plurality of modules is transportable from a construction location to the production location by towing or on floating barges. In one form, a transportable module is settled into the body of shallow water by adjusting the ballast or buoyancy of the module through the addition of a ballasting material. 25 In one form, a module includes a ballast storage compartment arranged around the periphery of the module or arranged toward the base of the module for ballasting. In one form, the ballast storage compartment is at least partially filled with one or both of a 3 0 solid ballasting material or a liquid ballasting material. In one form, the solid ballasting material is iron ore or sand. In one form, the liquid ballasting material is one or more of: water, condensate, - 6 monoethylene glycol (MEG), methanol, diesel, demineralised water, or, LPG. In one form, the production facility includes a liquefaction module for receiving a stream of treated gas from a gas processing module and liquefying the treated gas to produce LNG, 5 a storage module operatively associated with the liquefaction module for receiving and storing LNG, and, a berthing module including LNG transfer facilities to transfer the LNG from a storage module to an LNG Carrier, and, wherein the storage module has a sub structure in the form of a gravity based structure such that that the base of the storage module rests on the bottom of the body of shallow water. 10 In one form, the production facility includes a liquefaction module for receiving a stream of treated gas from a gas processing module and liquefying the treated gas to produce LNG, a storage module operatively associated with the liquefaction module for receiving and storing LNG, and, a berthing module including LNG transfer facilities to transfer the LNG 15 from a storage module to an LNG Carrier, and, wherein the liquefaction module has a sub structure in the form of a gravity based structure such that that the base of the liquefaction module rests on the bottom of the body of shallow water. In one form, the facility includes a liquefaction module for liquefying treated natural gas to 20 form LNG and a storage module for receiving and storing LNG from the liquefaction module, and wherein the storage module is arranged to act as a breakwater for the LNG Carrier. In one form, the facility includes a liquefaction module for liquefying treated natural gas to 25 form LNG and a storage module for receiving and storing LNG from the liquefaction modules, wherein the storage module includes at least one cryogenic storage tank for storing LNG and the cryogenic storage tank is hydrostatically stable when partially filled. In one form, the storage module includes at least one cryogenic storage tank for storing LNG and the cryogenic storage tank includes a plurality of internal baffles and a 30 supporting hull structure. In one form, the storage module includes at least one cryogenic storage tank for storing LNG and the cryogenic storage tank is a double containment, full containment, prismatic or membrane system storage tank with a primary tank constructed from, by way of -6A example, but not limited to stainless steel, aluminum, and/or 9%-nickel steel. In one form, storage module includes at least one cryogenic storage tank for storing LNG and the cryogenic storage tank includes pre-tensioned concrete. 5 In one form, the production facility includes a liquefaction module for receiving a stream of treated gas from a gas processing module and liquefying the treated gas to produce LNG, a storage module operatively associated with the liquefaction module for receiving and storing LNG, and, a berthing module including LNG transfer facilities to transfer the LNG from a storage module to an LNG Carrier, and wherein the storage module is arranged to 10 provide a breakwater to protect an LNG Carrier from wave impact whilst berthed during berthing loading. In one form, the storage module is an LNG Carrier. In one form, one or more of the plurality of modules is in the form of fixed platforms or jacket structures. In one form, one 15 or more of the plurality of modules is arranged on one or more steel or concrete barges or bricks. In one form, the production location is an offshore location. In one form, the production location is a near-shore location. 20 According to a second aspect of the present invention there is provided a method of using the LNG production facility of any one form of the first aspect of the present invention comprising the steps of: a) receiving natural gas from a well; 25 b) liquefying the natural gas to form LNG using a liquefaction module; c) transferring the LNG from the liquefaction module to a storage module; d) storing the liquefied natural gas in the storage module; and e) loading the LNG from the storage module onto an LNG Carrier. 30 BRIEF DESCRIPTION OF THE DRAWINGS In order to facilitate a more detailed understanding of the nature of the invention several embodiments of the present invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 is a schematic plan view of one embodiment of the present invention; -7 FIG. 2 is a process diagram illustrating the use of a plurality of independent construction locations, an assembly location and relocatability of the LNG production facility from a first location to a second location; FIG. 3 is a side view of one embodiment of the present invention illustrating 5 the use of jacket structures in deepwater and gravity based structures in shallow water; FIG. 4 is a schematicview of another embodiment of the present invention; FIG. 5 illustrates a flow chart for cooling of a refrigerant using one or more fin fan or air fin coolers with fans used to direct the flow of air towards the outside surface of the air fin coolers as the refrigerant passing through the tubes thereof; and, 10 FIG. 6 is a cross-sectional view of two air fin coolers stacked at an angle on a bridge in an A-frame arrangement to maximize the surface area available for cooling for a given footprint size available on the bridges. DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS 15 Particular embodiments of the present invention are now described. The terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs. 20 With reference to FIG.1, the present invention relates to a fixed LNG production facility 10 positioned in a body of water 12 at a production location 14, such as an offshore or near shore gas field. The term "fixed" as used throughout this specification means "set in position at a predetermined or prearranged location". It is to be clearly understood that 25 this does not imply that the production facility must remain at a given production facility permanently. The LNG production facility 10 comprises a plurality of spaced-apart bridge linked modules 16, each module having a pre-determined function associated with the production of LNG. The production location 14 can be remote offshore or near-shore. 30 The LNG production facility includes at least the following modules: a) at least one gas processing module 18 for receiving raw hydrocarbons from a producing well and treating the raw hydrocarbons to remove contaminants therefrom to produce a stream of treated gas; b) at least one liquefaction module 20 for receiving the stream of treated -8 gas from a gas processing module 18 and liquefying the natural gas to produce LNG; c) at least one storage module 22 operatively associated with the liquefaction module 20 for receiving and storing LNG; and, d) at looot one berthing module 24 including LNC transfer facilities 20 Lo 5 transfer the LNG from a storage module 22 to an LNG Carrier 28 on an as-needs basis. Other additional modules may be included in the fixed LNG production facility 10 of the present invention. Advantageously, utilities may be shared using a separate spaced apart utility module 32 which acts as a hub servicing some or all of the other modules in 10 the LNG production facility 10. Alternatively, each other module 16 may be associated with its own separate utility module. The utility module 32 provides such services as power, potable water, compressed air, nitrogen, and heated water to the liquefaction module 20 and/or the gas processing module 18. When the LNG production facility 10 is manned, accommodation for the personnel may be provided on the gas processing or 15 liquefaction modules 18 and 20 respectively, or a separate spaced-apart accommodation module 34 can be used for greater safety as discussed in greater detail below. A supply system 30 in the form of piping and associated pumps, manifolds and valves, etc is also provided for transferring treated gas from a gas processing module 18 to a liquefaction module 20 and for transferring LNG from a liquefaction module 20 to a storage module 22. 20 The plurality of spaced-apart modules 16 are linked by bridges 36, the bridges 36 being elevated at a clearance of at least at least 25 metres - 30 metres above the slash zone. The bridges 36 perform various functions. They can be used as walkways or used as roadways to facilitate vehicle access between the spaced-apart modules 16. More 25 advantageously, when the supply system 30, including piping and associated pumps, instrumentation, manifolds and valves etc are arranged on the bridges 36, several benefits are realised. Firstly, locating the supply system above the splash-zone means that the supply system 30 is exposed to a marine environment which is less severe than a sub-sea environment, leading to a reduction in costs as materials of construction. For example, 30 carbon steel piping painted with marine grade paint can be used instead of more expensive stainless steels. Secondly, locating the supply system above the splash zone leads to reduced costs associated with maintenance and inspection operations given that maintenance and inspection are easier to perform in a marine environment than a sub-sea environment. For example, maintenance can be carried out using floating barge cranes -9 (not shown) which are manoeuvrable along the bridges 36. Thirdly, arranging the supply system 30 on the bridges 36 leads to a reduction in the impact on the sub-sea environment which occurs when trenching is used to lay sub-sea pipelines. 5 With reference to FIG. 2, the modules 16 can be separately constructed at one or more independent construction location(s) 40 and then transported to the production location 14, where the modules are installed, bridge-linked and then operatively linked to produce and store LNG. Constructing the modules at a plurality of separate independent construction locations 40 provides a number of advantages over prior art methods. 10 Construction of each type of module can occur at different construction locations to take advantage of expertise of different suppliers located at different construction locations. Similarly, construction can occur at different times to allow overall construction time to be fast-tracked. For example, the construction of the liquefaction modules can take place in the Middle East, with construction of the storage modules taking place in South East Asia 15 and the construction of the gas processing module can occur in Australia, all to service the needs of a production location off the coast of Africa or the Gulf of Mexico. The bridges 36 are able to be constructed on site using a plurality of prefabricated sections. The sections are constructed to accommodate thermal expansion in use. In 20 one embodiment of the present invention, the prefabricated sections include sections of piping which can be joined together on-site. Each module 16 may comprise a plurality of similarly-sized sub-modules 42, which can be integrated at the production location 14 or at an independent assembly location 44. The 25 sub-modules 42 may be constructed a separate construction locations 40 and towed to a common assembly location 44 for integration. This option is particularly attractive if there is a restriction on the space available at the dry dock or "graving dock" or restrictions on the towable or installable size of a given module. Advantageously, once the sub-modules 42 have been assembled to form a module '16 at the assembly location 44, testing or 30 commissioning of the module 16 can be conducted before transportation of the module to the production location 14. It is particularly advantageous when such commissioning can be done at an assembly location onshore prior to transportation of the module to a production location offshore.

- 10 The present invention provides significant advantages over prior art offshore LNG plants in terms of flexibility. The bridge-linked modular construction allows for additional modules or sub-modules 42 to be added or removed, if applicable due to late changes to the process functionality. The number and size of the various modules 16 and/or sub 5 modules 42 can be tailored to suit the changing needs of a particular site or to suit the changing flow from a reservoir over its production life cycle of a gas reservoir - for example, the number of liquefaction modules 20 may vary from time to time. The flexibility of the LNG production facility 10 of the present invention allows economic exploitation of small offshore gas fields that would otherwise not be developed. This significantly 10 increases the number of gas reserves around the world that can be developed as LNG, particular those that are far from the mainland or those which would require onshore plants with significant civil engineering, environmental or social challenges. Moreover, the operating capacity of the LNG production facility 10 may change over time 15 based on a number of factors including depletion of hydrocarbons in the field over time, changes in the storage capacity of the LNG Carriers into which the LNG produced at the production facility is loaded, the desired peak production capacity of the production facility, the rate at which LNG from a storage module 22 is transferred to an LNG Carrier 28, and/or costs associated with operating the LNG production facility. Additional storage 20 modules 22 may be added at a latter date if it becomes apparent that production is higher than anticipated or loading schedules are longer than anticipated. In some cases, the production capability need only be small, for example, in the range of one to two million tonnes a year. When supply of gas at a particular location diminishes or increases or stops, the size and location of the modular LNG plant can change to suit the change in 25 conditions. In one embodiment, the modules 16 are transportable in that they are movable from the construction location(s) 40 to the production location 14 or the assembly location 44 by towing or on floating barges 46. This feature not only allows the modules to be deployed 30 where required but is also advantageous when maintenance or upgrading is required. To reduce frictional drag on the modules 16 during transport, the bow section of the substructure of the module 16 can be shaped (in an analogous manner to the bow of a ship).

- 11 The various modules 16 can equally be re-deployed at different locations at different times to suit LNG supply and demand. Similarly individual modules 16 or sub-modules 42 can be moved to another location where demand is higher. In one embodiment, individual modules 16 or sub-modules 42 can be reused or relocated or replaced at a point in time 5 when they are no longer required due to changes in the capacity of the production facility 10 or towards the end of the field life. Thus with reference to FIG. 2, one or more of the modules 16 can be moved from a first production location 14' to a second production location 14". 10 The modules 16 comprising the LNG production facility 10 of the present invention may take the form of fixed platforms or "jacket structures" 60 or a gravity based structure 62, depending on such relevant factors as the contours and depth of the bottom of the body of water 12 at the production location 14 and the type of module 16. In another embodiment, one or more of the modules 1 are arranged on one or more steel or concrete barges or 15 "bricks". Irrespective of the depth of the body of water 12, a gravity based structure is preferred for some types of modules 16 for maximum safety and stability against extreme weather conditions. By way of example, it is preferable to construct the sub-structure of the liquefaction module(s) 20 as a concrete gravity base structure using sub-modular construction and assembly for the topside equipment arranged on that substructure. The 20 gravity based structure is constructed using lightweight or semi-lightweight concrete (having a density of less than about 2000kg/ma), A key advantage of the use of a gravity based liquefaction module 20 is that it provides a stable base which allows the LNG plant to continue production in extreme weather conditions. Thus for greater stability, the spaced-apart bridge-linked modules are arranged at the production location 14 such that 25 at least a portion of a bottom surface 48 of each gas processing module 18 and/or each liquefaction module 20 rests upon a portion of a bottom 50 of the body of water 12. In one embodiment of the present invention, at least a portion of the production location 14 is located in shallow water. The water depth at the shallow water production location 30 14 may be in the range of 2 to 50 meters, preferably 10 to 35 meters, more preferably 15 to 30 meters or 2 to 20 meters. Each transportable module 16 is towed from the construction or assembly location, 40 or 44 respectively, to the production location 14 and then arranged in a suitable pre-determined position to suit the needs of the LNG production facility 10. If the pre-determined position is located in shallow water, settling is -12 achieved by adjusting the ballast or buoyancy of each transportable module 16, for example through the addition of water, iron ore or other suitable ballasting material. The transportable modules are settled into the shallow water such that at least a portion of the base 48 of each module 16 rests on the bottom 50 of the body of shallow water 12 to 5 secure the position of the module 16. This provides the shallow water modules 16 with greater stability. To facilitate the ballasting process, the shallow water modules 16 are provided with a ballast storage compartment 52 arranged around the periphery or toward the base 48 of 10 the module 16 for ballasting. In use, the ballast storage compartment 52 is at least partially filled with solid and/or liquid ballast material. For example, in certain embodiments, sand and/or iron ore may be used as solid ballast material. The amount of ballast required to secure the shallow water modules depends on a number of relevant factors including but not limited to the shear strength of the underlying clay or silt material 15 found at the bottom of the body of water. In one embodiment of the present invention, water, condensate, monoethylene glycol (MEG), methanol, diesel, demineralised water, diesel, LPG or combinations thereof are stored in the ballast storage compartments 52 to supplement the permanent liquid or solid 20 ballast used to ground the shallow water module 16. This reduces the number of additional storage tanks which would otherwise be needed and allows much larger quantities of the liquids to be stored at the LNG production facility 10 (enhancing facility operability) at minimal extra cost. 25 With reference to FIG.3, for modules which are intended to be located in deep water at the production location, such modules may be constructed in the form of a fixed platform, semi-submersible platforms (such as a tension-leg platform or a "SPAR") or "jacket" structure 60. These deep water modules 16 are arranged to support the various equipment used for the function of the given module above the waterline 62 (for ease of 30 operation and to reduce damage from overtopping waves and/or green water) with the base of the structure being secured in position relative to the bottom 50 of the body of water 12 at the production location 14.

-13 Combining the upstream gas receiving facilities and the downstream LNG processing facilities at a single production location has a number of advantages. Firstly, the need to install, operate, maintain and pay tariffs on an expensive gas pipeline to shore is removed, making production of stranded gas fields economically feasible. More importantly, 5 combining these facilities at a single production location provides a number of synergistic benefits. The upstream and downstream facilities are able to share personnel, consumables and power to reduce overall operating costs associates with the LNG production facility. A common utility module 32 is used to provide power to both the gas processing module 18 and the liquefaction module 20 to reduce overall sparing. Similarly, 10 the common utility module 32 is arranged to distribute air, water and nitrogen between the gas processing 18 and liquefaction module 20. Excess heat from power generation associated with the utility module 32 can be used to provide heating to the MEG (monoethyleneglycol) recovery system. 15 The proximity of the liquefaction module 20 to the wellhead 54 results in an increase in the throughput of the liquefaction module 20 allowing for an increase in throughput through the liquefaction module 20, compared the prior art in which the gas pressure is reduced during transport of the gas through a pipeline to an onshore LNG plant. Another advantage of receiving gas at wellhead pressures is that as the pressure of the reservoir 20 drops over its life, less compression of the gas is required to remove residual gas from the reservoir, Exemplary examples of embodiments of the fixed LNG production facility of the present invention are now described with reference to FIG. 1 and FIG. 4 for which like reference 25 numerals refer to like parts. In each of FIG. 1 and FIG. 4, a specific number of modules is shown with "future" modules associated with potential future process functionality shown in 'dotted' lines. However, it is to be understood that the specific number of each type of module may vary depending on such factors as the production location geometry, the quality of the wellhead gas, the production capacity of the LNG production facility and may 30 also vary over the production life of the field. A first embodiment of the present invention is illustrated in FIG. 1 which illustrates a fixed LNG production facility 10 which includes two gas processing modules 18 for conditioning the wellhead gas, two liquefaction modules 20 for liquefying treated natural gas to form - 14 LNG, a single utility module 32 including power generation, two storage modules 22 for receiving and storing LNG from the liquefaction modules 20, two berthing modules 24, two spaced-apart flares 56 and a supply system 30. In this embodiment, the accommodation module 34 is adjacent to the utility module 32 but is still spaced-apart at a safe distance 5 from both the gas processing module 18 and the liquefaction module 20 and the flares 56 to maximize safety. The utility module 32 can be arranged to provide a breakwater for the accommodation module 34 or vice versa if desired. The modules are linked by bridges 36. 10 In FIG.1 the contours of the production location 14 are such that the gas processing modules 18, the flares 56, the utility module 32 and the accommodation module 34 are arranged in deepwater and are constructed using 'jacket' substructures with plant equipment arranged on the platform topsides. The liquefaction modules 20 and storage modules 22 are constructed in shallow water and are concrete gravity based structures. 15 The storage modules 22 are arranged to act as a breakwater to reduce environmental loads on the liquefaction modules 20. In use, wellhead hydrocarbons are delivered to the gas processing modules 18 via a flow line from one or more wellhead(s) 54 located either sub-sea or on a production platform. 20 The wellhead hydrocarbons may be passed through a slug-catcher 55 to allow removal of condensate to ensure a steady flow of gas entering the gas processing modules 18. The gas processing modules include a separator for effecting initial separation of natural gas from particulates, natural gas liquids (NGL) and condensate. The NGL and condensate streams can be subjected to further fractionation to produce LPG or for use as 25 refrigerants, if desired. The separated natural gas is then subjected to conditioning on the gas processing modules 18 to remove contaminants prior to liquefaction. More specifically, hydrogen sulphide and carbon dioxide can be removed using a suitable process such as amine 30 absorption. When amine absorption is used, the absorber and regeneration equipment are located on the gas processing modules 18- The heat required for amine regeneration is taken from waste heat from gas turbines used to drive LNG train compressors. Advantageously, due to the proximity of the reservoir, the carbon dioxide so removed can be dewatered, compressed, liquefied and re-injected into the reservoir to reduce - 15 greenhouse gas emissions. The natural gas is subjected to further conditioning to remove water and other contaminants, such as mercury and heavy hydrocarbons prior to liquofootion. Romoval of water can be achieved using conventional methods, for eexmple a molecular sieve. 5 The treated natural gas from the gas processing modules is delivered to one or more liquefaction modules 20. The liquefaction module is designed to receive natural gas from the gas processing module and liquefy the natural gas to produce LNG which is sent out to the storage module(s). Liquefaction is achieved onboard each liquefaction module 10 using any liquefaction process well established in the art which typically involve compression, expansion and cooling. Such processes include processes based on a nitrogen cycle, the APCI C3/MRIm or Split MRTM or AP-XIr processes, the Phillips Optimized Cascade Process, the Linde Mixed Fluid Cascade process or the Shell Double Mixed Refrigerant or Parallel Mixed Refrigerant process. 15 Regardless of the choice of liquefaction process, a refrigerant is used to reduce the temperature of the treated wellhead gas to a temperature of around -1 60*C to form LNG, resulting in warming of the refrigerant to a temperature in the order of 50 - 70*C. In the embodiment illustrated in FIG. 5, the refrigerant is cooled using one or more fin fan or air 20 fin coolers 66 from a temperature in the order of 50-70*C to a temperature in the order of 30*C. One or more fans 66 are used to direct the flow of air towards the outside surface of the air fin coolers 66 with the refrigerant passing through the tubes thereof. Downstream of the air fin coolers 66, the refrigerant is directed to flow through one or more compressors 70 and one or more expanders 72 before recycle to the liquefaction 25 unit 74. The compressors 70 may be driven using gas turbines or electric motors depending on the power requirements and layout issues. Whilst it is possible to use water to cool the refrigerant, the use of ambient air is preferred as this is understood to be more environmentally friendly. If seawater is used as cooling 30 water, the best source is seawater extracted from a deep water location where the temperature is lower and the water is cleaner than near the waterline. When ambient air is used to cool the refrigerant, a large number of air fin coolers 66 are required to be used as the higher the inlet temperature to the compressor 70, the more -16 compression is required to cool the refrigerant. Due to the large amount of power required for operation of the liquefaction process, the layout of piping and process apparatus onboard the liquefaction module 20 is already quite congested. In order to address this problem, one aspect of the present invention is to locate the air fin coolers 66 5 on the bridges 36. Preferably, the air fin coolers 66 are located either on the bridge 36 linking the gas processing module 18 to the liquefaction module 20 or the bridge 36 linking the liquefaction module 20 to the storage module 22, or both. The size of each bridge 36 is adjusted to suit the footprint and weight of the air fin coolers 66 located thereon. 10 In the embodiment illustrated in FIG. 6 for which like reference numerals refer to like parts, the air fin coolers 66 are stacked at an angle on the bridge 36 in an A-frame arrangement to maximize the surface area available for cooling for a given footprint size available on the bridges 36. 15 Locating the air fin coolers 66 on the bridges 36 alleviates the problem to trying to fit the required number of air fin coolers within the available footprint of the liquefaction module 20. This allows the size of the liquefaction module 20 to be kept to a minimum (which has a flow on benefit of a reduction in cost) and further allows the remaining equipment located on the liquefaction module 20 to be optimised to maximise operating pressure. 20 The liquefaction module 20 and gas processing module 18 share common storage modules 22, the storage module being arranged to accommodate at least one cryogenic storage tank 80 for storing LNG and at least one non-cryogenic storage tank 82 for storing other liquids including but not limited to water, condensate, monoethylene glycol (MEG), methanol, diesel, demineralised water, diesel, LPG or combinations thereof. The 25 storage module(s) 22 are hydrostatically stable when partially filled to reduce sloshing. To reduce the effects of sloshing, in certain instances the storage tanks are provided with a plurality of internal baffles and has a supporting hull structure capable of withstanding the loads imposed from intermediate filling levels when the module is subject to harsh, multi directional environmental conditions. The cryogenic storage tank may be a double 30 containment, full containment, prismatic or membrane systems with a primary tank constructed from, by way of example, but not limited to stainless steel, aluminum, and/or 9%-nickel steel. The cryogenic storage tanks may include pre-tensioned concrete to provide structural resistance to the stored LNG, boil off gas pressure loads and to external hazards.

-17 With reference to FIG. 1, the offshore LNG production facility includes two berthing modules 24 each arranged in sufficiently deep water to allow an LNG Carrier 28 to berth directly alongside to load LNG transferred from the storage module(s) 22. In use, the LNG Carriers 28 berth at regular intervals at the LNG production facility 10 so as to 5 receive a cargo of LNG and may approach the berthing modules 24 from either direction depending on the prevailing weather conditions. Depending on the size of the LNG Carrier 28, the stern of the LNG Carrier 28 may extend beyond an end of the berthing module 24 when the LNG Carrier is berthed alongside the berthing module 24. This overhang of the LNG Carriers stern beyond the berthing module may expose the LNG 10 Carrier to adverse environmental conditions. To minimize this effect, the berthing module 28 has at least one lateral side which has a length of a sufficient size to allow a range of sizes of LNG carrier to be moored along alongside without overhang of the stern. The berthing module 24 can be fitted with fendering equipment (not shown) arranged to 15 absorb a substantial portion of a load generated by impact of the LNG Carrier 28 with the berthing module 24 during berthing. The berthing module may be designed to allow an LNG Carrier to moor on one or more lateral sides of the berthing module. In one embodiment, the berthing module is arranged to allow bi-directional berthing of an LNG Carrier with the longitudinal axis of the berthing module aligned to be substantially parallel 20 to the direction of the predominant current. Loading of LNG from the storage modules 22 to the LNG Carrier 28 is achieved using any of the loading methods well established in the industry. 25 The berthing module 24 includes LNG transfer equipment 26 to transfer LNG from the storage module 22 to the storage tanks (not shown) onboard the LNG Carrier 28. Any suitable LNG transfer equipment may be used such as a fixed or swivel joint loading arm, preferably fitted with an emergency release system. Between loading operations, the LNG transfer equipment 26 may be kept cold by re- circulation of a small quantity of LNG. The 30 LNG transfer equipment 26 may include an emergency safety system to allow loading to be stopped if required in a quick, safe, and controlled manner by closing the isolation valves on the unloading and tank fill lines and stopping the cargo pumps of the LNG carrier. The emergency safety system may be designed to allow LNG transfer to be restarted with minimum delay after corrective action has been taken.

- 18 After receiving its cargo of LNG, the LNG Carrier 28 travels to a delivery location (not shown) where the LNG is offloaded and regasified. The LNG Carrier can dock at an import terminal assnriated with nn onshore rogasificstion faoility or tronofor the LNG to a second LNG Carrier with onboard regasification capability or deliver the LNG to any other 5 suitable offshore storage and regasification facility. A second embodiment of the present invention is illustrated in FIG. 4 for which like reference numerals refer to like parts. In this embodiment, the LNG production facility 10 is arranged such that the storage modules 22 are integrated with the berthing modules 24. 10 The storage module(s) 22 are further arranged to provide a breakwater to protect the LNG Carrier 28 from wave impact whilst berthed during berthing loading. This embodiment is more suited for use in deepwater. The accommodation module 34 is arranged at a safe distance from the gas processing module 18, the flares 56, and the liquefaction modules 20. 15 Now that several embodiments of the invention have been described in detail, it will be apparent to persons skilled in the relevant art that numerous variations and modifications can be made without departing from the basic inventive concepts. For example, a LNG Carrier with onboard storage and regasification capability may be used as the storage 20 module and operate for a period of time as part of the LNG production facility. When the LNG Carrier is full, the LNG Carrier disconnects and travels to a mooring location where the LNG stored onboard the LNG Carrier is regasified onboard the LNG Carrier to form natural gas (NG) which is then transferred to an onshore gas distribution facility. The LNG Carrier then returns to pick up another load of LNG from the loading modules or another 25 export terminal. In the meantime, another LNG Carrier is temporarily stationed at the production location forming part of the LNG production facility. In one embodiment, the LNG Carrier serves the function of a storage module. The LNG Carrier may have an onboard regasification facility. All such modifications and variations are considered to be within the scope of the present invention, the nature of which is to be determined from the 30 foregoing description and the appended claims.

-.19 it will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents forms part of the common general knowledge in the art, in Australia or in any other country. In the summary of the invention, the description and claims which follow, except where the 5 context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Claims (28)

1. A fixed LNG production facility positioned in a body of water at a production location, the facility comprising a plurality of spaced-apart modules, each module provided with 5 plant equipment related to a pre-determined function associated with the production of LNG wherein at least a portion of the body of water is a body of shallow water such that the base of at least one of the spaced-apart modules rests on a bottom of the body of shallow water to secure the position of said module, and wherein the production facility comprises a variable number of modules for tailoring the production capacity of the LNG 10 production facility for the production location.

2. The LNG production facility of claim 1 wherein the body of shallow water has a depth in the range of 2 to 50 meters or 10 to 35 meters or 15 to 30 meters or 2 to 20 meters. 15

3. The LNG production facility of claim 1 or 2 wherein one or more of the plurality of modules is transportable from a construction location to an assembly location by towing or on floating barges.

4. The LNG production facility of claim 1 or 2 wherein one or more of the plurality of 20 modules is transportable from a construction location to the production location by towing or on floating barges.

5. The LNG production facility of claim 3 or 4 wherein a transportable module is settled into the body of shallow water by adjusting the ballast or buoyancy of the module through 25 the addition of a ballasting material.

6. The LNG production facility of claim 5 wherein a module includes a ballast storage compartment arranged around the periphery of the module or arranged toward the base of the module for ballasting. 30

7. The LNG production facility of claim 6 wherein the ballast storage compartment is at least partially filled with one or both of a solid ballasting material or a liquid ballasting material. 35

8. The LNG production facility of claim 6 wherein the solid ballasting material is iron ore - 21 or sand.

9. The LNG production facility of claim 6 wherein the liquid ballasting material is one or more of: water, condensate, monoethylene glycol (MEG), methanol, diesel, demineralised 5 water, or, LPG.

10. The LNG production facility of any one of the preceding claims wherein the production facility includes a liquefaction module for receiving a stream of treated gas from a gas processing module and liquefying the treated gas to produce LNG, a storage 10 module operatively associated with the liquefaction module for receiving and storing LNG, and, a berthing module including LNG transfer facilities to transfer the LNG from a storage module to an LNG Carrier, and, wherein the storage module has a sub-structure in the form of a gravity based structure such that that the base of the storage module rests on the bottom of the body of shallow water. 15

11. The LNG production facility of any one of the preceding claims wherein the production facility includes a liquefaction module for receiving a stream of treated gas from a gas processing module and liquefying the treated gas to produce LNG, a storage module operatively associated with the liquefaction module for receiving and storing LNG, 2 0 and, a berthing module including LNG transfer facilities to transfer the LNG from a storage module to an LNG Carrier, and, wherein the liquefaction module has a sub-structure in the form of a gravity based structure such that that the base of the liquefaction module rests on the bottom of the body of shallow water. 25

12. The LNG production facility of any one of the preceding claims wherein the facility includes a liquefaction module for liquefying treated natural gas to form LNG and a storage module for receiving and storing LNG from the liquefaction module, and wherein the storage module is arranged to act as a breakwater for the LNG Carrier. 30

13. The LNG production facility of any one of the preceding claims wherein the facility includes a liquefaction module for liquefying treated natural gas to form LNG and a storage module for receiving and storing LNG from the liquefaction modules, wherein the storage module includes at least one cryogenic storage tank for storing LNG and the cryogenic storage tank is hydrostatically stable when partially filled. - 22

14. The LNG production facility of claim 13 wherein the storage module includes at least one cryogenic storage tank for storing LNG and the cryogenic storage tank includes a plurality of internal baffles and a supporting hull structure. 5

15. The LNG production facility of claim 13 wherein the storage module includes at least one cryogenic storage tank for storing LNG and the cryogenic storage tank is a double containment, full containment, prismatic or membrane system storage tank with a primary tank constructed from, by way of example, but not limited to stainless steel, aluminum, 10 and/or 9%-nickel steel.

16. The LNG production facility of claim 13 wherein the storage module includes at least one cryogenic storage tank for storing LNG and the cryogenic storage tank includes pre tensioned concrete. 15

17. The LNG production facility of any one of the preceding claims wherein the LNG production facility includes a berthing module arranged in sufficiently deep water to allow an LNG Carrier to berth directly alongside the berthing module, and wherein the berthing module includes LNG transfer equipment to transfer LNG from the storage module to a 20 storage tank onboard the LNG Carrier.

18. The LNG production facility of claim 17 wherein the berthing module has at least one lateral side which has a length of a sufficient size to allow an LNG carrier to be moored along alongside without overhang of the LNG Carrier beyond an end of the berthing 25 module.

19. The LNG production facility of any one of claims 17 or 18 wherein the berthing module is arranged to allow an LNG Carrier to moor on one or more lateral sides of the berthing module whereby, in use, the LNG Carrier approaches the berthing module from a 30 direction that depends on the prevailing weather conditions.

20. The LNG production facility of any one of claims 17 or 18 wherein the berthing module is arranged to allow bi-directional berthing of an LNG Carrier with the longitudinal axis of the berthing module aligned to be substantially parallel to the direction of a - 23 predominant current.

21. The LNG production facility of any one of the preceding claims wherein the production facility includes a liquefaction module for receiving a stream of treated gas from 5 a gas processing module and liquefying the treated gas to produce LNG, a storage module operatively associated with the liquefaction module for receiving and storing LNG, and, a berthing module including LNG transfer facilities to transfer the LNG from a storage module to an LNG Carrier, and wherein the storage module is integrated with the berthing module. 10

22. The LNG production facility of any one of the preceding claims wherein the production facility includes a liquefaction module for receiving a stream of treated gas from a gas processing module and liquefying the treated gas to produce LNG, a storage module operatively associated with the liquefaction module for receiving and storing LNG, 15 and, a berthing module including LNG transfer facilities to transfer the LNG from a storage module to an LNG Carrier, and wherein the storage module is arranged to provide a breakwater to protect an LNG Carrier from wave impact whilst berthed during berthing loading. 20

23. The LNG production facility of any one of claims 1 to 22 wherein the storage module is an LNG Carrier.

24. The LNG production facility of any one of the preceding claims wherein one or more of the plurality of modules is in the form of fixed platforms or jacket structures. 25

25. The LNG production facility of any one of the preceding claims wherein one or more of the plurality of modules is arranged on one or more steel or concrete barges or bricks.

26. The LNG production facility of any one of the preceding claims wherein the 30 production location is an offshore location.

27. The LNG production facility of any one of the preceding claims wherein the production location is a near-shore location. - 24

28. A method of using the LNG production facility of any one of claims 1 to 28 comprising the steps of: a) receiving natural gas from a well; 5 b) liquefying the natural gas to form LNG using a liquefaction module; c) transferring the LNG from the liquefaction module to a storage module; d) storing the liquefied natural gas in the storage module; and e) loading the LNG from the storage module onto an LNG Carrier. 10