WO2022198294A1

WO2022198294A1 - Offshore hybrid gas export systems and methods

Info

Publication number: WO2022198294A1
Application number: PCT/BR2022/050104
Authority: WO
Inventors: Marcelo Igor LOURENÇO DE SOUZA; Rafael LOUZADA BODANESE; Luiz Germano Bodanese
Original assignee: Horton Do Brasil Tecnologia Offshore, Ltda.
Priority date: 2021-03-23
Filing date: 2022-03-23
Publication date: 2022-09-29
Also published as: BR112023019254A2

Abstract

An offshore system for producing and exporting hydrocarbon gas, the system comprising: a production platform configured to receive the hydrocarbon gas from one or more subsea wells in an offshore production field; a subsea manifold; a fluid transfer conduit extending from the production platform to the subsea manifold, wherein the fluid transfer conduit is configured to supply the hydrocarbon gas from the production platform to the subsea manifold; a first subsea gas storage device in selective fluid communication with the subsea manifold, wherein the first subsea gas storage device is configured to temporarily store the hydrocarbon gas; a first gas export assembly coupled to the subsea manifold and in selective fluid communication with the subsea manifold, wherein the first gas export assembly is configured to supply the hydrocarbon gas from the manifold to a first export vessel releasably coupled to the first gas export assembly.

Description

OFFSHORE HYBRID GAS EXPORT SYSTEMS AND METHODS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. provisional patent application Serial No. 63/164,927 filed March 23, 2021 , and entitled Offshore Hybrid Gas Export Systems and Methods,” which is hereby incorporated herein by reference in its entirety..

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

BACKGROUND

[0003] This disclosure relates generally to offshore systems and methods for the offshore exportation of hydrocarbon gas(es) (e.g., natural gas). More particularly, this disclosure relates to offshore systems and methods for the temporary subsea storage of natural gas, exportation of natural gas, offloading of natural gas, or combinations thereof.

[0004] In offshore hydrocarbon production fields, hydrocarbon gases including natural gas are produced by offshore platforms or vessels. Mature, developed fields often include subsea pipelines for receiving the produced hydrocarbon gases (e.g., natural gas) from one or more production platforms in the field, and subsequently transporting the hydrocarbon gases from the field to land for further processing, use, or transport to yet another location.

BRIEF SUMMARY OF THE DISCLOSURE

[0005] An offshore system for producing and exporting hydrocarbon gas comprises a production platform disposed in an offshore production field. The production platform is configured to receive the hydrocarbon gas from one or more subsea wells in the production field. In addition, the offshore system comprises a subsea manifold disposed in the production field. Further, the offshore system comprises a fluid transfer conduit extending from the production platform to the subsea manifold. The fluid transfer conduit is configured to supply the hydrocarbon gas from the production platform to the subsea manifold. Still further, the offshore system comprises a first subsea gas storage device in the production field and in selective fluid communication with the subsea manifold. The first subsea gas storage device is configured to temporarily store the hydrocarbon gas. Moreover, the offshore system comprises a first gas export assembly coupled to the subsea manifold and in selective fluid communication with the subsea manifold. The first gas export assembly is configured to supply the hydrocarbon gas from the manifold to a first export vessel releasably coupled to the first gas export assembly.

[0006] A method for producing and exporting hydrocarbon gas from an offshore production field comprises (a) producing the hydrocarbon gas from one or more subsea wells in the production field to a production platform disposed in the offshore production field. In addition, the method comprises (b) supplying the hydrocarbon gas to a subsea manifold disposed in the production field. Further, the method comprises (c)supplying the hydrocarbon gas from the subsea manifold to a first gas export assembly. Still further, the method comprises (d) supplying the hydrocarbon gas from the subsea manifold to a subsea gas storage device to temporarily store the hydrocarbon gas.

[0007] An offshore system for producing and exporting hydrocarbon gas comprises a production platform disposed in an offshore production field. The production platform is configured to receive the hydrocarbon gas from one or more subsea wells in the production field. In addition, the offshore system comprises a subsea manifold disposed in the production field. Further, the offshore system comprises a first fluid transfer conduit extending from the production platform to the subsea manifold. The first fluid transfer conduit is configured to supply hydrocarbon gas from the subsea manifold to the production platform. Still further, the offshore system comprises a first gas transfer assembly coupled to the subsea manifold and in selective fluid communication with the subsea manifold. The first gas transfer assembly is configured to offload hydrocarbon gas from a first vessel releasably coupled to the first gas transfer assembly to the subsea manifold. Moreover, the offshore system comprises a nearshore terminal in selective fluid communication with the subsea manifold and in fluid communication with a pipeline extending from the nearshore terminal onto land.

[0008] Embodiments described herein comprise a combination of features and characteristics intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical characteristics of the disclosed embodiments in order that the detailed description that follows may be better understood. The various characteristics and features described above, as well as others, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes as the disclosed embodiments. It should also be realized that such equivalent constructions do not depart from the spirit and scope of the principles disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For a detailed description of the disclosed embodiments, reference will now be made to the accompanying drawings in which:

[0010] Figure 1 is a schematic perspective view of an embodiment of an offshore hydrocarbon production and export system in accordance with the principles disclosed herein;

[0011] Figure 2 is a schematic perspective view of an embodiment of an offshore hydrocarbon production and export system in accordance with the principles disclosed herein; and

[0012] Figure 3 is a schematic perspective view of an embodiment of a nearshore hydrocarbon production and export system including an offloading terminal in accordance with the principles disclosed herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The following discussion is directed to various exemplary embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.

[0014] Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

[0015] Unless the context dictates the contrary, all ranges set forth herein should be interpreted as being inclusive of their endpoints, and open-ended ranges should be interpreted to include only commercially practical values. Similarly, all lists of values should be considered as inclusive of intermediate values unless the context indicates the contrary.

[0016] In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to... Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct engagement between the two devices, or through an indirect connection that is established via other devices, components, nodes, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a particular axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to a particular axis. For instance, an axial distance refers to a distance measured along or parallel to the axis, and a radial distance means a distance measured perpendicular to the axis. Any reference to up or down in the description and the claims is made for purposes of clarity, with “up”, “upper”, “upwardly”, “uphole”, or “upstream” meaning toward the surface of the borehole and with “down”, “lower”, “downwardly”, “downhole”, or “downstream” meaning toward the terminal end of the borehole, regardless of the borehole orientation. As used herein, the terms “approximately,” “about,” “substantially,” and the like mean within 10% (i.e. , plus or minus 10%) of the recited value. Thus, for example, a recited angle of “about 80 degrees” refers to an angle ranging from 72 degrees to 88 degrees.

[0017] As used herein, the term “export” and derivatives thereof (e.g., “exporting,” “exportation,” etc.) refer to the transfer of produced hydrocarbons (e.g., natural gas, CNG, etc.) or electricity generated with produced hydrocarbons from an offshore production platform or vessel to shore (i.e., land) for further processing, transport, use, or combinations thereof. Further, as used herein, the term “offload” and derivatives thereof (e.g., “offloading”) refer to the transfer of hydrocarbons (e.g., natural gas, CNG, etc.) from a vessel that transports the hydrocarbons from one location to another location (e.g., transfer of CNG from a vessel to a pipeline, transfer of oil from a tanker into a pipeline or to a hydrocarbon processing facility, etc.).

[0018] As previously described, in mature, developed offshore hydrocarbon production fields, subsea pipelines are typically available for exporting produced hydrocarbon gases such as natural gas from the field to land for further processing, use, or transport to yet another location. However, in undeveloped fields, new offshore fields, and environmentally sensitive offshore areas, subsea pipelines may not be available, and further, economics and/or environmental concerns may limit or prohibit installation of subsea pipelines.

[0019] Compressed natural gas (CNG) vessels provide one alternative to pipelines for transporting produced hydrocarbon gases from an offshore field. In particular, the CNG export vessel is coupled to one or more offshore production platforms or vessels, and produced hydrocarbon gases are supplied from the one or more offshore production platforms or vessels to the export vessel and stored on the export vessel in a compressed state. The CNG export vessel is decoupled from the one or more offshore production platforms or vessels once its storage capacity has been reached, and then the CNG export vessel transports the compressed hydrocarbon gases to an onshore or nearshore terminal for offloading. However, continuous production and transport of produced hydrocarbon gas by export vessels depends on the availability of export vessels throughout the operating lifetime of the field. For example, if an export vessel is not available for a period of time, production in the offshore field may need to be temporarily ceased. To reduce production downtime, operators may consider increasing the number of available export vessels, however, such an approach results in increased capital expenditures and transportation tariffs.

[0020] Gas-to-wire (GTW) and gas-to-liquids (GTL) technologies offer another alternative to pipelines for effectively transporting the value of produced hydrocarbon gases, which are converted to electricity or liquids in the field and subsequently transported to shore by wire or vessel, respectively. However, such technologies often require a temporary gas storage capacity to accommodate changes in produced gas volumes and/or to regulate the flow of hydrocarbon gases between the production platform or vessel and the gas conversion unit (GTW or GTL), and further, GTW technologies generally require a subsea electrical cable to transmit the produced electricity to shore.

[0021] Accordingly, there remains a need in the art for systems and methods for cost effectively exporting produced hydrocarbon gas(es) (e.g., natural gas) from an offshore production field to shore. Such systems and methods may be particularly beneficial in remote and/or undeveloped production fields that lack a pipeline infrastructure, as well as in offshore locations where installation and/or decommissioning of a pipeline may create environmental concerns.

[0022] Referring now to Figure 1 , an embodiment of an offshore production and export system 100 in accordance with the principles disclosed herein is shown. As will be described in more detail below, system 100 produces hydrocarbon gas (e.g., natural gas) and can temporarily store the produced hydrocarbon gas (as needed). However, offshore system 100 is located in a remote and/or undeveloped offshore field 10 that does not include a subsea pipeline for exporting produced hydrocarbon gas to shore or a subsea electrical cable for exporting electricity derived from produced hydrocarbon gas to shore. Accordingly, in this embodiment, the hydrocarbon gas produced by system 100 cannot be exported from field 10 to another remote location via a subsea pipeline, and further, the hydrocarbon gas produced by system 100 cannot be converted to electricity in field 10 and exported from field 10 to another remote location via a subsea electrical cable. In the embodiment shown in Figure 1 , the hydrocarbon gas produced by system 100 is natural gas that is compressed to convert it to “compressed natural gas” or CNG, which can be temporarily stored as CNG and exported as CNG. It should be appreciated that CNG is a form or type of natural gas, namely, natural gas that has been sufficiently compressed. [0023] Referring still to Figure 1 , in this embodiment, production and export system 100 includes a production platform 110 at the sea surface 11 , a subsea manifold 130 disposed on the sea floor 12, a plurality of subsea gas storage devices 150 disposed on the sea floor 12 proximal manifold 130, and a plurality of fluid export vessels 170 disposed at the sea surface 11. Production platform 110 is moored or otherwise held substantially stationary in the field 10 and receives natural gas produced from one or more subsea wells (not shown) in field 10. In addition, production platform 110 includes equipment (e.g., one or more compressors) for compressing the produced natural gas to convert the produced natural gas to CNG. In this embodiment, production platform 110 is a moored production vessel, and more specifically, a floating production and offloading (FPSO) vessel. However, in other embodiments, the production platform (e.g., platform 110) may be a semi-submersible offshore platform, a jackup platform, a spar platform, or other suitable type of offshore structure for producing hydrocarbons from one or more subsea wells.

[0024] Manifold 130 is disposed on the sea floor 12 and includes a plurality of conduit couplings 131 , 132, 133. In addition, manifold 130 includes a plurality of pipes and connectors that provide selective fluid communication between couplings 131, 132, 133 within manifold 130. For example, each coupling 131 , 132, 133 includes a remotely operated valve to control the flow of hydrocarbons (e.g., CNG) therethrough. As will be described in more detail below, in this embodiment, CNG flows into manifold 130 via conduit coupling 131 , CNG flows out of manifold via conduit couplings 133, and CNG can flow into or out of manifold 130 via conduit couplings 132. Accordingly, coupling 131 may also be referred to herein as a fluid or CNG “inlet,” each coupling 133 may also be referred to herein as a fluid or CNG “outlet,” and each coupling 132 may also be referred to herein as a fluid or CNG “inlet-outlet.” In this embodiment, manifold 130 is pigable such that a pipeline pig can be deployed and moved through the flow passages in manifold 130 using techniques known in the art (e.g., to clean the inside of manifold 130, to remove clogs in manifold 130, etc.).

[0025] Referring still to Figure 1, a transfer conduit 111 extends from platform 110 to manifold 130. In this embodiment, CNG flows from production platform 110 to manifold 130 via transfer conduit 111 , and thus, transfer conduit 111 may be described as having an inlet (not shown) in fluid communication with a supply of CNG on platform 110 (e.g., outlet of compressors) and an outlet 111b coupled to inlet 131 of manifold 130. Thus, transfer conduit 111 provides fluid communication between platform 110 and manifold 130, and in particular, supplies CNG from production platform 110 to manifold 130.

[0026] A fluid conduit 140 extends from each inlet-outlet 132 to gas storage devices 150, and a plurality of fluid conduits 141 extend between gas storage devices 150. Thus, fluid conduit 140 provides fluid communication between manifold 130 and gas storage devices 150, and fluid conduits 141 provide fluid communication between gas storage devices 150. In other words, gas storage devices 150 are fluidly interconnected in this embodiment. As will be described in more detail below, CNG can flow from manifold 130 to gas storage devices 150 via one or more fluid conduits 140, CNG can flow from gas storage devices 150 to manifold 130 via one or more fluid conduits 140, and CNG can flow between gas storage devices 150 via fluid conduits 141.

[0027] Subsea gas storage devices 150 rely on the external subsea pressure at the sea floor 12 to maintain and store CNG under pressure. In particular, each subsea gas storage device 150 includes an internal flexible membrane that functions as a storage vessel or bladder and is pressure equalized with the surrounding subsea environment. Examples of suitable subsea storage devices that can be used for subsea storage devices 150 in embodiments described herein are disclosed in US Patent Application Publication No. 2012/0260839, which is hereby incorporated herein by reference in its entirety.

[0028] Referring still to Figure 1, a fluid transfer assembly 160 is coupled to and extends from each outlet 133 of manifold 130. In this embodiment, each fluid transfer assembly 160 is a single turret loading (STL) system including a flow conduit 161 and a moored turret 162 that may be floating at the surface 11 or slightly submerged below the surface 11. In this embodiment, each fluid transfer assembly 160 supplies and loads CNG onto a corresponding export vessel 170. Accordingly, fluid transfer assemblies 160 may also be referred to as “export” assemblies, and further, each conduit 161 may be described as having an inlet 161a coupled to one outlet 133 of manifold 130 and an outlet 161b coupled to the corresponding turret 162 and export vessel 170. Thus, in this embodiment, each flow conduit 161 provides fluid communication between manifold 130 and the corresponding turret 162, and in particular, supplies CNG from manifold 130 to the corresponding turret 162 and export vessel 170. In general, fluid export assembly 160 can be any suitable STL system known in the art.

[0029] One export vessel 170 can releasably couple to each turret 162 at a given time, thereby enabling the corresponding fluid export assembly 160 to provide fluid communication between manifold 130 and that export vessel 170. Thus, when an export vessel 170 is coupled to a turret 162, CNG can be supplied from manifold 130 to that export vessel 170, thereby loading the CNG onto that export vessel 170 for export. [0030] Manifold 130 fluidly couples and can provide selective fluid communication between production platform 110, subsea gas storage devices 150, fluid export assemblies 160, and any export vessel(s) 170 coupled to fluid export assemblies 160. Thus, manifold 130 can be employed to (i) supply CNG from production platform 110 to storage devices 150 via conduits 111 , 140 for temporary storage; (ii) supply CNG from storage devices 150 to one or more fluid export vessels 170 via conduits 140, 141 , 161 and turret(s) 162; and (iii) supply CNG from production platform 110 to one or more fluid export vessels 170 (bypassing gas storage devices 150) via conduits 111 , 161 and turret(s) 162. Moreover, manifold 130 can enable any two or more of (i), (ii), and (iii) simultaneously. For example, manifold 130 can supply CNG from production platform 110 to one or more export vessels 170 via conduits 111 , 161 and turret(s) 162 while simultaneously supplying CNG from production platform 110 to storage devices 150 via conduits 111 , 140 for temporary storage. As another example, manifold 130 can supply CNG from production platform 110 to one or more export vessels 170 via conduits 111 , 161 and turret(s) 162 while simultaneously supplying CNG from storage devices 150 to one or more export vessels 170 via conduits 140, 141 , 161 , and turret(s) 162.

[0031] Referring still to Figure 1 , methods for operating offshore production and export system 100 will now be described. As previously described, natural gas is produced to production platform 110 from one or more subsea wells in field 10. The produced natural gas is compressed on production platform 110 and converted to CNG. The CNG on production platform 110 can be stored temporarily on production platform 110 in CNG storage tanks of platform 110; pumped from production platform 110 into gas storage devices 150 via conduits 111, 140, 141 and manifold 130; pumped from production platform 110 onto one or more export vessels 170 via conduit 111, manifold 130, and fluid export assemblies 160; or combinations thereof. Simultaneous or independent of any of the foregoing, CNG stored in gas storage devices 150 can be supplied from gas storage devices 150 to one or more export vessels via conduits 140, 141 , manifold 130, and fluid export assemblies 160. Thus, it should be appreciated that system 100 allows production platform 110 to continuously produce natural gas, which is converted to CNG that can be directly loaded onto one or more export vessels 170 for export if an export vessel 170 is available and coupled to a turret 162; or if no export vessels 170 are available, the CNG can simply be pumped into gas storage devices 150 for temporary storage until an export vessel 170 is available. This offers the potential to enhance reliability of system 100, as well as maximize operational and production time of production platform 110. In addition, when a export vessel 170 is connected to a turret 162, the CNG can be transferred simultaneously from both production platform 110 to the export vessel 170 and from gas storage devices 150 to the export vessel 170, thereby offering the potential for faster loading of the export vessel 170 as compared to loading an export vessel (e.g., export vessel 170) from a single source of CNG. Further, in the case that multiple export vessels 170 are available and coupled to turrets 162, system 100 can simultaneously load CNG to multiple export vessels 170. This, combined with subsea gas storage devices 150, provides redundancy and availability, thereby offering the potential to reduce the number of available export vessels 170 to export CNG from production platform 110 and associated capital expenditures, thereby increasing the economic feasibility of system 100.

[0032] As previously described, subsea gas storage devices 150 store CNG under pressure (i.e., at the ambient subsea pressure). Consequently, subsea gas storage devices 150 collectively function as a subsea gas accumulator. In this sense, subsea gas storage devices 150 can be considered a type of energy storage device that stores potential energy, and can release the potential energy upon demand. Such functionality of subsea gas storage devices 150 enable system 100 to accommodate variations in CNG demand for exportation with less compressor capacity on production platform 110, to respond more quickly to a temporary CNG demand for exportation, and to smooth out CNG flow variations within system 100.

[0033] Depending on the water depth at the subsea location of gas storage devices 150, they may not be able to supply the CNG stored therein at a sufficient pressure to fully load an export vessel 170, and thus, a combined CNG loading cycle may be applied. For example, one or more export vessels 170 may initially be supplied CNG from gas storage devices 150, however, once the pressure of CNG in gas storage devices 150 is insufficient to continue flowing the CNG in gas storage devices 150 to export vessel(s) 170, CNG is supplied directly from production platform 110 to the export vessel(s) 170 to fill the remaining capacity of the export vessel(s) 170. This approach first loads the export vessel(s) 170 with the lowest pressure CNG in system 100 (e.g., the CNG in gas storage devices 150), and then loads the export vessel(s) 170 with the next higher CNG in system 100 (e.g., the CNG from production platform 110). It should also be appreciated that filling any remaining capacity of the export vessel(s) 170 with CNG from production platform 110 enables production platform 110 (via its compressors) to sufficiently pressurize the CNG supplied to the export vessel(s) 170 to achieve the desired pressure of the CNG already loaded onto the export vessel(s) 170.

[0034] After a given export vessel 170 coupled to a turret 162 has been sufficiently filled with CNG supplied by production platform 110 and/or gas storage devices 150, the export vessel 170 decouples from the corresponding turret 162, leaves field 10, and transports the CNG loaded thereon to another location remote field 10 for offloading. In the manner described, system 100 produces hydrocarbon gas and exports the produced hydrocarbon gas from field 10 to another location for offloading.

[0035] Referring now to Figure 2, an embodiment of an offshore production and export system 200 in accordance with the principles disclosed herein is shown. Similar to system 100 previously described and shown in Figure 1 , system 200 produces hydrocarbon gas (e.g., natural gas), temporarily store the produced hydrocarbon gas (as necessary), and exports the produced hydrocarbon gas. Unlike system 100, which is located in field 10 that does not include a subsea pipeline or subsea electrical cable, offshore system 200 is located in an offshore field 20 that includes a subsea pipeline 21. As will be described in more detail below, pipeline 21 provides additional options and functionality for operating system 200 and exporting produced hydrocarbon gas (e.g., natural gas). In this embodiment, the hydrocarbon gas produced by system 200 is natural gas that is compressed to convert the natural gas to CNG, which can be temporarily stored as CNG and/or exported as CNG.

[0036] Referring still to Figure 2, in this embodiment, production and export system 200 is substantially the same as system 100 previously described. Accordingly, the differences between systems 100, 200 will be described it being understood the other features are generally the same. In addition, for purposes of clarity, like features of system 200 and previously described system 100 are given the same reference numerals. In particular, system 200 includes a production platform 110 at the sea surface 11, a subsea manifold 230 disposed on the sea floor 12, a plurality of subsea gas storage devices 150 disposed on the sea floor 12 proximal manifold 230, and a plurality of fluid export vessels 170 disposed at the sea surface 11. Production platform 110 and gas storage devices 150 are both as previously described. For example, natural gas is produced to production platform 110 from one or more subsea wells in field 20.

[0037] Manifold 230 is substantially the same as manifold 130 previously described with the exception that manifold 230 includes an additional conduit coupling 234. Manifold 230 includes a plurality of pipes and connectors that provide selective fluid communication between conduit couplings 131 , 132, 133, 234 within manifold 230. Each conduit coupling 131 , 132, 133, 234 includes a remotely operated valve to control the flow of fluids therethrough. As will be described in more detail below, in this embodiment, CNG flows into manifold 230 via conduit coupling 131 , CNG flows out of manifold via conduit couplings 133, and CNG can flow into or out of manifold 130 via conduit couplings 132, 234. Accordingly, coupling 131 may also be referred to herein as a fluid or CNG “inlet,” each coupling 133 may also be referred to herein as a fluid or CNG “outlet,” and each coupling 132, 234 may also be referred to herein as a fluid or CNG “inlet-outlet.” Thus, manifold 230 is disposed on the sea floor 12 and includes an inlet 131 as previously described, a plurality of inlet-outlets 132 as previously described, a plurality of outlets 133 as previously described, and inlet-outlet 234. Like manifold 130, in this embodiment, manifold 230 is pigable such that a pipeline pig can be deployed and moved through the flow passages in manifold 230 using techniques known in the art (e.g., to clean the inside of manifold 230, to remove clogs in manifold 230, etc.).

[0038] Referring still to Figure 2, a transfer conduit 111 as previously described extends from platform 110 to manifold 230. Similar to system 100, in this embodiment, CNG flows from production platform 210 to manifold 230 via transfer conduit 111 , and thus, transfer conduit 111 may be described as having an inlet (not shown) in fluid communication with a supply of CNG on platform 210 (e.g., outlet of compressors) and a fluid outlet 111b coupled to inlet 131 of manifold 230. Accordingly, transfer conduit 111 provides fluid communication between platform 210 and manifold 230, and in particular, supplies CNG from production platform 110 to manifold 230. [0039] A fluid conduit 140 as previously described extends from each inlet-outlet 132 to gas storage devices 150, and a plurality of fluid conduits 141 as previously described extend between gas storage devices 150. Thus, fluid conduit 140 provides fluid communication between manifold 230 and gas storage devices 150, and fluid conduits 141 provide fluid communication between gas storage devices 150. As will be described in more detail below, CNG can flow from manifold 230 to gas storage devices 150 via one or more fluid conduits 140, CNG can flow from gas storage devices 150 to manifold 230 via one or more fluid conduits 140, and CNG can flow between gas storage devices 150 via fluid conduits 141. A flow conduit 142 extends from inlet-outlet 234 to subsea pipeline 21. Thus, flow conduit 142 provides fluid communication between manifold 230 and pipeline 21. As will be described in more detail below, CNG can flow from pipeline 21 to manifold 230 via flow conduit 142 and CNG can flow from manifold 230 to pipeline 21 via flow conduit 142.

[0040] Referring still to Figure 2, a fluid transfer assembly 160 as previously described is coupled to and extends from each outlet 133 of manifold 230. As with system 100, in this embodiment, fluid transfer assemblies 160 supply and load CNG onto export vessels 170. Accordingly, fluid transfer assemblies 160 may also be referred to as “export” assemblies, and further, each conduit 161 may be described as having an inlet 161a coupled to a corresponding outlet 133 of manifold 130 and an outlet 161b coupled to the corresponding turret 162.

[0041] One export vessel 170 as previously described can releasably couple to each turret 162 at a particular time, thereby enabling the corresponding fluid export assembly 160 to provide fluid communication between manifold 230 and that export vessel 170. Thus, when an export vessel 170 is coupled to a turret 162, CNG can be supplied from manifold 230 to that export vessel 170.

[0042] Similar to manifold 130 previously described, manifold 230 fluidly couples and can provide selective fluid communication between production platform 110, subsea gas storage devices 150, fluid export assemblies 160, and any export vessel(s) 170 coupled to fluid export assemblies 160. However, in this embodiment, manifold 230 also couples and can provide selective fluid communication between any one or more of the foregoing (i.e., production platform 110, subsea gas storage devices 150, fluid export assemblies 160, and any export vessel(s) 170) and subsea pipeline 21. Thus, manifold 230 can be employed to (i) supply CNG from production platform 110 to storage devices 150 via conduits 111 , 140 for temporary storage; (ii) supply CNG from storage devices 150 to one or more fluid export vessels 170 via conduits 140, 141 , 161 and turret(s) 162; (iii) supply CNG from production platform 110 to one or more fluid export vessels 170 (bypassing gas storage devices 150) via conduits 111, 161 and turret(s) 162; (iv) supply CNG from production platform 110 to pipeline 21 (bypassing gas storage devices 150) via conduits 111 , 142; (v) supply CNG from pipeline 21 to gas storage devices 150 via conduits 142, 140, 141; (vi) supply CNG from pipeline 21 to export vessel(s) 170 (bypassing gas storage devices 150) via conduit 142, 161 and turret(s) 162; and (vii) supply CNG from gas storage devices 150 to pipeline 21 via conduits 140, 141 , 243. Moreover, manifold 230 can enable any two or more of (i), (ii), (iii), (iv), (v), (vi), and (vii) simultaneously.

[0043] Referring still to Figure 2, offshore production and export system 200 generally operates and functions in a similar manner as system 100 previously described. Namely, natural gas is produced to production platform 110 from one or more subsea wells in field 20, and the produced natural gas is compressed on production platform 110 to convert the natural gas to CNG. The CNG on production platform 110 can be stored temporarily on production platform 110 in CNG storage tanks (not shown); pumped from production platform 110 into gas storage devices 150 via conduits 111, 140, 141 and manifold 230; pumped from production platform 110 onto one or more export vessels 170 via conduit 111 , manifold 230, and fluid export assemblies 160; or combinations thereof. Simultaneous or independent of any of the foregoing, CNG stored in gas storage devices 150 can be supplied from gas storage devices 150 to one or more export vessels via conduits 140, 141 , manifold 230, and fluid export assemblies 160. Thus, it should be appreciated that system 100 allows production platform 110 to continuously produce natural gas, which is converted to CNG that can be directly loaded onto one or more export vessels 170 for export; or if no export vessels 170 are available, the CNG can simply be pumped into gas storage devices 150 for temporary storage until an export vessel 170 is available. Similar to system 100, this offers the potential to enhance reliability of system 200, as well as maximize operational and production time of production platform 110. In addition, when an export vessel 170 is connected to a turret 162, the CNG can be transferred simultaneously from production platform 110 to the export vessel 170 and from gas storage devices 150 to the export vessel 170, thereby offering the potential for faster loading of the export vessel 170 as compared to loading a export vessel (e.g., export vessel 170) from a single source of CNG. Further, in the case that multiple export vessels 170 are available and coupled to turrets 162, system 200 can simultaneously load CNG to multiple export vessels 170. This, combined with subsea gas storage devices 150, provides redundancy and availability, thereby offering the potential to reduce the number of export vessels 170 to export CNG from production platform 110 and associated capital expenditures, thereby increasing the economic feasibility of system 200.

[0044] Unlike system 100 previously described, system 200 includes additional functionality resulting from the coupling of manifold 230 and pipeline 21. In particular, CNG can be pumped from production platform 110 into pipeline 21 , thereby allowing pipeline 21 to accommodate excess produced CNG that cannot be accommodated by gas storage devices 150 or an export vessel 170; and further, CNG can be supplied from pipeline 21 to gas storage devices 150, thereby allowing gas storage devices 150 to accommodate CNG from pipeline 21 in cases where pipeline 21 is operating at full capacity and excess space for transportation of CNG in pipeline 21 is desired.

[0045] In one exemplary mode of operation, when an export vessel 170 is not available for exporting CNG, gas storage devices 150 receive CNG from production platform 110 and regulate the flow of CNG to pipeline 21 via manifold 230 and conduits 140, 142 to accommodate changes in pipeline demand over time. Any excess CNG accumulated in gas storage devices 150 is then transferred to export vessel(s) 170 when one or more export vessel(s) 170 are available for exporting CNG from system 200. However, if pipeline 21 is operating a full capacity and cannot accommodate additional CNG from production platform 110, and an export vessel 170 is not available for exporting CNG, gas storage devices 150 receive CNG from production platform 110 and receive excess CNG from pipeline 21. The CNG accumulated in gas storage devices 150 is then transferred to export vessel(s) 170 when one or more export vessel(s) 170 are available for exporting CNG from system 200. [0046] After a given export vessel 170 coupled to a turret 162 has been sufficiently filled with CNG supplied by production platform 110 and/or gas storage devices 150, the export vessel 170 decouples from the corresponding turret 162, leaves field 20, and transports the CNG loaded thereon to another location remote field 20 for offloading. In the manner described, system 200 produces hydrocarbon gas and exports the produced hydrocarbon gas to another location for offloading.

[0047] Referring now to Figure 3, an embodiment of a nearshore production and export system 300 in accordance with the principles disclosed herein is shown. System 300 shares some similarities with systems 100, 200 previously described. Accordingly, the differences between system 300 and systems 100, 200 will be described it being understood the other features are generally the same. In addition, for purposes of clarity, like features of system 300 and previously described systems 100, 200 are given the same reference numerals.

[0048] As shown in Figure 3, in this embodiment, system 300 is located in a nearshore field 30 that includes a nearshore terminal 31 disposed at the sea floor 12 and coupled to a pipeline 32 that extends from terminal 31 to the shore 40. Accordingly, as will be described in more detail below, in this embodiment, system 300 includes exporting capabilities, as well as offloading capabilities. Similar to systems 100, 200 previously described and shown in Figures 1 and 2, system 300 produces hydrocarbon gas (e.g., natural gas), and in particular produces natural gas that is compressed to convert the natural gas to CNG. However, unlike systems 100, 200, in this embodiment, system 300 does not include subsea storage devices 150.

[0049] Referring still to Figure 3, in this embodiment, production and export system 300 includes a production platform 310 at the sea surface 11 , a subsea manifold 330 disposed on the sea floor 12, and a plurality of fluid export vessels 170 disposed at the sea surface 11. As previously described, system 300 does not include gas storage devices 150.

[0050] As previously described, system 300 is located in nearshore field 30 that includes terminal 31 and pipeline 32, which enable exportation of CNG from production platform 310 and offloading of CNG from export vessels 170. Terminal 31 includes a plurality of fluid inlets 34, 35 and a fluid outlet 36. In addition, terminal 31 includes a plurality of pipes and connectors provide selective fluid communication between inlets 34, 35 and outlet 36 within terminal 31. Each inlet 34, 35 and outlet 36 includes a remotely operated valve to control the flow of gas therethrough. Pipeline 32 has an inlet 32a coupled to outlet 36 of terminal 31 and extends from terminal 31 to shore 40. Thus, pipeline 32 can receive CNG from terminal 31 and transport the CNG onto land for further processing, use, further transport, or combinations thereof. As will be described in more detail below, inlets 34, 35 receive CNG from export vessels 170 and production platform 310, respectively.

[0051] Production platform 310 is similar to production platform 110 previously described. Namely, production platform 310 is moored or otherwise held substantially stationary in the field 30 and receives natural gas produced from one or more subsea wells (not shown) in field 30. In addition, production platform 310 includes equipment (e.g., one or more compressors) for compressing the produced natural gas to convert the natural gas to CNG. In this embodiment, production platform 310 is a moored production vessel, and more specifically a floating production and offloading (FPSO) vessel. However, in other embodiments, the production platform (e.g., platform 310) may be a semi-submersible offshore platform, a jackup platform, a spar platform, or other suitable type of offshore structure for producing hydrocarbons from one or more subsea wells.

[0052] Manifold 330 is disposed on the sea floor 12 and includes a plurality of conduit couplings 331 , 332, 333. In addition, manifold 330 includes a plurality of pipes and connectors to provide selective fluid communication between couplings 331, 332, 333 within manifold 330. Each coupling 331 , 332, 333 includes a remotely operated valve to control the flow of fluid therethrough. As will be described in more detail below, in this embodiment, CNG flows out of manifold 330 via conduit coupling 331 , CNG flows out of manifold 330 via conduit couplings 333, and CNG flows into manifold 330 via conduit couplings 332. Accordingly, each coupling 331 , 333 may also be referred to herein as a fluid or CNG “outlet,” and each coupling 332 may also be referred to herein as a fluid or CNG “inlet.” In this embodiment, manifold 330 is pigable such that a pipeline pig can be deployed and moved through the flow passages in manifold 330 using techniques known in the art (e.g., to clean the inside of manifold 330, to remove clogs in manifold 330, etc.). [0053] Referring still to Figure 3, a fluid transfer conduit 311 extends from platform 310 to manifold 330. In this embodiment, CNG flows from manifold 330 to production platform 310 via fluid transfer conduit 311 , and thus, transfer conduit 311 may be described as having an outlet (not shown) in fluid communication with platform 310 (e.g., inlet of compressors) and a fluid outlet 311b coupled to outlet 331 of manifold 330. Thus, fluid transfer conduit 311 provides fluid communication between platform 310 and manifold 330, and in particular, supplies CNG from manifold 330 to production platform 310. In addition, a fluid transfer conduit 312 extends from platform 310 to terminal 31. In this embodiment, CNG flows from production platform 310 to terminal 31 via fluid transfer conduit 312, and thus, transfer conduit 312 may be described as having an inlet (not shown) in fluid communication with platform 310 (e.g., outlet of compressors) and a fluid outlet 312b coupled to inlet 35 of terminal 31. Thus, fluid transfer conduit 312 provides fluid communication between platform 310 and terminal 31 , and in particular, supplies CNG from production platform 310 to terminal 31 and pipeline 32. Accordingly, fluid transfer conduit 312 enables exportation of CNG from production platform 310 to terminal 31 and pipeline 32, and thus, may also be referred to as an “export” conduit.

[0054] Referring still to Figure 3, a fluid transfer assembly 160 as previously described is coupled to and extends from each inlet 332 of manifold 330. Each fluid transfer assembly 160 is as previously described. Namely, each fluid transfer assembly 160 includes a flow conduit 161 and a moored turret 162 that may be floating at the surface 11 or slightly submerged below the surface 11. In this embodiment, fluid transfer assemblies 160 offload CNG from export vessels 170. Accordingly, fluid transfer assemblies 160 may also be referred to as “offload” assemblies, and further, each conduit 161 may be described as having an outlet 161a coupled to one inlet 332 of manifold 330 and an inlet 161b coupled to the corresponding turret 162 and export vessel 170. Thus, in this embodiment, each flow conduit 161 provides fluid communication between manifold 330 and the corresponding turret 162, and in particular, supplies CNG from the corresponding turret 162 and export vessel 170 to manifold 330.

[0055] One export vessel 170 can releasably couple to each turret 162 at a given time, thereby providing fluid communication between manifold 330 and that export vessel 170. Thus, when an export vessel 170 is coupled to a turret 162, CNG can be supplied from that export vessel 170 to manifold 130, thereby offloading the CNG from vessel 170.

[0056] Manifold 330 fluidly couples and can provide selective fluid communication between production platform 310, offload assemblies 160, any export vessel(s) 170 coupled to offload assemblies 160, and terminal 31. Thus, manifold 330 can be employed to (i) offload CNG from CNG vessels 170 to terminal 31 and pipeline 32; (ii) supply CNG from CNG vessels 170 to production platform 310; and (iii) export CNG from production platform 310 to terminal 31 and pipeline 32. Moreover, manifold 130 can enable two or more of (i), (ii), and (iii) simultaneously.

[0057] Referring still to Figure 3, offshore production and export system 300 operates and functions in a different manner than systems 100, 200 previously described as production platform 310 can export CNG to pipeline 32 via conduit 312 and terminal 31 ; CNG vessels 170 can offload CNG to pipeline 32 via offload assemblies 160, manifold 330, and terminal 31 ; and CNG vessels 170 can offload CNG to pipeline 32 via offload assemblies 160, manifold 330, conduit 311 , production platform 310, conduit 312, and terminal 31. In particular, natural gas is produced to production platform 310 from one or more subsea wells in field 30, and the produced natural gas is compressed on production platform 310 to convert the natural gas to CNG. In this embodiment, the CNG on production platform 310 is pumped from platform 310 through conduit 312 and terminal 31 into pipeline 32, thereby directly exporting the CNG from platform 310 without the use of manifold 330, fluid transfer assemblies 160, or CNG vessels 170. In addition, CNG vessels 170 carrying CNG from another location remote field 30 (e.g., field 10 or field 20 previously described) can couple to turrets 162 and offload CNG. It should be appreciated that as a given CNG vessel 170 offloads CNG, the pressure of the CNG stored in tanks of the CNG vessel 170 will slowly decrease absent continued compressing. Accordingly, in this embodiment, CNG vessels 170 can offload CNG in a staged manner - when the pressure of the CNG is sufficient (i.e., greater than the pressure of CNG in pipeline 32), the CNG is offloaded through fluid transfer assemblies 160 and manifold 330 into terminal 31 and pipeline 32; however, when the pressure of CNG is insufficient (i.e., less than the pressure of CNG in pipeline 32), the CNG is offloaded from the CNG vessel 170 through fluid transfer assemblies 160, manifold 330, and conduit 311 to production platform 330, which then compresses and pressurizes the CNG (via compressors) such that it can be pumped from platform 310 through conduit 312 and terminal 31 into pipeline 32. Thus, once the pressure of the CNG in the storage tanks of the CNG vessel 170 is insufficient to be discharged directly into pipeline 32 (via fluid transfer assembly 160, manifold 330, and terminal 31), manifold redirects the CNG being offloaded from the CNG vessel 170 to production platform 330 (via conduit 311) to re-pressurize the CNG and supply it to pipeline 32 (via conduit 312 and terminal 31).

[0058] While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simply subsequent reference to such steps.

Claims

CLAIMS What is claimed is:

1. An offshore system for producing and exporting hydrocarbon gas, the system comprising: a production platform disposed in an offshore production field, wherein the production platform is configured to receive the hydrocarbon gas from one or more subsea wells in the production field; a subsea manifold disposed in the production field; a fluid transfer conduit extending from the production platform to the subsea manifold, wherein the fluid transfer conduit is configured to supply the hydrocarbon gas from the production platform to the subsea manifold; a first subsea gas storage device in the production field and in selective fluid communication with the subsea manifold, wherein the first subsea gas storage device is configured to temporarily store the hydrocarbon gas; a first gas export assembly coupled to the subsea manifold and in selective fluid communication with the subsea manifold, wherein the first gas export assembly is configured to supply the hydrocarbon gas from the manifold to a first export vessel releasably coupled to the first gas export assembly.

2. The offshore system of claim 1 , wherein the production platform is a floating production vessel.

3. The offshore system of claim 1, further comprising a second gas export assembly coupled to the subsea manifold and in selective fluid communication with the subsea manifold, wherein the second gas export assembly is configured to supply the hydrocarbon gas from the manifold to a second export vessel releasably coupled to the second gas export assembly; wherein each gas export assembly comprises a single turret loading (STL) system including a flow conduit and a moored turret; wherein the flow conduit of the first gas export assembly extends from a first outlet of the subsea manifold to the moored turret of the first gas export assembly; wherein the flow conduit of the second gas export assembly extends from a second outlet of the subsea manifold to the moored turret of the second gas export assembly.

4. The offshore system of claim 1 , further comprising a fluid conduit extending from the subsea manifold to the first subsea gas storage device, wherein the fluid conduit is configured to flow the hydrocarbon gas from the subsea manifold to the first subsea gas storage device and flow the hydrocarbon gas from the first subsea gas storage device to the subsea manifold.

5. The offshore system of claim 1 , wherein the offshore production field does not include a subsea pipeline for exporting the hydrocarbon gas produced by the production platform.

6. The offshore system of claim 1 , further comprising a flow conduit extending from the subsea manifold to a subsea pipeline extending through the offshore production field.

7. The offshore system of claim 6, wherein the flow conduit is configured to supply the hydrocarbon gas from the subsea manifold to the subsea pipeline and supply the hydrocarbon gas from the subsea pipeline to the subsea manifold.

8. A method for producing and exporting hydrocarbon gas from an offshore production field, the method comprising:

(a) producing the hydrocarbon gas from one or more subsea wells in the production field to a production platform disposed in the offshore production field;

(b) supplying the hydrocarbon gas from the production platform to a subsea manifold disposed in the production field; (c) supplying the hydrocarbon gas from the subsea manifold to a first gas export assembly; and

(d) supplying the hydrocarbon gas from the subsea manifold to a subsea gas storage device to temporarily store the hydrocarbon gas.

9. The method of claim 8, further comprising:

(e) supplying the hydrocarbon gas from the subsea manifold to a second gas export assembly during (c).

10. The method of claim 9, wherein (d) comprises: supplying the hydrocarbon gas from the subsea manifold to the subsea gas storage device before or during (e).

11. The method of claim 9, further comprising:

(f) supplying the hydrocarbon gas from the first subsea gas storage device to the subsea manifold during (e).

12. The method of claim 11 , further comprising:

(g) loading a first export vessel releasably coupled to a moored turret of the first gas export assembly during (e).

13. The method of claim 12, further comprising:

(h) supplying gas from the subsea manifold to a second gas export assembly during (c);

(i) loading a second export vessel releasably coupled to a moored turret of the second gas export assembly during (h).

14. The method of claim 8, further comprising: supplying hydrocarbon gas from a subsea pipeline extending through the production field to the subsea gas storage device; or supplying hydrocarbon gas from the subsea manifold to the subsea pipeline.

15. An offshore system for producing and exporting hydrocarbon gas, the system comprising: a production platform disposed in an offshore production field, wherein the production platform is configured to receive the hydrocarbon gas from one or more subsea wells in the production field; a subsea manifold disposed in the production field; a first fluid transfer conduit extending from the production platform to the subsea manifold, wherein the first fluid transfer conduit is configured to supply hydrocarbon gas from the subsea manifold to the production platform; a first gas transfer assembly coupled to the subsea manifold and in selective fluid communication with the subsea manifold, wherein the first gas transfer assembly is configured to offload hydrocarbon gas from a first vessel releasably coupled to the first gas transfer assembly to the subsea manifold; a nearshore terminal in selective fluid communication with the subsea manifold and in fluid communication with a pipeline extending from the nearshore terminal onto land.

16. The offshore system of claim 15, wherein the production platform is a floating production vessel.

17. The offshore system of claim 15, further comprising a second gas transfer assembly coupled to the subsea manifold and in selective fluid communication with the subsea manifold, wherein the second gas transfer assembly is configured to offload hydrocarbon gas from a second vessel releasably coupled to the first gas transfer assembly to the subsea manifold.

18. The offshore system of claim 17, wherein each gas export assembly comprises a flow conduit and a moored turret; wherein the flow conduit of the first gas export assembly extends from a first inlet of the subsea manifold to the moored turret of the first gas export assembly; wherein the flow conduit of the second gas export assembly extends from a second inlet of the subsea manifold to the moored turret of the second gas export assembly.

19. The offshore system of claim 17, wherein the first fluid transfer conduit extends from the production platform to an outlet of the manifold.

20. The offshore system of claim 15, further comprising a second fluid transfer conduit extending from the production platform to the nearshore terminal, wherein the second gas transfer assembly is configured to export hydrocarbon gas from the production platform to the terminal and the pipeline.

21. The offshore system of claim 15, wherein the production platform is configured to pressurize the hydrocarbon gas supplied by the subsea manifold.