Patent Publication Number: US-2016236756-A1

Title: Tandem and side-by-side mooring offlaoding systems and associated methods

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/879,503, filed Sep. 18, 2013, which is incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates generally to mooring systems. More specifically, in certain embodiments the present disclosure relates to systems for mooring a vessel to a structure and associated methods. 
     Floating production storage and offloading vessels (FPSOs) and floating storage and offloading vessels (FSOs) are commonly used in offshore oil and gas operations to temporarily store and then offload produced oil from subsea wells. An FPSO may designed to receive crude oil produced from subsea wells or a nearby platform, process that crude oil, and then store the processed oil until it can be offloaded to a tanker or transported through a pipeline. An FSO is a simplified FPSO without the ability to process crude oil. An FSO typically receives and stores oil that has already been processed at a platform, and then offloads the stored oil to a tanker or through a pipeline. FPSOs and FSOs are particularly suited in offshore regions where there is no pipeline infrastructure in place for transporting produced oil to shore. In particular, the FPSO/FSO is employed to store the produced oil until it can be offloaded for transport to another location. 
     Typically, FPSOs and FSOs are ship-shaped floating vessels or barges that are moored to the sea floor when receiving crude or processed oil from a platform. In order to offload crude oil, a shuttle vessel may be moored and connected to the FPSO or FSO, or alternatively to the platform itself, and then transfer can take place. U.S. Patent Application Publication No. 2010/00212570, the entirety of which is hereby incorporated by reference, describes an example of such a system. 
     Conventional mooring systems for offloading, such as offloading buoys or tandem offloading using tugs for station keeping, may suffer from several drawbacks. These conventional systems may not be designed for the transfer of natural gas or for emergency offloads, and can be prohibitively costly or risky to operate safely. It is desirable to develop a mooring system that is particularly suited for the transfer of natural gas and also for emergency or temporary offloading. 
     SUMMARY 
     The present disclosure relates generally to mooring systems. More specifically, in certain embodiments the present disclosure relates to systems for mooring a vessel to a structure and associated methods. 
     In one embodiment, the present disclosure provides a mooring system comprising: an offshore structure comprising one or more hawsers; a vessel; a first mooring line; and a second mooring line. 
     In another embodiment, the present disclosure provides a method for mooring a vessel comprising: providing a vessel; providing an offshore structure comprising one or more hawsers; providing a first mooring line; providing a second mooring line; attaching the first mooring line to the vessel; attaching the second mooring line to the vessel; and attaching the one or more hawsers to the vessel. 
     In another embodiment, the present disclosure provides a method for offloading oil and/or gas from a structure comprising: providing a side-by-side mooring system comprising an offshore structure comprising two hawsers, a vessel, a first mooring line, and a second mooring line; connecting the vessel to the first mooring line, the second mooring line, and the two hawsers; transferring oil and/or gas from the offshore structure to the vessel; and disconnecting the vessel from the first mooring line, the second mooring line, and the two hawsers. 
     In another embodiment, the present disclosure provides a method for offloading oil and/or gas from an offshore structure comprising: providing a tandem mooring system comprising an offshore structure comprising a hawser, a vessel, a first mooring line, and a second mooring line; connecting the vessel to the first mooring line, the second mooring line, and the hawser; transferring oil and/or gas from the offshore structure to the vessel; and disconnecting the vessel from the first mooring line, the second mooring line, and the hawser. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the above recited features and advantages of the disclosure may be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to the embodiments thereof that are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are, therefore, not to be considered limiting of its scope. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness. 
         FIG. 1  illustrates a mooring system. 
         FIG. 2  illustrates a side-by-side mooring system. 
         FIG. 3  illustrates a tandem mooring system. 
       The features and advantages of the present disclosure will be readily apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates generally to mooring systems. More specifically, in certain embodiments the present disclosure relates to systems for mooring a vessel to a structure and associated methods. 
     The description that follows includes exemplary apparatuses, methods, techniques, and instruction sequences that embody techniques of the inventive subject matter. However, it is understood that the described embodiments may be practiced without these specific details. 
     Referring now to  FIG. 1 ,  FIG. 1  illustrates mooring system  100 . In certain embodiments, mooring system  100  may comprise offshore structure  110 ; vessel  120 ; first mooring line  130 ; second mooring line  140 ; and hawser  150 . 
     In certain embodiments, offshore structure  110  may comprise a floating liquid natural gas facility. The floating liquid natural gas facility may comprise one or more liquid natural gas storage tanks and cryogenic offloading equipment. In other embodiments, offshore structure  110  may comprise a floating structure floating on sea surface  170 . Examples of suitable floating structures include FPSOs, FSOs, spars, TLPs, semi-submersibles, or other floating structures known in the art. In certain embodiments, offshore structure  110  may be connected to sea floor  160  with one or more catenary or taut mooring lines  165 . Alternatively offshore structure  110  may be a fixed structure such as a pier, compliant tower, gravity based structure, jack-up platform, or jacket platform resting on sea floor  160 . 
     In certain embodiments, offshore structure  110  may comprise one or more winches  111 . In certain embodiments, offshore structure  110  may comprise one or more transfer devices  112 . In certain embodiments, the one or more transfer devices  112  may be capable of offloading oil and/or gas from offshore structure  110 . In certain embodiments, the one or more transfer devices  112  may comprise a hose or a loading arm. 
     In certain embodiments, vessel  120  may comprise any vessel capable of transporting oil and/or natural gas. In certain embodiments, vessel  120  may be a liquid natural gas carrier vessel. In other embodiments, vessel  120  may be a shuttle tanker. Vessel  120  may comprise storage facilities  121  capable of storing oil and/or gas. In certain embodiments, not illustrated in  FIG. 1 , one or more hoses  112  of offshore structure  110  may be connected to storage facility  121  of vessel  120  to facilitate transfer of oil and/or gas from offshore structure  110  to vessel  120 . 
     In certain embodiments, vessel  120  may further comprise one or more bollards or mooring bitts  122 . In certain embodiments, not illustrated in  FIG. 1 , first mooring line  130 , second mooring line  140 , and hawser  150  may be attached individually to at least three different bollard or mooring bitts  122  of vessel  120 . 
     In certain embodiments, first mooring line  130  and second mooring line  140  may each comprise chain, wire, polyester, HMPE segments, or any combination thereof. In certain embodiments, first end  131  of first mooring line  130  may be anchored to sea floor  160 . In certain embodiments, first end  131  of first mooring line  130  may be attached to chain  132  which is attached to anchor or pile  133  on sea floor  160 . In certain embodiments, first end  141  of second mooring line  140  may be anchored to sea floor  160 . In certain embodiments, first end  141  of second mooring line  140  may be attached to chain  142  which is attached to anchor or pile  143  on sea floor  160 . In certain embodiments, anchor  133  and/or anchor  143  may comprise mooring connectors linked to conventional anchors, vertical load anchors, or suction piles. 
     In certain embodiments, first mooring line  130  may comprise buoy  134  attached directly or indirectly to first mooring  130  at buoyed point  135 . In certain embodiments, second mooring line  140  may comprise buoy  144  attached directly or indirectly to second mooring  140  at buoyed point  145 . In certain embodiments, buoy  134  and/or buoy  144  may be submersible buoys. In certain embodiments, buoy  134  and/or buoy  144  may be modular or single mooring buoys of elastomer or foam construction, connected via chain-throughs, pick-ups, or pendants. In certain embodiments, buoy  134  and buoy  144  may be connected to buoyed points  135  and  145  respectively through buoy lines  136  and  146 . 
     In certain embodiments, first mooring line  130  may further comprise marker buoy  138 . In certain embodiments, marker buoy  138  may be floating on sea surface  170 . In certain embodiments, marker buoy  138  may be a small float or high-visibility buoy to help pick up messenger lines. In certain embodiments, second mooring line  140  may further comprise marker buoy  148 . In certain embodiments, marker buoy  148  may be floating on sea surface  170 . In certain embodiments, marker buoy  148  may be a small float or high-visibility buoy to help pick up messenger lines. In certain embodiments, marker buoy  138  and marker buoy  148  may be connected to each other by chord line  180 . In certain embodiments, chord line  180  may comprise a lightweight synthetic line composed of polyester or HMPE segments. 
     In certain embodiments, not illustrated in  FIG. 1 , second end  139  of first mooring line  130  may be connected to bollard or mooring bitt  122  of vessel  120  and second end  149  of second mooring line  140  may be connected to bollard or mooring bitt  122  of vessel  120 . 
     In certain embodiments, hawser  150  may comprise a nylon or HMPE line with pick-up equipment such as messenger lines, connecting shackles, floats, and weight chains. In certain embodiments, hawser  150  may comprise a single hawser  150  or multiple hawsers  150 . In certain embodiments, first end  151  of hawser  150  may be attached to the winch  111  of vessel  110 . In certain embodiments, not illustrated in  FIG. 1 , second end  152  hawser  150  may be attached to the one or more bollards or mooring bitts  122  of vessel  120 . 
     Referring now to  FIG. 2 ,  FIG. 2  illustrates a side-by-side mooring system  200 . In certain embodiments, side-by-side mooring system  200  may comprise any of the features of mooring system  100 . Furthermore, each of the individual components of side-by-side mooring system  200  may comprise the same features of each of the individual components of mooring system  100 . 
     As can be seen in  FIG. 2 , side-by-side mooring system  200  may comprise structure  210 , vessel  220 , first mooring line  230 , second mooring line  240 , and two hawsers  250 . 
     In certain embodiments, structure  210  may be floating on sea surface  170  and attached to sea floor  160  by one or more mooring lines  265 . In certain embodiments, two hawsers  250  may connect structure  210  to vessel  220 . In certain embodiments, first ends  251  of hawsers  250  may be attached to one or more winches  211  of structure  210 . In certain embodiments, second ends  252  of hawsers  250  may be attached to one or more bollards or mooring bitts  222  of vessel  220 . In certain embodiments, one or more transfer devices  212  of structure  210  may be connected to storage facility  221  of vessel  220  to facilitate transfer of oil and/or gas from structure  210  to vessel  220 . 
     In certain embodiments, vessel  220  may be moored to the seafloor  260  by mooring lines  230  and  240 . In certain embodiments, mooring line  230  may comprise a first end  231  anchored to sea floor  260  by anchor  233  and chain  232 , second end  239  connected to bollard or mooring bitt  222  of vessel  220 , buoy  234  connected to buoyed point  235  by buoyed line  236 , and marker buoy  238 . In certain embodiments, mooring line  240  may comprise a first end  241  anchored to sea floor  260  by anchor  243  and chain  242 , second end  249  connected to bollard or mooring bitt  222  of vessel  220 , buoy  244  connected to buoyed point  245  by buoyed line  246 , and marker buoy  248 . In certain embodiments, a chord line  280  may connected marker buoy  238  to marker buoy  248 . 
     As can be seen in  FIG. 2 , side-by-side mooring system  200  allows for a vessel to be moored to a structure in a side-by-side fashion where the vessel is secured to the seafloor by 2 points of contact and secured to the structure by two points of contact. In such a system, the vessel is pointed parallel with the structure. In such a system, the relative motions between the vessel and the structure are smaller compared to a tandem mooring system, allowing for shorter loading arms. Shorter loading arms may minimize heat loss and mechanical stresses during transfers. 
     Referring now to  FIG. 3 ,  FIG. 3  illustrates a tandem mooring system  300 . In certain embodiments, tandem mooring system  300  may comprise any of the features of mooring system  100  and certain features of side-by-side mooring system  200 . Furthermore, each of the individual components of tandem mooring system  300  may comprise the same features of each of the individual components of mooring system  100 . 
     As can be seen in  FIG. 3 , tandem mooring system  300  may comprise an offshore structure  310 , a vessel  320 , a first mooring line  330 , a second mooring line  340 , and hawser  350 . 
     In certain embodiments, offshore structure  310  may be floating on sea surface  370  and attached to sea floor  360  by one or more mooring lines  370 . In certain embodiments, hawser  350  may connect offshore structure  310  to vessel  320 . In certain embodiments, first end  351  of hawser  350  may be attached to winch  311  of offshore structure  310 . In certain embodiments, second end  352  of hawser  350  may be attached to one or more bollards or mooring bitts  322  of vessel  320 . In certain embodiments, one or more transfer devices  312  of offshore structure  310  may be connected to storage facility  321  of vessel  320  to facilitate transfer of oil and/or gas from offshore structure  310  to vessel  320 . 
     In certain embodiments, vessel  320  may be moored to the seafloor  360  by mooring lines  330  and  340 . In certain embodiments, mooring line  330  may comprise a first end  331  anchored to sea floor  360  by anchor  333  and chain  332 , second end  339  connected to bollard or mooring bitt  322  of vessel  320 , buoy  334  connected to buoyed point  335  by buoyed line  336 , and marker buoy  338 . In certain embodiments, mooring line  340  may comprise a first end  341  anchored to sea floor  360  by anchor  343  and chain  342 , second end  349  connected to bollard or mooring bitt  322  of vessel  320 , buoy  344  connected to buoyed point  345  by buoyed line  346 , and marker buoy  348 . In certain embodiments, a chord line  380  may connected marker buoy  338  to marker buoy  348 . 
     As can be seen in  FIG. 3 , tandem mooring system  200  allows for a vessel to be moored to a structure in a tandem fashion where the vessel is secured to the seafloor by 2 points of contact and secured to the structure by one point of contact. In such a system, the vessel is pointed directly toward the structure. Such a system may allow for an easier, more controlled approach maneuvering to the structure. Lines  330  and  340  may provide increasing resistance to the vessel as it advances. Such an orientation also makes use of bow chain stoppers that are commonly found in most tankers, and that easily and safely connected to hawsers. 
     In one embodiment, the present disclosure provides a method for offloading oil and/or gas from a structure comprising: providing a side-by-side mooring system comprising a structure, a vessel, a first mooring line, a second mooring line, and two hawsers; connecting the vessel to the first mooring line, the second mooring line, and the two hawsers; transferring oil and/or gas from the offshore structure to the vessel; and disconnecting the vessel from the first mooring line, the second mooring line, and the two hawsers. 
     As used herein, the term “side-by-side” is used to indicate that the vessel and the offshore structure are in a parallel arrangement as illustrated in  FIG. 2 . 
     In another embodiment, the present disclosure provides a method for offloading oil and/or gas from a structure comprising: providing a tandem mooring system comprising an offshore structure comprising a hawser, a vessel, a first mooring line, and a second mooring line; connecting the vessel to the first mooring line, the second mooring line, and the hawser; transferring oil and/or gas from the offshore structure to the vessel; and disconnecting the vessel from the first mooring line, the second mooring line, and the hawser. 
     As used herein, the term “tandem” is used to indicate that the vessel and the offshore structure are in a perpendicular arrangement as illustrated in  FIG. 3 . 
     To facilitate a better understanding of the present invention, the following examples of specific embodiments are given. In no way should the following examples be read to limit, or to define, the scope of the invention. 
     EXAMPLES 
     Example 1—Side-by-Side Offloading Procedure 
     The following example provides details on how side-by-side offloading may be preformed. A liquid natural gas carrier vessel may approach a floating liquid natural gas facility. The vessel may then be connected to two mooring lines and then two hawsers from the facility. The facility may then winch in the hawsers by first winching in a single hawser and then winching in the remaining hawser. Once the vessel is in a side-by-side arrangement with the facility, liquid natural gas loading arms from the facility may be attached to the vessel and liquid natural gas may be transferred from the facility to the vessel. After the transfer is complete, the loading arms may be disconnected from the vessel and the facility may winch out the two hawsers allowing the mooring lines to pull the vessel away from the facility. The vessel may then be disconnected from the hawsers and the mooring lines and the facility may take back in the hawsers. 
     Example 2—Tandem Offloading Procedures 
     The following example provides details on how side-by-side offloading may be preformed. A liquid natural gas carrier vessel may approach a floating liquid natural gas facility. The vessel may then be connected to two mooring lines and then a hawser from the facility. The facility may then winch in the hawser. Once the vessel is in a side-by-side arrangement with the facility, liquid natural gas loading arms from the facility may be attached to the vessel and liquid natural gas may be transferred from the facility to the vessel. After the transfer is complete, the loading arms may be disconnected from the vessel and the facility may winch out the hawser allowing the mooring lines to pull the vessel away from the facility. The vessel may then be disconnected from the hawser and the mooring lines and the facility may take back in the hawser. 
     While the embodiments are described with reference to various implementations and exploitations, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is not limited to them. Many variations, modifications, additions and improvements are possible. 
     Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter.