Abstract:
During an offloading operation between a first and a second body, an operating envelope of an offloading system can be displaced to compensate for a drifting movement of one of the bodies. By appropriately displacing the operating envelope, offloading operation can continue under safe conditions even though the working limit of the original operating envelope is breached due to the drifting movement of one of the bodies.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    Embodiments of the invention relate to system and method for displacing an operating envelope of an offloading system to ensure continuity of offloading operation without compromising on safety. 
         [0003]    2. Description of Related Art 
         [0004]    Presently, transferring or offloading of hydrocarbon fluid between two bodies in an offshore environment is commonly carried out using mechanical loading arms or cryogenic flexible hoses. These and other existing offloading apparatuses are inherently limited by its operating envelope. 
         [0005]      FIG. 1  illustrates the top view representation of an operating envelope of an existing offloading apparatus provided on a first body (e.g. jack-up platform  10 ). The offloading apparatus may be represented by an offloading origin point  12 . The operating envelope  14  defines a maximum working area around the offloading origin point  12  for safe offloading between the first body and a second body (e.g. marine vessel) (not shown). In an offloading operation, the first and the second bodies are connected via hoses for fluid transfer. Due to offshore environmental conditions, the second body may drift away from the first body. If the second body drifts within the operating envelope  14 , the offloading operation may continue safely. However, if the second body drifts to a position at the working limit  15  of the operating envelope  14 , the offloading operation has to be terminated by emergency shutdown procedures. Any further drifting of the second body to a position beyond the operating envelope  14  (e.g. at position  16 ) would activate emergency disconnection procedures to separate the transfer hose from the second body before the mechanical limit  17  of the offloading apparatus is reached. 
       SUMMARY 
       [0006]    According to one aspect of the invention, an offloading system comprises: a cantilever mounted on a deck, the cantilever is movable in a longitudinal direction of the cantilever between a retracted position and an extended position, the cantilever having an operational end which extends beyond the deck in the extended position; a transverse platform mounted on the operational end of the cantilever and movable between a transverse direction of the cantilever; a plurality of transfer hoses having a first end connected to a hydrocarbon fluid storage and having a second end to be connected to a marine vessel for fluid transfer between the hydrocarbon fluid storage and the marine vessel; and a transfer hose handling system mounted on the transverse platform and operable to manipulate the plurality of transfer hoses to and from the marine vessel, wherein after connecting the plurality of transfer hoses to the marine vessel, the transverse platform is movable in the transverse direction of the cantilever to adjust a transverse reach of the transverse platform and/or the cantilever is movable in the longitudinal direction of the cantilever to displace an operating envelope of the offloading system. The offloading system may be provided on a fixed or moving body. 
         [0007]    According to another aspect of the invention, a method for displacing an operating envelope of an offloading system, comprises: positioning a marine vessel at a distance from a jack-up platform having an offloading system which comprises: a cantilever mounted on a deck of the jack-up platform, the cantilever being movable in a longitudinal direction of the cantilever between a retracted position and an extended position, the cantilever having an operational end which extends beyond the deck in the extended position, a transverse platform mounted on the operational end of the cantilever and movable along a transverse direction of the cantilever, and a plurality of transfer hoses, each having a first end connected to a hydrocarbon fluid storage and each having a second end to be connected to the marine vessel for fluid transfer between the hydrocarbon fluid storage and the marine vessel; a transfer hose handling system mounted on the transverse platform and operable to manipulate the plurality of transfer hoses to and from the marine vessel; extending the operational end of the cantilever in the longitudinal direction towards the marine vessel; connecting the plurality of transfer hoses to the marine vessel; and displacing an operating envelope of the offloading system by moving the transverse platform in the transverse direction to adjust a transverse reach of the transverse platform and/or by moving the cantilever in the longitudinal direction to adjust a longitudinal reach of the cantilever. 
         [0008]    The method may further comprise returning the marine vessel to a pre-drifted position; and returning the displaced operating envelope of the offloading system to the pre-drifted position by moving the transverse platform in the transverse direction to adjust a transverse reach of the transverse platform and/or by moving the cantilever in the longitudinal direction to adjust a longitudinal reach of the cantilever. 
         [0009]    As will be apparent from the present disclosure, embodiments of the invention are capable of displacing an operating envelope of an offloading system which is to transfer hydrocarbon between a first body which is fixed or moving, and a second moving body. The displaced operating envelope is capable of compensating for a displacement of the second body from its original desired position so that a continuing offloading operation may not need to be disrupted due to a breach of the working limit of the original operating envelope. Accordingly, by displacing an operating envelope to a new position, safety standards for offloading operation can be maintained while reducing offloading downtime. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Embodiments of the invention are disclosed hereinafter with reference to the drawings, in which: 
           [0011]      FIG. 1  illustrates an operating envelope of an existing offloading apparatus; 
           [0012]      FIG. 2  is an overview arrangement of a jack-up platform and a marine vessel for a hydrocarbon fluid transfer or offloading operation; 
           [0013]      FIG. 3  is a close-up view of the jack-up platform which is provided with an offloading system; 
           [0014]      FIG. 4  is a close-up view of the offloading system of  FIG. 3 ; and 
           [0015]      FIGS. 5A to 5K  illustrate a method of displacing an operating envelope of an offloading system, in which: 
           [0016]      FIG. 5A  illustrates a cantilever of the offloading system disposed in a retracted position, 
           [0017]      FIG. 5B  illustrates a marine vessel maintained in position relative to the jack-up platform, 
           [0018]      FIG. 5C  illustrates the cantilever being extended in a longitudinal (Y) direction towards the marine vessel, 
           [0019]      FIG. 5D  illustrates the transfer hoses having moved onto the marine vessel and connected to the manifolds on the marine vessel, 
           [0020]      FIG. 5E  is a close-up view of  FIG. 5D , 
           [0021]      FIG. 5F  illustrates the transfer hoses connected to the manifolds of the marine vessel and the transfer skid disconnected from the transfer hose handling system on the jack-up platform while slack ropes or wires connect the ERCs of the transfer hoses to the transfer hose handling system, 
           [0022]      FIG. 5G  is a close-up view of  FIG. 5F , 
           [0023]      FIG. 5H  illustrates the arrangement of the offloading system when an offloading operation is taking place, 
           [0024]      FIG. 5I  is a simplified top view of  FIG. 5H  and illustrates an original operating envelope of the offloading system, 
           [0025]      FIG. 5J  shows that the marine vessel has drifted from the original position illustrated in  FIG. 5I  to a new position relative to the jack-up platform, and 
           [0026]      FIG. 5K  illustrates a new or displaced operating envelope. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    In the following description, numerous specific details are set forth in order to provide a thorough understanding of various illustrative embodiments of the invention. It will be understood, however, to one skilled in the art, that embodiments of the invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure pertinent aspects of embodiments being described. In the drawings, like reference numerals refer to same or similar functionalities or features throughout the several views. 
         [0028]      FIG. 2  is an overview arrangement of a first body, e.g. jack-up platform  10 , and a second body, e.g. marine vessel  20  such as a Liquefied Natural Gas (LNG) carrier or tanker, for a hydrocarbon fluid transfer or offloading operation. The jack-up platform  10  may be provided with gas processing, liquefaction, and/or hydrocarbon fluid storage facilities. The marine vessel  20  may be maintained in position relative to the jack-up platform  10  by suitable methods, e.g. spread mooring, dynamic positioning. 
         [0029]      FIG. 3  is a close-up view of the jack-up platform  10  which is provided with an offloading system  400 ;  FIG. 4  is a close-up view of the offloading system  400 . 
         [0030]    Referring to  FIGS. 3 and 4 , the offloading system  400  at least comprises a cantilever  410 , a transverse platform  420 , a plurality of cryogenic transfer hoses  422  and a transfer hose handling system  430 . The cantilever  410  is movably mounted on a deck  12  of the jack-up platform  10 . The cantilever  410  is movable or skiddable in a longitudinal direction of the cantilever  410  (Y-direction) between a retracted position and an extended position, including intermediate positions therebetween. The cantilever  410  has an operational end which extends beyond the deck  12 . The transverse platform  420  is movably mounted at the operational end of the cantilever  410 . The transverse platform  420  is movable or skiddable in a transverse direction of the cantilever  410  (X-direction) between a leftmost position and a rightmost position, including intermediate positions therebetween. The transfer hoses  422  are provided at the transverse platform  420 . Each of the transfer hoses  422  has a first end connected to or disposed in fluid communication with a hydrocarbon fluid storage  450  at the jack-up platform  10  and a second end to be connected to a marine vessel  20  to facilitate fluid transfer between the hydrocarbon fluid storage  450  and the marine vessel  20 . The transfer hose handling system  430  is provided on the transverse platform  420  and operable to manipulate the plurality of transfer hoses  422  to and from the marine vessel  20 . 
         [0031]    Upon connecting the plurality of transfer hoses  422  to manifolds of the marine vessel  20 , the transverse platform  420  remains movable in a transverse (X) direction of the cantilever  410  between a leftmost position and a rightmost position to adjust a transverse reach of the transverse platform  420 . Also, the cantilever  410  remains movable in the longitudinal (Y) direction, to adjust a longitudinal reach of the cantilever  410 . By moving the cantilever  410  and/or transverse platform  420  in their respective directions, the operational end of the cantilever  410 , including the transfer hose handling system  430  with its transfer hoses  422 , is repositioned. This repositioning results in displacing the original operating envelope to a new operating envelope. If the marine vessel  20  is located within the new (or displaced) operating envelope, offloading operation may continue or take place safely. Hence, by displacing an operating envelope when the marine vessel  20  is approaching the working limit of the operating envelope, emergency shutdown and disconnection of the offloading system from the marine vessel may be delayed or even refrained altogether. 
         [0032]    Still referring to  FIGS. 3 and 4 , a plurality of first ends of the transfer hoses  422  may be connected to a hydrocarbon fluid storage  450  via a series of pipes or hoses interposed therebetween. Particularly, the first ends of the transfer hoses  422  are connected to a first plurality of rigid pipes (not shown in  FIG. 4 , see  440  in  FIG. 5E ) which are located on the transverse platform  420 . The first plurality of rigid pipes  440  are connected to a first plurality of flexible hoses  442  which are in turn connected to a second plurality of rigid pipes  444  which are disposed on the cantilever  410 . The first plurality of flexible hoses  442  are arranged with a slack to allow the transverse platform  420  move in a transverse (X) direction to the cantilever  410  without affecting or damaging the second plurality of rigid pipes  444 . The second plurality of rigid pipes  444  are connected to a second plurality of flexible hoses  446  which are in turn connected to a third plurality of rigid pipes  448  which are disposed on the deck  12 . The second plurality of flexible hoses  446  are arranged with a slack to allow the cantilever  410  move in a longitudinal (Y) direction to the cantilever without affecting or damaging the third plurality of rigid pipes  448 . The third plurality of rigid pipes  448  may be connected to the hydrocarbon fluid storage  450  either directly or indirectly through other pipes. 
         [0033]    In the illustration of  FIG. 4 , the transfer hose handling or lifting system  430  comprises an extendable lifting arm  432  having a spreader frame  434  movably attached thereto. The lifting arm  432  and the spreader frame  434  are motorized to manipulate or lift a transfer skid  436  supporting the transfer hoses  422 . Particularly, the transfer hose handling system  430  may lift the transfer hoses  422  from a parking position on the transverse platform  420 , support the transfer hoses  422  while they are being transferred to a marine vessel  20 , lower the transfer hoses  422  onto the marine vessel  20 , and return the transfer hoses  422  to the parking position. It is to be appreciated that other types of offloading system, transfer hose handling or lifting system not shown or described herein may be employed with embodiments of the invention. Examples of transfer hose handling system as described in U.S. patent application Ser. No. 13/236,262 filed on 19 Sep. 2011 (published as US  2012 -0067434 A1), U.S. patent application Ser. No. 13/407,538 filed on 28 Feb. 2012 (published as US 2012-0230772 A1), and U.S. patent application Ser. No. 13/407,577 filed on 28 Feb. 2012 (published as US 2012-0152366 A1) are incorporated herein by reference. 
         [0034]    A method of displacing an operating envelope of an offloading system is described in the following paragraphs with reference to  FIGS. 5A to 5K . 
         [0035]    At a jack-up platform  10  provided with an offloading system  400  according to the invention, the cantilever  410  of the offloading system  400  is disposed in a retracted position (see  FIG. 5A ). A marine vessel  20  approaches the jack-up platform  10  and at an appropriate safety distance from the jack-up platform  10 , the marine vessel  20  is maintained in position relative to the jack-up platform  10  by mooring or dynamic positioning (see  FIG. 5B ). 
         [0036]    The offloading system is then prepared for offloading operation. Particularly, the cantilever  410  is extended in a longitudinal (Y) direction towards the marine vessel  20  (see  FIG. 5C ). Extending the operational end of the cantilever  410  towards the marine vessel  20  moves the transfer hose handling system  430  towards the marine vessel  20 . The cantilever  410  and/or the transverse platform  420  may be suitably adjusted (respectively in the Y and X directions) to a desired position relative to the marine vessel  20  before the transfer hoses  422  are transferred or moved over to the marine vessel  20  and connected to the manifolds on the marine vessel  20  (see  FIG. 5D  and  FIG. 5E  which is a close-up view of  FIG. 5D ). 
         [0037]    The sequence of transferring or moving the transfer hoses  422  to the marine vessel  20  and connecting to the manifolds depends on the type of hose handling system provided. For illustrative purpose, a transfer hose handling system described by U.S. patent application Ser. No. 13/407,577 (published as US 2012-0152366 A1) is used here. It is to be appreciated that other types of transfer hose handling system may be suitably deployed with embodiments of the present invention. In  FIGS. 5F and 5G  which is a close-up view of  FIG. 5F , the transfer hoses  422  are supported by a transfer skid  436 . Quick Connect/Disconnect Couplers (QCDCs)  439  are provided in the transfer skid  436  to connect the transfer hoses  422  to the manifolds of the marine vessel  20 . Emergency Release Couplers (ERCs)  438  which allow quick disconnection of the transfer hoses  422  from the marine vessel  20  during emergency conditions are also provided at the transfer hoses  422 .  FIG. 5F  illustrates the transfer hoses  422  connected to the manifolds of the marine vessel  20  and the transfer skid  436  disconnected from the transfer hose handling system  430  on the jack-up platform  10  while slack ropes or wires connect the ERCs  438  of the transfer hoses  422  to the transfer hose handling system  430 . The slack ropes allow the transfer hoses  422  to be retrieved when the transfer hoses  422  are disconnected and fallen away from the marine vessel  20  during emergency release.  FIG. 5G  shows a slack rope attached to an ERC  438  of a transfer hose  422 , a transfer skid disposed  436  on the marine vessel  20 , and QCDCs  439  of the transfer hoses  422  connected to the manifolds of the marine vessel  20  to establish fluid communication between the marine vessel  20  and the jack-up platform  10 . 
         [0038]      FIG. 5H  illustrates the arrangement of the offloading system  400  when an offloading operation is taking place. During an offloading operation, the transfer hose handling system  430  supports a spreader bar  437  and slack ropes which are attached to the ERCs (not shown in  FIG. 5H ). If the ERCs  438  are disconnected and detached from the marine vessel  20 , the detached transfer hoses  422  would be supported by the transfer hose handling system  430  via the spreader bar  437  and slack ropes. 
         [0039]      FIG. 5I  is a simplified top view of  FIG. 5H  and illustrates an original operating envelope  510  or reference position of an operating envelope of the offloading system  400 . The original operating envelope  510  defines a maximum working region which the marine vessel  20  or a fluid transfer connection  502  between the marine vessel  20  and transfer hoses  422  is allowed to drift while an offloading operation can safely take place. If the marine vessel  20  or fluid transfer connection  502  moves to a position beyond the original operating envelope  510 , an emergency shutdown of the offloading operation and/or disconnection of the offloading system  400  from the marine vessel  20  would have to take place. 
         [0040]    In  FIG. 5J , it is shown that the marine vessel  20  has drifted from the original position illustrated in  FIG. 5I  to a new position relative to the jack-up platform  10  such that the marine vessel  20  or fluid transfer connection  502  is located at the edge of the working limit of the original operating envelope  510  illustrated in  FIG. 5I . 
         [0041]    In anticipation of any further drifting of the marine vessel  20  or fluid transfer connection  502  beyond the original operating envelope  510 , the original operating envelope  510  is displaced so that the drifted marine vessel  20  or displaced fluid transfer connection  502  remains located within the working limit of the new or displaced operating envelope.  FIG. 5K  illustrates a new or displaced operating envelope  520  to this purpose. Displacement of the operating envelope is achieved by moving the transverse platform  420  in the transverse (X) direction to adjust a transverse reach of the transverse platform and/or by moving the cantilever  410  in the longitudinal direction (Y) to adjust a longitudinal reach of the cantilever  410 . If the drifted marine vessel  20  or fluid transfer connection  502  remains within the new or displaced operating envelope, emergency shutdown and disconnection of the offloading system from the marine vessel may be delayed or even refrained altogether. The offloading operation may continue without disruption while the drifted marine vessel  20  may be recovered to the original or pre-drifted position. After recovery of the marine vessel  20  to the original or pre-drifted position, the displaced operating envelope  520  may be returned to the original or pre-drifted operating envelope  510  by adjusting the reach of the cantilever  410  and/or transverse platform  420  accordingly. 
         [0042]    Offshore environmental conditions can cause a marine vessel to drift from a desired position and this will result in sudden disruption to offloading operation. The disruption involves halting hydrocarbon fluid flow if the position of the drifted marine vessel exceeds the working limit of the original operating envelope. In certain instances, the ERCs of the transfer hoses are activated to disconnect the transfer hoses from the marine vessel if the position of the drifted marine vessel exceeds the allowable working limit of the operating envelope. Resuming hydrocarbon fluid flow and reconnecting transfer hoses to the marine vessel require multiple procedures which are time consuming. Accordingly, by displacing an operating envelope to a new position which will place a drifted marine vessel within limits of the new operating envelope, embodiments of the invention are advantageous in ensuring continuity of offloading operation without compromising on safety. 
         [0043]    It will be appreciated that modifications may be made to the above disclosure in certain embodiments. While the present disclosure describes a fixed body as the first body and a moving body as the second body, the present disclosure also applies to two moving bodies, e.g. two marine vessels. 
         [0044]    Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the invention. Furthermore, certain terminology has been used for the purposes of descriptive clarity, and not to limit the disclosed embodiments of the invention. The embodiments and features described above should be considered exemplary, with the invention being defined by the appended claims.