Abstract:
A riser for use in subsea operations that is parked subsea deployed as needed onto wellheads disposed proximate where the riser is parked. A base anchored into the seafloor provides a pedestal for parking the riser. The riser emits a beacon signal so it can be located when needed. When parked, the riser can be kept in a vertical orientation by a buoyancy module mounted on an upper portion of the riser. A workboat, or other vessel, attaches to the parked riser and positions it onto a designated wellhead. An extension connects the riser to platform or other vessel above the sea surface.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to production of oil and gas wells, and in particular to a device and method for deploying a riser subsea. More particularly, the present invention relates to parking a riser subsea and moving the riser to an adjacent wellhead for wellhead operations. 
     2. Description of Related Art 
     Subsea risers are tubular members extending from the sea surface to seafloor. One option when encasing a drill string during drilling a well subsea, a riser typically spans between a drilling rig to a subsea wellhead mounted on the seafloor. The riser usually remains coupled to the subsea wellhead until after the well is completed. Fluids produced from the well generally flow from the wellhead into a flow line that discharges into a manifold connected to flow lines from other wellheads. Fluids converging in the manifold are delivered to above the sea surface via a main flow line. Over time, a producing well typically undergoes maintenance or workover procedures that require a riser be reconnected to the wellhead, this is usually a smaller diameter that can act as a conduit for wellbore fluids during well testing or a conduit for tools and gauges etc during well workover operations, so that the well can be accessed from above the sea surface. During such maintenance procedures the riser can be connected to drilling rig or a surface vessel on its upper end. In either instance, the riser is redeployed from a storage site or manufacturing facility and transported to the wellhead being maintained, which is a time consuming and costly step. 
     SUMMARY OF THE INVENTION 
     Disclosed herein is an apparatus for and method of subsea operations. In an example a method of deploying a riser is disclosed that includes initially running the riser from a conventional vessel, mobile drilling rig, or other site. In an example embodiment, the riser incorporates buoyancy such it can be moved from a given location or well site to another well site or location. Also, the riser can be parked subsea for a period of time then moving and mounting the riser onto a wellhead. An upper end of the riser can then be coupled to a facility above sea surface and the wellhead can be accessed from above the sea surface through the riser. The method may optionally include providing a riser mount on the seafloor on which the riser is parked. In an alternative example, a riser section can be attached to the upper end of the riser. In another alternative embodiment, a beacon can be emitted from the parked riser so that the riser can be located subsea. Alternatively, the riser can be parked onto a subsea wellhead. An optional buoyancy module can be added on the riser for maintaining the riser in a substantially vertical orientation. The steps of moving the riser from a parking location to a wellhead can be repeated. 
     Yet further disclosed is a riser assembly that includes a riser mount set in the seafloor and spaced apart from a proximate wellbore. The riser assembly includes a riser section having a lower end selectively parked on the riser mount and selectively engagable with a subsea wellhead positioned on the wellbore. A riser extension can selectively connect between an upper end of the riser section and a vessel at sea level, so that when the riser section is engaged with the wellhead and the riser extension is connected to the riser section, the wellhead is accessible through the riser section and riser extension from the vessel. A beacon can be included on the riser section. Optionally, a buoyancy module can be provided on the riser section that has a chamber selectively containing a gas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side schematic view of an embodiment of a subsea exploration/production riser in accordance with the present disclosure. 
         FIG. 2  is a side schematic view of the riser of  FIG. 1  being moved from a parked to a deployed position. 
         FIG. 3  is a side schematic view of an example embodiment of the riser of  FIG. 2  in a deployed position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The apparatus and method of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. This subject of the present disclosure may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. For the convenience in referring to the accompanying figures, directional terms are used for reference and illustration only. For example, the directional terms such as “upper”, “lower”, “above”, “below”, and the like are being used to illustrate a relational location. 
     It is to be understood that the subject of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the subject disclosure and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the subject disclosure is therefore to be limited only by the scope of the appended claims. 
     Referring now to  FIG. 1  an example embodiment of a portion of a riser assembly  10  is shown in a side view. The riser assembly  10  is shown parked on a riser mount  12  that anchors into the sea floor  14 . In the embodiment of  FIG. 1 , the riser mount  12  is shown made up of a planar base  16  resting on the sea floor  14  and a substantially cylindrical pedestal  18  projecting upward from the base  16 . In an optional embodiment, the pedestal  18  is profiled substantially similar to a mandrel typically found on an upper end of a wellhead assembly. An anchor pin  20  is shown in dashed outline that extends into the sea floor  14  for affixing the riser mount  12  in place and providing a stable support on which the riser assembly  10  may be parked. The sea floor  14  will dictate the design of the base  16  and anchor pin  20 , and when the sea floor  14  is considered “soft”, skirts (not shown) may be added for added support that extend from the base  16  and into the sea floor  14 . In the example of  FIG. 1 , riser assembly  10  is made up primarily of a tubular assembly and is shown having a lower riser package  22  on its lower most end. Shown coaxially to and adjacent to the lower riser package  22  is an emergency disconnect package  24 . An elongated tubular riser body  26  is shown mounted on an upper end of the emergency disconnect package (EDP)  24 . Connectors may be included within the EDP  24  that secure the riser assembly  10  to the pedestal  18 . Thus in one example use of the riser assembly  10 , the riser mount  12  is set within the sea floor  14  specifically to provide a fixture on which the riser assembly  10  may be parked for a period of time before being deployed for use with wellbore operations. The riser assembly  10  can be configured so that its upper end is safely below the draft of ships and out of the way of seagoing vessels. In an example embodiment, the uppermost two or three riser joints of a typically sized riser could be removed to avoid ship traffic. In an alternate embodiment of the riser assembly  10  though, at least some of the riser assembly  10  can be above the sea surface. 
     A buoyancy module  28  is further shown provided with the riser assembly  10  on a portion of the riser body  26 . The buoyancy module  28  is for maintaining the riser assembly  10  in a substantially vertical orientation while in the parked position, and may include substances having a density lower than sea water. In the example of  FIG. 1 , a chamber  30 , shown in dashed outline, is provided within the buoyancy module  28 . Alternatively, the buoyancy module  28  may contain multiple chambers  30  or be completely or partially filled with substances such as foam or constituents having densities less than sea water. While parked, care should be taken while “tuning” the buoyancy module  28  so that the upward force exerted by the buoyancy module  28  onto the riser assembly  10  is enough to maintain the riser assembly  10  vertical, while not pulling the riser mount  12  from the sea floor  14 . So that the riser assembly  10  may be located while subsea and after having been parked for a period of time, a beacon  32  is shown that emits a signal or signals. The signals, in one example embodiment, may be a single continuous signal, or discreet signals that are used for locating the riser assembly  10 . 
     Illustrated in  FIG. 1  are wellhead assemblies  34  on the sea floor  14  and at a location proximate to the riser mount  12 . Flow lines  36  attached to the wellhead assemblies  34  and are piped along the sea floor  14  to a manifold  38 . Production fluid from wellbores  40  beneath the wellhead assemblies  34  is directed to production facilities through the flow lines  36  and manifold  38 . Initial deployment of the riser assembly  10  may be from a drilling rig or other suitable vessel. Alternatively, initial deployment may be towed out by a lesser vessel of opportunity, in sections of nominally 150 to 300 m or more (with a suitable deployment frame and buoyant supports) and fully assembled in situ with ROV support from the same vessel that is also then used to effect intervention operations, without the need for instance a derrick, or handling tower. 
     Shown in  FIG. 2 , is an example of the work boat  44  at the sea surface  46  transporting riser assembly  10 A from the riser mount  12  and towards one of the wellhead assemblies  34 . In this example, a tubular riser section or extension  48  is attached to the upper end of the riser body  26  wherein, the riser extension  48  is suspended from a line  49  depending from the workboat  44 . Optionally, the line  49  may depend from a vessel other than a workboat  44 . In an alternative, the line  49  can attach directly to the upper end of the riser body  26 . In the example of  FIG. 2 , a connection joint  50  provides connection between the riser body  26  and riser extension  48 . In one example embodiment, the connection joint  50  is a riser tensioner joint. An example of a tensioner joint is described in Fraser, Jr., et al., U.S. Pat. No. 6,017,168, which is assigned to the assignee of the present application. 
     Referring now to  FIG. 3 , the riser assembly  10 A is shown having been attached to and deployed onto a wellhead assembly  34 . The riser assembly  10 A extends upward from the wellhead assembly  34  through the sea and attaches on its upper end to a platform  52  shown above the sea surface  46 . The platform  52  can be any craft or vessel for conducting subsea operation such as a mobile drilling unit (MODU), intervention vessel, floating production facility, ship, and the like. As discussed above, the riser assembly  10  can be configured so it is a set distance beneath the sea surface and below the draft of passing ships. For such embodiments, the riser extension  48  would make up the difference in distance between the riser assembly  10  of  FIG. 1  and the riser assembly  10 A of  FIG. 3 . Also as discussed above, the distance from the upper end of the riser assembly  10  and sea surface can be roughly 100 feet, meaning the riser extension  48  can include about two to three riser joints. 
     A valve  54  is shown in a pipe extending from the wellhead assembly  34  into the flow line  36 . When accessing the wellhead  34  and wellbore  40 , the valve  54  may be closed, thereby isolating the flow line  36  and manifold  38  from wellbore operations. Also illustrated in  FIG. 3  is a charging connection  56  for selectively providing gas or other substances to within the buoyancy module  28 . In one example of use, a remotely operated vehicle (ROV)  58  is shown subsea that may be used to charge the buoyancy module  28  while it is beneath the sea surface  46 . Charging the buoyancy module  28  may be required to tension the riser assembly  10 A when it is mounted on the wellhead assembly  34 . The recharging gas can be provided with the ROV  58 , from a line (not shown) deployed from above the sea surface, or from a vessel (not shown) sent subsea with the ROV  58 . 
     After completing operations through the riser assembly  10 A between the platform  52  and wellhead assembly  34  and/or wellbore  40 , the riser assembly  10 A may be removed from the wellhead assembly  34 . The riser assembly  10 A can then be moved to another wellhead assembly or returned to the riser mount  12  as illustrated in  FIG. 2 . Upon or prior to being returned to the riser mount  12 , the tubular riser extension  48  can optionally be removed from the riser assembly  10 A. Either embodiment of the riser assembly  10 ,  10 A may be parked for an indefinite period of time for retransportation and later use. 
     While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.