Patent Publication Number: US-2018030791-A1

Title: Lifting Apparatus for Subsea Equipment

Description:
BACKGROUND 
     This section is intended to provide background information to facilitate a better understanding of the various aspects of the described embodiments. Accordingly, it should be understood that these statements are to be read in this light and not as admissions of prior art. 
     In most offshore drilling operations, a wellhead at the sea floor is positioned at the upper end of the subterranean wellbore lined with casing, a blowout preventer (BOP) stack is mounted to the wellhead, and a lower marine riser package (LMRP) is mounted to the BOP stack. The upper end of the LMRP typically includes a flex joint coupled to the lower end of a drilling riser that extends upward to a drilling vessel at the sea surface. A drill string is hung from the drilling vessel through the drilling riser, the LMRP, the BOP stack, and the wellhead into the wellbore. 
     During drilling operations, drilling fluid, or mud, is pumped from the sea surface down the drill string, and returns up the annulus around the drill string. In the event of a rapid invasion of formation fluid into the annulus, commonly known as a “kick”, the BOP stack and/or LMRP may actuate to help seal the annulus and control the fluid pressure in the wellbore. In particular, the BOP stack and LMRP include closure members, or cavities, designed to help seal the wellbore and prevent the release of high-pressure formation fluids from the wellbore. Thus, the BOP stack and LMRP function as pressure control devices. 
     The LMRP and BOP stack are large, heavy pieces of subsea equipment that often require the use of a gantry crane to be moved or lifted into position. For example, to move the LMRP or the LMRP coupled to the BOP stack within an offshore oil rig, the LMRP can be hoisted using the gantry crane on the rig. In some situations, the LMRP attaches to the gantry crane using a lift ring coupled to a load shoulder of the LMRP. The LMRP lift ring can have as few as two lift points coupled to the load shoulder of the LMRP. Typically, the lift ring is securely fastened to the load shoulder. Each lift point on the lift ring is equally spaced from the center of the LMRP to match a crane block spacing on the offshore vessel (e.g., an offshore oil rig). Thus, the lift points can have a fixed center-to-center spacing (e.g., 2500 mm, 2750 mm, 2800 mm, etc.). The crane block spacing can vary from offshore vessel to offshore vessel. This requires the lift rings to be specifically fabricated according to the crane block spacing available on the offshore vessel. It requires a long lead time and a generous amount of welding and machining to ensure the lift ring matches the crane block spacing, resulting in a costly design. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of the embodiments of the invention, reference will now be made to the accompanying drawings in which: 
         FIGS. 1 a  and 1 b    depict a schematic view of an offshore system for drilling and/or producing a wellbore, according to one or more embodiments; and 
         FIG. 2  depicts a schematic view of a crane block assembly and a subsea BOP stack assembly, according to one or more embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure provides lifting points for subsea equipment. Specifically, the disclosure provides lifting points on a lower marine riser package (LMRP) including elevator links that pivot within the LMRP to adjust to multiple crane block spacings. 
     An LMRP can include a riser flex joint, a riser adapter, a BOP (such as an annular BOP), and control units. The LMRP can serve as an additional pressure control system in conjunction with the BOP stack. The LMRP can be a large, heavy piece of subsea equipment that often requires the use of a gantry crane to be moved or lifted on an offshore vessel and, in the rare emergency situation, from the seabed using a heavy lift vessel. The LMRP can include elevator links that mount to a load bearing structure of the LMRP via a pinned connection. The elevator links can be designed to pivot and be adjusted to fit a variety of crane block spacings available on offshore vessels. The elevator links can be constrained to provide a stable lifting mechanism. Further, the elevator links can be used to lift the LMRP or the LMRP with a subsea BOP stack attached. 
       FIGS. 1 a  and  b    show an offshore drilling system  3  including an offshore vessel  5 , a subsea BOP stack assembly  10 , and a wellhead assembly  11 . The offshore vessel  5  includes a crane  7  (such as a gantry crane) that can be used to move or hoist the BOP stack assembly  10  while it is onboard the offshore vessel  5 . For example, the crane  7  may be used to move the BOP stack assembly over the moon pool of the offshore vessel  5 . The wellhead assembly  11  is formed at the upper end of a bore into the seabed  12 . The BOP stack assembly  10 , in this example, includes a lower marine riser package  15  (LMRP) and a BOP stack  16 . The LMRP  15  and the BOP stack  16  are connected in such a way that there is a continuous bore  20  from the lower end of the BOP stack  16  through to the upper end of the LMRP  15 . The lower end of the BOP stack  16  is connected to the upper end of the wellhead  11  and is sealed in place. The upper part of the LMRP  15  can connect to the end of a riser pipe  22 , which connects the BOP assembly  10  to the offshore vessel  5  shown in  FIG. 1   a.    
     Within the bore  20 , a tubular string  23  is provided. Such a string may incorporate a number of different types of components, including simple piping, joint members, bore guidance equipment and may have attached at its lower end, a test tool, a drill bit or a simple device which allows the circulation or the flow of desired fluids through the well. Alternatively, the string  23  may take the form of casing, tubing, coiled tubing, wire line or cables, or other components which is necessary to pass through the BOP stack assembly  10  into the wellhead  11 . 
       FIG. 2  shows the crane  7  and the BOP stack assembly  10 , in accordance with one or more embodiments. The LMRP  15  can include a lifting assembly  200  to attach the LMRP  15  to the crane  7  or any other suitable hoisting mechanism. The lifting assembly  200  includes elevator links  210  that adjustably attach to the crane  7 . As an example, the elevator link  210  can include a stem  211  coupled between a pivot loop  212  and a crane loop  213  releasably attachable to the crane  7 . Each elevator link  210  may be made of any material suitable for supporting weight, for example, each elevator link  210  can include a unitary forged body comprising a steel alloy. 
     Referring to  FIGS. 1 a    and  2 , an offshore lifting system  30  can include the crane  7  and the BOP stack assembly  10  with the lifting assembly  200 . The crane  7  can include two or more crane blocks  31 . The crane  7  can attach to the LMRP  15  using the crane blocks  31  and move the LMRP  15  within the offshore vessel  5 . In particular, the crane blocks  31  can be axially spaced from each other based on a predetermined, fixed spacing  33  (e.g., 2500 mm, 2750 mm, or 2800 mm, etc.). In one or more embodiments, the crane blocks  31  can include extension devices  35  that are configured to mate with the crane loops  213  of the lifting assembly  200  and support the weight of the BOP stack assembly  10  as it is hoisted and moved by the crane  7 . 
     The spacing between the crane loops  213  can be adjusted by pivoting the elevator links  210  on pins  214  to fit within the predetermined spacing  33  to allow the crane loops  213  to releasably couple to the crane blocks  31 . To do so, each elevator link  210  is adjustably coupled to a load bearing structure  215  at the pivot loop  212  using the pin  214  and a locking plate (not shown) received in the pin  214  to secure the pin  214  and the elevator link  210  to the load bearing structure  215 . The load bearing structure  215  can include a stab plate on the LMRP  15 . The pins  214  can include a pin, peg, bolt, or other protrusion located on the load bearing structure  215 . The pins  214  can include any suitable device configured to receive the pivot loop  212  and support at least some of the weight of the LMRP  15  on the load bearing structure  215 . Optionally, the pins  214  pass through the pivot loops  212  and into ports  216  located on the load bearing structure  215 . In one or more embodiments, the pins  214  may be integral with the load bearing structure  215 . The pins  214  allow the elevator links  210  to pivot on the pivot loops  214  in the directions indicated by the arrows  220  to match the predetermined spacing  33  of the crane blocks  31 . 
     The lifting assembly  200  can include one or more constraining devices(s)  217  to releasably couple the elevator links  210  to each other and/or to the LMRP structure. In one or more embodiments, the constraining device  217  may include one or more clamps, fasteners, or any suitable fastening device. The constraining  217  can stabilize the connection between the crane blocks  31  and the lifting assembly  200 . In one or more embodiments, the constraining device  217  can create a fixed connection between the crane  7  and the lifting assembly  200  by preventing the elevator links  210  from pivoting on the pins  214 . The elevator links  210  can be positioned to have a spacing from the crane loops  213  within the predetermined spacing  33  of the crane blocks  31 . 
     With the elevator links  210  properly adjusted and secured, the crane blocks  31  can be releasably coupled to the elevator links  210 . Once attached to the crane blocks  31 , the LMRP  15  can be moved, raised, lowered, or positioned within the offshore vessel  5  using the crane  7 . 
     The lifting assembly  200  can have a load capacity sufficient to lift the load of the LMRP  15 , the load of the BOP stack assembly  10 , or the load of the LMRP  15  mounted to one or more devices. In one or more embodiments, the lifting assembly  200  can have a load capacity of up to about 500 metric tons or more. The load bearing structure  215  can support this load at the pins  214 . The lifting assembly  200  can be used to hoist the LMRP  15 , the BOP stack assembly  10 , or any suitable arrangement of the LMRP  15  mounted to one or more devices. A subsea BOP stack such as the BOP stack  16  can be engageable with the load bearing structure  215  such that the LMRP  15  supports the BOP stack  16  while the LMRP is hoisted by the crane  7  of  FIG. 1   
     This discussion is directed to various embodiments of the invention. The drawing figures are not necessarily to scale. Certain features of the embodiments may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. It is to be fully recognized that the different teachings of the embodiments discussed may be employed separately or in any suitable combination to produce desired results. In addition, one skilled in the art will understand that the description has broad application, and 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. 
     Certain terms are used throughout the 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, unless specifically stated. In the 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. In addition, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. The use of “top,” “bottom,” “above,” “below,” and variations of these terms is made for convenience, but does not require any particular orientation of the components. 
     Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present disclosure. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. 
     Although the present invention has been described with respect to specific details, it is not intended that such details should be regarded as limitations on the scope of the invention, except to the extent that they are included in the accompanying claims.