Abstract:
The present disclosure is directed to a method and system of laying pipe using a sacrificial pipe string to extend the length of an A&amp;R winch wire. In one aspect, present disclosure is directed to a method of positioning a flowpipe on a sea floor from a vessel. The method includes lowering a first end of a flowpipe from the vessel. Additionally, the method includes connecting a pipeline end termination to a second end of the flowpipe. Also, the method includes connecting a first end of a sacrificial pipe to the pipeline end termination. In addition, the method includes connecting a winch wire to a second end of the sacrificial pipe. Furthermore, the method includes lowering the sacrificial pipe with the winch wire so that the pipeline end termination rests on the sea floor. Additionally, the method includes disconnecting the sacrificial pipe from the pipeline end termination.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of priority of U.S. Provisional Application No. 61/286,167 Filed Dec. 14, 2009 entitled “Method of Using Sacrificial Pipe String,” the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This application relates to a method of laying pipe in a deep drilling field. 
       BACKGROUND 
       [0003]    It is well known to lay pipe on a sea floor for conveying oil, gas, and the like between two sites, such as a production well and adjacent production platform. Typically, a pipelaying vessel is used to discharge the pipe from a pipe storage drum on the vessel down into the sea while the vessel advances on the sea surface. Typical pipe frequently adopts the shape of a catenary between the pipelaying vessel and the sea floor. The pipe may be a flexible pipe or, alternatively, it may be a rigid (metal-walled) pipe, which requires to be passed through a straightener on the vessel after it has been drawn off the pipe storage drum. This removes the plastic deformation that it may have undergone when it was initially wound onto the drum. 
         [0004]    During pipelaying operations, it is necessary to complete the laying of each pipe length by lowering onto the sea floor the surface end (i.e. the second end) of the pipe that is being laid. To lay the pipe, an abandonment and recovery (A&amp;R) winch has conventionally been used. The winch line, which may take the form of wire, cable, or synthetic rope, is attached to an end portion of the pipe and the winch is operated to lower and lift the pipe, as required. 
         [0005]    However, in some circumstances, such as when laying pipe in a very deep field, the winch line on the A&amp;R winch may be too short to reach the sea floor. Regulations prohibit splicing the winch line to make it longer, and because the winch lines are expensive, it may be cost prohibitive to outfit each vessel with an extra long winch line that might be seldom used. In addition, because the winch lines have such large diameters to provide sufficient strength, they require large storage drums. Since space on a vessel can be limited, storage space for larger drums also may be limited. 
         [0006]    The subject matter of the present disclosure overcomes one or more of the shortcomings of the prior art. 
       SUMMARY 
       [0007]    The present disclosure is directed to a method and system of laying pipe using a sacrificial pipe string to extend the length of an A&amp;R winch wire. In one aspect, present disclosure is directed to a method of positioning a flowpipe on a sea floor from a vessel. The method includes lowering a first end of a flowpipe from the vessel. Additionally, the method includes connecting a pipeline end termination to a second end of the flowpipe. Also, the method includes connecting a first end of a sacrificial pipe to the pipeline end termination. In addition, the method includes connecting a winch wire to a second end of the sacrificial pipe. Furthermore, the method includes lowering the sacrificial pipe with the winch wire so that the pipeline end termination rests on the sea floor. Additionally, the method includes disconnecting the sacrificial pipe from the pipeline end termination. 
         [0008]    In another aspect, the present disclosure is directed to a method of positioning a flowpipe on a sea floor from a floating vessel. The method includes determining that a depth to the sea floor is inaccessible via a winch wire. Also, the method includes lowering a first end of a flowpipe from the vessel. Additionally, the method includes connecting a pipeline end termination to a second end of the flowpipe. Furthermore, the method includes connecting a first end of a sacrificial pipe to the pipeline end termination. In addition, the method includes connecting a winch wire to a second end of the sacrificial pipe. Additionally, the method includes lowering the sacrificial pipe with the winch wire until the pipeline end termination rests on the sea floor. Also, the method includes disconnecting the sacrificial pipe from the pipeline end termination. 
         [0009]    A further method for positioning a flowpipe on a sea floor from a floating vessel is disclosed. The method includes determining that the sea floor is inaccessible via a winch wire. Additionally, the method includes creating a perceived length of the winch wire different than the actual length so that the sea floor is accessible via the perceived length of the winch wire. The creating the perceived length of the winch wire includes connecting a sacrificial pipe to the winch wire, so that the perceived length of the winch wire is increased by the sacrificial pipe&#39;s length. Also, the method includes positioning the flowpipe on the sea floor at the depth using the perceived length of the winch wire. 
         [0010]    A system for laying flowpipe on a sea floor from a floating vessel is disclosed. The system includes a sea-going vessel comprising a winch. The winch having a winch wire having a winch wire length. The winch wire length being less than a distance from the sea-going vessel to the sea floor. Also, the system includes a flowpipe segment disposed on the sea floor. Additionally, the system includes a PLET disposed at an end of the flowpipe at a depth greater than the winch wire length. Furthermore, the system includes a sacrificial pipe having a pipe length. The sacrificial pipe being connected to and disposed between the PLET and the winch wire. The winch wire and the sacrificial pipe lengths together exceeding the distance from the vessel to the sea floor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. 
           [0012]      FIG. 1  shows an exemplary system for laying pipe on a sea floor. 
           [0013]      FIG. 2  is a flow chart detailing a method using the exemplary system of  FIG. 1  for laying pipe on a sea floor. 
           [0014]      FIG. 3  is an illustration of a vessel lay system for use on a vessel with a sacrificial pipe, a PLET, and a flowpipe from the exemplary system of  FIG. 1 . 
           [0015]      FIG. 4  is an illustration of the sacrificial pipe, PLET, and flowpipe being fed off the vessel from the exemplary system of  FIG. 1 . 
           [0016]      FIG. 5  is an illustration of the sacrificial pipe connected between a winch wire and the PLET from the exemplary system of  FIG. 1 . 
           [0017]      FIG. 6  is an illustration of the PLET and a section of the sacrificial pipe showing an interface used as a disconnection point between the PLET and the sacrificial pipe from the exemplary system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
         [0019]      FIG. 1  shows an exemplary system  100  for laying pipe on a sea floor. In the example shown, system  100  includes a vessel  102 , a lay system  104 , an abandonment and recovery (A&amp;R) winch wire  106 , a sacrificial pipe  108 , a pipeline end termination  110  (PLET), a flowpipe  112 , and a remote operated vehicle (ROV)  114 . As will be described in greater detail below, the system  100  and the accompanying method described herein enable pipelayers to lay a flowpipe along a sea floor at depths that exceed the length of an abandonment and recovery (A&amp;R) winch wire. 
         [0020]    In addition, system  100  and the accompanying method described herein may be useful when the straight line length of the wire exceeds the sea depth, but other factors such as the cantenary shape of the A&amp;R winch wire  106  and/or the layback distance of vessel  102  relative to the PLET  110  affect the wire&#39;s ability to reach the sea floor. Therefore, any discussion herein of the length of A&amp;R winch wire  106  not being long enough to reach the sea floor and/or the length of A&amp;R winch wire  106  being shorter than the depth to the sea floor are meant to include circumstances when the A&amp;R winch wire  106  does not reach the sea floor due to factors such as the cantenary shaper of A&amp;R winch wire  106 , layback distance of vessel  102 , and/or other similar factors. 
         [0021]      FIG. 2  illustrates an exemplary method  200  using system  100  for extending the perceived length of the A&amp;R winch wire  106  using sacrificial pipe  108 . As used herein, the term “perceived length” of the A&amp;R winch wire  106  corresponds to the actual length of the A&amp;R winch wire  106  combined with the actual length of sacrificial pipe  108  used to reach the sea floor. Also, as used herein, sacrificial pipe is the length of pipe used only to increase the perceived length of the winch wire, and is not used for transportation of obtained oil, gas, or the like. The method may be particularly advantageous when a pipelayer determines that the sea floor is in water deeper than the actual length of the A&amp;R winch wire  106 . In other words, the method&#39;s advantages arise when the sea floor is inaccessible via the A&amp;R winch wire  106 . 
         [0022]    As shown in  FIG. 1 , A&amp;R winch wire  106  has a length extending from a proximal end  116  to a distal end  118  of A&amp;R winch wire  106 . For purposes of this explanation, the winch wire  106  is shorter than the depth D 1  of the water. The distance between the water depth D 1  and the length of the A&amp;R winch wire  106 , taking into account any catenary shape of sacrificial pipe  108  and/or A&amp;R winch wire  106  between the vessel  102  and the sea floor may be used to determine the length of sacrificial pipe  108  necessary to lengthen the perceived length of A&amp;R winch wire  106 . As discussed above, the perceived length of A&amp;R winch wire  106  corresponds to the actual length of the A&amp;R winch wire  106  combined with the actual length of sacrificial pipe  108  used to reach the sea floor. Therefore, combining the sacrificial pipe  108  with the A&amp;R winch  106  alters the perceived length of A&amp;R winch wire  106  so that the system  100  can lay flowpipe  112  along the sea floor at depth D 1 , where the depth D 1  exceeds the actual length of A&amp;R winch wire  106 . 
         [0023]    Referencing  FIG. 2 , method  200  begins at a step  202  by initiating discharge of the flowpipe  112  in a conventional manner using PLET  110  from vessel  102 . In one example, vessel  102 , is a Seven Oceans vessel provided by Subsea 7. The flowpipe  112  may be a flexible pipe or, alternatively, it may be a rigid (metal-walled) pipe or other type of conventional pipe. In one example, flowpipe  112  is a rigid pipe such as a straight carbon steel pipe. In other examples, flowpipe  112  is a flexible pipe composed of intermeshing materials that enable flexibility. It should be noted that the various types of flowpipes and/or sacrificial pipes described herein are for exemplary purposes only and are not to be construed as limiting the present disclosure to a specific type of flowpipe and/or sacrificial pipe. 
         [0024]    At a step  204 , flowpipe  112  that is rolled on the vessel&#39;s main reel is spooled off the vessel  102 . At a step  206 , once the complete flowpipe  112  has been spooled off the reel, the pipe is cut and PLET  110  is installed on the end of flowpipe  112 . This may be accomplished by welding the PLET  110  to the flowpipe  112  while the PLET  110  is in the workstation of a lay system, such as lay system  104  on the vessel  102 . At a step  208 , instead of attaching the A&amp;R winch line  106  to the PLET yoke, sacrificial pipe  108  is attached the PLET yoke. This step is described in greater detail with reference to  FIG. 3 . 
         [0025]      FIG. 3  shows vessel  102  with lay system  104  disposed thereon. For example, lay system  104  can be a vertical lay system, a reel lay system, or any other type of lay system. Here, the lay system  104  is feeding out flowpipe  112  off the vessel  102 . Attached to a distal end  120  of the flowpipe  112  and still in the lay system  104 , rests the PLET  110 . At a proximal end  122  of the yoke of the PLET, the sacrificial pipe  108  has been secured to support the PLET  110 . In some instances, the sacrificial pipe  108  is the same dimension as the flowpipe  112 , and in some cases, may be identical in structure to the flowpipe  112 . For example, in some cases, the sacrificial pipe  108  may be from the same roll or spool as the flowpipe  112 . 
         [0026]    At a step  210 , once the sacrificial pipe  108  has been attached to the PLET  110 , the sacrificial pipe  108  is paid out over the stern of the vessel  102 . This is shown in  FIG. 4 , where the flowpipe  112 , the PLET  110 , and the sacrificial pipe  108  are being lowered from the vessel  102  toward the sea floor. Moreover, it is contemplated that the flowpipe  112 , the PLET  110 , and the sacrificial pipe  108  can be lowered from the stern of the vessel (as shown in  FIG. 4 ), the moon pool of the vessel, the side of the vessel, the bow of the vessel, and at any other location from the vessel. 
         [0027]    It should be noted that the catenary shape that sacrificial pipe  108  assumes when placed into the water is taken into account in determining the necessary length of sacrificial pipe needed in order to reach the sea floor. In that regard, for example, factors such as the maximum bend radius, stress and/or strain tolerances, and the shape of sacrificial pipe  108  are considered in determining the necessary length of sacrificial pipe  108  needed in order to reach the sea floor. 
         [0028]    At a step  212 , once the distal end  118  of the sacrificial pipe  108  reaches the workstation on the stern of the vessel  102 , the sacrificial pipe is cut and an A&amp;R head  124  (see  FIG. 5 ) is installed onto the distal end of the sacrificial pipe, such as by welding and in turn, the A&amp;R head  124  is connected to the A&amp;R winch wire  106 . 
         [0029]    At a step  214 , the A&amp;R winch lowers the flowpipe  112 , PLET  110 , and sacrificial pipe  108  to the sea floor. This is shown in  FIGS. 1 and 5 , with the flowpipe  112  and PLET  110  in place on the sea floor. The sacrificial pipe  108  extends between the PLET  110  and the A&amp;R winch wire  106  so that together, the sacrificial pipe  108  and winch wire  106  reach to the sea floor. In other words, combining the sacrificial pipe  108  with the A&amp;R winch  106  alters the perceived length of A&amp;R winch wire  106  so that the system can lay flowpipe  112  along the sea floor at depths exceeding the actual length of A&amp;R winch wire  106 . 
         [0030]    Moreover, as shown in  FIG. 1 , vessel  102  may be moved (i.e. positioned) relative to the installed PLET  110  located on the sea floor. In other words, vessel  102  may be positioned at a layback distance L that represents an optimal position of vessel  102  relative to the point along the sea floor at which PLET  110  is installed. The layback distance L ensures that any strain and/or stress placed on sacrificial pipe  108  is minimized as the pipe assumes a catenary shape. Minimizing strains and/or stresses on sacrificial pipe  108  helps the sacrificial pipe  108  and the A&amp;R winch wire  106  to properly position the PLET  100  and flowpipe  112  at the correct position along the sea floor. 
         [0031]    At a step  216 , once the flowpipe  112  is verified as installed in the correct position, the sacrificial pipe  108  is disconnected from the PLET  110  sub-sea by a remotely operated vehicle (ROV)  114 . The ROV  114  is shown in  FIG. 5  and is configured to disconnect the sacrificial pipe  108  from the PLET  110 .  FIG. 6  identifies an interface  126  at which the sacrificial pipe  108  is disconnected from the PLET  110 . 
         [0032]    In some examples, the sacrificial pipe  108  is removed without PLET layback. More particularly, vessel  102  may be positioned relative to PLET  110  so that the layback distance L is minimized. By removing the layback distance L, the stern of vessel  102  is aligned over PLET  110  which allows for a recovery of the sacrificial pipe  108  along a straight path. For example, the straight path may represent a path involving the shortest distance between vessel  102  and the PLET  110  along the sea floor. The use of a straight path reduces the likelihood of sacrificial pipe  108  swinging within the water depths when the ROV  114  disconnects the sacrificial pipe  108  from the PLET  110 . After proper positioning of vessel  102 , at a step  218 , the sacrificial pipe  108  is then recovered to the surface by the A&amp;R winch wire  106  and back onto the vessel&#39;s main reel for disposal. 
         [0033]    The foregoing has outlined features of several embodiments. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.