Abstract:
A protector for protecting the internal bore of a pipeline bend from a line being pulled through the pipeline bend during servicing operations including a first liner section which will travel along the pipeline to the pipeline bend bend but which will not pass through the pipeline bend, a one or more of second liner sections which will pass through the bend but are connected to the first liner section, releaseably connecting the liner sections to a service pig, pulling the liner sections into the pipeline with the service pig until the first liner section encounters the bend and stops, continuing travel with the service pig and releasing the service pig from the liner sections, and constraining a line connected to the service pig to be positioned within the liner sections rather than contacting the pipeline bend.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to the method of protecting a bend in a pipeline from abrasion and galling due to the drag friction of a tubing string or wireline which is pulled through the pipeline bend. 
       BACKGROUND OF THE INVENTION 
       [0002]    A majority of offshore oil and gas is produced form platforms which are erected on the seafloor and extend to above the water surface. Oil and gas is typically transported to and from these offshore platforms along pipelines laid on the seafloor. When these pipelines arrive to or depart from one of these platforms, a bend is used at the intersection of the seafloor and the platform and a vertical section of pipe or riser extends up to the platform deck. At the platform deck will be valves and piping to communicate the pipeline with equipment and/or wells on the deck of the platform. 
         [0003]    Subsea pipelines which transport oil tend to have the waxy components of the oil come out of solution and bond to the wall of the pipeline, up to in some cases completely blocking the pipelines. In consistence, the waxy blockage appears to be exactly like black shoe polish. In most cases, a layering on the walls of the pipeline is seen and a cleaning pig passes through the pipeline to remove the waxy layering. In some cases instead of simply cleaning the layer of wax off the pipeline wall, it chips it off until it accumulates into a blockage. 
         [0004]    When subsea pipelines which transport gas encounter the proper pressure/temperature combination and there is some water in the pipeline, a hydrate is formed. The hydrate looks a lot like crushed ice and will form quickly to create a blockage to stop the flow in the pipeline. 
         [0005]    In either of these cases the flow of production is stopped and causes an expensive loss of production. In the case of a hydrate blockage, the operator can simply wait a few days, weeks, or months and the hydrate will melt naturally if pressure is bled off from one end or the other of the pipeline. In the case of the waxy or paraffin blockage, it is permanent until fixed. 
         [0006]    As “fixing” these problems typically required mechanical drilling of the blockage, hot oil injection, or chemical dissolving of the blockage, communication to the blockage in the pipeline must be established. The characteristic way to establish this communication is by inserting a string of coiled tubing. A hose would work as well, but the strings of coiled tubing for up to 5 miles in length exist in the market. The hoses do not exist in the market at this length, and would be very expensive in comparison if they did. 
         [0007]    Crawford U.S. Pat. No. 6,651,744 shows a coiled tubing string with a thruster pig (10) attached to the end for this purpose and illustrates in FIG. 12 the coiled tubing reel (150), and various other pieces of required equipment. Of note is a 5D bend section (15) which is at the intersection of the seafloor pipeline and the vertical riser. “5D” means that the bend radius of the centerline of that pipe section is 5 times the outer diameter of the pipeline. Sending equipment down the vertical pipe section around the 5D bend and then going out up to 5 miles is a very difficult goal to achieve, and is a common requirement of many offshore pipelines. If you imagine that in a 4.5 inch outer diameter pipeline this bend radius is 22.5 inches, then the steel coiled tubing must negotiate this bend. 
         [0008]    The first problem in navigating this bend is that bending 1 to 1¾ inch outside diameter coiled tubing to a radius of 22.5 inches substantially bends and unbends the coiled tubing as it passes, both going and coming back which has a deteriorating effect on the coiled tubing. Secondly, the high loading on the inside of the pipeline bend and the outside diameter of the coiled tubing when it is being plastically bent tends to cause galling on both pipes, which destroys the integrity of whichever one(s) is galled. Thirdly, the force of pulling the coiled tubing back through the bend from its extended travel position is added to the force of pulling the coiled tubing back, pulling the pig back, and swabbing the fluid behind the coiled tubing back. At some point, you simply cannot pull the coiled tubing back and have caused a worse problem than the blockage itself. 
         [0009]    When any or all of these factors is a concern, the only solution is to pick the pipeline up off the seafloor, saw it in half, and attach expensive connectors to the pipeline. This allows the operator to go directly into the end of the pipeline without having to pass a difficult bend. A complication to this is that before the operator can saw the pipeline in half, the pressure must be completely removed from the pipeline. Additionally, as you are sawing into a pipeline with at the least gas fumes in it, you may cause a spark. 
         [0010]    An additional problems when going around the pipeline bends is that any equipment to pass the bend must be by definition very short or it simply will not pass and the bending of the coiled tubing tends to import moment loading on the equipment, such as the thruster pig at the end of the coiled tubing. 
         [0011]    Offshore platforms with vertical riser pipes have been utilized in the offshore industry as long as it has existed, since the mid 1950&#39;s. Coiled tubing became available as an oilfield service tool in the mid 1960&#39;s and the marriage of these two systems happened shortly thereafter. The industry is still dealing with the problem of how to reasonably get the coiled tubing around the bends, and the most common answer today is to expensively pick the pipeline up and avoid the problem. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    The object of this invention is to provide a method of installing a protective liner in the bend between a subsea pipeline and a vertical pipe riser at a platform. 
         [0013]    A second object of this invention is to provide a method of protecting a thruster pig from the side forces resulting from the bend in the coiled tubing after going through the bend between a subsea pipeline and a vertical pipe riser at a platform. 
         [0014]    A third objective of this invention is protect the sealing cup of a thruster pig from being heavily worn on one side due to the weight of the thruster pig. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a partial half section of a subsea pipeline and the vertical riser which would be near an offshore platform, with service equipment to facilitate this method landed on the top of the vertical riser. 
           [0016]      FIG. 2  is the partial half section of  FIG. 1  with the work window opened and a thruster pig assembly being inserted into the bore. 
           [0017]      FIG. 3  is the partial half section of  FIG. 2  with the thruster pig assembly fully inserted into the bore. 
           [0018]      FIG. 4  is the partial half section of  FIG. 3  with the end of the coiled tubing string engaging the thruster pig assembly and a bend liner being connected to the thruster pig assembly. 
           [0019]      FIG. 5  is the partial half section of  FIG. 4  having the thruster pig assembly run down into the bend at the base of the vertical riser. 
           [0020]      FIG. 6  is the partial half section of  FIG. 5  with the thruster pig assembly out of the bend and into the pipeline, and the bend liner in the bend. 
           [0021]      FIG. 7  is the partial half section of  FIG. 6  with the thruster pig assembly released from the bend liner and running out into the pipeline. The bend liner is protecting the bend from damage by the coiled tubing passing through. 
           [0022]      FIG. 8  is a half section of a bend liner in the curved shape which it would have when it is in the bend. 
           [0023]      FIG. 9  is a section of the bend liner of  FIG. 8  taken along lines “ 9 - 9 ”. 
           [0024]      FIG. 10  is a section of the bend liner of  FIG. 8  taken along lines “ 10 - 10 ”. 
           [0025]      FIG. 11  is a half section of one of the sections of the bend liner with rollers substituted for the low friction material to make it better suited to accommodate a wire rope. 
           [0026]      FIG. 12  is half section of a thruster pig assembly which is similar to the thruster pig assembly first shown in  FIG. 2 , but is adapted to be in the central portion of the coiled tubing string rather than at the end and is adapted to assist in pulling the coiled tubing back rather than pulling it out to the blockage site. 
           [0027]      FIG. 13  is an enlargement of the central portion of  FIG. 12 . 
           [0028]      FIG. 14  is the thruster pig assembly of  FIG. 12 , but being shown passing through a pipeline bend. 
           [0029]      FIG. 15  is an enlargement of the central portion of  FIG. 14 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    Referring now to  FIG. 1 , a half section view of a complete system  10  on the side of an offshore platform (not shown) which is prepared for the method of this invention. Seafloor pipeline  12  has a blockage  14  at some distance from the bend  16  at the base of a vertical riser  18 . Vertical riser  18  has a top flange  20  with pressure control equipment  22  landed on top of it. Pressure control equipment  22  represents valves during regular production and blowout prevention equipment during service operations. Above pressure control equipment  22  is a working window  24  and service equipment  26  above that. Working window  24  is a pressure vessel with side openings to allow the insertion of tools into the well bore. Service equipment  26  comprises a variety of items which will change from location to location. These items might include a stripper for sealingly engaging the coiled tubing, slips to temporarily support the coiled tubing or to stop the coiled tubing in an emergency, a coiled tubing injector head to push or pull the coiled tubing into our out of the pipeline, etc. Coiled tubing  28  is shown entering the top if the injector head, but is not shown having gone in far enough to be seen in the control equipment  20 . 
         [0031]    Referring now to  FIG. 2 , doors  40  and  42  have been opened by releasing bolt  46  and thruster pig assembly  48  has been started to be placed into the bore  50 . Thruster pig assembly  48  comprises thruster pig  52 , ball joint  54 , and coiled tubing connector  56 . It should be noted that both thruster pig  52  and coiled tubing connector  56  include a ball joint mechanism to allow the flexibility to allow this operation thru the work window  24 . 
         [0032]    Referring now to  FIG. 3 , thruster pig assembly  48  is fully in bore  50  and is temporarily supported on bars  60 . The lower end  62  of coiled tubing  28  is being lowered to engage the coiled tubing connector  56 . 
         [0033]    Referring now to  FIG. 4 , the lower end  62  of coiled tubing  28  is engaged with coiled tubing connector  56  and the end  70  of bend protector  72  is attached to the coiled tubing connector  56 . The likely method of connection will be with a shear pin which will be discussed later. 
         [0034]    Referring now to  FIG. 5 , coiled tubing  28  is lowered until the bend protector  72  is fully within bore  50 , doors  40  and  42  are closed, bolts  46  are engaged and tightened, thruster pig assembly  48  is in the bend  16 , and the bend liner is following. 
         [0035]    Referring now to  FIG. 6 , thruster pig assembly  48  is not fully in the pipeline  12  and bend protector  72  is in the bend  16 . Sections  74  of bend protector  72  are short enough and flexible enough to pass through the bend  16 . Section  76  of bend protector  72  is long enough and is of a shape such that it will not navigate the curve of bend  16  and therefore acts as a position stop to cause the bend protector  72  to remain in bend  16  as thruster pig assembly  48  travels out into the pipeline. When thruster pig assembly  48  returns to the bend  16  it will engage the bend protector  72  and push it back up the vertical riser  18 . 
         [0036]    Referring now to  FIG. 7 , additional pressure for force applied to thruster pig assembly  48  causes it to release from the bend protector and travel further into the pipeline. As the thruster pig assembly  48  travels into the pipeline and pulls the coiled tubing behind it, the bend liner  72  protects the bend of the pipeline from wear and galling by the coiled tubing. 
         [0037]    Referring now to  FIG. 8 , a half section of the bend protector  72  as was shown in  FIG. 7  is shown in greater detail. Section  74  is shown as individual sections  74 A- 74 F. Each of these individual sections has an insert  80  of low friction material such as Teflon provided in a curve generally matching the curve of the bend  16  to slide the coiled tubing against. The coiled tubing will be engaging a surface  82  of a low friction material and the individual sections  74 A- 74 F will be engaging the bend  16  with a steel on steel contact to insure that the bend liner  72  will remain in place when the coiled tubing is travelling out, or is coming back. Similarly, section  76  is outfitted with a low friction insert  84  with surface  86  for engaging the coiled tubing. End  70  of bend protector  72  has a shear pin  88  for attaching to coiled tubing connector  56  on the end of the thruster pig assembly  48  as seen in  FIG. 4 . The shear pin  88  is conveniently in this case a hollow pin which threads into both pieces so that no loose pieces will be left in the pipeline. 
         [0038]    Referring now to  FIG. 9  which is taken from section “ 9 - 9 ” of  FIG. 8 , coiled tubing  90  is shown bent around and engaging surface  82 . Pin portions  92  and  94  act as connections and pivots between individual sections  74 C and  74 D and can be round pins welded into holes on individual section  74 C. Spring pin  96  would be inserted at each end of insert  80  to retain it in position. It can be noted that individual sections  74 C and  74 D do not contact the pipe bend  16  at the center position  98 , but rather clearance  100  allows it to contact at  102  and  104 . This angular contact amplifies the force of contact to give an ever greater difference in the forces as was discussed with respect to  FIG. 8 . The force  106 A of coiled tubing  28  around the bend of pipe happens in the plane  106 B as indicated by section line “ 8 - 8 ” passes through the centerline  106 C of pipeline bend  16 , however it is supported at contacts  102  and  104  as forces  106 D and  106 E which are each shown graphically as ½ of the force  106 A. Forces  106 F and  106 G are the normal to the surface forces associated with forces  106 D and  106 E respectively, and they are larger by the inverse of the cosine of the angle  106 H, meaning that the friction force causing normal contact force has increased assisting the bend protector in remaining in position as the coiled tubing is pulled back through the pipeline bend  16 . This angular contact can be pushed to about 45 degrees to each side which would amply the force about 41% over plain steel on steel contact. 
         [0039]    Referring now to  FIG. 10 , shear pin  88  is illustrated as an all thread brass piece with a hex  108  broached all the way through to make it easy to install, remove and to shear. This style construction means that both ends of the shear pin will be positively restrained rather than being lost in the pipeline to cause other problems. 
         [0040]    Referring now to  FIG. 11 , individual section  110  is shown with rollers  112  A-D being mounted on axles  114  A-D rather than having an insert  80  of low friction material such as Teflon. A wire rope  116  is shown being guided in the rollers  112  A-D. As a wire rope such as  116  is often a steel twisted wire, it has the potential to not only saw in to the bend  16 , but also into the insert  80  of  FIG. 8 . By having rollers, the bend liner can be adapted to handle the use of wire rope pigs such as are illustrated in U.S. Pat. No. 7,998,276. 
         [0041]    Referring now to  FIG. 12 , thruster pig assembly  120  is shown in pipeline  12 , having ball×ball socket adaptors  122 A and  122 B on each end, then ball×ball adaptors  124 A and  124 B connected, then ball socket×buff-weld adaptors  126 A and  126 B at each end for welding to coiled tubing strings. Thruster pig assembly  120  is similar to thruster pig assembly  48  seen on  FIG. 7 , except thruster pig assembly  48  was a terminal type for the end of the coiled tubing for primarily pulling out into the pipeline. The ability to use thruster pig assembly  48  for returning forces is limited by column buckling forces of the coiled tubing. Thruster pig assembly  120  is intended for the middle of a coiled tubing string for the opposite purpose of pulling the coiled tubing back rather than pulling it out. Otherwise the mechanisms of the pigs can be similar. 
         [0042]    Referring now to  FIG. 13  which is an enlargement of the center section of  FIG. 12 , thruster pig assembly  120  is shown in greater detail. Thruster pig  120  has 3 central bores at approximately 30 degrees,  130 ,  132 , and  134 . Bore  130  is only partially shown and simply communicates the flow inside the central bore  136  in either direction as indicated by arrows  138  and  140 . Bore  132  directs flow as indicated by arrows  142 A-F from the proximate end of the pig to the distal end during travel of the coiled tubing out into the pipeline. Check valve  144  has a weak spring  146  so as to block reversed flow but not to cause a significant pressure differential in the outward trip. On the trip out to the blockage located in the pipeline, it is as if this thruster pig does not exist. 
         [0043]    Bore  134  has check valve  150  with stronger spring  152  which will cause a predetermined pressure differential across thruster pig assembly  120  when flow is coming in the direction of arrows  154 A-E. This predetermined pressure differential will combine with the cross sectional sealing area within the pipeline to give a predetermined force to assist the coiled tubing in being recovered from the pipeline. Rather than long lengths of coiled tubing being drug back by pulling around a bend such as was indicated at  16 , it can be pulled by the force across one or more thruster pig assemblies  120 . The dominant force in coiled tubing will be tension without the column buckling tendency, but some limited force can also push the coiled tubing ahead of the pig. 
         [0044]    Thruster pig assembly  120  is illustrated as being welded. into the coiled tubing string but other options are available. Slip type connectors and threaded connectors are available in some cases. Specifically in the case of slip type connectors, coiled tubing can be run through the thruster pig assembly until the appropriate connection point, the slips set, and then the pig can be run with the coiled tubing. Design requirements of this type pig make it increasingly difficult to pass 5D bends, and tend to be limited to applications with larger radius bends. 
         [0045]    Sealing cups  160  comprise a metal seal carrier  162  and a resilient cup member  164 . O-ring type seal  165  seals between the metal seal carrier  162  and the pig  166 . The two sealing cups  160  have an inner spacer ring  167  with O-ring type seals  168  and  169  which allows the two sealing cups  160  to be identical and perform the additional benefit of redundant sealing. It will be noted that there is a gap inside each of the sealing cups  160  as the internal bore  170  of the sealing cups  160  is larger than the outer diameter  172  of pig body  166 . Pig guide bushings  180  and  182  are of a low friction material mount to pig body  166  and assist the thruster pig assembly to slide along the pipeline, but as they must be smaller than the internal diameter of the pipeline, they will slide eccentrically to the centerline of the pipeline. This means that if sealing cups  160  are rigidly mounted to pig body  174 , they will be pressed more tightly on one side that the other, accentuating the wear on that side and limiting the service life of the thruster pig assembly  120 . However, sealing cups  160  are mounted in such a way as to have clearances to allow the sealing cups  160  to remain concentric to the pipeline bore and give a uniform lower stress to the resilient cup members  164 . This means rather than the resilient cup members  164  having to support the weight of all the metal parts of the thruster pig assembly and handle any moments caused from the coiled tubing, they simply glide in a centralized state. 
         [0046]    Referring now to  FIG. 14 , thruster pig assembly  120  is shown going through an extreme pipe bend such as was indicated as  16  in  FIG. 1 . 
         [0047]    Referring now to  FIG. 15  which is an enlargement of the central section of  FIG. 14 , pig guide bushings  180  and  182  are shown to be close to contacting the pipeline internal diameter at  180  and  182  and various parts of pig body  174  is close to contacting the pipeline internal diameter at  184 ,  186 ,  188 , and  190 . If the sealing cups  160  were held in a centralized position they would be crushed on the inside of the bend and would not be touching the inside of the pipe internal bore on the outside of the bend. In  FIG. 15 , sealing cups  160  have been allowed to slide down and to the left in the view to not be crushed on the upper right side and to remain in sealing contact on the lower left side. The ability of sealing cups  160  to float relative to the pig body improve their performance both in straight long distance travel and in short distance travel around bends. 
         [0048]    The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art haying the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.