Abstract:
A apparatus and method of using the apparatus for removing a blockage in a subsea pipeline without retrieval of the pipeline to the surface. The apparatus components include a hot tap saddle, a drill assembly, a fluid blaster assembly and a support frame. The hot tap saddle component has a first portion and a second portion, with the first and second portions being configured to clampingly engage in a sealing relationship to the subsea pipeline. The first portion of the saddle includes a first and second opening with the first opening extending generally upwardly and configured for connecting to a drill assembly and the second opening being positioned generally at an angle to the first opening and configured for connecting to a fluid blaster assembly. The fluid blaster assembly including a nozzle, a hose and a high pressure pump with the fluid blaster assembly being contained within a pressure vessel. The fluid blaster assembly is configured for mounting to the second opening of the hot tap saddle component. The support frame assembly is configured for gripping and supporting the subsea pipeline on the sea floor while the fluid blaster assembly operates to remove a blockage in the subsea pipeline with the pipeline being under pressure and without severing the pipeline.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to subsea pipeline hot tapping operations, and more particularly relates to subsea pipeline fluid blasting operations conducted through a pipeline hot tap. 
     2. Description of the Related Art 
     Subsea crude oil pipelines are often plugged by localized accumulations of paraffin, hydrate and other deposits. A paraffin blockage is caused by the paraffin precipitating out of the crude oil and packing in the pipe. The paraffin is very waxy and can clog or plug the pipeline. Plugging of pipelines is a well known problem. Pipeline operators attempt to prevent this problem by requiring regular pigging of the pipeline or through the injection of solvents or chemicals in the pipeline to prevent paraffin build-up. 
     Nonetheless, plugging of pipelines does occur. Typically, the paraffin blockage is removed from a subsea pipeline by raising the pipeline to the surface and severing the pipeline. The pipeline can then be mechanically cleaned or the plugged section replaced. With the plug removed, the pipeline is reconnected and lowered back down to the sea floor. 
     It is desirable to have an apparatus and method of using the apparatus for removing any blockage in a subsea pipeline due to paraffin or hydrates or other materials that may percipitate from crude oil, and more generally to blockages of any sort that can be removed by fluid blasting or chemical decomposition. It is also desirable to be able to remove a plug in a subsea pipeline without retrieval of the pipeline to the surface. It is also desirable to be able to remove a plug in a subsea pipeline without severing the pipeline. It is also desirable to be able to remove the plug with the pipeline under pressure while protecting the environment from oil spills. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for removal of pipeline blockages in a subsea pipeline without retrieval of the pipeline to the surface and an apparatus that can be used to implement this method. The plug is removed underwater with either divers or a remotely operated vehicle. The method and apparatus of the present invention provides for the removal of the plug with the pipeline under pressure and includes provisions to prevent the escape of pipeline fluid, thus protecting the environment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to more fully understand the drawings referred to in the detailed description of the present invention, a brief description of each drawing is presented, in which: 
     FIG. 1 is a sectional elevational view of the hot tap fluid blaster apparatus connected to a subsea pipeline; 
     FIG. 2 is an elevational view showing the lowering of a support frame assembly to the sea floor; 
     FIG. 3 is an elevational view showing the lifting of the pipeline off of the sea floor; 
     FIG. 4 is an elevational view showing the landing of a hot tap tee; 
     FIG. 5 is an elevational view showing the hot tap tee clamped to the pipeline; 
     FIG. 6 is an elevational view showing the landing of the drill assembly; 
     FIG. 7 is an elevational view showing the landing of the fluid blaster assembly; 
     FIG. 8 is an elevational view showing the assembled hot tap fluid blaster apparatus; 
     FIG. 9 is an elevational view showing the drill assembly and the fluid blaster assembly recovered and the pipeline set on the sea floor; and 
     FIG. 10 is an elevational view showing the recovery of the support frame assembly. 
    
    
     DETAILED DESCRIPTION OF INVENTION 
     The hot tap fluid blaster apparatus, generally designated as reference  20 , will now be described with specific reference to the drawings. Referring to FIGS. 1 and 8, the hot tap fluid blaster apparatus  20  comprises a hot tap saddle or tee  22 , a drill assembly  24 , a fluid blaster assembly  26 , and a support frame assembly  28  (FIG.  8 ). 
     Referring to FIGS. 2 and 8, the support frame assembly  28  includes an upright framework  30  attached to a base  32  adapted to vertically support the upright framework  30  on the sea floor F. As shown in FIG. 2, the support frame assembly  28  may include a plurality of vertical legs  34  attached to the base  32  to provide support to the support frame assembly  28 . The support frame assembly  28  includes a lower pipe gripper  36  for gripping onto the pipeline P. The pipe gripper  36  is preferably hydraulically controlled. The support frame assembly  28  also includes a vertical guide member  38  for reasons which will be explained below. It is to be understood that the support frame assembly  28  is similar to commercially available support frame assemblies. 
     Referring to FIGS. 1 and 5, the hot tap tee  22  is a split clamp  40  and  42  having a first port  42   a  extending upwardly from the first clamp  42  which is sized and shaped for connection of the drill assembly  24  and a second port  42   b  placed at an angle from the first port  42   a  which is sized and shaped for connection of the fluid blaster  26 . Preferably, the hot tap tee  22  is adapted to be operated by a remotely operated vehicle (ROV)  15  (FIG.  3 ). The hot tap tee  22  uses a sealing system to seal the longitudinal joints of the split clamp  40  and  42 . These joints are clamped by a series of studs and nuts installed by the ROV  15 . The circumferential seal to the pipe P is accomplished by additional seals (not shown) that are pressed against the pipe P by an ROV-operated seal energizing system. All seals are permanently locked in place during the installation and no further action is required to maintain the seal. Preferably, an ROV pressure test port is provided to confirm the integrity of the seal before drilling operations are started. 
     It is to be understood that the hot tap tee  22  is similar to commercially available hot tap tees. The seals and the clamping configuration has not been changed. The one feature that has been added to the hot tap tee  22  is the second port  42   b  for connection of the fluid blaster  26 . 
     Referring to FIG. 1, the drill assembly  24  includes a drill machine  44  that is a field proven device with a long history of land and diver assisted operations. The drill machine  44 , preferably hydraulically driven, includes a combination pilot drill and shell cutter  46 . The pilot drill and shell cutter  46  has a special feature to retain and remove a coupon cut by the shell cutter  46 . Such a drill  44  is well known in the art. The drill machine  44  is sealed against pressure loss during drilling. The drill assembly  24  includes a drill conduit  54  through which the drill  44  extends. 
     Referring to FIG. 1, the drill assembly  24  is mounted to a hot tap tee shutoff valve  48  with an ROV collet connector  52  that allows quick installation and removal of the hot tap drill assembly  24 . An ROV hot stab connects the hot tap drill assembly  24  to the ROV&#39;s hydraulic system during the drilling operation. Automatic feed of the pilot drill and shell cutter  46  is accomplished by a pressure compensated gearbox  44   a  connected to the drill machine  44 . The hot tap drill and shell cutter  46  cuts a hole h into the pipeline P as will be explained below. The hole size will depend on the pipe diameter and fluid blaster hose size. The drill assembly  24  is sealed against the pressure in the pipeline P so that when the drill  46  makes the hole h in the pipeline P, the fluid or material in the pipeline P pressurizes the interior of the drill assembly  24  through the shutoff valve  48  and the drill conduit  54 . 
     Still referring to FIG. 1, an inverted cone  50  is preferably located above the shutoff valve  48  to provide guidance for the drill assembly  24  as it is lowered to the hot tap tee  22 . A collet connector  52  is preferably used to connect the drill assembly  24  to the hot tap tee  22 . The collet connector  52  includes a male portion  52   a  and a female portion  52   b  adapted to releasably mate with each other. Collet connectors are well known devices. Preferably, the male portion  52   a  is located within the inverted cone  50  and the female portion  52   b  is connected to the lower end of the drill conduit  54  of the drill assembly  24 . Although not shown, it is desirable to include an isolation valve just above the female portion  52   b  of the collet connector  52  to prevent leakage of the pipeline fluid from the drill conduit  54  and the drill assembly  24  after drilling the hole h. 
     The fluid blaster  26  is a field proven concept that has been used for many years by plumbers and sewer pipe cleaning professionals. A specialized rotary nozzle  56  on a 400 ft. long hose  58  is introduced into the pipeline to break up and clear the paraffin blockage. The hose  58  is advanced, by a motor driven hose reel  60 , into the pipeline through the hole previously drilled by the hot tap drill. Once inside the pipeline rearward facing jets (not shown) in the nozzle  56  pull the hose  58  into the pipe as the nozzle  56  advances through the pipe. When the nozzle  56  reaches the blockage, forward travel automatically stops until sufficient material has been removed to allow the nozzle  56  to advance. Tunneling through the blockage with a small bore hole is prevented because the cutting jets are nearly perpendicular to the pipe centerline. No forward jets are used. The nozzle  56  has a rotating head feature (not shown) that removes the blocking material radially out to the walls of the pipe as the nozzle  56  advances. 
     As shown in FIG. 1, the fluid blaster  26  is contained inside a pressure vessel  62  that prevents any leakage of pipeline fluid out of the system. The vessel  62  is fitted with an isolation valve  64  and an ROV operated collet connector  66 . The hot tap tee  22  includes a connector  67  and a shutoff valve  68  for quick and simple connection the fluid blaster  26 . An inverted cone  70  is preferably located above the shutoff valve  68 . The collet connector  66  includes a male portion  66   a  and a female portion  66   b  adapted to releasably mate with each other. Preferably, the male portion  66   a  is located within the inverted cone  70  and the female portion  66   b  is connected to the lower end of the vessel  62 . A high pressure pump  72 , powered by the ROV, provides pressure to the fluid blaster nozzle  56 . Filtered seawater or other fluid from outside the fluid blaster vessel is used as the primary blockage clearing fluid. An ROV operated connector  74  on the outside of the vessel  62  allows the use of externally supplied fluids, such as diesel fuel or solvents, as the clearing fluid. The hydraulically powered hose reel  60  with a level wind capability provides retrieval of the fluid blaster hose  58  and nozzle  56 . ROV readable pressure gauges and a hose length meter (not shown) provides continuous monitoring of the water blasting operation. The ROV supplies hydraulic fluid to the hose reel  60  and pump  72  via hot stab connections. 
     The operation of the inventive apparatus to remove a plug in a subsea pipeline is shown in FIGS. 2-10 and described as follows. The insertion point or location of the hot tap tee  22  is identified on the pipeline, and the support frame  28  is then lowered to the seabed by the support vessel (FIG.  2 ). The ROV guides and positions the support frame  28  as it is lowered so that the pipe gripper attaches itself to the pipeline P using an automatic latching system. Two additional lifting frames (not shown) may be landed on the pipeline P on either side of the support frame  28  to provide additional support for the pipeline P so that bending stresses at the hot tap location are reduced or eliminated (FIG.  3 ). 
     The ROV provides power to the support frame  28  and lift frames, if used, to lift the pipeline P off the sea floor (FIG.  4 ). Each frame is raised in increments sufficiently small to prevent excessive stress on the pipeline P. When the pipeline P has been raised to sufficient height above the sea floor, the ROV makes a visual inspection of the pipe surface that will be covered by the hot tap tee  22 . The ROV uses water jet cleaning or wire brushes to clean the pipe P as needed. The ROV then uses a manipulator held gauging tool to confirm that the pipe P is sufficiently round and straight to provide a leak tight seal. 
     As shown in FIG. 4, the hot tap tee  22  is guided on to the pipeline P by the dedicated support frame  28 . The support frame  28  is placed on the pipeline P before the pipeline P is lifted from the seabed. This method is used to avoid inadvertent bending loads being applied to the pipeline P during deployment. The support frame  28  may be deployed with the hot tap tee  22  attached. Depending on sea conditions and vessel capabilities during the installation, the hot tap tee  22  may be deployed separately and mated to the support frame  28  on the sea floor. Stabbing guides are provided for separate deployment. The support frame  28  and integrated hot stab tee  22  provides rigid support of the pipeline P during installation and operation of the HTFP. 
     If the hot tap tee  22  was not deployed with the support frame  28 , it can now be lowered by the support vessel and docked with the support frame  28 . With the hot tap tee  22  in place (FIG.  5 ), the ROV operates the support frame  28  to raise the pipe P into the clamping section of the hot tap tee  22 . When the pipe P contacts the hot tap tee  22 , the ROV operates a hydraulic valve to close the tee clamping section around the pipe P. The ROV then installs and tightens the longitudinal seal bolts. When this is complete, the ROV energizes the circumferential seals. The ROV then connects to the test port to pressurize the internal volume of the hot tap tee  22  to confirm a leak tight connection of the hot tap tee  22  to the pipe P. 
     With the hot tap tee  22  and support frame  28  firmly secured to the pipeline P, the drilling machine  24  is lowered by the support vessel (FIG.  6 ). The ROV guides the drilling machine  24  to the stabbing guide on the hot tap tee  22  and sets the collet connector  52 . The ROV opens the shutoff valve  48  on the hot tap tee drilling port  42   a . The ROV connects a hot stab hydraulic connection to the drilling machine  24  and drills a 3″ diameter hole in the pipeline P. 
     After the coupon has been cut, the drill motor is reversed to retract the drill and the coupon into the drilling machine body. The ROV then closes the shutoff valve  48  on the hot tap tee drilling port  42   a . The drilling machine  24  may be removed at this point. 
     The fluid blaster  26  and guide frame  27  are then lowered by the support vessel (FIG.  7 ). The guide frame  27  is secured to the hot tap tee  22  and pipeline P by the ROV. The fluid blaster  26  is then landed on the hot tap tee  22  and the ROV sets the collet connector  66 . The ROV can then open the shutoff valve  68  on the hot tap tee  22  and the isolation valve  64  on the fluid blaster  26 . The ROV docks with the fluid blaster control panel and connects a hot stab hydraulic supply (FIG.  8 ). Using the hose length meter as a guide, the ROV operates the hose reel  60  to advance the hose  58  through the 3″ hole cut by the drilling machine  24  and into the pipeline P. A metal guide protects the hose  58  from chafing against the cut edge of the hole. When the hose  58  is  2  to  3  ft. into the pipeline P, the ROV places the hose reel  60  in free spool mode and turns on the high pressure pump  74 . The fluid blaster nozzle  56  then pulls the hose  58  through the pipe P removing the paraffin blockage as it advances. The ROV monitors the operation with the hose length meter and pressure gauges. Once the blockage has been cleared or maximum hose length has been extended, the ROV turns off the high pressure pump  74  and powers the hose reel  66  to retract the hose  58 . When the hose length meter indicates that the hose  58  is fully retracted, the ROV closes the hot tap tee shutoff valve  68 . The pipeline P can now be pigged to confirm that the blockage has been cleared. 
     On completion of operations, the ROV closes the fluid blaster isolation valve  64  and releases the collet connectors  66  and  52  respectively on the fluid blaster  26  and hot tap drill  24  (FIG.  9 ). The drilling machine  24  and fluid blaster  26  are recovered to the surface by the support vessel (FIG.  10 ). Special collet connectors with blind flanges are lowered by the support vessel and installed by the ROV on the hot tap tee shutoff valves. After a visual inspection, the ROV can then pull the release pins to disconnect the hot tap tee  22  from the support frame  28 . The ROV then operates the lifting mechanism on the support frames  28  to lower the pipeline P to the seabed. Once the pipeline P is resting securely on the seabed, the ROV can pull two release pins on each pipe gripper  36  to release the support and lifting frames  28  from the pipeline. The support and lifting frames can now be recovered to the support vessel. The pipeline P is now ready for normal service. 
     It is to be understood that all of the components of the hot tap fluid blaster apparatus  20  may be operated by divers or a remotely operated vehicle (ROV)  15  and suitable for use at any water depths. The modular components of the hot tap fluid blaster apparatus  20  can be deployed from a diver support vessel. Individual components of the hot tap fluid blaster apparatus  20  are retrievable for contingency intervention. The hot tap fluid blaster apparatus  20  incorporates sealed housings to contain pipeline fluids during the tapping and blockage clearing operations. Shutoff valves and isolation valves provide minimal fluid loss during disconnection. At the conclusion of the blockage clearing operations, the tools are recovered to the surface leaving substantially only the clamp-on hot tap tee  22  on the pipeline P. The hot tap tee  22  is fitted with two ROV operated shutoff valves and each valve has a blind flange installed on the outlet. The pipeline P is returned to normal operation with the hot tap tee  22  sealing the pipeline P at the intervention point. Normal pigging operations can be used with the hot tap tee  22  in place. Life expectancy for the hot tap tee seals can reasonably be expected to exceed 20 years. 
     The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the details of the illustrated apparatus and construction and method of operation may be made without departing from the spirit of the invention.