Patent Publication Number: US-9416625-B2

Title: System and method for subsea structure obstruction remediation using an exothermic chemical reaction

Description:
RELATION TO PRIORITY 
     This application claims the benefit of Provisional Application 61/817,245 for “Hydrate Remediation Using Exothermic Chemical Reaction,” filed Apr. 29, 2013. 
    
    
     FIELD OF THE INVENTION 
     The following inventions generally relate to methods and apparatuses which can be used to remove a plug that is present within a subsea structure such as a production system pipeline, riser, subsea well equipment, or the like. These plugs are generally solid gas hydrates or paraffinic in nature and are generally formed by operating the production system at temperature and pressure levels conducive to formation of solid wax or hydrate crystals within the produced fluid stream. The solid crystals agglomerate within the structure, eventually blocking, or significantly curtailing, the production flow from the subsea well, resulting in loss of revenue from the subsea production facility. 
     In addition, hydrate masses may form around subsea well equipment due to gas sublimation from shallow sub-surface methane hydrate deposits that are locally heated by the well in production. This free gas is trapped and re-forms into solid hydrate masses within the external confines of the subsea equipment packages, blocking service access to the equipment, and interfering with mechanical operation of critical external moving parts. 
     In general, a solid hydrate or paraffin plug can be removed by adding enough heat to the plug to change the physical state of the plug material into a transportable fluid, e.g. a liquid or a gas. 
    
    
     
       FIGURES 
       The figures supplied herein disclose various embodiments of the claimed invention. 
         FIG. 1  is a view of an exemplary system in partial perspective of various alternative embodiments; 
         FIG. 2  is a view of an exemplary system in partial perspective and various alternative embodiments; 
         FIG. 3  is a view of an exemplary system in partial perspective and various alternative embodiments; 
         FIGS. 4-11  are schematic views of an exemplary system and various alternative embodiments; 
         FIG. 12  is a view in partial perspective of a subsea environment; 
         FIG. 13  is a view in partial perspective of a subsea environment showing reservoirs being lowered into that environment; and 
         FIG. 14  is a view in partial perspective of a subsea environment showing fluids from the reservoirs being introduced into that environment via a skid. 
     
    
    
     DESCRIPTION OF VARIOUS EMBODIMENTS 
     In all of these methods and apparatuses, subsea structures  200 , 201  may comprise production piping, a structure such as a subsea piece of equipment, or the like; the obstruction may comprise an internal plug or external mass comprising a hydrate or paraffin or the like or a combination thereof; and the two chemical reactants typically comprise ammonium chloride NH 4 Cl and sodium nitrite NaNO 2 . By way of example and not limitation, other chemicals that can be used include hydrochloric acid (HCl) and ammonium hydroxide (NH 4 OH); hydrochloric acid (HCl) and sodium hydroxide (NaOH); hydrogen peroxide (H 2 O 2 ) and a solution containing metal ions; and the like; or a combination thereof. 
     Referring generally to  FIG. 1 , in an embodiment system  1  for providing a hot fluid to subsea structures  200  and/or  201  comprises a plurality of reservoirs  12 , located subsea, adapted to contain chemical reactants; reaction chamber  22 ; a corresponding plurality of chemical reactant fluid conduits  14  providing fluid pathways between a corresponding one of the plurality of reservoirs  12  and reaction chamber  22 ; insulated chamber  32  adapted to surround an area of a subsea structure  200  containing obstruction  4 ; and one or more hot fluid conduits  24  in fluid communication with reaction chamber  22  and insulated chamber  32 , these hot fluid conduits  24  comprising one or more internal baffles designed to blend the chemical reactants. Additional hot fluid conduits  40  may provide a further fluid pathway between hot fluid conduits  24  and insulated chamber  32 . 
     Insulated chamber  32  may comprise a selectively releasable insulated chamber adapted to selectively disengage from subsea structure  200 , such as skid  37  or clampable structure. 
     In a further embodiment, referring generally to  FIG. 2 , system  1  for providing a hot fluid subsea comprises a plurality of reservoirs  12 , located on or at vessel  100 , adapted to contain chemical reactants; reaction chamber  22 ; a corresponding plurality of chemical reactant fluid conduits  14  providing fluid pathways between a corresponding one of the plurality of reservoirs  12  and reaction chamber  32 ; one or more heater tubes  33  pre-installed and wrapped around an area of subsea structures  200  or  201  containing obstruction  4 ; and one or more hot fluid conduits  24  in fluid communication with reaction chamber  32  and heater tubes  33 . Hot fluid conduits  24  comprise one or more internal baffles designed to blend the chemical reactants as they are in and pass through hot fluid conduits  24 . Additional hot fluid conduits  40  may provide a further fluid pathway between hot fluid conduits  24  and insulated chamber  32 . 
     Referring to either  FIG. 1  or  FIG. 2 , in a further embodiment, system  1  comprises a plurality of reservoirs  12  adapted to contain chemical reactants; reaction chamber  22 ; a corresponding plurality of chemical reactant fluid conduits  14  providing fluid pathways between a corresponding one of the plurality of reservoirs  12  and reaction chamber  22 ; and one or more hot fluid delivery conduits  24 , comprising one or more internal baffles adapted to blend the chemical reactants, in fluid communication with reaction chamber  22 . Reservoirs  12  may be located subsea  300 , on or at vessel  100 , or a combination thereof. 
     In these embodiments, additional hot fluid delivery conduits  41  are adapted to be manipulated by and connectable to remotely operated vehicle (ROV)  120 . ROV  120  may be controlled by ROV cage  110  such as via umbilical  121 . 
     Referring now generally to  FIG. 3 , in a further embodiment, system  2  for providing a hot fluid subsea comprises a plurality of reservoirs  12  adapted to contain chemical reactants; one or more manifolds  60  disposed downstream from the plurality of reservoirs  12 ; a corresponding plurality of chemical reactant fluid conduits  14  providing fluid pathways between a corresponding one of the plurality of reservoirs  12  and manifold  60 ; baffled mixing conduit  24  in fluid communication with and located downstream from manifold  60 , where baffled mixing conduit  24  is adapted to mix fluid entering into baffled mixing conduit  24  inside baffled mixing conduit  24  via its baffles; one or more mixing fluid supply conduits  15  in fluid communication with manifold  60  and baffled mixing conduit  24 ; reaction chamber  22  in fluid communication with and located downstream from baffled mixing conduit  24 ; and one or more hot fluid conduits  15  in fluid communication with reaction chamber  22 . As with the other configurations, hot fluid may exit reaction chamber  22  in many ways such as via hot fluid conduits  40  ( FIG. 1 ) which may provide a further fluid pathway between reaction chamber  22  and insulated chamber  32  and/or via hot fluid delivery conduits  41  ( FIG. 1 ) adapted to be manipulated by and connectable to ROV  120 . 
     It will be appreciated by those of ordinary skill in these arts that manifold  60  could comprise two pieces of tubing and a t-fitting as well as equivalent structures. 
     As illustrated by  FIGS. 4-7 , various other embodiments may exist. By way of example and not limitation, a simple system may comprise reservoirs  12  connected by fluid conduits  41  to wand  122  ( FIG. 4 ) which can be maneuvered and manipulated by ROV  120  ( FIG. 1 ) to deliver a stream of hot fluid  123  to an area near obstruction  4 . In a further embodiment, baffled chamber  24  may be disposed in-between reservoirs  12  and wand  122 , where all components are in fluid communication as indicated ( FIG. 5 ). In a further embodiment, reaction chamber  22  may be disposed in-between reservoirs  12  and wand  122 , where all components are in fluid communication as indicated ( FIG. 6 ). In a further embodiment, baffled chamber  24  may be disposed upstream from reaction chamber  22 , in-between reservoirs  12  and reaction chamber  22 , and reaction chamber  22  disposed upstream from and connected to wand  122 , where all components are in fluid communication as indicated ( FIG. 7 ). In any of these embodiments, reservoirs  12  may be located on supporting vessel  100 , subsea  300 , or the like, or a combination thereof. 
     As illustrated by  FIGS. 8-11 , additional other embodiments may exist. By way of example and not limitation, a simple system ( FIG. 8 ) may comprise reservoirs  12  connected by fluid conduits  14  to insulated chamber  32  which, as discussed above, may be skid  37  ( FIG. 14 ), a selectively engaged/disengaged insulated chamber  32  ( FIG. 1 ), or a set of preinstalled fluid coils and/or heater tubes  33  ( FIG. 1 ) disposed about the area with obstruction  4 . In a further embodiment, baffled chamber  24  may be disposed in-between reservoirs  12  and insulated chamber  32 , where all components are in fluid communication as indicated ( FIG. 9 ). In a further embodiment, reaction chamber  22  may be disposed in-between reservoirs  12  and insulated chamber  32 , where all components are in fluid communication as indicated ( FIG. 10 ). In a further embodiment, baffled chamber  24  may be disposed upstream from reaction chamber  22 , in-between reservoirs  12  and reaction chamber  22 , and reaction chamber  22  disposed upstream from and connected to insulated chamber  32 , where all components are in fluid communication as indicated ( FIG. 11 ). In any of these embodiments, reservoirs  12  may be located on or at supporting vessel  100 , subsea  300 , or the like, or a combination thereof. If located on or at supporting vessel  100 , weights  35  ( FIGS. 13-14 ) may be provided to aid with keeping conduits  14  in place. 
     In any of these embodiments reaction chamber  22  ( FIG. 1 ) may be adapted to maintain mixed reactant fluid for a predetermined period of time such as, by way of example and not limitation, around one minute to around one and a half minutes or more while the reaction takes place and the fluid heats up to a desired temperature. 
     In any of these embodiments at least one of chemical reactant fluid conduits  14  may comprise coiled tubing. 
     In any of these embodiments pump  50 , which may be a low pressure pump, may be present and in fluid communication with at least one of reservoirs  12 , where pump  50  may be adapted to pump a chemical fluid from reservoir  12  with which it is in fluid communication at a predetermined constant or variable rate into a corresponding conduit  14  in fluid communication with manifold  60  ( FIG. 3 ). Pump  50  may be in fluid communication with the hot fluid and adapted to mix ambient seawater into the hot fluid. 
     In any of these embodiments temperature sensor  39  ( FIG. 1 ) may be present and operatively in communication with reaction chamber  22 . Temperature sensor  39  may be operatively in communication with an external delivery point for the heated fluid, e.g. wand  122  ( FIG. 1 ), either in conjunction with or independently of reaction chamber  22 . 
     In any of these embodiments one or more first flow restrictors  26  ( FIG. 1 ) may be provided and adapted to be in fluid communication with the corresponding plurality of chemical reactant fluid conduits  14 , where flow restrictor  26  is adapted to adjust flow rates of the reactants delivered to reaction chamber  22 . 
     In any of these embodiments one or more flow diverters  42  may be present and in fluid communication with hot fluid conduits  40  and adapted to selectively divert the flow of heated fluid away from subsea structure  200 . 
     In any of these embodiments controllable valve  44 , which may be remotely controllable, may be present and in fluid communication with the hot fluid conduit, where controllable valve  44  adapted to shut off flow of the heated fluid from reaction chamber  22  ( FIG. 1 ). 
     In the operation of exemplary embodiments, referring generally to  FIGS. 12-14 , in a first method obstruction  4  ( FIG. 1 ) such as a hydrate or paraffin plug, may be removed from structure subsea  200  or  201  ( FIG. 1 ) by selectively combining two or more chemical reactants obtained from two chemical reactant reservoirs  12  ( FIG. 1 ) in reaction chamber  22  ( FIG. 1 ) to create a hot fluid by an exothermic chemical reaction between the two chemical reactants. In this first method, reaction chamber  22  is disposed subsea, preferably proximate subsea structure  200 . The resultant hot fluid is then routed through one or more fluid conduits  24  ( FIG. 1 ) which comprise one or more internal baffles adapted to thoroughly blend the reactants, and then to insulated chamber  32  ( FIG. 1 ) which surrounds an area of subsea structure  200  containing obstruction  4 . The hot fluids may be routed via conduits  40  from fluid conduits  24  to insulated chamber  32 . Once present at that area, the area around obstruction  4  is heated with the hot fluid. 
     As described above, reservoirs  12  ( FIG. 1 ) may comprise fluid reservoirs located proximate seabed  300  ( FIG. 1 ) and/or fluid reservoirs located on or at supporting vessel  100  ( FIG. 1 ). The chemical reactants comprise fluids which delivered to reaction chamber  22  ( FIG. 1 ), typically via separate coiled tubing strings  14  ( FIG. 1 ). 
     In a further embodiment, obstruction  4  may be removed from structure  200  ( FIG. 1 ) by selectively combining two or more chemical reactants obtained from a corresponding set of chemical reactant reservoirs  12  ( FIG. 1 ) in reaction chamber  22  ( FIG. 1 ) to create a hot fluid by an exothermic chemical reaction between the two chemical reactants. Once combined, the resultant hot fluid is routed through a pre-installed heater tube  33  ( FIG. 1 ) wrapped around an area of structure  200  ( FIG. 1 ) containing obstruction  4  and that area heated with the hot fluid. 
     In a further embodiment, obstruction  4  may be removed from structure  201  ( FIG. 1 ) by selectively combining two or more chemical reactants obtained from a corresponding set of chemical reactant reservoirs  12  ( FIG. 1 ) in reaction chamber  22  ( FIG. 1 ) to create a hot fluid by an exothermic chemical reaction between the two chemical reactants. The resultant hot fluid may then be routed through an ROV-deployed heating wand  122  ( FIG. 1 ) and a stream of hot fluid  123  ( FIG. 1 ) directed at an area where obstruction  4  is present, such as an external mass, and the area around the obstruction heated with the hot fluid. 
     In a further embodiment, obstruction  4  ( FIG. 3 ) may be removed from structure  200  ( FIG. 3 ) by selectively combining two or more chemical reactants obtained from a corresponding set of chemical reactant reservoirs  12  ( FIG. 3 ) in manifold  60  ( FIG. 3 ). The chemical reactants are then routed from manifold  60  through one or more fluid conduits  15  ( FIG. 3 ) to baffled mixing chamber  24  ( FIG. 3 ) which has been adapted to blend the reactants. This mixed fluid is then routed into reaction chamber  22  ( FIG. 3 ) for a predetermined amount of time, by way of example and not limitation of around one minute to around one and a half minutes or more, to create a hot fluid by an exothermic chemical reaction between the chemical reactants. Once heated to the required temperature, the heated fluid is then routed through one or more heated fluid conduits  40  ( FIG. 3 ) to an area of structure  200  ( FIG. 3 ) proximate obstruction  4  and that area heated with the hot fluid. 
     In certain embodiments, one or more of the chemical reactant reservoirs  12  ( FIG. 1 ) may be in fluid communication with controllable pump  50  ( FIG. 1 ) which pumps its respective chemicals at predetermined varying rates. 
     In any of these methods, reservoirs  12  ( FIG. 1 ) may be located proximate seabed  300  ( FIG. 1 ), on or at supporting vessel  100  ( FIG. 1 ), or the like, or a combination thereof. If fluid reservoirs  12  are located on supporting vessel  100 , the chemical reactants may comprise fluids delivered to reaction chamber  22  ( FIG. 1 ) via separate coiled tubing strings  14  ( FIG. 1 ). 
     As also described above, reaction chamber  22  ( FIG. 1 ) may be disposed proximate subsea structure  200  or  201  ( FIG. 1 ). 
     Oilfield production systems often use composite thermoplastic flexible pipes, and external thermoplastic or synthetic rubber insulation is used on steel pipes. These materials have an external temperature limit, and systems  1  ( FIG. 1 ) or  2  ( FIG. 3 ) may further comprise one or more temperature sensors  39  ( FIG. 1 ) disposed at or near one or more predetermined positions with respect to reaction chamber  22  ( FIG. 1 ), e.g. at reaction chamber  22 , external delivery point(s) for the heated fluid such as  123  ( FIG. 1 ), or the like, or a combination thereof. The temperature of the hot fluid can then be controlled using feedback from temperature sensors  39  ( FIG. 1 ). In all of these methods, controlling the temperature may comprise optimizing an aqueous concentration of the stored reactants; adjusting a bulk flowrate of the reactants delivered to reaction chamber  22 ; adjusting a ratio of the reactants delivered to reaction chamber  22  to achieve a desired temperature; mixing ambient seawater into the hot fluid using pump  50  ( FIG. 1 ), which may be a low pressure pump, in fluid communication with the hot fluid; diverting the flow of heated fluid away from subsea structures  200  or  201  ( FIG. 1 ); shutting off flow of the heated fluid from reaction chamber  22  using controllable valve  44  ( FIG. 1 ); releasing insulated chamber  32  ( FIG. 1 ) from around subsea structure  200  to allow heated fluid to simply escape into the environment; or the like; or a combination thereof. These controls may be manual and/or automated with software and sensors such as temperature sensor  39 . 
     In all of these methods, once the reactants are combined in reaction chamber  22  ( FIG. 1 ), at some point the fluid mixture travels through conduits  24  ( FIG. 1 ) which comprise one or more internal baffles which are designed to blend the reactants, typically thoroughly, and may comprise steel. 
     One of ordinary skill in these arts will realize that  FIGS. 1 and 2 , while illustrating different embodiments, having many components in common and that reference elements present in  FIG. 1  above may also apply to the same corresponding elements in  FIG. 2 . 
     The foregoing disclosure and description of the invention is illustrative and explanatory. Various changes in the size, shape, and materials, as well as in the details of the illustrative construction and/or an illustrative method may be made without departing from the spirit of the invention.