Patent Publication Number: US-8522881-B2

Title: Thermal hydrate preventer

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a non-provisional application that claims the benefit of commonly assigned U.S. Provisional Application No. 61/488,083, filed May 19, 2011, entitled “Thermal Hydrate Preventer,” the entire disclosure of which is hereby incorporated by reference herein for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     In certain circumstances, uncontrolled release of crude oil may occur from a subsea well. While careful steps are taken to avoid such uncontrolled release, once release occurs it is exceedingly important to move quickly and effectively to capture the oil being released to minimize environmental damage while further steps are taken to stop the flow of oil. Recent events have underscored the importance and difficulty of dealing with an uncontrolled subsea well. 
     BRIEF SUMMARY OF THE INVENTION 
     The terms “invention,” “the invention,” “this invention” and “the present invention” used in this patent are intended to refer broadly to all of the subject matter of this patent and the patent claims below. Statements containing these terms should not be understood to limit the subject matter described herein or to limit the meaning or scope of the patent claims below. Embodiments of the invention covered by this patent are defined by the claims below, not this summary. This summary is a high-level overview of various aspects of the invention and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to the entire specification of this patent, all drawings and each claim. 
     In some embodiments, a system for servicing an undersea well can include a submersible isolation bell for capturing effluent being exhausted from the well, and an umbilical. A power cable supplies electric power to the submersible isolation bell, for example, for heating of the interior of the submersible isolation bell to prevent and/or discourage the formation of methane hydrates and/or the precipitation of other byproducts. Diluents may be supplied to the submersible isolation bell to further discourage the formation of hydrates and/or precipitation of other byproducts. The diluents may be heated locally at the submersible isolation bell, using electric power supplied by the power cable. A conformable seal may substantially seal the submersible isolation bell to a riser or other structure at the wellhead. 
     In other embodiments, a method of servicing an undersea well includes providing a well servicing system that further includes a submersible isolation bell, and/or an umbilical connected to the submersible isolation bell. The umbilical further includes a collection conduit for carrying effluent from the well to a collection station. The umbilical may further include a power cable for transmitting electrical power to the submersible isolation bell. The system can be deployed by lowering the submersible isolation bell over the well and disposing the submersible isolation bell over the well. 
     According to other embodiments, a well servicing system can include an umbilical that includes a collection conduit for carrying effluent from the well to a collection station, at least one power cable, and/or a fitting connected to the umbilical. The fitting can be sized to fit within a piece of equipment at the wellhead. The system may further include a diluent carrying conduit for carrying diluent to the well. In some embodiments, the system may include an electric heater powered via the power cable and positioned to heat diluent in the diluent carrying conduit near a lower end of the umbilical. The system may also include a seal configured to deploy at the piece of equipment at the wellhead to substantially prevent effluent from escaping the well other than through the collection conduit. 
     According to other embodiments, a well servicing system can include an umbilical made of coiled tubing and/or sized for insertion into an existing drill stem. The umbilical can include a diluent carrying conduit. The system may also include at least one power cable carrying power to a lower portion of the umbilical, and/or an electric heater powered via the at least one power cable and/or positioned to heat diluent flowing from the diluent carrying conduit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Illustrative embodiments of the present invention are described in detail below with reference to the following drawing figures. 
         FIG. 1  illustrates a simplified view of an undersea well in a state of uncontrolled release. 
         FIG. 2  schematically illustrates placement of a lower marine riser package cap system over the undersea well of  FIG. 1  according to some embodiments of the invention. 
         FIG. 3  illustrates a hydrate dissociation curve. 
         FIG. 4  illustrates a system in accordance with embodiments of the invention for capturing effluent from an undersea well that is in a state of uncontrolled release according to some embodiments of the invention. 
         FIG. 5  illustrates a cross section view of a submersible isolation bell, in accordance with embodiments of the invention. 
         FIG. 6  illustrates a cross section view of an umbilical in accordance with embodiments of the invention according to some embodiments of the invention. 
         FIG. 7  illustrates a cross section view of a combined umbilical according to some embodiments of the invention. 
         FIG. 8  shows a combined umbilical with clamps according to some embodiments of the invention. 
         FIG. 9  shows a combined umbilical with an outer tube according to some embodiments of the invention. 
         FIG. 10  illustrates a submersible isolation bell with multiple connection points, in accordance with embodiments of the invention. 
         FIG. 11  illustrates a well servicing system according to other embodiments. 
         FIG. 12  illustrates a well servicing system in according with some embodiments of the invention. 
         FIG. 13  illustrates a detailed view of a portion of the system of  FIG. 12  according to some embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The subject matter of embodiments of the present invention is described here with specificity to meet statutory requirements, but this description is not necessarily intended to limit the scope of the claims. The claimed subject matter may be embodied in other ways, may include different elements or steps, and may be used in conjunction with other existing or future technologies. This description should not be interpreted as implying any particular order or arrangement among or between various steps or elements except when the order of individual steps or arrangement of elements is explicitly described. 
       FIG. 1  illustrates a simplified view of an undersea well  101  in a state of uncontrolled release. The release may occur for any number of reasons. For example, the release may be due to equipment failure after the well  101  has penetrated a high-pressure oil-bearing reservoir  102  beneath the seafloor  103 . In the example of  FIG. 1 , a blowout preventer (BOP) stack  104  is still in place over well  101 , and a riser  105  above BOP stack  104  has been cut so that a length of riser  105  protrudes above BOP stack  104 . There are various other configurations of a well in a state of uncontrolled release. Crude oil and other products are escaping as effluent  106  from well  101  into the ocean. Effluent  106  may rise and spread on the ocean surface  107 . 
     A previous technique for capturing at least some of the effluent  106  involved placement of a lower marine riser package cap (LMRP cap) over well riser  105 .  FIG. 2  schematically illustrates placement of an LMRP cap system  201  using a conventional drillship  202 . LMRP cap system  201  includes a funnel-like LMRP cap  203  and other equipment  204 , and is lowered from drillship  202  in a manner similar to the way drilling equipment is lowered into a well. Sections of pipe  205  are assembled one at a time as LMRP cap system  201  is lowered. 
     Once LMRP cap  203  is in place, at least some of effluent  106  is captured and travels up pipe  205  to a collection reservoir aboard drillship  202 . Liquids may be collected, and natural gas may be flared off. 
     The operation of LMRP cap  203  is complicated by the remoteness of undersea well  101 , by the conditions at sea floor  103 , and by the interactions between the components of effluent  106  and the surrounding seawater. 
     For example, effluent  106  may exit well under intense pressure and at a temperature of about 60° C. (140° F.). At an ocean depth of approximately 1524 meters (5,000 feet), the hydrostatic pressure of seawater is about 150 bar (about 2,200 pounds per square inch). The water temperature at the seafloor may be about 4° C. (39° F.). If effluent  106  is allowed to contact seawater at these conditions, ice-like crystals of methane hydrates may form. These crystals are often called simply “hydrates”. If hydrates are allowed to form during the use of LMRP cap  203 , pipe  205  may be plugged and the collection of effluent  106  frustrated. 
       FIG. 3  illustrates a hydrate dissociation curve  301 , showing the temperature and pressure conditions under which hydrates will form. For combinations of temperature and pressure above and to the left of hydrate dissociation curve  301 , within hydrate envelope  302 , hydrates will form when methane comes in contact with seawater. For combinations of temperature and pressure below and to the right of hydrate dissociation curve  301 , hydrates will not form. Moreover, crystalline hydrates will dissociate into liquid water and gaseous methane in conditions outside of hydrate envelope  302 . The particular well operating conditions marked in  FIG. 3  are merely examples, and it will be understood that embodiments of the invention may be utilized at wells in other operating conditions. 
     In order to maintain the flow of effluent  106  through pipe  205  the effluent can be maintained at temperature and pressure combinations outside of the hydrate envelope and/or significant contact between effluent  106  and seawater can be maintained. In some cases, where hydrates have already formed, it may also be necessary to dissociate any hydrates that block valves, piping, or tubing needed for effluent removal. Because seawater is a nearly infinite heat sink and the seawater surrounding LMRP cap  203  is most likely cold, maintaining effluent  106  at satisfactory temperature and pressure combinations can be challenging. LMRP cap  203  may be heated, for example by pumping heated fluids from drillship  202 . To further discourage the formation of hydrates and to mitigate the effects of other precipitates that may form from effluent  106 , one or more diluents such as methanol may also be pumped into LMRP cap  203  to mix with effluent  106 . For example, tars, asphaltenes, or other precipitates may form from effluent  106 , and may be at least partially dissolved or dissociated by the diluents. 
       FIG. 4  illustrates a system  400  in accordance with embodiments of the invention for capturing effluent from an undersea well that is in a state of uncontrolled release. System  400  includes a submersible isolation bell  401  configured to engage with riser  105 , BOP stack  104 , or other structure at the top of well  101  near seafloor  103 . System  400  also includes an umbilical  402  connected to submersible isolation bell  401 . An umbilical is an elongate line or tube that carries electrical power, fluid, control signals, or other services or combinations of services. 
     Umbilical  402  includes a collection conduit that may be made of coiled tubing (CT) for carrying oil and other products from well  101  to a collection station, for example aboard a support vessel  403 . Coiled tubing is used for various purposes in the drilling field, and can be any continuously-milled tubular product manufactured in lengths that require spooling onto a take-up reel or spool such as spool  409  during manufacturing. Coiled tubing may be manufactured in lengths of up to 40,000 feet or more. Coiled tubing may be transported to a wellsite in its coiled state, and at least partially straightened before being deployed into service. Upon being taken out of service, the coiled tubing may be wound back onto a spool. Most coiled tubing is made of metal, for example low-alloy high strength carbon steel, although other metals, plastics, and/or composites can be used. 
     When umbilical  402  is constructed using coiled tubing, it can be deployed and recovered relatively quickly, as compared with pipe  205 . Submersible isolation bell  401  and/or umbilical  402  can be prefabricated and held at the ready in a region where undersea drilling is taking place. If an uncontrolled release incident occurs, system  400  can then be transported a relatively short distance to the wellsite and deployed to begin capture of effluent from the well soon after any wellsite preparations and construction of any required fittings are complete. 
     Should the initial deployment be unsuccessful, system  400  can be retracted and redeployed relatively quickly by coiling umbilical  402  back aboard support vessel  403 , modifying equipment at submersible isolation bell  401 , and lowering submersible isolation bell  401  back to well  101 . 
     In other embodiments, an umbilical utilizing drill pipe may also be used. For example, submersible isolation bell  401  may be attached to drill pipe  205  and may be deployed in much the same way as LMRP cap  203  described above Submersible isolation bell  401  and related equipment may be stored on drillship  202  in case of a need for rapid deployment. While the embodiments described herein are illustrated as using coiled tubing any type of tubing can be used. 
     System  400  further comprises at least one power cable for transmitting electrical power to submersible isolation bell  401 . In previous efforts to prevent hydrate formation, systems have provided heat at the wellhead by pumping heated fluids from the ocean surface to the wellhead. This prior method may result in significant heat loss as the heated fluids may cool during the trip to the wellhead. Systems in accordance with embodiments of the invention transmit energy to the wellhead area in the form of electricity, which can then be used to generate heat locally at submersible isolation bell  401 , and may also be used for other purposes as described in more detail below. Heated fluids may still also be pumped from the surface, if desired. A conductor or multiple conductors may be integrated within umbilical  402 , or may be provided in a separate cable or umbilical. 
     It may be possible to heat diluents or other fluids present at submersible isolation bell  401  to higher temperatures using local electric heating than would be possible using heated fluid pumped from the surface. Because of the elevated pressures present near sea floor  103 , higher temperatures may be reached using local heating without causing boiling of fluids. In addition, heat losses occurring during fluid transfer from the surface may be reduced. 
     System  400  may also include a diluent carrying conduit  404 , which may be integrated with umbilical  402  or may be provided in a separate umbilical, as shown in  FIG. 4 . Diluents carried by diluent carrying conduit  404  may include methanol, diesel fuel, a combination of methanol and diesel fuel, or any other kind of diluent. In some embodiments, the combination of diesel and methanol can vary, for example, the combination can include 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% diesel by volume or mass. In some embodiments, multiple conduits can be used to carry different diluents. For example, two conduits can be used: a first conduit can carry diesel and a second conduit can carry methanol. These separate conduits can be used, for example, to keep the combined diluents from combusting within the conduit. Moreover, in some embodiments, conduit  404  can include valves near or at bell  401  that can stop both the flow of diluent to bell  401  and/or to restrict combustion from proceeding from bell  401  to support vessel  403 . Furthermore, bell  401  can include combustion sensors that can be used to close the conduit valves or that may change the diluent delivered in these conduits to a combustion suppressing substance or may allow combustion suppressing substance to enter bell  401  in the event of combustion. 
     One or more integral electric heaters may also be included within or near diluent carrying conduit  404 , powered by the umbilical electric power cable. Moreover, in some embodiments, the diluents may be heated at the surface prior to being carried through diluent carrying conduit  404 . 
     In some embodiment, umbilical  402  may further include various electrical cables for powering and/or communicating with sensors or other equipment at submersible isolation bell  401 . Other kinds of service carrying lines may also be provided, for example one or more fiber optic lines may carry data such as images or video from submersible isolation bell  401  to support vessel  403 . An electric submersible pump  406  may also be included at submersible isolation bell  401 , for assisting in lifting the captured effluent through the collection conduit to support vessel  403 . 
     In some embodiments, umbilical  402  may be insulated along at least part of its length, to help maintain the temperature of fluid carried in umbilical  402 , for instance, to further discourage the formation of hydrates. One or more integral electric heaters may also be included within or near umbilical  402 , and can be powered by the umbilical electric power cable. Such an integral electric heaters may also extend along the length or portions of the length of the umbilical. 
     Installation and operation of system  400  can be assisted by one or more remotely operated vehicles  407 , which may be operated from support vessel  403  or from another tender vessel  408 . Support vessel  403  may also carry equipment for handling coiled tubing, one or more generators for generating electric power, and other equipment beneficial to the operation of system  400 . 
       FIG. 5  illustrates a cross section view of submersible isolation bell  401  in more detail, in accordance with embodiments of the invention. In  FIG. 5 , submersible isolation bell  401  is shown in place over riser  105  and in operation. 
     Submersible isolation bell  401  can be made of a strong material, for example a steel alloy, and may be weighted for additional stability, and may include chambers that can admit and expel sea water to further control the buoyancy of submersible isolation bell  401 . Submersible isolation bell  401  can be configured to engage with a severed riser  105  or another structure at the wellhead, to substantially inhibit the flow of effluent  106  outside of submersible isolation bell  401 . The interior of submersible isolation bell  401  can be kept at a positive pressure in relation to the surrounding ocean, to inhibit the uptake of cold surrounding seawater  501  that may encourage the formation of hydrates. Submersible isolation bell  401  may also be thermally insulated, to inhibit heat loss to the surrounding seawater  501 . 
     Sealing measures may be implemented to further isolate the interior of submersible isolation bell  401  from the surrounding seawater  501 . For example, a conformable seal or gasket  502  may be placed between submersible isolation bell  401  and riser  105  or other structure. In some embodiments, seal or gasket  502  may be made of a highly conformable open cell foam that may be non-buoyant and semi-permeable. Seal or gasket  502  can be used so that a small portion of effluent  106  can be continually exhausted from submersible isolation bell  401 , as shown at  503 , to help ensure that surrounding seawater  501  is not admitted into submersible isolation bell  401 . Seal or gasket  502  can be porous to allow effluent  106  to escape into surrounding seawater  501 . Seal or gasket  502  may be, for example, made of a TEMBO® foam available from Composite Technology Development, Inc., of Lafayette, Colo., USA. Seal or gasket  502  and other fittings may be fabricated case-by-case for particular well installations, as the size, shape, degree of damage, and other aspects of the equipment remaining at sea floor  103  may vary from well to well. A fastening mechanism  504  may be provided for securely attaching submersible isolation bell  401  to the well structure, and may also be fabricated to fit a particular well situation. While fastening mechanism  504  is shown as two L-shaped latches that can be deployed to engage with a convenient part of riser  105  assembly or parts of BOP stack  104 , any suitable fastening system may be used, for example pins, hooks, bolts, or other kinds of fasteners or combinations of fasteners. 
     One or more closeable vents  505  may be provided for venting submersible isolation bell  401  during installation. Closeable vents  505  can be closed once submersible isolation bell  401  is in place, to further contain effluent  106 . 
     Additional connections may be provided for attaching additional umbilicals to submersible isolation bell  401 , for example to carry additional solvents or diluents to submersible isolation bell  401 , to carry additional effluent  106  to support vessel  403  or another vessel, to carry additional power or signals, or for other purposes. 
     Electric power may be generated aboard support vessel  403  and supplied by power cable  506  for various purposes at submersible isolation bell  401 . For example, electric submersible pump  406  may be powered using power from power cable  506 . Diluent or other fluids supplied through diluent carrying conduit  404  may be heated, for example using heater  507  (e.g., electrical and/or resistance heater) or other means, so that diluents introduced into submersible isolation bell  401 , from nozzle  508 , are heated to enhance their effectiveness and to further discourage the formation of hydrates and the precipitation of other by products. 
     Additional heat may also be introduced generally into the interior of submersible isolation bell  401  using heater  509  (e.g., electrical and/or resistance heater) or other means. Fins  510  or other structures may be provided to assist in dispersion of heat within submersible isolation bell  401 . Heater  509  or similar heaters maybe especially useful for startup of the system, to prevent formation of hydrates during the installation of submersible isolation bell  401 . 
     Electric power may be utilized for other purposes as well, for example, for closing closable vents  505 , powering any sensors or communications equipment present at submersible isolation bell  401 , or for other purposes. The amount of power supplied for heating, for example by heaters  507  and/or  509 , may be controllable in response to temperature measurements made at submersible isolation bell  401 . For example, sufficient power may be supplied to keep the conditions within submersible isolation bell and umbilical  402  well outside of hydrate envelope  302 . 
       FIG. 6  illustrates a cross section view of umbilical  402 , in accordance with embodiments of the invention. Oil flow cross section  601  is the main channel of umbilical  402  and can be used to allow oil, effluent and/or other material to flow there through. Umbilical  402  can be surrounded by coiled tubing  602 , which can be welded at weld  603 . Coiled tubing  602  may be of any size useful for carrying oil and deployable from support vessel  403  to typical ocean depths. For example, equipment exists for handling coiled tubing in diameters up to at least 6.5 inches or more. Such tubing may be available in lengths of several thousand feet. Coiled tubing  602  may in turn be surrounded by heater  604  of any suitable type, and thermal insulation  605 . Power cable  506 , shown as comprising three insulated conductors may be affixed using clamp  607  (e.g., cable clamp) or similar device. Power cable  506  could also comprise a different number of conductors, for example two conductors. 
     In some embodiments, umbilical  402  may be combined with other structures, enabling simultaneous deployment from support vessel  403 . For example,  FIG. 7  illustrates a cross section view of a combination of umbilical  402 , diluent carrying conduit  404 , and power cable  506 , connected by clamp  607 .  FIGS. 8 &amp; 9  show examples of a combined umbilical that includes umbilical  402 , diluent carrying conduit  404 , and power cables  506 . In some embodiments, multiple clamps  607 , such as those designed for use on riser tubes, may be placed at intervals along the length of an umbilical and can be used to couple the various conduits, umbilicals, cables, cords, etc. In such embodiments, there may be no need for clamp  607 . 
     In other embodiments, all the umbilical components (and possibly other components) may be disposed within an outer umbilical  611  that is continuous or mostly continuous (e.g., with a handful of breaks) tube that extends from support vessel  403  to effluent  106  and/or well  101 .  FIG. 9  shows an example of such an umbilical. Such umbilicals may be fabricated by the techniques described in co-pending U.S. patent application Ser. No. 13/177,368, filed Jul. 6, 2011, and titled “Coiled Umbilical Tubing”, previously incorporated by reference. 
     In other applications, a submersible isolation bell in accordance with embodiments of the invention may include additional connection points for additional umbilicals, cables, conduits, or other structures, which may be deployed from one or multiple support vessels. By way of example,  FIG. 10  shows a submersible isolation bell  801  with multiple connection points  802 . In the illustrated arrangement, an additional umbilical  803  is connected to one of connection points  802 , and is deployed from a second support vessel  804 . Additional umbilical  803  may carry oil or other effluent from well  101  to second support vessel  804 , may provide additional electric power to submersible isolation bell  801 , may carry signals to and from additional sensors placed at submersible isolation bell  801 , and/or may provide other support to the operation to recover effluent  106  from well  101 . Additional umbilical  803  may perform a combination of functions. 
       FIG. 11  illustrates a portion of a well servicing system  900  according to other embodiments. System  900  may be deployed in a manner similar to system  400  and may provide similar features and benefits, but connects differently to the wellhead equipment. In other embodiments, system  900  may be used to unclog a pipe or well. System  900  includes umbilical  402  and fitting  901  that can connect to the lower end of umbilical  402 . To unclog pipes or wells, umbilical  402  can be fed into a clogged pipe or well through riser  105 . 
     Umbilical  402  can include a collection conduit for carrying effluent from the well to a collection station, and/or at least one power cable  506 . Fitting  901  can be sized to fit within a piece of equipment at the wellhead, for example riser  105 . Fitting  901  can be a standard or custom fitting that is designed to fit with a specific riser, pipe or well. Fitting  901  may also comprise a seal  902  configured to deploy at the wellhead to substantially prevent effluent  106  from escaping the well other than through the collection conduit of umbilical  402 . For example, seal  902  may be mechanically expandable or hydraulically inflatable to substantially seal against the inner wall of riser  105 . Moreover seal  902  may also act as a centralizer that, for example, centers fitting  901  or umbilical  402 , pump  406 , conduit  404 , or a combination of these within riser  105 . 
     A diluent carrying conduit  404  may also be provided, for carrying diluent to the well, for example from support vessel  403 . Either or both of umbilical  402  and diluent carrying conduit  404  may be made of coiled tubing and deployed by uncoiling the coiled tubing from a spool as fitting  901  is lowered to the well. Alternatively, system  900  may be implemented using conventional drill pipe. 
     Heater  507  may be provided, drawing its power from power cable  506 . Heater  507  can be positioned to heat diluent supplied via diluent carrying conduit  404  near a lower end of umbilical  402 . The heated diluent may mix with effluent  106  to heat effluent  106  to prevent the formation of hydrates before or while effluent  106  travels through the collection conduit of umbilical  402 . System  900  thus provides local heating of effluent  106 , and may be able to reach higher temperatures than would be achievable by piping pre-heated diluent from the ocean surface. 
     Electric submersible pump  406  may also be provided, to assist in lifting effluent  106  through the collection conduit to the collection station. Electric submersible pump  406  may be powered via power cable  506 . 
       FIGS. 12 and 13  illustrate a system  1000  according to some embodiments of the invention. System  1000  may be useful, for example, for intervening in the case of a well  1001  whose integrity has not been breached, but that is clogged or otherwise affected by the formation of hydrates within drill pipe  1002 . 
     System  1000 , for example, includes a drillship  1003  equipped with coiled tubing handling equipment. Drill pipe  1002  is plugged or restricted by a hydrate plug  1004 . Hydrate plug  1004  is shown as having formed near the bottom of drill pipe  1002 , near BOP stack  104 , but such a plug may form in other locations as well. 
     In accordance with embodiments of the invention, an umbilical  1005  is made at least in part of coiled tubing, and is uncoiled from a spool and lowered into drill pipe  1002 . The lower end of umbilical  1005  is shown in more detail in  FIG. 13 . Umbilical  1005  can be sized for insertion in drill pipe  1002 , and can include a diluent carrying conduit  1101  and at least one power cable  1102  that carries power to the lower portion of umbilical  1005 . Electric heater  1104  can draw power from power cable  1102 , and can be positioned to heat diluent flowing from diluent carrying conduit  1101 . The heated diluent can dissolve or otherwise dissociate hydrate plug  1004 , whose residue is carried by the flowing diluent back up the annular space between umbilical  1005  and drill pipe  1002 . 
     Once hydrate plug  1004  has been removed, umbilical  1005  can be removed from drill pipe  1002  and normal operations may be resumed. 
     While electric heater  1104  is shown in  FIG. 13  as being disposed over a small portion of umbilical  1005  near lower end  1103 , and electric heater  1104  are shown as being on the outside of umbilical  1005 , other arrangements are possible. For example, electric heater  1104  may extend over all or a significant portion of the length of umbilical  1005 , to gradually heat diluent in diluent carrying conduit  1101  on its way to lower end  1103  of umbilical  1005 . Also, both power cable  1102  and electric heater  1104  could be inside the outer casing of umbilical  1005 . Methods of constructing such an umbilical are described in co-pending U.S. patent application Ser. No. 13/177,368, filed Jul. 6, 2011, and titled “Coiled Umbilical Tubing”, previously incorporated by reference. 
     Different arrangements of the components depicted in the drawings or described above, as well as components and steps not shown or described are possible. Similarly, some features and subcombinations are useful and may be employed without reference to other features and subcombinations. Embodiments of the invention have been described for illustrative and not restrictive purposes, and alternative embodiments will become apparent to readers of this patent. Accordingly, the present invention is not limited to the embodiments described above or depicted in the drawings, and various embodiments and modifications can be made without departing from the scope of the claims below.