Patent Publication Number: US-8973665-B2

Title: System and method for performing intervention operations with a compliant guide

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present document is based on and claims priority to U.S. Provisional Application Ser. No. 60/908,101, filed Mar. 26, 2007; and International Application No. PCT/US2008/057303, filed Mar. 18, 2008. 
    
    
     BACKGROUND 
     The retrieval of desired fluids, such as hydrocarbon based fluids, is pursued in subsea environments. Production and transfer of fluids from subsea wells relies on subsea installations, subsea flow lines and other equipment. Additionally, preparation and servicing of the subsea well relies on the ability to conduct subsea intervention work. A big challenge in subsea intervention work is controlling pressure so that pressurized borehole fluids in the subsea well are contained within the borehole during intervention operations. 
     Subsea intervention work involves numerous challenges not normally faced when working on land wells or offshore platforms. In most cases, intervention in subsea wells is performed from a floating platform or ship by extending the borehole to a surface location by a tensioned riser. This approach allows pressurized borehole fluids to move upwardly to the surface through the riser which can span hundreds or thousands of feet of sea water. The cost of such platforms is high, however, and the availability of vessels capable of adequately performing this type of intervention work is limited. 
     In shallow waters, subsea intervention work can be performed with a specially equipped vessel having subsea lubricators, subsea pressure control equipment, and wave motion compensating systems. In most cases, guide wires extending from a wellhead all the way to the vessel combined with the aid of professional divers is required. Additionally, this approach requires that equipment is conveyed and guided from the vessel to the subsea installation through open waters. Once the subsea lubricator is connected to the subsea installation and the tools are inside, the conveyance cable remains exposed to open waters. Additionally, pressure control must be exercised at the seabed. Because existing non-rig intervention capability is limited to shallow water wireline and slickline operations, most intervention on subsea wells is currently performed with expensive and scarce heavy drilling units. 
     SUMMARY 
     In general, the present invention provides a technique for subsea intervention operations which utilizes a compliant guide, e.g. a spoolable compliant guide, which extends between a surface location and a subsea installation. The overall system is designed to facilitate deployment of tool strings into a subsea well. For example, at least a portion of the compliant guide can be used as a subsea lubricator during pressure deployment of tool strings to reduce the height of the subsea lubricator or to completely eliminate the need for a separate subsea lubricator. In alternate or other applications, a tool entry guide can be connected into the subsea installation to facilitate deployment of tool strings into the subsea well. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
         FIG. 1  is a schematic front elevation view of a subsea intervention system, according to an embodiment of the present invention; 
         FIG. 2  is a schematic front elevation view similar to that of  FIG. 1  but showing an intervention tool string being deployed into a compliant guide, according to an embodiment of the present invention; 
         FIG. 3  is a schematic front elevation view similar to that of  FIG. 1  but showing the intervention tool string deployed proximate a subsea lubricating seal, according to an embodiment of the present invention; 
         FIG. 4  is a schematic front elevation view similar to that of  FIG. 1  but showing the intervention tool string being deployed into a subsea wellbore, according to an embodiment of the present invention; 
         FIG. 5  is a schematic front elevation view of an embodiment of the subsea intervention system, according to an alternate embodiment of the present invention; 
         FIG. 6  is a schematic front elevation view similar to that of  FIG. 5  but showing the intervention tool string being deployed into a tool entry guide, according to an embodiment of the present invention; 
         FIG. 7  is a schematic front elevation view similar to that of  FIG. 5  but showing the intervention tool string being locked in place for engagement with a conveyance extending through the compliant guide, according to an embodiment of the present invention; and 
         FIG. 8  is a schematic front elevation view similar to that of  FIG. 5  but showing the intervention tool string being deployed into the subsea wellbore, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
     The present invention generally relates to a technique for intervening in subsea installations, such as subsea wells. The technique also provides unique ways of utilizing a compliant guide, such as a spoolable compliant guide, to facilitate intervention operations with a variety of tool strings. For example, the compliant guide can be used as a subsea lubricator for the pressure deployment of tool strings during intervention operations. The compliant guide also can be used in conjunction with a tool entry guide that enables insertion of tool strings from a position external to the compliant guide. 
     In using the compliant guide as a subsea lubricator, the compliant guide is coupled to a subsea installation, and a lower portion of the compliant guide is generally used as the subsea lubricator. In some applications, the lower portion of the compliant guide can serve as the entire subsea lubricator. In other applications, the lower portion of the compliant guide can serve as a subsea lubricator in combination with a separate or supplemental subsea lubricator. The compliant guide can be utilized as a subsea lubricator when deploying a variety of tool strings, e.g. tool strings having relatively small diameters. In other applications, such as intervention operations deploying larger diameter tool strings, the tool entry guide can be used to insert the tool string from a location external to the compliant guide. 
     Use of the compliant guide enables pressure deployment of tool strings in an efficient and advantageous manner. As referenced above, utilizing the compliant guide as a subsea lubricator during the pressure deployment of tool strings reduces the required height of a conventional subsea lubricator or completely eliminates the need for a conventional subsea lubricator. Alternatively, certain tool strings, e.g. large diameter tool strings with relatively short tools, can be deployed through the tool entry guide and a short subsea lubricator. 
     Additionally, many other aspects of subsea intervention equipment and operations can be improved by utilizing the lower portion of the compliant guide as the subsea lubricator. For example, bending forces on the subsea intervention installation are reduced due to its reduced height. Also, use of the compliant guide as a subsea lubricator improves the efficiency of the pressure deployment of tool strings during subsea intervention operations. Furthermore, the risk of environmental damage during the deployment sequence is reduced. The elimination of subsea tool handling equipment and elimination of the conventional subsea lubricator also simplifies the process of pressure deployment of tool strings. There also is greater flexibility in the variety of tool string types that can be deployed. For example, the tool strings are not limited to tools that can be stored inside the subsea equipment, and the tool string length is not limited by the length of conventional subsea lubricators. 
     Referring generally to the Figures, examples of the compliant guide systems and techniques discussed above are illustrated. In  FIG. 1 , an intervention system  20  is illustrated according to an embodiment of the present invention. In this embodiment, system  20  comprises a guide  22 , such as a compliant guide which may be in the form of a spoolable compliant guide. In other applications, guide  22  may comprise a riser, such as a flexible riser. In the embodiment illustrated, compliant guide  22  is coupled between a subsea installation  24  and a surface vessel  26 , such as an intervention vessel located at a surface  28  of the sea. Subsea installation  24  may be located on or at a seabed floor  30 . The compliant guide  22  may be pressurized to control the high pressure borehole fluids. 
     Compliant guide  22  comprises a lower portion  32  that may serve as a compliant guide subsea lubricator  34 . In other applications, additional portions of compliant guide  22  or the entire compliant guide  22  can be utilized as the subsea lubricator  34 . The compliant guide subsea lubricator  34  can be adjusted to accommodate tool strings of a variety of lengths and configurations. Depending on the intervention application, compliant guide subsea lubricator  34  can be used as the sole lubricator or in combination with a shortened conventional subsea lubricator  36 , as represented by dashed lines in  FIG. 1 . It also should be noted that in other applications, the subsea lubricator  34  can be formed as part of other types of guides, such as flexible risers, hybrid risers, or tensioned risers. 
     In the embodiment illustrated, compliant guide  22  is flexible and may be arranged in a variety of curvilinear shapes extending between a surface location, e.g. intervention vessel  26 , and subsea installation  24 . This flexibility allows the compliant guide  22  to be arranged in a variety of configurations, as desired, to facilitate deployment or retraction of tool strings. By way of example, compliant guide  22  may be constructed as a tubular member formed from a variety of materials that are sufficiently flexible, including metal materials of appropriate cross-section and composite materials. 
     In this embodiment, compliant guide  22  is filled with a buffer fluid  38 , such as seawater, introduced into the interior of compliant guide  22 . In some applications, other buffer fluids  38  can be used, e.g. environmentally friendly greases for friction reduction or for pressure sealing; fluids designed for hydrate prevention; weighted mud; and other appropriate buffer fluids. The level and pressure of buffer fluid  38  can be controlled from the surface to both maintain control over borehole fluids and to facilitate movement of an intervention tool string  40 . 
     Once compliant guide  22  is coupled between subsea installation  24  and intervention vessel  26 , the intervention tool string  40  can be deployed for a desired intervention operation. In one embodiment, intervention tool string  40  is conveyed from intervention vessel  26  down through compliant guide  22  to compliant guide subsea lubricator  34 . The tool string is then moved through subsea installation  24  via a conveyance  42 , as described in greater detail below. The compliant guide  22  also provides the path along which the intervention tool string  40  can be retrieved to the surface. For example, an intervention tool string  40  can be delivered to the subsea installation and upon completion of a specific intervention operation, the tool string  40  can be retrieved to the surface and interchanged with another intervention tool string. This process is readily repeated as many times as necessary to complete the entire intervention operation. 
     Conveyance  42  may be a flexible, cable-type conveyance, such as a wireline or slickline However conveyance  42  also may comprise stiffer mechanisms including coiled tubing and coiled rod. Compliant guide  22  can be arranged to facilitate passage of the intervention tool string  40  without requiring a pushing force, at least in some applications. In other words, the curvilinear configuration of compliant guide  22  is readily adjustable via, for example, locating or moving intervention vessel  26  so as to avoid bends or deviated sections that could interfere with the passage of intervention tool string  40 . The desired orientation of the compliant guide also may be changed from one intervention operation to another or during a given intervention operation depending on parameters, such as current, subsea obstacles, surface obstacles and other environmental factors. 
     Although subsea intervention operations can be performed on a variety of subsea installations  24 , one example is illustrated in  FIG. 1 . In this example, the subsea installation  24  comprises a subsea wellhead  44 , that may comprise a Christmas tree, coupled to a subsea well  46 . Subsea installation  24  also comprises a subsea lubricating seal  48  that may be deployed directly above subsea wellhead  44 . Lubricating seal  48  can be used to close the borehole of subsea well  46  during certain intervention procedures. A blowout preventer  50  may be positioned above lubricating seal  48  and may comprise one or more cut-and-seal rams able to cut through the interior of the subsea installation and seal off the subsea installation during an emergency disconnect. The subsea installation  24  also may comprise additional blowout preventers as well as a subsea stripper assembly  52  positioned above blowout preventer  50 . Additionally, a connector  54  is positioned to enable coupling of compliant guide  22  with subsea installation  24 . The subsea installation  24  also may comprise other devices, such as emergency disconnect devices that allow an operator to perform an emergency disconnection. 
     Generally, subsea lubricating seal  48  acts as a pressure barrier between subsea wellhead  44  and compliant guide  22 . The subsea stripper assembly  52  cooperates to maintain the pressure seal between the wellbore and compliant guide  22  while conveyance  42  is moved in and out of subsea well  46 . The stripper assembly  52  may comprise multiple stripper elements to ensure the integrity of the assembly. Furthermore, the one or more blowout preventers  50  may comprise rams, e.g. hydraulically operated rams, able to secure the well with or without conveyance  42  extending through subsea installation  24 . 
     Additionally, intervention system  20  comprises a subsea fluid separation seal  56  positioned generally at the bottom of compliant guide  22  to help block incursion of well fluids into an interior  58  of the compliant guide  22 . For example, subsea fluid separation seal  56  can be positioned within the lower end of compliant guide  22 , or it can be positioned at other locations by the lower end of compliant guide  22 , e.g. proximate the one or more blowout preventers  50  or stripper assembly  52 . It should be noted that the interior  58  is filled with buffer fluid  38  which can be used to regulate the pressure differential acting on subsea fluid separation seal  56 . Fluid separation seal  56  may comprise, for example, a fixed dynamic seal which is permanently placed in the lower part of compliant guide  22 . In this embodiment, the fluid separation seal  56  opens and closes around the conveyance  42  to let the tool string pass during, for example, deployment. Alternatively, subsea fluid separation seal  56  can be mounted as a retrievable seal which can be conveyed up and down inside the compliant guide  22  together with conveyance  42 . In this latter embodiment, the fluid separation seal is locked in place once it reaches the appropriate locking location within or by the lower end of compliant guide  22 . Furthermore, the pressure within compliant guide  22  can be adjusted to create a desired pressure differential over subsea fluid separation seal  56  to facilitate various intervention operations. Fluid separation seal  56  separates buffer fluid  38  from borehole fluids by sealing against conveyance  42 , e.g. against coiled tubing, coiled rod, wireline, slickline, or other conveyances, while allowing movement of the conveyance  42  into and out of subsea well  46 . 
     The compliant guide  22  also can be used in cooperation with a variety of additional or alternate components that facilitate intervention operations. Some of these components facilitate the conveyance and retrieval of intervention tool string  40  from, for example, deep water locations with a variety of conveyances, including cable-type mechanisms. Other components improve the longevity of the system or aid in carrying out emergency procedures. 
     For example, an emergency disconnect  59  can be provided at surface vessel  26  proximate an upper end  60  of compliant guide  22 . Emergency disconnect  59  has a cutting and sealing capacity to selectively seal off fluid flow. Alternate or additional emergency disconnects can be placed at other locations, such as at or proximate subsea installation  24 . Additionally, a surface stripper assembly  62  can be mounted on surface vessel  26 . Surface stripper assembly  62  may be utilized for well pressure control when subsea lubricating seal  48  is open and communication with subsea well  46  is established for certain tool string deployment sequences. Depending on the operation, a wide variety of other components can be incorporated into the system, including side entry subs, coiled tubing/coiled rod injection heads, connection and disconnection devices for compliant guide  22 , umbilicals and remotely operated vehicles, controls and other components utilized in various intervention operations. 
     In conducting a pressure deployment sequence for a well intervention operation, subsea well  46  is initially closed, and the pressure in compliant guide  22  is released to inflow test, i.e. negative pressure test, subsea lubricating seal  48 . The inflow test ensures the integrity of subsea lubricating seal  48 . Upon successful completion of the inflow test, tool string  40  can be deployed into the upper portion of compliant guide  22 , as best illustrated in  FIG. 2 . In this particular embodiment, the subsea fluid separation seal  56  is deployed with tool string  40 , as illustrated. 
     The tool string  40  and a subsea fluid separation seal  56  are run down through compliant guide  22  to compliant guide subsea lubricator  34  and into proximity with subsea lubricating seal  48 , as illustrated in  FIG. 3 . Because the lower portion of compliant guide  22  functions as the subsea lubricator in whole or in part, tool strings of a wide variety of lengths and configurations can be deployed. Once tool string  40  is properly positioned proximate subsea lubricating seal  48 , the surface stripper assembly  62  is closed and the compliant guide system is pressure tested for integrity. Following successful completion of a positive pressure test, the pressure within compliant guide  22  is adjusted to a pressure generally matching the wellhead pressure at wellhead  44 . The pressure within compliant guide  22  can be adjusted with standard pressure control equipment, for example, mounted on surface vessel  26 . After adjusting the pressure within compliant guide  22 , subsea fluid separation seal  56  is locked in place generally at a lower end of compliant guide  22 , either within or below compliant guide  22 . The subsea fluid separation seal  56  separates wellbore fluids from buffer fluid  38  within compliant guide  22 . 
     Once subsea fluid separation seal  56  is activated, subsea lubricating seal  48  is opened, and tool string  40  is run into subsea well  46  for performance of the planned intervention services, as illustrated best in  FIG. 4 . When the tool string  40  is moved past subsea wellhead  44 , the subsea stripper assembly  52  can be activated and used as the primary seal for controlling the wellbore pressure. After completion of the intervention operation, the tool string  40  is retrieved up through compliant guide  22  by simply reversing the deployment sequence. 
     In this embodiment, use of compliant guide  22  as a subsea lubricator  34  in conjunction with the deployment sequence described reduces the necessary height of or eliminates the need for any standard subsea lubricator. This, in turn, reduces the height of subsea installation  24  which reduces bending forces acting on the subsea installation. Furthermore, the use of compliant guide  22  between surface vessel  26  and the subsea installation eliminates the need for wave motion compensation. The compliant guide also reduces the risk of wellbore fluid leakage to the environment, because any leaks are contained within compliant guide  22  and can be circulated out to the surface vessel  26 . Additionally, medium standard handling equipment can be used for installation of tool string  40  to conveyance  42  which simplifies the deployment process compared to conventional subsea deployment systems. As mentioned above, some applications can be designed to utilize the subsea lubricator  34  as part of other guide components, including flexible risers, hybrid risers, and tensioned risers. 
     Another embodiment of intervention system  20  is illustrated in  FIG. 5 . In this embodiment, a tool entry guide  64  is coupled to subsea installation  24  below compliant guide  22 . Tool entry guide  64  can be used to accommodate deployment of a variety of tool strings, including larger diameter tool strings that can be more difficult to deploy through compliant guide  22 . The tool entry guide  64  comprises a tool entry guide inlet  66  which is located externally of compliant guide  22 . In the embodiment illustrated, an angled tool guide section  68  forms a passageway between inlet  66  and a primary tool guide section  70  generally aligned with the lower portion of compliant guide  22  and subsea well  46 . Tool entry guide  64  further comprises one or more isolation valves  72 , such as the pair of isolation valves  72  positioned at guide inlet  66 . By using tool entry guide  64 , it is not necessary to disconnect compliant guide  22  during deployment of tool string  40  which reduces the pollution risk. Additionally, the ability to maintain connection of the compliant guide decreases the time required for a deployment sequence. 
     In conducting a pressure deployment sequence for a well intervention operation, compliant guide  22  is initially run and connected to tool entry guide  64  via connector  54 . Conveyance  42  along with a tool string connector  74  and subsea fluid separation seal  56  are run through compliant guide  22  to a location generally proximate the top of tool entry guide  64 . Tool string  40  is lowered through the sea via a running line  76 , such as a wireline or a slickline, or a running line dispensed from a crane  78  mounted on surface vessel  26 . The tool string  40  is run externally of compliant guide  22  and into tool entry guide inlet  66 . From inlet  66 , the tool string  40  moves downward along angled tool guide section  68  and generally into primary tool guide section  70 , as illustrated best in  FIG. 6 . 
     Once tool string  40  is positioned in tool entry guide  64 , the tool string is locked in place by a tool lock  80 , as illustrated in  FIG. 7 . Running line  76  is then disconnected and retrieved. The isolation valves  72  are then closed to seal off tool entry guide inlet  66 , and conveyance  42  is lowered until tool string connector  74  engages tool string  40 . 
     The compliant guide  22  is then pressure tested, and tool lock  80  is released following successful pressure testing. At this point, pressure within compliant guide  22  is adjusted until generally balanced with the wellbore pressure. After the desired pressure balance is achieved, the separation seal  56  is activated. When the separation seal  56  is activated, the subsea lubricating seal  48  can be opened, and tool string  40  along with conveyance  42  can be run into subsea well  46 , as illustrated in  FIG. 8 . Upon completion of the desired intervention operation, tool string  40  can be retrieved simply by reversing the above described deployment sequence. 
     Intervention system  20  facilitates deployment of many types of tool strings in a dependable and efficient manner. Use of a lower section of the compliant guide or of a flexible riser as part of or as the entire subsea lubricator greatly improves the intervention procedures with a variety of tool strings. Furthermore, use of the tool entry guide provides further adaptability and other improvements to the intervention operation by readily accommodating other types of tool strings, including larger diameter tool strings. 
     Although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Accordingly, such modifications are intended to be included within the scope of this invention as defined in the claims.