Patent Application
20080185153
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.
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. However, the cost of platforms is high and the availability of vessels capable of adequately performing intervention work is limited.
A variety of existing techniques are currently used for intervention work. In shallow waters, for example, 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. Because existing non-rig intervention capability is limited to shallow water wireline and slick line operations, most intervention on subsea wells is currently performed with expensive and scarce heavy drilling units.
In general, the present invention provides a technique for subsea intervention operations. An intervention vessel is coupled with a subsea well system via a compliant guide. The structure and arrangement of the compliant guide enables passage of a variety of intervention tools and a variety of conveyance mechanisms to facilitate performance of intervention operations. The intervention operations can be performed on, for example, a subsea well or a subsea flowline.
Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and:
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 or subsea flowlines. The technique enables intervention tools to be conveyed via different methods of conveyance through a compliant guide, such as a spoolable compliant guide, that is coupled between the subsea installation and a vessel on the sea surface. The technique also enables the use of a variety of conveyances in non-rig deep water interventions.
Intervention tools are conveyed from the surface vessel and through the compliant guide to an entry point of the subsea installation which may be located on the seabed. For tools or completion components having a larger outside diameter, a subsea lubricator can be used for deployment. A dynamic seal is positioned to prevent well fluids from entering the compliant guide, thus reducing concerns related to incursion of hydrocarbons into the compliant guide. The technique and utilization of the compliant guide enables subsea intervention in a variety of different scenarios, with a variety of different intervention tools, and with a variety of interchangeable conveyance systems.
The compliant guide is arranged to accommodate flexible conveyance systems of the type that are generally unsuitable for transmitting a pushing force, e.g. a cable-type conveyance system. This enables the use of cable-type conveyance systems, e.g. wireline or slickline conveyance systems, in deep water intervention operations. The compliant guide is flexible and can undergo dynamic and temporary (or long-term) changes in shape to facilitate tool string passage when the tool string is coupled to a flexible conveyance system.
The ability to use different conveyances or to interchange conveyances during a given operation greatly enhances the adaptability of the present system to a variety of intervention environments and operations. When starting an intervention job, the execution of certain operations depends on the real state of the subsea installation determined once access is gained to the installation. During the planning stage of the intervention, an intervention team considers all possible scenarios and defines contingency plans to handle unexpected conditions. The present compliant guide intervention technique provides the intervention team with great flexibility in conveying a variety of intervention tools with a variety of conveyances to the subsea installation.
By way of example, a conventional seabed “carousel system” would require that all intervention tools for the carousel be identified and loaded into the system before the system is lowered to the bottom of the sea. The present technique, however, provides a relatively simple way of conveying tools, thereby enabling the changing of intervention tools at the surface and the conveyance of those tools through the compliant guide to the subsea installation. This provides intervention operations that are faster and more efficient while reducing the risks involved with subsea connections and disconnections. Additionally, the ability to change conveyances also can greatly increase the efficiency of the overall intervention operation. For example, if after gaining access to the subsea well and attempting an intervention operation with one type of conveyance, the intervention team may determine the operation would be more successful with another type of conveyance. In this scenario, the present technique allows the conveyance to simply be changed and used with the same compliant guide rather than requiring changing out all of the equipment involved. The use of a single system for different conveyances also reduces deck space requirements for the surface vessel.
Coupling a compliant guide between the subsea installation and the surface vessel also eliminates the need for motion compensation systems often otherwise required to compensate for the relative movement of the surface vessel with respect to the subsea installation. This again simplifies the operating procedures and further reduces the deck space requirements of the surface intervention vessel.
The use of an enclosed compliant guide also enables faster run-in of intervention tools. The operator can run the intervention tools to the subsea installation at higher speeds without having to worry about the actual path followed by the tool string and the conveyance and without having to deploy remotely operated vehicles to guide the tool string into a lubricator of the subsea installation. Furthermore, placement of a dynamic seal at the bottom of the compliant guide reduces the risk of environmental contamination. In the event a small leak passes through the dynamic seal, the fluid is contained and isolated within the compliant guide. Additionally, the enclosed compliant guide allows control over the pressure within the guide through the use of surface pressure control equipment so as to reduce the pressure differential across the dynamic seal. This enables the construction of a simpler dynamic seal.
The compliant guide system also lowers the risk of pollution because the operator does not need to disconnect for each tool change out. Furthermore, the compliant guide is capable of resolving the problem of subsea grease injection as the use of the compliant guide under pressure allows an operator to benefit from a low pressure differential and thus work wit a much simpler seal below the surface. On-surface grease injection can be utilized to seal in high pressure differential applications.
Referring generally to
Compliant guide 22 is flexible and may be arranged in a variety of curvilinear shapes extending between intervention vessel 26 and subsea installation 24. For example, compliant guide 22 may be arranged generally in a serpentine or S-shape that curves along radii selected to facilitate the passage of intervention tools and conveyances. Compliant guide 22 also 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.
Once compliant guide 22 is coupled between subsea installation 24 and intervention vessel 26, intervention tools 32 may be conveyed from intervention vessel 26 down through compliant guide 22 and subsea installation 24 via a conveyance 34. The compliant guide 22 also provides the path along which the intervention tool or tools 32 can be retrieved to the surface. For example, an intervention tool or tool string 32 can be delivered to the subsea installation and upon completion of a specific intervention operation, the tool 32 can be retrieved to the surface and interchanged with another intervention tool or tool string. This process is readily repeated as many times as necessary to complete the entire intervention operation.
Conveyance 34 may be a flexible, cable-type conveyance, such as a wireline or slickline. However conveyance 34 also may comprise stiffer mechanisms including coiled tubing and coil rod. When a cable-type conveyance 34 is used to convey intervention tool string 32, compliant guide 22 is arranged to facilitate passage of the intervention tool string 32 without requiring a pushing force. In other words, the curvilinear configuration of compliant guide 22 is readily adjustable via, for example, locating intervention vessel 26 so as to avoid bends or deviated sections that could interfere with the gravity induced passage of intervention tools 32. The flexibility of compliant guide 22 enables its configuration to be adjusted, if necessary, simply by moving intervention vessel 26 in an appropriate direction, e.g. a direction as indicated by one of the arrows 36 or 38. Dynamic changes can temporarily be made to compliant guide 22 to change the shape of the compliant guide for facilitating the passage of a tool string. In some applications, a tractor 40 also can be used to pull the conveyance through compliant guide 22. The tractor 40 can be included in tool string 32.
Although a variety of subsea installations 24 can be utilized depending on the particular environment and type of intervention operation, one example is illustrated in
In the embodiment illustrated, dynamic seal 46 is generally positioned at the top end of a subsea lubricator 52 of subsea installation 24. In some applications, a lower portion of compliant guide 22 also can be utilized as part of the lubricator to enable the use of much longer tool strings and/or a reduction in length of subsea lubricator 52. By way of example, the dynamic seal 46 can be attached at the lower end of compliant guide 22, or it can be mounted at the top of the subsea lubricator 52. In some embodiments having the dynamic seal combined with a closed environment of the compliant guide 22 reduces or eliminates the need for a subsea grease injection system when using a flexible conveyance 34, e.g. an electric line or braided line conveyance. It also should be noted that subsea lubricator 52 can be used to deploy tools that have a relatively large outside diameter.
Subsea installation 24 also may comprise a variety of additional components. As illustrated, subsea installation 24 comprises a lubricating valve 54 that may be deployed directly above subsea wellhead 42. Lubricating valve 54 can be used to close the borehole of subsea well 44 during certain intervention operations, such as tools change outs. A blowout preventor 56 may be positioned above lubricating valve 54 and may comprise one or more cut-and-seal rams 58 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 a second blowout preventor 60 positioned above blowout preventor 56 and comprising one or more sealing rams 62 able to seal against the conveyance 34. Additionally, an emergency disconnect device 64 may be located at a suitable location above blowout prevent or 60. Emergency disconnect device 64 can be used when the operator desires to perform an emergency disconnection at the subsea installation 24.
The compliant guide 22 also can be used in cooperation with a variety of components that facilitate intervention operations. Some of these components facilitate the conveyance and retrieval of intervention tools 32 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, a dynamic seal 66 can be positioned at or above an upper end 68 of compliant guide 22. Dynamic seal 66 enables the selective pressurization of fluid 50 disposed in interior 48 of compliant guide 22. As described above, the ability to pressurize fluid 50 enables, for example, control over differential pressures exerted on subsea dynamic seal 46, thereby improving the life of the seal and/or lowering the required functional specifications for the seal.
An emergency disconnection device 70 also can be disposed at upper end 68 of compliant guide 22. The emergency disconnection device 70 comprises cut and seal capabilities to enable disconnection from the compliant guide 22 while providing positive pressure sealing at the upper end of the compliant guide. In this embodiment, the emergency disconnection device 70 comprises a buoyant member 72. A buoyant member 72 maintains upper end 68 of compliant guide 22 suspended in the water for later retrieval by intervention vessel 26 once the emergency disconnection situation is over and intervention operations can resume.
One or more swivel connections also can be formed along compliant guide 22. For some applications, the swivel connections can be used to reduce or eliminate torque applied by compliant guide 22 to the subsea installation 24. Additionally, the one or more swivel connections extend the operating envelope for intervention vessel 26. For example, the ability of compliant guide 22 to swivel enables intervention vessel 26 to adjust the configuration of compliant guide 22 and/or to orient itself in a desired direction. The intervention vessel can be turned to orient itself with its bow against the wind, waves and currents and to deploy the serpentine, i.e. S-shaped, compliant guide 22 in any direction with respect to subsea installation 24. The desired orientation of the compliant guide may change from one intervention operation to another or during a given intervention operation depending parameters, such as current, subsea obstacles, surface obstacles and other environmental factors. By way of example, a swivel 74 can be located proximate a bottom end 76 of compliant guide 22, and a swivel 78 can be positioned proximate upper end 68 of compliant guide 22. One alternative configuration is to locate a single swivel 80 generally in a middle region of compliant guide 22.
In one embodiment, compliant guide 22 is arranged to facilitate conveyance of intervention tools 32 with cable-type conveyances 34 by connecting upper end 68 to intervention vessel 26 and suspending a relatively long section of the compliant guide below the intervention vessel. Closer to the bottom end 76 of compliant guide 22, a flotation device 82 is attached to the compliant guide to provide an upward, buoyant force. This maintains compliant guide 22 in a generally serpentine or S-shaped configuration conducive to the passage of intervention tools 32 to a deep water location or other subsea installation location. The flotation device or devices 82 maybe clamped or otherwise fastened to the compliant guide to maintain the curvature of the compliant guide within a desired range without creating any bends having radii shorter than desired for suitable passage of intervention tools 32. The flotation device or devices 82 can be designed as bending stiffeners to further maintain a desired curvature through at least a section of compliant guide 22. One or more bend restrictors 84 also can be combined with compliant guide 22 to help prevent undue bending of the compliant guide. For example, a bend restrictor 84 can be installed on the vessel side of compliant guide 22 proximate, for example, upper end 68. In configurations such as those illustrated, the compliant guide 22 can be utilized in a variety of environments without requiring tethers.
For some intervention operations, a return hose 86 (shown in dashed lines) can be used to enable procedures that benefit from movement of fluids. For example, return hose 86 can be used to circulate fluids through compliant guide 22, to flush the compliant guide, to pump tools up or down within the compliant guide, and for other fluid based procedures. In many of these applications, the return hose 86 is connected between the Christmas tree 42 and appropriate fluid tanks and/or manifolds on the intervention vessel 26.
In the embodiment illustrated in
Intervention system 20 and compliant guide 22 can be adapted to a variety of intervention operations and environments. In each of these cases, the system enables a more efficient overall operation and adaptation to changing parameters. The intervention system 20 enables the interchangeability of a variety of intervention tools and intervention conveyances. Additionally, the system facilitates the use of cable-type conveyances and other flexible conveyances for conveying intervention tools to a variety of locations, including deep water locations. The configuration of the compliant guide also can be adjusted during or between intervention operations.
Accordingly, 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.
