Patent Application
20140034329
This invention regards a system, an arrangement and a method capable of functioning as a backup system to primary rig heave compensator systems.
Subsea wells offshore are typically developed using floating vessels to accommodate equipment, personnel, and operations necessary to drill and complete a well in order to initiate production of hydrocarbons from a given reservoir forming the target for the well. Additionally, testing and intervention work is typically executed through the use of such floating vessels. It is to be understood, however, that such a floating vessel also could be used in context of other types of subsea wells, for example water or gas injection wells.
It is understood that a floating vessel will be subjected to vertical movement due to the action of the waves of the sea (or a lake), which in turn introduces a challenge with respect to equipment utilized during operations carried out on the floating vessel. Such operations may include, but are not limited to, operations of drilling, completion, well testing, and well intervention. During operation at sea, said equipment will be subjected to vertical movement unless compensated for such movement.
As a floating vessel moves up and down in response to the waves, e.g. a drill string and a drill bit extending down below the vessel from a load-bearing structure, such as a top drive located within a drilling rig, will also move up and down.
As it is essential that the weight on the drill bit, i.e. the downward force applied to the bit, is kept as constant as possible, such up and down movements of the drill bit are undesirable and provide for inefficient drilling progress, hence is counterproductive. Heave will remove weight from the drill bit as the rig moves up in conjunction with the high crest of a wave, while weight will be added to the drill bit as the rig moves down into the low point between two waves. Should hydrocarbons start to flow from a reservoir and into a wellbore being drilled, a valve arrangement is utilized to prevent such hydrocarbons from discharging into the natural environment and onto the floating drilling vessel. Such a valve arrangement is commonly referred to as a Blow Out Preventer (BOP), which is capable of sealing around, or cutting and sealing above, a drill pipe cut by shear rams in the BOP.
In other operations, which may include well testing and well intervention, e.g. wireline operations and coiled tubing operations, several sections of a high-pressure riser, commonly referred to as workover riser, are connected between equipment located at the seafloor, such as a subsea wellhead or a subsea Christmas tree, and the floating drilling vessel. The workover riser provides a barrier element for allowing control of pressurized hydrocarbon fluids present in the reservoir, and hence in the wellbore. A subsea valve arrangement, such as a subsea BOP, is also utilized in such operations to provide a system capable of sealing the well in case of an uncontrolled discharge of hydrocarbons from the reservoir. During such operations, hydrocarbon fluids may be present throughout the wellbore and the workover riser, and discharge at surface rig level is typically prevented by means of a valve arrangement located at surface, commonly referred to as a surface flow tree. A surface flow tree, or similar equipment attached to a workover riser, extending upwards from equipment located on the seafloor to the rig, is usually supported by, and kept in tension by, the top drive and drawworks forming part of the drilling rig on a floating drilling vessel. Various types of lifting equipment is utilized to connect the surface flow tree to the top drive, but also to hold the workover riser in tension as required to prevent high loads from acting on the equipment on the seafloor. Such lifting equipment may include, but Is not limited to, rigid bails, tension frames, and soft slings.
Well completion involves the use of production tubulars, which typically extend downwards from the wellhead and the Christmas tree to the producing zones bound by the reservoir(s) targeted by the well(s). Some parts of a completion operation will require equipment to be in tension in a manner similar to that described above. This may comprise setting the upper lock and seal mechanism of the production tubular, commonly referred to as a tubing hanger, inside the wellhead. At this point, a landing string, which is typically made up of several sections of drill pipe, will be connected to said tubing hanger at the wellhead, and also to the top drive at the floating drilling vessel via said lifting equipment. Similar to the description above, the weight of the system is controlled by holding said landing string in tension, thereby maintaining a known force at the level of said tubing hanger.
A vertical movement of a rig, as inflicted by waves of the sea, will impose tensional and compressive forces to said workover riser or landing string and accompanying equipment. These forces may be of a magnitude capable of fracturing or breaking such tubulars or equipment due to stress resulting from these forces.
Such failure may, in turn, carry severe consequences, for example personnel injury and death, due to uncontrolled movement of equipment, or due to discharge of hydrocarbons to the surrounding environment, commonly referred to as a “blowout”, which may also result in permanent pollution to the natural environment.
In order to avoid such potential severe consequences, it is therefore critical to maintain a stationary position of the equipment and tubular strings discussed above with respect to a geodetic point, such as the seafloor. Hence, it is essential that the vertical movement of the rig is compensated for with respect to this stationary equipment when used for various well operations, for example drilling, completion, well testing, and well intervention. Based on this, all floating drilling vessels are equipped with a heave compensation system for ensuring that a load-bearing unit, such as a top drive, is heave-compensated. This implies that all equipment connected to the top drive, such as equipment located on the seafloor, is not unduly subjected to heave-related forces acting on the floating vessel. A functional heave compensation system is therefore critical to protect such equipment from the effects of heave-related, vertical movement of the floating vessel. Contrary, however, an inoperative and/or malfunctioning heave compensation system may allow for transmission of tensional and compressive forces to said equipment during various well operations, which in turn may result in severe consequences, for example failed equipment, personnel injury and death, and/or discharge of hydrocarbons to the environment (i.e. a “blowout”).
It would therefore be advantageous, or even critical in a harsh environment, to provide such a floating vessel with a backup heave compensation system capable of temporarily replacing the main heave compensation system should the main system become Inoperative and/or malfunction.
Floating drilling vessels are generally not equipped with a backup heave compensation system, implying that only one compensation system exists to prevent potential severe consequences of the types described hereinbefore. For this reason, such a floating vessel may therefore comprise a weak link disposed at a known location in the equipment (e.g. a workover riser or a landing string) extending from the drilling rig and down to other equipment (e.g. a subsea BOP) located on the seafloor. Should the main heave compensation system then become inoperative or malfunction during a well operation, the noted weak link will fail so as to prevent failure of critical equipment, such as the subsea BOP, which is required to prevent a blowout should, for example, a workover riser or landing string fail. However, such a weak link arrangement still entails a potential for severe or dramatic consequences, for example failed equipment, personnel injury and death, and/or discharge of hydrocarbons to the surrounding environment.
It would therefore be advantageous, or even critical when in harsh environments, to provide such a floating vessel with a backup heave compensation system capable of temporarily replacing the main heave compensation system should the main system become inoperative and/or malfunctions. Accordingly what is needed is a lifting arrangement capable of being utilized to connect various equipment, for example a surface flow tree or a landing string, to the top drive which is located within the drilling rig. Said lifting equipment further comprises a backup heave compensation apparatus capable of temporarily replacing the primary heave compensation system located on the floating drilling vessel.
US 2005/0077049 A1 appears to represent the closest prior art and discloses an apparatus and a method for protecting against problems associated with the heave of a floating drilling rig. The publication discloses an inline compensator in which a plurality of cylinders and pistons housed within a tubular housing and a plurality of low-pressure and high-pressure accumulators cooperate so as to provide a backup heave compensation system in the event that the primary heave compensation system falls or becomes inoperative. According to this publication, the typical inline compensator utilizes a plurality of hydraulic cylinders that act in opposite directions and that have different piston areas, and such that the piston rods of the cylinders are extended and retracted at different pressure levels to account for heave. More particularly, US 2005/0077049 A1 discloses a pair of inline compensators installed vertically between a hoisting beam and a production head or a surface tree. Parallel piston rods connect the hoisting beam to corresponding pistons within parallel cylinders of the inline compensators, thereby collectively defining a portal structure (or gantry structure). When activated due to inoperation or failure of the primary heave compensation system, this structural arrangement allows the hoisting beam to move up and down as said piston rods move in and out of their respective cylinders to account for heave movements of the floating drilling rig. These undulating, vertical movements of the hoisting beam also imply that the height, or vertical extent, of said portal structure will vary due to heave of the drilling rig. Any equipment rigged up within this portal structure, e.g. wireline equipment, may therefore become adversely affected by such undulating, vertical movements of the hoisting beam. As such, equipment present within the portal structure may collide with the hoisting beam or any other equipment suspended therefrom and/or attached thereto, for example equipment suspended from a hoist attached underneath the hoisting beam. Such adverse affects will obviously provide for an unsafe working environment and potential damage to equipment in vicinity of the inline compensator arrangement.
Further, U.S. Pat. No. 3,208,728 A, U.S. Pat. No. 4,039,177 A and US 2006/0196671 A1 also describe various heave compensation apparatuses for floating drilling or intervention vessels.
The primary objective of the present invention is to remedy or reduce at least one disadvantage of the prior art, or at least to provide a useful alternative to the prior art.
It is also an objective of the invention to provide a backup heave compensation system for the primary rig heave compensation system on a floating drilling vessel. The invention also includes an associated lifting arrangement capable of operating as a backup heave compensator on the drilling vessel. Said backup system is structured in a manner allowing it to be in a static, inoperative position during normal operation of the primary rig heave compensation system. The backup system is also structured In a manner allowing it to become operative, hence allowing it to compensate for heave-related, vertical movements of the floating drilling vessel, should the primary heave compensation system malfunction or become inoperative.
It is further an objective of the present invention to allow for safe handling of said lifting arrangement, but also to allow for safe handling and rig-up of equipment, e.g. wireline equipment, within said lifting arrangement, and by means of lifting and handling equipment associated with the lifting arrangement.
The objectives are achieved by means of features disclosed in the following description and in the subsequent claims.
According to a first aspect of the invention, a backup heave compensation system on a floating drilling vessel is provided. The drilling vessel comprises a rig structure for carrying out well operations in a subsea well, said rig structure comprising a primary heave compensation system operatively connected to a load-bearing structure capable of supporting a tubular structure connected between the floating drilling vessel and the subsea well, said backup heave compensation system comprising:
Each cylinder may also comprise a low-pressure volume located at the opposite side of each piston relative to said high-pressure volume. Said low-pressure volume may contain a gas, for example air, nitrogen or another suitable gas. Further, said low-pressure volume may be vented to the outside, for example to the outside atmosphere or to a low-pressure gas system.
In one embodiment, said load-bearing structure may comprise a top drive.
Moreover, the first and/or the second transverse element of the rigid frame structure may comprise a rigid, transverse beam.
Furthermore, the transverse portal element of the portal structure may comprise a rigid, transverse beam.
Said cylinder-piston arrangement of the lifting arrangement may also comprise a releasable piston locking system structured for selective locking of said pistons in said cylinders, thereby allowing the portal structure to be locked with respect to the frame structure. Such a piston locking system is useful to ensure that the pistons are fixed at a desired position, for example in a mid-position, in the cylinders when the lifting arrangement is in a static, inoperative position in an operational mode, i.e. after the rig-up mode, which is during normal operation of the primary rig heave compensation system. As such, the releasable piston locking system may comprise at least one pressure-containment means structured for selective locking of a given hydraulic pressure in said high-pressure volume of each cylinder. Said pressure-containment means may comprise e.g. a suitable valve means. Further, the piston locking system may comprise at least one mechanical lock structured for selective locking of the pistons to said cylinders. Moreover, said mechanical lock may be hydraulically operated. Yet further, the piston locking system may be operatively connected to said control system for selective control and operation of the piston locking system.
Furthermore, the lifting arrangement of the backup heave compensation system may comprise a releasable frame locking system structured for selective locking of the rigid frame structure to the portal structure when the lifting arrangement is retracted in a rig-up mode. Such a frame locking system is useful to ensure that the piston rods of the portal structure are fixed in a fully retracted state within the cylinders of the frame structure during rig-up. As such, the releasable frame locking system may comprise at least one mechanical lock. Said mechanical lock may be arranged between the rigid frame structure and said transverse portal element of the portal structure, such as shown in
In another embodiment, the portal structure may be positioned above the rigid frame structure so as to form an upper part of said lifting arrangement, whereby the frame structure forms a lower part of the lifting arrangement. When structured in this manner, the transverse portal element of the rigid portal structure may comprise a connection interface for releasable connection to the load-bearing structure of said rig structure.
According to this embodiment, said first transverse element forms an upper transverse element of the frame structure, and said second transverse element forms a lower transverse element of the frame structure;
Further to this embodiment, the frame structure may comprise at least one lifting device for releasable connection to equipment to be lifted with respect to said lifting arrangement. As such, said lifting device may comprise at least one winch. Said lifting device may also be connected to the upper transverse element of the frame structure.
Yet further to this embodiment, the frame structure may comprise at least one movable manipulator arm for guiding equipment to be moved with respect to said lifting arrangement. As such, said movable manipulator arm may be connected to the lower transverse element of the frame structure. As an alternative or addition, said movable manipulator arm may be connected to at least one of said cylinders of the frame structure. According to this embodiment, the frame structure may also comprise a work platform for carrying out various well-related work, for example rig-up work, wireline operations, coiled tubing operations, etc.
In an alternative embodiment, the portal structure may be positioned below the rigid frame structure so as to form a lower part of said lifting arrangement, whereby the frame structure forms an upper part of the lifting arrangement. When structured in this manner, said first transverse element forms an upper transverse element of the frame structure, and said second transverse element forms a lower transverse element of the frame structure;
According to this alternative embodiment, the transverse portal element of the portal structure may form a lower transverse portal element of the portal structure;
Further to this alternative embodiment, said lower transverse element of the frame structure may comprise at least one lifting device for releasable connection to equipment to be lifted with respect to said lifting arrangement. As such, said lifting device may comprise at least one winch.
Yet further to this alternative embodiment, said transverse portal element of the portal structure may comprise at least one movable manipulator arm for guiding equipment to be moved with respect to said lifting arrangement. The frame structure and/or the portal structure may also comprise a work platform for carrying out various well-related work, for example rig-up work, wireline operations, coiled tubing operations, etc.
Said tubular structure, which is connected between the floating drilling vessel and the subsea well, may also comprise e.g. a so-called workover riser or a landing string.
In another embodiment of the backup heave compensation system, said piston rods of the portal structure in the lifting arrangement may be hollow;
According to a second aspect of the invention, a lifting arrangement capable of operating as a backup heave compensator on a floating drilling vessel is provided. The lifting arrangement comprises:
Each cylinder may also comprise a low-pressure volume located at the opposite side of each piston relative to said high-pressure volume. Said low-pressure volume may contain a gas, for example air, nitrogen or another suitable gas. Further, said low-pressure volume may be vented to the outside, for example to the outside atmosphere or to a low-pressure gas system.
The first and/or second transverse element of the rigid frame structure may comprise a rigid, transverse beam.
Moreover, the transverse portal element of the portal structure may comprise a rigid, transverse beam.
Furthermore, said cylinder-piston arrangement may comprise a releasable piston locking system structured for selective locking of said pistons in said cylinders, thereby allowing the portal structure to be locked with respect to the frame structure. Such a piston locking system is useful to ensure that the pistons are fixed at a desired position, for example in a mid-position, in the cylinders when the lifting arrangement is in a static, inoperative position in an operational mode, i.e. after the rig-up mode, which is during normal operation of the primary rig heave compensation system. As such, the releasable piston locking system may comprise at least one pressure-containment means structured for selective locking of a given hydraulic pressure in said high-pressure volume of each cylinder. Said pressure-containment means may comprise e.g. a suitable valve means. Further, the piston locking system may comprise at least one mechanical lock structured for selective locking of the pistons to said cylinders. Said mechanical lock may be hydraulically operated. Yet further, the piston locking system may be structured for connection to said control system for selective control and operation of the piston locking system.
Moreover, the lifting arrangement may comprise a releasable frame locking system structured for selective locking of the rigid frame structure to the portal structure when the lifting arrangement is retracted in a rig-up mode. Such a frame locking system is useful to ensure that the piston rods of the portal structure are fixed in a fully retracted state within the cylinders of the frame structure during rig-up. As such, the releasable frame locking system may comprise at least one mechanical lock. Said mechanical lock may be arranged between the rigid frame structure and said transverse portal element of the portal structure, such as shown in
In one embodiment, the transverse portal element of the portal structure may comprise a connection interface for releasable connection to a load-bearing structure on said floating drilling vessel. According to this embodiment, the second transverse element of the frame structure may also comprise a connection interface for releasable connection to equipment to be lifted via the lifting arrangement. Further to this embodiment, the frame structure may comprise at least one lifting device for releasable connection to equipment to be lifted with respect to the lifting arrangement. As such, said lifting device may comprise at least one winch. Said lifting device may also be connected to the first transverse element of the frame structure.
Yet further to this embodiment, the frame structure may comprise at least one movable manipulator arm for guiding equipment to be moved with respect to the lifting arrangement. As such, said movable manipulator arm may be connected to the second transverse element of the frame structure. As an alternative or addition, said movable manipulator arm may be connected to at least one of said cylinders of the frame structure. According to this embodiment, the frame structure may also comprise a work platform.
In an alternative embodiment, the first transverse element of the frame structure may comprise a connection interface for releasable connection to a load-bearing structure on said floating drilling vessel.
Further to this alternative embodiment, the transverse portal element of the portal structure may comprise a connection Interface for releasable connection to equipment to be lifted via the lifting arrangement.
Yet further to this alternative embodiment, the second transverse element of the frame structure may comprise at least one lifting device for releasable connection to equipment to be lifted with respect to the lifting arrangement. As such, said lifting device may comprise at least one winch.
Furthermore, the transverse portal element of the portal structure may also comprise at least one movable manipulator arm for guiding equipment to be moved with respect to the lifting arrangement. According to this alternative embodiment, the frame structure and/or the portal structure may also comprise a work platform for carrying out various well-related work, for example rig-up work, wireline operations, coiled tubing operations, etc.
In another embodiment of the lifting arrangement, said piston rods of the portal structure may be hollow;
As such, the invention presented herein comprises, among other things, a lifting arrangement to be utilized to connect equipment extending from e.g. a subsea wellhead, or from a Christmas tree, to e.g. a top drive on a floating drilling vessel. Such equipment may be utilized in various well operations, for example well completions, well testing, and well interventions. The invention further comprises a backup heave compensation system capable of being in a static mode or in an operative mode, the modes of which are further controlled by the status of the primary heave compensation system present on a floating drilling vessel. The invention further comprises functionality for ensuring safe handling of the lifting arrangement itself in addition to safe handling and rig-up of equipment placed within the lifting arrangement, such as equipment related to well intervention operations, for example wireline operations and coiled tubing operations.
In one preferred embodiment, the invention comprises a lifting arrangement equipped with a series of components forming parts of a backup heave compensation system and further simplifying rig-up for various well operations, for example well completions, well testing, and well interventions. Further to this preferred embodiment, such components comprise a lower frame part and an upper frame part, the parts of which provide both mutual and individual functionality critical for the objective of the invention. Mutual functionality is related to a backup heave compensation system, while individual functionality is related to components required to allow for safe handling of the lifting arrangement and, additionally, components which allow for safe handling and rig-up of equipment within the lifting arrangement.
In alternative embodiments, the individual functionality of the upper and lower frame parts may be opposite, further meaning that the lifting arrangement still have the same purpose, but components and individual functionality is opposite. However, the mutual functionality related to a backup heave compensation system is the same.
In one embodiment of the present invention, the lower frame is represented by a rigid structure comprising a rigid lower beam, a rigid upper beam, and intermediate rigid legs connecting the upper and lower beams. The rigid legs are shaped as cylinders, each capable of holding a piston-and-rod arrangement within a cylinder, and further to provide required seals and fluid communication ports to accommodate for a hydraulic cylinder system. Further to this embodiment, said upper frame is represented by a rigid structure comprising a rigid upper beam and rigid legs connected to the upper beam. The rigid legs are shaped as piston rods connected each to a piston at the lower end thereof. The piston rods and pistons are shaped so as to fit into the cylinder-shaped legs of the lower frame, thereby forming an extendable frame once the pistons and piston rods are inserted and connected inside the cylinder-shaped legs of the lower frame. The pistons, piston rods, and the cylinders collectively form a hydraulic system capable of being operated and controlled through use of hydraulic means and/or electric means, as understood by one skilled in the art. In this context, electric means may refer to sensing devices used to convey various types of information, for example relative positions of the pistons within the cylinders, and/or pressures within high and low-pressure volumes of said cylinders.
Further to a preferred embodiment, the lower frame may comprise a rigid upper beam, a rigid lower beam, and cylinder-shaped legs comprising components for enabling safe handling of said lifting arrangement during rig-up. The upper and lower beams of the lower frame may be equipped with a hook system capable of holding the weight of the complete lifting arrangement during rig-up, which is beneficial to ensure safe handling. The upper and lower beams are further equipped with lifting points enabling a balanced handling of the complete lifting arrangement according to the invention. The lower rigid beam is equipped with an interface to typical valve arrangements, such as a surface flow tree, and/or equipped with a releasable locking system, which may be operated hydraulically and/or mechanically.
Further to the preferred embodiment, the lower frame may be equipped with components for allowing safe handling and rig-up of equipment within the lifting arrangement described herein. As such, the upper beam of the lower frame may be equipped with one or several winches utilized to lift equipment into and out of the lifting arrangement during well operations, for example wireline operations or coiled tubing operations. One skilled in the art will understand that such a winch may be of a hydraulic type or an electrical type. The lower frame may further comprise a manipulator arm capable of guiding equipment into and out of the frame, further preventing sideways movement and related hazards pertaining to a hanging load. Said manipulator arm will provide vertical, horizontal, and rotational movement. One skilled in the art will understand that such a manipulator arm may be attached to one of the cylinder-shaped legs, or to the lower rigid beam of the lower frame. The lower frame may further comprise a work platform to provide a safe working environment for personnel required during handling of equipment rigged up within the lifting arrangement described herein. In this context, handling may refer to rig-up sequences and also to maintenance of equipment located within and/or being a part of the frame. It should further be noted that the lower frame provides for a predefined distance between the upper and lower rigid beams of the lower frame, which in turn implies that said predefined distance remains unchanged in all situations, including a situation where the upper frame is extended or retracted in relation to the lower frame, which in turn implies that equipment rigged up within the lower frame, for example wireline equipment, will not be affected by the relative movement between the upper and lower frame parts. One skilled in the art will understand benefits related to this predefined distance as it provides for a safe working environment for personnel situated within, and the equipment rigged up within, the lower frame and, further, that collisions are avoided in situations where the upper frame is extended or retracted in relation to the lower frame.
Further to the preferred embodiment, the upper frame may comprise a rigid upper beam and piston rod-shaped legs, and the upper frame may also be equipped with components for allowing safe handling of the lifting arrangement during rig-up. The rigid upper beam may be equipped with a sub shaped to Interface with lifting equipment forming part(s) of the drilling rig, such as an elevator system. Further, the rigid upper beam may be equipped with two connection points shaped to interface with other typical lifting equipment utilized in drilling rigs, such as rigid bails. One skilled in the art will understand the various types of lifting equipment and interfaces described herein.
One skilled in the art will understand that the position of the rigid upper beam of the upper frame can be changed in relation to the rigid upper beam of the lower frame. This change may be carried out by manipulation of a hydraulic system connected to the present piston-cylinder arrangement once the upper and lower frame parts are connected via said piston-and-cylinder components. The lifting arrangement may comprise a releasable frame locking system, e.g. a mechanical frame locking system including one or more releasable mechanical locks, providing a frame locking functionality when the piston is fully retracted into the cylinders, further entailing that the rigid upper beam of the upper frame will be located adjacent to the rigid upper beam of the lower frame. Such a frame locking system and locking functionality can be controlled externally so as to alternate between rig-up mode and operational mode for the lifting arrangement, where each mode may include different mechanical strength ratings. This functionality may be included as it may prove beneficial to allow for a higher mechanical strength during rig-up as compared to an operational setting. It should be noted, however, that different mechanical settings are not a requirement for the invention presented herein, but merely a functionality that may be beneficial in some settings.
The preferred embodiment may further comprise a hydraulic circuit to allow for operation of the hydraulic compensation functionality of the lifting arrangement. One skilled in the art will understand that such a hydraulic circuit can be shaped in various ways, but for the preferred embodiment it is illustrated as follows: the upper side of the pistons represent a high-pressure chamber filled with hydraulic fluid, while the lower side of the piston represent a low-pressure chamber which may be filled with a gas, for example air or nitrogen. The high-pressure chambers are connected to external conduits via flow ports in the top of the cylinders, where said conduits are placed along the external side of the cylinders. Alternatively, the high-pressure chambers may be connected, via the inside of hollow piston rods, to hydraulic conduits connected to flow ports in the top of the piston rods. These conduits are further connected to a manifold and a control system required to operate all system functionality related to the lifting arrangement. It should be noted that winches and manipulator arm part of the lower frame may be connected via the same conduits and control system. The control system described herein may comprise components required for system functionality related to operation of components included therein and for automatic activation of the backup heave compensation system, whereby the mode of the lifting arrangement may be changed from a static mode to a heave compensated mode.
This in turn is related to the operational status of the primary heave compensation system available on the floating drilling vessel. The components in the control system may comprise e.g. pressure and/or temperature sensors, hydraulic valves, safety valves, automated valves, pressure relief valves, and rupture discs, all of which are components understood by one skilled in the art. It should be noted that the control system may be part of the lifting arrangement, but one skilled in the art will understand that such a control system may also be placed in other locations having cabled and/or wireless communication with all relevant conduits and system components.
The control system may be further connected, via a conduit, to an accumulator system and a hydraulic pumping unit which may be placed in a nearby location. The accumulator system may be part of the lifting arrangement or, as described for the preferred embodiment, a separate unit placed at a near location, and further connected to a volume of gas, for example nitrogen bottles or a gas compressor. The accumulator system may comprise one or several cylinder bodies, where each cylinder body may comprise two chambers separated internally by a moving piston arrangement. The lower side of the piston may represent a high-pressure hydraulic fluid chamber connected to the control system of the lifting arrangement via a conduit, while the upper side of the piston may represent a high-pressure gas chamber connected to the volume of pressurized gas described herein. The hydraulic pumping unit will be connected to the control system of the lifting arrangement via a conduit, and the control system can be used to direct hydraulic fluid from the hydraulic pumping unit to all hydraulic systems incorporated in the system represented by the invention herein.
The lifting arrangement may be changed from a rig-up mode to an operational mode by extending the upper frame with respect to the lower frame and into a mid-position, further implying that that the piston parts of the upper frame will be placed in the centre of the cylinder parts of the lower frame. As mentioned above, the lifting arrangement may comprise a mechanical lock to be used during rig-up and handling of the lifting arrangement. By manipulation of the control system, this locking mechanism is opened and followed by pressurizing the accumulators with gas pressure to a predetermined value, which will be in accordance with the weight of the components extending from the rig to the subsea equipment, for example a workover riser. Alternatively, the accumulators are pressurized, as described herein, prior to opening the locking mechanism described herein. The rig-load support element, such as a top drive, is utilized to ensure tension in the system. Once the accumulators are pressurized with gas, the control system is manipulated further to establish hydraulic fluid communication between the cylinder parts of the lifting arrangement and the accumulators, whereupon the mechanical locks can be opened and the top drive can be elevated to extend the hydraulic pistons into a mid-position in the cylinders. System pressure of the lifting arrangement is then tuned to a predetermined value in accordance with the weight of the workover riser and recommended tension, after which the hydraulic fluid communication between the cylinders and accumulator is closed. This procedure ensures that the system is set to an operational mode so as to provide a backup heave compensation system. Operation of the control system may be carried out from a remote location, for example from the driller's cabin.
In a preferred embodiment of the invention, the control system may comprise several stages of functionality related to the automatic activation of the backup heave compensation system, which includes the lifting arrangement. In a situation where a primary heave compensator in a rig cease to operate In a normal manner, vertical movement as inflicted by the waves of the sea will apply compressive and tensional forces to the piston/cylinder arrangements, which in turn will result in pressure decreases and increases, respectively, within a high-pressure volume within the cylinders. A first stage activation comprises components required to sense a positive or negative differential pressure (i.e. pressure difference) exceeding a predetermined value, whereupon an electronic circuit will execute actions necessary to operate a valve so as to allow hydraulic fluid to move between the cylinder parts of the lifting arrangement and the accumulator.
A second stage of the control system may comprise a mechanically operated pressure relief valve which, upon a predetermined pressure change, will open so as to allow hydraulic fluid to move between the cylinder parts of the lifting arrangement and the accumulator.
A third stage of the control system may comprise a mechanical rupture system which, upon a predetermined pressure change, will break so as to allow hydraulic fluid to move between the cylinder parts of the lifting arrangement and the accumulators.
The three stages of automatic activation of the backup system described above will cause the upper frame of the lifting arrangement to move up and down in relation to the lower frame as the floating drilling vessel moves up and down as inflicted by the waves of the sea. In such a situation, the upper rigid beam of the upper frame will move up and down in relation to the upper rigid beam of the lower frame, and hence in relation to the lower frame. The upper rigid beam and lower rigid beam of the lower frame, however, remain stationary in relation to each other, further implying that personnel situated within, and equipment rigged up within, the lower frame, for example wireline personnel and equipment, will not be in danger of collision with any moving parts of the lifting arrangement comprised of the upper and lower frame parts.
One skilled in the art will understand that the description of the control system, and also the operation of the lifting arrangement disclosed herein, is based on the use of one control system and method, but that several other control systems and methods can be utilized to achieve the same system functionality.
The invention will now be described by way of non-limiting embodiments of the invention, referring also to the accompanying figures, in which:
The figures are somewhat schematic and only depict details and equipment necessary for the understanding of the invention. Moreover, the figures may be somewhat distorted with respect to relative dimensions of details and components shown therein. Furthermore, the figures are simplified with respect to the shape and richness in detail of such components and equipment shown therein. Hereinafter, equal, equivalent or corresponding details of the figures will be given substantially the same reference numbers.
Finally, the descriptions and drawings presented herein only represent examples of embodiments related to the invention. Further, any concept, system and method as well as combination(s) of concept(s), system(s) and method(s) described in any text or figure herein could be extended to apply in conjunction or combination with other concepts, systems and methods described in the art. All combinations of concepts, systems and/or methods also comprise part of the objective of the invention. All interfacing, combination and utilisation with existing equipment, techniques and methods also comprise part of the invention.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NO12/50079 | 4/26/2012 | WO | 00 | 9/4/2013 |
| Number | Date | Country | |
|---|---|---|---|
| 61480239 | Apr 2011 | US |
