LOCKING MECHANISM
A device for heave compensation of a tool unit that is suspended via one or more wires from a mast mounted on a platform, each wire at a first end being attached to the mast via an attachment and running via a first heave compensation unit, and each wire at a second end being attached to a second heave compensation unit that is connected to the tool unit. The second heave compensation unit includes a movable compensation mechanism, which at its first end is attached to the wire and which at its second end is attached to the tool unit. The second heave compensation unit includes a releasable locking device with which the motions of the compensation mechanism can be selectively prevented and allowed.
The invention relates to well operations, especially in connection with production of hydrocarbons from underground formations. More specifically, the invention relates to a device for heave compensation of equipment on a moving vessel, as disclosed in the preamble of the independent claims.
BACKGROUND OF THE INVENTIONDuring the recovery of hydrocarbons from wells in underground formations, the operator must sometimes carry out work in the wells. Such work may be maintenance or other technical operations, such as perforating, replacing or reperforating pipes, changing flow regulators, isolating production zones, monitoring production and logging pressure, flow and temperature. A motivating factor for the work is to increase the recovery rate of the well. This work, which is referred to by the collective term ‘well intervention’, is difficult to perform from conventional surface platforms, especially when subsea wells are involved. It is well known that subsea wells are less maintained than platform wells and hence have lower recovery rates. It is therefore desirable to have systems that are suitable for maintenance of subsea wells.
A distinction is made between light well intervention and heavy well intervention. Today, light well intervention is carried out with the aid of wireline operations from a ship. Heavy well intervention (which includes the whole spectrum of intervention work) is usually carried out from a special moored, semi-submersible rig that is connected to the wells via a riser (pipe for gas and/or liquid). The special rig fills the gap between the ordinary drilling rigs and the vessels that carry out light well intervention using wireline operations, and has, inter alia, substantially lower costs than an ordinary drilling rig.
To further optimise costs, it is therefore desirable that such special rigs are of maximum flexibility, such that, for example, in addition to carrying out heavy well intervention they can also carry out light well intervention using wireline-operated tools.
Known floating intervention rigs have a drilling machine suspended from a tower via a heave compensation system for compensating for wave motions, which may comprise a combined hoisting and compensation cylinder. The tower and the cylinder are mounted on deck. In an ordinary device, the drilling machine is suspended from wires (so-called drill line), which run over guide pulleys at the top of the mast, via reversing pulleys at the top of the cylinder, to a fixed point at the top of the mast. The drilling machine can therefore be hoisted up and down by moving the cylinder, and the cylinder also compensates—within certain tolerances—for the motions of the rig such that the drilling machine is kept as steady as possible when carrying out intervention operations. A combined hoisting and compensation cylinder of this kind is capable of handling large loads, typically in the order of 250 tonnes.
This device is used, for example, when landing large weights on the seabed or inside the drilling riser, as well as during drilling, and can be operated in passive or active compensation mode when there is a need for greater accuracy and control of the compensation.
The prior art comprises WO 2007/145503 A1, which describes a device and a method for heave compensation. A mast is mounted on a floating vessel, a first compensation means that is attached via wire means on one side of the mast, and the other end of the wire means is further connected to a second heave compensation means attached to a tool unit for carrying out drilling operations. The second heave compensation means and the tool unit are moved along guide rails in the mast with the aid of dollies/lever arms.
There are stringent requirements as regards the ability of the well intervention rig to—very accurately—compensate for the movements of the rig. Heave compensation requirements are often concretised as an ability to compensate weight change, positioning accuracy and speed limitation. In known well intervention rigs, however, the size of the combined hoisting and compensation cylinder, and the friction in the guide pulleys and reversing pulleys make it difficult to satisfy one or more of these requirements. There is therefore a need for a device that is capable of obtaining greater accuracy in heave compensation than is the case with known well intervention rigs. The invention meets this need and has other advantages in addition.
SUMMARY OF THE INVENTIONTherefore, a device is provided for heave compensation of a tool unit which is suspended via one or more wire means in a mast mounted on a platform, each wire means at a first end being attached to the mast via an attachment and running via a first heave compensation unit, and each wire means at its other end being attached to a second heave compensation unit that is connected to the tool unit, characterised in that the second heave compensation unit comprises a movable compensation means which at its first end is attached to the wire means and which at its second end is attached to the tool unit, and that the second heave compensation unit comprises a releasable locking means with which the motions of the compensation means can selectively be prevented and allowed.
In an embodiment, the compensation means is attached to the wire means via a connecting unit and is attached to the tool unit via a link element, the connecting unit and the link element being movable in relation to one another, and where the locking means is movable for selectively and releasably limiting the motions of the connecting unit and the link element in relation to one another.
In an embodiment, the locking means comprises a locking bolt with a central, narrowed portion and broad shoulder portions at each end of the bolt.
In an embodiment, the link element comprises a through hole having a first portion and a second portion, the first portion having a larger opening than the second portion. The first portion has a dimension that allows passage of the shoulder portions whilst the second portion has a dimension that does not allow passage of the shoulder portions, but does allow passage of the central portion. In an embodiment, the first portion has a circular cross-section and the second portion is elongate.
In an embodiment, the wire means runs between the second heave compensation unit and the first heave compensation unit via guide pulleys that are mounted at an upper part of the mast, and run via the first heave compensation unit between the guide pulleys and the attachment in the mast.
In an embodiment, the first heave compensation unit is connected at a first end to the platform and at a second end is movably attached to said wire means via reversing pulleys and a cylinder.
In an embodiment, the device comprises locking means with which the movements of the compensation units can selectively be prevented, and the compensation units transfer loads between the tool unit and the wire unit as substantially rigid bodies.
In an embodiment, the first heave compensation unit functions as an active heave compensator whilst the second heave compensation unit functions as a passive heave compensator.
In an embodiment, the second heave compensation unit is an integral part of the tool unit. The first and second heave compensation units are preferably hydraulically operated.
The second heave compensation unit can quickly and simply be installed on any drilling machine, without structural modifications of the drilling machine.
These and other characteristic features of the invention will be elucidated in the following description of preferred, non-limiting embodiments, with reference to the accompanying schematic drawings, wherein:
With reference to
In the illustrated embodiments, the mast is constructed of a lattice structure in a known way, and will therefore not be described in more detail here. Similarly, the heave compensation units are driven by fluid reservoirs, regulating valves and systems, gas tanks and hydraulic power units. These components are well known to the skilled person and are therefore not referred to in more detail here.
The mast is equipped with guide rails 9 for a drilling machine 11 in a known way. Furthermore, with reference to
Three embodiments of the compensator are described below.
First EmbodimentReferring to
The cylinders 22a,b are equipped with a lock 23 with which the cylinders can be locked in the retracted position when the system is not in use. The load from the drilling machine 11 is transferred to the lifting wires via the cylinders 22a,b and the connecting link 24.
Fluid reservoirs and control units for the heave compensation cylinders 22a,b are in accordance with the prior art and are therefore not discussed in more detail here.
Second EmbodimentReferring to
The cylinder 27 is equipped with lock 23 with which the cylinders can be locked in collapsed position when the compensator 20′ is not in use. The load from the drilling machine 11 is transferred to the hoisting wires via the cylinder 27 and the connecting link 28.
The
With reference to
The connecting piece 32, to which the compensator cylinder 31 and the wires 6 are fastened, comprise two plate elements 32a,b arranged spaced apart and fastened together by means of upper bolts 81 and lower bolts 83. The lock 30, with its hydraulic actuating mechanism, is also attached to the connecting piece (hydraulic connecting lines are not shown, as they are prior art). The lock 30 comprises a housing 30′ with a locking bolt 87, a locking bolt cylinder 88 and a position sensor 89 for the locking bolt. The locking bolt 87 has a central narrowed portion 87b, and broad portions (flanges) 87a at each end.
In this illustrated embodiment, the link element 33 also has a plate form, and is disposed between the plate elements 32a,b of the connecting piece in such a way as to be movable. The cylinder rod 26 of the compensator cylinder 31 (whose housing is fastened to the connecting piece) is secured to the link element 33 via a fastening bolt 84. The link element 33 is provided with a through “keyhole” 82, which is adapted for receiving the locking bolt 87. The keyhole 82 is elongate and has a lower portion 82a that has a larger opening than the above-lying, slightly narrower portion 82b of the keyhole.
The broad end portions 87a of the locking bolt 87 have a cross-sectional dimension that allows passage through the lower, broad portion 82a of the keyhole and into the respective support holes 37 in the side plates 32a,b, but does not allow passage through the above-lying portion 82b. The central, narrowed portion 87b of the locking bolt has a cross-sectional dimension that allows movement of the locking bolt up and down in the keyhole, also in the slightly narrower portion 82b.
The task of the compensator 21″ is to hold tool that has been lowered into the well in an accurate position without subjecting equipment installed in the well to weights greater than typically ±500 kg whilst the main heave compensation is in progress with the aid of the combined hoisting and heave compensation cylinder 4, with associated accumulator tanks and other necessary, known equipment (not shown). The compensator 21″ with compensation cylinder 31 takes the “peaks” of the damping from the main compensator 4.
The compensator 21″ may thus have at least the following two functions:
- a) Damping/minimising vertical motion and controlling/minimising load against components inside the well from tools that may be lowered down into it; and
- b) Reducing the load between the shaft of the drilling machine and the top of the drill pipe when they are to be screwed together (thread-saver).
Although the compensator 21″ is described here as being made up of a lower link element 33 that is movably arranged between the two side plates 32a,b of the connecting piece 32, the invention should not be limited to such designs, as a variant may be an inverted configuration where the lower link element has two side plates and the connecting piece comprises one element that is movably arranged therebetween. The invention should also not be limited to plate-shaped elements.
Features Common to the EmbodimentsThe combined hoisting and heave compensation cylinder 4 and associated components (in the following also referred to as Stage 1) are used when landing large loads on the seabed or inside the drilling riser, and during drilling. In such situations, the compensator 20; 20′; 20″ is not necessarily in use, i.e., the cylinders are locked via their respective locking mechanisms 23; 30.
For heave compensation, Stage 1 can be operated in passive compensation mode or in active compensation mode.
In situations where greater accuracy and control of the compensation are required, as for example, during well intervention, Stage 1 will be operated in active compensation mode. Stage 1 will therefore be able to achieve heave compensation down to a certain minimum level.
The compensator 20; 20′; 20″ (in the following also referred to as Stage 2) is used together with Stage 1 in order to further increase sensitivity and accuracy, and to ensure that the power of the drilling machine does not exceed a defined minimum value. Stage 2 then functions as a passive heave compensator. The compensator in Stage 2, which may have a relatively short stroke length, is constructed such that the cylinder piston is held stationary until loaded with a predefined weight. When such a predefined weight has been reached, the compensator in Stage 2 will compensate by either retracting or extending the cylinder rod 26.
Examples of situations in which the need for a Stage 2 is present include landing of lighter equipment within the casing and subsea safety valves.
A two-stage heave compensator of this kind can thus—very accurately—compensate for the motions of the rig. Within given operational parameters (e.g., max heave motion of rig), Stage 1 and Stage 2 in combination can compensate for a relatively small weight change and obtain major positioning accuracy at a limited speed. As mentioned above, a combined hoisting and compensation cylinder can typically handle loads of the order of 250 tonnes. In such a connection, a relatively small weight change may be of the order of ±500 kg, and the positioning accuracy can be of the order of ±10 cm.
Stage 1 can handle large loads and most of the heave. The compensator 20; 20′; 20″ (Stage 2) is however substantially smaller than Stage 1 and thus generates less packing friction. In addition, the compensator in Stage 2 is located on top of the drilling machine 11 such that it does not take with it other friction than that in the compensator 20; 20′; 20″, and possibly some from the well.
The compensator 20; 20′; 20″ is thus able to reduce the load amplitude from Stage 1 to a load oscillation that is within the requirement for weight change compensation.
The device according to the invention functions in this way as a two-stage heave compensator, where the combined hoisting and heave compensation cylinder 4 (Stage 1) handles the large loads, whilst the compensator 20; 20′; 20″ (Stage 2, which has better sensitivity and greater accuracy) is able to compensate for loads that are smaller than Stage 1 is adapted to compensate for.
In an embodiment, the load for which the compensator 20; 20′; 20″ is designed to compensate may be of the order of 8-10% of the load capacity of the hoisting system.
It will be appreciated that the device for heave compensation can be used for purposes other than well intervention.
The numerical values in the description above have been included to illustrate the application of the invention, and should not be regarded as a limitation of the invention.
Claims
1. A device for heave compensation of a tool unit that is suspended via one or more wires from a mast mounted on a platform, each wire at a first end being attached to the mast via an attachment and running via a first heave compensation unit, and each wire at a second end being attached to a second heave compensation unit that is connected to the tool unit,
- wherein the second heave compensation unit comprises a movable compensation mechanism, which at its first end is attached to the one or more wires and which at its second end is attached to the tool unit, and the second heave compensation unit comprises a releasable a locking device with which the motions of the compensation mechanism can be selectively prevented and allowed.
2. The device as disclosed in claim 1, wherein the compensation mechanism is attached to the one or more wires via a connecting unit and is attached to the tool unit via a link element, and wherein the connecting unit and the link element are movable in relation to one another, and wherein the releasable locking device is movable for selectively and releasably limiting the motions of the connecting unit and the link element in relation to one another.
3. The device as disclosed in claim 2, wherein the releasable locking device comprises a locking bolt with a central, narrowed portion and broad shoulder portions at each end of the bolt.
4. The device as disclosed in claim 2, wherein the link element comprises a through hole with a first portion and a second portion, the first portion having a larger opening than the second portion.
5. The device according to claim 4, wherein the first portion has a dimension that allows passage of the shoulder portions whilst the second portion has a dimension that does not allow passage of the shoulder portions but does allow passage of the central portion.
6. The device according to claim 4, wherein the first portion has a circular cross section and the second portion is elongate.
7. The device as disclosed in claim 1, wherein said one or more wires between the second heave compensation unit and the first heave compensation unit runs via guide pulleys which are mounted at an upper portion of the mast, and run via the first heave compensation unit between the guide pulleys and the attachment in the mast.
8. The device as disclosed in claim 1, wherein the first heave compensation unit is connected at a first end to the platform and at a second end is movably attached to the one or more wires via reversing pulleys and a cylinder.
9. The device as disclosed in claim 1, comprising a locking mechanism with which the motions of the compensation units can selectively be prevented and the compensation units transfer loads between the tool unit and the one or more wires as substantially rigid bodies.
10. The device as disclosed in claim 1, wherein the first heave compensation unit functions as an active heave compensator whilst the second heave compensation unit functions as a passive heave compensator.
11. The device as disclosed in claim 3, wherein the link element comprises a through hole with a first portion and a second portion, the first portion having a larger opening than the second portion.
12. The device according to claim 5, wherein the first portion has a circular cross section and the second portion is elongate.
13. The device as disclosed in claim 2, wherein the first heave compensation unit is connected at a first end to the platform and at a second end is movably attached to the one or more wires via reversing pulleys and a cylinder.
14. The device as disclosed in claim 2, comprising a locking mechanism with which the motions of the compensation unit scan selectively be prevented and the compensation units transfer loads between the tool unit and the one or more wires as substantially rigid bodies.
15. The device as disclosed in claim 3, comprising a locking mechanism with which the motions of the compensation unit scan selectively be prevented and the compensation units transfer loads between the tool unit and the one or more wires as substantially rigid bodies.
16. The device as disclosed in claim 4, comprising a locking mechanism with which the motions of the compensation unit scan selectively be prevented and the compensation units transfer loads between the tool unit and the one or more wires as substantially rigid bodies.
17. The device as disclosed in claim 5, comprising a locking mechanism with which the motions of the compensation unit scan selectively be prevented and the compensation units transfer loads between the tool unit and the one or more wires as substantially rigid bodies.
18. The device as disclosed in claim 6, comprising a locking mechanism with which the motions of the compensation unit scan selectively be prevented and the compensation units transfer loads between the tool unit and the one or more wires as substantially rigid bodies.
19. The device as disclosed in claim 7, comprising a locking mechanism with which the motions of the compensation unit scan selectively be prevented and the compensation units transfer loads between the tool unit and the one or more wires as substantially rigid bodies.
20. The device as disclosed in claim 8, comprising a locking mechanism with which the motions of the compensation unit scan selectively be prevented and the compensation units transfer loads between the tool unit and the one or more wires as substantially rigid bodies.
Type: Application
Filed: Oct 11, 2012
Publication Date: Aug 28, 2014
Inventor: Gjerulf Ottersland (Kristiansand)
Application Number: 14/351,098
International Classification: E21B 15/02 (20060101);