WO2014173457A1

WO2014173457A1 - Drilling derrick

Info

Publication number: WO2014173457A1
Application number: PCT/EP2013/058747
Authority: WO
Inventors: Eirik Strøm UTHAUG; Arne GÜRTNER; Ola Ravndal
Original assignee: Statoil Petroleum As
Priority date: 2013-04-26
Filing date: 2013-04-26
Publication date: 2014-10-30

Abstract

A method of positioning a drilling derrick on a floating drilling vessel, the method comprising: dynamically translating the drilling derrick on the floating drilling vessel in response to a detected translation of the floating drilling vessel with respect to a location on a sea bed for compensating for the translation of the floating drilling vessel with respect to the sea bed.

Description

Drilling Derrick

TECHNICAL FIELD The invention relates to the field of drilling operations and to drilling operations from floating mobile offshore drilling vessels.

BACKGROUND Drilling operations in water with medium to shallow depths, which is roughly between 50 and 500 meters, be carried out from moored semi-submersed vessels such as drilling vessels. During a drilling operation, the drilling vessel stays in substantially the same position with respect to the sea bed to avoid tension or bending of a drill string extending from the vessel to the sea bed. In deeper waters, which corresponds to a depth of roughly more than 500 meters, a drill vessel may be kept in substantially the same position with respect to the sea bed using dynamic positioning with the vessel's propellers and rudders. In water with a depth of less than 100 meters, a so-called jack- up platform may be used, which is a platform which has a plurality of legs which can be placed on the sea bed and which can support a platform on an elevated position above the water surface.

SUMMARY

It is an object of the present invention to provide a mobile offshore drilling vessel whereby a drilling derrick is substantially stationary with respect to a location at the sea bed.

According to a first aspect, there is provided a method of positioning a drilling derrick on a floating drilling vessel, the method comprising: dynamically translating the drilling derrick on the floating drilling vessel in response to a detected translation of the floating drilling vessel with respect to a location on a sea bed for compensating for the translation of the floating drilling vessel with respect to the sea bed. The step of translating may comprise translating the derrick in a horizontal plane and may further comprise moving the drilling derrick along any of a first axis and a second axis, wherein the first and second axes are independent of each other. The method may further comprise determining a location of the floating drilling vessel with respect to the location on the sea bed; and calculating a required translation of the drilling derrick with respect to the floating drilling vessel. A Global Positioning System may be used to determine a location of the floating drilling vessel with respect to the location on the sea bed.

According to a second aspect, there is provided a positioning assembly for positioning a drilling derrick on a floating drilling vessel, the positioning assembly being arranged to receive the derrick, and further being arranged to be coupled to the floating drilling vessel, such that in use the drilling derrick is translatable with respect to the floating drilling vessel.

The drilling derrick may be translatable in a substantially horizontal plane. The positioning assembly may comprise a first portion and a second portion, wherein the first portion received the drilling derrick and is movably connected to the second portion, and wherein the second portion is movably connected to the floating drilling vessel such that the first portion and the second portion are movable in two independent directions with respect to the floating drilling vessel. The first portion may be movable along first guiding rails provided on the second portion and the second portion may be movable along second guiding rails provided on the floating drilling vessel.

The first and second guiding rails may be substantially perpendicular to each other. The positioning assembly may further comprise one or more actuators for moving the first and second portions.

The positioning assembly may further comprise: a sensor for detecting a location of the floating drilling vessel; a computer device for determining a required movement of the drilling derrick with respect to the floating drilling vessel in response to the sensed location of the drilling vessel; the computer device being further arranged to instruct the translation of the drilling derrick with respect to the floating drilling vessel. According to a third aspect, there is provided a computer device comprising: a receiver for receiving location data relating to a floating drilling vessel; a processor for determining a required location of a drilling derrick relative to the floating drilling vessel in response to the location of the floating drilling vessel; and a transmitter for sending instructions to translate the drilling derrick relative to the floating drilling vessel.

The instructed translation of the drilling derrick relative to the floating drilling vessel may be in a horizontal plane. The instructed translation of the drilling derrick relative to the floating drilling vessel may comprise a first axis component and a second axis component. The location data relating to a floating drilling vessel may comprise Global Positioning System data.

According to a fourth aspect, there is provided a computer program comprising non- transitory computer readable code which, when run on a computer device, causes the computer device to behave as a computer device according to the method as described above.

According to a fifth aspect, there is provided a computer program product comprising a non-transitory computer readable medium and a computer program as described above, wherein the computer program is stored on the non-transitory computer readable medium.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 illustrates schematically a perspective view of a drilling derrick on a movable platform.

Figure 2 illustrates schematically a side view of a drilling derrick with a drilling riser extending to the sea bed.

Figure 3 is a flow diagram showing exemplary steps for positioning a drilling derrick on a vessel.

Figure 4 illustrates schematically in a block diagram an exemplary computer device. DETAILED DESCRIPTION

Drilling operations in water with medium to shallow depths may be carried out from moored semi-submersed vessels such as drilling vessels. During a drilling operation, the drilling vessel maintains substantially the same position with respect to the sea bed to avoid tension or bending of a drill string extending from the vessel to the sea bed. At shallower depths, small variations from the position over the well head can lead to large angular deflections of a drill string. In water with a depth of less than 100 meters, a so-called jack-up platform is generally used, which is a platform which has a plurality of legs which can be placed on the sea bed and which can support a platform on an elevated position above the water surface. The hull of a jack-up platform is not in direct contact with the water during use and is therefore not affected by the movement of the water. However, jack-up platforms suffer from ice loading in arctic waters, and the forces generated by ice can damage the jack-up platform. Jack-up platforms can therefore typically not be used during cold seasons when ice is expected.

During drilling, a drill string extends from a drilling vessel to a fixed position at the sea bed such as a blow-out preventer (BOP). In shallow water, a relative motion of a drilling vessel with respect to the sea bed will more quickly give rise to a large deflection angle of the drill string with respect to a vertical orientation when compared to deeper waters in which the distance to the sea bed is larger. In order to protect the integrity of both the well head and the BOP, there are restrictions on how the drilling string connecting the drilling rig to the BOP may move with respect to the sea bed. A typical limit for the offset of the drill string relative to the vertical is around 1 degree. The motion of a drilling vessel relative to the well head can be restricted by dynamic positioning, whereby the vessel's propellers and rudders are used to keep the vessel substantially stationary with respect to the well head, or by mooring lines which anchor the vessel to the sea bed.

In ice infested waters, large forces are applied by the ice onto a vessel and it would be difficult to compensate for these forces completely with dynamic positioning or with anchoring systems. A jack-up drilling vessel generally cannot be used in ice infested waters because it may be unable to withstand the forces acting upon it owing to ice loading. The inventors have appreciated that the position of a drilling derrick with respect to the drilling vessel may be actively controlled to compensate for a movement of the drilling vessel with respect to the sea bed. Active control would also allow for drilling from a drilling vessel which motion is not compensated for through either dynamic positioning or mooring systems. A drilling derrick which is movable with respect to the drilling vessel enables the use of floating drilling vessels in ice operations at water depths of less than 100 meters, also when no mooring or anchoring system is able to secure a vessel in a substantially fixed position with respect to the seabed to allow drilling operations from floaters.

The drilling derrick is installed on a positioning assembly on the drilling vessel at the top of an opening through which a drill string extends towards the sea bed. This opening is also called the moon pool area of a drilling vessel. The positioning assembly on which the derrick is mounted may be adapted to move the derrick in a substantially horizontal plane to compensate for horizontal offsets of the vessel from its intended position. The compensation may keep the drill string offset angle within acceptable limits for the BOP and top hole of the well, even where movement of the vessel would otherwise take the drill string offset angle outside acceptable limits.

An embodiment of the invention is illustrated in Figure 1. A drilling derrick (1 ) is translatably mounted via a positioning assembly on a vessel (2). A drill string extends from the drilling derrick to the sea bed through a moon pool area (3) of the vessel. Translation in horizontal plane is achieved in this embodiment by two platforms (4, 5) which make up the positioning assembly and are movable in two respective independent directions in the plane of the vessel. The first platform (4) is translatable along a first axis (X) with respect to the second platform (5). The connection between the first and second platform may be in the form wheels or sliders which are guided by guide rails. A metal on metal slider is one specific example of a connection, whereby the interface between two metal surfaces is provided with a high pressure lubricant to enable sliding. The high pressure lubricant provides effectively a hydrodynamic bearing. The second platform (5) is connected to the hull of the vessel by way of wheels or sliders which are guided by a second set of guide rails (6). The second platform (5) is movable along a second axis (Y) which is perpendicular to the first axis (X). The motion of the drilling derrick with respect to the vessel is restricted by the size of the moon pool.

By dynamically moving the derrick on the two platforms 4, 5 to compensate for movement of the vessel, the derrick can be maintained in a location substantially above the well head to minimize the angle of deflection of the drill string.

The motion of the drilling derrick with respect to the vessel may be actively controlled. A sensor may detect a motion of the vessel or may anticipate a motion of the vessel as a result of ice movement. As a result of the detected or anticipated movement, actuators are arranged to move the first and second platforms to compensate for the movement such that the drilling derrick stays substantially in the same position with respect to the sea bed. The angle of the drilling riser may thus be kept constant, or at least be reduced to fall within acceptable limits.

In addition to the controlled motion in the plane of the vessel, active heave compensation may be used for reducing or eliminating the motion of the vessel in vertical direction due to wave motion using known heave compensation techniques. The control system may thus reduce the motion of the riser containing the drill string and a resulting tension in the riser.

The present invention enables drilling operations in ice infested areas in general and in particular in ice infested areas with a shallow depth, such as a depth of 40 to 100 meters.

Figure 2 illustrates schematically a drilling derrick (1 ) positioned on a vessel (2) with a drilling riser (7) extending through a moon pool area (3) towards the sea bed (10). The vessel floats at the surface of the sea (9). The derrick is placed on a platform (4, 5) which is movable with respect to the ship (2). The platform is capable of compensating for the motion of the ship in the direction indicated with an arrow A, thereby reducing the deflection angle and keeping the indicated angle a between the riser and the sea bed close to 90°. The deviation from this straight angle, also referred to as the offset angle, is preferably below 1 degree and more preferably substantially zero. Figure 3 is a flow diagram showing exemplary steps for dynamically positioning a drilling derrick. The following numbering corresponds to that of Figure 3:

51 . The drilling vessel carrying the drilling derrick is positioned above a fixed position on the sea bed corresponding to a well.

52. A location of the vessel relative to the fixed position is detected. This may be done, for example using GPS positioning techniques. Motion of the vessel by wave or ice loading action can therefore be accurately measured.

53. The location data of the vessel is processed by a computer device and a desired location of the derrick is calculated to compensate for the location of the vessel. S4. The computer device sends signals to the actuators controlling the platforms of the positioning assembly to move in order to maintain the derrick in its required location above the well head.

Figure 4 illustrates schematically in a block diagram a computer device (15) that is arranged to control positioning of the drilling derrick. The computer device is provided with a processor (16) and a receiver (17) for receiving signals from positioning sensors in order to determine the precise location of the vessel relative to the well head at the sea bed. On the basis of the received location, the processor determines how to move the derrick on the positioning assembly in order to maintain its location substantially above the well head at the sea bed. A transmitter (18) is provided for sending positioning signals to actuators that can move the positioning assembly to ensure that the derrick remains in the required position.

A non-transitory computer readable medium in the form of a memory (19) may also be provided that can be used to store data. It may also be used to store a computer program (20) which, when executed by the processor, causes the computer device to behave as described above. The techniques described above can be used in combination with existing dynamic positioning or anchoring systems. It allows the use of floating drilling vessels, particularly in shallow arctic waters, even where ice loading may be expected. It will be appreciated by a person of skill in the art that various modifications may be made to the above described embodiments without departing from the scope of the present disclosure. Different embodiments have been described above, but the skilled person will readily be able to devise other options for moving the drilling derrick with respect to the vessel in response to a motion of the vessel.

Claims

CLAIMS:

1 . A method of positioning a drilling derrick on a floating drilling vessel, the method comprising:

dynamically translating the drilling derrick on the floating drilling vessel in response to a detected translation of the floating drilling vessel with respect to a location on a sea bed for compensating for the translation of the floating drilling vessel with respect to the sea bed.

2. The method according to claim 1 , wherein translating comprises translating the derrick in a horizontal plane.

3. The method according to claim 1 or 2, wherein translating comprises moving the drilling derrick along any of a first axis and a second axis, wherein the first and second axes are independent of each other.

4. The method according to any one of claims 1 , 2 or 3, further comprising:

determining a location of the floating drilling vessel with respect to the location on the sea bed; and

calculating a required translation of the drilling derrick with respect to the floating drilling vessel.

5. The method according to claim 4, further comprising using a Global Positioning System to determine a location of the floating drilling vessel with respect to the location on the sea bed.

6. A positioning assembly for positioning a drilling derrick on a floating drilling vessel, the positioning assembly being arranged to receive the derrick, and further being arranged to be coupled to the floating drilling vessel, such that in use the drilling derrick is dynamically translatable with respect to the floating drilling vessel.

7. The positioning assembly according to claim 6 wherein the drilling derrick is translatable in a substantially horizontal plane.

8. The positioning assembly according to claim 6 or 7, wherein the positioning assembly comprises a first portion and a second portion, wherein the first portion received the drilling derrick and is movably connected to the second portion, and wherein the second portion is movably connected to the floating drilling vessel such that the first portion and the second portion are movable in two independent directions with respect to the floating drilling vessel.

9. The positioning assembly according to claim 8, wherein the first portion is movable along first guiding rails provided on the second portion and wherein the second portion is movable along second guiding rails provided on the floating drilling vessel.

10. The positioning assembly according to claim 9, wherein the first and second guiding rails are substantially perpendicular to each other.

1 1 . The positioning assembly according to any one of claims 6 to 10, wherein the positioning assembly further comprises one or more actuators for moving the first and second portions.

12. The positioning assembly according to any one of claims 6 to 1 1 , wherein the positioning assembly further comprises:

a sensor for detecting a location of the floating drilling vessel;

a computer device for determining a required movement of the drilling derrick with respect to the floating drilling vessel in response to the sensed location of the drilling vessel;

the computer device being further arranged to instruct the translation of the drilling derrick with respect to the floating drilling vessel.

13. A computer device comprising:

a receiver for receiving location data relating to a floating drilling vessel;

a processor for determining a required location of a drilling derrick relative to the floating drilling vessel in response to the location of the floating drilling vessel; and a transmitter for sending instructions to dynamically translate the drilling derrick relative to the floating drilling vessel.

14. The computer device according to claim 13, wherein the instructed translation of the drilling derrick relative to the floating drilling vessel is in a horizontal plane.

15. The computer device according to claim 13 or 14, wherein the instructed translation of the drilling derrick relative to the floating drilling vessel comprises a first axis component and a second axis component.

16. The computer device according to any one of claims 13 to 16, wherein the location data relating to a floating drilling vessel comprises Global Positioning System data.

17. A computer program comprising non-transitory computer readable code which, when run on a computer device, causes the computer device to behave as a computer device according to any one of claims 13 to 16.

18. A computer program product comprising a non-transitory computer readable medium and a computer program according to claim 17, wherein the computer program is stored on the non-transitory computer readable medium.