EP3252263B1

EP3252263B1 - Device and method for drilling a large diameter borehole

Info

Publication number: EP3252263B1
Application number: EP17174261.2A
Authority: EP
Inventors: Anthonius Johannes Maria PROVOOST; Steven Francis Josephine ALEN; Dieter Wim Jan Rabaut
Original assignee: Geosea NV
Current assignee: Deme Offshore Holding NV
Priority date: 2016-06-03
Filing date: 2017-06-02
Publication date: 2019-04-03
Anticipated expiration: 2037-06-02
Also published as: PT3252263T; ES2732779T3; EP3252263A1; DK3252263T3; PL3252263T3; BE1023852B1

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a device and method for drilling a shaft of large diameter in an underwater bottom.
The underwater bottom can for instance consist of rock, clay and/or related materials, and can form part of the sea, of sea arms, streams and rivers, docks, storage reservoirs, access channels to locks or inlet docks. Drilling a shaft of large diameter can for instance be applicable in order to arrange piles in the substrate or to realize piles by filling the shaft with a binder during or after the drilling, and curing this binder.
Of large diameter is understood in the context of this application to mean a shaft diameter of at least 1 m, more preferably of at least 3 m, still more preferably of at least 5 m and most preferably of at least 7m.

BACKGROUND OF THE INVENTION

A known device for drilling a shaft in a substrate comprises a casing tube which can be arranged in the substrate, a drill string which can be lowered into the casing tube and which is provided with a drill head with cutting tools, rotation means for setting the drill string into rotation in the casing tube, and discharge means for the dislodged ground material. Suitable discharge means comprise a water column which is arranged in the casing tube, wherein the dislodged ground material is discharged using a flow maintained in the hollow drill string by the water column and by air bubbles introduced on a lower side. Such an airlift is frequently applied.
The known device is however less suitable for drilling a shaft of large diameter. Not only is a casing tube needed which likewise has a large diameter, the drilling itself and the discharge of the dislodged ground material which is maintained by the flow moreover progress too slowly. Both effects result in a drilling efficiency which is open to improvement. This is particularly the case when drilling has to take place in an underwater bottom which is relatively hard, for instance with a compression strength (Unconfined Compression Strength UCS) of at least 200 MPa.
US 4,742,876 A discloses a device for drilling a shaft in an underwater bottom. The device comprises a drill string to be driven with a drill string drive in the underwater bottom. The drill string is provided at a drilling end with two cutting heads which are rotationally driven. The cutter heads are connected to a horizontal support plate by means of a vertical plate. Discharge means for the cut bottom parts cut are also disclosed.

SUMMARY OF THE INVENTION

The invention has for its object to provide a device and method for drilling a shaft of large diameter in an underwater bottom, which at least partially obviate the above stated and other drawbacks.
The invention provides for this purpose a device according to claim 1. A device is particularly provided for drilling a shaft of large diameter in an underwater bottom, comprising a drill string to be driven into the underwater bottom by means of a drill string drive, wherein the drill string is provided on a drilling end with a support plate which runs transversely of a longitudinal direction of the drill string, is connected non-rotatably to the drilling end and is provided with a number of cutter heads, wherein the cutter heads can be actively driven by means of a cutter head drive and wherein the device further comprises discharge means for the ground portions cut with the cutter heads. The cutter heads are disposed along concentric circles in a peripheral direction (55) of the support plate.
The device according to the invention can have an increased drilling efficiency relative to the known device during drilling of a shaft of large diameter in an underwater bottom. The drill string is for this purpose driven into an underwater bottom with the drill string drive, for instance by setting the drill string and the support plate connected non-rotatably thereto into rotation, wherein the cutter heads provided on the support plate are actively driven with the cutter head drive and wherein the cut ground portions are discharged by the discharge means. The chosen support plate diameter substantially determines the diameter of the drilled shaft. The support plate preferably has a diameter of at least 1 m, more preferably at least 3 m, still more preferably at least 5 m and most preferably at least 7 m.
A further advantage of the device according to the invention is that the use of a casing tube is not necessary in order to achieve a desired drilling efficiency. In the known method it is necessary to arrange a casing tube in order to obtain the desired airlift for discharging the dislodged ground material. In order to obtain the airlift a water column is arranged in the space between the coaxially disposed casing tube and drill string. The water column provides for a pressure difference between the upper side and the lower side of the drill string, whereby a flow is maintained in the space between the drill string and the casing tube, which flow discharges the dislodged ground material to the upper side of the drill string. In order not to lose the water pressure, the casing tube is preferably arranged in a manner such that it admits substantially no water on its lower side. This is problematic, particularly when the casing tube has a large diameter. The invented device needs no casing tube.
For proper operation the cutter heads arranged on the support plate have to be actively driven, although the cutter heads themselves can in principle be selected from many types of cutter head. The active driving ensures that the power required for a good cutting action is utilized where it is needed, i.e. at the position where the bottom is cut. A preferred embodiment of the device according to the invention makes use of cutter heads comprising a revolving body which can be rotated around a rotation axis with the cutter head drive and which is provided along its peripheral surface with a number of cutting tools for penetrating the bottom. In an embodiment the rotation axis of the cutter head runs substantially perpendicularly of the longitudinal direction of the drill string. It is however also possible to provide an embodiment wherein the rotation axis of the cutter head forms an angle other than zero with the longitudinal direction of the drill string.
A further increased drilling efficiency is achieved with an embodiment wherein the revolving body is symmetrical relative to a plane running perpendicularly of the rotation axis and is provided on end surfaces with the cutting tools. The cutting tools preferably run substantially tangentially to a jacket surface of the cutter head.
Drilling efficiency is understood in the context of this application to mean the quantity of ground material which is drilled and discharged per unit of time and per unit of power. Substantially is understood to mean at least 80%, more preferably at least 90%, still more preferably at least 95% and most preferably 100% of the indicated quantity.
peripheral direction (55) According to the invention, the cutter heads are disposed along concentric circles in a peripheral direction (55) of the support plate. The concentric circles may have a diameter amounting to a fraction of the diameter of the support plate, wherein the fraction preferably amounts to between 0-95%, more preferably between 20 and 90%, and most preferably between 50 and 80%. The cutter heads can be distributed regularly over the peripheries of the circles, wherein the number of cutter heads along a periphery can be chosen freely. It is also possible to place cutter heads on only a part of the circle periphery of a concentric circle.
In a useful embodiment the rotation axis of the cutter heads runs substantially perpendicularly of the peripheral direction (55) of the support plate. Cutter heads of two concentric circles are preferably disposed in overlapping manner, which is understood to mean that concentric operational sections of the cutter heads overlap each other. Substantially every ground portion situated under the support plate is hereby actively cut. It is thus possible to distribute the cutter heads over a lower surface of the support plate such that their connections to the support plate run along a helical line.
Because the cutter heads are actively driven in the invented device, the drilling efficiency can be considerably increased, for instance relative to a device wherein, although a rotating support plate is provided, this plate is provided with cutter heads disposed in stationary manner. Such cutter heads are moved through the substrate by the rotation of the support plate, although this takes place at different speeds. A cutter head placed on a concentric circle of relatively large diameter will have a higher throughfeed speed than a cutter head placed on a concentric circle of relatively small diameter. A cutter head placed close to the centre of the support plate will even be almost at a standstill. The invented device enables the rotation speed of the cutter heads to be controlled individually, subject to the position of the cutter head on the support plate. If desired, the design of the cutter heads can also be adapted to the position on the support plate.
The revolving direction of (some of) the cutter heads can be chosen to match the rotation direction of the support plate, so that their rotation speeds add up. It is however also possible to choose the revolving direction of (some of) the cutter heads to oppose the rotation direction of the support plate, so that their rotation speeds partially compensate each other.
In a further embodiment of the device according to the invention the support plate has a thickness direction and the support plate is provided with throughfeed openings running in the thickness direction for throughfeed of a fluid through the support plate. In an embodiment wherein use is made of a casing tube the fluid can comprise a flushing fluid such as for instance water, air, bentonite, mud and/or foam. In an embodiment wherein use is not made of a casing tube the fluid can comprise surrounding water. The openings are intended to create a favourable fluid flow for discharging ground portions cut by the cutter heads to the discharge means. Axes of the throughfeed openings can run substantially perpendicularly of an upper or lower surface of the support plate, but can also form an angle other than zero therewith. In addition to the throughfeed openings, the rotating cutter heads can themselves also have an effect on the fluid flow such that it is suctioned in the direction of the discharge means.
In a suitable embodiment a device is provided wherein the discharge means comprise throughfeed conduits for the ground portions cut with the cutter heads, which conduits debouch from a lower side of the support plate into a discharge conduit running through the drill string, or in an intermediate space of the drill string and a casing tube arranged therearound, as far as a discharge side situated above water. The throughfeed conduits run through the support plate in the thickness direction of the support plate.
The discharge conduit debouches on a discharge side thereof into a discharge part running transversely of the longitudinal direction of the drill string in a preferred embodiment of the device. The discharge part protruding transversely of the drill string ensures that the discharged cut ground portions come to lie adjacently of the drill string and can be collected in or on a storage location suitable for this purpose. The discharge part is preferably coupled to the discharge conduit by means of a rotating seal which holds the discharge part stationary. In this embodiment the discharge conduit co-rotates with the drill string, but the discharge part is held stationary.
In order to enable the cut ground portions to be suctioned in through the throughfeed conduits of the support plate, in an embodiment of the invention the discharge means comprise a pump mounted on the lower side of the drill string and connected to the discharge and throughfeed conduits. The throughfeed conduits are connected here to a suction side of the pump, while the discharge conduit is connected to a pressure side of the pump. Suitable pumps comprise the usual dredge pumps.
The drive means have to be supplied with a suitable power. Suitable powers for driving the pump (or pumps) which discharge the cut ground portions to a discharge side which generally lies higher than the pump comprise at least 500 kW and usually 1000 kW and more. Suitable powers for driving the cutter heads on the support plate comprises at least 1500 kW and usually 2000 kW and more. To enable such relatively great powers to be transmitted to the pump(s) and cutter heads arranged on or in the vicinity of the support plate an embodiment of the device is characterized in that an upper side of the drill string is provided with a work platform which co-rotates with the drill string and is therefore connected non-rotatably to the drill string. The work platform preferably comprises the drive means for the drill string and is also provided with power units for the discharge means and/or for the cutter heads. In this embodiment these power means co-rotate with the drill string, which allows great powers to be transmitted to the discharge means, such as the pump, and to the cutter heads. This measure further increases the drilling efficiency.
The device according to the invention is particularly suitable for use under water, wherein the device is placed on a suitable floating device. A suitable embodiment comprises a jack-up platform provided with the device according to the invention. A jack-up platform is placed on an underwater bottom using spud poles, and thus forms a more stable support for the device than for instance a vessel or pontoon.
An embodiment of the jack-up platform further comprises a moon pool through which the drill string can be lowered, and lifting means for lifting and lowering the drill string. It is however also possible to lower the drill string onto or into the underwater bottom adjacently of the work deck of the jack-up platform, for instance from a lattice structure suspended from the work deck over a side edge.
The drill string can be displaced in a longitudinal direction of the drill string relative to the work deck using suitable means. It is thus possible the suspend the drill string from a lifting crane provided on the work deck. It is however advantageous to provide an embodiment of the jack-up platform which, in addition to lifting means, also comprises securing means for fixing the drill string in a longitudinal position relative to the work deck. This can for instance be done with a rack and pinion or with hydraulic cylinders, or a combination of such means.
In yet another embodiment the jack-up platform further comprises a power unit for the drill string drive.
The device and method according to the invention are applied in particularly advantageous manner for drilling shafts of large diameter in a substrate with a UCS (unconfined compression strength) of 5-150 MPa.
Finally, it is stated that the embodiments of the invention described in this patent application can be combined in any possible combination of these embodiments, and that each embodiment can individually form the subject-matter of a divisional patent application.

BRIEF DESCRIPTION OF THE FIGURES

Other details and advantages of the invention will become apparent from the following description of an embodiment of the device for drilling a shaft in an underwater bottom. This description is given solely by way of example, without the invention being limited thereto. The reference numerals relate to the accompanying figures. In the figures:

Figure 1 is a schematic side view of a device according to the invention;
Figure 2 is a schematic bottom view of a support plate provided with cutter heads according to an embodiment of the invention; and
Figure 3 is a schematic detail view of the embodiment shown in figure 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring to figure 1, a device 1 is shown for drilling a shaft 100 of large diameter 101 in a bottom 102 lying under the water level 103. The bottom 102 preferably comprises rock, but can also comprise clay and/or related materials. Bottom 102 for instance has a compression strength of 230-350 MPa. The shaft can for instance have a diameter 101 of 7-10 m and more.
Device 1 comprises a drill string 2 which can be set into rotation in rotation direction 21 by means of a drill string drive in the form of a drilling table 20 provided with hydraulic motors 23. In order to transmit rotation torques the jacket surface of drill string 2 is provided with a number of strips 24 which are distributed over the jacket surface in the peripheral direction (55) and which can be received in recesses (not shown) of drilling table 20. Drill string 2 runs in a vertical direction 22 in a moon pool 30 of work deck 31 of a jack-up platform 3 (not fully shown) and into bottom 102, and can be moved in the vertical direction 22 by means of lifting means connected to work deck 31 and taking the form of vertically directed hydraulic cylinders 32. Hydraulic cylinders 32 are each connected on a side where they are pushed out to a support collar 33 which is releasably connected to drill string 2. Pushing out or retracting hydraulic cylinders 32 enables drill string 2 to be moved up and downward, as shown by arrows 34. In the shown embodiment the releasable connection between support collar 33 and drill string 2 comprises securing means in the form of a number of pins 35 which engage on or in the outer wall of the drill string for the purpose of anchoring. Moving pins 35 away from drill string 2 and toward drill string 2 as according to arrows 36 enables the drill string to be uncoupled from and coupled to support collar 33. A connection between work deck 31 and drill string 2 is obtained in the same way via securing means in the form of pins 37 connected to work deck 3 and movable as according to arrows 38. With pins 35 in coupled state and pins 37 in uncoupled state, drill string 2 can be moved in vertical direction 22, for instance in order to penetrate the bottom 102. With pins 35 in uncoupled state and pins 37 in coupled state drill string 2 can be connected to work deck 31 in a fixed vertical position.
Work deck 31 of jack-up platform 3 further comprises a power unit 43 which supplies the hydraulic pressure oil for the drive means (20, 23). Work deck 31 can also be provided with a control room 44 from which the different components of the device are controlled. The control preferably takes place radiographically, shown symbolically with numeral 45.
An upper side of drill string 2 is provided with a work platform 4 which co-rotates with drill string 2. Work platform 4 is for this purpose rigidly connected to an upper side of drill string 2 using transverse plates 40. Arranged on work platform 4 are the drive means (20, 23) for drill string 2, as well as power units (41, 42) for cutter heads 6 to be further discussed hereinbelow and for discharge means for the cut ground portions, likewise to be further discussed hereinbelow. The power units (41, 42) preferably supply a great power in the order of magnitude of respectively 2000 kW and 1000 kW for the hydraulic components. Work platform 4 co-rotates with drill string 2 in order to enable such power to be supplied hydraulically to the lower side of drill string 2.
Drill string 2 is provided on a drilling end (lower side) with a support plate 5 running transversely of a longitudinal direction 25 of drill string 2, connected non-rotatably to the drilling end and provided on a bottom surface with a number of cutter heads 6. Cutter heads 6 can be actively driven with a cutter head drive in the form of hydraulic motors 50. The power is supplied from work platform 4 by power unit 41 and supplied via hydraulic conduits 26 running in drill string 2 to hydraulic motors 50.
Device 1 also comprises discharge means for the ground portions cut with cutter heads 6. The discharge means comprise throughfeed conduits 70 (see figure 3) which debouch from a lower side of support plate 5 into a discharge conduit 71, this running through drill string 2 as far as a discharge side 72 lying above the water surface 103. The discharge means further comprise a pump 73 which is mounted on the lower side of drill string 2 and is connected to the discharge and throughfeed conduits, and which suctions in a mixture of water and cut ground portions through throughfeed conduits 70 and upward through discharge conduit 71 as according to arrows 74, wherein the mixture leaves the discharge conduit via the discharge side as according to arrow 76. In order to support the flow to throughfeed conduits 70 support plate 5 is provided with throughfeed openings 52 provided over the thickness of support plate 51 for throughfeed of surrounding water through support plate 5 as according to arrows 53.
In order to support discharge conduit 71 during drilling, drill string 2 is provided with a number of ribs which are disposed distributed in axial direction and which connect an outer surface of discharge conduit 71 to the inner wall of drill string 2. Discharge side 72 of discharge conduit 71 comprises a discharge part 77 which runs transversely of the longitudinal direction 25 of drill string 2 and is coupled to discharge conduit 71 by means of a rotating seal 78. This seal 78 corotating partially with drill string 2 ensures that discharge part 77 is held stationary and does not co-rotate with drill string 2.
As is shown particularly clearly in figure 3, in the shown embodiment cutter heads 6 are embodied as a revolving body which is rotated around a rotation axis 60 with the cutter head drive (41, 26, 50). Provided along the peripheral surface of each cutter head 6 are cutting tools 61 which penetrate the underwater bottom during use. The rotation axes 60 of cutter heads 6 run substantially perpendicularly of the longitudinal direction 25 of drill string 2, as is shown clearly in figure 2. According to figure 3, rotation axes 60 of cutter heads 6 run substantially in radial directions 54 of support plate 5. The revolving body is symmetrical relative to a central plane 62 running perpendicularly of the rotation axis and is provided on end surfaces with cutting tools 61, which in the shown embodiment run substantially perpendicularly of the jacket surface of each cutter head 6.
Cutter heads 6 are arranged along concentric circles 56a, 56b in a peripheral direction 55 of support plate 5, wherein rotation axis 60 of cutter heads 6 runs perpendicularly of the peripheral direction 55 of support plate 5. Cutter heads 6 of two concentric circles 56a, 56b are disposed in overlapping manner, which indicates that an operational area of a cutter head 6 overlaps with an operational area of a cutter head on an adjacent concentric circle. The operational area of a cutter head 6 comprises the part of the revolving body on which cutting tools 61 are situated.
By setting drill string 2 into rotation on the upper side thereof and pushing it downward with hydraulic cylinders 34 the support plate 5 provided with cutter heads 6 is likewise set into rotation and driven into the underwater bottom, wherein the ground is dislodged by the action of cutting tools 61. Although drill string 2 runs substantially vertically in the shown figures, it can if desired be adjusted to any angle relative to the bottom surface or relative to jack-up platform work deck 31. During drilling surrounding water situated in the already drilled trench 100 will be suctioned in via the throughfeed openings 52 of support plate 5 by pump 73. Because of the pressure difference caused by pump 73 between the inlet and outlet side of the pump, the surrounding water and dislodged ground portions entrained herein flow via throughfeed conduits 70 and into discharge conduit 71 in the direction indicated with arrows 74. An upward flow is thus maintained in discharge conduit 71 of drill string 2, in which flow the dislodged ground portions are discharged to the upper side of drill string 2. In order to further improve the discharge of the dislodged ground portions air can optionally be injected into discharge conduit 71, preferably at a position lying higher relative to pump 73.
The invented device and method are particularly suitable for drilling a shaft of relatively large diameter in cohesive substrates, for instance in order to form and/or arrange foundation piles therein.
The invention is not limited to the embodiment described here, and many modifications could be made thereto, to the extent these modifications fall within the scope of the appended claims.

Claims

Device (1) for drilling a shaft (100) of large diameter (101) in an underwater bottom (102), comprising a drill string (2) to be driven into the underwater bottom (102) by means of a drill string drive (50), wherein the drill string (2) is provided on a drilling end with a support plate (5) which runs transversely of a longitudinal direction (25) of the drill string (2), is connected non-rotatably to the drilling end and is provided with a number of cutter heads (6), wherein the cutter heads (6) can be actively driven by means of a cutter head drive (50) and wherein the device (1) further comprises discharge means (70, 71, 73) for the ground portions cut with the cutter heads (6), wherein the cutter heads (6) are disposed along concentric circles (56a, 56b) in a peripheral direction of the support plate (5).
Device (1) according to claim 1, wherein the cutter heads (6) comprise a revolving body which can be rotated around a rotation axis with the cutter head drive (50) and which is provided along its peripheral surface with a number of cutting tools for penetrating the bottom (102).
Device (1) according to claim 2, wherein the revolving body is symmetrical relative to a plane running perpendicularly of the rotation axis and is provided on end surfaces with the cutting tools.
Device (1) according to claim 2 or 3, wherein the cutting tools run substantially perpendicularly of a jacket surface of the cutter head.
Device (1) according to any one of the foregoing claims, wherein the rotation axis of the cutter heads (6) runs substantially perpendicularly of the peripheral direction of the support plate (5).
Device (1) according to any one of the foregoing claims, wherein cutter heads (6) of two concentric circles (56a, 56b) are disposed in overlapping manner.
Device (1) according to any one of the foregoing claims, wherein the support plate (5) has a thickness direction and is provided with throughfeed openings running in the thickness direction for throughfeed of a fluid, preferably surrounding water, through the support plate (5).
Device (1) according to any one of the foregoing claims, wherein the discharge means (70, 71, 73) comprise throughfeed conduits for the ground portions cut with the cutter heads (6), which conduits debouch from a lower side of the support plate (5) into a discharge conduit running through the drill string (2) as far as a discharge side situated above water.
Device (1) according to claim 8, wherein the discharge side of the discharge conduit comprises a discharge part running transversely of the longitudinal direction (25) of the drill string (2).
Device (1) according to claim 9, wherein the discharge part is coupled to the discharge conduit by means of a rotating seal which holds the discharge part stationary.
Device (1) according to any one of the foregoing claims, wherein the discharge means (70, 71, 73) comprise a pump mounted on the lower side of the drill string (2) and connected to the discharge and throughfeed conduits.
Device (1) according to any one of the foregoing claims, wherein an upper side of the drill string (2) is provided with a work platform (4) which co-rotates with the drill string (2).
Device (1) according to claim 12, wherein the work platform (4) comprises the drive means for the drill string (2) and power units for the discharge means (70, 71, 73) and/or for the cutter heads (6).
Jack-up platform provided with a device (1) according to any one of the foregoing claims.