Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DRILLING APPARATUS AND METHOD FOR PRODUCING A BORE
The invention relates to a drilling apparatus for producing a bore in the
bottom of a body
of water from a floating platform which is exposed to lifting motions, in
particular a wave
motion of the body of water, with a drilling drive for applying a torque, a
drill string com-
prising at least one drill string element, which is displaceable in the axial
direction rela-
tive to the drilling drive and comprises at least one abutment strip extending
in axial di-
rection, which is in engagement with the drilling drive and/or at least one
abutment strip
of an adjacent drill string element for torque transmission for the formation
of a contact
surface, and a carrier device along which the drill string is substantially
vertically dis-
placeable, according to the generic term of patent claim 1.
The invention furthermore relates to a method for producing a bore in the
bottom of a
body of water from a floating platform which is exposed to lifting motions, in
particular a
wave motion of the body of water, in which a drilling drive applies a torque
to a drill
string, wherein the drill string comprises at least one drill string element
which is dis-
placeable in an axial direction, the torque is transmitted from the drilling
drive and/or an
abutment strip of an adjacent drill string element by means of at least one
abutments
strip extending in the axial direction, whereby during the drilling operation
a contact sur-
face is formed at the at least one abutment strip, according to the generic
term of patent
claim 8.
Bores in the bottom of a body of water can be easily implemented by a drilling
appa-
ratus from a floating platform, in particular a ship, a pontoon or a floating
barge. In case
of the floating platform undesired motions of the drilling apparatus relative
to the bore
hole may occur, which is problematic for a secure and precise implementation
of the
bore. The motions can thereby occur in parallel and/or perpendicularly to the
bore hole
axis. The motions of a floating platform that can be exposed on a body of
water in par-
ticular to wave motions and/or tidal movements can be several decimeters to
some me-
ters high.
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In order to balance out wave motions, it is known from EP 1 103 459 Al or US
5,209,302 to provide controlled positioning cylinders. However, construction-
wise this is
very complex. Further drilling devices with compensators for balancing out
wave mo-
tions are disclosed in US 3,917,006 A or US 3,653,636 A.
For producing a bore in the bottom of a body of water often a kelly drilling
method is
applied. In this drilling method, a drilling apparatus with a kelly bar is
used, which is a
telescopic boring bar. The kelly bar, at which a drilling tool is located in a
lower area,
can thereby compensate length variations during the drilling operation.
In case of a floating use of the kelly drilling method for drilling in the
bottom of a body of
water from a floating platform, problems with the wave motions may occur as
well, if the
axial displacement is blocked. If the distance between the borehole bottom or
the drilling
tool, respectively, and the drilling apparatus caused by wave motions is
reduced, a high
bending load of the kelly bar may occur in the drilling operation. This
problematic bend-
ing stress may lead to an overstress of the telescopic drill string that is
detrimental for
the material on the one hand, and on the other hand to an irregular detaching
of soil
material at the borehole bottom. Even damage in the drilling apparatus and
hazard to
the platform may occur.
The invention is based on the object of providing a drilling apparatus and a
method
for producing a bore, in particular in a bottom of a body of water from a
floating platform,
by which drilling can be implemented particularly efficiently and non-
destructive.
On the one hand, the object is solved according to the invention by a drilling
apparatus
comprising the features of the claim 1, and on the other hand with a method
for produc-
ing a bore with the features of the claim 8. Preferred embodiments of the
invention are
specified in the respective dependent claims.
The drilling apparatus according to the invention is characterized in that a
control unit is
provided, which is designed to control and reduce the torque of the drilling
drive during
the drilling operation to a threshold value at which the at least one drill
string element is
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further axially displaceable to compensate for lifting motions when there is
friction on the
contact surface.
A basic idea of the invention is to compensate relative movements of the
drilling appa-
ratus relative to the borehole bottom by a reliable extension and retraction
of the drill
string. The drill string can be a single rod with only one drill string
element or be com-
posed of several drill string elements, in particular through a screw
connection. The
torque transmission takes place from the abutment elements at the drilling
drive to the
abutment strips of the drill string. The invention is thereby based on the
finding that dur-
ing the drilling operation high compression forces are exerted on the axial
abutment
strips in the circumferential direction. This leads to correspondingly high
adhesive and
friction forces, so that an axial displacement of the drill string element can
be blocked.
The reliable displacement is achieved according to the invention in that the
friction at
the contact surfaces of the drill string element is controlled and reduced to
an extent
that suffices for the method. Thereby, the reduction of the friction is
achieved by reduc-
ing the torque, which is provided for the compression force and thus the
adhesive / fric-
tion force at the contact surfaces. The invention constitutes so to speak an
ABS system,
i.e. an anti-blocking system, for drill strings. In this way it is made
possible to reliably
compensate for example a lifting motion of the body of water in the axial
direction of the
drill string. Overstresses are thus avoided. However, the invention can also
be applied
in drilling onshore.
Lifting motions for the present invention can principally mean all movements
in an axial
direction of a drill string, which change the distance between a drilling
apparatus and a
borehole bottom during a bore process. The movements can principally have any
ampli-
tude and frequency, though they can be individual, irregular, recurring or
periodical. The
movements can also be regular and thus predictable, or coincidental. The axial
direction
may define an axial direction upward and/or downward.
A carrier device of a drilling apparatus as provided in the invention may
particularly also
be understood as drill mast or as a drill carriage.
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A contact surface may exist between the drilling drive and a drill string
element and/or
between the neighboring drill string elements. These may consist of several
contact par-
tial surfaces between the individual abutment strips that are in contact with
each other.
A threshold value at which the torque of the drilling drive can be reduced may
be zero or
even negative in order to shortly counter an undesired torsion. Preferably a
torque value
is defined with which the friction at the contact surfaces of the drill string
is reduced to a
sufficient extent in order to compensate for lifting motions.
In the area of the contact surface preferably a means for reducing the
friction is provid-
ed. This may be the arranging of a friction-reducing material or a
particularly smooth-
surface processing of the abutment strip. Alternatively or additionally, a
lubrication de-
vice is provided, which is preferably designed to supply oil or lubricating
grease to the
contact surface.
A particularly preferred embodiment of the invention is present when a
detector unit is
provided, which is designed to recognize the lifting motions. The detector
unit can
thereby be positioned on the floating platform or the drilling apparatus which
is located
on the floating platform. The detector unit may preferably be a linear
acceleration sen-
sor, which particularly determines accelerations in the axial direction of the
drill string.
From the measured accelerations, speeds and position changes regarding the
move-
ments in the axial direction can be determined by integration by the detector
unit as
such and/or an analysis unit connected to said detector unit. The detector
unit may also
be located in an immobile place, in particular onshore, and determine the
lifting motions.
The lifting motions of the body of water that are adjacent to the floating
platform can
thereby be directly measured, or, preferably, the lifting motions of the
drilling apparatus
can be directly determined. It can particularly be provided in this respect to
observe a
measuring mark, which is located on an upper surface of the body of water, or
prefera-
bly on the floating platform or the drilling apparatus with a position-
determining survey-
ing instrument, and in particular to pursue. From position changes conclusions
can be
drawn to the motions in the axial direction of the drill string.
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In a particularly efficient embodiment of the invention it can be provided
that the detec-
tor unit is coupled with the control unit, and that the torque can be reduced
through the
control unit when a lifting movement to be compensated is identified by the
detector
unit. The detector unit can determine occurring lifting motions and
communicates that to
the control unit. In this respect principally all determined lifting motions
can be consid-
ered and transmitted, or only those lifting motions which exceed a value that
is critical
for the drilling operation. Subsequently, the control unit communicating with
the drilling
drive can reduce the torque based on the transmitted lifting motions. For
this, single tor-
ques can be allocated to lifting motion values or lifting motion ranges. An
infinite ad-
justment of the torque can take place as well. Particularly preferred is that
the lifting mo-
tions, in particular those exceeding a predefined threshold value, can be
assigned to a
torque of zero, which corresponds to a stop of the rotary drive. Recurring, in
particular
periodic lifting motions by wave motions of a body of water can be predicted
by known
methods after the motion path was identified by the detector unit, among other
things by
means of a KALMAN filter. A compensation of such periodic lifting motions can
be
achieved with a periodic change of the torque. The reduction of the torque can
principal-
ly take place time or torque-controlled and be adjusted to the lifting
motions.
A particularly preferred embodiment variant of the invention is provided in
that a drill
string is a telescopic drill string with an external drill string element and
at least one inte-
rior drill string element, in particular a kelly bar. A telescopic drill
string, which can be
designed with or without locking mechanism for transmitting a force in the
axial direction
of the drill string, features outer and inner abutment strips forming contact
surfaces, in
which friction or friction forces, which might occur as adhesive forces or
dynamic fric-
tional forces, allow a torque transmission. A change of the occurring
friction, which can
be in proportion to the applied torque, effects that the drill string can be
telescopic ad-
justably and in reaction to the lifting motions. The drill string can be
mounted on a slide,
which is fastened in a moveable way to a mast of the drilling apparatus,
together with
the rotary drive. At a lower end of the string or at the lower end of the
internal lying drill
string element a polygon profile can be provided, to which a drilling tool is
fastened.
According to an enhancement of the invention, a particularly advantageous
variant can
be achieved in that the telescopic drill string consists of more than two
drill string ele-
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ments, in particular of three or four drill string elements fitted together.
The telescopic
drill string can be a kelly bar, which consists of an outer kelly, one or more
center kellies
and an inner kelly. Here, it is particularly preferred to provide two or three
center kellies.
The drill string elements may comprise several intermeshing abutment strips
that are
arranged radially offset, which form a contact surface when in each case two
adjacent
abutment strips are in mutual engagement, whereby the contact surface can be
the sur-
face comprising all individual contact surfaces between the abutment strips of
the drill
string elements.
For detaching soil material, it is particularly expedient, if a drilling tool
is arranged at a
lower area of one of the interior drill string elements. The drilling tool,
which can be a
rotary drilling tool, can be connected to the kelly bar by means of a square.
The rotary
drilling tool can be an auger, a drill bucket or a core drill for example.
Erosion tools can
be fastened to the drilling tool, which effect a detaching of the soil
material. Such ero-
sion tools may consist of, for instance, chisels, shovels or knives.
For compensating of lifting motions, it is provided according to a variant of
the invention
that the friction at the contact surface between the abutment strings is
dynamic friction
for compensating the lifting motion. If the friction at the abutment strings
for compensat-
ing the lifting motions is dynamic friction, a torque can also still be
transmitted during the
compensation. Consequently, even while compensating the lifting motions by the
drilling
tool a force can be exerted on the borehole bottom for detaching soil
material. It can
also be provided that the dynamic friction for compensating the lifting motion
is equal
zero, which can be caused by stopping the rotary drive. In the process, the
stopping can
be for a short time period, in particular for less than 1 s.
With respect to the method, the object according to the invention mentioned
above is
solved in that during the drill drive the torque is controlled and reduced to
a threshold
value by a control unit, at which value a friction force is produced at the
contact surface
at which the at least one drill string element is further axially displaceable
for compen-
sating a lifting motion. During the compensation of the lifting motion the
drilling tool can
in particular stay in contact with the borehole bottom, while the drilling
apparatus is mov-
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ing up and down. The torque transmission is thereby adjusted to the lifting
motions, in
particular reduced.
An advantageous variant of the method according to the invention foresees that
the dis-
tance between a drilling tool arranged at a lower portion of the telescopic
drill strings
and the drilling apparatus is changed when compensating the lifting motions. A
change
of the distance of the drilling tool can correspond to an axial change of the
length of the
telescopic drill strings. By the change of the distance it can be achieved
that a bending
of the drill strings is reduced when forces are exerted because of the lifting
motions, and
that a contact loss of the drilling tool with the borehole bottom is
prevented.
It is particularly advantageous for the method when it can be foreseen that
the lifting
motions are identified by a detection unit and these motions are communicated
to the
control unit. The control unit, which can be located on the body of water, on
the floating
platform and/or onshore, to the control can be communicated lifting motions by
means
of cabled or wireless data transmission. The communicated lifting motions may
contain
positions, position changes, speeds, speed changes and/or acceleration of the
body of
water, the drilling apparatus and/or the floating platform.
Another embodiment that is advantageous for the method according to the
invention is
when drill string is further driven while controlling and reducing the torque.
The torque
can thereby be reduced to any value greater than zero, whereby a torque can be
trans-
mitted further through the abutment string of the drill string. By further
driving the drill
string, an infinite detachment of soil material and/or pumping out or
conveying already
detached soil material can be carried out. For this purpose, facilities for
pumping or
conveying soil material can be provided.
An advantageous implementation of the method can foresee according to the
invention
that the friction force at the contact surface is a dynamic friction force.
The friction force
can principally be an adhesive friction force and/or a dynamic friction force.
In case of a
dynamic friction force it is particularly advantageous that a motion of the
telescopic drill
string can be allowed as sliding motion in the axial direction, while a
transmission of
forces for the torque transmission to the drilling tool can still be
permitted.
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It is particularly expedient for the method when it can be foreseen according
to another
embodiment variant of the method that an analysis unit is provided, by means
of which
process data of the torque and the lifting motion are analyzed and documented
during
the drilling operation. The process data can serve an operator for the visual
control or
an intelligent analyzing system for an automatic analysis. The method can
particularly
be optimized in this way. The documentation of the process data can also serve
for us-
ing process data of already terminated bores in order to reduce and control
the torque in
further bores within the framework of a knowledge-based information system.
This may
particularly serve the purpose to increase the progress of removing.
Principally, the occurring torques and the lifting motions during a bore can
be arbitrarily
recorded and/or illustrated. It can be particularly advantageous that the
torques occur-
ring during the drilling operation and the lifting motions are shown in a
visual display
unit. The visual display can serve a machine operator for monitoring the
drilling opera-
tion and to evaluate the reaction of the method to occurring lifting motions
for the com-
pensation of the same.
According to the invention it is furthermore foreseen to provide a method for
producing a
foundation element in a bottom of a body of water, whereby at least one bore
is pro-
duced in the bottom of the body of water and the foundation element is formed
in the at
least one bore. The method is characterized in that the bore is produced in
accordance
with the method for producing a bore in a bottom of a body of water from a
floating plat-
form. For forming the foundation element, a tube or pile element can be
introduced in
the bore. Alternatively or supplementary, a backfilling of the bore with a
hardenable me-
dium, in particular a cement suspension for forming the foundation element is
possible.
Foundation elements can be single pillars or elongated walls in the bottom of
the body
of water.
The invention is exemplified further hereunder with a preferred embodiment
example,
which is schematically illustrated in the attached drawings. The drawings
thereby show:
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Fig. 1 a schematic side view of a drilling apparatus according to the
invention on
a floating platform;
Fig. 2 a perspective view of a cut through a drill string from figure 1;
An embodiment of a drilling apparatus 100 according to the invention is
explained here-
under in connecting to figures 1 and 2.
The drilling apparatus 100 comprises a carrier device 30, a telescopic drill
string 10, a
drilling drive 40, and drilling tool 42 as main components. The drilling
apparatus 100 is
placed on a floating platform 4, which can be a pontoon or a ship floating on
a body of
water 8 with a bottom of a body of water 2. By means of a wave motion of the
body of
water 8 the floating platform 4, the drilling apparatus 100, and particularly
also the drill-
ing drive 40, the telescopic drill string 10 and the drilling tool 42 are
moved in an axial
direction 6. Said movements can be referred to as lifting motions.
The telescopic drill string 10 is arranged on a slide 34, which is moveable
mounted on a
mast 32 of the carrier device 30 in the axial direction 6. The telescopic
drill string 10 is
driven rotatably by the drilling drive 40 at a drill string element 12
arranged on the out-
side about the rotation axis defined by the axial direction 6. The telescopic
drill string 10
comprises a drill string element 12 arranged on the outside, a first internal
lying drill
string element 14, a second internal lying drill string element 15, and a
third internal ly-
ing drill string element 16, which are mounted extendible in the axial
direction 6. At the
third internal lying drill string element 16 a drilling tool 42 is provided at
a lower area,
which is an auger in this embodiment. The drilling tool 42 has a force-locking
connection
with the third internal lying drill string element 16 by means of a square
connection not
shown in the illustration. At the lower end of the borehole in the bottom of
the body of
water 2 there is the borehole bottom 3. The telescopic drill string 10 can
protrude
through the floating platform 4 or be passed laterally along the floating
platform.
Lifting motions caused by the body of water 8 lead to movements of the
floating platform
4 with the drilling apparatus 100 located thereon. In the embodiment these
movements
are identified by a detection unit 52, which is located on/at the floating
platform 4.
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Movements in the axial direction 6 can thereby occur downwardly in the
direction of the
bottom of the body of water 2 or upwardly in the opposite direction. The
detector unit 52
is connected to the control unit 50 through a data cable 54. The detector unit
52 trans-
fers information to the control unit 50 regarding the movements in the axial
direction 6,
whereby this information may also contain positions. The control unit 50 can
analyze,
process and use this information so as to control the drilling drive 40. For
this purpose,
the control unit 50 is connected to the drilling drive 40 via another data
cable 55. The
control of the drilling drive 40 through the control unit 50 thereby includes
a reducing of
the torque from a predefined threshold value as well as the re-increase of the
torque of
the drilling drive 40 back to the value of the torque existing before the
reduction.
The cut A-A plotted in Fig. 1 is illustrated in Fig. 2 from a perspective
view. Fig. 2 there-
by shows a cut through the extended internal lying drill string elements 14
and 15,
whereby the drill string element 15 lies within the drill string element 14.
The drill string
element 15 in this embodiment comprises two outwardly directed internal
abutment
strips 22, and the drill string element 14 comprises two inwardly directed
external abut-
ment strings 20. When a torque is applied, the external abutments strips 20
are each in
contact or in engagement with the internal abutment strips 22, whereby the
contact is
formed at a contact partial surface 24 each. At the contact partial surfaces
24 friction
forces occur in the drilling operation, which can occur as adhesive friction
forces or dy-
namic friction forces. For compensating the motion in the axial direction 6,
the contact
partial surfaces 24 slide onto each other in the axial direction 6. In case of
non-
compensation of the motions in the axial direction 6, the contact surfaces 24
adhere to
each other for transmitting the torque.
