Note: Descriptions are shown in the official language in which they were submitted.
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Title: Drilling system with a barrel drilling head driven by a downhole
tractor
Technical Field
The present invention relates to a drilling system for drilling out a sample
of a subterra-
nean formation, a well, or the like downhole, comprising a drilling head
having an at
least partly hollow cylindrical body with a circumferential rim, which has at
least one
cutting edge, a longitudinal axis going through a centre of the cylindrical
body, and a
driving unit for rotating the cylindrical body and the cutting edge for
cutting a piece out
of the formation.
Background
Drilling systems are used when drilling a well in a subterranean formation or
for taking
out a sample of the formation before drilling any further.
Known drilling systems for taking out a sample are constructed from a long
line of
pipes, the system thus extending from above surface to a destination downhole
where
the sample is to be taken. The system is mounted by mounting one pipe onto
another
just before the drilling operation on the drilling rig. The extension of the
pipes put to-
gether makes the mounting process complicated, and the process is moreover
time
consuming.
However, the long line of pipes creates a Weight On Bit (WOB) by the force of
gravity
which is needed for drilling downhole. Such a system creating weight on bit by
the
force of gravity is not very useful when drilling horizontally, e.g. for
taking out a sample,
since the force of gravity is substantially decreased when the pipes extend
horizontally.
Another known type of drilling system uses coiled tubing, i.e. a long,
continuous length
of pipe wound on a spool. The pipe is straightened prior to pushing into a
wellbore and
rewound to coil the pipe back onto the transport and storage spool. Although
substan-
tially less time consuming than the system described above, the equipment for
coiled
tubing drilling still takes a long time to transport to the site. Moreover,
coiled tubing drill-
ing still uses the force of gravity to create WOB, and thus does not solve the
problem of
drilling horizontally.
CONFIRMATION COPY
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Therefore, there is a need for a drilling system which is able to take out
samples also
when drilling horizontally.
Furthermore, in order to prevent a blowout when drilling downhole, the fluid
in the well
is mixed with a number of chemicals for making a differential pressure
downhole. How-
ever, due to the differential pressure, the above-mentioned systems sometimes
get dif-
ferentially stuck.
Thus, there is also a need for a drilling system reducing or even eliminating
the risk of
downhole systems getting differentially stuck.
Description of the Invention
An aspect of the present invention is, at least partly, to overcome the
disadvantages of
the drilling systems mentioned above, and to provide an improved drilling
system which
is able to take out a sample of the formation without getting stuck.
This aspect and the advantages becoming evident from the description below are
ob-
tained by a drilling system for drilling out a sample of a formation, a well,
or the like
downhole, comprising:
- a drilling head comprising:
- an at least partly hollow cylindrical body with a circumferential rim and a
longitu-
dinal axis going through a centre of the cylindrical body, the circumferential
rim having
at least one cutting edge,
- a driving unit for rotating the cylindrical body and the cutting edge for
cutting a piece
out of the formation, and
- a driving tool such as a downhole tractor for driving the drilling head
forward in the
well or formation.
By having a driving tool for driving the drilling head forward and provide a
weight on bit,
the drilling system can drill horizontally into the formation for drilling a
branch well or
taking out a sample for further investigation.
By combining a downhole tractor and a drilling head, the drilling operation
can be per-
formed substantially faster than when using coiled tubing or jointed pipes,
since the
equipment for using coiled tubing or jointed pipes takes longer time to
transport to the
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operation site and takes longer time to prepare at the operation site. A
downhole tractor
may easily and quickly be transported to the operation site compared to the
equipment
necessary for coiled tubing operations, and the preparation time at the
operation site is
thus substantially decreased, if not eliminated. Moreover, the downhole
tractor has
proven to be efficient enough to use for drilling operations also, since it
can provide a
sufficient WOB.
In one embodiment, the downhole tractor may be connected to and powered
through a
wireline.
In addition, the drilling system may further comprise at least one tightening
means for
providing a closing of the well above the drilling head for preventing a
blowout.
By having a tightening means, the well or hole in the formation can be divided
into an
upper part in relation to the bottom of the well or hole and a lower part
comprising the
drilling system or at least most of it. In this way, a blowout can be
prevented without
use of chemicals creating a differential pressure, and thus without risking
that the sys-
tem gets differentially stuck.
In one embodiment, the tightening means may be expandable.
Moreover, the cylindrical body may have a closed end opposite the cutting
edge.
In another embodiment, the circumferential rim may have a plurality of cutting
edges.
In addition, the circumferential wall may have at least one slot.
In yet another embodiment, the hollow body may have a length up to 10 metres.
Moreover, the drilling system may further comprise a gas cartridge or a pump
for infla-
tion of the tightening means with gas or fluid from the well.
Brief Description of the Drawings
The invention is explained in detail below with reference to the drawings, in
which
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Fig. 1 shows a drilling system according to the invention, and
Fig. 2 shows another embodiment of the drilling system according to the
invention.
The drawings are merely schematic and shown for an illustrative purpose.
Detailed description of the invention
Fig. 1 shows a drilling system 1 according to the present invention comprising
a barrel
drilling head 2, a driving unit 6 for rotating the barrel drilling head 2, and
a driving tool 8
such as a downhole tractor. The drilling system 1 is submerged into the well
or subter-
ranean formation 10 by the driving tool 8 which is powered through a wireline
11 by a
power means above surface.
The drilling head 2 is rotationally driven by the driving unit 6 at a certain
speed, and the
weight on bit (WOB) is controlled by the driving unit 6 so that the
longitudinal displace-
ment of the cutting edge 5 towards e.g. the formation 10 is held constant
during the
drilling process.
Due to the fact that the weight on bit (WOB) is created by the driving unit 6
and not just
by the force of gravity, the drilling system 1 can also drill horizontally,
e.g. for taking out
samples 7 horizontally.
The drilling head 2 has a partly hollow cylindrical body 3 that is closed at
one end 13
and has a circumferential rim 4 at the other end. The circumferential rim 4
has at least
one cutting edge 5 which, when rotated by the driving unit 6, cuts out a piece
7 or sam-
ple 7 of the formation 10. In this way, the drilling system 1 can be used for
both for drill-
ing a well downhole and for taking out samples 7 for further investigation.
Due to the fact that the drilling head 2 has a hollow cylindrical body 3, the
drilling head
2 is able to receive the sample 7 that is being cut out and bring it up with
the rest of the
system 1. In this embodiment, the inside of the hollow body 3 is 6 metres in
depth, and
the drilling system 1 is therefore able to cut out a sample 7 of almost 6
metres. In an-
other embodiment, the hollow body 3 may be as long as 10 metres.
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As shown in Fig. 1, the drilling system 1 further comprises a tightening means
9 posi-
tioned around the wireline 11 for closing a lower part of the well in order to
prevent a
blowout without using chemicals.
5 In this embodiment, the tightening means 9 is expandable. The expandable
tightening
means 9 is in the form of an expandable ring blown up by gas positioned in a
gas
chamber 12 or a gas cartridge 12 within the drilling system 1. In another
embodiment,
the fluid surrounding the drilling system 1 is used to expand the tightening
means 9 by
use of a pump 14 and a filter for filtrating the fluid before it is pumped
into the tightening
means 9. Preferably, the pump 14 and the filter are positioned in the part of
the drilling
system 1 between the connection to the wireline 11 and the downhole tractor 8.
The tightening means 9 may also be positioned around the downhole tractor 8 as
shown in Fig. 2. Hereby, the tightening means 9 need not be expanded as much
as
when positioned around the wireline, and the tightening means 9 can also be
non-
expandable, e.g. a rubber ring. Thus, the expansion of the tightening means 9
is
quicker and easier since the volume of the tightening means 9 need not be as
large as
if positioned around the wireline 11, and the gas chamber 12, gas cartridge
12, or
pump 14 can be positioned in the side of the downhole tractor 8 providing a
quick infla-
tion of the tightening means 9.
The driving unit 6 is an electrical motor which drives the drilling head 2.
The motor 6
has a shaft for driving the drilling head 2. The shaft may be connected to the
drilling
head 2 through a gear connection. In this way, one drilling head 2 may be
replaced by
another drilling head 2.
For providing a differential pressure below the expandable means 9, the
drilling system
1 comprises a pump 14 which may be any kind of suitable pump. In this
embodiment,
the pump 14 is a one-step centrifugal pump, but in another embodiment the pump
14
may be a multi-step centrifugal pump, a jet pump, or a piston pump.
