Note: Descriptions are shown in the official language in which they were submitted.
WO 94125721 PCT/EP94/01446
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DRILLING KICK-OFF DEVICE
The present invention relates to drilling deviated borehole
, branches in an underground formation from a single borehole. The
single borehole is in general a vertical borehole and in order to
reach widely spread targets one or more deviated borehole branches
are drilled from the single borehole.
In one way of drilling a deviated well use is made of a kick-
off device in the form of a steel wedge or whiPstQci~: arranged on
the bottom of the single well. On continuing drilling, the drill
bit follows the wedge and a deviated borehole branch is drilled.
After having drilled a short length of the deviated borehole
branch, the whipstock is removed and drilling in the deviated
branch is continued. See for a description of this method The
Petroleum Handbook, 6th Edition, Elsevier, 1983, pages 135-136.
When it is required to drill two of opposite borehole branches
the second borehole branch can be drilled using a whipstock orient-
ed in a direction opposite to the direction of the first borehole
branch.
A kick-off device used to drill more than one deviated borehole
branch is disclosed in USA patent specification No. 4 573 541. This
device comprises a tubular housing and three guide tubes arranged
in the housing of which two are curved away from the central
longitudinal axis of the housing. Drilling a deviated borehole
branch comprises arranging the device in the lower end of the cased
single borehole, guiding the drill bit into one of the two curved
guide tubes and continue drilling.
A disadvantage of this kick-off device is that the diameter of
the guide tubes is smaller than half the diameter of housing and
consequently the curved borehole branches have a diameter which is
much smaller than the diameter of the original borehole from which
they are drilled.
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US patent No. 2,693,342 discloses a deflector
located in a tool housing connected to a rotating upper pipe
member, whereby the rotative motion of the upper pipe member
is transmitted to a pair of lateral drill pipes via a gear
system.
Embodiments of the present invention provide an
improved kick-off device that allows drilling a pair of
opposite deviated borehole branches.
In one aspect of the present invention, there is
provided a re-entry device which can be removably placed in
a kick-off device having a guide element, the guide element
comprising two slanted guide ways, the re-entry device
comprising an open-ended liner having an elongated opening
in a wall of the liner, a slanted deflecting surface
arranged in the open-ended liner facing the elongated
opening, wherein when the re-entry device can be so placed
in the kick-off device that the slanted deflecting surface
meets one of the two slanted guide ways of the kick-off
device.
In some embodiments, the kick-off device in aid of
drilling a pair of opposite deviated borehole branches in an
underground formation from a single borehole according to
the present invention comprises an open-ended tube provided
at its upper end with connecting means, and a guide element
arranged in the open-ended tube near its lower end, which
guide element includes two slanted guide ways arranged on
opposite sides of the guide element, characterized in that
the connecting means joins the open ended tube to a string
of casing.
Suitably the slanted guide ways are concave.
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To avoid drilling through a metal wall, the wall
of the open-ended tube has elongated openings facing the
slanted guide ways.
The open-ended tube may also be provided at its
lower end with connecting means to join one or more
additional joints of casing to the lower end of the open-
ended tube in order to centralize the open-ended tube in the
single borehole.
The invention also relates to a re-entry device
which can be removably placed in the kick-off device of the
present invention, which re-entry device comprises an open-
ended liner having an elongated opening in its wall, a
slanted deflecting surface arranged in the open-ended liner
facing the elongated opening, wherein when the re-entry
device can be so placed in the kick-off device that the
slanted deflecting surface meets one of the two slanted
guide ways.
Suitably the re-entry device further comprises a
meeting element arranged in the lower end part of the open-
ended liner, which meeting element has a sole to allow the
meeting element to rest on the guide element and includes a
wedge-shaped part to allow placing the meeting element in a
predetermined position with respect to one of the slanted
guide ways.
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The invention will now be described by way of example in more
detail with reference to the accompanying drawings, wherein
Figure 1 shows schematically a side view of the kick-off
device according to the present invention;
j Figure 2 shows a cross-sectional view along line II-II of
Figure 1~
Figure 3 shows a longitudinal view along line III-III of
Figure 1~
Figure 4 shows schematically and not to scale a pair of oppo-
site deviated borehole branches drilled from a single borehole;
Figure 5 shows schematically a side view of a casing string
provided with the kick-off device of the present invention
Figure 6 shows a partial cross-sectional view along line VI-
VI of Figure 4; and
l~ Figure 7 shows schematically the kick-off device provided
with a re-entry device according to the invention.
Reference is now made to Figures 1 through 3. The kick-off
device 1 of the present invention comprises an open-ended tube 2
provided at its upper end with connecting means (not shown) to
join the open-ended tube to a string of casing, and a guide
element 4 arranged in the open-ended tube near its lower end 5.
The guide element 4 includes two slanted guide ways 6 and 7
arranged on opposite sides of the guide element 4. In the embodi-
ment shown the guide ways 6 and 7 are concave.
2~ The wall of the open-ended tube 2 has elongated openings 9
and 10 facing the slanted guide ways 6 and 7.
Reference is now made to Figures 4 through 6. Figure 4 shows
schematically and not to scale the drilling of a pair of opposite
deviated borehole branches 20 and 21 from a single borehole 22
drilled from a drilling rig 25 in an underground formation 27. The
single borehole 22 has been cased with a casing string 28 which
has been provided near its lower end with the kick-off device 1
according to the present invention. The casing string 28 is
cemented in the single borehole 22 in a conventional way, the
cementing operation will not be discussed here.
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The lower end of the casing string 28 is shown in more detail
in Figures 5 and 6. The kick-off device 1 is arranged between the
last section 30 of the casing string and a tail section 31, to
this end the open-ended tube 2 is provided at both ends with
connecting means. The tail section 31 comprises a joint of casing
and it serves to centralize the kick-off device 1 in the single
borehole 22. The connections between the sections are referred to
by reference numerals 32. The casing string 28 is furthermore
provided with centralizers 33 to centralize the casing string 28
in the single borehole 22 (see Figure 4).
To drill a deviated borehole branch a drill string assembly
50 (see Figure 6) having a drill bit 52 at its lower end is
lowered into the casing string 28. The guide element 4 deflects
the drill bit 52 and on rotating the drill bit 52 drilling a
deviated borehole branch is started. The concave form of the guide
ways 6 and 7 facilitates control of the direction of the drill bit
52 and the drill string assembly 50 as drilling continues.
This is also shown in,j:'igure 4, wherein the drill bit 52 is
shown in the deviated borehole branch 21. In Figure 9 it has been
assumed that branch 20 has already been drilled.
To facilitate entering in one of the deviated borehole
branches, a re-entry device can be lowered into the kick-off
device of the invention, the outer diameter of the re-entry device
being smaller than the inner diameter of the kick-off device. The
re-entry device arranged in the kick-off device is shown in Figure
7. The re-entry device is referred to by reference numeral 60 and
it has been removably placed in the kick-off device 1. The re-
entry device 60 comprises an open-ended liner 61 having an
elongated opening 62 in its wall, a slanted deflecting surface 64
arranged in the open-ended liner 61 facing the elongated opening
62. The re-entry device 60 has been so placed in the kick-off
device 1 that the slanted deflecting surface 64 meets the slanted
guide way 6 which is one of the two slanted guide ways 6 and 7.
To orient the re-entry device 60, it further comprises a
meeting element 66 arranged in the lower end part of the open-
ended
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liner 61, which meeting element 66 has a sole 67 to allow the
meeting element 66 to rest on the guide element 4 and includes a
wedge-shaped part 68 to allow placing the meeting element 66 in a
predetermined position with respect to one of the slanted guide
ways 6 or 7.
The re-entry device 60 is lowered into the casing string 28,
for example at the end of a drill string (not shown) to which it is
removably connected. After having placed the re-entry device 60 the
drill string is pulled out of the borehole.
When a tool has to be lowered into borehole branch 20 (see
tigure 4), the re-entry device 60 is placed in the kick-off
device 1 as shown in Figure 7. The tool (not shown) is then lowered
through the casing section and is guided along the slanted deflect-
ing surface 64 into the borehole branch.
To secure the re-entry device 60 in the kick-off device 1, the
re-entry device 60 may include a releasable lock assembly (not
shown).
The re-entry device 60 can also be used to drill one of the
deviated borehole branches. To this end drilling the deviated
borehole branch is started as described with reference to
Figures 4-6. When about 1 m has been drilled, the drill string
assembly is removed from the borehole, the re-entry device is
attached to the kick-off device and drilling the deviated borehole
branch is resumed.
To facilitate initial drilling of one of the deviated borehole
branches a directional drilling assembly including a downhole motor
and a bent-sub can be applied. With the directional drilling
assembly selectively oriented the bent-sub forces the drill bit
driven by the downhole motor through a selected one of the elongate
openings of the open-ended tube. Cement which is present in said
elongate opening due to cementing of the casing string in the
borehole is drilled out first whereafter drilling of said one
deviated borehole branch proceeds into the underground formation.
Initiation of the other deviated borehole branch is performed in a
similar way, whereby the drilling assembly is selectively oriented
WO 94/25721 PCTIEP94/01446
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so that the drill bit is forced through the other elongate opening
of the open-ended tube. Suitably a gyroscopic survey tool can be
used in aid of orienting the drilling assembly in the selected
orientation.
Unwanted repositioning of the re-entry device due to movement
of drilling or service tools through the borehole can be prevented
by running a suitable hold-down tool on top of the re-entry device.
