Note: Descriptions are shown in the official language in which they were submitted.
~S686
APPARATU~ FOR OPTIONAL STRAIGHT OR DIRECTIONAL DRILLI~G
UNDE~GROU~lD FORMATIONS
TECHNICAL FIELD
. . .
This invention relates to apparatus for selective
straight or directional drilling underground formations.
BACKGROUND ART
.
S European Patent Application No. ~085444 describes a
device which is capable of being used for straight drill-
ing or for drilling at an angle. In particular the appl-
ication describes a method and means for controlling the
course of a bore hole during drilling.
The method and means includes first and second stab-
ilisers which are arranged to support the housing for a
down-hole mo~or having an output shaft for connecting to
a drill bit. At least one of the st~bilisers is eccen~-
ric relative to the housing so that rotation of the hous-
ing will cause a change in the angle of the axis o' the
output shaft of the down-hole motor. Thus by controlling
the rotation of the housing and the length of time of
operation of the down-hole motor the course of the bore-
hole can be controlled.
The change in angle causes stresses to be introduced
into the housing which are transmitted to the drill bit
causing excesslve friction between the drill bit and the
wall of the bore-hole. Furthermore additional strains
are imposed on the stabilisers, the connections between
the drill string and the housing, between the down-hole
motor output shaft and the drill bit and between sections
of the housing. These stresses can lead to damage and/or
excessive wear of bearings.
It is an object of the present invention to provide
an improved device for use in underground drilling which
reduces the stress-related problems identified above.
SUMMARY OF THE INVENTION
According to the present invention we provide a de-
~
5686
vice for use in underground drilling of bore-holes com-
prising
a tubular housing;
a down-hole motor mounted in said housing and having
an output shaft;
means for connecting said output shaEt to a drill
bit
means for connecting said housing to a drill string;
first and second stabilisers mounted on said hous-
ing;
said housing comprising an upper section, an inter-
mediate section and a lower section connected to one an-
other, said first stabiliser being associated with said
lower section of said housing and said second stabiliser
_~ being associated with said upper section of said housing;
said upper section having a longitudinal ~xis and
said lower section having a longitudinal axis which is
arranged at an angle relative to the axis of said upper
section; and
said intermediate section having a longitudinal axis
which intersects said upper and lower section axes.
Preferably the upper and lower sections of the hous-
ing are connected to the intermediate section by angled
connectors, especially threaded connectors.
In one form of the invention said iritermediate sec-
tion includes a plurality of interchangeable elements
whereby the angle between the axes of the upper and lower
housing sections can be preset. Conveniently the length
of the intermediate section when preset at one angle is
different from the length of the intermediate section
when set at a different angle.
In this form of the invention it is preferred that
the lower housing section is provided with a connecting
portion which is set at an angle relative to the lower
section axis which is determined by the preset angle to
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the intermediate section.
The position of the first and/or second stabilisers
can be adjustable relative to the lower housing section
and/or upper housing section respectively.
It is preferred that at least the first ~tabiliser
had adjustable eccentricity. Suitable stabilisers
having adjustable eccentricity are described in German
Patent Application No. P34 03 239.8-24.
Thus is one embodiment the present invention
provides a device for use in underground directional
drilling of boreholes in which either a straight borehole
ma~ be drilled or wherein a borehole having a predeter-
mined radius of curvature may be drilled while said
device i9 positioned in a borehole comprising:
a tubular housing comprising upper, intermediate
and lower sections connected to one another;
a down-hole motor mounted in the upper section of
said housing and having an output shaft;
means for connecting said output shaft to a drill
bit located below the lower section of said housing;
means for connecting said housing to a drill string
such that the axis of said upper section is initially
essentially in alignment with the axis of said drill
string;
~irst and second stabilizers mounted on said housing;
said first stabilizer being associated with said
lower section of said housing and said second stabi-
lizer being associated with said upper section of said
housing;
said upper section having a longitudinal axis and
said lower section having a lonyitudinal axis which
is arranged at an angle relative to the axis of said
upper section; and
6aid intermediate section having a longitudinal
axis which intersects said upper and lower axes
whereby upon rotation of said drill bit by rotating
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4--
said drill string and simultaneously rotating said
motor an essen~ially straight borehole is drilled and
whereby rotating said drill bit by rotation of ~aid
motor while said drill string is not rotated a curved
borehole having a predetermined radius of curvature
is drilled.
In another embodiment the present invention
provides the method of directional drilling along
a known predetermined radius of curvature wherein a
d~ill string includes a bottom hole drilling assembly
comprised of at least an upper section and a lower
section and a downhole motor and wherein said upper
section includes at least an upper component at least
a portion of which oontacts the bore wall and said
lower section having an axis which is tilted with
respect to said upper section and said lower section
including a lower component at least a portion of
which contacts the bore wall and said lower
component being ~paced from a drill
bit connected to 6aid lower sectiorl and wherein said
downhole motor is connected to rotate said drill bit,
the method comprising:
assembling said drilling assembly to the drill string
such that when said drill bit is rotated only by said
25~ motor, said drilling assembly drills a hole having
a radius of curvature corresponding essentially to
said predetermined radius of curvature,
said step o~ assembling including the steps of
~a) mounting fiaid respective components such that
there iæ a p~edetermined known distance therebetween,
(b~ mounting said drill bit a predetermined known
distance below said lower component such that the
drill bit is on an axis which is tilted a known
amount with respect to the axis of said drill string,
``````` 1.~S686
-4a-
(cj said radius of curvature being determined by
the distance from a defined reference point to
said upper component and which distance forms a
radius for the radius of curvature, ~aid defined
point being defined by the intersection of one
line perpendicular to the midpoint between the
bit and the lower component and a second line per-
pendlcular to the midpoint between the upper and
lower components,
lowering said drill string and ~aid assembled bottom
hole drilling assemb~y into a borehole,
drilling a straight hole by simultaneously rotating
both said drill string and said drill bit, the rota-
tion of said drill bit being carried out by rotation
Of said downhole motor, and
whlle said drill string and bottom hole drilling
assembly are sti~l positioned in said bore hole,
rotating only said drill bit by operation of said
downhole motor to drill a hole having a known radius
of curvature which essentially corresponds to said
predetermined radius of curvature.
BRIEF DESCRIPTION OP THE DRAWINGS
Reference is now made to the accompanying drawings,
in which:-
Fig. 1 is a ~chematic diagram of a drilling device
for use in controlled drilling of a bore-hole according
to the invention;
Figc. 2 and 3 are schematic diagrams of alternative
drilling de~ices according to the invention;
Figs. 4 and 5 are detailed views on an enlarged
scale of parts of the device shown in Fig. 2;
Figs. 5 to 10 illus~rate diagrammatically altern-
ative embodiments of eccentric stabilisers for use in the
device of the invention;
Fig. 11 is a side view of a stabiliser with adjust-
able eccentricity;
86
-4b-
~ig. 12 is a cross-s2ction through the stabiliser
shown in Fig. 11;
Fig. 13 is a schematic diagram of a further device
according to the invention
Fig. 14 is a schematic diagram of a device according
to the invention with a lower stabiliser shown in differ-
ent positions; and
Fig. 15 is a diagram showing the relationship bet-
ween the radius of curvature of the drill hole profile
and the relative positions of the stabiliser and drill
bit.
DESCRIPTION OF THE PREFERRED EM~ODIMENTS
_ _ _ _ .
The device shown in Fig. 1 incorporates the concepts
,of European Patent Application No. 0085444~ The drilling
device 2 is shown in position in a bore-hole 1. It com-
prises a housing 3 connected to a drill string 4 by means
not shown. The connecting means may be a screw threaded
arrangement as shown in European Patent Application No.
0085444. The drill string 4 is arranged to be rotated by
a turntable 5 having a locking device 7 to prevent ro-
tation of the turntable 5 and drill string 4. The turn-
table 5 and locking device 7 are mounted on a derrick 6.
The locking device 7 controls the rotation of the
drill string 4 to permit, for example continuous rotation
2S or limited rotation for alignment purposes. When the
locking devic~ is in its locking condition it prevents
rotation of the drill string 4 and the housing 3.
The alternative embodiments of the drilling device
2, shown in ~igs. 2 and 3, have, as common features, a
housing 3 which consists of an upper section 9 concentric
with a tool main axis 8, a lower section 10 deflected
relative to the tool main axis 8, and an intermediate
section 11 connecting the lower section 10 to the upper
section 9.
356~36
--~c--
A motor ~not shown) may be arranged in the section 9
of the housing 3. The motor may be of any conventional
type, for example, a turbine motor, a vane motor, a
Moineau type motor or an electric motor. The motor rotor
is connected to a rotary drill bit 13 via a universal
joint and shaft leading through the intermediate section
11 and via a driven shaft 12 mounted in the lower housing
section 10.
A stabiliser 14 is located on the lower section 10
and a stabiliser 15 is located on the upper ~ection 9 or
slightly above it. The lower stabiliser 14 ensures that
~;3S686
the axis 16 of the lower section 10, which de~ermi.nes the
rotational axis of the driven shaft 12 and the rotary
drill bit 13, intersects with the main axis 8 near to the
rotary drill bit 13. The point of intersection, in the
embodiment of Fig. 2, is exactly at the cen~re of gravity
of the stabiliser 14.
The upper stabiliser 15 ensures that the angle of
deflection of the lower ection 10 is maintained relative
to the main axis 8, which angle is preset by the manner
in which sections 10, 11 and 9 are joined together. This
joining can be effected to provide a transition 17 by
short pipe bends, as shown in detail in Fig. 4, between
the upper section 9 and the intermediate section 11, or
by inclined, threaded connections fixed directly onto
sections 9, 11, as shown in Fig. 5.
By deflecting the axis of the lower housing section
10 and thus axes of the drive shaft 12 and the rotary
drill bit 13 relative to ~he main tool axis 8j with the
housing 3 in a fixed positon, the bore-hole 1 produced
has a bent profile pointing in the direction of the axis
16. If the housing 3 is also turned, the bent rotation
axis 16 also rotates, so that the resulting movement of
the rotary drill bit 13 will provide a bore-hole 1 hav-
ing a profile in the direction of the tool main axis 8.
Selective directlonal drilling or straight drilling can
thus be achieved in a simple manner by locking or turning
the rotary table 5 and hence the drill string 4 and hous-
ing ~.
By arranging the point of intersection of the ro-
tational axis 16 with the tool main axis 8 to be near tothe rotary drill bit 13 the bore-hole widens only slight-
ly when operating in the straight drilling mode and com-
pared with th~ directional drilling operation mode be-
cause of the eccentric movement of the rotary drill bit
13.
6~1~
The amount of bore-hole widening corresponds to
about twice the value of the axial displacement 27 bet-
ween the rotational axis 16 and the main tool axis 8 in
the area of the rotary drill bit 13; this axial displace-
ment 27 is also referred to as offset.
The offset 27 can be reduced to zero if an eccentric
stabiliser is used instead of the centric stabiliser 14
shown in Fig. 2; the eccentricity of the eccentric stab
iliser is arranged to compensate for the offset. Fig. 3
1~ shows such a modified embodiment in which the stabiliser
18 adjacent to the rotary drill bit 13 is an eccentric
stabiliser. Such an embodiment can be used to avoid
widening of the bore-hole during straight drilling and
also has the advantages that wear in the gauge area of
the rotary drill bit 13 and on the outer surface of the
stabiliser lB can be reduced and that bending stresses
can be kept away from the housing 3.
The drilling tool 2 can be operated with drill bits
13 of various diameter. This is facilitated by providing
interchangeable stabilisers. The eccentricity of the
lower stabiliser 18 can be preset. Figs. 6 to 12 illus-
trate various embodiments of eccentric stabiliser.
The stabiliser 18 shown in Figs. 6 and 7 consists in
each case of a carrier body 19 and a ribbed shell 20
which is fixed on the carrier body 19 by a positive conn-
ection. In the alternatives shown, the ribbed shell 20
can be aligned stepwise relative to the carrier body 19.
In the embodiment in Fig~ 6, the positive connections
between parts 19 and 20 are formed by splines 21 and in
the embodiment in Fig. 7 by radially distributed teeth
22.
The alternatives shown in Figs. 8 to 10 enable the
ribbed shell 20 to be interchanged and provide for con-
tinuous adjustment relative to the carrier body 19~ The
relative positions of the shell and carrier body can be
i~3S68G
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fixed by a frictional connection.
In Fig. 8, the ribbed shell 20 is fixed by an inter-
ference fit which is brought abou~ by applying hydraulic
pressure to expand the ribbed shell 20 forcing it onto
the carrier body and relieving the pressure load on the
ribbed shell 20. The shell 20 is provided with seals 23.
Fig. 9 shows how the ribbed shell 20 can be fixed by
means of a longitudinally slotted intermediate shell 24
which presents a conical threaded area to the ribbed
shell 20 and, when screwed together with the shell 19
locks it to the carrier body 19. In the alternative
shown in Fig. 10 the ribbed shell 20 is slotted along a
rib and is clamped to the carrier body 19 in ~he manner
of a clamping collar by several screws 25.
If the stabiliser 18 is deslred to have selected
preset eccentricity an embodiment such as shown in Figs.
ll and 12 can be selected. In addition to the carrler
body 19 and the ribbed shell 20, the stabiliser comprises
an eccentric intermediate shell 26. By turning the ribb-
,o ed shell 20 relative to the intermediate shell 26, the
amount of eccentricity of the stabiliser 18 can be chang-
ed stepwise between a maximum value and a minimum value,
retaining the possibility of alignment of the ribbed
shell 20 relative to the carrier body 19. The parts are
fixed by radially distributed teeth, as described with
respect to the embodiment of Fig. 7.
In the embodiments of the drilling tool 2 shown in
Figs. 13 and 14 the intermediate section 11 is designed
as a plurality of interchangeable elements so that the
angle between the axes of the upper and lower sections
can be preset. The embodiments are modifications of the
embodiment shown in Fig. 2 and similar reference numerals
are used for similar components.
When straight drilling, to minimise the disturbing
effects caused by the deflected section 10 of the drill-
~3S6~
--8--
ing tool 2, the deflection tendency of the drilling toolis determined so that exactly the required minimum radius
of curvature can be achieved during directional drilling.
The deflection tendency can be obtained by presetting a
corresponding deflection anyle ~ of the intermediate sec-
tion 11. This is illustrated in Fig. 13 by two further
angles represented by dotted lines 11' and lln, with 11"
corresponding to a deflection of 0, which is equivalent
to the intermediate section 11" being aligned coaxially
with the tool main axis 8.
In practice it is desirable to supply a set of at
least two interchangeable parts in which the intermediate
sections il, 11', 11" are bent at angles of varying de-
grees. The interchangeability is preferably provided by
means of threaded connections at the ends of the inter-
mediate section, which threaded connections are set at an
angle relative to the axis of the intermediate section to
ensure that the connecting angle matches the rest of the
drill string or the housing section 10.
If the intermediate sections are of the same length
they can only differ in their angular setting ~ . This
type of set of intermediate sections is advantageous for
unchanged use of the shaft which rotates inside the in-
termediate section 11 to drive the driven shaft 12. Al-
ternatively the set of intermediate sections can differ
in length and can be set at their upper and lower ends at
a uniform angle ~ , ~ to the upper housing section 9
and the lower housing section 10 respectively. Sets com-
bining both features can also be provided.
The length and deflection angle ~ of the intermed-
iate section 11 can be fixed and the angle ~ can be sel-
ected to suit the desired purpose. The housing section
10 is conveniently also designed as an interchangeable
part in order to obtain, by interchange, various angles
or, in combination with various deflection angles ~ ,
~Z35t;~3~
various angles ~e . Also various lengths of the housing
section 10 adjoining the intermediate section 11 can be
employed with the connection to the intermediate section
11, for example, being made by an angularly set thread.
A further possihility of setting the deflection
tendency of the drilling tool 2 is to change the distance
between th~ stabilisers 14 and 15 or the distance between
the stabiliser 14 and the rotary drill bit 13. Such an
arrangement is illustrated in Fig. 14. The first stabil-
1~ iser 14 is arranged in such a way that it can be adjust-
ably fixed in different positions on the lower housing
section 10. This facility, either on its own or in com-
bination with certain preset deflection angles and/or
certain preset lengths of the intermediate section 11 or
lower housing section 10, enables the deflection tendency
to be controlled.
The stabiliser 14 may also be of variable eccent-
ricity so that the bit offset, which changes when the
stabiliser 14 is displaced on the lower housing section
'~ 10 can be compensated. As the drill bit 13 is moved fur-
ther away the eccentricity of the stabiliser 14 is in-
creased; two further positions are shown by the dotted
lines at 14' and 14". To make a displacement on the
housing section possible, the stabiliser 14 may, for ex-
ample, be designed as shown and described in Figs. 9 and10 .
Fig. 15 illustrates the relationship between the
arrangement of the stabilisers 14 and 15 and the rotary
drill bit 13 and the radius of curvature of the di-
rectional drilling. Utilising a drilling device as shownin Figs. 13 and 14, the intersection points S14, S15 and
S13 of the housing axes with the centre transverse planes
of the stabilisers 14, 15 and the rotary drill bit 13
respectively are shown in Fig. 4. The centre point of
the arc of the drill hole profile achieved in this con-
~23568~
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fiquration is obtained by the intersection point M of thecentre verticals 17;18 on the respective connecting lines
19;20 between the intersection points S14, S15 of the
stabilisers 14 and 15 or the intersection points S14, S13
of the stabiliser 14 and the tool bit 13. The radius of
curvature R is then obtained from the distance of the
respective intersection points 514' 515 and 513 to the
intersection point M of the centre verticals. The conn-
ecting lines between the intersection points do not have
to coincide with the axes of the respective housing sec-
tions in every embodiment.
Finally, values are given for a practical embodiment
of the drilling tool of Fig. 14. The distance between
S14 and S15 corresponding to the length of line 19 is
8150 mm. The distance between S14 and S13 corresp~nding
to the lengt~ of line 20 is 1155 mm. Angle 2~ of section
11 to the tool main axis 8 is 0.6. In this configur-
ation, the radius R of 435 m. is obtained. The distance
between S14 and S13 can be increased from 1155 mm. to
1955 mm. ~and the distance 514 to S15 can be reduced) so
as to increase the deflection tendency and reduce the
radius of curvature R (cf. R', M' and S'14 in Fi~. 4).
