A METHOD AND A DEVICE FOR DIRECTIONAL DRILLING

PROCEDE ET DISPOSITIF DE FORAGE DIRECTIONNEL

English Abstract

A method and a device for directional drilling, especially for directional
drilling of holes in the crust of the earth, e.g. gas and oil wells (1), where
at least one shear jet (13) works an eccentrically located part face in
relation to the substantially circular working face of a rotary bit (5). A
device for directional drilling where one or more shear jets (13) are
rotationally disposed around a rotational axis (11) eccentrically placed in
relation to the axis (6) of the bit (5), and where the hit point of the shear
jets (13) is asymmetrically situated in relation to the rotational axis (11).
When the bit (5) rotates around the axis (6), the hit point of the shear jets
(13) keeps a predetermined orientation in relation to the rotational axis
(11), whereby the shear jets (13) sweep an area eccentrically located in
relation to the axis (6) of the bit (5).

French Abstract

L'invention porte sur un procédé et un dispositif de forage directionnel s'appliquant notamment au forage de puits (1) de pétrole ou de gaz dans l'écorce terrestre. Selon ce procédé, au moins un jet de cisaillement (13) travaille dans une zone partielle excentrique par rapport à la zone d'attaque pratiquement circulaire d'un trépan (5) pour forage rotary. Le dispositif de forage directionnel consiste en un ou plusieurs jets de cisaillement (13) fixés de façon rotative autour d'axes de rotation excentrés par rapport à l'axe de rotation (6) du trépan (5). Le point d'impact des jets de cisaillement est asymétrique par rapport à l'axe de rotation (11). Lorsque le trépan (5) tourne autour de son axe (6), le point d'impact des jets de cisaillement (13) conserve une orientation prédéterminée par rapport à l'axe de rotation (11), le jet de cisaillement (13) balayant ainsi une aire excentrée par rapport à l'axe (6) du trépan (5).

Claims

C l a i m s
1. A method for directional drilling of holes in the crust of
the earth, wherein the direction of a hole is changed by
eroding a portion of the hole's bottom and, possibly, also
wall by means of one or more shear jets, such as liquid jets
which are allotted high speed by means of suitable nozzles,
c h a r a c t e r i z e d i n that the shear jets (13)
erode the hole's (1) bottom and, possibly, wall in the
direction in which the hole (1) is desired to be extended,
simultaneously as a rotary bit (5) works the non-eroded
portion of the hole's (1) bottom, whereby the bit (5)
naturally will seek its way in the direction where the
bottom/wall of the bore hole (1) is eroded.
2. A device for directional drilling of holes in the crust of
the earth in accordance with the method as set forth in claim
1, comprising a rotary bit (5) having at least one nozzle (9)
to generate a liquid-based shear jet (13), wherein the nozzle
(9) is rotatable around an axis (11) substantially parallel
to the axis (6) of the bit (5) and eccentrically placed in
relation to the axis (6), and wherein the nozzle (9) is
adapted to direct at least one shear jet (13) obliquely out
from the axis (11) toward the bottom of the hole (1),
c h a r a c t e r i z e d i n that the nozzle (9) is
adapted to rotate about the axis (11) with the same speed
as the bit (5) and with a rotational direction opposite of
the rotational direction of the bit (5), so that the
direction of the shear jets (13) does not change when the
bit (5) rotates.

Description

CA 02216784 1997-09-29
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A METHOD AND A DEVICE FOR DIRECTIONAL D~TTTTNG
The invention relates to a method and a device for
directional drilling.
In connection with the drilling of holes in the crust of
the earth, e.g. gas and oil wells, it is often desirable to
be in a position of varying the direction of the bore hole.
In order to utilize a gas or oil field at a relatively large
distance from an oil installation, it is necessary to drill
wells ext~n~;ng laterally out from the oil installation.
Methods and devices for drilling wells having a moderate
deviation from a vertical line, are well known. It has
become more and more usual, especially in connection with
newer fields in the North Sea, to drill wells deviating
substantially from the vertical line, and there exist wells
of long extents close to horizontal. Optimum utilization of
an oil field requires that gas and oil wells can be drilled
in a predetermined direction and with a relatively high
accurancy. Also, when drawing cables through the ground,
there is a need for hole drilling in varying directions.
It is known to place a wedge or key, a socalled whipstock
(a guide key), within a bore hole in order to force the
bit laterally outwards in order to achieve a directional
change. Such a whipstock has several disadvantages which
can be ~ up in that they are time-consuming and
difficult to use, and it happens that they are difficult to

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remove or move after use. More modern directional drilling of
gas and oil wells uses a downhole motor operating the bit.
Then, the drill string does not rotate, it being usual to
use coiled tubing as drill string. Directional guidance is
achieved in that the rotational axis of the bit forms an
angle with the axis of the drill string, the bit thereby
trying to point laterally. If the bottom part of the drill
string, possibly the downhole motor, is assigned a
navigational aid giving the operator information concerning
the direction in which the drilling is taking place, the
operator may choose a drilling direction through a rotation
of the drill string. Also, it is known to dispose a separate
downhole directional unit remote operated from the surface,
such that the operator can choose drilling direction.
In spite of these known methods and devices, it appears to
be difficult to achieve the desired and guided drilling
direction. This may have several causes, but variations
within the formation in which the drilling is carried out,
has a major influence thereon. The bit has a tendency of
deviating from a hard zone towards a softer one. If one shall
drill laterally out through an existing vertical well, it
is often necessary to subject the bit to large and
disadvantageous lateral forces. This is particularly the case
if the drilling is to be carried out through the side of a
lined well.
In connection with horizontal bore holes, it is generally
a problem to achieve the desired resting force between bit
and formation, and the drilling rate decreases. Increased
drilling rate may, however, be achieved through the
arrangement of shear jets, e.g. a high speed abrasive liquid
flow, such as known from Norwegian patent No. 171,077, within
the cutting area of the bit.
The object of the invention is to provide a method and a
device giving an easily guidable drilling direction.

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The object is achieved through features as defined in the
following claims.
According to the invention, one or more shear jets are
disposed within the shearing or cutting area of the bit,
correspondingly to what is known from said Norwegian patent
No. 171,077, where the hitting points of the shear jets are
symmetrically positioned around a rotational axis around
which the shear jets can rotate. In accordance with the
invention, the hitting points of the shear jets are
asymmetrically disposed in relation to said rotational axis.
Using this principle, the bit itself will seek the desired
direction where the resistance against drilling is the least.
An examplary embodiment of the invention is described in the
following, reference being made to the attached drawings,
wherein:
Figure 1 diagrammatically shows a part of a well wherein
a drill string and a downhole equipment for directional
drilling are disposed;
Figure 2 shows, on a larger scale, from the side and partly
in section, a bit having an eccentrically placed and freely
suspended nozzle for supplying a shear jet;
Figure 3 shows the same bit as in figure 2 when the bit has
rotated half a revolution;
Figure 4 shows a shearing path for a shear jet, as seen in
the direction of drilling.
In figure 1, reference numeral 1 denotes a well where the
bottom end of a substantially vertical drill string 2 is
coupled to a tubular bend 3 and a downhole motor 4 adapted to
operate a bit S. By means of the bend 3, the rotational axis
6 of the bit 5 deviates from the axis 7 of the drill string
2. Thus, the drilling direction will deviate from the

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substantially vertical well 1. Upon rotating the drill string
2, the bit 5 may, as known, be brought to drill in another
direction.
In the bit 5, as known per se, an eccentrically placed nozzle
9 has been freely susp~n~ in a bearing 10. The nozzle 9 can
turn about a rotational axis 11 substantially parallel to the
axis 6 of the bit 5. Cutting fluid is supplied to the nozzle
9 through a supply hose 12. Out from the nozzle 9, a jet 13
of abrasive liquid flows. The direction of the jet 13
deviates from the direction of the rotational axis 11 of the
nozzle 9. However, the direction of the jet 13 is fixed as it
appears from figure 3 where the bit has rotated half a
revolution. The nozzle 9 is adapted to rotate about the axis
11 with the same speed as the bit 5 and with a rotational
direction opposite of the rotational direction of the bit 5,
so that the direction of the shear jets 13 does not change
when the bit 5 rotates. Thus, the jet 13 works an area within
a limited and eccentrically placed part face of the total
working face of the bit 5. The result is reduced resistance
against drilling in the direction defined by the eccentric
location of said part face. By altering the direction of the
jet 13, e.g. by turning the supply hose 12 a little, the part
face's location can be changed and, then, the drilling
direction will also be changed because the bit 5 seeks
towards a place exhibiting a lower resistance against
drilling.
In figure 4, the circle 14 denotes the wall of the well 1 as
seen in the direction of drilling, while 15 denotes the
working path of the jet 13 as the bit 5 rotates. As it
appears from figure 4, the jet 13 works on an eccentrically
placed part face of the total and substantially circular
working face of the bit 5. This is achieved in that the
hitting point of the shear jet 13 is eccentrically positioned
in relation to the rotational axis 11 of the nozzle 9. If
more than one shear jet 13 are used, the hitting points of
the shear jets 13 must be asymmetrically situated in relation

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s
to the rotational axis 11. Thus, the centre of gravity of
the area situated within the hitting points of the shear
jets 13 becomes eccentrically located in relation to the
rotational axis 11 of the shear jets.
The degree of directional guidance can be made to vary by
letting the shear jets 13 be selectively activatable. At a
desired point of time, one or more nozzles 9 may be closed
by adding particles to the flow within the supply hose 12.
The nozzles 9 may have differently sized outlet openings, and
adapted to be closed selectively by adding particles larger
than one nozzle's 9 outlet opening.
The direction of the shear jets 13 may also be variable and
controllable (guidable) in that the nozzles g are flexably
suspended and by varying the tension on the supply hose 12.
It goes without saying that the invention is not restricted
to the use of abrasive liquid jets, but that all suitable
shear and cutting jets may be utilized, such as it e.g.
appears from Norwegian patent No. 171,077.
Also, it goes without saying that the invention can be used
in connection with all kinds of directional drilling.

Representative Drawing