Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A METHOD AND SYSTEM FOR ~ l ~l~ING AND GUIDING A DRILL.
Field of the Invention
5 This invention relates to percussive in-the-hole (ITH) drilling and more particularly to a system for
steering and guiding a drill.
The present above-identified application discloses a drilling method and apparatus which departs
from prior art techniques which are solely dependent upon fluid-cutting for steering by lltili7ing
10 fluid pressure to effect a positive action on the drill head, to thereby direct the drilling head in the
desired direction. Such deflection of the drilling head is carried out while rotation of the drill string
is tPrmin~ted and once the deflection is completed, drilling is commenced in the new direction by
the normal rotation and advancement of the drill string. Other prior art techniques for subsurface
drilling require that rotation of the drill string be stopped, the drilling head segments adjusted for a
15 new direction of travel and rotation begin again. Such devices often use a beveled drill head, that is,
with one face of the drill head beveled in a direction of the longitudinal axis of the drill head or
other well known drill head configurations. Prior art methods and apparatus for steering a drilling
device are disclosed in United States Patent number 5,535,835 in the name of Walker; United
States Patent number 5,484,889 in the name of Gray; and, United States Patent number 5,054,565
20 in the name of Kinnan, and are herein incorporated by reference.
The presence of hard material such as rocks, hard soil debris or conversely the presence of soft
spots due to sand, wet soil, etc., may prevent a drilling head according to the prior art, whether a
beveled head or other well known drilling heads, *om getting a bite in the soil or rock adjacent the
2s end of the drilling head; this results in drilling in a direction offset from that desired because of
where the drill head gets a firm bite into adjacent soil. The aforementioned Kinnan patent discloses
a percussive drill which applies impact strokes to a pipe string, permitting a drill tip coupled
therewith to break up rocks and hard compacted soil, to engage the media so that the drill head can
move in a desired direction. Although the Kinnan patent may to some degree perform its intended
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Doc. No. 14-2 CA
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function, there is a need for a more controllable, steerable, drill capable of working in the presence
of hard material such as rock and hard soil debris.
It is an object of the invention to overcome some of the limitations presented in prior art devices.
s
It is a further object of the invention to provide a method and system that lends itself to retrofitting
existing percussive drilling systems.
It is a further object of the invention, to provide an in-the-hole (ITH) drilling system that is
0 relatively inexpensive to implement using cullelllly available drilling systems.
It is yet a further object of the invention to provide a method of steering an ITH drilling system
without the presence of an instrument at or about the ITH hammer for effecting steering.
5 Summary of the Invention
In accordance with the invention, in a subsoil drilling system having a rotatable drilling assembly,
means for providing rotary motion to the drilling assembly, pipe string means coupled to the
drilling assembly, and impacting means for applying a percussive force to said drilling assembly, a
20 method is provided of steering the rotatable drilling assembly comprising the steps of:
a) simultaneously rotating the drilling assembly about an axis and imparting a percussive force to
the drilling assembly and varying the rotational speed during a revolution so as to impart a greater
number of percussions while sweeping through a first arc comprising one portion of the revolution,
25 than while sweeping a same distance through a second portion of equal dimension of the
revolution; and
b) repeating step (a) a plurality of times.
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.
In accordance with the invention there is further provided, a method of steering a rotatable drill bit
in a percussive drilling system comprising the steps of:
a) rotating the rotatable drill bit while applying a percussive force to the drill bit, and
s b) varying the percussive force exerted such that, while sweeping through two equal angles
defining two non-overlapping regions within of one full rotation of the drill bit, the total percussive
force while sweeping through each of the two equal angles is unequal; and,
c) repeating steps (a) and (b) a plurality of times.
o The step of varying the percussive force may be accomplished by varying at least one of:
i) the number of percussions while sweeping through two equal angles defining two non-
overlapping regions within one full rotation, and,
ii) an interval of time while sweeping through two equal angles defining two non-overlapping
regions within one full rotation; and,
5 iii) the percussive force while sweeping through two equal angles defining two non-overlapping
regions within one full rotation;
In accordance with another aspect of the invention, a system is provided for steering a rotatable
drill bit comprising:
20 means for rotating the rotatable drill bit; and,
means for applying and varying a percussive force upon the rotatable drill bit while rotating the
rotatable drill bit.
In accordance with yet another aspect of the invention, a steerable drilling system is provided
2s comprising:
a rotatable drilling assembly;
means for providing rotary motion to the drilling assembly;
pipe string means coupled to the drilling assembly;
impacting means for applying a percussive force to said drilling assembly;
30 means for imparting a percussive force to the drilling assembly; and,
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control means for varying the rotational speed during a revolution of the rotatable drilling assembly
so as to impart a greater number of percussions while sweeping through a first arc comprising one
portion of the revolution, than while sweeping a same distance through a second portion of the
revolution.
s
Advantageously, the invention provides a method and system for steering a drill bit of a drilling
system wherein only moderate modifications are necessary to existing systems to achieve
controlled steering of the bit.
o ~rief Description of the Drawings
Exemplary embodiments of the invention will now be described in conjunction with the following
drawings, in which:
5 Fig. 1 a is a pictorial view of a an ITH drilling system including a triaxial acoustic detector for
det~rmining position of a drilling bit;
Fig. lb is a schematic block diagram of a circuit for bit location measurment;
20 Fig. 2a is a pictorial view shown partly in section, of an ITH drilling system;
Fig. 2b is a pictorial view shown partly in section, of a second embodiment an ITH drilling system
in accordance with the invention;
25 Fig. 3a is a front view of a drill string having an eccentric hammer in accordance with an
embodiment of the invention;
Fig. 3b is a front view of a drill sking having curved bit in accordance with an embodiment of the
invention;
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Fig. 3c is a front view of a drill string having an angular bit in accordance with an embodiment of
the invention,
Additional m~t~ri~l in Appendix I forms a part of this specification and further elaborates and
s provides examples relating to this invention and its use.
This invention provides a method and system for steering a down-hole drill bit while drilling.
Location of the bit position while in situ can be achieved by various means. Conventional
gyroscopic or other intertial navigation methods may be implemented, however locating a sensor in
the vicinity of a percussive drill at the bottom of a hole is not preferred, as these sensors must
withstand extreme shock and vibration.
An alternative to the down-hole installation of a sensor is to determine the bit position from the
surface. Further details regarding this approach addressed to one with skill in the art are found
within Appendix I.
Referring now to Fig. 2a, a conventional ITH drilling system is shown having a drill string 10, a
motor 12 coupled to rotate the drill string, a cylinder 1 4 within the drill string 10 housing a hammer
in the form of a movable piston 16 for exerting a percussive force to a rotatable drill assembly in
the form of a drill bit 18 disposed below. The drill bit 18 is coupled with the drill string 10 and
rotates therewith.
The operation of the system shown in Fig. 2a in accordance with prior art methods is as follows.
The ITH percussive drilling string is continuously rotated without varying its angular speed along
the circumference ofthe hole it is (1rilling. A non-varying percussive drilling force is
simultaneously applied.
In contrast, and in accordance with this invention, it is found that by varying the angular speed
along the circumference of the hole, the percussive hammer 16 can be forced to work more on one
side or portion of the hole, by slowing down the angular speed, and less on another other side or
Doc. ~o. 14-2 CA
~ 2201058
portion, by increasing the angular speed, thus generating a force imbalance around the bit, causing
the string to deviate away from a straight line.
This is exemplified more clearly with reference to Fig. 2b, wherein a longitudinal axis of the drill
5 bit 18 is offset from a longitudinal axis of the drill string by a distance "e". Here, by varying the
angular speed along the circumference of the hole during each of a plurality of revolutions, the
hammer is forced to work more on one side of the hole - by slowing down the angular speed - and
less on the other side - by increasing the angular speed. This generates a force imbalance around the
bit, causing the string to deviate away from a straight line.
Of course a similar effect can be realized by applying a substantially constant force and number of
percussions on one side of the hole while varying the number of, or force of, percussions on a
different side of the hole, while the drill bit is rotating at a constant speed, again forcing the
h~mmer to work more on one side of the hole, than the other.
In Fig. 2b, the lower portion of the movable piston is shown to have its longitudinal axis offset
from the longitudinal axis of the drill string 10. Of course this offsetting of the piston 16 in this
manner is optional.
20 In ITH percussive drilling the drill string is continuously rotating to provide indexing to the bit. In
these embodiments, a permanent offset is introduced between the bit axis and the axis of the drill
string as shown in Figs 3a, 3b, and 3c. This is a minor modification in the conventional hammer. In
the modified h~mmer with no rotation, the attack of the bit on the rock is coaxial with the axis of
the hole but is displaced by an eccentricity e (or at an angle ~d). Therefore, the bit impacts partially
25 to the side of the wall of the hole hence, instead of drilling in a straight line, it will deviate towards
the side of the wall being hit. Continuous drilling in this fashion results in a curved hole. In the case
of constant rotation, bit impacts to the side walls are symmetrical on all sides of the hole, resulting
in a substantially straight line trajectory. By varying angular speed along the circumference of the
hole, the eccentric hammer is forced to work more on one side of the hole - by slowing down the
30 angular speed - and less on other side - by increasing angular speed -thus generating a lateral force
~ ~ ~ n ~ ~ 5 8 Doc. No. 14-2 CA
imbalance around the bit, causing the string to deviate away from a straight line. This provides the
steering feature to the eccentric hammer.
A two-speed motor is sufficient to add this feature in the system. The necessary characteristics
S required for such a motor are high torque, and rapid transient response. Through speed control it is
possible to steer the modified drill in a desired trajectory. This proposed mechanism is referred to
as the 'Controlled Rotation Eccentric Hammer Mech~ni~m~" or "CRE Hammer Mech~ni~m "
In operation, in accordance with the embodiments shown in Figs. 3a, 3b, and 3c, if the drill string
I o is constantly rotated without varying its speed and without varying the percussive force of the
h:~mmer (not shown), as in normal operation, it will drill in the same direction as it was drilling
without this permanent offset except that the diameter of the hole will be slightly larger. This is
shown in Fig 4a where the expected shape of the drill string when it is not rotated at a constant
speed whereas Fig. 4b shows the expected straight line trajectory when modified system is rotated
15 at constant speed.
A steering controller (not shown) calculates the switching phase angle based on the error signal and
issues the command signal to the rotation system. Hence, it distributes the number of blows per unit
of the rotation angle along the circumference of the hole wall in a desired manner. This results in
20 steering of the drill bit in a desired direction.
In Appendix I a kinematic model of this system is provided for analyzing the steerability of the
CRE-Hammer.
25 A guidance system can be added to the system described heretofore without the installation of
down-hole instrumentation.
For bit location measurement, a remote sensing technique is achieved by lltili~ing acoustic source
location, using a triaxial hodogram method as is shown in Fig. 5. For steering actuation, a
30 Conkolled Rotation Eccentric Hammer Mech~ni.sm (CRE Hammer Mech~nism) is implemented. In
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this mech~ni~m the rotation of the bit is controlled along the rotation angle of the bit of an eccentric
hammer to achieve steering.
Numerous other embodiments may be envisaged without departing from the spirit and scope of the
s invention.
