Note: Descriptions are shown in the official language in which they were submitted.
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An Improved Directional Drilling Tool
Technical Field
The present invention relates to the field of oil and gas exploration, and in
particular
downhole drilling activities. More specifically, the present invention is a
remotely
controlled directional drilling tool for use in downhole drilling.
Background Art
It is known to utilise a Surface-Adjustable Bent (SAB) housing when drilling a
well
which has to follow a particular geometric path rather than one which is a
"straight-
hole". The SAB housing typically forms part of a downhole drilling motor and
is
located between the power and bearing sections of the motor. The SAB housing
comprises a fixed upper section connected to the power section of the motor,
and a
lower section which is rotatable relative to the upper section and connected
to the
bearing section and drill bit. The joint between the upper and lower sections
of the
SAB housing is angled such that the rotational axis of the lower section is at
an angle
a relative to the longitudinal axis of the upper section. The angle a is
typically in the
range of 0-3 , and the angle may be adjusted manually at the surface prior to
commencing a drilling operation.
Disclosure of invention
These SAB housings have several drawbacks. Firstly, the maximum bend angle
between the longitudinal axes of the upper and lower sections of the housing
is 2a,
but the maximum angle is limited to a smaller angle downhole due to space
constraints within the borehole. Secondly, any adjustment of the housing must
be
carried out manually at the surface, adding to the time and associated costs
of the
drilling operation.
A solution to these problems was presented in US4836303, in which the upper
section of the housing is radially offset from the longitudinal axis of the
motor such
that the longitudinal axis of the upper section is at an angle to the
longitudinal axis
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of the motor. In addition, the device can be remotely adjusted downhole,
thereby
avoiding the need for the drill string to be recovered to the surface for
adjustment of
the housing. These two features provide a greater range of angle adjustment
for the
housing. However, the drilling operation has to be halted and the drill string
lifted
off-bottom in order for the angular displacement of the upper and/or lower
sections
to be adjusted, thereby still involving a significant amount of non-drilling
time
(NDT) in any drilling operation.
It is an aim of the present invention to obviate or mitigate one or more of
these
disadvantages with existing tools.
According to a first aspect of the present invention there is provided a
directional
drilling tool, comprising:
a first end attachable to a drill string, and a second end attachable to a
drill
bit;
a swivel section intermediate the first and second ends and having a first
swivel member non-rotatably attached to the first end and a second swivel
member
rotatably coupled to the first swivel member and rotatable relative thereto
about a
first axis of rotation which is co-axial with a longitudinal axis of the tool;
a first actuator adapted to selectively rotate the second swivel member about
the
first axis of rotation;
an adjustable bend section having a first bend member non-rotatably
attached to the second swivel member and a second bend member rotatably
coupled to the first bend member, wherein the first bend member is co-axial
with
the longitudinal axis, and the second bend member is rotatable relative to the
first
bend member about a second axis of rotation which is at a non-zero angle
relative to
the longitudinal axis; and
a second actuator adapted to selectively rotate the second bend member
about the second axis of rotation.
The first actuator may be housed in the first swivel member. The first
actuator may
be a first motor drive comprising a first motor having a first rotating drive
shaft,
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wherein the first motor drive transforms an initial rotational motion of the
first
drive shaft into an intermediate axial motion, and transforms the axial motion
into a
final rotational motion of the second swivel member.
The first motor drive may further comprise:
a first drive member rotatably engaged with the first drive shaft;
a second drive member non-rotatably engaged with the first swivel member
and adapted to move axially relative to the first swivel member in response to
rotation of the first drive member; and
a first helical output shaft having a first end engaged with the second drive
member and a second end attached to the second swivel member, wherein axial
movement of the second drive member rotates the first output shaft and the
second
swivel member.
The first output shaft may be a follower shaft and the second drive member may
include a socket cam in which the first end of the first output shaft is
engaged.
The second actuator may be a second motor drive housed in the first bend
member,
the second motor drive lying along a drive axis which is at the non-zero angle
relative to the longitudinal axis of the tool.
The second motor drive may comprise a second motor having a second rotating
drive shaft, wherein the second motor drive transforms an initial rotational
motion
of the second drive shaft into an intermediate axial motion, and transforms
the axial
motion into a final rotational motion of the second bend member.
The second motor drive may further comprise:
a third drive member rotatably engaged with the second drive shaft;
a fourth drive member non-rotatably engaged with the first bend member
and adapted to move axially relative to the first bend member in response to
rotation of the third drive member; and
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a second helical output shaft having a first end engaged with the fourth drive
member and a second end attached to the second bend member, wherein axial
movement of the fourth drive member rotates the second output shaft and the
second bend member.
The second output shaft may be a follower shaft and the fourth drive member
may
include a socket cam in which the first end of the second output shaft is
engaged.
The drilling tool may further comprise a remote control system having an
operator
control interface, the control system adapted to activate the first and second
actuators in response to pre-programmed instructions and/or manual inputs at
the
control interface.
The control interface may include a graphical display means indicating the
path of
the tool.
According to a second aspect of the invention there is provided a directional
drilling
system, comprising:
a directional drilling tool according to the first aspect of the invention;
a drill bit attached to the second end of the tool;
a measuring device adapted to monitor the orientation and position of the
drill bit;
a remote control system having an operator control interface adapted to
receive manual tool control inputs; and
an electronic controller adapted to selectively activate the first and/or
second actuators of the tool in response to pre-programmed instructions and/or
signals from the measuring device and/or remote control system.
Each of the swivel and adjustable bend sections may further comprise one or
more
positional sensors adapted to communicate the rotational position of the
swivel and
adjustable bend sections to the controller.
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According to a third aspect of the invention there is provided a control
process for a
directional drilling tool having a first swivel member non-rotatably attached
to a
first end of the tool and a second swivel member rotatably coupled to the
first
swivel member and rotatable relative thereto about a first axis of rotation
which is
5 co-axial
with a longitudinal axis of the tool; a first actuator adapted to selectively
rotate the second swivel member about the first axis of rotation; a first bend
member non-rotatably attached to the second swivel member and a second bend
member rotatably coupled to the first bend member, wherein the first bend
member
is co-axial with the longitudinal axis, and the second bend member is
rotatable
relative to the first bend member about a second axis of rotation which is at
a non-
zero angle relative to the longitudinal axis; and a second actuator adapted to
selectively rotate the second bend member about the second axis of rotation,
the
process comprising the steps of:
receiving pre-programmed instructions and/or manual control inputs from a
remote control system regarding a desired drilling path of a drill bit
attached to the
drilling tool;
applying the instructions and/or control inputs to the first and/or second
actuators and commencing drilling on the desired path;
establishing the current orientation and position of the drill bit;
determining whether the current orientation and position of the drill bit
indicates that the drill bit remains on the desired drilling path;
checking for additional manual control inputs from the control system; and
applying any necessary modifications to the first and/or second actuator
positions based upon the determination step and/or additional control inputs.
The desired drilling path is selected based upon the pre-programmed
instructions
and/or manual control inputs. The determining step compares the current
orientation and position of the drill bit with the desired drilling path set
by the pre-
programmed instructions and/or manual control inputs. The step of applying any
necessary modifications therefore includes applying corrective feedback from
the
control system should the determining step have established that the drill bit
has
diverged from the desired drilling path.
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The process may further comprise the step of displaying the current drilling
path on
an operator control interface of the remote control system.
According to a fourth aspect of the invention there is provided a motor drive
for
rotating a first body relative to a second body, the motor drive comprising a
motor
having a rotating drive shaft, wherein the motor drive transforms an initial
rotational motion of the drive shaft into an intermediate axial motion, and
transforms the axial motion into a final rotational motion of the second body.
The motor drive may further comprise:
a first drive member rotatably engaged with the drive shaft;
a second drive member non-rotatably engaged with the first body and
adapted to move axially relative to the first body in response to rotation of
the first
drive member; and
a helical output shaft having a first end engaged with the second drive
member and a second end attached to the second body, wherein axial movement of
the second drive member rotates the helical output shaft and the second body.
The helical output shaft may be a follower shaft and the second drive member
may
include a socket cam in which the first end of the helical output shaft is
engaged.
Brief Description of Drawings
A preferred embodiment of the present invention will now be described by way
of
example only, with reference to the accompanying drawings in which:
Figure 1 is a schematic representation of a directional drilling tool;
Figures 2(a) and 2(b) are vertical section and side views, respectively, of a
motorised swivel forming part of the drilling tool of figure 1;
Figure 3 is a projected view of socket and shaft components of the swivel of
figure 2;
Figure 4 is a horizontal section through the swivel along line B-B of figure
2(a);
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Figures 5(a) and 5(b) are vertical section and side views, respectively, of an
adjustable bent sub forming part of the drilling tool of figure 1;
Figures 6(a) and 6(b) are vertical section and side views, respectively, of
the
adjustable bent sub of figure 5 in a first state;
Figures 7(a) and 7(b) are vertical section and side views, respectively, of
the
adjustable bent sub of figure 5 in a second state;
Figure 8 is a schematic representation of a downhole drilling system
incorporating the drilling tool of figure 1; and
Figure 9 is a flow chart illustrating the control process of the system of
figure
8.
Best Mode for Carrying Out the Invention
Figure 1 schematically shows a directional drilling tool according to the
present
invention. The drilling tool, generally designated 1, comprises a first or
upper end 2
connectable to a drill string (not shown) and a second or lower end 4
connectable to
a drill bit (not shown in figure 1). The tool 1 further comprises a motorised
swivel 6
having a first swivel member non-rotatably attached to the first end 2 and a
second
swivel member attached to the remainder of the tool 1. As will be explained in
more
detail below, the first and second swivel members may be selectively rotated
relative to one another so as to rotate the tool 1 relative to the drill
string.
Below the swivel 6, the tool 1 further comprises a dump valve section 8 and a
power
section 10, both of which are of a type known in the art. Below the power
section 10
is an adjustable bend section, also known as a bent sub, 12 having a first
bend
member attached to the power section 10 and a second bend member attached to
the remaining downstream components of the tool 1. The first and second bend
members may be selectively rotated relative to one another so as to rotate an
attached drill bit (not shown) relative to the swivel 6, dump valve 8 and
power
sections 10 of the tool 1. Completing the downstream elements of the tool 1
are a
transmission assembly 14 and a bearing section 16, which are again both of a
type
known in the art.
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Figures 2,3 and 4 show the components of the swivel 6 in more detail. The
swivel
comprises a first tubular member 18 and a second tubular member 20. The free
end
of the first member 18 is attached to a drill string by way of a threaded
connection
(not shown). The free end of the second member 20 is non-rotatably attached,
either directly or indirectly, to the power section 10 by a threaded
connection (not
shown). A bore 22 extends longitudinally through the swivel so as to permit
drilling
mud to pass into the power section 10 from the drill string above.
The swivel 6 includes an actuator adapted to selectively rotate the second
member
relative to the first member 18. In this preferred embodiment, the actuator is
a
motor drive housed in the first member 18. The motor drive includes a motor
compartment 24 located between the outer wall of the first member 18 and the
bore
22. Located within the motor compartment 24 is a high voltage (400-600V)
electric
15 motor 26, which has a thermally insulated coil and is adapted so as to
be highly
resistant to corrosion and abrasion. The motor 26 has a drive shaft 28 which
is
supported by a bearing 30 on a support plate 32 having a niche 34 in which the
bearing 30 is located. Figure 4 shows that the support plate 32 is non-
rotatably
fixed to the first tubular member 18 by four splines 36 that ensure the plate
32 and
20 niche 34 are properly aligned with the drive shaft 28 and bearing 30. A
sealing
sleeve 38 seals the motor 26 and motor compartment 24 from the bore 22.
The drive shaft 28 is engaged with an annular gear 40 which is co-axial with
the
bore 22. The gear 40 is integrally formed with, or non-rotatably attached to,
an
upper end of a first drive member in the form of a power screw 42. The screw
42 is
located within a second drive member, or socket, 44 which has an internal
thread
which engages with an external thread on the screw 42. The socket 44 has a
plurality of external splines 46 which engage with corresponding splines 47 on
the
internal surface of the first tubular member 18. The splines 46,47 prevent
relative
rotation between the socket 44 and first tubular member 18, but permit
relative
movement between the two in the axial direction. Thus, rotation of the gear 40
and
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power screw 42 by the motor 26 effects an axial movement of the socket 44
relative
to the screw 42 and first tubular member 18.
An output shaft 48 is connected to the socket 44 via a spiral socket cam SO,
as best
seen in figure 3. The output shaft 48 is a helical, or spiral, follower shaft
with a
polygonal cross section that could alternatively be hexagonal, octagonal or
square,
for example, and is threaded at its remote end 49. The socket cam 50 and
follower
shaft 48 cooperate with one another so that as the socket 44 moves axially,
the
output shaft 48 rotates. The threaded end 49 of the output shaft 48 is
connected to
the second tubular member 20 of the swivel 6. Hence, operation of the motor 26
will rotate the second tubular member 20 relative to the first tubular member
18,
such that the tool 1 and drill bit rotate relative to the remainder of the
drill string.
The socket 44 cannot move axially unless the power screw 42 is rotated.
Consequently, the socket 44 isolates the motor 26 from any reaction moments
from
the second tubular member 20. In the same way, the socket 44 provides a
locking
mechanism to the swivel 6 and tool 1 that locks the first and second tubular
members 18,20 at the chosen rotational angle relative to one another. This
arrangement adds to the overall reduction ratio of the drive and increases the
accuracy and sensitivity of the output.
The axial motion of the power screw 42 is limited in the downward direction
(when
viewed in figure 2) by a stopper (not shown) located on the splines 47 of the
first
tubular member 18 at the lower end of the member 18, whilst axial motion is
limited in the upward direction by a thrust bearing 52 and a locking nut 54 on
the
lower side of the support plate 32. The thrust bearing 52 reduces friction
during
rotation of the power screw 42, thus minimizing the required driving torque
from
the electric motor 26.
The swivel 6 is preferably filled with oil to reduce friction and to avoid
sticking of
the moving components. Accordingly, a number of seals are provided to prohibit
mud flowing through the bore 22 from contaminating the oil. A first oil seal
56 is
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provided between the first tubular member 18 and the output shaft 48 where the
output shaft 48 exits the lower end of the tubular member 18. A second oil
seal 58
is provided between the lower end of the power screw 42 and the output shaft
48,
whilst a third oil seal 60 is provided between the annular gear 40 and the
sealing
5 sleeve 38. A sealing gasket 62 is deployed between the adjacent ends of
the first and
second tubular members 18,20 to prevent any contamination or leakage between
the mud flowing through the bore 22 and the oil inside the swivel 6.
Figures 5 to 7 show the bent sub 12 in various states of operation. The bent
sub 12
10 includes an actuator, which in this preferred embodiment is housed in a
first tubular
member 118 and is comprised of components which are near-identical to those of
the swivel 6. The sub 12 comprises a first tubular member 118 having a
longitudinal axis Li shared with the overall tool 1, and a second tubular
member
120 having a longitudinal axis L2. The free ends of the first and second
members
118,120 are attached to the power section 10 and transmission assembly 14 of
the
tool 1, respectively, as shown schematically in figure 1. A bore 122 extends
longitudinally through the sub 12, and houses the output shaft 123 from the
power
section 10. The main difference between the swivel 6 and bent sub 12 is that
in the
bent sub 12 the second member 120 is mounted relative to the first member 118
such that it is rotatable about a rotational axis R which is at an angle a
relative to the
longitudinal axis L1 of the tool 1. The drive system components of the bent
sub 12
and the manner in which they effect rotation of the second member 120 relative
to
the first member 118 are the same as those of the swivel 6 described above,
but the
drive system of the bent sub 12 lies along a rotational axis R at the angle a
relative
to the axis L1. Those components will therefore not be described again in
detail
here.
An additional straight sleeve 119 is fitted to the upper end of the first
member 118
to ensure a straight connection with the power section 10 above. The output
shaft
123 passes through the bore 122 with enough space to accommodate the
eccentricity in the shaft motion, which is shown in Figure 6. Figure 7 shows
the
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maximum bend angle of the sub 12 and shows the shaft 123 passing freely
through
the bore 122 at that maximum angle.
The relative angular displacement 0 between the longitudinal axes L1,L2 of the
first
and second members 118,120 will follow an elliptical path with a maximum bend
angle between them of 2a, where a is the angle of the rotational axis R
relative to
the longitudinal axis L1 of the first member 118, as shown in Figure 7. The
bent sub
12 thus can create any desired bend angle for drilling between 0 and 2a.
Rotation of the swivel 6 then rotates the bend sub 12 to adjust the drilling
direction.
Tests have been carried out to show the correlation between the rotation of
the
second member 120 relative to the first member 118 and the resulting bend
angle
between the axes L1 and L2 in addition to the corresponding direction of the
tool
face. The study was made for a bent sub where the angle is a. The results
indicated
that as the second member 120 rotates 180 relative to the first member 118,
the
bend angle between the longitudinal axes L1,L2 of the first and second members
118,120 reaches 2a and then decreases as the second member 120 rotates through
360 .
Closed form expressions have been developed for calculating the bend angle and
direction based on simple trigonometry rules. The closed form expressions for
the
bend and direction are as follows:
= Bend Angle )6'
j= 2 sin-2(sin cc sin 612 )
= Direction Angle D
cos a ¨ cos
tan
_i
SIT!
where 0 is the relative angular displacement between the longitudinal axes L1
and
L2, and a is the angle of the rotational axis R relative to the longitudinal
axis L1.
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Figure 8 schematically illustrates a directional drilling system incorporating
the
directional drilling tool 1. The system comprises a drill bit 70 which is
attached to
the bearing section 16 of the tool 1 in a conventional manner, and a measuring
device adapted to monitor the real time orientation and position of the drill
bit 70.
The measuring device is preferably a measurement while drilling (MWD) tool 72.
The MWD tool 72 transmits its measurements to an electronic controller 74. In
two-
way communication with the controller 74 is a remote control system, which is
preferably a remote surface steering (RSS) unit 76. The RSS unit 76 may be
provided with a display means to graphically illustrate to an operator the
bend
angle and drilling direction of the tool based upon data received from the MWD
tool
72 and the controller 74. The RSS unit 76 also includes controls to allow the
operator to manually input drilling control commands to the controller 74.
The controller 74 can operate in automatic mode, where it will send control
signals
to the motors of the swivel 6 and/or bent sub 12 based on data received from
the
MWD tool 72 in order to keep the drill bit 70 on a preset path, or else in
manual
mode where it will send signals to the motors in response to manual inputs by
the
operator on the RSS unit 76. One or more sensors may be provided in each of
the
swivel 6 and bent sub 12 to send positional data back to the controller 74 so
that the
controller has real time positional information on the operational positioning
of the
swivel 6 and bent sub 12.
The flow diagram of figure 9 shows a control process for the system shown in
figure
8. Following a system start-up step 200, the process will await an input of
the
desired drilling path by an operator at input step 202. At process step 204,
drilling
operations will begin on the basis of data of input step 202. At decision step
206,
the process will establish if there have been any further data inputs from the
operator since the start of drilling. If not, the process will move to a
further decision
step 208 where it is determined whether measurement data from the MWD tool
indicates that the drilling process is within pre-set parameters relating to
the
desired drilling path. If the data indicates that the drilling is no longer
within the
required parameters, process step 210 applies corrections to the swivel and/or
bent
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sub in order to bring the drilling process back to the target path. If the
process
establishes at decision step 206 that further inputs have been made by the
operator,
this overrides any automated corrections and the process will skip decision
step
208 and proceed straight to process step 210 to implement the adjustment
manually requested by the operator.
Referring back to figures 2 to 5, process steps 204 and 210 will generate one
or
more control signals from the controller 74 to the motor 26, 126 of the swivel
6
- and/or bent sub 12. In response to a signal from the controller 74, the
drive shaft
28,128 of the motor 26,126 will rotate clockwise or anti-clockwise as
required. This
rotation of the drive shaft 28,128 will in turn rotate the gear 40,140 and
power
screw 42,142, and the socket 44,144 will axially slide towards or away from
the
output shaft 48,148, depending on the rotational direction of the motor drive
shaft
28,128. The engagement of the spiral socket cam 50,150 on the end of the
socket
44,144 with the spiral follower output shaft 48,148 will result in the
rotation of the
output shaft 48,148 as the socket 44,144 slides towards or away from the shaft
48,148. In this manner, whether in the swivel 6 or bent sub 12, the second
member
20,120 attached to the output shaft 48,148 will rotate relative to the fixed
first
member 18,118 in response to the signal(s) generated at process steps 204 and
210.
Once modification process step 210 has been completed, an optional display
step
212 may display the current drilling data on the RSS unit for the operator. If
the
decision step 208 determines that the drilling procedure is still within the
desired
limits, the process will skip the process step 210 and proceed straight to
display
step 212. Following the display step 212, the decision step 214 will determine
whether a system stop has been initiated, either manually by the operator or
automatically due to a malfunction detected by the controller 74. If no stop
is
initiated, the process will continue to input step 216 where the real-time
data being
received from the MWD tool is received. The process will then begin a further
loop
through the steps at processing step 204. If a system stop is determined at
decision
step 214, the process will pass to stop step 218 and shut down.
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Industrial Applicability
The present invention provides a directional drilling tool whose drilling
angle and
direction can be remotely adjusted simultaneously without interrupting the
drilling
operation. As the tool can be steered whilst drilling is ongoing, drilling
process
efficiency is maximised with minimal NDT.
The motor drive arrangements employed in both the swivel and bent sub provide
high accuracy rotational movements, as well as locking the rotating second
portions
at the desired angle relative to the fixed first portions. The drive
arrangements also
isolate the motors from any reactive loads from the drill bit.
The tool, system and method of the present invention are particularly suited
to
coiled tubing drilling operations. However, they may also be employed in other
direction drilling operations if desired.
Whilst the preferred embodiment of the directional drilling tool includes dump
valve as a top sub, it should be appreciated that in certain applications the
dump
valve is not necessary. In such instances, the dump valve may be replaced by
an
alternative top sub such as, for example, a crossover sub, float sub or flex
sub.
Furthermore, although the preferred actuators for the swivel and bent sub
within
the tool are motor drives other actuator arrangements may be used instead. For
example, the actuators may be hydraulically-operated clutches utilising the
reactive
torque coming from the power section of the tool. In this instance, the second
members of the swivel and bent sub would only rotate in one (anticlockwise)
direction. The clutches may be engaged and disengaged by adjusting the
hydraulic
pressure on a conical part male against a cooperating female part. This
engagement
and disengagement would be carried out by the remote control system on the
surface.
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The motor drive of the present invention is not limited to use in directional
drilling
tools and systems. The motor drive can be used in other applications, downhole
or
otherwise, where a first body is to be rotated relative to a second body. For
example, the motor drive could be employed in a swivel sub for use where
rotation
5 of the lower part of a work string relative to an upper part of the
string is desired.
These and other modifications and improvements may be incorporated without
departing from the scope of the present invention.
10
15
