Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CLIENT REFERENCE NO. 03-HE26
ELECTRO-MECHANICAL THRUSTER
BACKGROUND OF DISCLOSURE
Field of the Disclosure
[0001] Embodiments disclosed herein relate generally to thrusters that apply a
force to a
drill bit during the drilling of an underground formation. In another aspect,
embodiments
disclosed herein relate to control of a thrust force applied to a drill bit by
a thruster. More
specifically, embodiments disclosed herein relate to controlling a pressure or
differential
pressure across a thrust piston, thereby limiting the maximum applied thrust
force.
Background
[0002] Hydraulic thrusters are used for applying a force to an earth boring
drill bit,
independent of the drill string weight. Although thrusters may be used during
vertical or
inclined drilling, hydraulic thrusters are generally advantageous in
horizontal or near-
horizontal drilling. During horizontal drilling, especially in long horizontal
sections, a
significant portion of the weight of the drill stem is directed toward the low
side of the
hole, detracting from the weight available for bit thrust. Hydraulic thrusters
allow for
extended reach drilling, the drilling of multiple horizontal wells from a
single platform,
decreasing the drilling costs associated with producing reservoirs that are
offshore, in
arctic regions, mountains, or near large cities.
[0003] The thruster is a telescoping tube arrangement that allows the drill
bit to advance
while the tubing string is supported in a rather stationary position at the
surface. When
the thruster has advanced its full stroke, or a notable portion thereof, the
drill string is
lowered from the surface, causing the upper end of the thruster to slide down
and reset
the thruster for the next stroke. When the drilling kelly or the stand being
drilled down
by the top drive reaches the drill rig floor, circulation is interrupted and
another piece of
tubing is added to the string at the surface or the coiled tubing is further
unspooled into
the wellbore. This drilling procedure also causes the thruster to reset.
[0004] Hydraulic thrusters are described in, for example, U.S. Patent No.
4,615,401 and
patents referenced therein (U.S. Patent Nos. 3,298,449, 3,399,738, 3,797,589,
3,799,277,
4,040,494, and 4,040,495), each of which is assigned to the assignee of the
present
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invention. In the '401 patent, the hydraulic thruster includes a mandrel and
sleeve
forming two expandable chambers with wall anchors annularly disposed about the
sleeve responsive to a pressure differential between a chamber and the bore
hole
pressure. Valves and actuators are provided to extend and retract a piston
between two extremes of relative axial motion between the mandrel and sleeve.
[0005] Hydraulic thrusters are also described in U.S. Patent No. 5,205,364.
In the '364 patent, the hydraulic thruster includes a telescoping assembly for
transmitting hydraulic force to the drill bit at the bottom of the tool. The
internal
hydraulic characteristics of the tool may be varied to vary the force exerted
during
extension and retraction of the telescoping assembly. The hydraulic
characteristics are varied by varying the surface area within the drill tool
on which
the flow of drilling mud may act when producing the hydraulic force.
[0006] Other patents describing thrusters or equipment for controlling force
or weight on the bit, for example, may include U.S. Patent Nos. 5,316,094,
6,601,652, 7,156,181, 5,476,148, 5,884,716, 5,806,611, 6,003,606, 6,230,813,
and 6,286,592, and U.S. Patent Application Publication No. 20010045300.
[0007] Referring now to Figure 1, a simplified cross-sectional view of a prior
art thruster 1 is illustrated. Thruster 1, shown in the retracted position,
may
include an inner mandrel assembly 2, which may include one or more tubular
components. Threads 3 may connect inner mandrel assembly 2 to the lower drill
stem (not shown) toward the bit (not shown). Threads 4 may connect inner
mandrel assembly 2 to the upper drill stem (not shown). Inner mandrel assembly
2 is disposed in and is axially movable with respect to outer tubular assembly
5.
One or more anchor pistons 6 may be provided to anchor thruster 1 with respect
to the hole wall (not shown). Drilling fluid supplied to the bore 2A of inner
mandrel
2 and to the drill bit (not shown) defines a high pressure area, and drilling
fluid
returning from the bit in the annulus 7 formed between the outer tubular
assembly
6 and the hole wall defines a low pressure area. During thrusting, thrust
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mechanism 8 may be used to allow the high pressure drilling fluid into chamber
A,
allowing fluid in chamber B to escape to annulus 7, thus creating a pressure
differential across thrust mechanism 8,
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causing the inner mandrel 2 to advance in direction 9, and putting weight on
the bit
corresponding to the thrust force generated by the pressure differential.
[0008] A cross-sectional view of a simplified thrust mechanism 8, which may be
used in
the thruster of Figure 1, is illustrated in Figure 2. Thrust mechanism 8 may
include an
inner tubular member 12 and an outer tubular member 14. Drilling mud flowing
through
the bore 16 of inner tubular member 12 flows to the drill bit (not shown), and
returns to
the surface via annulus 18, such as between outer tubular member 14 and a
drill casing
(not shown). When mud is flowing through thruster 1 (Figure 1), bore 16 is at
a higher
pressure than fluid returning through annulus 18. A piston 20, separating a
first fluid
chamber 22 and a second fluid chamber 24, may transmit an axial force 26 to
inner
tubular member 12. During thrusting, high pressure drilling mud flows from the
bore 16
of the thruster 1 through inlet 28 into first fluid chamber 22, displacing
fluid in second
fluid chamber 24 through outlet 30 and causing the inner tubular member 12 to
advance
in the direction of axial force 26. The axial force 26 that is generated, for
example, may
be a function of the differential pressure between the fluid in bore 16 and
annulus 18.
[0009] Many of the patents cited above use such a differential pressure to
control the
force applied to the drill bit. Although not shown in Figure 2, thrust
mechanism 8 may
typically include ball valves, springs, and other mechanisms to control the
flow of fluid
into and from the high and low pressure chambers, respectively, during
thrusting and
retraction. One problem associated with this type of thruster technology
includes the
need to estimate the pressure and required thrust force prior to drilling. The
thruster and
the associated internal parts are generally selected and fabricated at the
surface prior to
installation on a drill string, and many of the parts used to control fluid
flow, such as
springs, check valves, flow orifices, and others, are sized and selected based
on an
expected downhole pressure.
[0010] Often, an actual downhole pressure differs from the expected downhole
pressure.
The difference between actual and expected downhole pressure, even by as
little as 25 or
50 psi, may result in ineffective control of the force applied to the drill
bit by the thruster,
often as a result of the thrust mechanism fully opening or fully closing.
Additionally,
fluctuations in pressure drop across the bit and changes in the weight of the
drilling fluid
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used (and hence bore pressure) may also result in ineffective control of the
force applied
to the drill bit by the thruster. Ineffective thruster control may lead to
stalls, motor wear,
stuck bits, and inefficient rate of penetration, among other problems known to
those
skilled in the art.
[0011] Various methods and apparatus have been proposed to compensate for a
change in
downhole conditions and to minimize the effect such changes have on the
operation of
the thruster and the force applied to the drill bit. For example, a pressure-
modulation
valve assembly is disclosed in U.S. Patent No. 6,102,138. Such methods and
apparatus
unnecessarily increase the total number of drilling components of a drill
string, where the
additional apparatus may be prone to failure or malfunction due to various
conditions
encountered during drilling.
[0012] Accordingly, there exists a need for a thruster that may control the
force applied
to a drill bit independent of the downhole pressure or the pressure drop
across the motor
and bit. Additionally, there exists a need for a thruster that may control the
force applied
to the bit independent of the pressure of the supplied drilling fluid.
SUMMARY OF THE DISCLOSURE
[0013] In one aspect, embodiments disclosed herein relate to a drilling
system, including:
a drill bit; and a thruster to apply a force to the drill bit. The thruster
may include: an
inner tubular member disposed within and configured to axially move within an
outer
tubular member; a thrust piston to transmit a hydraulic force to the inner
tubular member,
the thrust piston separating an upstream fluid chamber and a downstream fluid
chamber
between the inner and outer tubular members; at least one pressure switch
fluidly
connected to the downstream fluid chamber to control flow of a fluid to and
from the
downstream fluid chamber via at least one fluid inlet and at least one fluid
outlet.
[0014] In another aspect, embodiments disclosed herein relate to a thruster,
including: an
inner tubular member disposed within and configured to axially move within an
outer
tubular member; a thrust piston to transmit a hydraulic force to the inner
tubular member,
the thrust piston separating an upstream fluid chamber and a downstream fluid
chamber
between the inner and outer tubular members; a downstream valve member
mechanically
coupled to a downstream magneto-actuator and disposed in the downstream fluid
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chamber; and at least one pressure switch fluidly coupled to the downstream
fluid
chamber to control a position of the downstream valve member via the magneto-
actuator;
wherein the position of the downstream valve member affects a flow of a fluid
to and
from the downstream fluid chamber via at least one fluid inlet and at least
one fluid
outlet.
[0015] In another aspect, embodiments disclosed herein relate to a process to
drill an
underground formation. The process may include: supplying a fluid to a
thruster,
wherein the thruster includes: an inner tubular member disposed within and
configured to
axially move within an outer tubular member; a thrust piston to transmit a
hydraulic force
to the inner tubular member, the piston separating an upstream fluid chamber
and a
downstream fluid chamber between the inner tubular member and the outer
tubular
member; at least one pressure switch fluidly connected to the downstream fluid
chamber;
and regulating a flow of the fluid to and from the downstream fluid chamber in
response
to a signal from the at least one downstream pressure switch to maintain the
hydraulic
force applied to the inner tubular member proximate a hydraulic force set
point.
[0016] Other aspects and advantages will be apparent from the following
description and
the appended claims.
BRIEF DESCRIPTION OF DRAWINGS
[0017] Figure 1 is a simplified schematic drawing of a prior art thruster.
[0018] Figure 2 is a schematic drawing of a simplified thrust mechanism that
may be
used in the prior art thruster of Figure 1.
[0019] Figure 3 is a simplified schematic drawing of a thruster according to
embodiments
disclosed herein.
[0020] Figure 3A is a simplified schematic drawing of an actuator useful in
embodiments
of the thrusters described herein.
[0021] Figure 3B is a simplified schematic drawing of an actuator useful in
embodiments
of the thrusters described herein.
[0022] Figure 3C is a simplified schematic drawing of an actuator useful in
embodiments
of the thrusters described herein.
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[0023] Figure 4 is a simplified schematic drawing of a thruster according to
embodiments
disclosed herein.
[0024] Figure 5 is a simplified schematic drawing of a thruster according to
embodiments
disclosed herein.
[0025] Figure 6 is a simplified schematic drawing of a thruster according to
embodiments
disclosed herein.
DETAILED DESCRIPTION
[0026] In one aspect, embodiments disclosed herein relate to control of a
thrust force
applied to a drill bit by a thruster. More specifically, embodiments disclosed
herein relate
to controlling a pressure or differential pressure across a thrust piston,
thereby limiting
the maximum applied thrust force. Other embodiments disclosed herein relate to
a
method of drilling a formation using a thruster that may limit the thrust
force applied to
the bit independent of bore and annulus fluid pressures.
[0027] As described above, prior art thrusters generate an axial force based
upon a
difference in bore and annulus pressures. In contrast, thrusters disclosed
herein include
mechanisms to regulate the pressure in one or both of the upstream and
downstream fluid
chambers. The axial force generated according to embodiments disclosed herein,
for
example, may be a function of the differential pressure between the fluid in
the upstream
and downstream fluid chambers.
[0028] Referring now to Figure 3, a simplified schematic drawing of a thruster
50
according to embodiments disclosed herein is illustrated. Thruster 50 may
include an
inner tubular member 52 and an outer tubular member 54. Drilling mud flowing
through
the bore 56 of inner tubular member 52 flows to the drill bit (not shown), and
returns to
the surface via annulus 58, such as between outer tubular member 54 and a
drill casing
(not shown). When mud is flowing through thruster 50, bore 56 is at a higher
pressure
than fluid returning through annulus 58. A thrust piston 60, separating an
upstream fluid
chamber 62 and a downstream fluid chamber 64, may transmit an axial force 66
to inner
tubular member 52. During thrusting, high pressure drilling mud flows from the
bore 56
of the thruster 50 through inlet 68 into upstream fluid chamber 62, displacing
low
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pressure fluid in downstream fluid chamber 64 through outlet 70 and causing
the inner
tubular member 52 to advance in the direction of axial force 66.
[0029] To regulate thrust force, or differential pressure between the upstream
chamber 62
and the downstream chamber 64, for example, thruster 50 may include a pressure
switch
72, which may be in fluid communication with the downstream fluid chamber 64.
Pressure switch 72, in some embodiments, may be a pressure limit switch,
activating at a
pressure set point. When the fluid in chamber 64 reaches a pre-determined set
point
pressure, the pressure switch 72 may actuate. Upon actuation, pressure switch
72 may
send an electronic signal to a control mechanism (not shown) for regulating
the flow of
fluid into or out of downstream fluid chamber 64 through downstream inlet 74
and outlet
70.
[0030] By sending a signal to regulate the flow of fluid into and out of
downstream fluid
chamber 64, pressure switch 72 may limit the thrust force applied to the drill
bit, thus
avoiding the full on or full off scenarios often encountered with prior art
thrusters. For
example, by limiting the flow of fluid through outlet 70, pressure will build
in
downstream fluid chamber 64, limiting the applied thrust force. As another
example, by
allowing fluid to flow in through inlet 74, pressure will also increase in
downstream fluid
chamber 64, due to high pressure fluid in bore 56, limiting the applied thrust
force.
[0031] The control mechanism may in turn send a signal or a current to a valve
member
76 to regulate the flow of fluid into and out of downstream fluid chamber 64.
Valve
member 76 may include, for example, an actuator 78, a drive rod 80, and a gate
member
82. The signal or current transmitted to valve member 76 may cause actuator 78
to
extend or contract, as illustrated by the arrows, causing a similar
displacement in drive
rod 80, causing gate 82 to open and/or close fluid inlet 74 and/or fluid
outlet 70. Other
means of regulating fluid flow using a signal from a pressure switch are also
contemplated herein.
[0032] Actuator 78 may include any one of several types of actuators
responsive to
electronic signals or currents. For example, actuator 78 may include
magnetostrictive
actuators, shape memory alloy actuators, and linear motor actuators. Examples
of each of
these are illustrated in Figures 3A-3C.
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[0033] As illustrated in Figure 3A, actuator 78 may include a magnetostrictive
actuator,
including permanent magnets 84, drive rod 85, coil 86, preload springs 87, and
output rod
88. Upon application of a current through coil 86, drive rod 85 may expand or
contract in
response to the magnetic field generated, thereby displacing output rod 88 to
control the
position of the gate member 82 and thus control the flow of fluid to and from
the
downstream cavity 64.
[0034] As illustrated in Figure 3B, actuator 78 may include a shape memory
alloy
actuator, including shape memory alloy spring 90, piston 92, and drive rod 94.
Upon
application of an electrical current, shape memory alloy spring may expand or
contract,
thereby displacing piston 92 and drive rod 94 to control the position of the
gate member
82, and thus control the flow of fluid to and from the downstream cavity 64.
[0035] As illustrated in Figure 3C, actuator 78 may include a linear motor
actuator,
including a stationary member 96, a motive member 97, and a drive rod 98.
Linear motor
actuators may include flat linear motor actuators and, as illustrated, tubular
linear motor
actuators. In some embodiments, a signal sent from the control mechanism to
the linear
motor actuator may control the position of the motive member 97, and thus
drive rod 98,
with respect to stationary member 96. In other embodiments, a signal sent from
the
control mechanism to the linear motor actuator may control an output force
exerted on
drive rod 98. In this manner, the linear motor actuator may control the
position of gate
member 82, and thus control the flow of fluid to and from the downstream
cavity 64.
[0036] Referring now to Figure 4, a simplified schematic drawing of a thruster
100
according to embodiments disclosed herein is illustrated. Thruster 100 may
include an
inner tubular member 102 and an outer tubular member 104. Drilling mud flowing
through the bore 106 of inner tubular member 102 flows to the drill bit (not
shown), and
returns to the surface via annulus 108, such as between outer tubular member
104 and a
drill casing (not shown). When mud is flowing through thruster 100, bore 106
is at a
higher pressure than fluid returning through annulus 108. A thrust piston 110,
separating
an upstream fluid chamber 112 and a downstream fluid chamber 114, may transmit
an
axial force 116 to inner tubular member 102. During thrusting, high pressure
drilling
mud flows from the bore 106 of the thruster 100 through inlet 118 into
upstream fluid
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chamber 112, displacing low pressure fluid in downstream fluid chamber 114
through
outlet 120 and causing the inner tubular member 102 to advance in the
direction of axial
force 116.
[0037] To regulate thrust force, or differential pressure between the upstream
chamber
112 and the downstream chamber 114, for example, thruster 100 may include a
pressure
switch 122, which may be in fluid communication with each of the upstream
fluid
chamber 112 and the downstream fluid chamber 114. Pressure switch 122, in some
embodiments, may be a differential pressure limit switch, activating at a
differential
pressure set point. When the differential pressure of the fluid in upstream
and
downstream chambers 112, 114 reaches a pre-determined differential pressure
set point,
the pressure switch 122 may actuate. Upon actuation, pressure switch 122 may
send an
electronic signal to a control mechanism (not shown) for regulating the flow
of fluid into
or out of downstream fluid chamber 114 through downstream inlet 124 and outlet
120.
By sending a signal to regulate the flow of fluid into and out of downstream
fluid
chamber 114, pressure switch 122 may regulate the thrust force applied to the
drill bit, as
described above.
[0038] The control mechanism may in turn send a signal or a current to a valve
member
126 to regulate the flow of fluid into and out of downstream fluid chamber
114. Valve
member 126 may include, for example, an actuator 128, a drive rod 130, and a
gate
member 132. The signal or current transmitted to valve member 126 may cause
actuator
128 to extend or contract, as illustrated by the arrows, causing a similar
displacement in
drive rod 130, causing gate 132 to open and/or close fluid inlet 124 and/or
fluid outlet
120.
[0039] Referring now to Figure 5, a simplified schematic drawing of a thruster
150
according to embodiments disclosed herein is illustrated. Thruster 150 may
include an
inner tubular member 152 and an outer tubular member 154. Drilling mud flowing
through the bore 156 of inner tubular member 152 flows to the drill bit (not
shown), and
returns to the surface via annulus 158, such as between outer tubular member
154 and a
drill casing (not shown). When mud is flowing through thruster 150, bore 156
is at a
higher pressure than fluid returning through annulus 158. A thrust piston 160,
separating
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an upstream fluid chamber 162 and a downstream fluid chamber 164, may transmit
an
axial force 166 to inner tubular member 152. During thrusting, high pressure
drilling
mud flows from the bore 156 of the thruster 150 through inlet 168 into
upstream fluid
chamber 162, displacing low pressure fluid in downstream fluid chamber 164
through
outlet 170 and causing the inner tubular member 152 to advance in the
direction of axial
force 166.
[00401 To regulate thrust force, or differential pressure between the upstream
chamber
162 and the downstream chamber 164, for example, thruster 150 may include a
pressure
switch 172, which may be in fluid communication with the downstream fluid
chamber
164. Pressure switch 172, in some embodiments, may be a pressure limit switch,
activating at a pressure set point. When the fluid in chamber 164 reaches a
pre-
determined set point pressure, the pressure switch 172 may actuate. Upon
actuation,
pressure switch 172 may send an electronic signal to a control mechanism (not
shown)
for regulating the flow of fluid into or out of downstream fluid chamber 164
through
downstream inlet 174 and outlet 170. Thruster 150 may also include a pressure
switch
173, which may be in fluid communication with the upstream fluid chamber 162.
When
the fluid in chamber 162 reaches a pre-determined set point pressure, the
pressure switch
173 may actuate, sending an electronic signal to a control mechanism (not
shown) for
regulating the flow of fluid into or out of upstream fluid chamber 162 through
upstream
inlet 168 and upstream outlet 175. By sending a signal to regulate the flow of
fluid into
and out of upstream fluid chamber 162 and downstream fluid chamber 164,
pressure
switches 173, 172 may each, separately or collectively, limit the thrust force
applied to
the drill bit.
[00411 The control mechanism may in turn send a signal(s) or a current(s) to
valve
members 176, 177 to regulate the flow of fluid into and out of one or both of
upstream
and downstream fluid chambers 162, 164. Valve members 176, 177 may include,
respectively, for example, actuators 178, 179, drive rods 180, 181, and gate
members
182, 183. The signal(s) or current(s) transmitted to valve members 176, 177
may cause
actuators 178, 179 to extend or contract, as illustrated by the arrows,
causing a similar
displacement in drive rods 180, 181, causing gates 182, 183 to open and/or
close fluid
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inlets 174, 175 and/or fluid outlets 170, 171. In some embodiments, valve
action on both
sides of the thrust piston 160 is required in order to have hydraulic volume
flow in the
upstream and downstream chambers 162, 164.
[0042] Referring now to Figure 6, a simplified schematic drawing of a thruster
200
according to embodiments disclosed herein is illustrated. Thruster 200 may
include an
inner tubular member 202 and an outer tubular member 204. Drilling mud flowing
through the bore 206 of inner tubular member 202 flows to the drill bit (not
shown), and
returns to the surface via annulus 208, such as between outer tubular member
204 and a
drill casing (not shown). When mud is flowing through thruster 200, bore 206
is at a
higher pressure than fluid returning through annulus 208. A thrust piston 210,
separating
an upstream fluid chamber 212 and a downstream fluid chamber 214, may transmit
an
axial force 216 to inner tubular member 202. During thrusting, high pressure
drilling
mud flows from the bore 206 of the thruster 200 through inlet 218 into
upstream fluid
chamber 212, displacing low pressure fluid in downstream fluid chamber 214
through
outlet 220 and causing the inner tubular member 202 to advance in the
direction of axial
force 216.
[0043] To regulate thrust force, or differential pressure between the upstream
chamber
212 and the downstream chamber 214, for example, thruster 200 may include a
differential pressure switch 222, which may be in fluid communication with
each of the
upstream fluid chamber 212 and the downstream fluid chamber 214. When the
differential pressure of the fluid in upstream and downstream chambers 212,
214 reaches
a pre-determined differential pressure set point, the pressure switch 222 may
actuate,
sending an electronic signal to a control mechanism (not shown) for regulating
the flow
of fluid into or out of one or both of upstream and downstream fluid chambers
212, 214,
thereby limiting the thrust force applied to the drill bit.
[0044] The control mechanism may in turn send a signal(s) or a current(s) to
valve
members 226, 227 to regulate the flow of fluid into and out of one or both of
upstream
and downstream fluid chambers 212, 214. Valve members 226, 227 may include,
respectively, for example, actuators 228, 229, drive rods 230, 231, and gate
members
222, 223. The signal(s) or current(s) transmitted to valve members 226, 227
may cause
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actuators 228, 229 to extend or contract, as illustrated by the arrows,
causing a similar
displacement in drive rods 230, 231, causing gates 232, 233 to open and/or
close fluid
inlets 224, 225 and/or fluid outlets 220, 221. In some embodiments, valve
action on both
sides of the thrust piston 210 is required in order to have hydraulic volume
flow in the
upstream and downstream chambers 212, 214.
[0045] As described above, operation and control of the thrusters described
herein may
be affected by remote signals, such as by actuating valves and other thruster
components.
In some embodiments, the control settings for the valves, actuators, and
pressure switches
may be adjusted using remote signals.
[0046] In other embodiments, the operation and control of the thrusters
described herein
may be affected by down-linking a signal from the surface. For example, a
signal from
the surface may be used to communicate with the thruster control mechanism,
such as to
influence the forward movement of the thruster to initiate a change in
drilling rate, a
change in drilling direction, or other drilling parameters, for example. Down-
linking
signals, in some embodiments, may include a change in pump pressure at the
surface held
for a given period of time. In other embodiments, down-linking signals may
include a
positive and/or negative pressure pulses, such as may be actuated by a change
in
standpipe pressure, for example. In this manner, down-linking may be used to
accurately
position a well and improve drilling performance.
[0047] Embodiments disclosed herein may include one or more pressure switches
and/or
differential pressure switches to result in the desired thrust control. In
some
embodiments, the pressure switches may actuate upon increasing pressure or
pressure
differential. In other embodiments, the pressure switches may actuate upon
decreasing
pressure or pressure differential. In yet other embodiments, combinations of
pressure
switches actuating upon increasing and decreasing pressure differential may be
used,
such as where a valve member opens upon increasing pressure differential in
response to
a signal from a first pressure switch, and the valve member closes upon
decreasing
pressure differential in response to a signal from a second pressure switch.
Additionally,
embodiments may include pressure switches and differential pressure switches
in fluid
communication with one or more of the upstream chamber, the downstream
chamber, the
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inner tubular member bore, and the annulus between the outer tubular member
and the
hole wall, with the pressure switch actuating upon a give pressure or pressure
differential
so as to regulate thrust force.
[0048] As described above, use of pressure switches and actuators may provide
for
passive thrust force control. For example, a pressure switch may actuate at a
minimum or
maximum desired thrust force, sensing a fully opened or fully closed
condition, and
thereafter adjusting the pressures in the upstream and downstream chambers.
[0049] Embodiments disclosed herein may include one or more actuators to
result in
active thrust force control. In some embodiments, two or more actuators, of
the same or
different type, may be used in parallel, such as operating two or more gate
members, or in
series, such as to achieve a longer stroke length. Additionally, intermediate
components
may be used intermediate drive rod and gate member, such as lever arms and
bell cranks,
among others, so as to result in the desired valve action or stroke length.
[0050] Embodiments disclosed herein may include two or more actuators and
pressure
switches in parallel to control fluid flow into and from a fluid chamber. In
some
embodiments, the two or more pressure switches may include different pressure
set
points, such that a valve member may reset prior to a subsequent cycle, for
example.
Pressure set points may be varied minimally so as to maintain a similar
maximum thrust
force upon actuation of the various switch/actuator/valve combinations.
[0051] As described above, use of pressure switches and actuators in parallel
or series
may provide for active thrust force control. For example, when approaching a
fully
opened or fully closed condition, the pressure switches may actuate, adjusting
the
pressures in the upstream and downstream chambers and thereby operating the
thruster
within a desired range of thrust force.
[0052] In other embodiments, two or more actuators and pressure switches may
be used
in series to control fluid flow into and from a fluid chamber. For example,
two or more
pressure switches may include different set points, such that actuators extend
or contract
at different pressure set points. Upon actuation of a first pressure switch /
actuator pair, a
minimal flow opening may be provided to limit thrust force. If differential
pressure
continues to increase following actuation of the first pressure switch /
actuator pair, a
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PROVISIONAL PATENT APPLICATION
ATTORNEY DOCKET NO. 05516/333001
CLIENT REFERENCE NO. 03-HE26
second and subsequent pressure switch / actuator pairs may provide additional
flow area
to limit the thrust force applied to the bit. In this manner, thrust force may
vary less
significantly than an on/off type actuator / valve member.
[0053] Although described with reference to the pressure chambers, one skilled
in the art
will recognize that embodiments of thrusters disclosed herein may include
components
that may be typically included in thrusters, such as the thrusters described
in U.S. Patent
No. 4,615,401 and others mentioned above. For example, thrusters disclosed
herein may
include anchor assemblies, ball valves, seals, springs and spring assemblies,
threaded
connections, spacers, snap rings, bearings, pins, valve seats, and rods, among
others.
Components used to regulate fluid flow during resetting of the thruster may
also be
included.
[0054] In some embodiments, additional measurement and control devices may
also be
used to limit or control the thrust force. For example, a sensor measuring
rate of
penetration may be used to actuate the valve members, thereby controlling the
flow of
fluid into and from the upstream and downstream fluid chambers. In this
manner, rate of
penetration may be maintained within a desired range, such as within an
optimal range
for a particular drill bit. Stroke measurement devices or position sensors may
also be
used to indicate the thruster position, thereby allowing an operator to slow
the rate of
thrust toward the end of a stroke.
[0055] In some embodiments, power and currents supplied to the control
mechanisms,
pressure switches, and actuators may include electrical currents supplied from
batteries.
In other embodiments, power and currents may be supplied to the control
mechanisms,
pressure switches, and actuators may include electrical currents supplied from
downhole
generators, such as turbine generators and the like.
[0056] Advantageously, embodiments disclosed herein may provide for improved
thrust
force control, or improved control of the weight on bit. Actuators, pressure
switches and
valve members described herein may advantageously limit the pressure
differential
between upstream and downstream chambers, thus limiting the thrust force
transmitted
by the thrust piston to the inner tubular member. Additionally, for
embodiments limiting
the pressure or pressure differential within each fluid chamber, the maximum
thrust force
CA 02630108 2008-04-28
PROVISIONAL PATENT APPLICATION
ATTORNEY DOCKET NO. 05516/333001
CLIENT REFERENCE NO. 03-HE26
applied may be controlled independent of fluid pressure in the inner bore and
the annulus.
Embodiments disclosed herein, through limiting applied thrust force, may
advantageously maintain weight on bit within a desired range, improving rates
of
penetration, and decreasing motor wear and the occurrence of stuck bits and
stalls, among
other common problems known in the art.
[0057] While the disclosure includes a limited number of embodiments, those
skilled in
the art, having benefit of this disclosure, will appreciate that other
embodiments may be
devised which do not depart from the scope of the present disclosure.
Accordingly, the
scope should be limited only by the attached claims.
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