Note: Descriptions are shown in the official language in which they were submitted.
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EXTENDED REACH DRILLING APPARATUS & METHOD
Field of Invention
The present invention relates to an apparatus and method for drilling an
extended
reach well in a formation.
Back rg ound
= In the production of hydrocarbon fluid from an earth formation, wellbores
are
drilled to provide a conduit for hydrocarbon fluid to flow from a subterranean
reservoir to a
production facility at the surface. The ability to drill longer and deeper
wells at inclined
angles (referred to as extended reach drilling or ERD) is becoming
increasingly important
to the oil and gas industry. An ERD well is generally defined as a well with a
throw ratio of
approximately 2:1 where the throw ratio is the ratio of horizontal depth to
true vertical
depth (TVD). Some extended reach wells (characterized as ultra ERD wells) may
have
throw ratios as high as 6:1.
Traditionally wellbores are formed in two phases. In the first phase, a drill
string (or
drill pipe) with a drill bit attached to the lower end is rotated by a kelly
or rotary table
located at the surface. As the drill bit creates a hole in the earth, drilling
mud is circulated
through the annular space between the drill string and the wellbore wall to
cool the bit and
transport cuttings (rock chips from drilling) to the surface. In the next
phase, the drill string
and bit are removed and the wellbore is lined with a string of steel pipe
known as casing.
The casing serves to stabilize the newly formed wellbore and facilitate the
isolation of
certain areas of the wellbore adjacent to the hydrocarbon bearing formations.
Once the
casing is cemented in the wellbore, a smaller bit is inserted through the
casing and used to
drill deeper into the earth. This process is then repeated and numerous
sections of casing
are installed until the desired depth is reached. When the well is complete,
the entire string
of casing resembles an extended, inverted telescope.
To reduce costs and drilling time, a process known as "drilling with casing"
is often
employed. This process involves attaching the drill bit to the same string of
tubulars that
will be used to line the wellbore. Because the same string is used, both
phases of the
wellbore formation can be completed in a single trip. However, the traditional
nested
arrangement of casing in a well causes the available diameter for the
production of
hydrocarbon fluid to decrease with depth in a stepwise fashion. This becomes a
technical
and economic problem for deep wells with many separate casings because
drilling a small
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diameter deep hole becomes very challenging. To overcome this problem, the oil
and gas
industry has begun to experiment with new drilling and casing techniques that
involve
radially expanding individual casing strings as they are installed in the well
in order to
maximize the available diameter. One such technique is described in WO
2004/097168 Al,
which is herein incorporated by reference. This technique known as
"expandable"
technology, eliminates the aforementioned telescoping effect, and may enable
the drilling
of a "monodiameter well," a well in which every joint of casing used to line
the wellbore
has the same diameter.
Another recent development is the replacement of conventional drill pipe with
"coiled tubing." Whereas conventional drill pipe is assembled from relatively
short rigid
lengths of pipe, coiled tubing is a single strand of flexible pipe that is
capable of handling a
drilling assembly. A downhole drilling motor is used to create the mechanical
energy
necessary to rotate the drill bit and a tractor device that grips onto the
interior of the
wellbore maintains the proper ainount of weight on bit and holds the reactive
torque from
the motor.
Even with these recent advancements in drilling technology, operators still
encounter challenges drilling and running completions in extended reach wells.
One major
limitation is overcoming the friction incurred by the drill string rotating
and sliding on the
casing or formation. Frictional losses can reduce the weight on bit so much
that it is
impossible to drill with a reasonable penetration rate. Sufficient weight on
bit is required to
force the drill bit into the formation. Thus, the maximum drilling depth for
an ERD well is
often limited by the weight on bit, torque, or resistance of the drill string.
In addition to the frictional problem, disposal of cuttings and steering also
limit
drilling of ERD wells. Because ERD wells are so deep and long, cleaning the
cuttings from
the drill out of the hole poses a challenge. The need to steer the drill bit
through three
dimensional rock formations is also costly and time-consuming because the
operator is
often required to trip out of the hole multiple times to replace or change
equipment.
US-A-6,467,557 B1 discloses a means to overcome the challenges associated with
extended reach drilling using a rotary long reach drilling assembly. The tool
described
comprises an elongated conduit extending through a bore, a drill bit for being
rotated to
drill the bore, a 3D steering tool on the conduit for steering the bit, and a
tractor on the
conduit for applying force to the bit. The tractor includes a gripper which
can assume a
first position that engages an inner surface of the bore and limits movement
of the gripper
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relative to the inner surface. The gripper can also assume a second position
that permits
substantially free relative movement between the gripper and the inner surface
of the bore.
A propulsion assembly moves the tractor with respect to the gripper while the
gripper
position is in the first position.
W099/09290 discloses an extended reach drilling system for drilling a borehole
in
an underground formation. The ERD system comprises a drill bit, a motor for
driving the
drill bit, a drill-pipe to surface, a hydraulic cylinder/piston arrangement
for providing the
required weight on bit, the drill-pipe being coupled to a selected one of the
cylinder and the
piston of said cylinder/piston arrangement by swivel means allowing rotation
of the drill
pipe relative to one of the cylinder or the piston, the drill bit being
coupled to the other one
of the cylinder and the piston, and locking ineans for locking said selected
one of the
cylinder and the piston against the borehole wall, the locking means being
operable
between an engaged and a disengaged position.
W097/08418 discloses a method and apparatus for propelling a tool having a
body
through a passage. The tool includes a gripper including at least a gripper
portion, which
can assume a first position that engages an inner surface of the passage and
limits relative
movement of the gripper portion relative to the inner surface. The gripper
portion can also
assume a second position that permits substantially free relative movement
between the
gripper portion and the inner surface of the passage. The tool includes a
propulsion
assembly for selectively continuously moving the body of the tool with respect
to the
gripper portion while the gripper portion is in the first position.
There are several opportunities for improving existing drilling systems to
overcome
the challenges associated with extended reach wells. First, there is an
opportunity to
overcome the problems associated with frictional losses and maintaining weight
on bit.
Known systems may encounter difficulty achieving the penetration rate
necessary to drill
extended reach wells. Although tractors and other gripping devices apply some
additional
force to the drill bit, a tractor's grip on the inner surface of the bore may
be insufficient to
overcome the frictional losses especially if a rotary system is used. In
addition to the
problem associated with frictional loss, there is also an opportunity to
address the
telescoping problem posed by conventional casing methods. Generally, the
ability to drill a
deep well is limited by the available diameter in the deepest segment of the
nested casing.
Maximizing the diameter of this segment of casing would enable the operator to
drill
deeper extended reach wells.
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Summary of the Invention
The present inventions include a method for drilling a well in a formation
comprising inserting a thruster, a first conduit, and a drill bit into a
wellbore lined with a
previous casing and applying a force to the first conduit with the thruster
wherein the
thruster grips onto the previous casing.
The present inventions include an apparatus for drilling a well in a formation
through a wellbore lined with a previous casing comprising a drilling assembly
and a
thruster connectable to the drilling assembly; wherein the thruster is capable
of gripping
onto the previous casing and providing a force to the drilling assembly.
The present inventions include a method for drilling a well in a formation
comprising providing a wellbore lined with a previous casing, inserting a
first drilling
assembly comprising a drill bit at a distal end, a first conduit connectable
to the drill bit,
and a thruster connectable to first conduit, gripping the previous casing with
the thruster,
and drilling a well.
Brief Description of the Drawings
The present invention is better understood by reading the following
description of
non-limitative embodiments with reference to the attached drawings, wherein
like parts of
each of the figures are identified by the same reference characters, and which
are briefly
described as follows:
Figure 1 illustrates a side view of an extended/ultra extended reach drilling
apparatus and method.
Figure 2 illustrates a side view of another embodiment of the extended reach
drilling apparatus and method.
Detailed Description
Referring to Figure 1, wellbore 101 is shown extending through formation 102
and
is lined with previous casing 103. First conduit 104, drill bit 105, and
thruster 106 are
shown being inserted into wellbore 101. In this embodiment, first conduit 104
is a section
of drilling casing; however, other similar oilfield equipment (e.g. liner)
could be used.
Thruster 106 is shown in this embodiment as a tractor. Any substitute device
capable of
gripping or applying force could be used.
In operation, the drilling assembly (comprising first conduit 104, drill bit
105, and
thruster 106) is inserted into wellbore 101. In the embodiment shown, drill
pipe 107 is used
to perform this function; however, other oilfield equipment (e.g. coiled
tubing) may be
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used instead. After the drilling assembly is inserted, thruster 106 applies a
force to first
conduit 104 causing drill bit 105 to drill a hole and extend wellbore 101.
Thruster 106
provides the necessary weight on bit for penetration by gripping onto previous
casing 103.
The torque required to rotate drill bit 105 may be transferred by first
conduit 104. Although
it is shown as a liner in this embodiment, first conduit 104 may also be
drilling casing or
other oilfield equipment. It is also possible to insert a drill pipe inside
the liner to transmit
the torque to drill bit 105.
Once wellbore 101 is extended, first conduit 104 is removed from the drilling
assembly and hung against previous casing 103. First conduit 104 is optionally
secured in
place by expansion, cementing, or any other method. Drill pipe 107 is then
used to remove
the drilling assembly. A new drilling assembly is lowered into wellbore 101
comprising
drill bit 105, thruster 106, and second conduit (not shown). The steps are
then repeated
until the desired depth is reached.
Turning to Figure 2, wellbore 201 is shown extending through formation 202 and
is
lined with previous casing 203. Drilling assembly 204 is being lowered into
wellbore 201.
Thruster 205 and liner 206 are also shown being lowered into wellbore 201. In
the
embodiment shown, coiled tubing 207 is used to perform this function; however,
other
oilfield equipment (e.g. drill pipe) may be used instead of coiled tubing.
Drilling assembly
204 comprises drill bit 208, drill motor 209, steering mechanism 210, mud pump
211 to
drive steering mechanism 210, and expander 212. Additional components (not
shown) such
as directional assemblies, bent housings, bent subs, measurement while
drilling (MWD)
instruments, and other downhole tools may also be attached to drilling
assembly 204.
In operation, after drilling assembly 204 is inserted into wellbore 201, the
torque
required to drive drill bit 208 is provided by drill motor 211. The torque is
transferred via
the liner or via drill pipe or coiled tubing inserted in the liner. Thruster
205 applies a force
to liner 206 causing drill bit 208 to drill a hole and extend wellbore 201 and
holds the
reactive torque from the drill motor. Thruster 205 provides the necessary
weight on bit for
penetration by gripping onto previous casing 203.
Once wellbore 201 is extended, drilling casing 206 is removed from the
drilling
assembly and hung against previous casing 203. Drilling casing 206 is then
expanded using
expander 212. Optionally drilling casing 206 may be expanded against formation
202.
Drilling casing 206 may also be expanded to be the same diameter as previous
casing 203;
it may also be expanded so that it has a smaller diameter. Preferably drilling
casing 206 is
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expanded so that its outer diameter is substantially equal to the inner
diameter of previous
casing 203. Expander 212 may be a pig, cone, rotary expansion device, cyclic
expansion
device or any other expansion device. After expansion, drilling casing 206 is
then
optionally cemented in place. A new drilling assembly is lowered into wellbore
201 the
steps are then repeated until the desired depth is reached. The subsequent
drilling casings
may each be expanded so that the wellbore is monodiameter.
Those of skill in the art will appreciate that many modifications and
variations are
possible in terms of the disclosed embodiments, configurations, materials, and
methods
without departing from their spirit and scope. Accordingly, the scope of the
claims
appended hereafter and their functional equivalents should not be limited by
particular
embodiments described and illustrated herein, as these are merely exemplary in
nature.
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