Note: Descriptions are shown in the official language in which they were submitted.
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A PERMANENT BYPASS WHIPSTOCK ASSEMBLY FOR DRILLING AND
COMPLETING A SIDETRACK WELL AND PRESERVING ACCESS TO THE
ORIGINAL WELLBORE
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority benefit under 35 U.S.C. Section 119(e)
to U.S.
Provisional Patent Serial No. 61/184,930 filed on June 8, 2009 the entire
disclosure of which is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to drilling lateral wells or sidetrack
wells from a
primary wellbore to enhance the efficiency and productivity of oil and gas
wells.
BACKGROUND OF THE INVENTION
[0003] It is well known that hydrocarbons may be produced from subterranean
formations through a well that has been drilled into a hydrocarbon bearing
formation. In many
circumstances, it is desirable to then drill one or more additional wellbores
(often referred to as
"laterals") outward from the primary wellbore in an effort to increase the
productivity of the well
or to access additional hydrocarbons in adjacent formations. This can be an
effective and
economical way to substantially increase the profitability of a well and to
increase the overall
recovery of fluids from a single, primary well site and surface installation.
These lateral wells
may extend outwardly from the primary wellbore for substantial distances (e.g.
2000 feet or
more) or may be relatively short "drainholes" which extend only a few feet
(e.g. 100 feet or less)
into the formation.
[0004] During the drilling of a well, it is often necessary, for various
reasons, to alter,
i.e., sidetrack, the direction of the wellbore. The challenge when drilling
laterals is being able to
drill precisely on target. Drill rigs are expensive and several extra days of
rig time may
substantially reduce the profitability of drilling additional laterals.
Efficiently drilling laterals,
which directly and precisely exit the primary wellbore at the desired location
within the wellbore
first, requires cutting an opening or a window through heavy casing or liner.
[0005] A conventional technique for drilling laterals may involve the setting
of a kickoff
plug, or the like, in a primary wellbore. A kickoff plug may have a length
ranging from about SO
to 500 feet, and may comprise a cement composition. The kickoff plug typically
is set in the
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wellbore by lowering a drillstring or open-ended tubing string to the desired
depth and pumping
a cement composition into the wellbore. The cement composition is allowed to
cure to form a
plug. After the cement plug has formed, a drillstring may be used to
reinitiate drilling operations.
The drillstring and drill bit use the plug to drill in a new direction, so as
to thereby deflect the
drill string and change the direction in which the drilling proceeds. However,
the use of kickoff
plugs may be problematic due to the prevention of access to further production
of fluids from
lower portions of the original wellbore because the cement seals the well at
the deviation.
[0006] Another conventional method of forming a lateral wellbore uses a
whipstock
which is inserted into the main wellbore and fixed therein. The whipstock is
typically a steel
structure that includes a concave, slanted surface along its upper portion
arranged to direct
anything coming down the wellbore toward one side thereof. In particular, the
whipstock forms
a guide for gradually directing a cutting device from the main wellbore of the
well into and
through the wall of the existing wellbore where the new lateral wellbore will
be formed or cut.
Similar to the kick-off plug method, whipstocks are typically permanently
installed. A
conventional permanently installed whipstock prevents further access to lower
formations below
the installed whipstock. Furthermore, was require some amount of workover to
remain
productive which is prevented to some degree by the installation of a
permanent whipstock.
Thus, a whipstock which allows access to further formations and/or production
below the
whipstock is preferred.
[0007] While most whipstocks are permanent, removable whipstocks have been
developed, but have not be9n entirely satisfactory as the process of milling
and drilling over the
whipstock generally destroys or severely damages the whipstock. The process of
removing a
whipstock requires hooking the whipstock with a latching device that is
accessible from above,
The inherent topside location of the latching mechanism makes it vulnerable to
the damage
caused by the milling bit and it is not uncommon to have considerable delays
in pulling out the
temporary whipstock.
[0008] Furthermore, techniques for drilling windows through the side of a
cased wellbore
become particularly challenging when the production tubing is considerably
smaller than the
liner. With extra room in the liner, the milling drillbit tends to jump around
on the whipstock
and create extra damage to the whipstock and to other parts of the liner,
slowing down progress
and increasing the risk of problems, especially with respect to the recovery
and removal of the
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whipstock, The issue of small production tubing in a large liner occurs, for
example, when the
window is well above the bottom of the original borehole and the production
tubing is sized so to
maintain liquid flow with the gaseous components. It is a significant
advantage to use the gas in
the production fluids to carry the valuable liquids to the surface and large
diameter tubing is
known to frustrate that benefit by allowing the gaseous components to bypass
the liquids and
leave them at the bottom of the tubing.
SUMMARY OF THE INVENTION
[0009] In one embodiment of the present invention, there is a process for
drilling a
sidetrack wellbore from a tailpipe through a liner pipe and into a desired
formation, wherein the
process comprises installing a permanent bypass whipstock assembly into a
section of a length of
the tailpipe as part of a production assembly wherein the permanent bypass
whipstock assembly
is an elongated, generally cylindrical body in close proximity to the liner
with a primary path
extending from a first end to a second end wherein the tailpipe is releasably
connected to the first
end and the second end of the primary path through the permanent bypass
whipstock assembly
and where the permanent bypass whipstock assembly further includes a deviating
sidetrack path
whereby the deviating sidetrack path diverges from the primary path at an
incline for ultimately
forming the sidetrack wherein the downhole end of the deviating sidetrack path
is along a
peripheral side of the permanent bypass whipstock assembly and the uphole end
of the deviating
sidetrack path is closer to the first end of the permanent bypass whipstock
assembly whereby the
uphole end of the deviating sidetrack path opens to the primary path of the
permanent bypass
whipstock assembly; installing the production assembly into a wellbore with
the deviating
sidetrack path of the permanent bypass whipstock assembly aligned in a
predetermined direction
with for forming the sidetrack well that may later be drilled; installing a
diverter to close the
primary path below the desired location of the sidetrack path wherein the
diverter directs tools
and other equipment from the primary path within the permanent. bypass
whipstock assembly to
the sidetrack path of the permanent bypass whipstock assembly; installing a
milling system,
wherein the milling system includes a milling bit at the downhole end of a
drill string whereby
when the milling system reaches the diverter the path of the milling assembly
is deflected onto
the deviating sidetrack path whereby the milling system continues along the
sidetrack path
whereby the milling system forms a window in the liner; removing the milling
system; installing
a drill system, wherein the drilling system includes a drillbit located at the
downhole end of a
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drill string whereby the drill system runs through the primary path through
the permanent bypass
whipstock assembly, being diverted onto the deviating sidetrack path by the
diverter whereby the
drill system reaches the window formed in the liner by the milling system;
drilling a sidetrack
wellbore with the drill system; removing the drill system; and installing a
liner pipe casing into
the sidetrack wellbore.
[0010] In another embodiment of the present invention, there is a permanent
bypass
whipstock assembly for forming a sidetrack wellbore, wherein the permanent
bypass whipstock
assembly comprises an elongated cylindrical body, wherein the elongated
cylindrical body
includes a first end connected to an uphole end of the tailpipe and a second
end connected to -a
downhole and of the tailpipe, wherein the elongated cylindrical body includes:
a primary path
running through the elongated cylindrical body, wherein the primary path is
slightly offset
whereby the primary path is further defined by a thin walled portion and a
thick walled portion, a
deviating sidetrack path for forming a sidetrack wellbore diverges from the
primary path,
wherein the deviating sidetrack path is below a stabilizing portion and above
a deflector portion,
wherein the deviating sidetrack path diverges at an incline whereby the uphole
end of the
deviating sidetrack path is closer to the first end of the permanent bypass
whipstock assembly
and opens to the primary path of the permanent bypass whipstock assembly
whereby the
downhole end of the deviating sidetrack path is along a peripheral side of the
permanent bypass
whipstock assembly, a thin-walled portion, wherein the thin-walled portion is
elongated running
entire downhole length of the permanent bypass whipstock assembly, whereby an
interior
surface defines the primary path and an exterior surface is in close proximity
with the liner; and a
thick-walled portion, wherein the thick-walled portion includes: a stabilizing
portion, wherein
the stabilizing portion is a wedge shaped inverted trough defined by the
deviating sidetrack path,
wherein an interior surface of the stabilizing portion defines the primary
path and an exterior
surface of the stabilizing portion is in close proximity with the liner, and a
deflector portion,
wherein the def lector portion is wedge shaped with an inclined surface
defining the lower portion
of the deviating sidetrack path, wherein an interior surface of the deflector
further defines the
primary path and an exterior surface of the deflector is in close proximity
with the liner.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention, together with further advantages thereof, may best be
understood by
reference to the following description taken in conjunction with the
accompanying drawings in
which:
[0012] FIG, 1 is a schematic diagram of a primary wellbore.
[0013] FIG. 2 is a cross-sectional portion of FIG. 1.
[0014] FIG. 3 is detailed cross-sectional side view of a permanent bypass
whipstock
assembly inserted into a primary wellbore.
[0015] FIG. 4 is a cross-sectional view of the liner, tailpipe and permanent
bypass
whipstock assembly.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Reference will now be made in detail to embodiments of the invention,
one or
more examples of which are illustrated in the accompanying drawings. Each
example is provided
by way of explanation of the invention, not as a limitation of the invention.
It will be apparent to
those skilled in the art that various modifications and variations can be made
in the present
invention without departing from the scope or spirit of the invention. For
instance, features
illustrated or described as part of one embodiment can be used on another
embodiment to yield a
still further embodiment. Thus, it is intended that the present invention
cover such modifications
and variations that come within the scope of the appended claims and their
equivalents.
[0017] In the description which follows, like parts are marked throughout the
specification and drawing with the same reference numerals, respectively. The
drawing figures
are not necessarily to scale and certain features are shown in schematic form
or are exaggerated
in scale in the interest of clarity and conciseness.
[0018] In a conventional drilling operation, a primary wellbore extends into
an earth
formation for the production of oil and gas. The primary wellbore includes a
casing string which
is inserted into the wellbore after the wellbore has been drilled. The casing
string is generally
installed in a wellbore when the well is drilled to target depth or when the
sidewalls of the
wellbore are in danger of collapsing. If the sidewalls of the wellbore
collapse, the wellbore is
cased and drilling continues with a smaller drillbit. Once the target is
reached, a smaller
diameter casing or liner is installed to prevent the sidewalls from
collapsing. Typically, once the
casing string is installed, cement is forced down the inside of the casing
string and up the annulus
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tp seal the casing to the wellbore and prevent fluids from transiting along
the wellbore outside of
the casing from one formation to another.
[0019] A liner is installed within the casing within the primary wellbore.
Once a
production zone has been reached, a production tubing string is installed
within the liner to carry
hydrocarbons to the surface where such hydrocarbons are recovered and
transported to market.
Near the downhole end of the production tubing string, a production packer
assembly is installed
to seal a production annular space between the liner and the production tubing
string in order to
prevent fluids from escaping into other parts of the wellbore or formations
and to direct the
produced fluids into production tubing. Additionally, the production packer
assembly ensures the
fluids do not flow by the tubing by liner annulus to lower portions of the
wellbore.
[0020] Referring to FIG. I, at the downhole end of the production tubing
string 15 a
production packer assembly 24 is utilized to ensure fluids do not flow down
liner 14 to lower
portions of the wellbore. At the downhole end of the production tubing string
15 and below
production packer assembly 24 is a tailpipe 26.
[0021] As previously mentioned, it is sometimes desirable to drill a sidetrack
well from
within a wellbore. For clarity, it should be understood that conventional
wells are drilled
substantially vertically from the surface downward to or through the producing
formation.
However, wellbores may be drilled at a slanted or inclined orientation from
the vertical axis.
Likewise, deviation may produce a horizontal orientation. Sidetrack wells may
extend in any
direction from the original well and, in the case of a horizontal wellbore,
may extend upward or
downward.
[0022] Depicted in FIG. 1, tailpipe 26, located at the downhole end of a
production
tubing string 15 and running below production packer assembly 24, is
interrupted by the
installation of a permanent bypass whipstock assembly 62, which is utilized to
assist in the
efficient and economical formation of a sidetrack or lateral well. For
demonstrative purposes
only, and not by way of limitation, the present illustrated embodiments
provide for the use of
permanent bypass whipstock assembly 62 to form a sidetrack well which exits
liner 14 to the
right. Furthermore, for demonstrative purposes only the permanent bypass
whipstock assembly
is installed below the deepest production packer assembly, however, the
permanent bypass
whipstock assembly can be installed in the tailpipe below any production
packer assembly.
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[0023] In one embodiment, as shown in FIG. 2 which is a cross-section of FIG.
1,
permanent bypass whipstock assembly 62 generally has a cylindrical shape with
a relatively
straight primary path 64 slightly offset from liner axis 1 extending
therethrough. Referring back
to FIG. 1, permanent bypass whipstock assembly 62 preferably includes a thick
robust body
constructed of a durable material, such as steel, around primary path 64 and
potential sidetrack
path 66 to resist forces and pressures, such as drill bits, rotating equipment
and other downhole
insults, likely imposed as equipment is inserted therethrough.
[0024] Permanent bypass whipstock assembly 62 is securely connected to
tailpipe 26 at a
desired location within the string such that a portion of tailpipe 26 is above
permanent bypass
whipstock assembly 62 and an additional length of tailpipe 26 extends below
permanent bypass
whipstock assembly 62. Tailpipe 26 is assembled at the surface with permanent
bypass
whipstock assembly 62 installed in the desired location and the combined
assembly is
subsequently installed with the production assembly. In a preferred
embodiment, permanent
bypass whipstock assembly 62 replaces a section of tailpipe 26 by being
screwed or otherwise
secured in place. When installed, permanent bypass whipstock assembly 62 is
completely open
to the path of downhole production, thereby not interfering with the
production from the
wellbore below the installation of permanent bypass whipstock assembly 62, as
shown in FIG. 2.
[0025] In an embodiment, permanent bypass whipstock assembly 62 includes
several
components, a thin walled portion and a thick walled portion, as shown in FIG.
1. In an
embodiment of the present invention, thin-walled portion 102 is an elongated
piece running the
entire length of permanent bypass whipstock assembly 62. The interior surface
of thin walled
portion 102 defines primary path 64, while the exterior surface is in close
proximity with liner
14.
[0026] In another embodiment of the present invention, thick-walled portion
104 is
located along the peripheral surface opposite thin walled portion 102. Unlike
thin walled portion
102, thick-walled portion 104 includes sidetrack path 66, a whipstock portion
96, and an optional
stabilizing portion 94. Sidetrack path 66, located above whipstock portion 96,
provides an
inclined path by a sidetrack well is ultimately formed. In an alternate
embodiment of the present
invention, sidetrack path 66 is located below optional stabilizing portion 94
and above whipstock
portion 96 in an effort to provide a path for the formation of a sidetrack
well. Sidetrack path 66,
as shown in FIGS. 1, 3 and 4, appears to have an angle which is more
substantial and dramatic
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than would perhaps be preferred. The exaggerated or more dramatic angle is
drawn so that the
angle may be more easily seen by the reader. In the preferred embodiment, the
permanent
bypass whipstock assembly is quite long and the sidetrack path is also
relatively long compared
to what is shown in FIG. 3. The preferred angle is between 1.5 to 3 degrees.
[0027] Referring to FIG. 3, whipstock portion 96 is a wedge shaped member.
with an
inclined surface 95 defining the lower surface of sidetrack path 66. The
inclined surface of
whipstock portion 96 follows the natural incline of sidetrack path 66. The
interior wall of
whipstock portion 96 follows the natural slightly curved path of tailpipe 26
providing a guiding
mechanism for the formation of sidetrack well 60. Additionally, the interior
wall of whipstock
portion 96 defines primary path 64 of permanent bypass whipstock assembly 62.
The exterior
wall of whipstock portion 96 is in close proximity to the wall of liner 14.
[0028] In an alternate embodiment of the present invention, an optional
stabilizing
portion 94, can be installed above sidetrack path 66. Optional stabilizing
portion 94 can have a
wedge shape with an inverted trough defined by the upper surface sidetrack
path 66, which
follows the natural incline of sidetrack 66. The interior wall of stabilizing
portion 94 defines
primary path 64, following the natural curvature of tailpipe 26 which tailpipe
26 would have
followed had it not been interrupted by the insertion of stabilizing portion
94. The exterior wall
of stabilizing portion 94 is also in close proximity to the wall of liner 14.
[0029] Referring to FIG. 3, when it is desired to create sidetrack well 60, a
retrievable
diverter 72 is inserted to block the primary path 64 of permanent bypass
whipstock assembly 62.
Retrievable diverter 72 is designed to be installed by a simple wireline tool
and recovered in a
similar manner a latching mechanism, such as a keyhole 73. Diverter 72
includes a sloped top
surface which aligns with the desired location of the sidetrack via a
sidetrack path 66 whereby
tools inserted through tailpipe 26 are deflected onto sidetrack path 66.
Preferably, sidetrack path
66 is a gently sloped path with a circular cross section to provide stability
for any tools or
rotating equipment to be restrained while in sidetrack path 66. It is
important to recognize that
retrievable diverter 73 and permanent bypass whipstock assembly 62 perform
completely
different functions in the present invention. For example, permanent bypass
whipstock assembly
62 allows for complete downhole access when installed, while retrievable
diverter 72 eliminates
downhole access upon installation of the diverter.
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[0030] After diverter 72 is inserted, a drill string is directed downhole with
a milling bit
suited for the slow process of milling through the steel liner 14. Bit
pressure should be
concentrated on the whipstock surface recognizing that diverter 72 and the
corresponding surface
of sidetrack path 66 of permanent bypass whipstock assembly 62 will direct the
milling drillbit
against the location of liner 14 where a window is desired for sidetrack
wellbore 60. Once the
milling bit has fully opened the window, the drillstring is withdrawn and re-
installed with a
conventional drillbit to drill sidetrack well 60 to its full depth. Again,
diverter 72 and the
corresponding surfaces of sidetrack path 66 of permanent bypass whipstock
assembly 62 direct
the conventional drillbit to and through the window to form sidetrack 60.
Likewise, bit pressure
may be applied to the whipstock assembly. Any portion of the diverter that
encounters drilling
loads should be completely separate than the portion of the diverter
containing the retrieval
mechanism. In an embodiment, the diverter experience limited drilling loads.
In another
embodiment of the present invention, only the outer circumference of the
diverter experience
drilling forces.
[0031] Referring now to FIGS 3 & 4, when sidetrack well 60 is completely
formed, the
drillstring is withdrawn and a liner pipe 80 is installed into sidetrack 60
guided downhole by
diverter 72 and the corresponding surfaces of sidetrack path 66 of permanent
bypass whipstock
assembly 62.
[00321 Upon completion of formation of sidetrack well 60, including insertion
of liner
pipe 80 and perforation, if necessary, all of the necessary tools and
equipment are removed
whereby diverter 72 is retrieved to more fully open up downhole path 64 for
further work or
production. It is important to recognize that several sidetrack (multilateral)
wells can be formed
in a single primary wellbore using this technique where several permanent
bypass whipstock
assemblies are installed at various points in the tailpipe string. Likewise,
the sidetrack(s) and
existing production can be produced selectively by including a packer and
nipple below each
permanent bypass whipstock assembly. In an embodiment of the present
invention, the
production from the sidetrack wellbore is selectively produced by including a
packer above the
permanent bypass whipstock assembly. In another embodiment, the packer is
placed below the
permanent bypass whipstock assembly. In yet another embodiment, a packer is
placed above the
permanent bypass whipstock assembly Furthermore, the production from the
sidetrack well of
the permanent bypass whipstock assembly may contain multiple exit points.
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[0033] Permanent bypass whipstock assembly 62 is substantially larger in
diameter than
tailpipe 26 such that permanent bypass whipstock assembly 62 is in close
proximity to liner 14,
thereby reducing the clearance between tailpipe 26 and liner 14. As such, the
permanent bypass
whipstock assembly is essentially restricted from lateral movement inside
liner 14 due to their
relative diameters or sizes. The permanent bypass whipstock assembly reduces
the clearance to
no more than is necessary to run an additional permanent bypass whipstock
assembly and/or
packer assembly into the liner, thus eliminating the need for cement by
placing the permanent
bypass whipstock assembly in close proximity to the liner wall for a single
string exit.
Furthermore, by eliminating the need for cement, the original production below
the tailpipe can
be produced.
[0034] Finally, the scope of protection for this invention is not limited by
the description set
out above, but is only limited by the claims which follow. That scope of the
invention is
intended to include all equivalents of the subject matter of the claims. Each
and every claim is
incorporated into the specification as an embodiment of the present invention.
Thus, the claims
are part of the description and are a further description and are in addition
to the preferred
embodiments of the present invention. The discussion of any reference is not
an admission that
it is prior art to the present invention, especially any reference that may
have a publication date
after the priority date of this application.
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