Note: Descriptions are shown in the official language in which they were submitted.
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DOWNHOLE DRILLING APPARATUS
AND METHOD FOR USE OF SAME
BACKGROUND OF THE INVENTION
This invention relates in general to drilling a wellbore and, in
particular, to drilling an intersecting wellbore through a drill string
including
well casing or liner and a downhole drilling apparatus interconnected therein.
Without limiting the scope of the invention, its background is described
in connection with drilling a wellbore for hydrocarbon production, as an
example.
Heretofore, in this field, a typical drilling operation has involved
attaching a drill bit on the lower end of a drill string and rotating the
drill bit
along with the drill string to create a wellbore through which subsurface
formation fluids may be produced. As the drill bit penetrates the various
earth strata to form the wellbore, additional joints of drill pipe are coupled
to
the drill string. During drilling, drilling fluid is circulated through the
drill
string and the drill bit to force cuttings out of the wellbore to the surface,
and
to cool the drill bit.
Periodically as the drilling of the wellbore progresses, the drill bit and
drill string are removed from the wellbore and tubular steel casing is
inserted
into the wellbore to prevent the wall of the wellbore from caving in during
subsequent drilling. Typically, after casing is inserted into the wellbore,
the
annulus between the casing and wellbore is filled with a cement slurry that
hardens to support the casing in the wellbore. Thereafter, deeper sections of
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wellbore with progressively smaller diameters than the previously installed
casing may be drilled.
Once a predetermined depth is reached for each subsequent section of
wellbore, the drill bit and drill string are again removed from the wellbore
and
that section of the wellbore may be cased. Alternatively, however, a liner may
be used to case an open section of wellbore instead of a full casing string.
The
liner, which is a string of connected lengths of tubular steel pipe joints, is
lowered through the casing and into the open wellbore. At its upper end, the
liner is attached to a setting tool and liner hanger. The liner hanger
attaches
the liner to the previous casing such that the casing will support the weight
of
the liner.
The length of the liner is predetermined such that its lower end will be
proximate the bottom of the open wellbore, with its upper end, including the
liner hanger, overlapping the lower end of the casing above. As with the
casing, after the liner is inserted into the wellbore, the annulus between the
liner and the wellbore may be filled with a cement slurry that hardens to
support the liner in the wellbore.
It has been found, however, that in many well drilling operations it is
desirable to minimize rig time by utilizing the casing or liner string as the
drill string for rotating a drill bit, which may be left in the wellbore upon
the
completion of drilling a section of the wellbore. As such, this procedure does
not require the use of a separate liner or casing upon the withdrawal of the
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drill bit and drill string as in conventional drilling operations, and thereby
reduces the time needed to drill, case and cement a section of wellbore.
For example, attempts have been made to utilize the casing or liner
string as the drill string along with a drill bit that is rotatable relative
to the
casing or liner string. The drill bit is rotated by a downhole drill motor
that is
driven by drilling fluid. Upon completion of drilling operations, the -motor
and
the retrievable portions of the drill bit may be removed from the wellbore so
that further wellbore operations, such as cementing, may be carried out and
further wellbore extending or drilling operations may be conducted. This
system, however, requires the use of expensive and sometimes unreliable
downhole drill motors and a specially designed drill bit.
Alternatively, other attempts have been made to utilize the casing or
liner string as the drill string using conventional rotary techniques wherein
the drill bit is rotated by rotating the entire casing or liner string. This
=. approach, however, requires the use of a drill bit with minimal cutting
structure, since a drill out could not be performed through a typical drill
bit
having a full cutting structure, such as a tricone bit.
Therefore, a need has arisen for a drill string which may be used as a
well casing or liner, which includes a drill bit on its lower end, and which,
upon completion of drilling operations, may be retained within the wellbore
without the need to retrieve the drill bit or the drill string. A need has
also
arisen for such a well casing or liner string that may be left in the wellbore
along with a drill bit, and which does not require the use of expensive,
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unreliable or specialty equipment. Further, a need has arisen for such a well
casing or liner string which may be cemented in place along with a drill bit
having a full cutting structure.
SUMMARY OF THE INVENTION
The present invention, as exemplified by an embodiment disclosed
herein, comprises a downhole drilling apparatus that is interconnectable in a
casing or liner drill string and includes a drill bit connected thereto which,
upon completion of drilling operations, may be retained within the wellbore
without the need to retrieve the drill bit or the drill string. The apparatus
allows the well casing or liner to be left in the weilbore along with the
drill bit
and does not require the use of expensive, unreliable or specialty equipment.
The apparatus also allows for the well casing or liner to be cemented in place
along with a drill bit having a full cutting structure.
The downhole drilling apparatus includes a housing that is
interconnectable in a casing string. The housing has a window cut therein to
allow a subsequent drill bit and pipe string to pass therethrough during a
drill
out operation. To facilitate the deflection of the drill bit and pipe string
through the window, a whipstock is disposed within the housing. A filler
material is also disposed within the housing between the whipstock and the
window to prevent the flow of drilling fluids or cement through the window
prior to the drill out. The filler and the whipstock have a central bore that
permits the passage of fluids through the center of the downhole drilling
apparatus. One or more valves may be disposed within the central bore to
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control the flow of fluids therethrough. The valves may be, for example, back
pressure or float valves that allow one-way flow of fluids downwardly through
the apparatus.
A drill bit having a full cutting structure, such as a tricone bit, may be
operably coupled to the downhole drilling apparatus. The casing or liner
string may be used to rotate the drill bit. Alternatively, a downhole motor
may be coupled between the downhole drilling apparatus and the drill bit to
facilitate rotation of the drill bit, without the need for rotating the casing
string.
In another embodiment, a downhole drilling apparatus includes a
housing having a window, an alignment member disposed within the housing
and a back pressure valve assembly. The back pressure valve assembly
includes a central bore that permits the passage of fluids therethrough. Once
downhole, a whipstock may be run into the apparatus such that the whipstock
operably engages the alignment member. The alignment member orients the
whipstock within the housing relative to the window, so that the drill bit may
subsequently be deflected through the window.
In operation, either embodiment of the downhole drilling apparatus
may be interconnected in a casing or liner string having a drill bit disposed
on
its lower end. A first wellbore is drilled. Following the drilling of the
first
wellbore, the casing or liner string may be cemented within the wellbore. A
pipe string having another drill bit on its lower end is passed through the
casing or liner string, such that a drill out through the downhole drilling
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apparatus is performed to drill a second wellbore. The pipe string and drill
bit
that are used to create the second weilbore are deflected through the window
in the housing of the downhole drilling apparatus by the whipstock disposed
within the apparatus.
Thus, with the use of the downhole drilling apparatus, a casing or liner
string including a drill bit having a full cutting structure may be used as a
drill string to create a wellbore. The drill string may be cemented in place
within the wellbore, and thereafter have a drill out performed therethrough to
create an intersecting wellbore.
These and other features, advantages, benefits and objects of the
present invention will become apparent to one of ordinary skill in the art
upon
careful consideration of the detailed description of representative
embodiments of the invention hereinbelow and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention, including
its features and advantages, reference is now made to the detailed description
of the invention, taken in conjunction with the accompanying drawings of
which:
Fig. 1 is a schematic illustration of an offshore oil and gas platform
during a drilling operating wherein a downhole drilling apparatus embodying
principles of the present invention is utilized;
Fig. 2 is a schematic illustration of a first downhole drilling apparatus
embodying principles of the present invention;
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Fig. 3 is a cross sectional view of the downhole drilling apparatus of Fig.
2, taken along line 3-3;
Fig. 4 is a cross sectional view of the downhole drilling apparatus of Fig.
2, taken along line 4-4;
Fig. 5 is a schematic illustration of an offshore oil and gas platform
during a drilling operating wherein a downhole drilling apparatus embodying
principles of the present invention is being utilized in conjunction with a
downhole motor;
Fig. 6 is a cross sectional view of a second downhole drilling apparatus
embodying principles of the present invention before insertion of a whipstock
therein; and
Fig. 7 is a cross sectional view of the second downhole drilling
apparatus after insertion of a whipstock therein.
DETAILED DESCRIPTION
While the making and using of various embodiments of the present
invention are discussed in detail below, it should be appreciated that the
present invention provides many applicable inventive concepts which can be
embodied in a wide variety of specific contexts. The specific embodiments
discussed herein are merely illustrative of specific ways to make and use the
invention, and do not limit the scope of the invention.
Referring to Fig. 1, an offshore oil and gas platform is schematically
illustrated and generally designated 10. A semi-submersible platform 12 is
centered over a subterranean oil and gas formation 141ocated below sea floor
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16. A well 18 extends through the sea 20, penetrating sea floor 16 to form
wellbore 22, which traverses various earth strata. A wellbore extension is
formed by wellbore 24, which extends from wellbore 22 through additional
earth strata, including formation 14.
Platform 12 has a hoisting apparatus 26 and a derrick 28 for raising
and lowering pipe strings, such as drill string 30, including drill bit 32
located
in wellbore 24, and casing string 34, including drill bit 36, crossover
subassembly 38 and downhole drilling apparatus 40 located in wellbore 22.
As used herein, the term "casing string" is used to refer to a tubular string
which includes sections of casing or liner.
As in a typical drilling operation, wellbore 22 is formed by rotating drill
bit 36 while adding additional sections of pipe to casing string 34. When
drill
bit 36 reaches total depth, however, casing string 34 and drill bit 36 are not
retrieved from wellbore 22. Rather, casing string 34 and drill bit 36 are
cemented in place by cement 42 which fills the annular area between casing
string 34 and wellbore 22.
Cementing casing string 34 and drill bit 36 in place within wellbore 22
is a cost effective alternative to conventional drilling, in that significant
rig
time is saved by minimizing the number of trips into and out of wellbore 22.
At least one trip out of wellbore 22 and one trip into wellbore 22 are saved
by
using downhole drilling apparatus 40. Additionally, the use of downhole
drilling apparatus 40 avoids the possibility of collapse of wellbore 22,
particularly in unconsolidated or weakly consolidated formations.
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Alternatively, downhole drilling apparatus 40 may be used in
conjunction with conventional drilling operations once a conventional drill
string and bit have been tripped out of wellbore 22. For example, if wellbore
22 has traversed an unconsolidated or weakly consolidated formation and it is
likely that a collapse has occurred within wellbore 22, it may be necessary to
reopen that portion of wellbore 22. In this case, wellbore 22 may be reopened
using casing string 34 with downhole drilling apparatus 40 and drill bit 36.
Once cementing of wellbore 22 has been completed, wellbore 24 may be
drilled. Drill bit 32 creates wellbore 24 by traveling through window 44 of
downhole drilling apparatus 40, as will be more fully discussed with reference
to Figs. 2-4 below. As drill bit 32 and drill string 30 continue to form
wellbore
24, formation 14 is traversed. Note that the drill string 30 may include
another apparatus 40, if desired.
Even though Fig. 1 depicts wellbore 22 as a vertical wellbore, it should
be understood by those skilled in the art that wellbore 22 may be vertical,
substantially vertical, inclined or even horizontal. It should also be
understood by those skilled in the art that wellbore 22 may include
multilateral completions wherein wellbore 22 may be the primary wellbore
having one or more branch wellbore extending laterally therefrom, or wellbore
22 may be a branch wellbore. Additionally, while Fig. 1 depicts an offshore
environment, it should be understood by one skilled in the art that the use of
downhole drilling apparatus 40 is equally well suited for operation in an
onshore environment.
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Schematically illustrated in Fig. 2 is a downhole drilling apparatus 50
embodying principles of the present invention. Apparatus 50 has a pin end
52, so that the apparatus 50 is interconnectable in a drill string, such as
casing string 34 of Fig. 1. Downhole drilling apparatus 50 also has a box end
54 that may be threadedly connected to crossover subassembly 38 as depicted
in Fig. 1.
Apparatus 50 has a generally tubular housing 56 with a window 58 cut
through a sidewall thereof. Window 58 is generally elliptically shaped and is
sized such that a drill bit, such as drill bit 32 of Fig. 1, may pass
therethrough
during a drill out operation.
Now referring to Fig. 3, a cross sectional view of downhole= drilling
apparatus 50 taken along line 3-3 of Fig. 2 is depicted. Disposed within
housing 56 of apparatus 50 is a whipstock 60. A central bore 62 extends
through whipstock 60 to provide fluid passage for drilling mud and cement
through apparatus 50 during drilling and cementing operations. Valves 64,
66 are disposed within central bore 62 of the downhole drilling apparatus 50.
Valves 64, 66 may be back pressure or float valves that allow one-way flow of
drilling mud or cement through the apparatus 50. As an example, valves 64,
66 may be SuperSeal II back pressure valves, available from Halliburton
Energy Services, Inc. of Duncan, Oklahoma.
Whipstock 60 has an inclined upper surface, so that it directs a drill bit,
such as drill bit 32 of Fig. 1, through window 58 of downhole drilling
apparatus 50. Whipstock 60 may be constructed of any material, such as
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steel, having sufficient strength to deflect a drill bit through window 58.
Whipstock 60 may also provide additional torsional strength to the downhole
drilling apparatus 50.
A filler 68 occupies the volume between whipstock 60 and window 58 of
downhole drilling apparatus 50. Filler 68 prevents the flow of drilling mud or
cement through window 58 of apparatus 50. Filler 68 may be, for example,
concrete that has been poured into downhole drilling apparatus 50. Window
58 may also be filled with filler 68 to provide protection to window 58. Other
suitable solid materials, such as resins, may be used for filler 68, so long
as
they set sufficiently and permit the directional passage of a drill bit
througb
window 58 of apparatus 50.
In operation, when a drill bit, such as drill bit 32 of Fig. 1, encounters
whipstock 60, the drill bit cuts through filler 68 and is deflected laterally
by
whipstock 60 toward window 58 in housing 56. Window 58 is wider that the
outer diameter of the drill bit, permitting the drill bit to laterally exit
the
apparatus 50.
Referring now to Fig. 4, a cross sectional view of downhole drilling
apparatus 50 is depicted that is taken along line 4-4 of Fig. 2. Apparatus 50
includes housing 56, whipstock 60, filler 68 and window 58. As with typical
drill down shoes, downhole drilling apparatus 50 may have sufficient torsional
strength to rotate a drill bit, such as drill bit 36 of Fig. 1. The wall
thickness
of housing 56 and the size of window 58 will affect the torsional strength of
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downhole drilling apparatus 50. Of course, the window 58 should be
dimensioned to permit a drill bit to pass therethrough.
The shape of whipstock 60 can be varied to maximize its deflecting
capability. For example, whipstock 60 may be made concave or convex to
direct a drill bit, such as drill bit 32, through window 58 of downhole
drilling
apparatus 50. If whipstock 60 is made concave, drill bit 32 will encounter
window 58 at a position slightly below that where a straight whipstock 60
would direct the bit. Conversely, a convex whipstock 60 will force the
encounter of drill bit 32 with window 58 at a position above that of the flat-
surfaced whipstock 60.
Referring now to Fig. 5, an offshore oil and gas platform is
schematically illustrated and generally designated 70. A semi-submersible
platform 72 is centered over a subterranean oil and gas formation 74 located
below sea floor 76. A well 78 extends through the sea 80, penetrating sea
floor
76 to form wellbore 82, which traverses various earth strata. Wellbore 82 has
a wellbore extension that is formed by wellbore 84, which extends from
wellbore 82 through additional earth strata, including formation 74.
Platform 72 has a hoisting apparatus 86 and a derrick 88 for raising
and lowering pipe strings, such as drill string 90, including drill bit 92
located
in wellbore 84, and casing string 94, including drill bit 96, downhole motor
98,
crossover subassembly 100 and downhole drilling apparatus 102 located in
wellbore 82. Using downhole motor 98, it is not necessary to rotate casing
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string 94, including downhole drilling apparatus 102, in order to rotate drill
bit 96.
Drilling mud, used to cool drill bit 96 and carry cuttings to the surface,
also provides the power to operate downhole motor 98. As the drilling mud
travels through downhole motor 98, downhole motor 98 imparts rotation to
drill bit 96, so that wellbore 82 is drilled. Using downhole motor 98 in
conjunction with downhole drilling apparatus 102 reduces the torsional stress
typically encountered by downhole drilling apparatus 102 when casing string
94 is used to rotate drill bit 96. This reductiori in torsional stress allows
for
the use of a maximum width window 106 in downhole drilling apparatus 102.
When drill bit 96 reaches total depth, casing string 94, including drill
bit 96, downhole motor 98, crossover subassembly 100 and downhole drilling
apparatus 102, is not retrieved from wellbore 82. Rather, casing string 94 is
cemented in place by cement 104, which fills the annular area between casing
string 94 and wellbore 82.
Once cementing of wellbore 82 has been completed, wellbore 84 may be
drilled using downhole drilling apparatus 102. Drill bit 92 creates wellbore
84
by traveling through window 106 of downhole drilling apparatus 102 in the
manner discussed above with reference to Figs. 2-4.
Referring next to Fig. 6, a cross sectional view of another downhole
drilling apparatus 120 embodying principles of the present invention is
depicted. Downhole drilling apparatus 120 has a pin end 122, so that
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downhole drilling apparatus 12 is interconnectable in a drill string, such as
casing string 94 of Fig. 5, or to other downhole tools. Downhole drilling
apparatus 120 also has a box end 123 which may be threadedly connected to
crossover subassembly 100 as depicted in Fig. 5.
Apparatus 120 has a generally tubular housing 124 with a window 126
cut through a sidewall thereof. Window 126 is generally elliptically shaped
and is sized such that a drill bit, such as drill bit 92 of Fig. 5, may pass
therethrough during a drill out operation. Surrounding window 126 is a cover
or shield 128 that prevents the flow of drilling mud or cement through window
126. Apparatus 120 also has at least one alignment member 130, such as a
track, within housing 124.
Disposed within housing 124 is a back pressure valve assembly 132. A
central bore 134 extends through back pressure valve assembly 132 to provide
fluid passage for drilling mud and cement used during drilling and cementing
operations. Valves 136, 138 are disposed within central bore 134 of back
pressure valve assembly 132. Valves 136, 138 may be back pressure valves or
float valves that allow one-way flow of drilling mud or cement therethrough.
As best seen in Fig. 7, a whipstock 140 may be run into downhole
drilling apparatus 120 to direct a drill bit, such as drill bit 92 of Fig. 5,
through window 126 of apparatus 120. Whipstock 140 may be installed
within downhole drilling apparatus 120 following a cementing operation and
subsequent use of a conventional cementing plug 142. Whipstock 140 includes
one or more alignment lugs 144 that cooperate with track 130 of downhole
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drilling apparatus 120 to radially orient whipstock 140 with respect to window
126.
After cementing the casing string 94 within wellbore 82, including
installing the plug 142 in the drilling apparatus 120, the whipstock 140 is
conveyed into the drilling apparatus. The alignment track 130 and lugs 144
cooperatively engage and thereby radially orient the whipstock 140 to face
toward the window 126. A drill bit may then be deflected off of the whipstock
140 to cut through the shield 128, or the shield may be previously displaced
to
open the window 126, for example, by using a conventional shifting tool.
In the embodiments described above, the present invention provides the
ability to drill a wellbore using a well casing or liner string as the drill
string,
and using a drill bit having a full cutting structure. The use of a downhole
drilling apparatus embodying principles of the present invention as part of
the
drill string allows a well extension to be drilled from the existing wellbore,
without having to bore through a drill bit on the end of the casing or liner
string. Thus, trips into and out of the wellbore may be eliminated and a drill
bit having a full cutting structure may be used.
While this invention has been described with reference to illustrative
embodiments, this description is not intended to be construed in a limiting
sense. Various modifications and combinations of the illustrative
embodiments, as well as other embodiments of the invention, will be apparent
to persons skilled in the art upon reference to the description. It is,
therefore,
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intended that the appended claims encompass any such modifications or
embodiments.
