Note: Descriptions are shown in the official language in which they were submitted.
CA 02585476 2007-05-07
DRILLING WITH CONCENTRIC STRINGS OF CASING
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to methods and apparatus for forming a
wellbore in a well. More specifically, the invention relates to methods and
apparatus
for forming a wellbore by drilling with casing. More specifically still, the
invention
relates to drilling a well with drill bit pieces connected to concentric
casing strings.
Description of the Related Art
In well completion operations, a wellbore is formed to access hydrocarbon-
bearing formations by the use of drilling. Drilling is accomplished by
utilizing a drill
bit that is mounted on the end of a drill support member, commonly known as a
drill
string. To drill within the wellbore to a predetermined depth, the drill
string is often
rotated by a top drive or rotary table on a surface platform or rig, or by a
downhole
motor mounted towards the lower end of the drill string. After drilling to a
predetermined depth, the drill string and drill bit are removed and a section
of casing
is lowered into the wellbore. An annular area is thus formed between the
string of
casing and the formation. The casing string is temporarily hung from the
surface of
the well. A cementing operation is then conducted in order to fill the annular
area
with cement. Using apparatus known in the art, the casing string is cemented
into
the wellbore by circulating cement into the annular area defined between the
outer
wall of the casing and the borehole. The combination of cement and casing
strengthens the wellbore and facilitates the isolation of certain areas of the
formation
behind the casing for the production of hydrocarbons.
In some drilling operations, such as deepwater well completion operations, a
conductor pipe is initially placed into the wellbore as a first string of
casing. A
conductor pipe is the largest diameter pipe that will be placed into the
wellbore. The
top layer of deepwater wells primarily consists of mud; therefore, the
conductor pipe
often may merely be pushed downward into the wellbore rather than drilled into
the
wellbore. To prevent the mud from filling the interior of the conductor pipe,
it is
necessary to jet the pipe into the ground by forcing pressurized fluid through
the
inner diameter of the conductor pipe concurrent with pushing the conductor
pipe into
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the wellbore. The fluid and the mud are thus forced to flow upward outside the
conductor pipe, so that the conductor pipe remains essentially hollow to
receive
casing strings of decreasing diameter, as described below.
It is common to employ more than one string of casing in a wellbore. In this
respect, the well is drilled to a first designated depth with a drill bit on a
drill string.
The drill string is removed. A first string of casing or conductor pipe is
then run into
the wellbore and set in the drilled out portion of the wellbore, and cement is
circulated into the annulus behind the casing string. Next, the well is
drilled to a
second designated depth, and a second string of casing, or liner, is run into
the
drilled out portion of the wellbore. The second string is set at a depth such
that the
upper portion of the second string of casing overlaps the lower portion of the
first
string of casing. The second liner string is then fixed, or "hung" off of the
existing
casing by the use of slips which utilize slip members and cones to wedgingly
fix the
new string of liner in the wellbore. The second casing string is then
cemented. This
process is typically repeated with additional casing strings until the well
has been
drilled to total depth. In this manner, wells are typically formed with two or
more
strings of casing of an ever-decreasing diameter.
As more casing strings are set in the wellbore, the casing strings become
progressively smaller in diameter in order to fit within the previous casing
string. In a
drilling operation, the drill bit for drilling to the next predetermined depth
must thus
become progressively smaller as the diameter of each casing string decreases
in
order to fit within the previous casing string. Therefore, multiple drill bits
of different
sizes are ordinarily necessary for drilling in well completion operations.
Well completion operations are typically accomplished using one of two
methods. The first method involves first running the drill string with the
drill bit
attached thereto into the wellbore to concentrically drill a hole in which to
set the
casing string. The drill string must then be removed. Next, the casing string
is run
into the wellbore on a working string and set within the hole within the
wellbore.
These two steps are repeated as desired with progressively smaller drill bits
and
casing strings until the desired depth is reached. For this method, two run-
ins into
the wellbore are required per casing string that is set into the wellbore.
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The second method of performing well completion operations involves drilling
with casing, as opposed to the first method of drilling and then setting the
casing. In
this method, the casing string is run into the wellbore along with a drill bit
for drilling
the subsequent, smaller diameter hole located in the interior of the casing
string. In
a deepwater drilling operation, the conductor pipe includes a drill bit upon
run-in of
the first casing string which only operates after placement of the conductor
pipe by
the above described means. The drill bit is operated by concentric rotation of
the
drill string from the surface of the wellbore. After the conductor pipe is set
into the
wellbore, the first drill bit is then actuated to drill a subsequent, smaller
diameter
hole. The first drill bit is then retrieved from the wellbore. The second
working string
comprises a smaller casing string with a second drill bit in the interior of
the casing
string. The second drill bit is smaller than the first drill bit so that it
fits within the
second, smaller casing string. The second casing string is set in the hole
that was
drilled by the first drill bit on the previous run-in of the first casing
string. The second,
smaller drill bit then drills a smaller hole for the placement of the third
casing upon
the next run-in of the casing string. Again the drill bit is retrieved, and
subsequent
assemblies comprising casing strings with drill bits in the interior of the
casing strings
are operated until the well is completed to a desired depth. This method
requires at
least one run-in into the wellbore per casing string that is set into the
wellbore.
Both prior art methods of well completion require several run-ins of the
casing
working string and/or drill string to place subsequent casing strings into the
wellbore.
Each run-in of the strings to set subsequent casing within the wellbore is
more
expensive, as labor costs and equipment costs increase upon each run-in.
Accordingly, it is desirable to minimize the number of run-ins of casing
working
strings and/or drill strings required to set the necessary casing strings
within the
wellbore to the desired depth.
Furthermore, each run-in of the drill string and/or casing string requires
attachment of a different size drill bit to the drill string and/or casing
string. Again,
this increases labor and equipment costs, as numerous drill bits must be
purchased
and transported and labor must be utilized to attach the drill bits of
decreasing size.
Therefore, a need exists for a drilling system that can set multiple casing
strings within the wellbore upon one run-in of the casing working string.
Drilling with
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multiple casing strings temporarily attached concentrically to each other
increases
the amount of casing that can be set in one run-in of the casing string.
Moreover, a
need exists for a drill bit assembly which permits drilling with one drill bit
for
subsequent strings of casing of decreasing diameter. One embodiment of the
drilling
system of the present invention employs a drilling assembly with one drill bit
comprising drill bit pieces releasably connected. Thus, one drill bit is used
to drill
holes of decreasing diameter within the wellbore for setting casing strings of
decreasing diameter. In consequence, operating costs incurred in a well
completion
operation are correspondingly decreased.
SUMMARY OF THE INVENTION
The present invention discloses a drilling system comprising concentric
strings of casing having drill bit pieces connected to the casing, and a
method for
using the drilling system. In one embodiment, the concentric strings of casing
are
temporarily connected to one another. In another embodiment, the drill bit
pieces
are temporarily connected to one another form a drill bit assembly.
In one aspect of the present invention, the drilling system comprises
concentric strings of casing with decreasing diameters located within each
other. A
conductor pipe or outermost string of casing comprises the outer casing string
of the
system. Casing strings of ever-decreasing diameter are located in the hollow
interior
of the conductor pipe. The drilling system further comprises drill bit pieces
connected to the bottom of each casing string. The drill bit pieces are
releasably
connected to one another so that they form a drill bit assembly and connect
the
casing strings to one another.
Located on the outermost casing string on the uppermost portion of the casing
string of the drilling system are hangers connected atop the outermost casing
string
or conductor pipe which jut radially outward to anchor the drilling assembly
to the top
of the wellbore. These hangers prevent vertical movement of the outermost
casing
string and secure the drilling system upon run-in of the casing string. The
drilling
assembly is made up of drill bit pieces with cutting structures, where the
drill bit
pieces are releasably connected to each other. The outermost, first drill bit
piece is
connected to the conductor pipe and juts radially outward and downward into
the
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wellbore from the conductor pipe. A smaller, first casing string then contains
a
similar second drill bit piece which is smaller than the first drill bit
piece. As many
drill bits pieces and casing strings as are necessary to complete the well may
be
placed on the run-in string. The innermost casing string contains a drill bit
piece that
juts outward and downward from the casing string and also essentially fills
the inner
diameter of the innermost casing string. The drill bit piece disposed at the
lower end
of the innermost casing string contains perforations within it which allow
some fluid
flow downward through the innermost casing string. The drill bit pieces are
releasably connected to each other by progressively stronger force as the
casing
string diameters become smaller. In other words, the outer connections between
drill bit pieces are weaker than the inner connections between drill bit
pieces. A
working casing string is temporarily connected to the inner diameter of the
innermost
casing string of the drilling system by a threadable connection or tong
assembly.
Fluid and/or mud may be pumped into the working casing string during the
drilling
operation. The working casing string permits rotational force as well as axial
force to
be applied to the drilling system from the surface during the drilling
operation.
In another aspect of the invention, the drilling system comprises concentric
strings of casing. The concentric strings of casing comprise a conductor pipe
or
outermost string of casing and casing strings of ever-decreasing diameter
within the
hollow interior of the conductor pipe. The drilling system further comprises
at least
one drill bit piece disposed at the lower end of the outermost string of
casing. The
concentric strings of casing are releasably connected to one another.
In operation, the drilling system is lowered into the wellbore on the working
casing string. In some cases, the drilling system is rotated by applying
rotational
force to the working casing string from the surface of the well. However, as
described above, in some deepwater drilling operations, drilling into the well
by
rotation of the working string is not necessary because the formation is soft
enough
that the drilling system may merely be pushed downward into the formation to
the
desired depth when setting the conductor pipe. Pressurized fluid is introduced
into
the working casing string while the drilling system is lowered into the
wellbore.
When the drilling system is lowered to the desired depth, the downward
movement
and/or rotational movement stops. A cementing operation is then conducted to
fill
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the annular space between the wellbore and the conductor pipe. Next, a
downward
force is asserted on the working casing string from the surface of the
wellbore. The
downward force is calculated to break the connection between the drill bit
piece of
the conductor pipe and the drill bit piece of the first casing string. In the
alternative
embodiment, the force breaks the connection between the conductor pipe and the
first string of casing. The conductor pipe remains cemented in the previously
drilled
hole with its drill bit piece attached to it, while the rest of the drilling
system falls
downward due to the pressure placed on the assembly. In the alternative
embodiment, the conductor pipe remains cemented in the previously drilled hole
while the entire drill bit piece falls downward with the remainder of the
drilling
system. This process is repeated until enough casing strings are placed in the
wellbore to reach the desired depth. The innermost casing string retains the
final
remaining portion of the drill bit assembly. In the alternative embodiment,
the entire
drill bit piece is retained on the innermost casing string.
The drilling system of the present invention and the method for using the
drilling system allow multiple strings of casing to be set within the wellbore
with only
one run-in of the casing working string. The drill bit assembly of the present
invention permits drilling of multiple holes of decreasing diameter within the
wellbore
with only one run-in of the drilling system. Furthermore, the drilling system
of the
present invention uses one drill bit assembly rather than requiring running in
of a drill
string or casing working string for each drill bit piece of decreasing
diameter to drill
holes in which to place casing strings of decreasing diameter. Therefore,
operating
and equipment costs in a well completion operation using the drilling system
with the
drilling assembly are decreased.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features of the present
invention can be understood in detail, a more particular description of the
invention,
briefly summarized above, may be had by reference to embodiments, some of
which
are illustrated in the appended drawings. It is to be noted, however, that the
appended drawings illustrate only typical embodiments of this invention and
are
therefore not to be considered limiting of its scope, for the invention may
admit to
other equally effective embodiments.
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Figure 1 is a cross-sectional view of one embodiment of the drilling system of
the present invention in the run-in configuration.
Figure 2 is a cross-sectional view of the drilling system of Figure 1 disposed
in
a wellbore after the drilling system is run into a desired depth within the
welibore,
with a conductor pipe set within the wellbore.
Figure 3 is a cross-sectional view of the drilling system of Figure 1 disposed
in
a wellbore, with the conductor pipe and a first casing string set within the
wellbore.
Figure 4 is a cross-sectional view of the drilling system of Figure 1 disposed
in
a wellbore, with the conductor pipe, the first casing string, and the second
casing
string set within the welibore.
Figure 5 is a top section view of the concentric casing strings of the present
invention, taken along line 5-5 of Figure 1.
Figure 6 is a top section view of the drilling system of the present
invention,
taken along line 6-6 of Figure 1.
Figure 7 is a cross-sectional view of an alternative embodiment of the
drilling
system of the present invention in the run-in configuration.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 is a cross-sectional view of one embodiment of the drilling system 9
of the present invention in the run-in configuration. The drilling system 9
comprises
three concentric strings of casing, including a conductor pipe 12, a first
casing string
15, and a second casing string 18. The conductor pipe 12 has a larger diameter
than the first casing string 15, and the first casing string 15 has a larger
diameter
than the second casing string 18. Thus, the second casing string 18 is located
within
the first casing string 15, which is located within the conductor pipe 12.
Although the
drilling system 9 depicted in Figure 1 comprises three casing strings, any
number of
concentric strings of casing may be used in the drilling system 9 of the
present
invention. Optionally, the drilling system 9 comprises wipers (not shown)
disposed in
the annular space between the conductor pipe 12 and the first casing string 15
and/or disposed in the annular space between the first casing string 15 and
the
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second casing string 18. The wipers prevent unwanted solids from migrating
into the
annular spaces between casing strings and debilitating the operation of the
drill bit
assembly, which is discussed below. Figure 5, which is taken along line 5-5 of
Figure 1, shows the upper portion of the concentric strings of casing in a top
section
view.
A first drill bit piece 13 is disposed at the lower end of the conductor pipe
12.
In like manner, a second drill bit piece 16 is disposed at the lower end of
the first
casing string 15, and a third drill bit piece 19 is disposed at the lower end
of the
second casing string 18. Although the drilling system 9 in Figure 1 shows
three
casing strings with three drill bit pieces attached thereto, any number of
drill bit
pieces may be attached to any number of concentric strings of casing in the
drilling
system 9 of the present invention. The first drill bit piece 13 and second
drill bit
piece 16 jut outward and downward from the conductor pipe 12 and the first
casing
string 15, respectively. The drill bit pieces 13, 16, and 19 possess cutting
structures
22, which are used to form a path for the casing through a formation 36 during
the
drilling operation. The cutting structures 22 are disposed on drill bit pieces
13, 16,
and 19 on the lower end and the outside portion of each drill bit piece. The
innermost casing string, in this case the second casing string 18, comprises a
third
drill bit piece 19 which juts outward and downward from the second casing
string 18
and which also essentially fills the inner diameter of the second casing
string 18.
Perforations 21 are formed within the third drill bit piece 19 through which
fluid may
flow during the well completion operation. Figure 6, which is taken along line
6-6 of
Figure 1, represents a top section view of the drilling system 9, which shows
the
perforations 21.
Figure 6 represents a top section view of the drilling system 9 of the present
invention, which comprises concentric casing strings 12, 15, and 18 with a
drill bit
assembly attached thereupon. The drill bit assembly is described in reference
to
Figure 1 as well as Figure 6. The drill bit assembly comprises a first drill
bit piece 13
releasably connected to a second drill bit piece 16 by a first connector 14.
The
assembly further comprises a third drill bit piece 19 releasably connected to
the
second drill bit piece 16 by a second connector 17. The releasable connections
are
preferably shearable connections, wherein the first connector 14 holds the
first drill
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bit piece 13 to the second drill bit piece 16 with less force than the second
connector
17 holds the second drill bit piece 16 to the third drill bit piece 19. The
first drill bit
piece 13, the second drill bit piece 16, and the third drill bit piece 19 are
located on
the lower ends of concentric casing strings 12, 15, and 18, respectively.
The first, second and third drill bit pieces, 13, 16, and 19 respectively,
possess cutting structures 22 on their outer and bottom surfaces. As described
below, after the first drill bit piece 13 is released from the drill bit
assembly, the
cutting structures 22 on the outer surface of the second drill bit piece 16
are
employed to drill through the formation 36 to a depth to set the first casing
string 15.
Similarly, after the second drill bit piece 16 is released from the drill bit
assembly, the
cutting structures 22 on the outer surface of the third drill bit piece 19 are
employed
to drill through the formation 36 to a depth to set the second casing string
18.
As illustrated in Figure 1, the drilling system 9 also comprises hangers 23,
which are located on the upper end of the conductor pipe 12. The hangers 23
maintain the drilling system 9 in place by engaging the surface 31 of the
wellbore 30,
preventing the drilling system 9 from experiencing further downward movement
through the formation 36. Any member suitable for supporting the weight of the
drilling system 9 may be used as a hanger 23.
A casing working string 10 is connected to the inner diameter of the second
casing string 18. Any type of connection which produces a stronger force than
the
force produced by the connectors 14 and 17 may be used with the present
invention.
Figure 1 shows a type of connection suitable for use with the present
invention. A
threadable connection 11 is shown between the casing working string 10 and the
second casing string 18 which is unthreaded after the drilling operation is
completed
so that the casing working string 10 may be retrieved. Alternatively, the
casing
working string 10 may be shearably connected to the second casing string 18 by
a
tong assembly (not shown). The force produced by the shearable connection of
the
tong assembly must be greater than the force produced by the connectors 14 and
17. The tong assembly is connected to the lower end of the casing working
string 10
and extends radially through the annular space between the casing working
string 10
and the inner diameter of the second casing string 18. Upon completion of the
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drilling operation, the shearable connection is broken by a longitudinal force
so that
the casing working string 10 may be retrieved from the wellbore 30.
In the drilling system 9, the first drill bit piece 13 is releasably connected
to the
second drill bit piece 16 by the first connector 14. Similarly, the second
drill bit piece
16 is releasably connected to the third drill bit piece 19 by the second
connector 17.
The releasable connection is preferably a shearable connection. The first
connector
14 and the second connector 17 are any connectors capable of temporarily
connecting the two drill bit pieces, including weight sheared pins or locking
mechanisms. In the embodiment described above, the longitudinal force required
to
break the connection between the tong assembly and the second casing string 18
is
more than the longitudinal force required to break the second connector 17. In
the
same way, the longitudinal force required to break the second connector 17 is
more
than the longitudinal force required to break the first connector 14.
Accordingly, the
connection between the tong assembly and the second casing string 18 is
stronger
than the second connector, and the connection produced by the second connector
17 is stronger than the connection produced by the first connector 14.
The annular space between casing strings 12 and 15, as well as the annular
space between casing strings 15 and 18, may comprise sealing members (not
shown) to prevent migration of unwanted fluid and solids into the annular
spaces
until the designated point in the drilling operation. The sealing members
prevent
fluid flow into the annular spaces, thus forcing setting fluid to flow into
the desired
area outside of the casing string being set. The sealing members are released
along
with their respective connectors 14 and 17 at the designated step in the
operation.
Figure 7 shows an alternative embodiment of the drilling system 9 of the
present invention in the run-in configuration. In this embodiment, the
drilling system
9 is identical to the drilling system of Figure 1 except for the connectors of
the drilling
system 9 and the drill bit pieces. The numbers used to identify parts of
Figure 1
correspond to the numbers used to identify the same parts of Figure 7. in the
embodiment of Figure 7, one drill bit piece 40 is disposed at the lower end of
the
innermost casing string, which is the second casing string 18. Again, any
number of
concentric casing strings may be employed in the present invention. The drill
bit
piece 40 comprises perforations 21 which run therethrough and allow fluid flow
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through the casing working string 10 and into the formation 36. A first
connector 41
releasably connects the conductor pipe 12 to the first string of casing 15.
Similarly, a
second connector 42 releasably connects the first string of casing 15 to the
second
string of casing 18. The releasable connection is preferably a shearable
connection
created by either weight sheared pins or locking mechanisms. The force
required to
release the second connector 42 is greater than the force required to release
the first
connector 41. Likewise, the force created by the threadable connection 11 or
tong
assembly (not shown) is greater than the force required to release the second
connector 42.
In a further alternative embodiment, the drilling system 9 may employ a torque
key system (not shown). A torque key system comprises keys (not shown) located
on the inner casing string of the concentric strings of casing which engage
slots (not
shown) formed in the outer casing string of the concentric strings of casing.
The drill
bit pieces 13, 16, and 19 of Figure 1 and 40 of Figure 7 comprise a cutting
structure
(not shown) located above an inverted portion (not shown) of the casing
strings 12
and 15. The first torque key system (not shown) comprises keys (not shown)
disposed on the first casing string 15 and slots (not shown) disposed on the
conductor pipe 12. When the drilling system 9 is used to drill to the desired
depth
within the formation 36 to set the conductor pipe 12, the keys disposed on the
first
casing string 15 remain engaged within the slots disposed in the conductor
pipe 12,
thus restricting rotational movement of the first casing string 15 relative to
the
conductor pipe 12 so that the first casing string 15 and the conductor pipe 12
translate together. After the drilling system 9 has drilled to the desired
depth within
the wellbore 30, the key on the first casing string 15 is released from the
slot in the
conductor pipe 12, thereby allowing rotational as well as longitudinal
movement of
the first casing string 15 relative to the conductor pipe 12. Next, the
inverted portion
of the conductor pipe 12 is milled off by the cutting structure located above
the
inverted portion of the conductor pipe 12 so that the drill bit piece16 may
operate to
drill to the second designated depth within the wellbore 30 while the second
torque
key system of the first casing string 15 and the second casing string 18
remains
engaged. The second torque key system operates in the same way as the first
torque key system.
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In a further embodiment, a spline connection (not shown) may be utilized in
place of the torque key system to restrict rotational movement of the
conductor pipe
12 relative to the first casing string 15. In this embodiment, the conductor
pipe 12
and the first casing string 15 possess a spline connection (not shown). The
spline
connection comprises grooves (not shown) formed on an inner surface of the
conductor pipe 12 which mate with splines (not shown) formed on an outer
surface
of the first casing string 15. The spline, when engaged, allows the first
casing string
and the conductor pipe 12 to translate rotationally together when the drilling
system 9 is drilled to the desired depth, while at the same time allowing the
first
10 casing string 15 and the conductor pipe 12 to move axially relative to one
another.
When the releasable connection between the first casing string 15 and the
conductor
pipe 12 is released, the two casing strings 12 and 15 are permitted to rotate
relative
to one another. A second spline connection (not shown) may also be disposed on
the first casing string 15 and the second casing string 18.
15 Figures 2, 3, and 4 depict the first embodiment of the drilling system 9 of
Figure 1 in operation. Figure 2 is a cross-sectional view of the drilling
system 9 of
the present invention disposed in a wellbore 30, with the conductor pipe 12
set within
the wellbore 30. Figure 3 is a cross-sectional view of the drilling system 9
of the
present invention disposed in a wellbore 30, with the conductor pipe 12 and
the first
casing string 15 set within the wellbore 30. Figure 4 is a cross-sectional
view of the
drilling system 9 of the present invention disposed in a wellbore 30, with the
conductor pipe 12, the first casing string 15, and the second casing string 18
set
within the wellbore 30.
In operation, the drilling system 9 is connected to the casing working string
10
running therethrough. As shown in Figures 1 and 7, the casing working string
10
with the drilling system 9 connected is run into a wellbore 30 within the
formation 36.
While running the casing working string 10 into the wellbore 30, a
longitudinal force
and a rotational force are applied from the surface 31 upon the casing working
string
10. Alternatively, if the formation 36 is sufficiently soft such as in
deepwater drilling
operations, only a longitudinal force is necessary to run the drilling system
9 into the
desired depth within the wellbore 30 to set the conductor pipe 12. Pressurized
fluid
is introduced into the bore 33 of the casing working string 10 concurrently
with
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running the casing working string 10 into the wellbore 30 so that the fluid
and mud
that would ordinarily flow upward through the inner diameter of the casing
working
string 10 are forced to flow upward through the annular space between the
conductor pipe 12 and the wellbore 30.
As shown in Figure 2, when the entire length of the conductor pipe 12 is run
into the wellbore 30 so that the hangers 23 apply pressure upon the surface
31, the
longitudinal force and/or rotational force exerted on the casing working
string 10 is
halted. A cementing operation is then conducted in order to fill an annular
area
between the wellbore 30 and the conductor pipe 12 with cement 34.
Alternatively, if
the friction of the wellbore 30 is sufficient to hold the conductor pipe 12 in
place, a
cementing operation is not necessary. Figure 2 shows the conductor pipe 12 set
within the wellbore 30.
Subsequently, a first longitudinal force is applied to the casing working
string
10 from the surface 31. The first longitudinal force breaks the releasable
connection
between the first drill bit piece 13 and the second drill bit piece 16 that is
formed by
the first connector 14. Rotational force and longitudinal force are again
applied to
the casing working string 10 from the surface 31. The remainder of the
drilling
system 9 exerts rotational and longitudinal force on the formation 36 so that
a deeper
hole is formed within the wellbore 30 for setting the first casing string 15.
This hole is
necessarily smaller in diameter than the first hole formed because the drill
bit
assembly is missing the first drill bit piece 13 and is therefore of decreased
diameter.
Pressurized fluid is introduced into the bore 33 of the casing working string
10
concurrently with running the drilling system 9 further downward into the
wellbore 30
so that the fluid and mud that would ordinarily flow upward through the inner
diameter of the casing working string 10 are forced to flow upward in the
annular
space between the outer diameter of the first casing string 15 and the inner
diameter
of the conductor pipe 12.
As shown in Figure 3, when the first casing string 15 is drilled to the
desired
depth within the wellbore 30, the longitudinal and rotational forces applied
on the
casing working string 10 are again halted. A cementing operation is then
conducted
in order to fill an annular area between the conductor pipe 12 and the first
casing
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string 15 with cement 34. Figure 3 shows the first casing string 15 along with
the
conductor pipe 12 set within the wellbore 30.
In the next step of the drilling operation, a second longitudinal force is
applied
to the casing working string 10 from the surface 31. This second longitudinal
force is
greater than the first longitudinal force, as the second longitudinal force
must apply
enough pressure to the casing working string 10 to break the releasable
connection
between the second drill bit piece 16 and the third drill bit piece 19 formed
by the
second connector 17. Longitudinal and rotational forces are again applied to
the
remaining portion of the drilling system 9 so that the formation 36 is drilled
to the
desired depth by the remaining portion of the drill bit assembly. Again,
pressurized
fluid is run into the bore 33 in the casing working string 10 from the surface
31
concurrent with the rotational and longitudinal force to prevent mud and fluid
from
traveling upward through the casing working string 10. The mud and fluid
introduced
into the casing working string 10 exit the system by flowing upward to the
surface 31
through the annular space between the first casing string 15 and the second
casing
string 18. The hole that is formed by the remaining portion of the drilling
system 9 is
even smaller than the previous hole drilled by the drilling system 9 to set
the first
casing string 15 because the second drill bit piece 16 has released from the
drill bit
assembly, thus further decreasing the diameter of the drill bit assembly.
As shown in Figure 4, when the drilling system 9 has been drilled into the
formation 36 to the desired depth to set the second casing string 18, the
longitudinal
and rotational forces are again halted. A cementing operation is then
conducted in
order to fill an annular area between the first casing string 15 and the
second casing
string 18 with cement 34, thus setting the second casing string 18. The
completed
operation is shown in Figure 4.
At the end of the drilling operation, the remainder of the drilling system 9,
which comprises the third drill bit piece 19 and the second casing string 18,
permanently resides in the wellbore 30. The threadable connection 11 is
disconnected from the inner diameter of the second casing string 18, and the
casing
working string 10 and the threadable connection 11 are removed from the
welfbore
30.
14
CA 02585476 2007-05-07
The second embodiment depicted in Figure 7 works in much the same way as
the first embodiment of the present invention, with minor differences. Instead
of
using longitudinal force to release the connectors 14 and 17 between the drill
bit
pieces, the force is used to release the connectors 41 and 42 between the
concentric
strings of casing 12, 15, and 18. A first longitudinal force is used to break
the first
connector 41 between the conductor pipe 12 and the first casing string 15. A
second, greater longitudinal force is used to break the second connector 42
between
the first string of casing 15 and the second string of casing 18. Finally, the
threadable connection 11 is unthreaded after the drilling operation is
completed so
that the casing working string 10 may be retrieved. Alternatively, a third,
even
greater longitudinal force may used to break the shearable connection between
the
tong assembly (not shown) and the second casing string 18. Because drill bit
pieces
are not disposed at the lower end of casing strings 12 and 15, drill bit
pieces are not
left within the wellbore during the course of the operation, but remain
attached to the
drilling system 9 until the final stage. The drill bit piece 40 is carried
with the second
casing string 18 during the entire operation and remains attached to the
second
string of casing 18 within the wellbore upon completion of the drilling
operation. In
any of the embodiments described above, the connectors 14 and 17 or the
connectors 41 and 42 may alternatively comprise an assembly which is removable
from the surface using wireline, tubing, or drill pipe at the end of drilling
operation.
Furthermore, the connectors 14 and 17 and the connectors 41 and 42 may
comprise
an assembly that may be de-activated from the surface 31 of the wellbore 30 by
pressure within the casing strings 12, 15, and 18.
An alternate method (not shown) of setting the casing strings 12, 15, and 18
within the wellbore 30 involves using any of the above methods to drill the
casing
strings 12, 15, and 18 to the desired depth within the wellbore 30. However,
instead
of conducting a cementing operation at each stage in the operation after each
casing
string has reached its desired depth within the wellbore 30, each of the
casing
strings 12, 15, and 18 are lowered to the final depth of the entire drilling
system 9 (as
shown in Figure 4). Figure 4 is used for illustrative purposes in the
description
below, although other embodiments of the drilling system 9 described above may
be
used to accomplish this alternative method. The drilling system 9 is lowered
to the
desired depth for setting the conductor pipe 12 by rotational and longitudinal
forces.
CA 02585476 2007-05-07
Then, the rotational force is halted and the longitudinal force is utilized to
release the
first connector 14. The conductor pipe 12 is fixed longitudinally and
rotationally
within the wellbore 30 by the portion 45 of the formation 36 which extends
beyond
the remaining portion of the drilling system 9. The remaining portion of the
drilling
system 9 which comprises the first string of casing 15 and the second casing
string
18 is drilled to the second desired depth within the wellbore 30, and the
process is
repeated until the entire drilling system 9 has telescoped to the desired
depth within
the wellbore 30. Then, a cementing operation is conducted to set all of the
casing
strings 12, 15, and 18 within the wellbore 30 at the same time.
While the foregoing is directed to embodiments of the present invention, other
and further embodiments of the invention may be devised without departing from
the
basic scope thereof, and the scope thereof is determined by the claims that
follow.
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