U.S. patent application number 15/489924 was filed with the patent office on 2017-08-03 for plug for well drilling provided with ring-shaped ratchet structure.
This patent application is currently assigned to KUREHA CORPORATION. The applicant listed for this patent is KUREHA CORPORATION. Invention is credited to Masayuki OKURA, Takeo TAKAHASHI.
Application Number | 20170218720 15/489924 |
Document ID | / |
Family ID | 52992842 |
Filed Date | 2017-08-03 |
United States Patent
Application |
20170218720 |
Kind Code |
A1 |
TAKAHASHI; Takeo ; et
al. |
August 3, 2017 |
PLUG FOR WELL DRILLING PROVIDED WITH RING-SHAPED RATCHET
STRUCTURE
Abstract
A plug for well drilling comprising a mandrel and members
attached on an outer circumferential surface orthogonal to an axial
direction of the mandrel, wherein at least one of the members or
the mandrel is formed from a degradable material; a ring-shaped
ratchet structure formed from a plurality of interlocking parts
that allows movement of the member in one direction along the axial
direction of the mandrel and restricts movement in the opposite
direction is provided on an inner circumferential surface of the
member and the outer circumferential surface of the mandrel;
preferably further comprising a pushing jig including a ratchet
structure and a ring-shaped plate adjacent to the axial direction
leading side of the pushing jig. Additionally, a well drilling
method using the plug for well drilling, comprising degrading a
part or all of the plug after blocking a borehole.
Inventors: |
TAKAHASHI; Takeo; (Tokyo,
JP) ; OKURA; Masayuki; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KUREHA CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
KUREHA CORPORATION
TOKYO
JP
|
Family ID: |
52992842 |
Appl. No.: |
15/489924 |
Filed: |
April 18, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15029410 |
Apr 14, 2016 |
|
|
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PCT/JP2014/077832 |
Oct 20, 2014 |
|
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15489924 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 8/426 20130101;
E21B 33/1291 20130101; E21B 43/26 20130101; E21B 33/128 20130101;
E21B 29/02 20130101; E21B 33/1208 20130101; E21B 23/06
20130101 |
International
Class: |
E21B 33/12 20060101
E21B033/12; E21B 33/129 20060101 E21B033/129 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2013 |
JP |
2013-220224 |
Aug 29, 2014 |
JP |
2014-175337 |
Claims
1. A plug for well drilling comprising: a mandrel; and members
which are attached on an outer circumferential surface orthogonal
to an axial direction of the mandrel and comprise a slip, a wedge,
a pair of ring-shaped fixing members, and a diametrically
expandable circular rubber member; a1) the mandrel being formed
from a degradable material; a2) the pair of ring-shaped fixing
members and the diametrically expandable circular rubber member of
the members being formed from a degradable material; and b) a
ring-shaped ratchet structure orthogonal to the axial direction of
the mandrel being provided on an inner circumferential surface of
at least one of the members and the outer circumferential surface
of the mandrel, the ring-shaped ratchet structure being formed from
a plurality of interlocking parts that allow movement of the member
in one direction along the axial direction of the mandrel and
restrict movement in the opposite direction.
2. The plug for well drilling according to claim 1, wherein the
member attached on the outer circumferential surface orthogonal to
the axial direction of the mandrel, having the plurality of
interlocking parts formed on the inner circumferential surfaces
thereof, is one or a plurality of pushing jigs.
3. The plug for well drilling according to claim 2, wherein at
least one of the pushing jigs is one of the pair of ring-shaped
fixing members.
4. The plug for well drilling according to claim 2, wherein at
least one of the pushing jigs comprises a support ring formed from
at least one of a metal and a degradable material, and an inner
circumferential surface of the support ring contacts an outer
circumferential surface of a ratchet structured ring having
interlocking parts that form a ring-shaped ratchet structure on an
inner circumferential surface thereof.
5. The plug for well drilling according to claim 2, further
comprising a ring-shaped plate adjacent to a leading side along the
axial direction of the mandrel of at least one of the pushing
jigs.
6. The plug for well drilling according to claim 5, wherein the
ring-shaped plate is formed from at least one of a degradable
material and a metal.
7. The plug for well drilling according to claim 1, wherein at
least one of the following i) to iii) applies to the mandrel formed
from the degradable material: i) is formed from a degradable
material having a shearing stress of 30 MPa or greater at a
temperature of 66.degree. C.; ii) has a thickness reduction of less
than 5 mm after being immersed in water of a temperature of
66.degree. C. for one hour, and has a thickness reduction of 10 mm
or greater after being immersed in water of a temperature of
149.degree. C. for 24 hours; and iii) a tensile load capacity of
the interlocking parts of the ratchet structure is 5 kN or greater
at a temperature of 66.degree. C.
8. The plug for well drilling according to claim 1, wherein at
least one of the members attached on the outer circumferential
surface orthogonal to the axial direction of the mandrel is formed
from a degradable material having a shearing stress of 30 MPa or
greater at a temperature of 66.degree. C.
9. The plug for well drilling according to claim 1, wherein a gross
tensile load capacity is 100 kN or greater.
10. The plug for well drilling according to claim 1, wherein a
gross tensile load capacity of the ring-shaped ratchet structure is
50 kN or greater.
11. The plug for well drilling according to claim 1, wherein the
ring-shaped ratchet structure is formed so as to cover one or both
of the outer circumferential surface of the mandrel and the inner
circumferential surface of the members attached on the outer
circumferential surface orthogonal to the axial direction of the
mandrel.
12. The plug for well drilling according to claim 1, wherein the
pair of ring-shaped fixing members is capable of fixing the
diametrically expandable circular rubber member attached on the
outer circumferential surface orthogonal to the axial direction of
the mandrel in a compressed state.
13. The plug for well drilling according to claim 1, wherein at
least one of a combination of the slip and the wedge is disposed
between the pair of ring-shaped fixing members.
14. The plug for well drilling according to claim 13, comprising a
plurality of the combination of the slip and the wedge.
15. The plug for well drilling according to claim 1, wherein the
mandrel comprises a hollow part along the axial direction.
16. The plug for well drilling according to claim 1, wherein the
degradable material is an aliphatic polyester.
17. The plug for well drilling according to claim 16, wherein the
aliphatic polyester is polyglycolic acid.
18. The plug for well drilling according to claim 17, wherein the
polyglycolic acid has a weight average molecular weight from 180000
to 300000, and a melt viscosity recorded at a temperature of
270.degree. C. and a shear rate of 122 sec.sup.-1 from 700 to 2000
Pas.
19. The plug for well drilling described according to claim 1,
wherein the degradable material comprises a reinforcing
material.
20. A well drilling method using the plug for well drilling
according to claim 1, the method comprising degrading a part or all
of the plug for well drilling after blocking a borehole.
21. The well drilling method according to claim 20, comprising
degrading the ring-shaped ratchet structure.
22. The plug for well drilling according to claim 1, wherein: the
mandrel includes a hollow part; and a ratio of an outside diameter
of the hollow part to a diameter of the mandrel is at most 0.7.
23. The plug for well drilling according to claim 1, wherein the
slip is formed from a degradable material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. patent
application Ser. No. 15/029,410, filed on Apr. 14, 2016, which is a
National Stage Entry of International Application No.
PCT/JP2014/077832, filed on Oct. 20, 2014, which claims the benefit
under 35 U.S.C. .sctn.119(a) to Japanese Patent Application Nos.
2013-220224, filed on Oct. 23, 2013, and 2014-175337, filed on Aug.
29, 2014, all of which are hereby expressly incorporated by
reference into the present application.
TECHNICAL FIELD
[0002] The present invention relates to a plug for well drilling
used in well drilling for the purpose of producing hydrocarbon
resources such as petroleum, natural gas, or the like; and a well
drilling method.
BACKGROUND ART
[0003] Hydrocarbon resources such as petroleum, natural gas, and
the like have been excavated and produced through wells (oil wells
and gas wells; hereinafter referred to collectively as "wells")
having porous and permeable subterranean formations. As energy
consumption increases, deeper wells are being drilled, reaching
depths greater than 9000 m worldwide and greater than 6000 m in
Japan. In wells that are continuously excavated, methods in which
fluid pressure is used to form fractures in the productive layer
(also called "fracturing" or "hydraulic fracturing"), for the
purpose of continuously excavating hydrocarbon resources
efficiently from subterranean formations of which permeability has
decreased over time and subterranean formations of which
permeability is insufficient from the beginning, have received
attention.
[0004] Hydraulic fracturing is a method in which fractures are
generated in the productive layer by fluid pressure such as water
pressure (also simply called "hydraulic pressure" hereinafter).
Generally, a vertical hole is drilled, and then the vertical hole
is curved and a horizontal hole is drilled in a subterranean
formation several thousand meters underground. Fracturing fluid is
then fed into these boreholes (meaning holes provided for forming a
well, also called "downholes") at high pressure, and fractures and
the like are produced by the hydraulic pressure in the deep
subterranean productive layer (layer that produces the hydrocarbon
resource such as petroleum or natural gas), and the productive
layer is thereby stimulated in order to extract and recover the
hydrocarbon resource through the fractures and the like. The
efficacy of hydraulic fracturing has also been examined for the
development of unconventional resources such as shale oil (oil that
matures in shale) and shale gas.
[0005] Fractures and the like formed by fluid pressure such as
hydraulic pressure immediately close due to formation pressure when
the hydraulic pressure is no longer applied. To prevent a fracture
from closing, a proppant is included in the fracturing fluid (that
is, the well treatment fluid used in fracturing), which is fed into
the borehole, thereby distributing the proppant in the fracture.
Inorganic or organic materials are used as proppants included in
fracturing fluid, but silica and alumina and other inorganic
particles have been conventionally used, and sand particles such as
20/40-mesh sand have been widely used because they are capable of
preventing fracture closure in a very deep subterranean environment
under high-temperature and high-pressure for a long time.
[0006] Various types of water-based, oil-based, and emulsion-based
fluids are used as well treatment fluids such as fracturing fluid
and the like. Because the well treatment fluid must have the
function of transporting the proppant to the location where the
fracture is generated in the borehole, it generally must have a
prescribed viscosity, good proppant dispersibility, ease of
after-treatment, and low environmental load. Furthermore,
fracturing fluid sometimes contains a channelant in order to form
flow paths through which shale oil, shale gas, and the like can
pass among the proppant. Accordingly, in addition to the proppant,
various additives are used in well treatment fluid, such as
channelants, gelling agents, antiscale agents, acids for dissolving
rock and the like, friction-reducing agents, and the like.
[0007] The following method is typically used to produce fractures
by hydraulic pressure in the productive layer of a deep
subterranean production layer (layer that produces the hydrocarbon
resource, for example petroleum such as shale oil or natural gas
such as shale gas or the like) using fracturing fluid.
Specifically, a prescribed section of a borehole (downhole) drilled
into a subterranean formation several thousand meters deep is
partially plugged while blocking sequentially from the tip portion
of the borehole, and fracturing fluid is fed at high pressure into
the plugged section to produce fractures in the productive layer.
Thereafter, the next prescribed section (typically before the
leading section, specifically, the surface side section) is plugged
and fracturing is carried out. This process is repeated until the
necessary blocking and fracturing is completed.
[0008] Stimulation of the productive layer is sometimes also
performed again not only for drilling of new wells but for desired
sections of existing boreholes. In this case as well, the
operations of borehole plugging, fracturing, and the like may be
similarly repeated. Additionally, there are also cases where, to
perform finishing of the well, the borehole is plugged to block
fluid from below, and after the top portions finished, the plug is
released.
[0009] Various methods are known for subsequent plugging and
fracturing of boreholes from the tip portion of the borehole. For
example, Patent Documents 1 to 3 disclose plugs for well drilling
capable of plugging or fixing a borehole (also called a "frac
plug," "bridge plug," "packer," or the like).
[0010] For example, Patent Document 1 discloses a downhole plug for
well drilling (also simply called "plug" hereinafter), and
specifically discloses a plug comprising a mandrel (main body)
having a hollow part in the axial direction, a ring or annular
member along the axial direction on the outer circumferential
surface orthogonal to the axial direction of the mandrel, a first
conical member and slip, a malleable element foamed from elastomer,
rubber, or the like, a second conical member and slip, and an
anti-rotation feature. Sealing of the borehole by a downhole plug
for well drilling is performed as follows. Specifically, by moving
the mandrel in the axial direction thereof, as the gap between the
ring or annular member and the anti-rotation feature gets smaller,
the slip contacts the slanted face of the conical member, and by
proceeding along the conical member, it expands radially in the
outward direction, contacts the inside wall of the borehole, and is
fixed in the borehole to seal the borehole, and also, the malleable
element deforms by diametric expansion, contacts the inside wall of
the borehole, and seals the borehole. The mandrel has a hollow part
in the axial direction, and the borehole can be sealed by setting a
ball or the like therein. Patent Document 1 describes that metal
materials (aluminum, steel, stainless steel, and the like), fibers,
wood, composite materials, plastics, and the like are widely
exemplified as materials that form plugs, and that composite
materials containing a reinforcing material such as carbon fibers,
especially polymeric substances such as epoxy resin, phenol resin,
and the like, are preferred, and that the mandrel is formed from
aluminum or a composite material. On the other hand, Patent
Document 1 describes that, in addition to the previously described
materials, a material that degrades depending on temperature,
pressure, pH (acidic, basic), and the like may be used as the ball
or the like.
[0011] Patent Document 2 discloses a packer assembly for well
drilling where each packer is separably connected to each adjacent
packer. Patent Document 2 recites a packer provided with a mandrel
having a hollow part in the axial direction and, a slip, a slip
wedge, a resilient packer element, an extrusion limiter, and the
like along the axial direction on the outer circumferential surface
orthogonal to the axial direction of the mandrel.
[0012] Downhole plugs for well chilling are arranged sequentially
inside the well until the well is completed, but must be removed at
the stage when production of petroleum such as shale oil or natural
gas such as shale gas (hereinafter collectively called "petroleum
and natural gas" or "petroleum or natural gas") is begun. Because
the plug is not designed to be released and retrievable after use,
it is typically removed by destruction or by making it into small
fragments by pulverization, drilling out, or another method, but
substantial cost and time are required for pulverization, chilling
out, and the like. There are also plugs specially designed to be
retrievable after use (retrievable plugs), but since plugs are
placed deep underground, substantial cost and time are required to
retrieve all of them.
[0013] Patent Document 3 discloses a disposable downhole tool
(meaning a downhole plug or the like) or a member thereof
containing a degradable material that degrades when exposed to the
environment inside a well, and as the biodegradable material,
discloses a degradable polymer such as an aliphatic polyester such
as polylactic acid. Additionally, Patent Document 3 describes a
combination of a tubular body element having an axial-direction
flow bore, a packer element assembly comprising an upper sealing
element, a center sealing element, and a lower sealing element
along the axial direction on the outer circumferential surface
orthogonal to the axial direction of the tubular body member, a
slip, and a mechanical slip body. Furthermore, Patent Document 3
discloses that fluid flow in only one direction is allowed due to
the fact that a ball is set in the flow bore of the cylindrical
body part. However, Patent Document 3 does not disclose whether a
material containing a degradable material is used for a downhole
tool or any part thereof.
[0014] With the increase in demand with regards to energy resource
securement, environmental conservation and the like, and
particularly as the mining of unconventional resources spreads,
mining regulations such as those pertaining to mining at deeper
levels have become stricter and more diversified. Plugs for well
drilling (downhole tool) are transported to deep subterranean
levels where fracturing is performed using a wire-like element
(also called a "string", "stinger", "cable" or the like), move
various members attached to the mandrel or the outer
circumferential surface of the mandrel relatively so as to plug the
borehole, and must withstand the pressure of high-pressure fluid
and maintain plugging of the borehole during fracturing in which a
high-pressure fluid is used. Specifically, plugs for well drilling
such as downhole tools and downhole tool members must display
sufficient resistance against high loads applied thereto when being
transporting into the well, plugging a borehole and maintaining
that plugging during fracturing. Accordingly, it has been desired
that plugs for well drilling such as downhole tools and downhole
tool members have a structure whereby plugging can be maintained
and mechanical properties (strength, ductility, and other
tensile-related properties and/or compression properties) whereby
the plug can withstand pressures applied during operations
associated with fracturing in the environment within the well.
[0015] Particularly, there are cases where a degradable material
such as, for example, a decomposable resin material is used as the
mandrel or the various members attached to the outer
circumferential surface of the mandrel, that is, as a downhole tool
as a plug for well drilling or a part or all of the members
thereof, in order to make it possible to remove the plug or member
via degradation after fracturing is completed. In such cases, the
plug for well drilling must have sufficient strength to maintain
the plugging in the environment within the well during the period
until the completion of fracturing.
[0016] As mining regulations such as those pertaining to mining at
deeper levels have become stricter and more diversified, there is a
demand for a plug for well drilling and a well drilling method by
which well drilling costs or steps can be reduced by withstanding
the large load placed on the plug so as to reliably be transported
into the well, plug the borehole, and carry out fracturing; and
facilitating the removal of the plug and the securing of the flow
path.
CITATION LIST
Patent Literature
[0017] Patent Document 1: US Patent Application Publication No.
2011/0277989 A1 specification
[0018] Patent Document 2: US Patent Application Publication No.
2003/0183391 A1 specification
[0019] Patent Document 3: US Patent Application Publication No.
2005/0205266 A1 specification
SUMMARY OF INVENTION
Technical Problem
[0020] As mining regulations such as those pertaining to mining at
deeper levels have become stricter and more diversified, an object
of the present invention is to provide a plug for well drilling and
a well drilling method by which well drilling costs or steps can be
reduced by withstanding the large load placed on the plug so as to
reliably be transported into the well, plug the borehole, and carry
out fracturing; and facilitating the removal of the plug and the
securing of the flow path. A further object of the present
invention is to provide a well drilling method in which said plug
for well drilling is used.
Solution to Problem
[0021] As a result of diligent research to solve the problems
described above, the present inventors discovered that, in a plug
for well drilling comprising a mandrel and members attached on an
outer circumferential surface orthogonal to the axial direction of
the mandrel, the technical problems of the invention could be
solved by forming at least a portion of the members from a
degradable material and specifying a coupling mechanism of the
mandrel and the members. Thus the present invention was
completed.
[0022] Specifically, a first aspect of the present invention
provides: (1) a plug for well drilling comprising a mandrel and
members attached on an outer circumferential surface orthogonal to
an axial direction of the mandrel, wherein:
[0023] a) at least one of the members or the mandrel is formed from
a degradable material, and
[0024] b) a ring-shaped ratchet structure orthogonal to the axial
direction of the mandrel is provided on an inner circumferential
surface of at least one of the members and the outer
circumferential surface of the mandrel, the ring-shaped ratchet
structure being formed from a plurality of interlocking parts that
allow movement of the members in one direction along the axial
direction of the mandrel and restrict movement in the opposite
direction.
[0025] Another aspect of the present invention provides the plug
for well drilling described in (2), below.
[0026] (2) A plug for well drilling comprising a mandrel and
members attached on an outer circumferential surface orthogonal to
an axial direction of the mandrel, wherein:
[0027] a1l) the mandrel is formed from a degradable material;
[0028] a2) at least one of the members is formed from a degradable
material; and
[0029] b) a ring-shaped ratchet structure orthogonal to the axial
direction of the mandrel is provided on an inner circumferential
surface of at least one of the members and the outer
circumferential surface of the mandrel, the ring-shaped ratchet
structure being formed from a plurality of interlocking parts that
allow movement of the member in one direction along the axial
direction of the mandrel and restrict movement in the opposite
direction.
[0030] Yet other aspects of the present invention provide the plug
for well drilling described in (3) to (8), below.
[0031] (3) The plug for well drilling described in (1) or (2),
wherein the member attached on the outer circumferential surface
orthogonal to the axial direction of the mandrel, having the
plurality of interlocking parts formed on the inner circumferential
surfaces thereof is at least one selected from the group consisting
of a slip, a wedge, a pair of ring-shaped fixing members, and a
diametrically expandable circular rubber member.
[0032] (4) The plug for well drilling described in any one of (1)
to (3), wherein the member attached on the outer circumferential
surface orthogonal to the axial direction of the mandrel, having
the plurality of interlocking parts formed on the inner
circumferential surfaces thereof is one or a plurality of pushing
jigs.
[0033] (5) The plug for well drilling described in (4), wherein at
least one of the pushing jigs is one of the pair of ring-shaped
fixing members.
[0034] (6) The plug for well drilling described in (4) or (5),
wherein at least one of the pushing jigs comprises a support ring
formed from at least one of a metal and a degradable material, and
an inner circumferential surface of the support ring contacts the
outer circumferential surface of a ratchet structured ring having
interlocking parts that form a ring-shaped ratchet structure on an
inner circumferential surface thereof.
[0035] (7) The plug for well drilling described in any one of (4)
to (6), further comprising a ring-shaped plate adjacent to a
leading side along the axial direction of the mandrel of at least
one of the pushing jigs.
[0036] (8) The plug for well drilling described in (7), wherein the
ring-shaped plate is formed from at least one of a degradable
material and a metal.
[0037] Yet other aspects of the present invention provide the plug
for well drilling described in (9) to (21), below
[0038] (9) The plug for well drilling described in any one of (1)
to (8), wherein at least one of the following i) to applies to the
mandrel formed from the degradable material:
[0039] i) is formed from a degradable material having a shearing
stress of 30 MPa or greater at a temperature of 66.degree. C.;
[0040] ii) has a thickness reduction of less than 5 mm after being
immersed in water of a temperature of 66.degree. C. for one hour,
and has a thickness reduction of 10 mm or greater after being
immersed in water of a temperature of 149.degree. C. for 24 hours;
and
[0041] iii) a tensile load capacity of the interlocking parts of
the ratchet structure is 5 kN or greater at a temperature of
66.degree. C.
[0042] (10) The plug for well drilling described in any one of (1)
to (9) wherein, at least one of the members attached on the outer
circumferential surface orthogonal to the axial direction of the
mandrel is formed from a degradable material having a shearing
stress of 30 MPa or greater at a temperature of 66.degree. C.
[0043] (11) The plug for well drilling described in any one of (1)
to (10), wherein a gross tensile load capacity is 100 kN or
greater.
[0044] (12) The plug for well drilling described in any one of (1)
to (11), wherein a gross tensile load capacity of the ring-shaped
ratchet structure is 50 kN or greater.
[0045] (13) The plug for well drilling described in any one of (1)
to (12), wherein the ring-shaped ratchet structure is formed so as
to cover one or both of the outer circumferential surface of the
mandrel and the inner circumferential surface of the members
attached on the outer circumferential surface orthogonal to the
axial direction of the mandrel.
[0046] (14) The plug for well drilling described in any one of (3)
to (13), wherein the pair of ring-shaped fixing members is capable
of fixing the diametrically expandable circular rubber member
attached on the outer circumferential surface orthogonal to the
axial direction of the mandrel in a compressed state.
[0047] (15) The plug for well drilling described in any one of (3)
to (14) wherein, at least one of a combination of the slip and the
wedge is disposed between the pair of ring-shaped fixing
members.
[0048] (16) The plug for well drilling described in (15),
comprising a plurality of the combination of the slip and the
wedge.
[0049] (17) The plug for well drilling described in any one of (1)
to (16), wherein the mandrel comprises a hollow part along the
axial direction.
[0050] (18) The plug for well drilling described in any one of (1)
to (17), wherein the degradable material is an aliphatic
polyester.
[0051] (19) The plug for well drilling described in (18), wherein
the aliphatic polyester is polyglycolic acid.
[0052] (20) The plug for well drilling described in (19), wherein
the polyglycolic acid has a weight average molecular weight from
180000 to 300000, and a melt viscosity recorded at a temperature of
270.degree. C. and a shear rate of 122 sec.sup.-1 from 700 to 2000
Pas.
[0053] (21) The plug for well drilling described in any one of (1)
to (20), wherein the degradable material comprises a reinforcing
material.
[0054] Furthermore, yet another aspect of the present invention
provides: (22) a well drilling method using the plug for well
drilling described in any one of (1) to (21), the method comprising
degrading a part or all of the plug for well drilling after
blocking a borehole.
[0055] As an embodiment thereof; the following is provided: (23)
The well drilling method described in (22) comprising degrading the
ring-shaped ratchet structure.
Advantageous Effects of Invention
[0056] A first aspect of the present invention provides a plug for
well drilling comprising a mandrel and members attached on an outer
circumferential surface orthogonal to an axial direction of the
mandrel, wherein:
[0057] a) at least one of the members or the mandrel is formed from
a degradable material, and
[0058] b) a ring-shaped ratchet structure orthogonal to the axial
direction of the mandrel is provided on an inner circumferential
surface of at least one of the members and the outer
circumferential surface of the mandrel, the ring-shaped ratchet
structure being formed from a plurality of interlocking parts that
allow movement of the member in one direction along the axial
direction of the mandrel and restrict movement in the opposite
direction.
[0059] In light of mining regulations such as those pertaining to
mining at deeper levels becoming stricter and more diversified, and
as a result of the configuration described above, a plug for well
drilling is provided by which advantageous effects are provided in
that well drilling costs and steps can be reduced by withstanding
the large load placed on the plug so as to reliably be transported
into the well, plug the borehole, and carry out fracturing; and
facilitating the removal of the plug and the securing of the flow
path.
[0060] Additionally, another aspect and yet still another aspect of
the present invention provide a plug for well drilling comprising a
mandrel and members attached on an outer circumferential surface
orthogonal to an axial direction of the mandrel, wherein:
[0061] a1) the mandrel is formed from a degradable material;
[0062] a2) at least one of the members is formed from a degradable
material;
[0063] b) a ring-shaped ratchet structure orthogonal to the axial
direction of the mandrel is provided on an inner circumferential
surface of at least one of the members and the outer
circumferential surface of the mandrel, the ring-shaped ratchet
structure being formed from a plurality of interlocking parts that
allow movement of the member in one direction along the axial
direction of the mandrel and restrict movement in the opposite
direction; and furthermore
[0064] c) the plug for well drilling comprises one or multiple
pushing jigs enveloping the ring-shaped ratchet structure; and
[0065] d) the plug for well drilling comprises a ring-shaped plate
adjacent to a leading side along the axial direction of the mandrel
of at least one of the pushing jigs.
[0066] In light of mining regulations such as those pertaining to
mining at deeper levels becoming stricter and more diversified, and
as a result of the configuration described above, a plug for well
drilling is provided by which advantageous effects are provided in
that well drilling costs and steps can be reduced by withstanding
the large load placed on the plug so as to reliably be transported
into the well, plug the borehole, and carry out fracturing; and
facilitating the removal of the plug and the securing of the flow
path.
[0067] Additionally, another aspect of the present invention
provides a well drilling method using the plug for well drilling,
the method comprising degrading a part or all of the plug for well
drilling after blocking a borehole.
[0068] As mining regulations such as those pertaining to mining at
deeper levels have become stricter and more diversified, and as a
result of the method described above, a well drilling method is
provided by which advantageous effects are provided in that well
drilling costs and steps can be reduced by withstanding the large
load placed on the plug so as to reliably be transported into the
well, plug the borehole, and carry out fracturing; and facilitating
the removal of the plug and the securing of the flow path.
BRIEF DESCRIPTION OF DRAWINGS
[0069] FIG. 1A is a schematic cross-sectional view illustrating a
specific example of a plug for well drilling of the present
invention.
[0070] FIG. 1B is a schematic cross-sectional view illustrating a
state where a diametrically expandable circular rubber member of
the plug for well drilling is diametrically expanded.
[0071] FIGS. 2A, 2B, 2C, and 2D are schematic cross-sectional views
illustrating specific examples of a ring-shaped ratchet structure
orthogonal to the axial direction of the mandrel in the plug for
well drilling of the present invention.
[0072] FIG. 3 is a schematic partial cross-sectional view
illustrating a specific example of the plug for well drilling of
the present invention provided with the pushing jig.
[0073] FIG. 4A is a schematic partially enlarged cross-sectional
view illustrating the vicinity of the ratchet structure in a
specific example of the plug for well drilling of the present
invention provided with the pushing jig and the ring-shaped
plate.
[0074] FIG. 4B is a schematic partially enlarged cross-sectional
view illustrating the vicinity of the ratchet structure when the
ratchet structured ring of the pushing jig depicted in FIG. 4A is
in contact with the ring-shaped plate.
DESCRIPTION OF EMBODIMENTS
[0075] The present invention relates to a plug for well drilling
comprising a mandrel and members attached on an outer
circumferential surface orthogonal to an axial direction of the
mandrel, wherein:
[0076] a) at least one of the members or the mandrel is formed from
a degradable material, and
[0077] b) a ring-shaped ratchet structure orthogonal to the axial
direction of the mandrel is provided on an inner circumferential
surface of at least one of the members and the outer
circumferential surface of the mandrel, the ring-shaped ratchet
structure being formed from a plurality of interlocking parts that
allow movement of the member in one direction along the axial
direction of the mandrel and restrict movement in the opposite
direction. The present invention is described below while
referencing FIGS. 1A and 1B.
I. Plug for Well Drilling
1. Mandrel
[0078] The plug for well drilling of the present invention is
provided with a mandrel and members attached on the outer
circumferential surface orthogonal to the axial direction of the
mandrel. The mandrel 1 provided in the plug for well drilling of
the present invention is normally called a "core metal," of which
the cross-section has a substantially circular shape. The length of
the mandrel 1 is sufficiently long relative to the diameter of the
cross-section, and the mandrel 1 basically assures the strength of
the plug for well drilling of the present invention. In the mandrel
1 provided in the plug for well drilling of the present invention,
the diameter of the cross-section is selected as appropriate
according to the size of the borehole (by making it slightly
smaller than the inner diameter of the borehole, the plug can move
inside the borehole, while on the other hand, as will be described
later, there is a difference in diameter to an extent that enables
borehole plugging via the diametric expansion of a diametrically
expandable circular rubber member 5 or the like). The length of the
mandrel 1 is, for example, approximately 5 to 20 times the diameter
of the cross-section but is not limited thereto. Typically, the
diameter of the cross-section of the mandrel 1 is in a range of 5
to 30 cm.
[Hollow Part]
[0079] The mandrel 1 provided in the plug for well drilling of the
present invention may be solid, but from the perspectives of
securing a flow path at early stages of fracturing, reducing the
weight of the mandrel, and controlling the degradation rate of the
mandrel, the mandrel 1 is preferably a hollow mandrel comprising in
at least a portion thereof a hollow part along the axial direction
(the hollow part may be configured to penetrate the mandrel along
the axial direction, or it may be configured not penetrate the
mandrel along the axial direction). Additionally, in cases where
the mandrel 1 is force-transported the plug for well drilling into
a borehole using a fluid, the mandrel 1 preferably comprises the
hollow part along the axial direction. When the mandrel 1 has a
hollow part along the axial direction, the cross-sectional shape of
the mandrel 1 is a circular shape formed by two concentric circles
forming the diameter (outside diameter) of the mandrel 1 and the
outside diameter of the hollow part (corresponding to the inside
diameter of the mandrel 1). The ratio of the diameters of the two
concentric circles--that is, the ratio of the outside diameter of
the hollow part to the diameter of the mandrel (core rod) 1--is
preferably at most 0.7. The magnitude of this ratio has a
reciprocal relationship with the magnitude of the ratio of the
thickness of the hollow mandrel 1 to the diameter of the mandrel 1,
so determining the upper limit of this ratio can be considered
equivalent to determining a preferable lower limit of the thickness
of the hollow mandrel. When the thickness of the hollow mandrel is
too thin, the strength (in particular, the tensile strength) of the
hollow mandrel may be insufficient when the plug for well drilling
is placed inside a borehole or at the time of borehole plugging or
fracturing, which may, in extreme cases, result in damage to the
plug for well drilling Therefore, the ratio of the outside diameter
of the hollow part to the diameter of the mandrel 1 is more
preferably at most 0.6 and even more preferably at most 0.5.
[0080] The diameter of the mandrel 1 and/or the outer diameter of
the hollow part may be uniform along the axial direction of the
mandrel 1, but may also vary along the axial direction. That is,
bent portions such as convex parts, stepped parts, flanges, concave
parts (grooves), and also screw parts, or the like may be formed on
the outer circumferential surface of the mandrel 1 due to the fact
that the outside diameter of the mandrel 1 varies along the axial
direction. In addition, bent portions such as convex parts, stepped
parts, flanges, concave parts (grooves), and also screw parts, or
the like may be formed on the inner peripheral surface of the
mandrel 1 when the outside diameter of the hollow part varies along
the axial direction. Furthermore, the bent portions may comprise a
tapered part.
[0081] The convex parts, stepped parts, flanges, and concave parts
(grooves) provided on the outer circumferential surface and/or the
inner circumferential surface of the mandrel 1 can be used as
bearing sites when transporting the plug for well drilling into a
borehole, and can also be used as sites for attaching and/or fixing
other members to the outer circumferential surface and/or the inner
circumferential surface of the mandrel 1. In cases where the
mandrel 1 has a hollow part, the hollow part can be used as a seat
for holding a ball used to control the flow of a fluid.
[Material Forming the Mandrel]
[0082] The material forming the mandrel 1 provided in the plug for
well drilling of the present invention is not particularly limited.
Materials used conventionally in the forming of mandrels provided
in plugs for well drilling can be used. Examples include, metal
materials (aluminum, steel, stainless steel, and the like), fibers,
wood, composite materials, and resins. Specific examples include
composite materials including carbon fibers or similar reinforcing
materials, and particularly composite materials including an epoxy
resin, phenol resin, or similar polymeric substances. As the plug
for well drilling of the present invention will be able to reduce
the costs and steps of well drilling as a result of the plug being
removed following the completion of fracturing and the securing of
the flow path being facilitated, the mandrel 1 is preferably formed
from a degradable material.
[Degradable Material]
[0083] In the plug for well drilling of the present invention, in
cases where the mandrel 1 is formed from the degradable material,
as described hereinafter, biodegradable materials, degradable
materials having hydrolyzability, and other degradable materials
that can be chemically degraded through some other process can be
used as the degradable material.
[0084] Materials such as aluminum and similar metal materials are
commonly used to form the mandrel provided in conventional plugs
for well drilling. Such materials are prone to mechanical
degradation such as destruction, disintegration, or the like and
are not suitable as the degradable material forming the mandrel 1
provided in the plug for well drilling of the present invention.
However, materials in which the intrinsic strength of resin
decreases and the resin becomes weak due to a reduction in the
degree of polymerization or the like, resulting in it
disintegrating and losing its shape upon application of a very
small mechanical force, also qualify as degradable materials.
Examples of such degradable materials include composite materials
including a decomposable resin and a metal material (described
hereinafter).
[0085] In the plug for well drilling of the present invention, in
cases where the mandrel 1 is formed from the degradable material,
as described hereinafter, the degradable material is preferably a
hydrolyzable material that degrades in water of a certain or higher
temperature. Additionally, the degradable material is more
preferably an aliphatic polyester, and even more preferably
polyglycolic acid. Furthermore, the degradable material may
comprise a reinforcing material, and may also comprise other
compounding components. Additionally, in cases where the mandrel 1
is formed from the degradable material and also includes bent
portions such as convex parts, stepped parts, flanges, and concave
parts (grooves), and also screw parts, or the like, a curvature
radius of the bent portions is preferably from 0.5 to 50 mm.
[0086] The degradable material used in the plug for well drilling
of the present invention is described in further detail below The
degradable material may be a degradable material that is, for
example, biodegradable, meaning that it is degraded by
microorganisms in the soil in which the fracturing fluid and the
like are used, or hydrolyzable, meaning that it is degraded by a
solvent in the fracturing fluid, particularly by water, and also by
acids or alkalis if desired. Additionally, it may be a degradable
material that can be degraded chemically by some other method.
Preferably, the degradable material is a hydrolyzable degradable
material degraded by water of a certain or higher temperature.
[Decomposable Resin]
[0087] A decomposable resin is preferred as the degradable material
because it must have the strength expected for a material used in a
high-temperature, high-pressure deep subterranean environment while
also having excellent degradability. A decomposable resin means a
resin that is biodegradable, hydrolyzable, or can be degraded
chemically some other method, as described above. Examples of the
decomposable resin include aliphatic polyesters such as polylactic
acid, polyglycolic acid, and poly-.epsilon.-caprolactone, and
polyvinyl alcohols (partially saponified polyvinyl alcohols and the
like having a degree of saponification of 80 to 95 mol %) and the
like, but it is more preferably an aliphatic polyester. That is,
the degradable material is preferably an aliphatic polyester. The
decomposable resin may be one type alone or a combination obtained
by blending two or more types. Additionally, in cases where the
member attached on the outer circumferential surface orthogonal to
the mandrel 1 formed from the degradable material is a
diametrically expandable circular rubber member, examples of
degradable materials that can be used include aliphatic
polyester-based rubbers, polyurethane rubbers, natural rubbers,
polyisoprene, and similar biodegradable rubbers.
[Aliphatic Polyester]
[0088] The aliphatic polyester is, for example, obtained from
homopolymerization or copolymerization of an oxycarbonic acid
and/or a lactone, an esterification reaction of aliphatic
dicarboxylic acid and an aliphatic diol, or copolymerization of
aliphatic dicarboxylic acid, an aliphatic diol, and an oxycarbonic
acid and/or a lactone; and preferably dissolves rapidly in water
having a temperature from about 20 to 100.degree. C.
[0089] Examples of the oxycarbonic acid include, glycolic acid,
lactic acid, malic acid, hydroxypropionic acid, hydroxybutyric
acid, hydroxypentanoic acid, hydroxycaproic acid, hydroxyheptanoic
acid, hydroxyoctanoic acid, and similar aliphatic hydroxycarboxylic
acids having from 2 to 8 carbons, and the like. Examples of the
lactone include propiolactone, butyrolactone, valerolactone,
.epsilon.-caprolactone, and similar lactones having from 3 to 10
carbons, and the like.
[0090] Examples of the aliphatic dicarboxylic acid include, oxalic
acid, malonic acid, succinic acid, glutaric acid, adipic acid, and
similar aiphatic saturated dicarboxylic acids having from 2 to 8
carbons; maleic acid, fumaric acid, and similar aiphatic
unsaturated dicarboxylic acids having from 4 to 8 carbons; and the
like. Examples of the aliphatic diol include, ethylene glycol,
propylene glycol, butane diol, hexane diol, and similar alkylene
glycols having from 2 to 6 carbons; polyethylene glycol,
polypropylene glycol, polybutylene glycol, and similar polyalkylene
glycols having from 2 to 4 carbons; and the like.
[0091] One type alone or a combination obtained by blending two or
more types of components may be used to form these polyesters.
Furthermore, components that form an aromatic polyester such as
terephthalic acid may be used in combination provided that the
properties as a decomposable resin are not lost.
[0092] Examples of particularly preferable aliphatic polyesters as
the degradable resin include, polylactic acid (hereinafter referred
to also as "PLA"), polyglycolic acid (hereinafter referred to also
as "PGA"), and similar hydroxycarboxylic acid-based aliphatic
polyesters; poly-.epsilon.-caprolactone and similar lactone-based
aliphatic polyesters; polyethylene succinate, polybutylene
succinate, and similar diol-dicarboxylic acid-based aliphatic
polyesters; copolymers of these, including, for example,
poly(lactic-co-glycolic acid) (hereinafter referred to also as
"PGLA"); as well as mixtures of these; and the like. Another
example is an aliphatic polyester used by combining polyethylene
adipate/terephthalate or similar aromatic components.
[0093] From the perspective of the strength and degradability
required in the mandrel 1 of the plug for well drilling, the
aliphatic polyester is most preferably at least one type selected
from the group consisting of PGA, PLA, and PGLA, of which PGA is
even more preferred. The PGA encompasses not only homopolymers of
glycolic acid, but also copolymers containing not less than 50 mass
%, preferably not less than 75 mass %, more preferably not less
than 85 mass %, even more preferably not less than 90 mass %,
particularly preferably not less than 95 mass %, most preferably
not less than 99 mass %, and above all, preferably not less than
99.5 mass %, of glycolic acid repeating units. The PLA encompasses
not only homopolymers of L-lactic acid or D-lactic acid, but also
copolymers containing not less than 50 mass %, preferably not less
than 75 mass %, more preferably not less than 85 mass %, and even
more preferably not less than 90 mass %, of L-lactic acid or
D-lactic acid repeating units, and it may be a stereocomplex
polylactic acid obtained by mixing a poly-L-lactic acid and a
poly-D-lactic acid. As the PGLA, a copolymer in which the ratio
(mass ratio) of glycolic acid repeating units to lactic acid
repeating units is from 99:1 to 1:99, preferably from 90:10 to
10:90, and more preferably from 80:20 to 20:80, may be used.
(Melt Viscosity)
[0094] The aliphatic polyester, and preferably as the PGA, PLA,
and/or PGLA typically has a melt viscosity from 50 to 5000 Pas, but
preferably has a melt viscosity from 150 to 3000 Pas and more
preferably from 300 to 1500 Pas. The melt viscosity is measured
under a temperature of 240.degree. C. and a shear rate of 122
sec.sup.-1. If the melt viscosity is too low, the strength required
in the mandrel provided in the plug for well drilling may be
insufficient. If the melt viscosity is too high, a high melting
temperature will be required in order to manufacture the mandrel,
which may lead to thermal degradation of the aliphatic polyester,
insufficiency of degradation, and the like. The melt viscosity
described above is measured using a capirograph fitting with
capillaries (diameter 1 mm cp.times.length 10 mm) (Capirograph 1-C,
manufactured by Toyo Seiki Seisaku-Sho, Ltd.). A 20 g sample was
held at a predetermined temperature (240.degree. C.) for 5 minutes
and subsequently measured at a shear rate of 122 sec.sup.-1.
[0095] From the perspective of, for example, obtaining formability
whereby cracking does not occur when molding by
solidification-and-extrusion-molding, and the like, the PGA as the
aliphatic polyester particularly preferably has a weight average
molecular weight from 180,000 to 300,000, and a melt viscosity
measured at a temperature of 270.degree. C. and at a shear rate of
122 sec.sup.-1 from 700 to 2000 Pas. Of these, the PGA is
preferably a PGA having a weight average molecular weight from
190,000 to 240,000, and a melt viscosity measured at a temperature
of 270.degree. C. and at a shear rate of 122 sec.sup.-1 of 800 to
1200 Pas. The melt viscosity is measured according to the method
described above (the measurement temperature is set to 270.degree.
C.). The weight average molecular weight is measured using gel
permeation chromatography (GPC) under the conditions described
below. 10 .mu.l of the solution to be measured is obtained by
dissolving 10 mg of the PGA in hexafluoroisopropanol (HFlP) in
which sodium trifluoroacetate is dissolved at a concentration of 5
mM to obtain a 10 mL solution and, thereafter, filtering the
solution using a membrane filter.
<GPC Measurement Conditions>
[0096] Device: LC-9A, manufactured by Shimadzu Corporation
[0097] Columns: Two REP-806M columns (connected in series)+one
HFlP-LG precolumn manufactured by Showa Denko K.K.
[0098] Column Temperature: 40.degree. C.
[0099] Eluent: HFLP solution in which sodium trifluoroacetate is
dissolved at a concentration of 5 mM
[0100] Flow rate: 1 mL/min
[0101] Detector: Differential refractometer
[0102] Molecular weight calibration: Data of a molecular weight
calibration curve produced by using five types of
polymethylmethacrylates having standard molecular weights that are
different from each other (manufactured by Polymer Laboratories
Ltd.) are used.
[Other Blended Components]
[0103] The degradable material, preferably the decomposable resin,
more preferably the aliphatic polyester, and even more preferably
the PGA, may also contain or be blended with various additives as
other blended components, such as resin materials (other resins
when the degradable material is a decomposable resin), stabilizers,
degradation accelerators or degradation inhibitors, reinforcing
materials, and the like within a range that does not hinder the
object of the present invention. The degradable material preferably
contains a reinforcing material, and in this case, the degradable
material can be called a degradable composite material. When the
degradable material is decomposable resin, it is a so-called
reinforced resin. The mandrel formed from the reinforced resin
preferably is formed from an aliphatic polyester containing a
reinforcing material.
[Reinforcing Material]
[0104] As reinforcing materials, materials such as resin materials
conventionally used as reinforcing materials with the objective of
improving mechanical strength or heat resistance may be used, and
fibrous reinforcing materials or granular or powdered reinforcing
materials may be used. The reinforcing materials may be contained
typically in the amount of not greater than 150 parts by mass, and
preferably in the range of 10 to 100 parts by mass, relative to 100
parts by mass of the degradable material such as decomposable
resin.
[0105] Examples of fibrous reinforcing materials include inorganic
fibrous substances such as glass fibers, carbon fibers, asbestos
fibers, silica fibers, alumina fibers, zirconia fibers, boron
nitride fibers, silicon nitride fibers, boron fibers, and potassium
titanate fibers; metal fibrous substances such as stainless steel,
aluminum, titanium, steel, and brass; and organic fibrous
substances with a high melting point such as aramid fibers, kenaf
fibers, polyamides, fluorine resins, polyester resins, and acrylic
resins; and the like. Short fibers having a length of not greater
than 10 mm, more preferably 1 to 6 mm, and even more preferably 1.5
to 4 mm are preferable as the fibrous reinforcing materials.
Furthermore, inorganic fibrous substances are preferably used, and
glass fibers are particularly preferable.
[0106] As the granular or powdered reinforcing material, mica,
silica, talc, alumina, kaolin, calcium sulfate, calcium carbonate,
titanium oxide, ferrite, clay, glass powder, zinc oxide, nickel
carbonate, iron oxide, quartz powder, magnesium carbonate, barium
sulfate, and the like can be used. These reinforcing materials may
be each used alone or in combinations of two or more types. The
reinforcing material may be treated with a sizing agent or surface
treatment agent as necessary.
[Composite Material]
[0107] The mandrel 1 formed from the degradable material may be
formed from a composite material including the degradable material
and a metal or inorganic substance. Specific examples include
composite materials in which recessed portions such as indentations
having a predetermined shape are provided in a base material formed
from the degradable material such as a decomposable resin
exemplified by PGA, or the like; a metal (metal fragment or the
like) or an inorganic substance having a shape that matches the
shape of the recessed portion is fitted therein; and the base
material and the metal or inorganic substance are fixed using an
adhesive or wrapped and fixed with wires or fibers so that the
fixed state of the base material and the metal fragments or
inorganic substance is maintained.
[Ring-Shaped Ratchet Structure]
[0108] A ring-shaped ratchet structure orthogonal to the axial
direction of the mandrel is provided on the outer circumferential
surface of the mandrel 1 of the plug for well drilling of the
present invention. The ring-shaped ratchet structure is formed from
a plurality of interlocking parts that allow movement of the
members attached on the outer circumferential surface orthogonal to
the axial direction of the mandrel in one direction along the axial
direction of the mandrel and restrict movement in the opposite
direction. Note that in cases where multiple members attached on
the outer circumferential surface orthogonal to the axial direction
of the mandrel are present, each of the members may be provided
with the ring-shaped ratchet structure, or a portion, that is, at
least one of the members may be provided with the ring-shaped
ratchet structure. Further description of the ring-shaped ratchet
structure orthogonal to the axial direction of the mandrel will be
given later.
[Shearing Stress at a Temperature of 66.degree. C.]
[0109] In cases where the mandrel 1 of the plug for well drilling
of the present invention is formed from the degradable material,
the mandrel 1 preferably is formed from a degradable material
having a shearing stress of 30 MPa or greater at a temperature of
66.degree. C. Specifically, when the mandrel 1 is formed from the
degradable material having a shearing stress of 30 MPa or greater
at a temperature of 66.degree. C., the plurality of interlocking
parts, which constitute the ring-shaped ratchet structure
orthogonal to the axial direction of the mandrel, formed on the
outer circumferential surface of the mandrel 1 have no risk of
deforming or becoming damaged when subjected to high pressures in
the axial direction of the mandrel caused by the fracturing fluid
or the like. As a result, there is no need to reduce the number of
interlocking parts (also called "mountains") forming the ratchet
structure or excessively enlarge the cross-sectional area of the
mountains. The shearing stress at a temperature of 66.degree. C. of
the degradable material forming the mandrel 1 is preferably 40 MPa
or greater, and more preferably 50 MPa or greater. The upper limit
of the shearing stress at a temperature of 66.degree. C. is not
particularly limited, but is normally not greater than 600 MPa, and
often not greater than 450 MPa.
[Thickness Reduction After Water Immersion]
[0110] In cases where the mandrel 1 of the plug for well drilling
of the present invention is formed from the degradable material,
the mandrel 1 preferably has a thickness reduction of less than 5
mm after being immersed in water of a temperature of 66.degree. C.
for one hour, and a thickness reduction of 10 mm or greater after
being immersed in water of a temperature of 149.degree. C. for 24
hours. Specifically, when the mandrel 1 has a thickness reduction
of less than 5 mm, more preferably less than 4 mm, and even more
preferably less than 3 mm after being immersed in water of a
temperature of 66.degree. C. for one hour, there is little
probability that the degradable material forming the mandrel 1 will
degrade (as described above, "degrade" includes disintegration and
decreases in strength as well) in downhole environments of around
66.degree. C. As a result, there is no risk of the ring-shaped
ratchet mechanism interlocking parts deforming (including
shrinkage) and/or becoming damaged, and well treatment such as
fracturing, where high pressures are applied by the fluid in the
axial direction of the mandrel, and the like can be reliably
carried out according to a desired time schedule such as, for
example, from a few hours to a few days, to a week. The lower limit
of the thickness reduction after immersion in water of a
temperature of 66.degree. C. for one hour is not particularly
limited, and is preferably 0 mm, but may also be about 0.1 mm. At
the same time, when the mandrel 1 has a thickness reduction of 10
mm or greater, more preferably 12 mm or greater, and even more
preferably 15 mm or greater after being immersed in water of a
temperature of 149.degree. C. for 24 hours, the degradable material
forming the mandrel 1 will degrade (as described above, "degrade"
includes disintegration and decreases in strength as well), leading
to the deformation (including shrinkage) and/or damage of the
ring-shaped ratchet mechanism interlocking parts. As a result, the
plugging (fluid sealing) of the borehole by the plug for well
drilling can be released in a short period of time, for example,
from a few hours to a few days by bringing a fluid having a
temperature of, for example, 149.degree. C. into contact with the
mandrel 1 after the completion of fracturing and other well
treatment. The upper limit of the thickness reduction after
immersion in water of a temperature of 149.degree. C. for 24 hours
is not particularly limited, and is preferably 100% of the
thickness (or diameter) of the mandrel 1, but may also be about
95%.
[Tensile Load Capacity of the Interlocking Parts of the Ratchet
Structure at a Temperature of 66.degree. C.]
[0111] In the mandrel 1 of the plug for well drilling of the
present invention, as described later, a tensile load capacity of
the interlocking parts of the ratchet structure is preferably 5 kN
or greater at a temperature of 66.degree. C. If the tensile load
capacity (tensile load capacity of one mountain) of the
interlocking parts of the ratchet structure at a temperature of
66.degree. C. is too small, multiple interlocking parts will need
to be provided in the ratchet structure, and the length of the
ratchet structure will be too long.
2. Members Attached on the Outer Circumferential Surface Orthogonal
to the Axial Direction of the Mandrel
[0112] The plug for well drilling of the present invention is
provided with a mandrel and members attached on the outer
circumferential surface orthogonal to the axial direction of the
mandrel. Specifically, various members are attached on the outer
circumferential surface of the mandrel in order to efficiently and
reliably transport the plug, plug the borehole, and carry out
fracturing, and for the purpose of improving the ease of handling
of the plug. Examples of the members include members attached on
the outer circumferential surface orthogonal to the axial direction
of the mandrel, members attached on the outer circumferential
surface along the axial direction of the mandrel, members attached
on the outer circumferential surface in another direction relative
to the axial direction of the mandrel, and the like. The present
invention relates to a plug for well drilling provided with members
attached on the outer circumferential surface orthogonal to the
axial direction of the mandrel (hereinafter also referred to as
"outer circumferential surface-attached members"). The present
invention is described below while referencing FIGS. 1A and 1B, and
FIGS. 2A, 2B, 2C, and 2D.
[0113] Provided that the outer circumferential surface-attached
members are members used conventionally in plugs for well drilling,
they are not particularly limited, and examples thereof include at
least one selected from the group consisting of slips 2a and 2b,
wedges 3a and 3b, a pair of ring-shaped fixing members 4a and 4b,
and a diametrically expandable circular rubber member 5. Note that
in FIGS. 1A and 1B, and FIGS. 2A, 2B, 2C, and 2D, a specific
example in which two pairs of the combination of the slip and the
wedge is illustrated but, as described later, one pair of the
combination of the slip and the wedge may be provided, or three
pairs or more may be provided. Additionally, a plurality of the
pair of ring-shaped fixing members may be provided, or one ring of
the pair of ring-shaped fixing members may be excluded.
Furthermore, a plurality of the diametrically expandable circular
rubber member 5 may be provided, or any of the slips, wedges,
ring-shaped fixing members, or diametrically expandable circular
rubber members may be excluded.
[Material Forming the Outer Circumferential Surface-Attached
Members]
[0114] The material forming the outer circumferential
surface-attached members provided in the plug for well drilling of
the present invention is not particularly limited. Materials used
conventionally in the forming of outer circumferential
surface-attached members provided in plugs for well drilling can be
used. Examples include, metal materials (aluminum, steel, stainless
steel, and the like), fibers, wood, composite materials, and
resins. Specific examples include composite materials including
carbon fibers or similar reinforcing materials, and particularly
composite materials including an epoxy resin, phenol resin, or
similar polymeric substances. As the plug for well drilling of the
present invention will be able to reduce the costs and steps of
well drilling as a result of the plug being removed following the
completion of fracturing and the securing of the flow path being
facilitated, at least one of the outer circumferential
surface-attached members is preferably formed from the degradable
material.
[Degradable Material]
[0115] In the plug for well drilling of the present invention, in
cases where at least one of the outer circumferential
surface-attached members is formed from a degradable material, as
described above with regards to the mandrel 1, the degradable
material is preferably a decomposable resin, more preferably an
aliphatic polyester, and even more preferably PGA. The members
formed from the degradable material, that is, the at least one of
the outer circumferential surface-attached members, are preferably
formed from a degradable material having a shearing stress of 30
MPa or greater at a temperature of 66.degree. C., and the
degradable material is the same as that previously described for
the mandrel 1.
[Slips and Wedges]
[0116] A combination of slips 2a and 2b and wedges 3a and 3b is
known in plugs for well drilling as a means for securing the plug
to the borehole. Specifically, the slips 2a and 2b formed from a
metal, inorganic substance, resin, or similar material are placed
so as to be in slidable contact with the upper surface of the
wedges 3a and 3b formed from material such as a compound resin
material. Due to the movement of the wedges 3a and 3b via force in
the axial direction of the mandrel 1 being applied, the slips 2a
and 2b ride up on the upper surface of the slated surface of the
wedges 3a and 3b and move outward orthogonal to the axial direction
of the mandrel 1. The outermost circumferential surface of the
slips 2a and 2b, orthogonal to the axial direction of the mandrel
1, contacts an inside wall H of the borehole and, thus, the plug is
secured to the inside wall H of the borehole. The slips 2a and 2b
may be provided with one or more bent portions such as convex
parts, stepped parts, grooves, rough surfaces (corrugation), or the
like at the parts making contact with the inside wall H of the
borehole in order to make the plugging (sealing) of the space
between the plug and the borehole even more reliable. Additionally,
the slips 2a and 2b may be pre-divided into a predetermined number
of sections in the circumferential direction orthogonal to the
axial direction of the mandrel 1, or, as illustrated in FIGS. 1A
and 1B, may be provided with breaks that stop partway--not
pre-divided into a predetermined number of sections--from one end
to the other end along the axial direction. In cases where breaks
are provided, the wedges 3a and 3b advance to the lower surface of
the slips 2a and 2b due to force in the axial direction of the
mandrel 1 being applied to the wedges 3a and 3b. As a result, the
slips 2a and 2b split and separate along the breaks and an extended
line thereof and each of the pieces subsequently move outward
orthogonal to the axial direction of the mandrel 1. Note that this
structure is known in the art. Note that in cases where the slips
2a and 2b or the wedges 3a and 3b are formed from the degradable
material and also include a bent portion, a curvature radius of the
bent portion is preferably from 0.5 to 50 mm.
[Pair of Ring-Shaped Fixing Members]
[0117] At least one combination of the slips 2a and 2b and the
wedges 3a and 3b are preferably placed between the pair of
ring-shaped fixing members 4a and 4b so that the wedges 3a and 3b
can be made to move when force in the axial direction of the
mandrel 1 is applied thereto. Specifically, the pair of ring-shaped
fixing members 4a and 4b are configured such that they can slide
along the axial direction of the mandrel 1 on the outer
circumferential surface of the mandrel 1 and such that the spacing
therebetween can be changed. In addition, they are configured such
that a force in the axial direction of the mandrel 1 can be applied
to the pair of wedges 3a and 3b by coming into contact directly or
indirectly with the end part along the axial direction of the one
or the plurality of wedges 3a and 3b. Individual shapes and sizes
of the pair of ring-shaped fixing members 4a and 4b are not limited
provided that they can perform the functions described above.
However, from the perspective of being able to effectively apply
force in the axial direction of the mandrel 1 to the wedges 3a and
3b, the edge surfaces of the pair of ring-shaped fixing members 4a
and 4b on each side contacting the wedges 3a and 3b are preferably
flat. Each ring of the pair of ring-shaped fixing members 4a and 4b
is preferably a circular ring which completely surrounds the outer
circumferential surface of the mandrel 1, but may also have breaks
or deformed places in the circumferential direction. In addition,
as for the shape in which the circle is separated in the
circumferential direction, the circle may be formed as desired. As
each of the rings of the pair of ring-shaped fixing members 4a and
4b, a plurality of rings may be placed adjacently in the axial
direction so as to form a wide ring-shaped fixing member (having a
long length in the axial direction of the mandrel 1).
[0118] The pair of ring-shaped fixing members 4a and 4b may have
the same or similar compositions, shapes and structures, or the
compositions, shapes and structures may be different. For example,
each of the ring-shaped fixing members may differ in outside
diameter or length in the axial direction of the mandrel 1. In
addition, for example, one of the rings of the pair of ring-shaped
fixing members 4a and 4b may also be configured in a state
disenabling sliding relative to the mandrel 1, as desired. In this
case, due to the fact that the other ring-shaped fixing member of
the pair of ring-shaped fixing members 4a and 4b slides on the
outer circumferential surface of the mandrel 1, each ring of the
pair of ring-shaped fixing members 4a and 4b contacts the edge
along the axial direction of the wedges 3a and 3b. The description
above should not be construed to limit the present invention and,
as desired, the pair of ring-shaped fixing members 4a and 4b may be
configured such that one of the rings of the pair of ring-shaped
fixing members 4a and 4b is in a state disenabling sliding with
respect to the mandrel 1. Examples of a such configurations include
configurations wherein the mandrel 1 and one ring of the pair of
ring-shaped fixing members 4a and 4b are integrally formed (in this
case, the ring-shaped fixing member cannot slide freely with
respect to the mandrel 1); and where a jaw clutch or similar clutch
mechanism and/or mating mechanism is used (in this case, switching
between states where the rings can and cannot slide with respect to
the mandrel 1 is enabled). As the plug for well drilling in which
the mandrel 1 and one of the rings of the pair of rings 4a and 4b
are formed integrally, a plug for well drilling in which these
components are formed by integral molding or a plug for well
drilling formed by machining is provided. Note that in cases where
the pair of ring-shaped fixing members 4a and 4b are formed from
the degradable material and also include a bent portion, a
curvature radius of the bent portion is preferably from 0.5 to 50
mm.
[0119] The plug for well drilling may be provided with a plurality
of the pair of ring-shaped fixing members 4a and 4b. In this case,
at least one of each of the combinations of the slips 2a and 2b and
the wedges 3a and 3b and/or the diametrically expandable circular
rubber member 5 may be placed, individually or in combination, at
positions between the one or the plurality of the pair of rings 4a
and 4b.
[Diametrically Expandable Circular Rubber Member]
[0120] The plug for well drilling of the present invention may be
provided with at least one diametrically expandable circular rubber
member 5 placed at a position between the pair of ring-shaped
fixing members 4a and 4b on the outer peripheral surface orthogonal
to the axial direction of the mandrel 1. Preferably, the pair of
ring-shaped fixing members 4a and 4b described above can be
configured such that the diametrically expandable circular rubber
member 5 attached on the outer circumferential surface orthogonal
to the axial direction of the mandrel 1 is fixed in a compressed
state. That is, due to the diametrically expandable circular rubber
member 5 directly or indirectly contacting the pair of ring-shaped
fixing members 4a and 4b, force in the axial direction of the
mandrel 1 is transmitted on the outer circumferential surface of
the mandrel. As a result, the diametrically expandable circular
rubber member 5 diametrically shrinks by being compressed in the
axial direction of the mandrel 1 and diametrically expands in the
direction orthogonal to the axial direction of the mandrel 1. The
circular rubber member 5 expands in diameter, and the outward part
in the direction orthogonal to the axial direction comes into
contact with the inside wall H of the borehole, and additionally,
the inward part in the direction orthogonal to the axial direction
comes into contact with the outer circumferential surface of the
mandrel 1, thereby plugging (sealing) the space between the plug
and the borehole. The diametrically expandable circular rubber
member 5 is fixed in a compressed state by the pair of ring-shaped
fixing members 4a and 4b. That is, a state of contact of the outer
circumferential surface of the mandrel 1 with the inside wall H of
the borehole can be maintained, with the diametrically expandable
circular rubber member 5 being in a compressed state in the axial
direction of the mandrel 1 and the diametrically expandable
circular rubber member 5 being in an expanded state in the
direction orthogonal to the axial direction of the mandrel 1, while
fracturing is subsequently performed, which yields the function of
maintaining the seal between the plug and the borehole.
[0121] The diameter expandable circular rubber member 5 is not
limited with regard to its material, shape, or structure as long as
it has the function described above. For example, by using a
circular rubber member 5 having a shape in which the cross-section
in the circumferential direction orthogonal to the axial direction
of the mandrel 1 has an inverted U-shape, it can expand in diameter
toward the vertex of the inverted U-shape as the tip portion of the
U-shape is compressed in the axial direction of the mandrel 1. The
diametrically expandable circular rubber member 5 comes into
contact with the inside wall H of the borehole and the outer
circumferential surface of the mandrel 1 when diametrically
expanded so as to plug (seal) the space between the plug and the
borehole, and a gap is present between the plug and the borehole
when the diametrically expandable circular rubber member 5 is not
expanded. Therefore, the length of the diametrically expandable
circular rubber member 5 in the axial direction of the mandrel 1 is
preferably from 10 to 70% and more preferably from 15 to 65% with
respect to the length of the mandrel 1. As a result of this
configuration, the plug for well drilling of the present invention
has a sufficient sealing function, which yields a function of
assisting to secure the plug to the borehole after sealing.
[0122] The plug for well drilling may comprise a plurality of
diametrically expandable circular rubber members 5, and by so
doing, it can plug (seal) the space between the plug and the
borehole at a plurality of positions in the axial direction of the
mandrel 1, and the function of assisting to secure the plug to the
borehole can be achieved even more reliably. In cases where the
plug for well drilling comprises a plurality of diametrically
expandable circular rubber members 5, the composition, shape,
structure, position in the axial direction of the mandrel 1, and
the relative positional relationship with the pair of ring-shaped
fixing members 4a and 4b of the plurality of diametrically
expandable circular rubber members 5 may be selected as
desired.
[0123] It is necessary that the sealing function of the
diametrically expandable circular rubber member 5 is not lost even
when it comes in contact with higher pressures and/or the
fracturing fluid used in fracturing under deep subterranean
high-temperature and high-pressure environments. Therefore,
typically, the diametrically expandable circular rubber member 5 is
preferably a rubber material having superior heat resistance, oil
resistance, and water resistance. For example, nitrile rubber,
hydrogenated nitrile rubber, acrylic rubber and the like are often
used. In cases where the diametrically expandable circular rubber
member 5 is formed from the degradable material, examples of the
degradable material that can be used include at least one
degradable rubber selected from the group consisting of urethane
rubber, natural rubber, isoprene rubber, ethylene propylene rubber,
butyl rubber, styrene rubber, acrylic rubber, aliphatic polyester
rubber, chloroprene rubber, polyester-based thermoplastic
elastomer, and polyamide-based thermoplastic elastomer.
Additionally, the diametrically expandable circular rubber member 5
may be a rubber structure formed from a plurality of rubber members
such as a laminated rubber or may be a structure formed by
laminating other members. Furthermore, the diametrically expandable
circular rubber member 5 may be provided with one or more bent
portions such as convex parts, stepped parts, grooves, rough
surfaces (corrugation), or the like at the parts making contact
with the inside wall H of the borehole in order to further ensure
the plugging (sealing) of the space between the plug and the
borehole and the assistance of the fixing the plug to the borehole
at the time of diameter expansion.
3. Ring-Shaped Ratchet Structure Orthogonal to the Axial Direction
of the Mandrel
[0124] The plug for well drilling of the present invention
comprising the mandrel 1 and the outer circumferential
surface-attached members is provided with a ring-shaped ratchet
structure orthogonal to the axial direction of the mandrel 1 on an
inner circumferential surface of at least one of the members and
the outer circumferential surface of the mandrel 1. The ring-shaped
ratchet structure is formed from a plurality of interlocking parts
that allow movement of the members in one direction along the axial
direction of the mandrel 1 and restrict movement in the opposite
direction.
[0125] In other words, in the plug for well drilling of the present
invention comprising the mandrel 1 and the outer circumferential
surface-attached members, the mandrel and the outer circumferential
surface-attached members cooperate to plug a borehole and enable
fracturing. As mining regulations such as those pertaining to
mining at deeper levels have become stricter and more diversified,
the mandrel 1 and the outer circumferential surface-attached
members provided in the plug for well drilling must be able to
withstand the large load placed on the plug so that the plug can
reliably be transported into the well, the borehole can be plugged,
and fracturing can be carried out. Due to the fact that the plug
for well drilling of the present invention has a unique structure
in that it is provided with the ring-shaped ratchet structure, it
can reliably be transported into the well, the borehole can be
plugged, and fracturing can be carried out
[0126] Specifically, when a borehole is plugged and fracturing is
carried out, 8,000 weight pound or greater of high hydraulic
pressure is applied, resulting in a typical load of 50 kN or
greater, in some cases 100 kN or greater, and depending on the
amount of high hydraulic pressure applied, 200 kN or greater or
even 300 kN or greater being applied to the plug for well drilling.
The plug for well drilling of the present invention is provided
with the ring-shaped ratchet structure orthogonal to the axial
direction of the mandrel 1 on an inner circumferential surface of
at least one of the members and the outer circumferential surface
of the mandrel. The ring-shaped ratchet structure is formed from a
plurality of interlocking parts that allow movement of the member
in one direction along the axial direction of the mandrel 1 and
restrict movement in the opposite direction. Particularly, it is
preferable that the necessary number of the interlocking parts be
formed and/or the interlocking depth be further increased (increase
the cross-sectional area of the interlocking parts) so that the
ratchet structure will have a gross tensile load capacity capable
of withstanding a load of 50 kN or greater. The gross tensile load
capacity of the ratchet structure is more preferably made to be 100
kN or greater, and even more preferably 200 kN or greater, and the
upper limit thereof is typically 500 kN.
[Interlocking Parts]
[0127] More specifically, as illustrated in FIGS. 2A, 2B, 2C, and
2D, ring-shaped tooth part r1 orthogonal to the axial direction of
the mandrel 1 is formed on the outer circumferential surface of the
mandrel 1 (in FIGS. 2A, 2B, 2C, and 2D, four teeth are
schematically depicted), and a toothed member T is attached to the
inner circumferential surface of an outer circumferential
surface-attached member (in FIG. 2A, the slip 2a is depicted; in
FIG. 2B, the wedge 3a is depicted, in FIG. 2C, the ring-shaped
fixing member 4a is depicted; in FIG. 2D, the diametrically
expandable circular rubber member 5 is depicted), which results in
ring-shaped tooth part r2 orthogonal to the axial direction of the
mandrel 1 being formed (in FIGS. 2A, 2B, 2C, and 2D, four teeth are
schematically depicted); and the ratchet mechanism interlocking
part R is formed from the tooth part r1 and the tooth part r2 (in
FIGS. 2A, 2B, 2C, and 2D, four of the interlocking parts are
schematically depicted). When a force in the right-left direction
as shown by the arrow in FIGS. 2A, 2B, 2C, and 2D is applied,
movement of the outer circumferential surface-attached member is
restricted due to the presence of the interlocking parts, and the
coupled state of the mandrel 1 and the outer circumferential
surface-attached member is maintained.
[0128] On the other hand, when a force in the left-right direction
as shown by the arrow in FIGS. 2A, 2B, 2C, and 2D is applied, the
ring-shaped tooth part r2 formed on the inner circumferential
surface of the outer circumferential surface-attached member is
enabled to move over the ring-shaped tooth part r1 formed on the
outer circumferential surface of the mandrel 1. Thus, the
interlocking parts are configured so as to allow movement of the
outer circumferential surface-attached member.
[0129] The tensile load capacity of each of the interlocking parts
depends on the magnitude of the shearing stress of the material
with the smaller shearing stress of the materials forming the tooth
part r1 and the tooth part r2 that constitute the interlocking
part, in the temperature of the environment where the interlocking
parts are present. For example, in a case where one of the tooth
parts is formed from PGA as the degradable material, and the other
tooth part is formed from a metal, the shearing stress at
66.degree. C. (equivalent to about 150.degree. F.) of the PGA will
be 56 MPa, which is normally smaller than the shearing stress of a
metal. Accordingly, if, for example, the area of the interlocking
parts of the tooth parts is 400 mm.sup.2, the tensile load capacity
of the interlocking parts is calculated from the shearing stress of
the PGA and is approximately 22 kN.
[0130] The tensile load capacity at a temperature of 66.degree. C.
of the interlocking parts of the ring-shaped ratchet structure can
be adjusted on the basis of the selection of the material forming
the tooth parts and particularly on the basis of the selection of
the type of degradable material, cross-sectional area of the
interlocking parts of the tooth parts, and the like, but the
tensile load capacity is preferably 5 kN or greater, more
preferably 8 kN or greater, and even more preferably 10 kN or
greater. The upper limit of the tensile load capacity at a
temperature of 66.degree. C. of the interlocking parts is typically
100 kN. When making these selections, considering that the plug for
well drilling of the present invention is provided with the mandrel
1 and at least one of the outer circumferential surface-attached
members formed from the degradable material, various parameters
must be taken into account such as the strength of the mandrel 1,
the effect of degradation in the environment the plug for well
drilling is used, and the like in cases where, as discussed later,
the tooth parts are formed on the outer circumferential surface of
the mandrel 1 that is formed from the degradable material.
[Ring-Shaped Ratchet Structure]
[0131] In order to provide the ring-shaped ratchet structure with a
gross tensile load capacity capable of withstanding the load
generated when plugging a borehole and carrying out fracturing, for
example 50 kN at a temperature of 66.degree. C., the ratchet
structure should have the required number of the interlocking parts
in accordance with the tensile load capacity of the interlocking
parts at a temperature of 66.degree. C. For example, in a case
where the tensile load capacity of the interlocking parts at a
temperature of 66.degree. C. is 5 kN or greater, a ratchet
structure having ten of the interlocking parts (also called "10
mountains") should be provided. The number of the tooth parts
(interlocking parts) in the ring-shaped ratchet structure can be
set as appropriate, taking into account the tensile load capacity
of the interlocking parts at a temperature of 66.degree. C. and the
gross tensile load capacity required of the ratchet structure in
borehole environments, and is typically in a range of 2 to 20 and
often in a range of 3 to 15. For example, a ratchet structure
having a gross tensile load capacity of about 130 kN can be
configured by providing five tooth parts (interlocking parts)
formed from PGA (PGA has a shearing stress at a temperature of
66.degree. C. of 56 MPa) that have a width of 4 mm and a depth of
2.4 mm.
[0132] With the ring-shaped ratchet structure orthogonal to the
axial direction of the mandrel in the plug for well drilling of the
present invention, due to the fact that the required number of
interlocking parts described above are provided on the outer
circumferential surface of the mandrel and the inner
circumferential surface of the outer circumferential
surface-attached members, movement in one direction along the axial
direction of the mandrel is allowed and movement in the opposite
direction is restricted.
[0133] The interlocking parts formed on the outer circumferential
surface of the mandrel and the inner circumferential surface of at
least one of the outer circumferential surface-attached members are
formed by directly engraving the tooth parts via machining or the
like into one or both of the outer circumferential surface of the
mandrel and the inner circumferential surface of the outer
circumferential surface-attached member. Additionally, due to the
fact that the metal ring-shaped member or the like provided with
the tooth part for forming the interlocking parts is used, the
ring-shaped ratchet structure may be formed so as to cover one or
both of the outer circumferential surface of the mandrel and the
inner circumferential surface of at least one of the outer
circumferential surface-attached members.
[0134] The ring-shaped ratchet structure may be formed from a
metal, and specifically may be formed from aluminum or iron (carbon
steel, stainless steel, or the like). In many cases, the
ring-shaped ratchet structure can be obtained by engraving the
required number of tooth parts for forming the interlocking parts
by machining the aluminum, iron, or similar metal material and, as
necessary, inserting the toothed member, having its shape adjusted
into a ring shape, on the outer circumferential surface of the
mandrel or, as illustrated in FIGS. 2A, 2B, 2C, and 2D, on the
inner circumferential surface of at least one of the outer
circumferential surface-attached members, and fixing and covering
via a standard method.
[0135] Additionally, the ring-shaped ratchet structure may be
formed from the decomposable resin or similar degradable material.
In many cases, the tooth parts forming the interlocking parts can
be formed by machining the inner circumferential surface of at
least one outer circumferential surface-attached members or the
outer circumferential surface of the mandrel formed from the
degradable material. Furthermore, it is preferable that the
ring-shaped ratchet structure is formed from the degradable
material because, after a given period of time passes following the
completion of blocking treatment via fracturing, due to the
decomposition of the degradable material, the volume of the tooth
parts forming the interlocking parts of the ratchet structure will
decrease and the interlock will release and, as a result of the
decomposition of the ratchet structure, part or all of the plug for
well drilling will decompose.
[Pushing Jig]
[0136] A seal between the plug and the borehole and the fixing of
the plug are necessary in order to carry out well treatment, such
as fracturing or the like where high fluid pressure is applied,
using the plug for well drilling of the present invention which is
provided with the ring-shaped ratchet structure having the
plurality of interlocking parts formed on the outer circumferential
surface of the mandrel 1 and the inner circumferential surface of
at least one of the outer circumferential surface-attached members.
As described above, typically, the diametrically expandable
circular rubber member 5 diametrically shrinks by being compressed
in the axial direction of the mandrel 1 and diametrically expands
in the direction orthogonal to the axial direction of the mandrel
1, and the outward part thereof contacts the inside wall H of the
borehole and, additionally, the inward part in the direction
orthogonal to the axial direction comes into contact with the outer
circumferential surface of the mandrel 1, thereby plugging
(sealing) the space between the plug and the borehole. Moreover, as
a result of force in the axial direction of the mandrel 1 being
applied, the slips 2a and 2b move outward orthogonal to the axial
direction of the mandrel 1 along with the movement of the wedges 3a
and 3b and the outermost circumferential surface of the slips 2a
and 2b contacts the inside wall H of the borehole and, thus, the
plug is secured to the inside wall H of the borehole. That is, with
the plug for well drilling of the present invention, it is required
that the diametrically expandable circular rubber member 5, and the
slips 2a and 2b and the wedges 3a and 3b be movable in the axial
direction of the mandrel 1 and be fixable at predetermined
positions; and also required that the diametrically expandable
circular rubber member 5 and the like have resilience, can
withstand the high fluid pressure applied when carrying out well
treatment such as fracturing, and that the predetermined positions
of the members can be maintained. Accordingly, with the plug for
well drilling of the present invention, the members attached on the
outer circumferential surface orthogonal to the axial direction of
the mandrel 1 preferably include one or a plurality of pushing jigs
having interlocking parts that form a ring-shaped ratchet structure
on an inner circumferential surface thereof.
[0137] As described previously, the movement in the axial direction
of the diametrically expandable circular rubber member 5 and the
slips 2a and 2b and the wedges 3a and 3b is typically carried out
by directly or indirectly contact with the pair of ring-shaped
fixing members 4a and 4b. The plug for well drilling may comprise
at least one of the pushing jigs as one of the rings of the pair of
ring-shaped fixing members 4a and 4b (hereinafter, also referred to
as "ring-shape fixing member 4a ", for convenience). Additionally,
in the plug for well drilling, as a member separate from the
ring-shape fixing member 4a, at least one of the pushing jigs may
be an outer circumferential surface-attached member arranged along
the axial direction of the mandrel 1.
[0138] The shape, structure, and material of the pushing jig having
interlocking parts that form a ring-shaped ratchet structure on the
inner circumferential surface thereof are not particularly limited,
provided that they perform the functions described above and, for
example, the pushing jig may be formed from a metal, inorganic
material, resin (or decomposable resin), composite material (e.g.
reinforcing material-containing resin), or the like. From the
perspectives of the resilience of the diametrically expandable
circular rubber member 5 and the like, the strength to withstand
the fluid pressure caused by fracturing fluid and the like, and
degradability, at least one of the pushing jigs is preferably
formed from a metal and/or degradable material, and may also be
formed from a combination of a metal and/or degradable material and
other materials. In cases where the plug for well drilling
comprises a plurality of pushing jigs having interlocking parts
that form a ring-shaped ratchet structure on the inner
circumferential surface thereof as a member attached on the outer
circumferential surface orthogonal to the axial direction of the
mandrel 1, the plurality of pushing jigs may be attached in a
connected manner or in an isolated manner along the axial direction
of the mandrel 1; and the shape, structure, and material of the
pushing jigs may be substantially the same or may differ.
[0139] FIG. 3 illustrates a schematic partial cross-sectional view
of a specific example of a pushing jig S (hereinafter also referred
to as "pushing jig S (4a)", as it is equivalent to the ring-shape
fixing member 4a). The pushing jig S (4a) illustrated in FIG. 3 is
provided with a ring-shaped pushing jig body S1 (formed integrally
with S11 in the drawing) formed from, for example, the degradable
material (PGA, or the like), and a ratchet structured ring T1
having interlocking parts that form a ring-shaped ratchet structure
on the inner circumferential surface thereof (member equivalent to
the toothed member T in FIGS. 2A, 2B, 2C, and 2D; however, in FIG.
3, five interlocking parts are schematically depicted); and the
inner circumferential surface of the pushing jig body S1 is in
contact with the outer circumferential surface of the ratchet
structured ring T1. In FIG. 3, the contact surface between the
inner circumferential surface of the pushing jig body S1 and the
outer circumferential surface of the ratchet structured ring T1 has
a tapered shape diametrically shrinking toward the right side of
FIG. 3. A pushing jig screw S2 formed from, for example, the
degradable material (PGA, or the like) is screwed onto the trailing
end (located on the left side of FIG. 3; fluid pressure from the
fracturing fluid or the like is applied from the left side) along
the axial direction of the mandrel 1 of the pushing jig body S1.
Shape and size of the pushing jig S are not particularly limited
and can be appropriately determined taking the material and well
environment into consideration, but a range of the thickness is
typically from 2 to 20 mm and is often from 3 to 15 mm, and a range
of the width (length in the axial direction of the mandrel 1) is
typically from 10 to 100 mm and is often from 15 to 50 mm.
[0140] Furthermore, the pushing jig body S1 of the pushing jig S
specifically depicted in FIG. 3 as a preferred aspect is further
provided with a support ring S11, as a separate part, formed from a
metal (e.g. aluminum) and/or the degradable material on an inner
side orthogonal to the axial direction of the mandrel 1, which is
in contact with the outer circumferential surface of the ratchet
structured ring T1. In this case, the inner circumferential surface
of the pushing jig body S1 described previously contacts the outer
circumferential surface of the support ring S11 and, as a result,
the inner circumferential surface of the support ring S11 contacts
the outer circumferential surface of the ratchet structured ring
T1. A thickness of the support ring S11 is not particularly limited
and can be appropriately determined taking the material, shape,
thickness, and length of the pushing jig, the applied fluid
pressure, the well environment, and the like into consideration,
but a range of the smallest thickness to the greatest thickness is
typically from 0.5 to 15 mm and is often from 1 to 10 mm. Note that
the configuration of the pushing jig body S1 and the configuration
and material of the pushing jig S should not be construed to be
limited by this specific example.
[0141] Because the pushing jig S illustrated in FIG. 3 is provided
with the configuration described above, when fluid pressure from
the fracturing fluid or the like is applied from the trailing side
(the left side in FIG. 3) along the axial direction of the mandrel
1, continual, strong force will press the diametrically expandable
circular rubber member 5, and the slips 2a and 2b and the wedges 3a
and 3b toward the leading side (the right side in FIG. 3) along the
axial direction of the mandrel 1 and, as a result, the seal between
the plug and the borehole can be maintained. Additionally, due to
the fact that the pushing jig body S1 of the pushing jig S is
provided with the support ring S11 formed from a metal and/or the
degradable material, the pushing jig S can be provided with high
strength and, particularly, risk of the ratchet structured ring T1
moving in the diametric expansion direction due to high fluid
pressure and leading to the loss of the interlocking of the
interlocking parts in the ratchet structure, can be mitigated. For
example, by providing the support ring S11 formed from aluminum,
the diametric expansion can be suppressed, even when hydraulic
pressure of about 100 kN is applied. That is, at least one of the
pushing jigs S preferably comprises the support ring S11 formed
from a metal and/or the degradable material, wherein an inner
circumferential surface of the support ring S11 contacts the outer
circumferential surface of the ratchet structured ring T1 having
interlocking parts that form a ring-shaped ratchet structure on the
inner circumferential surface thereof.
[Ring-Shaped Plate]
[0142] As shown in the schematic partially enlarged cross-sectional
views FIGS. 4A and 4B which illustrate the vicinity of the ratchet
structure, the plug for well drilling of the present invention
preferably is further provided with a ring-shaped plate P adjacent
to the leading side along the axial direction of the mandrel 1 of
at least one of the pushing jigs S (in FIGS. 4A and 4B, a specific
example of a plug for well drilling provided with one of the
pushing jigs S is depicted). That is, with the plug for well
drilling of the present invention, there is a risk that, due to the
mandrel 1 and the pushing jig S, which are connected via the
ratchet mechanism interlocking part, being pressed upon with great
force by the fluid pressure from the fracturing fluid or the like
toward the leading side (the right side in FIGS. 3, 4A and 4B)
along the axial direction of the mandrel 1, the pushing jig S,
specifically the ratchet mechanism interlocking part T1 may, as
illustrated in FIG. 4B, slip under the inner side of the pushing
jig body S1 due to being pressed strongly toward the right side of
FIG. 4A via the ratchet structure, and protrude on the leading side
along the axial direction of the mandrel 1 while pressing and
expanding the pushing jig body S1. In such a case, the interlocking
of the interlocking parts in the ratchet structure will be lost
and, in extreme cases, the mandrel 1 may detach from the ratchet
structure and jut out from the leading end of the plug for well
drilling. As illustrated in FIG. 4B, the plug for well drilling of
the present invention is provided with the ring-shaped plate P
adjacent to the leading side along the axial direction of the
mandrel 1 of the pushing jig S. Due to this configuration, even if
the ratchet structured ring T1 slips under the inner side of the
pushing jig body S1, the tip of the ratchet structured ring T1 will
contact the ring-shaped plate P and, as a result, movement of the
pushing jig S, specifically the ratchet structured ring T1, can be
suppressed from moving toward the leading side along the axial
direction of the mandrel 1. Accordingly, the interlocking of the
interlocking parts in the ratchet structure will not be lost and
the mandrel 1 will not detach from the ratchet structure.
[0143] The inner diameter of the ring-shaped plate P is
substantially the same as the outer diameter of the mandrel 1 and
the outer diameter of the ring-shaped plate P is less than the
outer diameter of the pushing jig S. If the outer diameter of the
ring-shaped plate P is greater than the outer diameter of the
pushing jig S, the ring-shaped plate P may be subjected to fluid
pressure from fracturing fluid or the like, or may contact the
inside wall H or the like of a borehole when setting the downhole
tool provided with the mandrel 1 in a borehole, which may lead to
damage, deformation, or the like. In cases where the inner diameter
of the ring-shaped plate P is less than the outer diameter of the
pushing jig S, the ring-shaped plate can be integrally provided so
as to be embedded at a position contacting the leading side of the
pushing jig S along the axial direction of the mandrel 1. In cases
where the plug for well drilling is provided with a plurality of
the pushing jigs S as members attached on the outer circumferential
surface orthogonal to the axial direction of the mandrel 1, each of
the plurality of pushing jigs S is preferably provided with a
ring-shaped plate P adjacent to the leading side along the axial
direction. Furthermore, in cases where the plurality of pushing
jigs S is attached in a connected manner along the axial direction
of the mandrel 1, the ring-shaped plates P can be integrally
provided so as to be embedded at positions contacting the trailing
sides along the axial direction of the mandrel 1 of the pushing
jigs S positioned on the leading side along the axial direction of
the mandrel 1. In cases where the ring-shaped plate P is integrally
provided so as to be embedded at a position contacting the leading
side and/or the trailing side along the axial direction of the
mandrel 1 of the pushing jig S, by providing a ring-shaped plate P
that has been split into multiple sections in the circumferential
direction, the ring-shaped plate P can be broken into small pieces
after use and will not hinder the production of petroleum, natural
gas, and the like.
[0144] A length along the axial direction of the mandrel 1 of the
ring-shaped plate P is not particularly limited as long as pressure
of the other outer circumferential surface-attached members
interposed by the pushing jig S is not obstructed, and is typically
in a range from 5 to 50% and often from 10 to 30% of the length in
the axial direction of the mandrel of the pushing jig S. The
ring-shaped plate P may be formed from a material such as a metal
(aluminum, carbon steel, or the like), an inorganic material, a
resin (or a decomposable resin as the degradable material), a
composite material (reinforcing material-containing resin, or the
like), or the like, and is preferably formed from the degradable
material and/or a metal. As operations to remove the ring-shaped
plate P after the completion of well treatment such as fracturing
and the like will be unnecessary or simple, the ring-shaped plate P
more preferably has the degradable material as a main component.
Additionally, from the perspective of the strength of the contact
of the pushing jig S, specifically the ratchet structured ring T1,
preferably the contacting location is formed from a metal and the
other locations are formed from the degradable material. Note that
in cases where the ring-shaped plate P has been split into multiple
sections in the circumferential direction and provided, there is an
advantage in that degradation is accelerated when the ring-shaped
plate P is formed from the degradable material and, moreover, even
if the ring-shaped plate P is not formed from the degradable
material, by forming, for example, the pushing jig S from the
degradable material there is an advantage in that the ring-shaped
plate P will be easily split into small pieces along with the
degradation of the pushing jig S.
[0145] In the plug for well drilling of the present invention, due
to the selection of the structure and material of the pushing jig S
(preferably provided with the support ring S11) and the ring-shaped
plate P previously described, the tensile load capacity of the
interlocking parts in the ratchet structure at a temperature of
66.degree. C. and the gross tensile load capacity of the ratchet
structure in downhole environments can be made greater than in
cases where the pushing jig S and the ring-shaped plate P are not
provided. Additionally, by appropriately designing the value of the
tensile load capacity of the interlocking parts in the ring-shaped
ratchet structure at a temperature of 66.degree. C. and the number
of the interlocking parts, a plug for well drilling having a gross
tensile load capacity as a plug of 100 kN or greater in downhole
environments can be obtained and, furthermore, preferably a plug
for well drilling having a gross tensile load capacity as a plug of
200 kN or greater and more preferably of 300 kN or greater can be
obtained. The upper limit of the gross tensile load capacity of the
plug for well drilling is not particularly limited but, from the
perspective that it is not necessary to exceed the upper limit of
the hydraulic pressure applied when carrying out fracturing or
other well treatment, is typically 1000 kN or less and often 800 kN
or less.
4. Plug for Well Drilling
[0146] The plug for well drilling of the present invention
comprises a mandrel and outer circumferential surface-attached
members, wherein:
[0147] a) at least one of the members or the mandrel is formed from
a degradable material, and
[0148] b) a ring-shaped ratchet structure orthogonal to the axial
direction of the mandrel is provided on an inner circumferential
surface of at least one of the members and the outer
circumferential surface of the mandrel, the ring-shaped ratchet
structure being formed from a plurality of interlocking parts that
allow movement of the member in one direction along the axial
direction of the mandrel and restrict movement in the opposite
direction. The plug for well drilling of the present invention can
further comprise other members normally provided in plugs for well
drilling. For example, in cases where the mandrel is provided with
a hollow part along the axial direction, a ball (may be formed from
a metal, resin, or similar material, or from a degradable material)
can be provided in the hollow part for the purpose of controlling
the flow of a fluid. Additionally, the mandrel and outer
circumferential surface-attached members of the plug for well
drilling, and also the other members described above may be
provided with a member such as, for example, an anti-rotation
member or the like for coupling and releasing the members with/from
each other or other members. The entire plug for well drilling
provided with the mandrel and the outer circumferential
surface-attached members of the present invention may be formed
from the degradable material.
[Plugging of the Borehole]
[0149] As described above, with the plug for well drilling of the
present invention, for example, due to the forces in the axial
direction of the mandrel being applied to the pair of ring-shaped
fixing members, the forces in the axial direction of the mandrel
are transmitted to the diametrically expandable circular rubber
member and, as a result, the diametrically expandable circular
rubber member is compressed in the axial direction of the mandrel
and, along with the reduction of distance of the axial direction
(diametric compression), the diametrically expandable circular
rubber member expands in a direction orthogonal to the axial
direction of the mandrel. The circular rubber member diametrically
expands and the outward part in the direction orthogonal to the
axial direction comes into contact with the inside wall H of the
borehole, and additionally, the inward part in the direction
orthogonal to the axial direction comes into contact with the outer
circumferential surface of the mandrel, and the slips ride up on
the upper surface of the slated surface of the wedges and move
outward orthogonal to the axial direction of the mandrel. The
outermost circumferential surface of the slips orthogonal to the
axial direction of the mandrel contacts an inside wall of the
borehole, thereby plugging (sealing) the space between the plug and
the borehole (borehole plugging). Then, in the state where the
space between the plug and the borehole has been plugged (sealed),
fracturing can be performed. After the well treatment such as
fracturing has been completed, the diametrically expandable
circular rubber member remains inside the borehole in the
diametrically-expanded state, and by working together with the
combination of the slip and wedge, can fix the plug for well
drilling at a predetermined position of the borehole. Due to the
fact that the plug for well drilling of the present invention is
provided with the ring-shaped ratchet structure orthogonal to the
axial direction of the mandrel, even in cases where high pressures,
for example, pressures exceeding 50 kN are applied to the plug for
well drilling during fracturing, relative movement along the axial
direction of the mandrel and the outer circumferential
surface-attached members is restricted and the plugging of the
borehole is maintained. Furthermore, when the aforementioned
plugging (sealing) or the like is performed in a downhole which is
a high-temperature environment where the members of the plug for
well drilling end up degrading in a short time, a treatment method
can be employed in which the seal performance (strength and the
like) can be maintained for a desired time by controlling the
ambient temperature of the plug for well drilling by injecting
fluid from above ground (cooldown injection).
[Degradation of the Plug for Well Drilling]
[0150] When the production of oil, natural gas or the like begins
after the completion of fracturing in the various prescribed
sections, typically, the drilling of the well would be completed,
and the well finished. At this time, with the plug for well
drilling of the present invention, at least one of the members
formed from the degradable material and attached on the outer
circumferential surface orthogonal to the axial direction of the
mandrel and, if desired, additionally the mandrel formed from the
degradable material, can be easily degraded and removed. With the
plug for well drilling of the present invention, by degrading or
reducing the strength of the mandrel or the outer circumferential
surface-attached members formed from the degradable material, in a
short period of time following the completion of fracturing, the
interlocking of the ring-shaped ratchet mechanism interlocking
parts is released, degradation of the ring-shaped ratchet structure
occurs, and the sealing of the borehole by the plug is removed at
an early stage. Therefore, the degradation and removal of the plug
for well drilling can be facilitated and hydrocarbon resources can
be efficiently mined. As a result, with the plug for well drilling
of the present invention, the substantial cost and time
conventionally required to remove, recover, or destroy or
fragmentize, by pulverization, perforation, or another method, many
plugs for well drilling remaining inside a well after the
completion of the well become unnecessary, which makes it possible
to reduce the costs and/or steps of well drilling and completion.
Furthermore, it is preferred that the members of the plug for well
drilling remaining after the well treatment disappear completely by
the time production begins, but even if they do not disappear
completely, as long as they are in a state that their strength
decreases and they can be disintegrated by stimulation such as
water flow in the downhole, the disintegrated members of the plug
for well drilling can be easily recovered by flowback or the like,
and since it does not cause clogging in the downhole or fractures,
it does not hinder production of the petroleum, natural gas, or the
like. Additionally, normally, the higher the downhole temperature,
the shorter the time required for degradation and strength decrease
of the members of the plug for well drilling. Furthermore,
depending on the well, the moisture content in the subterranean
formation is sometimes low, and in this case, degradation of the
downhole tool can be accelerated by allowing the water-based fluid
used during fracturing to remain in the well without recovering it
after fracturing.
II. Method for Manufacturing Plug for Well Drilling
[0151] Provided that a plug for well drilling of the present
invention is a plug for well drilling comprising a mandrel and
outer circumferential surface-attached members, wherein: a) at
least one of the members or the mandrel is formed from a degradable
material, and b) a ring-shaped ratchet structure orthogonal to the
axial direction of the mandrel is provided on an inner
circumferential surface of at least one of the members and the
outer circumferential surface of the mandrel, the ring-shaped
ratchet structure being formed from a plurality of interlocking
parts that allow movement of the member in one direction along the
axial direction of the mandrel and restrict movement in the
opposite direction;
[0152] the manufacturing method thereof is not particularly
limited. For example, the plug for well drilling may be obtained
by: molding each of the members provided in the plug for well
drilling via a known method such as injection molding, extrusion
molding (including solidification-and-extrusion molding),
centrifugal molding, compression molding, or the like; machining
each of the obtained members by cutting, perforating, or the like
as necessary; and then assembling the members by known methods; and
then either directly forming the ring-shaped ratchet structure
orthogonal to the axial direction of the mandrel or covering the
outer circumferential surface of the mandrel and/or the inner
circumferential surface of the outer circumferential
surface-attached members with the ring-shaped ratchet
structure.
[0153] With the plug for well drilling of the present invention, in
cases where the mandrel formed from the degradable material and the
outer circumferential surface-attached members formed from the
degradable material are integrally formed, the mandrel formed from
the degradable material and the members formed from the degradable
material and attached on the outer circumferential surface
orthogonal to the axial direction of the mandrel are preferably
integrally formed via integral molding by injection molding,
extrusion molding (including solidification-and-extrusion molding),
centrifugal molding, or the like, or by cutting or similar
machining.
III. Well Drilling Method
[0154] According to a well drilling method using the plug for well
drilling comprising the mandrel and the outer circumferential
surface-attached members of the present invention, in which a part
or all of the plug for well drilling is degraded after the blocking
of the borehole, when the fracturing in the various prescribed
sections is completed, or the digging of the well is finished and
the well completed, and the production of oil, natural gas, or the
like begins, at least one of the members attached on the outer
circumferential surface orthogonal to the axial direction of the
mandrel and/or, if desired, additionally the mandrel formed from
the degradable material, can be easily degraded and removed, via
biodegrading, hydrolyzing, or degrading chemically by some other
method. Additionally, according to the well drilling method of the
present invention in which the ring-shaped ratchet structure is
degraded as a result of the degradation or strength decrease of the
mandrel or the outer circumferential surface-attached members
formed from the degradable material, the degradation and removal of
the plug for well drilling can be carried out even easier and
hydrocarbon resources can be efficiently mined. As a result, with
the well drilling method of the present invention, the substantial
cost and time conventionally required to remove, recover, or
destroy or fragmentize, by pulverization, perforation, or another
method, many plug for well drilling remaining inside wells after
the completion of the wells become unnecessary, which makes it
possible to reduce the cost or steps of well drilling.
INDUSTRIAL APPLICABILITY
[0155] The present invention provides a plug for well drilling
comprising a mandrel and members attached on an outer
circumferential surface orthogonal to an axial direction of the
mandrel, wherein:
[0156] a) at least one of the members or the mandrel is formed from
a degradable material, and
[0157] b) a ring-shaped ratchet structure orthogonal to the axial
direction of the mandrel is provided on an inner circumferential
surface of at least one of the members and the outer
circumferential surface of the mandrel, the ring-shaped ratchet
structure being formed from a plurality of interlocking parts that
allow movement of the member in one direction along the axial
direction of the mandrel and restrict movement in the opposite
direction.
[0158] In light of mining regulations such as those pertaining to
mining at deeper levels becoming stricter and more diversified, and
as a result of the configuration described above, a plug for well
drilling is provided by which advantageous effects are provided in
that well drilling costs and steps can be reduced by withstanding
the large load placed on the plug so as to reliably be transported
into the well, plug the borehole, and carry out fracturing; and
facilitating the removal of the plug and the securing of the flow
path. Therefore there is high industrial applicability.
[0159] Additionally, the present invention provides a well drilling
method using the plug for well drilling, the method comprising
degrading a part or all of the plug for well drilling after
blocking a borehole.
[0160] As mining regulations such as those pertaining to mining at
deeper levels have become stricter and more diversified, and as a
result of the configuration described above, a well drilling method
is provided by which advantageous effects are provided in that well
drilling costs and steps can be reduced by withstanding the large
load placed on the plug so as to reliably be transported into the
well, plug the borehole, and carry out fracturing; and facilitating
the removal of the plug and the securing of the flow path.
Therefore there is high industrial applicability.
REFERENCE SIGNS LIST
[0161] 1: Mandrel [0162] 2a and 2b: Slips [0163] 3a and 3b: Wedges
[0164] 4a and 4b: Ring-shaped fixing members [0165] 5:
Diametrically expandable circular rubber member [0166] H: Inside
wall of the borehole [0167] R: Ratchet mechanism interlocking part
[0168] T: Toothed member [0169] r1 and r2: Teeth [0170] S(4a):
Pushing jig (ring-shaped fixing member) [0171] S1: Pushing jig body
[0172] S11: Support ring [0173] S2: Pushing jig screw [0174] T1:
Ratchet structured ring [0175] P: Ring-shaped plate
* * * * *