DOWNHOLE PLUG WITH PROTECTIVE MEMBER

Abstract

A plug excellent in pressure resistance is provided. A downhole plug (20) includes a mandrel (1), a center element (2), at least one lip (3), and a pressure transmission means. When the center element (2) is deformed by applying a pressure of 50 MPa to the downhole plug (20) in the axial direction, a ratio (b/a) of an axial length (b) of a part where the mandrel (1) and the center element (2) are in contact with each other, to a maximum axial length (a) of the center element (2) in a cross section along the axial direction is less than 0.5.

Description

TECHNICAL FIELD

The present invention relates to a plug and, in particular, to a downhole plug used to plug a wellbore.

BACKGROUND ART

Various tools called downhole tools have been developed to recover shale oil or shale gas. As one type of these downhole tools, downhole plugs such as bridge plugs and frac plugs are known (e.g., Patent Document 1). One of the functions of the downhole plug is to plug the wellbore during hydraulic fracturing.

As a method of hydraulic fracturing, for example, a downhole plug is installed to a predetermined position of a wellbore, and the downhole plug is operated to be set to a well wall while an elastic member included in the downhole plug is deformed to plug the wellbore. Thereafter, a method is employed in which water is pumped from the ground into the wellbore, and hydraulic pressure is applied to a part closer to the ground than the downhole plug set to the well wall, thereby causing a crack in the subterranean formation through a perforation formed separately using an explosive or the like.

Therefore, downhole plugs are required to withstand high hydraulic pressure from the ground and keep the wellbore plugged while being set to the well wall. On the other hand, Patent Document 2 discloses a downhole tool using a polymer composite material containing fibers as a material in order to improve hydraulic pressure resistance.

CITATION LIST

Patent Document

• Patent Document 1: US 2017/234,103
• Patent Document 2: US 2010/288,488

SUMMARY OF INVENTION

Technical Problem

However, when high hydraulic pressure is applied after the elastic member of the downhole plug is deformed to plug the wellbore, there is a problem that other components constituting the downhole plug are damaged due to unintended deformation of the elastic member, and that the pressure resistance of the downhole plug is reduced.

Therefore, an object of the present invention is to provide a downhole plug having excellent pressure resistance.

Solution to Problem

In order to solve the above problems, the present invention provides a plug for plugging a wellbore, including: a cylindrical body; an annular elastic member configured to surround an outer peripheral surface of the cylindrical body and to be deformed under pressure; at least one protective member configured to surround the outer peripheral surface of the cylindrical body and to prevent at least a part of the elastic member from coming into contact with the cylindrical body; and a pair of pressure transmission means configured to sandwich the elastic member in an axial direction of the plug and to apply pressure to the elastic member in the axial direction to compress the elastic member.

When the elastic member is deformed by applying a pressure of 50 MPa to the plug in the axial direction, a ratio (b/a) of an axial length (b) of a part of the elastic member where the cylindrical body and the elastic member are in contact with each other, to a maximum axial length (a) of the elastic member in a cross section along the axial direction is less than 0.5.

Advantageous Effects of Invention

According to the present invention, a downhole plug excellent in pressure resistance can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a cross-section of a downhole plug at a predetermined position in a wellbore, according to Embodiment 1 of the present invention.

FIG. 2 is a schematic view of a cross section of a downhole plug when subjected to hydraulic pressure at a wellbore, according to Embodiment 1 of the present invention.

FIG. 3 is an enlarged schematic view of a part of a cross section of the downhole plug when subjected to hydraulic pressure at a wellbore, according to Embodiment 1 of the present invention.

FIG. 4 is a schematic view of a cross section of a downhole plug at a predetermined position in a wellbore, according to Embodiment 2 of the present invention.

FIG. 5 is a schematic view of a cross section of the downhole plug when subjected to hydraulic pressure at the wellbore, according to Embodiment 2 of the present invention.

FIG. 6 is an enlarged schematic view of a part of a cross section of a downhole plug at a predetermined position in a wellbore, according to Embodiment 3 of the present invention.

FIG. 7 is an enlarged schematic view of a part of a cross section of the downhole plug when subjected to hydraulic pressure at the wellbore, according to Embodiment 3 of the present invention.

FIG. 8 is an enlarged schematic view of a part of a cross section of a downhole plug at a predetermined position in a wellbore, according to Embodiment 4 of the present invention.

FIG. 9 is an enlarged schematic view of a part of a cross section of the downhole plug when subjected to hydraulic pressure at a wellbore, according to Embodiment 4 of the present invention.

FIG. 10 is a schematic view illustrating a part of a cross section of a lip, according to Embodiment 5 of the present invention.

DESCRIPTION OF EMBODIMENTS

Embodiment 1

A downhole plug (plug) according to Embodiment 1 of the present invention is a plug for plugging a wellbore. The downhole plug according to Embodiment 1 can have a first form in which the downhole plug is installed from the ground to a predetermined position in a wellbore, a second form in which the downhole plug is actuated and set to the wellbore, and a third form in which the downhole plug is subjected to hydraulic pressure. The first form corresponds to FIG. 1, and the third form corresponds to FIG. 2. The second form is not illustrated. FIG. 1 is a schematic view of a cross section of a downhole plug in a first form in a predetermined position in a wellbore, according to the present Embodiment 1. FIG. 2 is a schematic view of a cross section of a downhole plug in a third form under hydraulic pressure, according to the present Embodiment 1. In FIG. 1 and FIG. 2, only one of the cross sections of the downhole plug that are symmetrical with respect to the axis (the dashed line in the drawings) is illustrated.

Hereinafter, the downhole plug according to the present Embodiment 1 will be described in detail with reference to FIGS. 1 and 2.

1. First Form of Downhole Plug

A first form of the downhole plug will be described with reference to FIG. 1. FIG. 1 illustrates a situation where there is a gap between a well wall and the downhole plug in the well.

As illustrated in FIG. 1, the downhole plug 20 includes a mandrel (cylindrical body) 1, a center element (elastic member) 2, a lip (protective member) 3, sockets (pressure transmission means) 4a and 4b, cones (pressure transmission means) 5a and 5b, and slips (pressure transmission means) 6a and 6b. The downhole plug 20 further includes equalizer rings (pressure transmission means) 7a and 7b, a load ring (pressure transmission means) 8, and a bottom 9. The downhole plug 20 has a cylindrical shape as a whole. In the following description, the term “axis” or “axial direction” simply refers to the axis or axial direction of the downhole plug 20 having a cylindrical shape as a whole.

Hereinafter, each member will be described in detail.

Mandrel

The mandrel 1 is a member for securing the strength of the downhole plug 20, and is a hollow member that is disposed along the axis at the center of the downhole plug 20. Various members for constituting the downhole plug 20 as a whole are deployed on the outer peripheral surface of the mandrel 1.

Examples of the material for forming the mandrel 1 include metal materials such as aluminum, steel, and stainless steel, fibers, wood, composite materials, and resins. The mandrel 1 may be formed of, for example, a composite material containing a reinforcing material such as carbon fiber, specifically, for example, a composite material containing a polymer such as an epoxy resin and a phenol resin.

In particular, the mandrel 1 is preferably formed of a degradable resin or a degradable metal. This facilitates removal of the downhole plug 20 after performing well treatment using the downhole plug 20.

In the present specification, the term “degradable resin or degradable metal” means a resin or metal which can be degraded or embrittled to be easily disintegrated, by biodegradation or hydrolysis, dissolution in water or hydrocarbons in a wellbore, or any chemical method.

Examples of the degradable resin include aliphatic polyesters based on hydroxycarboxylic acid such as polylactic acid (PLA) and polyglycolic acid (PGA), lactone-based aliphatic polyesters such as poly-caprolactone (PCL), diol-dicarboxylic acid-based aliphatic polyesters such as polyethylene succinate and polybutylene succinate, copolymers thereof, for example, such as glycolic acid-lactic acid copolymers, mixtures thereof, and further aliphatic polyesters in combination with aromatic components such as polyethylene adipate/terephthalate.

Examples of the water-soluble resin include polyvinyl alcohol, polyvinyl butyral, polyvinyl formal, polyacrylamide (which may be N, N-substituted), polyacrylic acid, and polymethacrylic acid, and copolymers of monomers forming these resins, for example, such as ethylene-vinyl alcohol copolymer (EVOH) and acrylamide-acrylic acid-methacrylic acid interpolymer.

Examples of the degradable metal include, for example, metal alloys containing magnesium, aluminum, and calcium as main components.

Center Element

The center element 2 is an annular rubber member for filling the gap between the mandrel 1 and the well wall in the downhole plug 20 to plug the wellbore, and is deformed under pressure. The center element 2 is deployed around the outer peripheral surface of the mandrel 1.

The thickness, elasticity, inner diameter, outer diameter, or width in the axial direction, or the like of the center element 2 may be appropriately determined according to the size of the mandrel 1, the pressure applied to the downhole plug 20, or the like.

The center element 2 is preferably formed of a material that does not lose the function of plugging the wellbore even under a high-temperature and high-pressure environment such as 100° C. and 30 MPa. Examples of preferable materials for forming the center element 2 include nitrile rubber, hydrogenated nitrile rubber, acrylic rubber, and fluororubber, or the like. Moreover, a degradable rubber such as aliphatic polyester rubber, polyurethane rubber, natural rubber, polyisoprene, acrylic rubber, aliphatic polyester rubber, polyester-based thermoplastic elastomer, and polyamide-based thermoplastic elastomer can be used.

Lip

The lip 3 is a member that prevents at least a part of the center element 2 from contacting the mandrel 1 to prevent damage to the mandrel 1 when the downhole plug 20 is used to plug a wellbore. In the present Embodiment 1, since the lip 3 is inserted between the mandrel 1 and the center element 2, at least a part of the center element 2 is prevented from contacting the mandrel 1. The lip 3 may be at least partially inserted between the mandrel 1 and the center element 2 when pressure is applied to the downhole plug 20.

As will be described in detail later, when the downhole plug 20 receives hydraulic pressure and the center element 2 is compressed, a force is applied to the mandrel 1 from the center element 2. In the third form after the center element 2 is deformed under the hydraulic pressure, since the part of the center element 2 in contact with the mandrel 1 is reduced by the lip 3, it is possible to reduce the force received by the mandrel 1 from the center element 2. This can prevent damage to the mandrel 1. Since the damage of the mandrel 1 is prevented by the lip 3, a downhole plug having excellent pressure resistance can be provided.

As described above, the mandrel 1 is a member for ensuring the strength of the downhole plug 20. However, depending on the material or thickness of the mandrel 1, the strength of the mandrel 1 may not be sufficient for the force received from the center element 2 in some cases. The material forming the mandrel 1 is as described in the section of [Mandrel], but in general, a resin material has lower strength than a metal material, and among resin materials, a non-composite material containing no reinforcing material has lower strength. Thus, even when the strength of the mandrel 1 is not sufficient, the pressure resistance of the downhole plug 20 is ensured because the downhole plug 20 includes the lip 3.

The lip 3 according to the present Embodiment 1 is an annular member deployed around the outer peripheral surface of the mandrel 1, and is integrated with a cone 5a described later. That is, the lip 3 is provided as a part of the cone 5a. Specifically, the inner peripheral edge of the cone 5a in contact with the mandrel 1 protrudes toward the center element 2, and the entire inner peripheral surface of the cone 5a including the protruding part is in contact with the mandrel 1. This protruding part corresponds to the lip 3. The inner peripheral edge of the cone 5a in contact with the mandrel 1 protrudes toward the center element 2 while being in contact with the mandrel 1, thereby preventing a part of the center element 2 from contacting the mandrel 1.

The length of the lip 3 is designed based on the third form described later.

The thickness of the lip 3 is not particularly limited as long as it does not prevent the lip 3 from moving between the center element 2 and the mandrel 1 when the cone 5a moves toward the center element 2 under pressure. In addition, the thickness may be constant, or the thickness may change so as to decrease toward the tip of the lip 3 which is the protruding portion. Alternatively, the lip 3 may be designed such that the thickness on the side close to the cone 5a is constant and the thickness on the side close to the tip decreases toward the tip.

The material of the lip 3 is not particularly limited, and the material described as the material for forming the mandrel 1 can be used. Among them, for the same reason as the mandrel 1, it is preferable that the lip 3 is formed of a degradable resin or a degradable metal.

Pressure Transmission Means

The pressure transmission elements constituting the pressure transmission means include sockets 4a and 4b, cones 5a and 5b, slips 6a and 6b, equalizer rings 7a and 7b, and a load ring 8.

Socket

The sockets 4a and 4b are arbitrary members that constitute pressure transmission means, and they retain the deformation of the center element 2 when the center element 2 is deformed under the axial pressure of the downhole plug 20 in the wellbore.

The sockets 4a and 4b are annular members surrounding the outer peripheral surface of the mandrel 1. The sockets 4a and 4b are mounted adjacent to one end of the center element 2, and the sockets 4a and 4b contact each other. The socket 4b is mounted in contact with the mandrel 1 but the socket 4a is not mounted in contact with the mandrel 1. That is, the sockets 4a and 4b have the same outer diameter, while the socket 4a has a larger inner diameter. The socket 4a is movably deployed on the socket 4b.

The material of the socket is not particularly limited, and the materials described above as the material for forming the mandrel 1 can be used. Among them, for the same reason as the mandrel 1, it is preferable that the socket is formed of a degradable resin or a degradable metal. It is preferable that the socket 4a is made of a material that can be deformed under pressure so as to expand its diameter.

Cone

The cones 5a and 5b are members constituting a pressure transmission means, and transmit pressure directly and indirectly to the center element 2, respectively.

Cones 5a and 5b are mounted to surround the outer peripheral surface of the mandrel 1. The cone 5a is mounted adjacent the end of the center element 2 opposite to the end that the sockets 4a and 4b contact. On the other hand, the cone 5b is mounted adjacent to the sockets 4a and 4b on the outer peripheral surface of the mandrel 1 on the side opposite to the center element 2. That is, the sockets 4a and 4b are interposed between the cone 5b and the center element 2.

The cone 5a is a hollow conical member. In the present specification, the term “conical” means a cone, a truncated cone, or a combined shape of a cylinder therewith. The hollow shape is a shape along the outer peripheral surface of the mandrel, and is usually a cylindrical shape.

As described above, in the present Embodiment, the lip 3 is provided integrally with the cone 5a. Accordingly, the cone 5a has a shape in which the hollow conical solid having an outer diameter increasing from the end of the mandrel 1 toward the center element 2 is joined on the side of the center element 2 by a hollow cylindrical solid having a diameter smaller than the maximum diameter of the above conical solid.

On the other hand, the cone 5b is a hollow conical member and has a shape in which the outer diameter increases from the end of the mandrel 1 toward the center element 2.

The material of the cone is not particularly limited, and the materials described above as the material for forming the mandrel 1 can be used. Among them, for the same reason as the mandrel 1, it is preferable that the cone is formed of a degradable resin or a degradable metal.

(Slip)

The slips 6a and 6b are members constituting a pressure transmission means, and indirectly transmit pressure to the center element 2. The slips 6a and 6b are deployed around the outer peripheral surface of the mandrel 1 and are in contact with the cones 5a and 5b, respectively.

Each of the slips 6a and 6b is an annular member whose inner diameter decreases from the center element 2 side toward the end of the mandrel 1.

The material of the slip is not particularly limited, and the materials described above as the material for forming the mandrel 1 can be used. In particular, for the same reason as the mandrel 1, it is preferably formed of a degradable resin or a degradable metal.

Equalizer Ring

The equalizer rings 7a and 7b are arbitrary members constituting the pressure transmission means, and have a function of making the diameter expansion of the slips 6a and 6b uniform when shifting from the first form to the second form and from the second form to the third form, which will be described later, and also indirectly transmit pressure to the center element 2. Equalizer rings 7a and 7b are mounted around the outer peripheral surface of the mandrel 1 and are in contact with slips 6a and 6b, respectively.

The material of the equalizer ring is not particularly limited, and the material described as the material for forming the mandrel 1 can be used. Among them, for the same reason as the mandrel 1, it is preferable that the equalizer ring is formed of a degradable resin or a degradable metal.

Load Ring

The load ring 8 is a member constituting a pressure transmission means, and directly receives a pressure applied from the ground surface side of a wellbore and transmits the pressure to an adjacent member, thereby indirectly transmitting the pressure to the center element 2. The load ring 8 is deployed around the outer peripheral surface of the mandrel 1, and is in contact with the equalizer ring 7a.

The material of the load ring is not particularly limited, and the material described as the material for forming the mandrel 1 can be used. Among them, for the same reason as the mandrel 1, it is preferable that the load ring is formed of a degradable resin or a degradable metal.

In the present specification, the term “a pair of pressure transmission means” does not mean that the two pressure transmission means provided to sandwich the center element 2 have exactly the same configuration. That is, as long as they function as the pressure transmission means, the configuration included in each pressure transmission means may be different. Further, since the hydraulic pressure is normally received from only one side of the plug, the pressure transmission means on one side functions to transmit the pressure to the center element 2, and the pressure transmission means on the other side functions to receive the center element 2. As used herein, the term “pressure transmission means” will be used to include such a function.

Other Members

In addition to the above-described members, the downhole plug 20 may include a bottom 9 or the like as illustrated in FIG. 1. The bottom 9 is attached so as to surround the outer peripheral surface of the mandrel 1, but the arrangement of the bottom 9 may be appropriately determined as necessary. In addition, the material of the bottom 9 is not particularly limited as long as it can exhibit the respective functions, and the material described as the material for forming the mandrel 1 can be used. Among them, for the same reason as the mandrel 1, it is preferable that the bottom 9 is formed of a degradable resin or a degradable metal.

2. Second Form of Downhole Plug

The second form of the downhole plug is one in which the downhole plug 20 is activated and set to the well.

After the downhole plug 20 is disposed at a predetermined position in the well, the downhole plug 20 is activated to expand the diameter of the center element 2 and bring it into contact with the well wall, thereby plugging the gap between the mandrel 1 and the well wall and expanding the diameter of the slips 6a and 6b. The downhole plug 20 is set in a predetermined position within the well by contacting the well wall. Hereinafter, the change from the first form to the second form will be described with reference to FIG. 1 illustrating the first form.

When the downhole plug 20 is activated in the well, at least one of a pair of pressure transmission means moves in the axial direction of the mandrel 1 toward the center element 2, so that the center element 2 is compressed in the axial direction, thereby increasing the outer diameter of the center element 2. As a result, the outer peripheral surface of the center element 2 is brought into contact with the well wall 12 to plug the gap between the mandrel 1 and the well wall. This sets the downhole plug 20 to the well.

In particular, when the downhole plug 20 is activated, the slips 6a and 6b slide on the inclined surfaces of the cones 5a and 5b, respectively, and the slips 6a and 6b contact the well wall 12. At the same time, pressure is transmitted to the center element 2 indirectly from the cone 5b and directly from the cone 5a and the sockets 4a and 5b, so that the center element 2 is compressed and deformed.

When compressed, the center element 2 expands in a direction perpendicular to the axial direction of the mandrel 1 and contacts the well wall 12, thereby setting the downhole plug 20 to the well. Additionally, when the center element 2 is deformed under pressure and the center element 2 is pressed against the sockets 4a and 4b, the socket 4a is expanded in the diameter and slides on the inclined surface of the socket 4b and contacts the well wall 12. Thus, the downhole plug 20 changes into the second form.

3. Third Form of Downhole Plug

The third form of the downhole plug is the form when the downhole plug 20 is under hydraulic pressure. Hereinafter, the third form of the downhole plug 20 will be described with reference to FIG. 2.

After the downhole plug 20 is set at a predetermined position in the well, a frac ball 10 is inserted into the well and seated on a ball seat 13 of the downhole plug 20 to plug the hollow part of the mandrel 1, which completes the plugging of the wellbore. Thereafter, water is injected from the mine mouth to apply hydraulic pressure from the mine mouth side toward the bottom side of the wellbore. The downhole plug 20 changes into a third form in which the mandrel 1 is moved toward the bottom side of the wellbore under pressure from the mine mouth side toward the bottom side of the wellbore.

When hydraulic pressure is applied to the downhole plug 20 of the second form from the mine mouth side, the mandrel 1 moves according to the hydraulic pressure. At this time, one of a pair of the pressure transmission means on the mine mouth side moves toward the bottom side of the wellbore due to the hydraulic pressure from the mine mouth side, thereby further compressing the center element 2 in some cases. Thus, the downhole plug 20 changes into the third form.

Further, in the third form, the cone 5a and the socket 4 sandwiching the center element are located closer to each other than in the first form. That is, in the third form, a part where the mandrel 1 and the center element 2 are in contact with each other is smaller than that in the first form. The part where the center element 2 and the mandrel 1 are in contact with each other will be described later.

4. Contact Part Between Center Element and Mandrel

As described above, the center element 2 is in contact with the mandrel 1, and the contact is prevented in part by the lip 3. In the third form, pressure is applied in the axial direction of the downhole plug 20, and the distance between the cone 5a having the lip 3 and the sockets 4a and 4b is reduced, whereby the center element 2 is compressed. Thus, in the third form, the region where the center element 2 and the mandrel 1 are in contact with each other is different from that in the first form above. Specifically describing the contact part between the center element 2 and the mandrel 1 in the third form, in the third form of the downhole plug 20, the ratio (b/a) of the total length (b) of the part where the mandrel 1 is in contact with the center element 2 to the maximum axial length (a) of the center element 2 when a pressure of 50 MPa is applied to the downhole plug 20 in the axial direction is less than 0.5.

Here, “when a pressure of 50 MPa is applied in the axial direction” means that a pressure is applied from one side to the other side in the axial direction of the downhole plug 20. This is based on the assumption that pressure is applied from the mine mouth side of the downhole plug 20 toward the bottom side of the well when hydraulic pressure is applied from the mine mouth.

Here, the “maximum axial length (a) of the center element 2” is a width of the center element 2 in the axial direction in a cross section along the axial direction of the downhole plug 20 as illustrated in FIG. 2. Namely, it is a length in the axial direction of the downhole plug 20 in the orthogonal projection of the center element 2 onto the mandrel 1 or the well wall 12. A specific example will be described later in Embodiment 4, but when there are a plurality of center elements 2, the sum of the axial length of each element is denoted by (a).

As illustrated in FIG. 2, the “length (b) of the axial part where the mandrel 1 and the center element 2 are in contact with each other” is the axial length of the part where the mandrel 1 and the center element 2 are in contact with each other in the cross section along the axial direction of the downhole plug 20. When the length of the part of the outer periphery of the mandrel 1 in contact with the center element 2 is not constant, the average value is used as (b). Although a specific example will be described later in Embodiment 3, when there are a plurality of parts where the mandrel 1 and the center element 2 are in contact with each other in a certain cross section, the sum of the axial lengths of the plurality of portions is defined as (b).

The ratio of (b) to (a) is less than 0.5 as described above, but the ratio may be preferably as small as possible, for example, preferably less than 0.25, more preferably less than 0.1, and most preferably 0. A ratio of (b) to (a) of 0 means that (b)=0.

As the ratio of (b) to (a) is smaller, that is, as the part where the mandrel 1 and the center element 2 are in contact with each other in the third form is smaller, the force applied from the center element 2 to the mandrel 1, that is, the force for fastening the mandrel 1 is smaller, so that the breakage of the mandrel 1 can be more effectively prevented. In addition, when the center element 2 is compressed and deformed, it is presumed that the deformation is largest in the vicinity of the center part in the axial direction of the center element 2 and the force applied to the mandrel 1 is strongest. When the ratio (b/a) is less than 0.5, the lip 3 is present at the center part of the axial length of the center element 2. Therefore, it is possible to prevent the center element 2 and the mandrel 1 from coming into contact with each other in a part where the force applied to the mandrel 1 is the largest, and it is possible to more reliably prevent damage to the mandrel 1.

The pressure applied to the downhole plug in the well during hydraulic fracturing is usually about 30 to 70 MPa. Therefore, if the ratio (b/a) when a pressure of 50 MPa is applied to the downhole plug 20 is less than 0.5, the ratio (b/a) can be less than 0.5 even in an actual use environment. Therefore, the excellent pressure resistance of the downhole plug 20 according to the present Embodiment 1 is exhibited in an actual use environment.

Modified Example

A modified example of the present Embodiment 1 will be described. In the downhole plug 20 described above, also in the third form, the center element 2 and the mandrel 1 are in contact with each other with a predetermined length (that is, b>0). However, by increasing the axial length of the lip 3, in the third form, the contact of the center element 2 with the mandrel 1 may be completely blocked by the lip 3, that is, (b)=0. FIG. 3 illustrates a case where (b)=0. FIG. 3 is an enlarged schematic view of a part of a cross section of a downhole plug 20 in a third form in which hydraulic pressure is received in a wellbore, according to a modified example of Embodiment 1. As illustrated in FIG. 3, in the third form of the downhole plug 20 according to the modified example, the tip of the lip 3 extending from the cone 5a reaches the socket 4 and is in contact with the socket 4. As a result, the lip 3 sinks into the entire inner peripheral surface of the center element 2 that is in contact with the mandrel 1 in the first form. Therefore, the contact of the center element 2 with the mandrel 1 is completely blocked by the lip 3, and there is no shaft part where the mandrel 1 is in contact with the center element 2 (that is, (b)=0). As a result, the force applied from the center element 2 to the mandrel 1 is further reduced, and damage to the mandrel 1 can be more reliably prevented.

Further, when (b)=0, since the tip of the lip 3 reaches the socket 4, the lip 3 also functions as a rod. Therefore, excessive deformation of the center element 2 can be prevented, and the pressure resistance in the axial direction is improved.

In the subsequent embodiments, members having the same functions as those described in the section of [Embodiment 1] are denoted by the same reference numerals, and description thereof will not be repeated.

Embodiment 2

A downhole plug according to Embodiment 2 of the present invention will be described with reference to FIGS. 4 and 5. The first form of the downhole plug corresponds to FIG. 4, and the third form corresponds to FIG. 5. FIG. 4 is a schematic view of the cross section of a downhole plug at a predetermined position in a well, according to the present Embodiment 2. FIG. 5 is a schematic view of a cross section of a downhole plug when subjected to hydraulic pressure at a wellbore, according to Embodiment 2 of the present invention. In FIG. 4 and FIG. 5, only one of the cross sections of the downhole plug that are symmetrical with respect to the axis (the dashed line in the drawings) is illustrated.

In the downhole plug 21 according to Embodiment 2, as illustrated in FIGS. 4 and 5, the lip 3 is not integral with the cone 5a, but is an annular member that exists separately from the cone 5a. Although the lip 3 and the cone 5a are separate bodies, they are provided on the outer peripheral surface of the mandrel 1 so as to be in contact with each other. Specifically, the lip 3 is located on the side of the cone 5a that is in contact with the center element 2, and is in contact with the inner peripheral edge of the cone 5a. The inner diameter of the lip 3a is the same as the inner diameter of the cone 5a, and the outer diameter of the lip 3 is smaller than the outer diameter of the cone 5a. Therefore, also in Embodiment 2, similarly to Embodiment 1, on the side of the cone 5a of the center element 2, the contact between the center element 2 and the mandrel 1 is prevented by the lip 3. Since the lip 3 is in contact with the cone 5a, when the cone 5a moves toward the center element 2, the lip 3 is also pushed and moved.

The lip 3 and the cone 5a may be in contact with each other, and may not be fixed to each other or may be fixed to each other by another means.

Although the boundary between the lip 3 and the cone 5a is not particularly limited, for example, as illustrated in FIGS. 4 and 5, in the cross section of the downhole plug 21, the boundary may be a perpendicular line drawn from the end of the center element 2 in contact with the cone 5a to the mandrel 1.

Embodiment 3

A downhole plug according to Embodiment 3 of the present invention will be described with reference to FIGS. 6 and 7. The first form of the downhole plug corresponds to FIG. 6, and the third form corresponds to FIG. 7.

FIG. 6 is an enlarged schematic view of a part of a cross section of the downhole plug at a predetermined position in a well, according to the present Embodiment 3. In the description with reference to FIGS. 6 and 7, since there is no need to distinguish between the socket 4a and the socket 4b, the sockets 4a and 4b are collectively illustrated as the socket 4, and hereinafter also referred to as the socket 4.

The position of the lip 3 is not particularly limited as long as (b/a) is less than 0.5 when a pressure of 50 MPa is applied to the downhole plug.

Specifically, as illustrated in FIG. 6(a), the lip 3 may be integrated with the socket 4 instead of being integrated with the cone 5a.

Alternatively, the lip 3 may be divided into two portions as illustrated in FIGS. 6 (b) and 6(b′) and may be formed integrally with the socket 4 and with the cone 5a respectively. With regard to the two separate lips 3, the lip 3 integral with the socket 4 may be longer, or the lip 3 integral with the cone 5a may be longer, or both may have the same length.

As illustrated in FIG. 6(c), the lip 3 may be independent of both the socket 4 and the cone 5a and may not be in contact with either the socket 4 or the cone 5a. Here, the number of the lips 3 may be one or more.

Further, the lip 3 may be a combination of any of the forms described above.

FIG. 7 is an enlarged schematic view of a part of a cross section of the downhole plug when hydraulic pressure is applied to a wellbore, according to Embodiment 3 of the present invention.

As described above, the position of the lip 3 is not limited as long as the ratio of (b) to (a) illustrated in FIG. 7 is less than 0.5 when a pressure of 50 MPa is applied to the downhole plug. Although each of FIG. 7 illustrates a form in which (b/a) is larger than 0, the case of (b)=0 illustrated in FIG. 3 is preferable.

As illustrated in FIG. 7(c), when there are a plurality of parts where the mandrel 1 and the center element 2 are in contact with each other, the sum of the axial lengths (b1) and (b2) of the plurality of parts is defined as (b).

In the case where at least one of the lips 3 described in the section of [Embodiment 3] is integrated with the socket 4 or the cone 5a, as described in the section of [Embodiment 2], the lip 3 may be in contact with the socket 4 or the cone 5a while being independent thereof.

Embodiment 4

A downhole plug according to Embodiment 4 of the present invention will be described with reference to FIGS. 8 and 9. The first form of the downhole plug corresponds to FIG. 8, and the third form corresponds to FIG. 9.

The downhole plug according to the present invention may have a form in which the center element 2 is divided into a plurality of portions and arranged along the axis of the mandrel 1 as illustrated in FIG. 8(a) as long as (b/a) is less than 0.5 when a pressure of 50 MPa is applied to the downhole plug. In addition, (a) is the sum of the maximum lengths of the plurality of center elements.

Here, the thickness, elasticity, inner diameter, outer diameter, or width in the axial direction of the plurality of center elements may be the same or different. However, from the viewpoint of preventing breakage of the mandrel, in each of the plurality of center elements, the length of the part where the mandrel and the center element are in contact with each other is preferably smaller than the maximum length of each center element.

As illustrated in FIG. 8(b), a partition 11 may be provided between the plurality of center elements. The partition 11 is not particularly limited as long as it is an annular member surrounding the mandrel 1, and may be a part or all of the above-described pressure transmission means. The material of the partition 11 is not particularly limited, but is preferably formed of a degradable resin or a degradable metal from the viewpoint of facilitating removal of the downhole plug 20 after performing well treatment.

FIG. 9 is an enlarged schematic view of a part of a cross section of a downhole plug when hydraulic pressure is applied to a wellbore, according to Embodiment 4 of the present invention.

As described above, when a pressure of 50 MPa is applied to the downhole plug, in case that the ratio of (b) to (a) illustrated in FIG. 9 is less than 0.5, the partition 11 may or may not be provided between the plurality of center elements. Although each of FIG. 9 illustrates a mode in which (b/a) is larger than 0, the case of (b)=0 illustrated in FIG. 3 is preferable.

As illustrated in FIG. 9(b), in the case where a plurality of center elements are present, the sum of the maximum axial lengths (a1) and (a2) of the plurality of center elements is defined as (a).

Embodiment 5

The lip 3 is attached so as to surround the outer peripheral surface of the mandrel 1, but the form does not have to be annular. That is, when a pressure of 50 MPa is applied to the downhole plug, in case that (b/a) is less than 0.5, the lip 3 may be divided into two or more portions at the outer periphery of the mandrel 1.

This will be described with reference to FIG. 10. FIGS. 10(a), (b) and (c) illustrate cross sections taken perpendicular to the axis of the lip 3, and FIGS. 10(a), (b′) and (c′) show side views along the axial direction of the lip.

FIGS. 10(a), (a′), (b) and (b′) illustrate a lip 3 formed of two members of the lips 3a and 3b. FIGS. 10(c) and 10 (c′) illustrate a lip 3 formed of three members of the lips 3a, 3b and 3c. In FIG. 10(c′), the lip 3c has an annular shape, but may be divided into two or more portions on the outer periphery of the mandrel 1 as with the lips 3a and 3b.

Also, each split lip may be integral with the socket or the cone, or may be separate.

Further, as illustrated in FIG. 10 (b), the angle of the parting plane of the lip 3 is not limited and may not necessarily be parallel to the mandrel axis. In the downhole plug including the lip 3 of Embodiment 5, since the length of the portion, in the outer peripheral of the mandrel 1, in contact with the center element 2 is not constant, the average value thereof is used as (b).

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments are also included in the technical scope of the present invention.

Summary

A plug for plugging a wellbore includes: a cylindrical body; an elastic member with annular shape configured to surround an outer peripheral surface of the cylindrical body and to be deformed under pressure; at least one protective member configured to surround the outer peripheral surface of the cylindrical body and to prevent at least a part of the elastic member from coming into contact with the cylindrical body; and a pair of pressure transmission means configured to sandwich the elastic member in an axial direction of the plug and to apply pressure to the elastic member in the axial direction to compress the elastic member, where, when the elastic member is deformed by applying a pressure of 50 MPa to the plug in the axial direction, a ratio (b/a) of an axial length (b) of a part of the elastic member where the cylindrical body and the elastic member are in contact with each other, to a maximum axial length (a) of the elastic member in a cross section along the axial direction is less than 0.5.

According to this configuration, when pressure is received from one side in the axial direction of the plug, the elastic member sandwiched between a pair of pressure transmission means provided on the outer peripheral surface of the cylindrical body is compressed and deformed via a pair of pressure transmission means provided on the outer peripheral surface of the cylindrical body. At this time, at least a part of the elastic member is prevented from coming into contact with the cylindrical body by the protective member also provided on the outer peripheral surface of the cylindrical body. Specifically, when the elastic member is deformed by applying a pressure of 50 MPa in the axial direction, a ratio (b/a) of a length (b) in the axial direction of a part where the cylindrical body and the elastic member are in contact with each other to a maximum axial length (a) of the elastic member in a cross section along the axial direction is less than 0.5. When the elastic member is compressed and deformed, a force is applied from the elastic member to the cylindrical body. However, since the part where the elastic member and the cylindrical body are in contact with each other falls within the above range, the force applied to the cylindrical body is reduced. As a result, breakage of the cylindrical body can be prevented, and the plug has excellent pressure resistance.

At least one of the protective members may be integrated with one of the pressure transmission elements constituting the pressure transmission means.

Further, at least one of the protective members may be independent of the pressure transmission means.

Further, a plurality of protective members are provided, and one of the plurality of protective members are integrated with one of the pressure transmission elements constituting one of the pair of pressure transmission means, and another one of the plurality of protective members is integrated with one of the pressure transmission elements constituting the other of the pair of pressure transmission means.

In addition, one of the pressure transmission elements integrated with the protective member is a conical member which is in contact with an end of the elastic member and whose outer diameter increases from an end of the cylindrical body toward the elastic member.

The protective member may be annular. According to this configuration, the cylindrical body of the plug can be more effectively prevented from coming into contact with the elastic member. Therefore, the plug is excellent in pressure resistance.

Additionally, the length (b) may be 0. According to this configuration, since the cylindrical body of the plug is not in contact with the elastic member, the plug is further excellent in pressure resistance.

EXAMPLES

An embodiment of the present invention will be described below. The present invention is not limited to the examples below, and it goes without saying that various aspects are possible with regard to the details thereof.

Example 1

When the center element was deformed by applying a pressure of 50 MPa in the axial direction of the downhole plug, a hydraulic pressure resistance test was performed on a downhole plug in which the ratio (b/a) of the axial length (b) of the part where the mandrel and the center element were in contact with each other to the maximum axial length (a) of the center element in a cross section along the axial direction was 0.

The downhole plug was placed in a metal tube having an inner diameter that is 1.1 times the outer diameter of the downhole plug, such that the axes of the downhole plug and the tube were parallel. The inside of the cylinder was maintained at 90° C., and a hydraulic pressure of 60 to 63 MPa was applied in the axial direction of the downhole plug to plug the cylinder. Then, the time period during which the tube was kept plugged was measured.

The results are shown in Table 1.

Comparative Example 1

The same operation as in Example 1 was performed except that a downhole tool in which the axial length (a) of the center element and the axial length (b) of the part where the mandrel and the center element were in contact with each other in the cross section along the axial direction were equal to each other was used, the temperature was set to 90 to 93° C., and the hydraulic pressure was set to 50 to 53 MPa.

Comparative Example 2

The same operation as in Example 1 was performed except that a downhole tool in which the axial length (a) of the center element and the axial length (b) of the part where the mandrel and the center element were in contact with each other in the cross section along the axial direction were equal to each other was used, the temperature was set to 90 to 93° C.

	TABLE 1
			Hydraulic
		Temperature	pressure	Retention
	b/a	[° C.]	[MPa]	time
Example 1	0	90	60 to 63	24 hours
				or longer
Comparative Example 1	1	90 to 93	50 to 53	6 hr 20 min
Comparative Example 2	1	90 to 93	60 to 63	1 hr 55 min

REFERENCE SIGNS LIST

• 1 Mandrel (Cylindrical body)
• 2 Center element (Elastic member)
• 3, 3a, 3b, 3c Lip (Protective member)
• 4, 4a, 4b Socket (Pressure transmission means)
• 5a, 5b Cone (Pressure transmission means)
• 6a, 6b Slip (Pressure transmission means)
• 7a, 7b Ring (Pressure transmission means)
• 8 Load ring (Pressure transmission means)
• 9 Bottom
• 10 Ball
• 11 Partition
• 12 Well wall
• 13 Ball seat
• 20, 21 Downhole plug (Plug)

Claims

1. A plug for plugging a wellbore, comprising:

a cylindrical body;

an annular elastic member configured to surround an outer peripheral surface of the cylindrical body and to be deformed under pressure;

at least one protective member configured to surround the outer peripheral surface of the cylindrical body and to prevent at least a part of the elastic member from coming into contact with the cylindrical body; and

a pair of pressure transmission means configured to sandwich the elastic member in an axial direction of the plug and to apply pressure to the elastic member in the axial direction to compress the elastic member, wherein

at least one of the protective members is integrated with one of the pressure transmission elements constituting the pressure transmission means,

one of the pressure transmission elements integrated with the protective member is in contact with an end of the elastic member and is a conical member whose outer diameter increases from an end of the cylindrical body toward the elastic member, and

when the elastic member is deformed by applying a pressure of 50 MPa to the plug in the axial direction, a ratio (b/a) of an axial length (b) of a part of the elastic member where the cylindrical body and the elastic member are in contact with each other, to a maximum axial length (a) of the elastic member in a cross section along the axial direction is less than 0.5.

2. (canceled)

3. (canceled)

4. The plug according to claim 1, comprising

a plurality of the protective members, wherein

one of the plurality of protective members is integrated with one of the pressure transmission elements constituting one of the pair of pressure transmission means, and

another one of the plurality of protective members is integrated with one of the pressure transmission elements constituting the other of the pair of pressure transmission means.

5. (canceled)

6. (canceled)

7. (canceled)

8. A plug for plugging a wellbore, comprising:

a cylindrical body;

an annular elastic member configured to surround an outer peripheral surface of the cylindrical body and to be deformed under pressure;

at least one protective member configured to surround the outer peripheral surface of the cylindrical body and to prevent at least a part of the elastic member from coming into contact with the cylindrical body; and

a pair of pressure transmission means configured to sandwich the elastic member in an axial direction of the plug and to apply pressure to the elastic member in the axial direction to compress the elastic member, wherein

when the elastic member is deformed by applying a pressure of 50 MPa to the plug in the axial direction, an axial length (b) of a part of the elastic member where the cylindrical body and the elastic member are in contact with each other is 0.

9. The plug according to claim 8, wherein

the protective member is annular.