Tail pipe tie-back sealing method, tie-back plug and tail pipe fracturing construction method

Abstract

The invention belongs to the technical field of oil and gas exploitation, and particularly relates to a tail pipe tie-back sealing method, a tie-back plug and a tail pipe fracturing construction method. According to the tail pipe tie-back sealing method, a tie-back plug is connected with a tie-back barrel at the top of a tail pipe hanger in a shaft in a sealed mode, the tie-back plug is inserted into the tie-back barrel through a feeding pipe string, and floating sealing is formed by the tie-back plug and the tie-back barrel.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas exploitation, and in particular relates to a tail pipe tie-back sealing method, a tie-back plug and a tail pipe fracturing construction method. Background Art

[0002] The exploitation of unconventional oil and gas is difficult and often requires the use of hydraulic fracturing methods to transform reservoirs and thereby increase the production capacity of oil and gas wells.

[0003] One of the prerequisites for safe hydraulic fracturing construction is to have a tieback fracturing string that is resistant to high pressure and sufficiently sealed. The existing tieback fracturing string is mainly composed of a feed pipe string, a tieback plug, a tieback tube, a tail pipe hanger and a lower tail pipe string.

[0004] After the existing tie-back plug is inserted into the tie-back tube at the top of the tail pipe hanger, it will be anchored in the tie-back tube through its self-locking device, playing a role of tightening and sealing. However, after the hydraulic fracturing is completed, when the delivery pipe string and the tie-back plug on the top of the tie-back tube are recovered, the self-locking device often cannot be released normally due to unexpected circumstances, resulting in the inability to remove the delivery pipe string and the tie-back plug. In addition, due to the constraints of the tie-back tube length and construction process, the tie-back plug cannot be inserted into the tie-back tube or cannot be anchored normally after insertion due to human errors in calculating the retraction distance, which will cause relatively serious problems and bring certain economic losses to the oil industry. Summary of the invention

[0005] In view of the above-mentioned technical problems, the present invention aims to provide a tail pipe tie-back sealing method, which can solve at least one of the above-mentioned technical problems.

[0006] The present invention also provides a return plug, which can solve at least one of the above technical problems.

[0007] The present invention also proposes a tail pipe fracturing construction method, which can solve at least one of the above technical problems.

[0008] According to the present invention, a tail pipe tie-back sealing method is provided, in which a tie-back plug is sealedly connected to a tie-back tube at the top of a tail pipe hanger in a wellbore, and the tie-back plug is inserted into the tie-back tube by sending a pipe string, so that the tie-back plug and the tie-back tube form a floating seal.

[0009] In a specific embodiment, after the tie-back plug and the tie-back tube form a floating seal, the annulus between the delivery pipe string and the wellbore is pressurized to form annulus ring pressure.

[0010] In a specific embodiment, the tie-back plug includes a body, an upper end portion of which is provided with a lifting joint for connecting in series with the feed pipe, and an outer wall of the body is provided with a sealing assembly for forming a floating seal with the tie-back cylinder.

[0011] In a specific embodiment, before inserting the tie-back plug into the tie-back tube through the delivery pipe string, the length variation of the pipe string in the initial state and the working state is calculated, and the position of the sealing assembly on the body in the initial state is designed according to the length variation, so as to avoid the sealing assembly from being separated from the tie-back tube in the working state. The pipe string is an integral pipe string structure formed by connecting the delivery pipe string and the tie-back plug, or the pipe string is the delivery pipe string.

[0012] In a specific embodiment, the calculation formula of the length change is as follows:

[0013] △L=K(W-W0)L / 100EF,

[0014] Where:

[0015] △L-length change;

[0016] K-the influence coefficient of the joint of the pipe string, which is 0.85 to 0.95;

[0017] L-length of the string in the initial state, m;

[0018] E- elastic coefficient of the material of the string, 2.059*10 5 MPa;

[0019] F- cross-sectional area of ​​the pipe string, cm 2 ;

[0020] W-upward force on the bottom of the tie-back plug, N;

[0021] W0-Friction resistance of the sealing assembly of the return plug in the return tube, N.

[0022] In a specific embodiment, the calculation formula of the upward force W borne by the bottom of the reconnection plug is as follows:

[0023] W=(P-P0+P1)*S,

[0024] Where:

[0025] P-pressure inside the pipe string, MPa;

[0026] S- Cross-sectional area of ​​the bottom of the return plug, cm 2 ;

[0027] P0-annulus pressure outside the delivery pipe string, MPa;

[0028] P1-The pressure difference between the outside of the tie-back tube and the inside of the tie-back plug, MPa.

[0029] In a specific embodiment, in an initial state, the depth to which the sealing assembly is inserted into the tie-back cylinder is greater than the length change.

[0030] In a specific embodiment, a plurality of the sealing assemblies are arranged on the lower outer wall of the body.

[0031] In a specific embodiment, adjacent sealing components are axially connected.

[0032] In a specific embodiment, a guide head is provided at the lower end of the body.

[0033] According to the present invention, a reconnection plug is also provided for implementing the tail pipe reconnection sealing method provided according to the present invention, comprising a main body, a lifting joint for being connected in series with the feed pipe is provided at the upper end of the main body, a sealing assembly for forming a floating seal with the reconnection tube is provided on the outer wall of the main body, and a guide head is provided at the lower end of the main body.

[0034] According to the present invention, a tail pipe fracturing construction method is also provided, comprising the following steps:

[0035] Insert the tie-back plug into the tie-back tube by sending in the pipe string, so that the tie-back plug and the tie-back tube form a floating seal;

[0036] Pressurizing the annulus between the delivery pipe string and the wellbore to form annulus pressure;

[0037] Pressurizing the inside of the delivery pipe string to perform fracturing construction;

[0038] After the fracturing operation is completed, the delivery pipe string and the tie-back plug are lifted up and recovered.

[0039] Compared with the prior art, the advantages of the present application are as follows.

[0040] The tie-back plug of the present invention is inserted into the tie-back tube to form a floating seal, that is, after the tie-back plug is inserted into the tie-back tube, the outer wall of the tie-back plug forms a sliding seal with the inner wall of the tie-back tube through the sealing assembly. When the delivery pipe string is extended and retracted by external force in the well, the sealing assembly of the tie-back plug can move axially relative to the tie-back tube. As long as the sealing assembly is always within the range of the tie-back tube, the sealing effect of both can be guaranteed, thereby providing a guarantee for the implementation of the fracturing process. Through this floating sealing method, there is no need to set a self-locking device. On the one hand, it can simplify the structure of the tie-back plug. On the other hand, it can avoid the problem that the tie-back plug cannot be inserted (the self-locking device cannot be anchored normally) during the process of the tie-back fracturing string entering the well, and it is difficult to lose the hand during the process of recovering the tie-back fracturing string.

[0041] The tie-back plug of the present invention is sealed with the tie-back tube through a multi-channel sealing assembly, which can realize high-pressure floating sealing during the fracturing process, reduce construction risks and save well construction costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be described below with reference to the accompanying drawings.

[0043] Figure 1 A schematic diagram of an embodiment of a return plug according to the present invention;

[0044] Figure 2 A cross-sectional schematic diagram of an embodiment of a sealing assembly of a tie-back plug according to the present invention;

[0045] Figure 3 A schematic diagram showing an embodiment of a sealing assembly of a tie-back plug according to the present invention is shown.

[0046] The reference numerals in the figures are as follows:

[0047] 2. Return plug; 21. Main body; 22. Pull joint; 23. Sealing assembly; 24. Guide head.

[0048] In the present application, all drawings are schematic drawings, which are only used to illustrate the principles of the present invention and are not drawn according to the actual scale. DETAILED DESCRIPTION

[0049] The present invention will be described below with reference to the accompanying drawings.

[0050] It should be noted that, in the present application, the direction of the tie-back plug according to the present invention close to the wellhead after entering the well is described as "up", "front" or similar terms, while the direction of the tie-back plug away from the wellhead after entering the well is described as "down", "back" or similar terms.

[0051] It is easy to understand that the existing tie-back fracturing string includes a tie-back tube, a liner hanger and a liner string. The liner hanger is anchored and sealed with the casing wall of the wellbore, the liner string is coaxially arranged below the liner hanger, the space between the liner and the casing wall is filled with cementing cement slurry, and the tie-back tube is coaxially arranged above the liner hanger. The structure of the tie-back fracturing string is well known to those skilled in the art and will not be described in detail here.

[0052] Figure 1 The structure of the return plug 2 according to the present invention is shown. Figure 1As shown, the tie-back plug 2 includes a main body 21 and a sealing assembly 23. In this embodiment, the body 21 is tubular, and the sealing assembly 23 is arranged on the outer wall of the body 21. The body 21 of the tie-back plug 2 can be inserted into the tie-back tube (not shown in the figure). After the body 21 is inserted into the tie-back tube, the sealing assembly 23 seals the outer wall of the body 21 and the inner wall of the tie-back tube, so that the tie-back plug 2 and the tie-back tube form a floating seal, that is, a moving pair is formed between the tie-back plug 2 and the tie-back tube, and the tie-back plug 2 can move axially relative to the tie-back tube. As long as the sealing assembly 23 is within the length range of the tie-back tube, the seal between the tie-back plug 2 and the tie-back tube can be achieved. By means of this floating seal, there is no need to set a self-locking device. On the one hand, it can simplify the structure of the tie-back plug 2, and on the other hand, it can avoid the problem that the tie-back plug cannot be inserted (the self-locking device cannot be anchored normally) during the process of the tie-back fracturing string entering the well, and it is difficult to lose the hand during the process of recovering the tie-back fracturing string.

[0053] In a specific embodiment, a lifting joint 22 for connecting to a feeding pipe string (not shown in the figure) is provided at the upper end of the body 21 .

[0054] In a specific embodiment, a guide head 24 is provided at the lower end of the body 21. The guide head 24 can guide the tie-back plug 2 during the process of entering the well.

[0055] In a preferred embodiment, the guide head 24 is a horseshoe-shaped guide head, which can avoid subsequent drilling and removal.

[0056] In this embodiment, a plurality of sealing components 23 are arranged on the lower outer wall of the body 21. By arranging a plurality of sealing components 23, the sealing effect between the tie-back plug 2 and the tie-back tube can be improved, and high-pressure sealing can be achieved. The sealing component 23 is arranged at the lower part of the body 21. When the tie-back plug 2 is inserted into the tie-back tube, the sealing component 23 can extend into the interior of the tie-back tube. The distance that the sealing component 23 extends into the tie-back tube is greater than the length change of the delivery pipe string in the working state, thereby ensuring that the sealing component 23 is always located within the length range of the tie-back tube, ensuring the sealing effect.

[0057] In a specific embodiment, four groups of sealing assemblies 23 are sequentially arranged on the outer wall of the body 21, and adjacent sealing assemblies 23 are axially connected. It is easy to understand that adjacent sealing assemblies 23 are axially connected, which means that adjacent sealing assemblies 23 are connected end to end, or the interval between adjacent sealing assemblies 23 is very small, and the size of the interval is used to compensate for the axial expansion of the sealing assembly 23 during sealing compression. The sealing assembly 23 is composed of a vulcanized ring sealing rubber member, which can form a seal with the inner surface of the return cylinder, and can achieve a high-pressure resistant sealing effect.

[0058] According to the present invention, the tie-back tube in this embodiment has a longer axial length than the tie-back tube in the prior art. The length of the tie-back tube in the prior art is usually about 2.1m, while the length of the tie-back tube in this embodiment is greater than 2.1m, for example, it can be set to 3.1m, so as to adapt to the length variation of the delivery pipe string, so that the sealing assembly 23 of the tie-back plug 2 is always within the length range of the tie-back tube. The lengthened tie-back tube is safer and can ensure a good sealing effect under higher construction pressure.

[0059] According to the present invention, in a specific embodiment, a tail pipe tie-back sealing method is also provided. The tie-back plug 2 is inserted into the tie-back tube by feeding the pipe string, so that the tie-back plug 2 and the tie-back tube form a floating seal. Specifically, the tie-back plug 2 and the tie-back tube form a floating seal, which means that in the subsequent construction process, when the length change of the feeding pipe string causes the tie-back plug 2 to move axially relative to the tie-back tube, the sealing component 23 of the tie-back plug 2 is always within the length range of the tie-back tube, and the sealing effect of the tie-back plug 2 and the tie-back tube is ensured.

[0060] In a preferred embodiment, after the tie-back plug 2 and the tie-back tube form a floating seal, the annulus between the feed pipe string and the wellbore is pressurized to form an annulus ring pressure. By setting the annulus ring pressure value, a certain pressure exists in the external annulus of the feed pipe string and the tie-back tube above the liner hanger to ensure the floating seal of the sealing plug 2 in the tie-back tube, and the floating seal effect in the subsequent fracturing construction process is ensured by the annulus ring pressure.

[0061] According to the present invention, before the tie-back plug 2 is inserted into the tie-back barrel by sending the pipe string, the length change of the pipe string in the initial state and the working state is calculated, and the position of the sealing assembly 23 on the body 21 in the initial state is designed according to the length change, so as to avoid the sealing assembly 23 from being separated from the tie-back barrel in the working state.

[0062] The pipe string refers to the whole pipe string formed after the incoming pipe string and the tie-back plug 2 are connected. It is easy to understand that since the length of the tie-back plug 2 accounts for a very small part of the entire pipe string, the present invention has a low requirement for the length accuracy. As long as the axial movement stroke of the sealing component 23 in the tie-back tube during subsequent construction is calculated in advance to be less than the distance from the lowest sealing component 23 to the top of the tie-back tube, the sealing effect can be guaranteed. Even if the length change of the tie-back plug 2 is not calculated, the sealing requirements of the present invention can be met. Therefore, in the calculation process, only the length change of the incoming pipe string can be calculated.

[0063] The initial state refers to the state before the delivery pipe string enters the well, or the state before the well is pressurized after the delivery pipe string enters the well. The working state refers to the state of the delivery pipe string when the subsequent downhole process is implemented after the tie-back plug 2 is sealed with the tie-back tube.

[0064] In a specific embodiment, the calculation formula of the length change is as follows:

[0065] △L=K(W-W0)L / 100EF.

[0066] The parameters in the formula are as follows.

[0067] △L is the length change.

[0068] K is the influence coefficient of the joint of the tubing string, which is 0.85 to 0.95. It is easy to understand that the input pipe string of the tubing string is composed of multiple tubing strings connected in series, and the adjacent tubing strings are connected by joints. The input pipe string of the tubing string and the tie-back plug 2 are also connected by joints. These joints are the joints of the tubing string.

[0069] L is the length of the pipe string in the initial state, m.

[0070] E is the elastic coefficient of the material of the pipe string. In this embodiment, the elastic coefficient of the material of the pipe string is 2.059*10 5 MPa. When each section of the string is made of different materials, each section is calculated separately, and then the calculated values ​​of each section are added together to obtain the length change of the string.

[0071] F is the cross-sectional area of ​​the pipe string, cm 2 The cross-sectional area of ​​the tubing string refers to the annular cross-sectional area of ​​the tubing string that makes up the feed tubing string and the annular cross-sectional area of ​​the tieback plug, that is, the axial projection area of ​​the tubing string and the tieback plug.

[0072] It is easy to understand that when the delivery pipe string is composed of pipe strings of different sizes, each pipe string is calculated separately first, and then the calculated values ​​of each pipe string are added together to obtain the length change of the delivery pipe string. The same is true for the tie-back plug.

[0073] W0 is the friction resistance that needs to be overcome when all the sealing components of the reconnection plug 2 completely enter the reconnection tube and move axially in the reconnection tube, N.

[0074] W is the upward force borne by the bottom of the reconnection plug 2, N.

[0075] In a specific embodiment, the calculation formula of the upward force W borne by the bottom of the reconnection plug is as follows:

[0076] W=(P-P0+P1)*S.

[0077] The parameters in the formula are as follows.

[0078] P is the pressure inside the feed pipe string, MPa.

[0079] S is the cross-sectional area of ​​the bottom of the tie-back plug 2, cm 2In this embodiment, the force-bearing cross-sectional area of ​​the bottom of the reconnection plug 2 is the axial projection area of ​​the guide head 24 .

[0080] P0 is the annular pressure value outside the delivery pipe string, MPa. In this embodiment, P0 is the pressure in the annular space between the delivery pipe string and the wellbore.

[0081] P1 is the pressure difference between the outside of the tie-back tube and the inside of the tie-back plug, in MPa. In this embodiment, P1 is the pressure inside the tie-back plug 2 minus the pressure outside the tie-back tube.

[0082] Specifically, during the subsequent underground construction, P, P0, and P1 will change during the construction process. By substituting the limit values ​​of P, P0, and P1 during the subsequent underground construction process into the above calculation formula, the limit value of the length change amount is obtained.

[0083] By calculating the change in length of the pipe string sent in, the axial movement distance of the tie-back plug 2 in the tie-back tube caused by the frequent high pressure in the pipe during the subsequent downhole construction process can be calculated, thereby ensuring that the sealing assembly 23 of the tie-back plug 2 is always maintained in the tie-back tube during the entire downhole construction process, thereby achieving a floating sealing effect.

[0084] According to the present invention, in the initial state, the depth to which the sealing assembly 23 is inserted into the tie-back cylinder is greater than the limit value of the length change.

[0085] In a specific embodiment, the subsequent downhole construction is specifically a fracturing construction.

[0086] According to the present invention, a tail pipe fracturing construction method is also provided, comprising the following steps.

[0087] Step one, insert the reconnection plug 2 into the reconnection tube through the delivery pipe string, so that the reconnection plug and the reconnection tube form a floating seal. Specifically, the reconnection plug 2 is fixedly connected to the lower end of the delivery pipe string through the lifting joint 22, and then the reconnection plug 2 is delivered into the well through the delivery pipe string. After the reconnection plug 2 enters the well, the guide head 24 at the bottom of the reconnection plug 2 first contacts the reconnection tube, and at this time, the drilling platform weight gauge has a slight resistance display. Continue to lower the delivery pipe string, and the sealing assembly 23 at the bottom of the reconnection plug 2 enters the reconnection tube. At this time, the drilling platform weight gauge has a continuous and obvious and continuously increasing resistance display. Continue to lower the delivery pipe string. When the reconnection plug 2 is fully inserted into the reconnection tube, the drilling platform weight gauge has a more obvious resistance display. At this time, the reconnection plug 2 is in place, and the sealing assembly 23 of the reconnection plug 2 is in full contact with the inner wall of the reconnection tube to form a high-pressure sealing structure.

[0088] Step 2: pressurize the annulus between the delivery pipe string and the wellbore to form an annulus pressure. In this embodiment, the annulus pressure is 5-15MPa, preferably 10MPa.

[0089] Step three, pressurize the incoming pipe string to perform fracturing construction. At this time, due to the high pressure in the incoming pipe string, an upward force will be generated on the cross-sectional area at the bottom of the reconnection plug 2. Under the action of this force, the sealing component 23 will move upward relative to the reconnection tube. The distance that the sealing component 23 moves upward relative to the reconnection tube is the length change of the incoming pipe string. After reaching the balance point of the construction pressure, the sealing component 23 is relatively static and sealed, and the fracturing construction of the current section is carried out. After a section of fracturing is completed, the pressure in the pipe is vented. At this time, the upward force changes, and the sealing component moves downward, and so on. During the entire fracturing process, the sealing component 23 always plays a good sealing role in the reconnection tube.

[0090] Step 4: After the fracturing operation is completed, the input pipe string and the tie-back plug 2 are lifted up to be recovered. Since there is no fixed connection between the tie-back plug 2 and the tie-back tube, the input pipe string can be directly lifted up to drive the tie-back plug 2 to separate from the tie-back tube, completing the recovery of the input pipe string and the tie-back plug 2.

[0091] In a preferred embodiment, the sealing assembly 23 will have a certain friction resistance when inserted into the tie-back tube, which can be read through the drilling platform weight gauge. There are multiple sealing assemblies 23. When multiple sealing assemblies 23 enter the tie-back tube, the drilling platform weight gauge keeps changing until the reading is stable, and the friction resistance W0 at this time is recorded. The subsequent sealing assembly 23 must overcome this friction resistance when floating in the tie-back tube. Therefore, in the process of calculating the length change, the friction resistance of the sealing assembly 23 can be considered on the basis of the calculation formula of the length change provided by the present invention, so that the calculation result is more accurate.

[0092] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0093] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0094] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0095] Finally, it should be noted that the above is only a preferred embodiment of the present invention and does not constitute any limitation to the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for a person skilled in the art to modify the technical solutions described in the aforementioned embodiments or to replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A liner tie-back sealing method, wherein a tie-back plug is sealedly connected to a tie-back tube at the top of a liner hanger in a wellbore, characterized in that: The tie-back plug is inserted into the tie-back cylinder by sending in the pipe string, so that the tie-back plug and the tie-back cylinder form a floating seal.

2. The tail pipe tie-back sealing method according to claim 1, characterized in that: After the tie-back plug and the tie-back tube form a floating seal, the annulus between the delivery pipe string and the wellbore is pressurized to form annulus ring pressure.

3. The tail pipe tie-back sealing method according to claim 1 or 2, characterized in that: The return plug comprises a body (21), a lifting joint (22) for connecting in series with the feed pipe is arranged at the upper end of the body (21), and a sealing assembly (23) for forming a floating seal with the return tube is arranged on the outer wall of the body (21).

4. The tail pipe tie-back sealing method according to claim 3, characterized in that: Before inserting the tie-back plug into the tie-back barrel by sending the pipe string, the length change of the pipe string in the initial state and the working state is calculated, and the position of the sealing component (23) on the body (21) in the initial state is designed according to the length change, so as to prevent the sealing component (23) from being separated from the tie-back barrel in the working state.

5. The tail pipe tie-back sealing method according to claim 4, characterized in that: The calculation formula of the length change is as follows: △L=K(W-W0)L / 100EF, Where: △L-length change; K-the influence coefficient of the joint of the pipe string, which is 0.85 to 0.95; L-length of the string in the initial state, m; E- elastic coefficient of the material of the pipe string; F- cross-sectional area of ​​the pipe string, cm 2 ; W-upward force on the bottom of the tie-back plug, N; W0-Friction resistance of the sealing assembly of the return plug in the return tube, N.

6. The tail pipe tie-back sealing method according to claim 5, characterized in that: The calculation formula for the upward force W borne by the bottom of the return plug is as follows: W=(P-P0+P1)*S, Where: P-pressure inside the pipe string, MPa; S- Cross-sectional area of ​​the bottom of the return plug, cm 2 ; P0-annulus pressure outside the delivery pipe string, MPa; P1-The pressure difference between the outside of the tie-back tube and the inside of the tie-back plug, MPa.

7. The tail pipe tie-back sealing method according to claim 4, characterized in that: In an initial state, the sealing assembly (23) is inserted into the tie-back cylinder to a depth greater than the length change.

8. The tail pipe tie-back sealing method according to claim 3, characterized in that: A plurality of sealing components (23) are arranged on the lower outer wall of the body (21).

9. The tail pipe tie-back sealing method according to claim 7, characterized in that: Adjacent sealing components (23) are axially connected.

10. The tail pipe tie-back sealing method according to claim 3, characterized in that: A guide head (24) is provided at the lower end of the body (21).

11. A return plug, characterized in that: A method for implementing the tail pipe tie-back sealing method according to any one of claims 1 to 10, comprising a main body (21), a lifting joint (22) for connecting to the feed pipe string is provided at the upper end of the main body (21), a sealing assembly (23) for forming a floating seal with the tie-back tube is provided on the outer wall of the main body (21), and a guide head (24) is provided at the lower end of the main body (21).

12. A tail pipe fracturing construction method, characterized in that: The steps include: Insert the tie-back plug into the tie-back tube by sending in the pipe string, so that the tie-back plug and the tie-back tube form a floating seal; Pressurizing the annulus between the delivery pipe string and the wellbore to form annulus pressure; Pressurizing the inside of the delivery pipe string to perform fracturing construction; After the fracturing operation is completed, the delivery pipe string and the tie-back plug are lifted up and recovered.

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