CN110878679A

CN110878679A - Tail pipe string

Info

Publication number: CN110878679A
Application number: CN201811038017.0A
Authority: CN
Inventors: 张冠林; 郭朝辉; 姚辉前; 张新亮; 徐明会; 梁晓阳; 秦德威; 张明华
Original assignee: Shelfoil Petroleum Equipment And Services Co Ltd; China Petroleum and Chemical Corp; Sinopec Research Institute of Petroleum Engineering
Current assignee: Shelfoil Petroleum Equipment And Services Co Ltd; China Petroleum and Chemical Corp; Sinopec Research Institute of Petroleum Engineering
Priority date: 2018-09-06
Filing date: 2018-09-06
Publication date: 2020-03-13
Anticipated expiration: 2038-09-06
Also published as: CN110878679B

Abstract

The present invention relates to a tailpipe string including a flow reducing device and a float shoe disposed downstream of the flow reducing device, the flow reducing device and the float shoe being configured such that, in a first state, a closed space is formed between the flow reducing device and the float shoe, and a weight-reducing fluid is contained in the closed space. The tail pipe string can be smoothly put into a horizontal well and an extended reach well.

Description

Tail pipe string

Technical Field

The invention relates to the technical field of oil and gas well cementing and completion, in particular to a tail pipe string.

Background

With the continuous exploration and development of deep-sea oil and gas fields and unconventional oil and gas fields and the continuous development of drilling technology, long horizontal wells and extended reach wells are more and more. The vertical depth of the well is shallow, and the horizontal section is long, so that the tail pipe string has large friction resistance with the well wall or the upper layer sleeve wall in the horizontal section and the deflecting section. This seriously affects the normal running of the tail pipe string and may even cause the differential pressure to clamp the casing pipe, thereby bringing about significant economic loss.

In the prior art, the tail pipe string is usually sent in a smashing mode when the friction resistance is large and the tail pipe string is difficult to run, namely, the tail pipe string is rushed and braked violently. However, the hidden troubles of sticking the card, advancing the tool and lowering the tail pipe are brought.

Therefore, there is a need for a tailpipe string that can be run in smoothly.

Disclosure of Invention

In order to solve the problems, the invention provides a tail pipe string which can be smoothly put into a horizontal well and a large-displacement well.

According to the invention, a tailpipe string is proposed, comprising a flow reducer and a float shoe arranged downstream of the flow reducer, the flow reducer and the float shoe being configured such that, in a first state, a closed space is formed between the flow reducer and the float shoe, in which closed space a weight-reducing fluid is accommodated.

When the tail pipe string is lowered into a horizontal well, drilling fluid is prevented from being poured into the tail pipe string due to the fact that a closed space is formed between the drag reducer and the floating shoes. The weight of the tail pipe string can be lower due to the weight reduction fluid in the closed space, so that the buoyancy of the tail pipe string is increased, and the friction between the tail pipe string and the outer casing wall is reduced. Therefore, the tail pipe string can be smoothly put into a well without the need of 'rush and brake', and the hidden troubles of sticking, advance action of a tool, insufficient tail pipe lowering and the like can be avoided.

In one embodiment, the drag reducer comprises: the outer pipe body is connected with the tail pipe string parts at the upstream and downstream; the middle pipe body is sleeved in the outer pipe body and is tightly matched with the outer pipe body; the inner pipe body is sleeved in the middle pipe body and is tightly matched with the middle pipe body, the inner pipe body comprises a columnar side wall and a bottom wall which closes the side wall at the downstream of the side wall, and a flow hole which penetrates through the side wall is formed in the side wall; wherein in a first state the flow opening is aligned with a sidewall of the centertube body such that the sidewall of the centertube body closes the flow opening, and in a second state the inner tube body is moved relative to the centertube body such that the flow opening is not aligned with the sidewall of the centertube body, the flow opening communicating the inner tube body and the outer tube body.

In one embodiment, a positioning groove is formed on an inner surface of a sidewall of the outer tube, a restriction groove is formed on a sidewall of the middle tube, the inner tube is fitted in the middle tube and connected to the middle tube by a first shear pin, the inner tube includes a first tube portion located upstream of the flow hole, an outer surface of a sidewall of the first tube portion is capable of being fitted to an inner surface of a sidewall of the middle tube, the inner tube of the first tube portion further includes a second tube portion located upstream of the first tube portion, a depression recessed with respect to an outer surface of a sidewall of the first tube portion is formed on an outer surface of a sidewall of the second tube portion, and the resistance reducer further includes a stopper provided between the outer tube and the inner tube, and inserted into the restraining groove, wherein in a first state the locating groove, the restraining groove and the first body portion are aligned, the stop is inserted into the locating groove and the restraining groove against a sidewall of the first body portion, and in a second state the first shear pin shears, the inner body moves downstream relative to the middle body until a recess on the second body portion is aligned with the locating groove and the restraining groove, and the stop moves out of the locating groove and into the recess.

In one embodiment, an upstream facing surface of the stopper is configured to be inclined toward an outside, and/or a downstream facing surface of the stopper is configured to be inclined toward an outside, and the positioning groove and the restricting groove are shaped to match the shape of the stopper.

In one embodiment, the float shoe comprises: a housing, a one-way valve housed within the housing, the one-way valve configured to allow passage of fluid only in an upstream to downstream direction; the pressure-bearing mechanism is positioned at the downstream of the one-way valve and comprises an outer sleeve which is sleeved in the shell and is tightly matched with the side wall of the shell, a blocking part which extends inwards along the radial direction is constructed at the upstream end of the outer sleeve, and an inner stop block which is sleeved in the outer sleeve, the inner stop block is tightly matched with the outer sleeve and is connected together through a second shearing pin, the upstream end of the inner stop block is constructed to be capable of abutting against the blocking part, and the inner stop block is constructed to be provided with a baffle plate which extends to the position where the inner space of the outer sleeve can be sealed along the transverse direction.

In one embodiment, the plug assembly comprises: the outer surface of the side wall of the first cylinder is provided with a first rubber plug which is tightly matched with the pipe string wall of the tail pipe string, and the upstream end of the first cylinder is connected with the tail pipe hanger through a fifth shearing pin; the outer surface of the side wall of the second cylinder body is provided with a second rubber plug which is tightly matched with the tube string wall of the tail tube string, and the upstream end of the second cylinder body is connected with the downstream end of the first cylinder body through a third shearing pin; and the ball seat is sleeved in the second cylinder and is connected with the second cylinder through a fourth shearing pin.

In one embodiment, the ball seat comprises a receiving portion for receiving a pressure building ball, and a first through hole which is configured at the downstream of the receiving portion and penetrates through the side wall of the ball seat along the radial direction, the rubber plug assembly further comprises a tray which is positioned at the downstream of the ball seat, the tray extends along the transverse direction and is fixedly connected with the side wall of the second cylinder, and a second through hole which penetrates through the tray along the longitudinal direction is configured on the tray; wherein the ball seat is movable downstream and captured by the tray after the fourth shear pin shears, the first and second through-holes allowing fluid flow through the second barrel.

In one embodiment, the first rubber plug is an anti-rotation rubber plug.

In one embodiment, the tailpipe string further includes a float collar disposed between the choke and the float shoe.

In one embodiment, the upstream end of the float collar is configured with anti-rotation trays and the downstream end of the drag reducer is configured with corresponding anti-rotation teeth.

Compared with the prior art, the invention has the advantages that: allowing the tail pipe string to be smoothly lowered into horizontal wells and extended reach wells.

Drawings

The invention is described in more detail below with reference to the accompanying drawings. Wherein:

FIG. 1 shows a tailpipe string according to an embodiment of the present invention;

figure 2 shows a plug assembly in a liner string according to one embodiment of the present invention;

FIG. 3 shows a drag reducer in a tailpipe string according to an embodiment of the present invention;

FIG. 4 shows a float collar in a tailpipe string according to an embodiment of the present invention;

FIG. 5 shows a float shoe in a tailpipe string in accordance with an embodiment of the present invention;

fig. 6 shows another state of the tailpipe string of fig. 1.

In the drawings, like parts are provided with like reference numerals. The figures are not drawn to scale.

Detailed Description

The invention will be further explained with reference to the drawings.

Fig. 1 shows a schematic diagram of a tailpipe string 100 according to an embodiment of the present invention. The liner string 100 includes a string of drill pipes and running tool 110, liner hanger 120, plug assembly 130, choke 140, float collar 150 and float shoe 160 arranged in sequence from upstream to downstream. In the case shown in fig. 1, the drag reducer 140 is fixed in position in the tailpipe string and spaced apart from the float shoe 160. An enclosed space is formed between the flow reducer 140 and the float shoe 160 that does not allow fluid in other portions of the fluid tailpipe string or fluid in the outer casing (not shown). A weight-reducing fluid is contained within the enclosed space. In this state, the friction between the tail pipe string 100 and the outer casing is small, and the tail pipe string 100 can be allowed to smoothly run into the horizontal well and the extended reach well.

It should be understood that the weight-reducing fluid herein may be any suitable fluid, preferably air, having a density less than that of the drilling fluid.

In this context, "upstream" refers to the side near the wellhead and "downstream" refers to the side near the bottom of the well.

The drill string and running tool 110 and liner hanger 120 are well known to those skilled in the art and will not be described further herein.

The respective structures in the tailpipe string 100 and the operation of the tailpipe string 100 will be described in more detail with reference to fig. 1 to 6.

Figure 2 shows one embodiment of a plug assembly 130 in a liner string 100.

The plug assembly 130 includes a first plug member that includes a first barrel 131 and a first plug 132 disposed on the outer surface of the sidewall of the first barrel 131, the first plug 132 configured to be capable of mating with the string wall of the tail pipe string. The upstream end of the first barrel 131 is connected to the liner hanger 130 by a fifth shear pin.

The plug assembly 130 further includes a second plug member that includes a second barrel 134 and a second plug 135 disposed on the outer surface of the sidewall of the second barrel 134, the second plug 135 being configured to mate with the string wall of the tail string. The upstream end of the second cylinder 134 is connected to the downstream end of the first cylinder 131 by a third shear pin 136.

The plug assembly 130 further includes a ball seat 137 configured with a generally cylindrical body and connected to the second cylinder 134 of the second plug member by a fourth shear pin 138. The ball seat 137 has a receiving portion formed on a body thereof for receiving a pressure-building ball, and the receiving portion is of a structure known to those skilled in the art and will not be described herein. In addition, the body of the ball seat 137 may be further configured with a first through-hole 137A penetrating through a sidewall of the ball seat in a radial direction at a downstream with respect to the seating portion.

Accordingly, the plug assembly may also include a tray 139. A tray 139 is located within the second cylinder 134 and extends in a radial direction to be connected to an inner surface of the sidewall of the second cylinder 134. A second through bore 139A is formed in the tray 139 and is configured to communicate with the first through bore 137A after the fourth shear pin 138 has sheared, the ball seat 137 has contacted the tray 137 to allow fluid to flow from within the ball seat 137 into the second cylinder 134 and thence into the downstream tailpipe string portion.

Fig. 3 shows one embodiment of a drag reducer 140 in a tailpipe string 100.

The choke reducer 140 includes an outer body 141, and the outer body 141 is configured in a cylindrical shape and can be connected to the tail pipe string portions upstream and downstream. It should be understood that the outer tube 141 is part of the tube string wall of the liner string 100. A positioning groove 141A is formed on an inner surface of the sidewall of the outer tube body 141, and the positioning groove 141A is a blind groove. In the embodiment shown in fig. 3, outer tube 141 comprises an upstream tube and a downstream tube downstream of and connected to the upstream tube. The downstream end of the upstream tube body can be inserted into the upstream end of the downstream tube body to effect a connection therebetween. A bottom wall and a downstream side wall of the positioning groove 141A are configured on the inner surface of the side wall of the downstream pipe body. The end surface of the downstream end of the upstream pipe body is configured as the upstream side wall of the positioning groove 141A. Thereby, when the upstream pipe body and the downstream pipe body are joined together, the positioning groove 141A can be formed.

The resistance reducer 140 further includes a middle tube 142, and the middle tube 142 is also cylindrical, and is disposed in the outer tube 141 and can be tightly fitted with the outer tube 141. A corresponding third plug 149 is configured on the outer surface of the sidewall of the upstream end of the middle tube body 142, the third plug 149 being configured to mate with the inner surface of the sidewall of the outer tube body 141. The outer surface of the sidewall of the downstream end of the middle tube body 142 is configured with a fourth rubber plug 148, and the fourth rubber plug 148 is configured to be capable of tightly fitting with the inner surface of the sidewall of the outer tube body 141. A limiting groove 142A penetrating in the radial direction is formed in the sidewall of the middle tube body 142. In the first state, the restriction groove 142A can be aligned with the positioning groove 141A on the outer body 141.

Preferably, the middle tube 142 includes a first tube at the upstream and a second tube at the downstream, and the downstream end of the first tube is inserted into the upstream end of the second tube for connection. The downstream end of the first tube inserted into the second tube is aligned with the inner tube 143.

The damper 140 further includes an inner tube 143, and the inner tube 143 is cylindrically configured, is fitted into the middle tube 142, and is connected to the middle tube 142 by a first shearing pin 144. The inner tube 143 includes a cylindrical hollow sidewall and a bottom wall 146 closing the sidewall at a downstream end thereof. Flow openings 147 are formed in the side wall and extend in the radial direction. In the first state, the flow hole 147 is opposed to and closed by the sidewall of the middle tube body 142, thereby separating the inner space of the inner tube body 143 from the inner space of the outer tube body 141 at the downstream. In the second state, the flow hole 147 is misaligned with the sidewall of the middle tube body 142, thereby allowing the flow hole 147 to be opened. Thereby, the inner space of the inner tube 143 may communicate with the inner space of the outer tube 141 located downstream.

In addition, the side wall of the inner tube 143 further includes a first tube portion 143A located upstream of the flow hole 147. In the first state, the first tubular body portion 143A can be aligned with the positioning groove 141A on the outer tubular body 141 and the restriction groove 142A on the middle tubular body 142. The sidewall of the inner tube further includes a second tube portion 143B upstream of the first tube portion 143A, the second tube portion 143B having a recess configured on an outer surface thereof, the recess having an outer diameter smaller than that of the first tube portion 143A. In the second state, the recess of the second tubular body portion 143B is aligned with the positioning groove 141A of the outer tubular body 141 and the restriction groove 142A of the middle tubular body 142. First shear pin 144 joins inner tube 143 and middle tube 142 together upstream of second tube portion 143B.

In addition, the drag reducer 140 further includes a stopper 145. In the first state, the stopper 145 is inserted into the positioning groove 141A and the restriction groove 142A at the same time, and is abutted by the first tubular body portion 143A so as not to escape from the positioning groove 141A. In the second state, the stopper 145 is simultaneously inserted into the restriction groove 142A and the recess, and thus is released from the positioning groove 141A.

Preferably, the upstream surface and the downstream surface of the stopper 145 are configured to be inclined, both toward the outside (i.e., the side on which the outer tube 141 is located). Thus, the stopper 145 has a substantially trapezoidal cross section, and the bottom surface of the trapezoid having a smaller length faces the outer tube 141. Accordingly, the upstream and downstream sidewalls of the positioning groove 141A on the outer tube body 141 and the sidewalls of the restriction groove 142A on the middle tube body 142 are also configured to be matched. This arrangement can facilitate the transition of the stopper 145 between the first state and the second state.

Preferably, the length of the edge of the stopper 145 facing the inner tube 143 in the longitudinal direction (i.e., the direction from upstream to downstream) is smaller than the length of the recess in the longitudinal direction, in particular about 1/3 the length of the latter at most. This arrangement is advantageous in ensuring smooth operation of the stopper 145.

Preferably, the downstream end of the central tube body 142 is configured with anti-rotation teeth 148, which teeth 148 can mate with anti-rotation support trays 154 on the float collar 150, which is located downstream, as described below.

Fig. 4 illustrates one embodiment of a float collar 150 in a tailpipe string 100.

The float collar 150 includes a cylindrical housing 151, and a check valve 153 disposed in the housing, the check valve 153 being connected to the housing 151 through a cement body 152. The check valve 153 is configured to allow fluid flow only in the upstream to downstream direction.

The float collar 150 may also include an anti-rotation support tray 154 that fits within the housing 151 upstream of the cement body 152 and one-way valve 153, and that is capable of engaging the anti-rotation teeth 148 described above.

Fig. 5 shows one embodiment of a float shoe 160 in a tailpipe string 100.

The float shoe 160 includes a housing 161, and a check valve 163 disposed in the housing 161, the check valve 163 being connected to the housing 161 by a cement body 162. The check valve 163 is configured to allow fluid flow only in the upstream to downstream direction.

Preferably, the float shoe 160 further includes a pressure-containing mechanism disposed within the housing 161 downstream of the one-way valve 163. The bearing mechanism comprises an outer sleeve 164, and the outer sleeve 164 is sleeved in the shell 161 and fixedly connected with the shell 161. The outer sleeve 164 is generally cylindrical and cylindrical, and its upstream end is configured with a stop 164A that extends radially inwardly but does not close the inner cavity of the outer sleeve 164. The compression mechanism further includes an internal stop 165 that is nested within outer sleeve 164 and is connected to outer sleeve 164 by a second shear pin 166. The upstream end of the inner stopper 165 can abut against the downstream surface of the stopper 164A. The internal stop 165 includes a cylindrical body that is connected to the outer sleeve 164. The internal stop 165 further includes a baffle 165A that extends in the transverse direction (radial direction) to close the upstream end of the body and to close the inner cavity (interior space) of the outer sleeve 164.

The pressure-containing mechanism prevents fluid from flowing from downstream to upstream. Thus, when the tail pipe string 100 is run in, the check valve 163 of the float shoe 160 can be prevented from receiving a large pressure from the downstream, and thus the spool of the check valve 163 can be prevented from being crushed. The method is favorable for avoiding the backflow of cement slurry after the completion of well cementation slurry replacement, and further can ensure the well cementation quality.

The cementing operation is performed by the above-described liner string 100 as follows.

First, the tailpipe string 100 is assembled in accordance with the structure shown in fig. 1. It should be noted here that prior to accessing the choke 140, it is ensured that the tailpipe string is not grouted, thereby ensuring that the enclosed space between the choke 140 and the float shoe 160 of the assembled tailpipe string 100 is filled with the weighting fluid (air).

The entire liner string 100 is then run into the well. Grout may be injected into the tailpipe string 100 during the run in process. At this time, the tailpipe string 100 upstream of the choke reducer 140 may be filled with drilling fluid. This helps to apply pressure to the tailpipe string 100 so that it can be run into the well smoothly. Because the closed space between the resistance reducer 140 and the float shoe 160 is filled with the weight reducing fluid, the friction between the tail pipe string 100 and the horizontal well section of the horizontal well is small, and the running-in process of the tail pipe string 100 can be smoothly carried out.

After the tail pipe string 100 is placed to the designed position, the tail pipe string 100 is pressed to 9-10Mpa, the hanging operation of the tail pipe hanger 120 is completed, and then the hanging test and releasing operation are completed according to the operation rules of the conventional hanger.

Thereafter, the pressure is continuously held to 25-30MPa to disconnect the first shear pin 144 of the resistance reducer 140. The column pump is pressed back to 0 MPa. By this operation, the connection between the inner tube 143 and the middle tube 142 of the resistance reducing device 140 can be disconnected. Since the inner pipe 143 is filled with drilling fluid under pressure and the outer pipe 141 downstream of the inner pipe 142 is filled with air, the inner pipe 143 moves downstream (i.e., to the right in fig. 3) under the action of the pressure difference, i.e., the inner pipe is switched from the first state to the second state. After the inner tube 143 moves to the position where the recess of the second tube 143B is overlapped (aligned) with the stopper 145, the stopper 145 is pressed into the recess and pressed out of the positioning groove 141A of the outer tube 141. At this time, the connection between the middle tube 142 and the outer tube 141 is disconnected. Meanwhile, the flow holes 147 can be misaligned with the sidewall of the middle pipe body 142 due to the downstream movement of the inner pipe body 143, and thus the inner space of the inner pipe body 141 can communicate with the inner space of the downstream outer pipe body 141. Thereby, the closed space between the choke 140 and the float shoe 160 disappears and the drilling fluid can flow downstream from the choke 140.

Grouting is continued until the pressure in the tailpipe string 100 is 6-7MPa, so that the second shear pin 166 of the float shoe 160 is disconnected and the column pump is pumped back to 0 MPa. By this operation, the connection between the outer sleeve 164 and the inner stopper 165 of the pressure-containing mechanism is disconnected, and thereby the inner stopper 165 is moved downstream, and the inner space of the outer sleeve 164 is cleared, allowing the drilling fluid to flow from upstream to downstream.

Therefore, the whole tail pipe string 100 is communicated with the inside and the outside, and can perform circulating operation to discharge air in the tail pipe string 100. For example, after a cycle is established, a minimum of one and a half cycles.

After the circulating pump pressure is stable, a pressure-holding ball can be put into the tail pipe string 100. The hold down ball can fall into the ball seat 137 of the plug assembly 130. Thereby, the pressure is suppressed to 5-6MPa, so that the third shear pin 136 is sheared off. Thereby, the connection between the second plug member and the first plug member is broken, carrying the ball seat 137 along with it to move downstream and engage the middle tube 142 of the choke reducer 140. The second rubber plug member continues to push the middle tube body 142 and the inner tube body 141 of the choke stopper 140 together to move downstream until the anti-rotation teeth at the downstream end of the middle tube body 142 engage the anti-rotation support tray 154 of the float collar 150.

Then, the pressure is continuously held to 9-10MPa, so that the fourth shear pin 138 is disconnected. This operation disconnects ball seat 137 from second barrel 134 and ball seat 137 moves downstream to reestablish the cycle.

For example, after not less than one and a half cycles, the liner string 100 is grouted.

Then, the drill rod rubber plug 200 is thrown from the wellhead and the slurry replacement operation is carried out. The drill rod plug 200 moves downstream under the action of the displacement fluid until it reaches and is compounded with the first plug member. The composite pump pressure may be, for example, 10 to 12 MPa. At this time, the fifth shear pin 133 is sheared.

And continuously replacing the slurry, so that the combined drill rod rubber plug 200 and the first rubber plug member move downwards until the combined drill rod rubber plug 200 and the second rubber plug member are engaged and pressed, and the slurry replacing operation is completed. At this time, the tail pipe string 100 is in the state shown in fig. 6.

And finally, the well is lifted out and sent into the drilling tool 110, and the well is closed and the well is cured, so that the whole well cementing operation is completed.

The tailpipe string 100 described above is particularly useful in deep horizontal wells and extended reach wells. The floating weight of the tail pipe string 100 can be effectively reduced through the weight reducing fluid (air) in the tail pipe string 100, so that the positive pressure of the tail pipe string on the borehole wall is reduced, the purpose of reducing the running friction of the tail pipe string is achieved, and the effect of quickly and safely running the tail pipe string is finally achieved.

In addition, the inner pipe 143 and the middle pipe 142 of the choke reducer 140 can be effectively cleaned after the tail pipe string 100 is put in place by the arrangement of the second rubber plug member. This ensures that the drill pipe plug 200 can be smoothly lowered to the float collar 150 during subsequent slurry replacement operations.

In addition, the arrangement of the anti-rotation teeth and the anti-rotation support tray 154 can effectively prevent the inner pipe body 143 and the middle pipe body 142 from blocking the water hole of the float collar, and meanwhile, the flow area can be increased, and the well cementation quality is improved. In addition, the drillability of the inner pipe body 143 and the middle pipe body 142 after the cementing is finished can be effectively ensured, and the drilling and plugging cost is reduced. For this purpose, corresponding anti-rotation mechanisms can also be constructed on the drill rod rubber plug 200, the first rubber plug member and the second rubber plug member.

While the invention has been described with reference to a preferred embodiment, various modifications may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In particular, the technical features mentioned in the embodiments can be combined in any way as long as there is no structural conflict. It is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A tailpipe string comprising a flow reducer and a float shoe disposed downstream of the flow reducer, the flow reducer and the float shoe being configured such that, in a first state, an enclosed space is formed between the flow reducer and the float shoe, a weight-reducing fluid being contained within the enclosed space.

2. The tailpipe string according to claim 1, wherein the choke reducing means comprises:

an outer tube body connected with the tail tube string parts of the upstream and downstream,

a middle tube body sleeved in the outer tube body and tightly matched with the outer tube body, and

the inner pipe body is sleeved in the middle pipe body and is tightly matched with the middle pipe body, the inner pipe body comprises a cylindrical side wall and a bottom wall closing the side wall at the downstream of the side wall, and a flow hole penetrating through the side wall is formed in the side wall;

wherein in a first state, the flow holes are aligned with the side walls of the middle tube body such that the side walls of the middle tube body close the flow holes,

in a second state, the inner pipe body is moved relative to the middle pipe body until the flow hole is not aligned with the side wall of the middle pipe body, and the flow hole is communicated with the inner pipe body and the outer pipe body.

3. The tailpipe string according to claim 2,

positioning grooves are formed on the inner surface of the side wall of the outer tube body,

a limiting groove penetrating through the side wall is formed on the side wall of the middle pipe body,

the inner pipe body is sleeved in the middle pipe body and connected with the middle pipe body through a first shearing pin, the inner pipe body comprises a first pipe body part positioned at the upstream of the flow hole, the outer surface of the side wall of the first pipe body part can be attached to the inner surface of the side wall of the middle pipe body, the inner pipe body of the first pipe body part further comprises a second pipe body part positioned at the upstream of the first pipe body part, and a concave part which is concave relative to the outer surface of the side wall of the first pipe body part is constructed on the outer surface of the side wall of the second pipe body part,

the resistance reducer further includes a stopper disposed between the outer pipe body and the inner pipe body and inserted into the restriction groove,

wherein, in a first state, the positioning groove, the restricting groove and the first tubular body portion are aligned, the stopper is inserted into the positioning groove and the restricting groove against by a side wall of the first tubular body portion,

in a second condition, the first shear pin shears, the inner pipe body moves downstream relative to the middle pipe body until a recess in the second pipe body portion is aligned with the locating groove and the restraining groove, and the stop moves out of the locating groove and into the recess.

4. The tailpiece string according to claim 3, wherein the upstream facing surface of the stopper is configured to be inclined outwardly and/or the downstream facing surface of the stopper is configured to be inclined outwardly, the shape of the positioning groove and the limiting groove being configured to match the shape of the stopper.

5. The tailpipe string according to any one of claims 1 to 4, wherein the float shoe comprises:

a shell body, a plurality of first connecting rods and a plurality of second connecting rods,

a one-way valve housed within the housing, the one-way valve configured to allow passage of fluid only in an upstream to downstream direction; and

a pressure-bearing mechanism located downstream of the one-way valve, the pressure-bearing mechanism comprising,

an outer sleeve sleeved in the shell and tightly matched with the side wall of the shell, wherein a blocking part extending inwards along the radial direction is constructed at the upstream end of the outer sleeve, and

the sleeve is sleeved with an inner stop block, the inner stop block is tightly matched with the outer sleeve and connected together through a second shearing pin, the upstream end of the inner stop block is constructed to be capable of abutting against the blocking part, and the inner stop block is constructed with a baffle plate which extends to the inner space of the outer sleeve along the transverse direction and can seal the inner space of the outer sleeve.

6. The liner string according to any one of claims 1 to 5, further comprising a plug assembly disposed upstream of the choke reducer, the plug assembly comprising:

the outer surface of the side wall of the first cylinder is provided with a first rubber plug which is tightly matched with the pipe string wall of the tail pipe string, and the upstream end of the first cylinder is connected with the tail pipe hanger through a fifth shearing pin;

the outer surface of the side wall of the second cylinder body is provided with a second rubber plug which is tightly matched with the tube string wall of the tail tube string, and the upstream end of the second cylinder body is connected with the downstream end of the first cylinder body through a third shearing pin; and

and the ball seat is sleeved in the second cylinder and is connected with the second cylinder through a fourth shear pin.

7. The tailpipe string according to claim 6, wherein the ball seat comprises a receiving portion for receiving a pressure build-up ball, and a first through hole formed downstream of the receiving portion and extending through a side wall of the ball seat in a radial direction,

the rubber plug component further comprises a tray, the tray is located at the downstream of the ball seat, the tray extends along the transverse direction and is fixedly connected with the side wall of the second barrel, and a second through hole penetrating through the tray along the longitudinal direction is formed in the tray;

wherein the ball seat is movable downstream and captured by the tray after the fourth shear pin shears, the first and second through-holes allowing fluid flow through the second barrel.

8. The liner string according to claim 6 or 7, wherein the first rubber plug is an anti-rotation rubber plug.

9. The tailpipe string according to any one of claims 1 to 8, further comprising a float collar disposed between the choke reducer and the float shoe.

10. The tailpipe string according to claim 9, wherein the upstream end of the float collar is configured with anti-rotation trays and the downstream end of the drag reducer is configured with corresponding anti-rotation teeth.