CN209083268U - Flow channel switching device and gravel filling pipe column thereof - Google Patents

Abstract

The application discloses runner conversion equipment and gravel packing tubular column thereof, wherein, runner conversion equipment includes: an outer tube assembly; the outer pipe assembly is provided with a central flow passage and a wall clamping flow passage; the outer wall of the outer pipe assembly is provided with an overflowing hole communicated with the wall clamping flow passage; a sliding valve tube; the sliding valve tube can move along the length direction of the outer tube assembly; the pipe wall of the sliding valve pipe is provided with a communicating hole; a ball seat for bearing a plugging ball is arranged on the inner wall of the sliding valve pipe below the communicating hole; wherein the slide valve tube has a first position and a second position below the first position; when the sliding valve pipe is positioned at the first position, the communication hole is blocked; when the sliding valve pipe is located at the second position, the communication hole communicates the double-walled flow passage with the central flow passage, and the overflowing hole is blocked. The flow passage switching device and the gravel packing tubular column thereof switch the flow passage direction through simple operation.

Description

Flow channel switching device and gravel filling pipe column thereof

Technical Field

The application relates to a flow passage switching device and a gravel packing tubular column thereof, which can be used for acid washing operation of the gravel packing tubular column in a sand production well of an oil field.

Background

Sand production from a well can cause abrasion and damage to downhole equipment, surface equipment, and tools (e.g., pumps, separators, heaters, pipelines), and can also cause plugging of the well bore, reduce or force shut-down of the well. Therefore, the selection of a reasonable sand control completion technology is very important for the development and exploitation work of the oil and gas field.

Compared with other sand control technologies, gravel packing sand control has the advantages of good sand control effect, long soil working life and the like. Therefore, the gravel pack completion technology is the preferred mode for developing sand-prone reservoirs with oil and gas wells. In the well completion operation, open hole gravel packing sand control is more economical, a reservoir is not damaged by cement slurry, stratum sand migration can be effectively prevented, a low-permeability zone close to a well hole is prevented from being formed by ten stratum sand migration, meanwhile, the stratum can be supported, the well wall is prevented from collapsing, the annulus between the gravel packing stratum and the sieve tube can block the stratum sand, the rush to the sieve tube is reduced, and the service life of the sieve tube is prolonged.

At present, the operation of flow channel switching during the acid washing operation of the gravel packing pipe column is complex, and the flow channel communicating vessel in the pipe column generally needs to be replaced. Therefore, a simple and reliable flow channel switching device is needed to switch the flow channels of the fluid.

SUMMERY OF THE UTILITY MODEL

The utility model aims at providing a runner conversion equipment and gravel packing tubular column thereof, when can carry out the borehole operation under the normal condition, can also when needing to carry out the pickling operation, through succinct operation, switch the runner trend, realize the pickling operation.

The technical scheme of the application is as follows:

a flow channel switching device comprising:

an outer tube assembly; the outer pipe assembly is provided with a central flow passage and a wall clamping flow passage; the lower end of the double-wall flow passage is communicated with the lower part of the outer pipe assembly; the outer wall of the outer pipe assembly is provided with an overflowing hole communicated with the wall clamping flow passage;

a sliding valve tube disposed within the outer tube assembly forming a portion of the central flow passage; the sliding valve tube can move along the length direction of the outer tube assembly; the pipe wall of the sliding valve pipe is provided with a communicating hole; a ball seat for bearing a plugging ball is arranged on the inner wall of the sliding valve pipe below the communicating hole; wherein,

the slide valve tube has a first position and a second position below the first position; when the sliding valve pipe is positioned at the first position, the communication hole is blocked; when the sliding valve pipe is located at the second position, the communication hole communicates the double-walled flow passage with the central flow passage, and the overflowing hole is blocked.

As a preferred embodiment, the outer tube assembly comprises an outer sleeve; the outer sleeve is sleeved outside the sliding valve pipe; a part of the double-walled flow passage is formed between the outer sleeve and the sliding valve pipe; the communication hole is positioned on the outer sleeve;

part of the tube wall of the sliding valve tube protrudes outwards along the radial direction to form a convex part which is attached to the inner wall of the outer sleeve; when the sliding valve pipe is positioned at the first position, the convex part is positioned above the communication hole; when the sliding valve pipe is located at the second position, the bulge blocks and blocks the overflowing hole.

As a preferred embodiment, the cross section of the boss is annular; the bulge part is provided with a through flow channel which penetrates through the outer pipe assembly along the length direction of the outer pipe assembly; the through flow channel forms part of the double-wall flow channel; when the sliding valve pipe is located at the second position, the through flow passage communicates the upper part and the lower part of the sliding valve pipe.

As a preferred embodiment, the device further comprises a limiting member; the limiting piece can limit the sliding valve pipe at the second position.

As a preferred embodiment, the inner wall of the outer tube assembly is further provided with a receiving groove; the limiting piece comprises an elastic ring positioned in the accommodating groove; when the sliding valve pipe is positioned at the first position, the elastic ring is sleeved outside the sliding valve pipe; the elastic ring is positioned above the sliding valve tube and contracts in the radial direction when the sliding valve tube is positioned at the second position.

In a preferred embodiment, the elastic ring is an open circular ring.

As a preferred embodiment, the outer tube assembly further comprises an upper joint, a connecting tube; the connecting pipe is connected between the upper joint and the outer sleeve; a step part is arranged on the inner wall of the connector; the accommodating groove is formed between the lower end of the upper joint and the step part.

As a preferred embodiment, the outer tube assembly further comprises a lower tube; the lower pipe is coaxially provided with a central through hole; the central through hole forms part of the central flow passage; the pipe wall of the lower pipe is provided with a connecting channel forming part of the wall clamping flow passage; the connecting channel is communicated between the outer sleeve and the sliding valve pipe; the connecting passage forms an opening at a lower end of the lower tube.

As a preferred embodiment, the inner wall of the outer tube assembly is provided with a limiting step; the sliding valve pipe is in contact with the limiting step when located at the second position; the sliding valve pipe cannot move downwards continuously when contacting the limiting step.

In a preferred embodiment, the outer wall of the sliding valve pipe is provided with a shearing pin; the sliding valve tube moves to the second position after the shear pin is sheared.

In a preferred embodiment, the upper end of the outer sleeve is connected to the lower end of the connecting pipe through an internal thread, and the lower end of the outer sleeve is connected to the upper end of the lower pipe through an internal thread.

A gravel packing string comprising: a flow channel switching device as claimed in any preceding embodiment.

Has the advantages that:

the flow channel conversion device in the embodiment can solve the problem that the flow channel switching of the fluid in the tubular column is complex during the acid washing operation of the gravel packing tubular column, effectively promotes the progress of the whole construction operation, and has the advantages of simple and convenient operation, high efficiency, low cost and good acid washing effect.

Specific embodiments of the present invention are disclosed in detail with reference to the following description and the accompanying drawings, which specify the manner in which the principles of the invention may be employed. It should be understood that the embodiments of the present invention are not so limited in scope. The embodiments of the invention include many variations, modifications and equivalents within the spirit and scope of the appended claims.

Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments, in combination with or instead of the features of the other embodiments.

It should be emphasized that the term "comprises/comprising" when used herein, is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps or components.

Drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive exercise.

FIG. 1 is a schematic view of a flow passage switching device with a sliding valve tube in a first position according to the present disclosure;

fig. 2 is a schematic view of the slide valve tube of fig. 1 in a second position.

Detailed Description

In order to make those skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments in the present application, shall fall within the scope of protection of the present invention.

It will be understood that when an element is referred to as being "disposed on" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and the like as used herein are for illustrative purposes only and do not represent the only embodiments.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Please refer to fig. 1 and fig. 2. The embodiment of the present application provides a flow channel switching device, including: outer tube assembly 100, sliding valve tube 200. Wherein the outer tube assembly 100 is provided with a central flow passage 101 and a double-walled flow passage 150; the lower end of the double-walled flow passage 150 is communicated with the lower part of the outer pipe assembly 100; the outer wall of the outer tube assembly 100 is provided with an overflowing hole 11 which leads into the double-walled flow passage 150.

The sliding valve tube 200 is disposed within the outer tube assembly 100 and forms part (of the length) of the center flow passage 101. The sliding valve tube 200 is movable along the length of the outer tube assembly 100. A communicating hole 205 is formed in the wall of the sliding valve tube 200; a ball seat 203 for receiving the blocking ball 110 is provided on the inner wall of the sliding valve tube 200 below the communication hole 205.

Wherein the slide valve tube 200 has a first position and a second position below the first position; when the slide valve tube 200 is in the first position, the communication hole 205 is blocked; when the slide valve tube 200 is in the second position, the communication hole 205 communicates the double-walled flow passage 150 with the center flow passage 101, and the overflowing hole 11 is blocked.

During normal operation using the flow path switching device, fluid enters the gravel pack string, enters the center flow path 101, passes through the slide valve tube 200, and is discharged downhole. After entering the double-walled flow passage 150, the liquid at the bottom of the well is discharged outwards through the overflowing hole 11 on the outer pipe assembly 100, enters the outer annular space of the pipe column and is pumped out of the well.

During the pickling operation, a plugging ball 110 (which may also be referred to as a pickling ball) is put into the column. The ball 110 is seated on the ball seat 203 and is sealed off via the central flow passage 101. The blow-down occurs outside the well, causing the sliding valve tube 200 to slide from the first position to the second position. When the pickling solution enters the column, it enters the central flow channel 101 above the plugging ball 110, and then enters the double-walled flow channel 150 through the communication hole 205. Since the overflow hole 11 is now blocked, the pickling solution cannot flow out of the column through the overflow hole 11, but only flows down the double-walled flow channel 150 and finally into the bottom of the well.

It can be seen that the flow channel switching device in the embodiment solves the problem of switching of the flow channels in the gravel packing string during the acid washing operation of the gravel packing string, effectively improves the progress of the whole construction operation, and has the advantages of simple and convenient operation, high efficiency, low cost and good acid washing effect.

The outer tube assembly 100 includes an outer sleeve 10. Wherein, the outer sleeve 10 and the sliding valve tube 200 are straight tube structures. The outer sleeve 10 is sleeved outside the sliding valve tube 200. The outer sleeve 10 and the sliding valve tube 200 form a part of the double-walled flow passage 150 therebetween. The communication hole 205 is located on the outer sleeve 10. The communication hole 205 radially penetrates the wall of the outer tube 10 to communicate the inside and outside of the outer tube 10. The communication hole 205 may be provided with two or more. The plurality of communication holes 205 are uniformly distributed on the wall of the outer sleeve 10 along the circumferential direction of the outer sleeve 10.

In the present embodiment, a part of the tube wall of the slide valve tube 200 protrudes outward in the radial direction to form a convex portion 201 which is attached to the inner wall of the outer sleeve 10. When the slide valve tube 200 is in the first position, the projection 201 is located above the communication hole 205. When the sliding valve tube 200 is located at the second position, the protrusion 201 blocks and seals the overflowing hole 11. The protrusion 201 may be a block body, and the shielding area thereof only needs to be larger than the area of the communication hole 205.

Specifically, the cross section of the boss 201 is annular. The boss 201 is provided with a through flow passage 202 that penetrates the outer tube assembly 100 in the longitudinal direction thereof. The through flow passage 202 forms part of the double-walled flow passage 150. When the slide valve tube 200 is located at the second position, the through flow path 202 communicates the upper and lower portions thereof. When the slide valve pipe 200 is in the first position, the through flow path 202 is positioned above the communication hole 205.

As shown in fig. 1 and 2, the outer diameter of the sliding valve tube 200 above the boss 201 and the outer diameter of the portion below the boss 201 are smaller than the outer diameter of the boss 201. The ball seat 203 is located below the communication hole 205. The ball seat 203 is a stepped structure formed by reducing an inner diameter, and the blocking ball 110 cannot pass through the ball seat 203. When the blocking ball 110 is dropped on the ball seat 203, blocking the central flow passage 101 at the position of the ball seat 203, an uphole blow may drive the sliding ball seat 203 from the first position to the second position.

To facilitate positioning of the slide valve tube 200, the flow passage switching device may further include a stopper. The limiting member can limit the position of the sliding valve tube 200 at the second position. The position-limiting member may be an elastic element, wherein the position-limiting member may have an elastic force that contracts in the radial direction.

As shown in fig. 1 and 2. The inner wall of the outer tube assembly 100 is also provided with a receiving groove. The retaining member comprises an elastic ring 15 located in the receiving recess. When the sliding valve tube 200 is located at the first position, the elastic ring 15 is sleeved outside the sliding valve tube 200. When the slide valve tube 200 is located at the second position, the elastic ring 15 is located above the slide valve tube 200 and is contracted in the radial direction.

In the present embodiment, when the slide valve tube 200 is located at the second position, the elastic ring 15 is contracted to the normal state, and the elastic ring 15 is located above the slide valve tube 200 to restrain the slide valve tube 200. The elastic ring 15 is located in the receiving groove so as not to move with the sliding valve tube 200.

In the present embodiment, the outer diameter of the sliding valve tube 200 is larger than the inner diameter of the elastic ring 15 in the normal state, so that the sliding valve tube 200 radially expands the elastic ring 15 when in the first position, so that the elastic ring 15 is sleeved outside the sliding valve tube 200. When the sliding valve tube 200 is in the first position, the elastic ring 15 tightens the sliding valve tube 200, thereby positioning the sliding valve tube 200 and preventing the sliding valve tube 200 from moving in the outer tube assembly 100. Specifically, the elastic ring 15 is an open circular ring.

Specifically, the outer tube assembly 100 further includes an upper joint 20 and a connecting tube 30. The connection tube 30 is connected between the upper joint 20 and the outer tube 10. And a step part is arranged on the inner wall of the connector. The receiving groove is formed between the lower end of the upper joint 20 and the stepped portion.

In this embodiment, the upper end of the upper joint 20 is provided with external threads to connect the upper assembly. The internal thread (female snap) of the upper end of the connection pipe 30 connects the external thread of the lower end of the upper joint 20. The upper joint 20 and the inside of the connection pipe 30 form a part of the center flow passage 101. The wall thickness of the upper joint 20 and the connecting pipe 30 is greater than that of the outer sleeve 10.

In the present embodiment, the elastic ring 15 is caught in the annular receiving groove between the stepped portion and the lower end of the upper joint 20. The inner wall of the upper end of the sliding valve tube 200 is provided with a guide slope (not shown). The inner diameter of the guide inclined plane is gradually reduced when the guide inclined plane extends from top to bottom. The introduction of the blocking ball 110 from the upper connector 20 into the sliding valve tube 200 is facilitated by the presence of the lead-in ramp.

In this embodiment, the outer tube assembly 100 further includes a down tube 40. The lower tube 40 is coaxially provided with a central through hole 41. The central through hole 41 forms part of the central flow passage 101. The lower tube 40 has a connecting channel 42 on the wall thereof to form part of the double-walled flow passage 150. The connecting channel 42 opens between the outer sleeve 10 and the sliding valve tube 200. The connecting passage 42 is opened at the lower end of the lower tube 40.

Specifically, the lower tube 40 may be provided with a plurality of connecting channels 42 on the tube wall in the circumferential direction; the connecting passage 42 forms a plurality of openings at the upper end face of the lower tube 40 and a plurality of openings at the lower end (face) of the lower end (e.g., a plurality of circular holes at the inner slope of the lower end in fig. 1 and 2). The lower end of the central through hole 41 is provided with a female (internal) thread for connection to a lower tubular string.

The inner wall of the outer tube assembly 100 is provided with a limiting step 43. The slide valve tube 200 is in contact with the limit step 43 when located at the second position. The slide valve tube 200 cannot move down further when contacting the limit step 43. When the slide valve tube 200 is located at the second position, the lower end surface thereof may contact the limiting step 43 to be limited. Through being equipped with spacing step 43, can remind the outer slide valve pipe 200 of well in order to remove to the second position, be convenient for carry out work next step. Meanwhile, the sliding valve pipe 200 is prevented from moving down excessively to damage the tool.

To prevent the sliding valve tube 200 from moving in advance and causing the failure of switching the flow passage. The outer wall of the sliding valve pipe 200 is provided with a shear pin 204. The sliding valve tube 200 moves to the second position after the shear pin 204 is sheared. Wherein shear pin 204 is located above downtube 40. When slide valve tube 200 is in the first position, shear pin 204 is positioned above lower tube 40 and contacts the upper end face of lower tube 40. When the shear pin 204 is pressed out of the well to the shear pressure of the shear pin 204, the shear pin 204 on the slide valve tube 200 is cut off by the upper end face of the lower tube 40 and then moved downward.

The upper end of the outer sleeve 10 is connected to the lower end of the connection pipe 30 through an internal thread. The lower end of the outer sleeve 10 is connected to the upper end of the lower pipe 40 by internal threads. The boss 201 of the slide valve tube 200 moves between the connection tube 30 and the lower tube 40. The outer wall of the lower end of the sliding valve pipe 200 is provided with a sealing ring which seals between the sliding valve pipe 200 and the lower pipe 40 to prevent liquid leakage.

In assembling the flow path switching device according to the present embodiment, the elastic ring 15 is first placed on the step portion of the inner wall of the connection pipe 30. The upper connector 20 is then coupled to the female terminal of the coupling pipe 30 to form a receiving groove for receiving the elastic ring 15. The end of the slide valve tube 200 having the lead slope is inserted into the connection tube 30 from the bottom to the top, and the elastic ring 15 is opened by the slide valve tube 200. At this time, the slide valve tube 200 is also inserted into the connection tube 30, and the connection tube 30 is abutted against the boss portion 201 of the slide valve tube 200. The shear pin 204 is installed in an installation hole formed in the outer wall of the slide valve tube 200. The outer jacket tube 10 is then connected to the connecting tube 30 by a pin joint, and finally the lower tube 40 is screwed to the outer jacket tube 10. It can be seen that the flow channel switching device provided by the embodiment is very convenient to assemble.

Refer to fig. 1 and 2. The two working states of the flow channel switching device provided by the embodiment during operation are as follows:

in a normal operation state: as shown in fig. 1, after entering the column, the liquid first flows into the sliding valve tube 200 through the inner hole of the upper joint 20, then flows through the central through hole 41 (inner hole) of the lower tube 40, then flows back to the connecting channel 42 of the lower tube 40 through the bottom hole, enters the cavity (part of the wall-sandwiched channel) between the outer sleeve 10 and the sliding valve tube 200 through the connecting channel 42 of the lower tube 40, and then flows out of the column through the overflowing hole 11 on the outer wall of the outer sleeve 10.

In the pickling operation state: as shown in fig. 2, after the plugging ball 110 is thrown, the outside of the well is pressurized. The shear pin 204 is sheared and the slide valve tube 200 moves downward and eventually snaps over the stop step 43 of the central bore 41 of the lower tube 40. The original stretched elastic ring 15 recovers the original size and is clamped at the front section of the sliding valve tube 200 to limit the sliding valve tube 200. When the pickling solution enters the column and enters the slide valve tube 200 through the inner hole of the upper joint 20, the solution flows into the cavity between the outer sleeve 10 and the slide valve tube 200 through the communication hole 205 through which the slide valve tube 200 moves backward, enters the double-walled channel, the overflowing hole 11 on the side wall of the outer sleeve 10 is blocked and blocked by the downward movement of the boss 201 of the slide valve tube 200, and therefore the solution flows into the connecting channel 42 of the lower tube 40 through the through flow passage 202 on the slide valve tube 200, and finally enters the bottom hole.

In summary, the present embodiment has the following advantages:

(1) the structure is simple and reliable, and is not easy to damage;

(2) the field operation is simple, the working hours are saved, the flow channel switching can be completed only by putting the acid-washing ball (the blocking ball 110) and pressing the shearing pin 204 during the operation, and the production cost and the labor intensity of workers are reduced;

(3) the implementation mode solves the problem of switching of the fluid flow channels in the tubular column during the acid washing operation of the gravel packing tubular column, effectively improves the progress of the whole construction operation, and has the advantages of simple and convenient operation, high efficiency, low cost and ideal effect.

There is also provided in an embodiment of the present application a gravel pack string comprising: a flow channel switching device as claimed in any preceding embodiment.

Any numerical value recited herein includes all values from the lower value to the upper value that are incremented by one unit, provided that there is a separation of at least two units between any lower value and any higher value. For example, if it is stated that the number of a component or a value of a process variable (e.g., temperature, pressure, time, etc.) is from 1 to 90, preferably from 20 to 80, and more preferably from 30 to 70, it is intended that equivalents such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 are also expressly enumerated in this specification. For values less than 1, one unit is suitably considered to be 0.0001, 0.001, 0.01, 0.1. These are only examples of what is intended to be explicitly recited, and all possible combinations of numerical values between the lowest value and the highest value that are explicitly recited in the specification in a similar manner are to be considered.

Unless otherwise indicated, all ranges include the endpoints and all numbers between the endpoints. The use of "about" or "approximately" with a range applies to both endpoints of the range. Thus, "about 20 to about 30" is intended to cover "about 20 to about 30", including at least the endpoints specified.

All articles and references disclosed, including patent applications and publications, are hereby incorporated by reference for all purposes. The term "consisting essentially of …" describing a combination shall include the identified element, ingredient, component or step as well as other elements, ingredients, components or steps that do not materially affect the basic novel characteristics of the combination. The use of the terms "comprising" or "including" to describe combinations of elements, components, or steps herein also contemplates embodiments that consist essentially of such elements, components, or steps. By using the term "may" herein, it is intended to indicate that any of the described attributes that "may" include are optional.

A plurality of elements, components, parts or steps can be provided by a single integrated element, component, part or step. Alternatively, a single integrated element, component, part or step may be divided into separate plural elements, components, parts or steps. The disclosure of "a" or "an" to describe an element, ingredient, component or step is not intended to exclude other elements, ingredients, components or steps.

It is to be understood that the above description is intended to be illustrative, and not restrictive. Many embodiments and many applications other than the examples provided will be apparent to those of skill in the art upon reading the above description. The scope of the present teachings should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications, are hereby incorporated by reference for all purposes. The omission in the foregoing claims of any aspect of the subject matter that is disclosed herein is not intended to forego such subject matter, nor should the inventors be construed as having contemplated such subject matter as being part of the disclosed inventive subject matter.

Claims (12)

1. A flow channel switching device, comprising:

an outer tube assembly; the outer pipe assembly is provided with a central flow passage and a wall clamping flow passage; the lower end of the double-wall flow passage is communicated with the lower part of the outer pipe assembly; the outer wall of the outer pipe assembly is provided with an overflowing hole communicated with the wall clamping flow passage;

a sliding valve tube disposed within the outer tube assembly forming a portion of the central flow passage; the sliding valve tube can move along the length direction of the outer tube assembly; the pipe wall of the sliding valve pipe is provided with a communicating hole; a ball seat for bearing a plugging ball is arranged on the inner wall of the sliding valve pipe below the communicating hole; wherein,

the slide valve tube has a first position and a second position below the first position; when the sliding valve pipe is positioned at the first position, the communication hole is blocked; when the sliding valve pipe is located at the second position, the communication hole communicates the double-walled flow passage with the central flow passage, and the overflowing hole is blocked.

2. The flow channel switching device of claim 1, wherein: the outer tube assembly comprises an outer sleeve; the outer sleeve is sleeved outside the sliding valve pipe; a part of the double-walled flow passage is formed between the outer sleeve and the sliding valve pipe; the communication hole is positioned on the outer sleeve;

part of the tube wall of the sliding valve tube protrudes outwards along the radial direction to form a convex part which is attached to the inner wall of the outer sleeve; when the sliding valve pipe is positioned at the first position, the convex part is positioned above the communication hole; when the sliding valve pipe is located at the second position, the bulge blocks and blocks the overflowing hole.

3. The flow channel switching device of claim 2, wherein: the cross section of the bulge part is annular; the bulge part is provided with a through flow channel which penetrates through the outer pipe assembly along the length direction of the outer pipe assembly; the through flow channel forms part of the double-wall flow channel; when the sliding valve pipe is located at the second position, the through flow passage communicates the upper part and the lower part of the sliding valve pipe.

4. The flow channel switching device according to claim 2 or 3, wherein: the device also comprises a limiting piece; the limiting piece can limit the sliding valve pipe at the second position.

5. The flow channel switching device of claim 4, wherein: the inner wall of the outer pipe assembly is also provided with an accommodating groove; the limiting piece comprises an elastic ring positioned in the accommodating groove; when the sliding valve pipe is positioned at the first position, the elastic ring is sleeved outside the sliding valve pipe; the elastic ring is positioned above the sliding valve tube and contracts in the radial direction when the sliding valve tube is positioned at the second position.

6. The flow channel switching device of claim 5, wherein: the elastic ring is an open circular ring.

7. The flow channel switching device of claim 5, wherein: the outer pipe assembly further comprises an upper joint and a connecting pipe; the connecting pipe is connected between the upper joint and the outer sleeve; a step part is arranged on the inner wall of the connecting pipe; the accommodating groove is formed between the lower end of the upper joint and the step part.

8. The flow channel switching device of claim 7, wherein: the outer tube assembly further comprises a lower tube; the lower pipe is coaxially provided with a central through hole; the central through hole forms part of the central flow passage; the pipe wall of the lower pipe is provided with a connecting channel forming part of the wall clamping flow passage; the connecting channel is communicated between the outer sleeve and the sliding valve pipe; the connecting passage forms an opening at a lower end of the lower tube.

9. The flow channel switching device of claim 8, wherein: the inner wall of the outer pipe assembly is provided with a limiting step; the sliding valve pipe is in contact with the limiting step when located at the second position; the sliding valve pipe cannot move downwards continuously when contacting the limiting step.

10. The flow channel switching device of claim 1, wherein: the outer wall of the sliding valve pipe is provided with a shearing pin; the sliding valve tube moves to the second position after the shear pin is sheared.

11. The flow channel switching device of claim 8, wherein: the upper end of the outer sleeve is connected with the lower end of the connecting pipe through internal threads, and the lower end of the outer sleeve is connected with the upper end of the lower pipe through internal threads.

12. A gravel pack string, comprising: a flow channel switching device according to any of claims 1 to 11.