CN219864944U - Underground throttle - Google Patents

Abstract

The utility model discloses an underground throttle, which comprises a cylinder assembly and a nozzle, wherein the nozzle is arranged at one end of the cylinder assembly, the nozzle is provided with a nozzle opening, the inner diameter of the nozzle opening is gradually increased along the axial direction of the nozzle, the nozzle opening comprises an inner port, an outer port and a round chamfer inner wall, and the round chamfer inner wall is arranged between the inner port and the outer port. The circumferential side shape of the nozzle opening is set to be inverted round, so that the impact of solid phase particles on the wall surface can be slowed down, the maximum erosion rate can be reduced, great help is provided for alleviating erosion, and the erosion resistance is superior to that of a straight cylindrical nozzle.

Description

Underground throttle

Technical Field

The utility model relates to the technical field of throttling devices, in particular to an underground throttling device.

Background

The choke can set up a minor diameter nozzle in the one end near the shaft bottom, and the pressure can reduce when gas passes through the choke, reaches the effect of throttle depressurization. When the ultrahigh-pressure sulfur-containing gas passes through the throttle, the gas can carry solid particles, and the solid particles obtain larger kinetic energy to impact the inner wall surface of the tool when passing through the throttle, so that the material locally generates stress concentration, plastic deformation and microcracks are caused, and the material is damaged in volume due to the action of high-frequency alternating impact load.

Disclosure of Invention

The present utility model aims to solve at least one of the technical problems existing in the prior art. Therefore, the utility model provides the underground throttle, the internal structure of the throttle is optimized around the nozzle, and the influence on erosion of the inner wall of the throttle in the ultra-high pressure sulfur-containing environment is relieved.

A downhole choke according to an embodiment of the first aspect of the utility model comprises:

a barrel assembly;

the nozzle is arranged at one end of the barrel assembly, the nozzle is provided with a nozzle opening, the inner diameter of the nozzle opening is gradually increased along the axial direction of the nozzle, the nozzle opening comprises an inner port, an outer port and a round chamfer inner wall, and the round chamfer inner wall is arranged between the inner port and the outer port.

The downhole choke according to the embodiment of the first aspect of the utility model has at least the following beneficial effects: the circumferential side shape of the nozzle opening is set to be inverted round, so that the impact of solid phase particles on the wall surface can be slowed down, the maximum erosion rate can be reduced, great help is provided for alleviating erosion, and the erosion resistance is superior to that of a straight cylindrical nozzle.

According to an embodiment of the first aspect of the present utility model, the downhole choke comprises a fixed sleeve, a nozzle sleeve and a connecting piece, wherein the fixed sleeve is arranged at one end of the barrel assembly, the nozzle and the nozzle sleeve are both arranged in the fixed sleeve, the nozzle sleeve is arranged at the periphery of the nozzle, and the connecting piece penetrates through the fixed sleeve and the nozzle sleeve to fix the nozzle.

According to an embodiment of the first aspect of the utility model, the material of the nozzle is alloy steel 08Cr2AlMo.

According to the downhole choke in the first aspect of the embodiment of the utility model, the cylinder assembly comprises an outer cylinder, an inner cylinder and a central cylinder, wherein the outer cylinder, the inner cylinder and the central cylinder are sequentially arranged along the axial direction, the inner cylinder is arranged between the outer cylinder and the central cylinder, the fixed sleeve is arranged on the central cylinder, and the central cylinder is communicated with the nozzle.

According to an embodiment of the first aspect of the present utility model, the material of the central cylinder is nickel-based alloy Incoloy945.

According to an embodiment of the first aspect of the utility model, a first seal is provided between the stationary sleeve and the central barrel, and a second seal is provided between the stationary sleeve and the nozzle.

According to the downhole choke provided by the embodiment of the first aspect of the utility model, a sand prevention cover is arranged on the periphery of the nozzle, and the sand prevention cover is arranged on the fixed sleeve.

According to the downhole choke of the embodiment of the first aspect of the utility model, a fishing head is arranged at the other end of the cylinder assembly, which is opposite to the sand prevention cover.

According to an embodiment of the first aspect of the present utility model, the downhole choke comprises a fixing mechanism, the fixing mechanism comprises a clamping block, an elastic piece and a base, the base is arranged on the inner cylinder, a hole for the clamping block to extend is formed in the outer cylinder, the clamping block is movably arranged on the base and suitable for extending from the hole, and the elastic piece is arranged between the clamping block and the base.

According to the downhole choke in the first aspect of the utility model, the clamping block comprises at least two feet, each foot is arranged on the base, and the elastic piece is sleeved on each foot.

Additional aspects and advantages of the utility model will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the utility model.

Drawings

The utility model is further described below with reference to the drawings and examples;

FIG. 1 is a schematic diagram of an embodiment of the present utility model;

FIG. 2 is an enlarged view of A in FIG. 1;

FIG. 3 is an enlarged view of B in FIG. 1;

fig. 4 is a gas-solid two-phase erosion cloud diagram with a nozzle opening in a round chamfer shape and r1=2mm in the embodiment of the utility model;

fig. 5 is a gas-solid two-phase erosion cloud diagram with a nozzle opening in a round chamfer shape and r2=4mm in the embodiment of the utility model;

fig. 6 is a gas-solid two-phase erosion cloud diagram with a nozzle opening in a round chamfer shape and r1=8mm in the embodiment of the utility model;

fig. 7 is a gas-solid two-phase erosion cloud diagram with a nozzle opening in a right-angled shape, h1=4mm, θ1=45° chamfer angle in the embodiment of the utility model;

fig. 8 is a gas-solid two-phase erosion cloud diagram with a nozzle opening in a right-angled shape, h2=4mm, θ2=60° chamfer angle in the embodiment of the utility model;

FIG. 9 is a gas-solid two-phase erosion cloud with a nozzle opening in a straight line in an embodiment of the utility model;

fig. 10 is a solid phase particle concentration cloud with nozzle openings rounded and angular, r1=2mm in an embodiment of the utility model;

fig. 11 is a solid phase particle concentration cloud with nozzle openings rounded and angular, r2=4mm in an embodiment of the utility model;

fig. 12 is a solid phase particle concentration cloud with nozzle openings rounded and angular, r1=8mm in an embodiment of the utility model;

fig. 13 is a solid phase particle concentration cloud with nozzle openings in a right angled shape, h1=4mm, θ1=45° chamfer in an embodiment of the utility model;

fig. 14 is a solid phase particle concentration cloud with nozzle openings in a right angled shape, h2=4mm, θ2=60° chamfer in an embodiment of the utility model;

FIG. 15 is a solid particle concentration cloud with a straight nozzle opening in an embodiment of the utility model.

Reference numerals:

1-salvaging head, 2-outer cylinder, 3-inner cylinder, 4-central cylinder, 5-fixture block, 6-elastic piece, 7-base, 8 feet, 9 first sealing piece, 10-sand prevention cover, 11-nozzle sleeve, 12-fixed sleeve, 13-nozzle and 14-connecting piece.

Detailed Description

Embodiments of the present utility model are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative only and are not to be construed as limiting the utility model.

In the description of the present utility model, it should be understood that references to orientation descriptions such as upper, lower, front, rear, left, right, etc. are based on the orientation or positional relationship shown in the drawings, are merely for convenience of description of the present utility model and to simplify the description, and do not indicate or imply that the apparatus or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present utility model.

In the description of the present utility model, a number means one or more, a number means at least two, and more than, less than, exceeding, etc. are understood to not include the present number, and above, below, within, etc. are understood to include the present number. The description of the first and second is for the purpose of distinguishing between technical features only and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of the technical features indicated.

In the description of the present utility model, unless explicitly defined otherwise, terms such as arrangement, installation, connection, etc. should be construed broadly and the specific meaning of the terms in the present utility model can be reasonably determined by a person skilled in the art after combining the specific contents of the technical solutions.

Referring to fig. 1 to 3, the downhole choke of the embodiment of the first aspect of the present utility model is installed at a suitable position downhole, and can perform the functions of throttling and depressurization, and simultaneously, the temperature is reduced to effectively prevent the generation of hydrate, so as to ensure the production safety of a gas well. The downhole choke includes a barrel assembly and a nozzle 13.

Wherein nozzle 13 sets up the one end at the barrel subassembly, and nozzle 13 has the nozzle opening, along the internal diameter of the axial nozzle opening of nozzle 13 progressively increases, and the nozzle opening includes interior port, outer port and round chamfer inner wall, and round chamfer inner wall sets up between interior port and outer port. By setting the peripheral side shape of the nozzle opening to be a rounded shape, the impact of solid phase particles on the wall surface can be slowed down, and the maximum erosion rate can be reduced, which is greatly helpful for alleviating erosion, and the erosion resistance thereof is superior to that of the straight cylindrical nozzle 13.

The erosion failure of the nozzle 13 generally starts in the maximum erosion area and gradually spreads to the periphery. And the formation of the maximum erosion area is related to the speed and the number of impacts of the solid phase particles against the wall. The maximum erosion rate may be related to the trajectory of the solid phase particles. If the movement track of the solid phase particles can be changed by changing the internal structure of the restrictor, the impact of the solid phase particles on the wall surface is slowed down, the maximum erosion rate can be reduced, and great help is provided for alleviating erosion. The change of the flow field caused by the abrupt change of the cross section at the inlet of the nozzle 13 causes the solid phase particles to intensively strike the wall surface. The flow field is influenced by the shape of the nozzle 13, the erosion influence on the wall surface is studied in consideration of changing the shape of the inlet, and the nozzles 13 with different inlet shapes are designed below to comprise a linear nozzle 13, a round chamfer nozzle 13 and a square chamfer nozzle 13.

Referring to fig. 4 to 15, models of the inlet shapes of the different nozzles 13 are created, and the same parameters are set by dividing the grids for analysis of erosion of particles in the fluid. Wherein the differential pressure Δp=105 MPa (inlet-outlet pressure: 120mpa→15 MPa), the particle diameter d=0.5 mm of the linear nozzle 13, the particle initial flow velocity v=20 m/s, the mass flow m=100×10-5kg/s, 1000 steps are calculated. And drawing a cloud picture of each flow field parameter by taking a tangent plane along the central axis. Wherein, the rounded nozzle 13 is set with three kinds of r1=2mm, r2=4mm, r3=8mm, the rounded nozzle 13 is set with two kinds of h1=4mm, θ1=45°, h2=4 mm, θ2=60°. Setting calculation parameters: the inlet pressure is 120MPa, the outlet pressure is 15MPa, the initial flow rate of the solid particles at the inlet is 20m/s, the diameter is 0.5mm, and the mass flow is 100 multiplied by 10 < -5 > kg/s. The impact angle function setting is consistent with the previous analysis simulation, and 1000 steps are calculated. And observing the obtained particle erosion cloud picture, and judging the erosion rate of the particles to the wall surface by using the cloud picture.

Specifically, gas-solid two-phase erosion cloud diagrams of throttles with different inlet shapes of the nozzle 13 are shown in fig. 4-9, and solid-phase particle concentration cloud diagrams of throttles with different inlet shapes of the nozzle 13 are shown in fig. 10-15.

Referring to the particle concentration distribution cloud of the straight nozzle 13, the particle concentration upstream of the nozzle 13 is much higher than the particle concentration downstream of the nozzle 13, and the particle concentration in the area near the wall upstream of the nozzle 13 is larger than that in the central area. This may be due to the change in pipe diameter cross section, where particles impact the wall to accumulate and then surge toward the orifice outlet. Due to the change of the section, the flow field fluctuates greatly, and solid particles are driven by gas to enter the small holes and then move in an arc manner to collide with the wall surface of the nozzle 13, and then rebound and continuously advance to be converged towards the center. The concentration of solid particles is similar to the velocity and pressure distribution, with the concentration being lower in the region of the nozzle 13 near the wall than in the central region. Further, observing the erosion rate cloud of the straight nozzle 13, the erosion area mainly occurs at the stage of the nozzle 13, and the maximum erosion rate reaches 9.40X10-5 kg/(m2.multidot.s). The erosion serious region is mainly concentrated at a certain section of the nozzle 13, and the erosion rate gradually decreases in the downstream direction. As the fluid passes through the nozzle 13 section, the pressure is converted to velocity due to the change in cross-sectional area, the velocity of the fluid and solid particles increases, and the kinetic energy increases. The fluid carries particles to the nozzle 13, and is flushed towards the small hole of the nozzle 13, and after entering the nozzle 13, the particles impact the wall of the nozzle 13 in an arc motion due to the large influence of the fluctuation of the fluid passing through the variable cross section. A large number of particles repeatedly strike the wall surface, and obvious erosion occurs in the area with the largest striking frequency by the particles.

Referring to the solid particle concentration cloud of the inverted rectangular nozzle 13, when the solid particles enter the nozzle 13, the direction is changed to enter along the chamfer direction by passing through the chamfer of the inlet of the nozzle 13. The particles continue to move linearly to strike the wall of the nozzle 13, rebound and then move towards the centre of the nozzle 13, and the track is repeated until the particles leave the section of the nozzle 13. The effect of the magnitude of the chamfer angle on the particle trajectory is also seen, with the greater the chamfer angle, the closer the area of maximum erosion rate is to the outlet end, within a range. Wherein the same applies to the inlet of the rounded nozzle 13, it can be explained that the larger the rounded corners, the closer the area of maximum erosion is to the outlet section. But h1=4 mm, the maximum erosion area of the θ1=45° chamfer is closer to the outlet section than the maximum erosion area of the h2=4 mm, θ2=60° chamfer. Then, since the solid particles of the former have insufficient kinetic energy when they strike the wall surface for the first time, the pressure in the nozzle 13 is converted into velocity, and the kinetic energy of the particles is increased, a hysteresis occurs in the area of maximum erosion, which may be the area of the second or third impact after rebound. The latter impacts the wall surface and reaches sufficient kinetic energy, and impacts the wall surface in a direction inclined by 30 °, and it is difficult to form a large amount of high-frequency impact effect.

Referring to the solid particle concentration cloud of the rounded nozzle 13, after the solid particles enter the nozzle 13 along the rounded corners, the particle distribution is concentrated in the center of the nozzle 13, which is also the reason why the rounded nozzle 13 has a smaller erosion rate and higher erosion resistance. The inverted circular inlet nozzle 13 stably changes the direction of particles, the particles are converged to the center of the nozzle 13 and move along a straight line after transition, the impact of solid particles on the wall surface is relatively uniform, and the impact of high frequency on the wall surface of the nozzle 13 cannot be performed, so that a relatively uniform erosion area is formed.

By integrating the particle concentration distribution diagrams, the nozzles 13 with different inlet shapes have different movement tracks of solid particles and have different erosion effects on the wall surface. The nozzle 13 with the chamfer inlet can divide the movement direction of particles, so that the nozzle cannot be confused and collided at high frequency like a straight line, the nozzle 13 with the chamfer inlet can smoothly transition the movement direction of particles, and the impact of solid phase particles on the wall surface is greatly reduced. From the above analysis, it can be considered that the erosion resistance of the throttle of the inverted circular inlet nozzle 13 is superior to that of the linear inlet nozzle 13 and the throttle of the inverted angular inlet nozzle 13.

From the data obtained by analysis of the above results, the maximum erosion rates of the various inlet-shaped nozzles 13 of table 1-1 below were produced.

TABLE 1-1 maximum erosion Rate of various inlet shape nozzles 13

It will be appreciated that by varying the shape of the inlet of the nozzle 13, the erosion resistance of the restrictor can be optimised by modeling the fluid results as is done. From erosion cloud pictures obtained by flow field analysis of throttlers with different inlet shapes, the nozzle 13 with the chamfer inlet can divide the movement direction of particles, so that the high-frequency collision is not disordered like a straight line, the movement direction of particles can be smoothly transited by the nozzle 13 with the chamfer inlet, and the impact of solid-phase particles on the wall surface is greatly reduced. From the above analysis, it can be considered that the erosion resistance of the throttle of the inverted circular inlet nozzle 13 is superior to that of the linear inlet nozzle 13 and the throttle of the inverted angular inlet nozzle 13.

In some embodiments of the present utility model, with continued reference to fig. 1, the cartridge assembly includes a fixing sleeve 12, a nozzle sleeve 11, and a connection member 14, the fixing sleeve 12 is disposed at one end of the cartridge assembly, the nozzle 13 and the nozzle sleeve 11 are both disposed within the fixing sleeve 12, and the nozzle sleeve 11 is disposed at the outer circumference of the nozzle 13, and the connection member 14 passes through the fixing sleeve 12 and the nozzle sleeve 11 to fix the nozzle 13. It will be appreciated that the fixing sleeve 12 mainly serves to fix the nozzle 13, and the nozzle sleeve 11 is pinned to the fixing sleeve 12 to fix the nozzle 13 within the fixing sleeve 12. Preferably, a second seal is provided between the stationary sleeve 12 and the nozzle 13. Specifically, the nozzle 13 adopts a two-stage step seal, so the inner wall of the fixing sleeve 12 is provided with a three-stage step to fix the nozzle 13 and achieve the sealing effect.

Preferably, the material of the nozzle 13 is alloy steel 08Cr2AlMo. It will be appreciated that in gas well production chokes, the high velocity of the fluid through the nozzle 13, and the high erosion resistance of the nozzle 13, various factors must be taken into account. According to the characteristics of the structure of the nozzle 13, and considering the requirements of the heat resistance and erosion resistance of the nozzle 13, alloy steel 08Cr2AlMo can be selected as the material of the nozzle 13.

In some embodiments of the present utility model, the cartridge assembly includes an outer cartridge 2, an inner cartridge 3, and a central cartridge 4, the outer cartridge 2, the inner cartridge 3, and the central cartridge 4 being disposed in axial sequence with the inner cartridge 3 disposed between the outer cartridge 2 and the central cartridge 4, a stationary sleeve 12 being disposed on the central cartridge 4, and the central cartridge 4 being in communication with the nozzle 13. The periphery of the nozzle 13 is provided with a sand control cover 10, and the sand control cover 10 is arranged on the fixed sleeve 12. Preferably, the other end of the barrel assembly opposite to the sand control cover 10 is provided with a fishing head 1. Preferably, a first seal 9 is provided between the fixed sleeve 12 and the central cylinder 4.

It can be understood that the fishing head 1 is connected with the outer cylinder 2, the outer cylinder 2 is connected with the central cylinder 4, the central cylinder 4 is connected with the fixed sleeve 12 through ladder-shaped threads, and the fixed sleeve 12 is connected with the sand prevention cover 10 through triangle-shaped threads. The fixed sleeve 12 connects the central cylinder 4 and the sand control cover 10, is a part which directly contacts high-pressure gas at the bottom of the well, and then transmits stress to the central cylinder 4. The outer cylinder 2 is a key part in the throttle, the left end of the whole throttle is provided with external threads, the left end of the throttle is connected with the fishing head 1, the right end of the outer cylinder is provided with internal threads, and the outer cylinder is connected with the central cylinder 4, so that the die shape is simplified.

It will be appreciated that during the production of gas well chokes, small amounts of sand will typically flow into the choking device and in severe cases will cause the nozzle 13 to become blocked. Thus, sand control cover 10 may be installed at the bottom of the restriction to prevent sand ingress. To prevent fine particles from entering the nozzle 13, a fine screen may be further installed inside the sand control cover 10.

Preferably, the material of the central cylinder 4 is nickel-based alloy Incoloy945. It is understood that the Incoloy945 alloy (UNS N09945) is suitable for downhole oil and gas applications requiring high strength and corrosion resistance in acid wells with high hydrogen sulfide and chloride content. It also prevents chloride stress corrosion cracking, and has excellent corrosion resistance, reduces chemicals, and helps to resist pitting, crevice corrosion and oxidizing environments. The alloy is resistant to sulfide stress corrosion cracking and stress cracking in an H2S environment, and is completely suitable for key parts of underground throttlers.

In some embodiments of the utility model, the cartridge assembly comprises a securing mechanism comprising a cartridge 5, a resilient member 6 and a base 7, the base 7 being disposed on the inner barrel 3, the outer barrel 2 being provided with a hole through which the cartridge 5 extends, the cartridge 5 being movably disposed on the base 7 and adapted to extend from the hole, the resilient member 6 being disposed between the cartridge 5 and the base 7. Preferably, the clamping block 5 comprises at least two feet 8, each foot 8 is arranged on the base 7, and each foot 8 is respectively sleeved with the elastic piece 6.

It is to be understood that the inner cylinder 3 is provided with 8 screw holes between the outer cylinder 2 and the central cylinder 4 on the inner cylinder 3, the screw holes that set are all used for connecting the base 7, four square holes on the cylinder wall of the outer cylinder 2 are the positions of installing the telescopic clamping block 5, the clamping block 5 that is connected by a spring stretches out from the square hole that sets up on the outer cylinder 2, the clamping block 5 passes through spring connection with the base 7, it is to be understood that the clamping block 5 bears pressure and shearing force in the working process, therefore, in order to ensure the smooth work of the clamping block 5, at least two feet 8 are arranged, and springs are respectively arranged on the feet 8, so that the stress of the clamping block 5 is more stable. Further, a conical groove is further formed in the outer wall of the inner cylinder 3, so that friction force between the outer cylinder 2 and the inner cylinder 3 is increased, and the inner cylinder 3 is prevented from loosening too much.

It should be noted that, the input and setting of the downhole choke according to the embodiment of the first aspect of the present utility model includes the following processes: after the underground throttle is assembled, the clamping block 5 is in a freely telescopic state, the working cylinder is firstly arranged at a position designed in advance for the oil pipe, the working cylinder is connected with the oil pipe and then is put into the well, the throttle is put into the oil pipe through steel wire operation, the throttle is planned to be placed in the preset working cylinder, when the throttle reaches the position of the working cylinder under the action of gravity, the clamping block 5 of the throttle collides with the convex neck part of the working cylinder, the clamping block 5 is extruded towards the inside of the throttle, the spring is compressed, and when the hollow position of the working cylinder is reached, the clamping block 5 is extruded by the outer wall, stretches out of the outer cylinder 2 again under the elasticity of the spring, and is clamped in the working cylinder, so that the throttle is fixed on the working cylinder. Fluid can only pass through the nozzle 13 in the well, thereby achieving a downhole choke, the setting of which is completed.

And (3) fishing: when the well bottom goes out of the state or the throttle breaks down, the fishing tool is lowered to the position of the throttle in the well by using the steel wire rope, after the fishing device clamps the fishing head 1, the steel wire rope is pulled up to shock, the clamping block 5 collides with the 10-degree inclined clamping surface on the inner wall of the working cylinder under the shock, the clamping block 5 is contracted through the extrusion spring after being extruded by the shock, the clamping block 5 is retracted into the outer cylinder 2, and the downhole throttle is fished out under the double effects of bottom hole pressure and pulling force.

The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.

The embodiments of the present utility model have been described in detail with reference to the accompanying drawings, but the present utility model is not limited to the above embodiments, and various changes can be made within the knowledge of one of ordinary skill in the art without departing from the spirit of the present utility model.

Claims (10)

1. A downhole choke, comprising:

a barrel assembly;

the nozzle is arranged at one end of the barrel assembly, the nozzle is provided with a nozzle opening, the inner diameter of the nozzle opening is gradually increased along the axial direction of the nozzle, the nozzle opening comprises an inner port, an outer port and a round chamfer inner wall, and the round chamfer inner wall is arranged between the inner port and the outer port.

2. A downhole choke according to claim 1, wherein: the barrel assembly comprises a fixed sleeve, a nozzle sleeve and a connecting piece, wherein the fixed sleeve is arranged at one end of the barrel assembly, the nozzle and the nozzle sleeve are arranged in the fixed sleeve, the nozzle sleeve is arranged at the periphery of the nozzle, and the connecting piece penetrates through the fixed sleeve and the nozzle sleeve to fix the nozzle.

3. A downhole choke according to claim 1 or 2, wherein: the material of the nozzle is alloy steel 08Cr2AlMo.

4. A downhole choke according to claim 2, wherein: the cylinder assembly comprises an outer cylinder, an inner cylinder and a central cylinder, wherein the outer cylinder, the inner cylinder and the central cylinder are sequentially arranged along the axial direction, the inner cylinder is arranged between the outer cylinder and the central cylinder, the fixed sleeve is arranged on the central cylinder, and the central cylinder is communicated with the nozzle.

5. The downhole choke as set forth in claim 4, wherein: the material of the central cylinder is nickel-based alloy Incoloy945.

6. The downhole choke as set forth in claim 4, wherein: a first sealing piece is arranged between the fixed sleeve and the central cylinder, and a second sealing piece is arranged between the fixed sleeve and the nozzle.

7. The downhole choke as set forth in claim 4, wherein: the periphery of the nozzle is provided with a sand prevention cover, and the sand prevention cover is arranged on the fixed sleeve.

8. The downhole choke as set forth in claim 7, wherein: and a salvaging head is arranged at the other end of the cylinder assembly, which is opposite to the sand prevention cover.

9. The downhole choke as set forth in claim 4, wherein: the cylinder assembly comprises a fixing mechanism, the fixing mechanism comprises a clamping block, an elastic piece and a base, the base is arranged on the inner cylinder, a hole for the clamping block to extend out is formed in the outer cylinder, the clamping block is movably arranged on the base and suitable for extending out from the hole, and the elastic piece is arranged between the clamping block and the base.

10. A downhole choke according to claim 9, wherein: the clamping block comprises at least two feet, each foot is arranged on the base, and the elastic piece is sleeved on each foot respectively.