An expandable tubular casing hanger

Abstract

The present application relates to an expansion pipe type casing hanger, comprising a casing assembly and an inner pipe assembly located in the casing assembly, the casing assembly comprising an expansion pipe with a reduced diameter section, the inner pipe assembly comprising an expansion cone for expanding the reduced diameter section to seat the casing assembly, a hanger structure being provided between the casing assembly and the inner pipe assembly below the expansion cone for hanging the casing assembly on the inner pipe assembly, the hanger structure comprising a key and a slot for hanger cooperation with the key, one of the key and the slot being provided on the casing assembly and the other being provided on the inner pipe assembly, the key having a stop position for stop cooperation with the slot in the axial direction of the casing assembly and a release position for releasing the stop by being circumferentially offset from the slot when the inner pipe assembly is lowered and rotated. The present application solves the technical problem of the prior art that the weight of the casing assembly is limited, and the hanger structure can be released by lowering and rotating the inner pipe assembly, without increasing the operation difficulty too much.

Description

TECHNICAL FIELD

[0001] The present application relates to an expansion pipe type casing hanger, belonging to the technical field of oil and gas well workover. BACKGROUND

[0002] Casing workover refers to lowering a small casing with a smaller inner diameter than the existing damaged casing into the existing damaged casing, suspending the small casing in the well section where the damaged casing is located by means of a hanger, and sealing the small casing from the damaged casing by means of a plugging agent, so as to establish a new intact wellbore. The core tool used in this technology is a casing hanger, among which the expansion pipe type hanger has the advantages of larger inner diameter after completion and port sealing, and its application degree has been continuously improved in recent years.

[0003] In the prior art, a utility model patent with the authorization announcement number CN201486494U discloses an expansion pipe hanger connecting device, which is composed of an expansion pipe, an expansion cone, an expansion cone connecting rod, a hanger short section, a release short section, a sand setting cylinder and a bottom plug. The expansion pipe and the hanger short section connected below the expansion pipe form a casing assembly for lowering into an oil well, the expansion pipe has a reduced diameter section, and the entire casing assembly is suspended on the expansion cone through the reduced diameter section of the expansion pipe. The upper part of the expansion cone connecting rod is used for connecting a drill rod or a tubing, and the expansion cone is fixed on the lower end of the expansion cone connecting rod through a ring. When the casing assembly is lowered into a set well section, the expansion cone connecting rod is lifted, and the expansion cone is lifted in the process, which will expand the expansion pipe, and the expanded outer wall of the expansion pipe will be pressed and fitted with the existing casing on the outside. The expansion cone connecting rod and the expansion cone thereon form an inner pipe assembly located in the casing assembly and used for expanding the expansion pipe. Then, a plugging agent is filled in the annulus between the casing assembly and the existing casing, and the casing assembly is fixed in the oil well.

[0004] The expansion pipe hanger connecting device suspends the casing assembly below through the tapered surface of the inner wall of the expansion pipe, and when the weight of the casing assembly suspended below is large, the expansion cone will move upward relative to the expansion pipe to overcome the resistance, expand the expansion pipe, and cause the casing to be seated and sealed before reaching the set well section, resulting in a downhole accident. Therefore, the expansion pipe hanger connecting device has the technical problem of limited weight of the suspended casing. SUMMARY

[0005] The present application aims to provide an expansion pipe type casing hanger to solve the technical problem of limited weight of the suspended casing in the prior art.

[0006] The present application adopts the following technical solutions:

[0007] The application discloses an expansion pipe type casing hanger, which comprises a casing assembly and an inner pipe assembly located in the casing assembly, wherein the casing assembly comprises an expansion pipe with a reduced diameter section, the inner pipe assembly comprises an expansion cone for expanding the reduced diameter section to enable the casing assembly to be sealed, a hanger structure is arranged between the casing assembly and the inner pipe assembly below the expansion cone and is used for hanging the casing assembly on the inner pipe assembly, the hanger structure comprises a key and a slot used for matching with the key, one of the key and the slot is arranged on the casing assembly, and the other is arranged on the inner pipe assembly, the key has a stop position matched with the slot in the axial direction of the casing assembly and a release position which is circumferentially staggered with the slot when the inner pipe assembly is lowered and rotated to release the stop, and the side wall of the slot is matched with the key in the circumferential direction of the casing assembly to prevent the casing assembly and the inner pipe assembly from releasing the stop when being relatively rotated

[0008] The casing assembly is hung on the hanger structure in the stop position, and the casing assembly is not hung on the reduced diameter section of the expansion pipe alone, so that a casing assembly with a larger weight can be hung, and a downhole accident caused by early sealing can be avoided.

[0009] Further, the key is arranged on the inner wall of the casing assembly, the outer wall of the inner pipe assembly is provided with a protruding block, and the slot is arranged on the protruding block.

[0010] Further, the key and the protruding block are arranged in two or more groups in the circumferential direction, respectively, an avoiding channel for the key is formed between two adjacent protruding blocks, and the width of the avoiding channel is slightly larger than the width of the key.

[0011] Further, the cross section of the protruding key is a rectangle with length extending in the up-down direction, the slot is a U-shaped slot matching the protruding key, and the slot width is slightly larger than the width of the protruding key. The protruding key is in the shape of a rectangle, and the slot is a U-shaped slot matching the protruding key, which ensures reliable hanging and facilitates insertion of the protruding key into the slot.

[0012] Further, the casing assembly comprises a connecting nipple connected to the lower end of the expansion pipe and a small casing connected to the lower end of the connecting nipple, and the protruding key or the slot arranged on the casing assembly is located on the connecting nipple. The hanging structure is arranged by additionally arranging a connecting nipple, and the structure of the existing small casing and expansion cone can be unchanged.

[0013] Further, the inner pipe assembly comprises an expansion nipple and a tension nipple connected to the lower end of the expansion nipple, and the expansion cone is fixed on the expansion nipple, and the protruding key or the slot arranged on the inner pipe assembly is located on the tension nipple. By additionally connecting a tension nipple, the structure of the existing expansion cone and expansion nipple can be unchanged.

[0014] Further, the expansion cone is installed on the expansion nipple from bottom to top, and the tension nipple is threadedly connected to the lower end of the expansion nipple. Without changing the structure of the existing expansion cone and expansion nipple, the tension nipple is installed on the lower end of the expansion nipple in a threaded manner to avoid the influence of the tension nipple on the installation of the expansion cone.

[0015] Further, the lower end of the expansion pipe and the upper end of the connecting nipple, the lower end of the connecting nipple and the upper end of the small casing are connected through threaded structures, and the threaded structures between the expansion pipe and the connecting nipple and between the connecting nipple and the small casing have the same screw direction; the upper end of the expansion nipple is provided with an upper joint for threadedly connecting with the oil pipe nipple, and the lower end of the expansion nipple and the tension nipple are connected through a threaded structure, the screw direction of the threads of the upper joint and the threads between the expansion nipple and the tension nipple is the same, and the screw direction of the threads of the upper joint and the threaded structure between the expansion pipe and the connecting nipple is the same. Since the casing hanger needs to overcome the resistance below by rotating to continue descending during the process of lowering into the oil well, the threaded structures between the adjacent two structures of the casing assembly and the inner pipe assembly are arranged to have the same screw direction, which can avoid loosening between the adjacent two structures of the casing assembly and the inner pipe assembly during the rotating process.

[0016] Further, the inflatable tube type casing hanger comprises a plug assembly for displacing the plugging agent in the casing assembly and the inner tube assembly, the plug assembly comprises a large plug connected to the lower end of the inner tube assembly, the large plug is a hollow cylinder, the plug assembly further comprises a small plug for embedding into the cavity of the large plug from top to bottom, the small plug is used for displacing the plugging agent in the inner tube assembly during embedding of the large plug from top to bottom, the large plug is used for displacing the plugging agent in the casing assembly after embedding of the small plug, the large plug and the small plug constitute a sealing structure for sealing the casing assembly to prevent backflow of the plugging agent. After completion of the well repair grouting, the plug assembly is used to displace the plugging agent in the inner tube assembly and the casing assembly, so as to avoid waste and pollution of the plugging agent, and the plug assembly prevents backflow of the plugging agent.

[0017] Further, the large plug is connected to the lower end of the inner tube assembly through a shear pin, the large plug is disconnected from the shear pin and moves downward after embedding of the small plug, the lower end of the casing assembly is connected to a flow limiting ring, the large plug is provided with a self-locking ring which is clamped into the flow limiting ring when the large plug moves downward to the position of the flow limiting ring, so as to realize sealing and fixing of the large plug and the small plug at the bottom of the casing assembly, and the bottom of the casing assembly is sealed. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a structural schematic view of the inflatable tube before expansion in embodiment 1 of the inflatable tube type casing hanger of the present application;

[0019] Figure 2 is a structural schematic view of the inflatable tube after expansion in embodiment 1 of the inflatable tube type casing hanger of the present application;

[0020] Figure 3 is Figure 1 is a schematic view of A-A cross section when the key and the slot are in the blocking position in embodiment 1 of the inflatable tube type casing hanger of the present application;

[0021] Figure 4 is Figure 3 is a schematic view of cooperation of three groups of keys and slots in embodiment 1 of the inflatable tube type casing hanger of the present application;

[0022] Figure 5 is Figure 1 is a schematic view of A-A cross section when the key and the slot are in the releasing position in embodiment 1 of the inflatable tube type casing hanger of the present application;

[0023] Figure 6 is Figure 5 is a schematic view of cooperation of three groups of keys and slots in embodiment 1 of the inflatable tube type casing hanger of the present application;

[0024] In the figure: 1, casing; 2, small plug; 3, tubing spool; 4, inflatable tube; 5, inflatable spool; 6, sealing element; 7, inflatable cone; 8, tension spool; 9, connecting spool; 10, pin; 11, small casing; 12, large plug; 13, flow limiting ring; 14, cementing accessory; 15, plugging agent; 16, key; 17, slot; 18, avoiding passage. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not intended to limit the present application, i.e., the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. The components of the embodiments of the present application generally described and shown in the accompanying drawings can be arranged and designed in various different configurations.

[0026] Therefore, the detailed description of the embodiments of the present application provided below in the accompanying drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative efforts fall within the scope of the present application.

[0027] It should be noted that the relationship terms such as "first" and "second" and the like that can appear are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any actual relationship or order between the entities or operations. Moreover, terms such as "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitations, the elements defined by the statement "including a" and the like do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0028] The features and performances of the present application are further described in detail below in combination with embodiments.

[0029] A specific embodiment 1 of the present application is an expandable-tube-type casing hanger, as shown in Figures 1-6 which includes an outer casing assembly and an inner pipe assembly located in the casing assembly, and a hanging structure is provided between the casing assembly and the inner pipe assembly for suspending the outer casing assembly on the inner pipe assembly, the casing assembly is supported by the hanging structure, when the inner pipe assembly needs to be pulled out of the casing assembly, the hanging structure is released from the hanging state, the inner pipe assembly is pulled up, the inner pipe assembly expands the casing assembly outward during the pulling-up process, and the casing assembly is seated in the oil well.

[0030] The casing assembly comprises an expansion pipe 4, a connecting nipple 9 and a small casing 11, the lower end of the expansion pipe 4 is provided with an internal thread, the upper end of the connecting nipple 9 is provided with an external thread matched with the internal thread of the lower end of the expansion pipe 4, the lower end of the connecting nipple 9 is provided with an internal thread, the upper end of the small casing 11 is provided with an external thread, and the small casing 11 is inserted into the lower end of the connecting nipple 9 and is threadedly connected with the connecting nipple 9. The expansion pipe 4 comprises a large-diameter section at the lower end and a necked section above the large-diameter section, the internal diameter of the necked section is smaller than that of the large-diameter section, and a sealing element is fixed on the outer wall of the necked section, the necked section is pressed against the sealing element after being radially expanded, the casing assembly is sealed with the existing casing 1 in the oil well, and the casing assembly is seated in the oil well.

[0031] The inner pipe assembly comprises an expansion nipple 5, an expansion cone 7 and a tension nipple 8. The upper end of the expansion nipple 5 is provided with an upper joint and an expansion cone mounting section, the upper joint is provided with an internal thread, and a tubing nipple 3 is connected to the upper joint through the internal thread, and the upper end of the tubing nipple 3 is used for connecting with a tubing or a drill pipe. The outer wall of the expansion cone mounting section is provided with an external thread, the expansion cone is screwed on the expansion cone mounting section from bottom to top, and the tension nipple is screwed on the lower end of the expansion nipple, i.e. the upper end of the tension nipple is provided with an internal thread matched with the external thread of the expansion cone mounting section.

[0032] The hanging structure comprises a key 16 and a slot 17 for matching with the key, the key 16 is arranged on the inner wall of the connecting nipple 9, the outer wall of the tension nipple 8 is provided with a radially protruding lug, the cross section of the lug is rectangular, the slot 17 is arranged on the upper side of the rectangular lug, the cross section of the key 17 is a rectangle with the length extending along the up-down direction, the slot 17 is a U-shaped slot matched with the key, and the width of the U-shaped slot is slightly larger than the width of the key.

[0033] In the embodiment, the lug and the key 16 are one-to-one corresponding, and three of each are uniformly and circumferentially arranged, and an avoiding channel 18 for the key to pass through in the axial direction is formed between the two adjacent lugs, and the width of the avoiding channel 18 is slightly larger than the width of the key. When the key 16 is inserted into the slot 17 in the axial direction, the key 16 is in a blocking position, the key 16 is axially blocked with the slot 17, and the hanging matching of the key 16 and the slot 17 realizes that the casing assembly is hung on the inner pipe assembly. At the same time, the side wall of the slot circumferentially blocks the key 16, avoids the key from being taken out of the slot when the inner pipe assembly rotates, and realizes that the inner pipe assembly drives the casing assembly to rotate; when the inner pipe assembly is lowered and rotated, the key 16 is taken out of the slot 17 and circumferentially deviated from the slot, at this time, the key is in a releasing position, so that the key can pass through the avoiding channel, the key and the slot are disengaged, and then the inner pipe assembly is lifted, the expansion cone is expanded to make the casing assembly seated.

[0034] In the embodiment, the lower end of the casing assembly is connected with the flow limiting ring 13 and the cementing accessory 14, which is a one-way valve structure. During cementing, the cementing agent, i.e. the cement slurry, is injected downward from the upper end of the inner tube assembly, and the one-way valve ensures that the cementing agent can only flow downward into the space between the casing assembly and the outer casing, and the cementing agent below the one-way valve cannot flow back into the inner tube assembly.

[0035] After the cementing agent is injected, a part of the cementing agent remains in the inner tube assembly and the casing assembly. The inflatable tube type casing hanger of the embodiment further comprises a rubber plug assembly for displacing the cementing agent in the casing assembly and the inner tube assembly. The rubber plug assembly comprises a large rubber plug 12 and a small rubber plug 2. The large rubber plug 12 is connected to the lower end of the inner tube assembly by the shear pin 10, and the large rubber plug 12 is a hollow cylinder. After the injection of the cementing agent is completed, the small rubber plug 2 is lowered from the upper end of the inner tube assembly. During the lowering process, the cementing agent in the inner tube assembly is extruded downward. The outer wall of the lower end of the small rubber plug is provided with a self-locking ring. When the small rubber plug is moved downward and embedded in the inner cavity of the large rubber plug, the self-locking ring on the small rubber plug is clamped in the large rubber plug, and the large rubber plug and the small rubber plug are sealingly connected. Then, the large rubber plug and the small rubber plug are moved downward together to extrude the cementing agent in the casing assembly downward into the space between the casing assembly and the outer casing, until the self-locking ring on the large rubber plug is clamped into the flow limiting ring 13, and the large rubber plug and the small rubber plug are fixed at the bottom of the casing assembly to prevent the cementing agent from flowing back into the casing assembly.

[0036] In the embodiment, in order to avoid thread loosening during the rotation of the inner tube assembly and the casing assembly, the rotation directions of the thread structures between the adjacent two sections of the inner tube assembly and the casing assembly are the same, so as to avoid reverse buckling and thread loosening.

[0037] In the actual use of the inflatable tube type casing hanger, the running string is threadedly connected with the tubing spool 3, wherein the running string is a tubing or a drill pipe. Then, the inflatable tube type casing hanger is lowered to the designated hanging position, and the inflatable tube type casing hanger is rotated during the lowering process to ensure that the small casing 11 is centered. During the lowering process, the key 16 is always located in the slot 17 and seated on the protrusion. The torque is transmitted through the circumferential blocking cooperation between the key and the slot, so as to rotate the inner tube assembly to drive the casing assembly.

[0038] After the expansion pipe type casing hanger is run to the designated hanging position, a specified amount of cement slurry is pumped into the pipe string by a cement truck, then a small rubber plug 2 is dropped into the inner pipe assembly, displacement fluid is pumped into the pipe string by a pump truck, and the small rubber plug 2 is made to tightly adhere to the pipe wall and run downward by hydraulic action, when the pump pressure is increased, it is indicated that the self-locking ring of the small rubber plug 2 has entered the annular step in the large rubber plug 12, the inner part of the casing assembly is sealed, the pump pressure is continuously increased until the pump pressure suddenly drops, indicating that the shear pin 10 between the load-bearing nipple 8 and the large rubber plug 12 is sheared, the pump pressure is increased again, and the composite rubber plug composed of the small rubber plug 2 and the large rubber plug 12 runs downward, the self-locking ring of the large rubber plug 12 is set in the annular step in the flow resistance ring 13, and the pressure bumping, sealing and self-locking are completed, at this time, the blocking agent 15 in the small casing 11 is completely displaced from the cementing accessory 14 into the annular space outside the small casing 11, and the pipe string can be rotated multiple times during or after the cementing process to improve the cementing quality.

[0039] After the cementing is completed, the inner pipe assembly is lowered, the insertion slot 17 of the load-bearing nipple 8 is aligned with the protruding key 16 inside the connecting nipple 9, the load-bearing nipple 8 is rotated by a certain angle, the avoidance channel 18 of the load-bearing nipple 8 is aligned with the protruding key 16 inside the connecting nipple 9, and the inner pipe assembly becomes a free state, as shown in Figure 5 and 6 The pump pressure is continuously increased, the displacement fluid forms a hydraulic piston force between the load-bearing nipple 8 and the expansion pipe 4, the expansion cone 7 is pushed upward, the expansion pipe 4 is expanded, the sealing element 6 on the expansion pipe 4 is firmly anchored on the original oil layer casing 1, and the expansion operation is completed after the pump pressure suddenly drops, the pipe string is pulled up, and the tubing nipple 3, the expansion nipple 5, the expansion cone 7 and the load-bearing nipple 8 are pulled out, so that the small casing 11 is hung.

[0040] As another embodiment of the present application, different from embodiment 1, the connecting nipple and the load-bearing nipple can not be provided, at this time, the protruding block and the protruding key are arranged on the inner wall of the expansion pipe and the outer wall of the expansion nipple respectively.

[0041] As another embodiment of the present application, different from embodiment 1, the protruding block is not arranged on the load-bearing nipple, but an insertion slot and an avoidance channel are directly arranged on the outer wall of the load-bearing nipple, at this time, the overall outer diameter size of the load-bearing nipple is larger.

[0042] As another embodiment of the present application, different from embodiment 1, the positions of the protruding block and the protruding key are interchanged, that is, the protruding key is arranged on the load-bearing nipple, and the protruding block is arranged on the connecting nipple, at this time, the opening of the insertion slot faces downward.

[0043] As another embodiment of the present application, different from embodiment 1, the number of the protruding block and the protruding key can be self-set according to the diameter size of the casing assembly and the inner pipe assembly, in order to ensure the hanging stability, the number of the protruding block and the protruding key should be arranged to be more than two and uniformly distributed in the circumferential direction.

[0044] The above merely illustrates the preferred embodiments of the present application, and is not used to limit the present application. The patent protection scope of the present application is defined by the claims, and any equivalent structural changes made according to the content of the specification and drawings of the present application should also be included in the protection scope of the present application.

Claims

1. An expandable tubular casing hanger comprising a casing assembly and an inner tube assembly located within the casing assembly, the casing assembly comprising an expandable tubular (4) having a reduced diameter section, the inner tube assembly comprising an expansion cone (7) for expanding the reduced diameter section to seat the casing assembly, characterised in that, The hanging structure is arranged between the sleeve assembly and the inner tube assembly below the expansion cone (7) and is used for hanging the sleeve assembly on the inner tube assembly, the hanging structure comprises a protruding key (16) and a slot (17) used for hanging cooperation with the protruding key (16), one of the protruding key (16) and the slot (17) is arranged on the sleeve assembly, and the other is arranged on the inner tube assembly, the protruding key (16) has a blocking position which is in axial blocking cooperation with the slot (17) along the sleeve assembly and a release position which is circumferentially staggered with the slot (17) when the inner tube assembly is lowered and rotated to release the blocking, the side wall of the slot (17) is in circumferential blocking cooperation with the protruding key (16) along the sleeve assembly to prevent the sleeve assembly and the inner tube assembly from releasing the blocking when relatively rotating, the protruding key (16) is arranged on the inner wall of the sleeve assembly, the protruding block is arranged on the outer wall of the inner tube assembly, and the slot (17) is arranged on the protruding block, the protruding key (16) and the protruding block are respectively arranged with more than two in circumferential intervals, the adjacent two protruding blocks form an avoiding channel (18) for the protruding key (16) to pass through, and the width of the avoiding channel (18) is slightly larger than the width of the protruding key (16) to facilitate the passing of the protruding key.

2. The swellable tubular casing hanger of claim 1, wherein, The protruding key (16) is in rectangular cross section with the length extending along the up-down direction, and the slot (17) is a U-shaped slot matched with the protruding key (16), and the slot width of the slot (17) is slightly larger than the width of the protruding key (16).

3. The swellable tubular casing hanger of claim 1, wherein, The sleeve assembly comprises a connecting nipple (9) connected to the lower end of the expansion pipe (4) and a small sleeve (11) connected to the lower end of the connecting nipple (9), and the protruding key (16) arranged on the sleeve assembly is arranged on the connecting nipple (9).

4. The swellable tubular casing hanger of claim 3, wherein, The inner tube assembly comprises an expansion nipple (5) and a tension nipple (8) connected to the lower end of the expansion nipple (5), and the expansion cone (7) is fixed on the expansion nipple (5), and the slot (17) arranged on the inner tube assembly is arranged on the tension nipple (8).

5. The swellable tubular casing hanger of claim 4, wherein, The expansion cone (7) is installed on the expansion nipple (5) from bottom to top, and the tension nipple (8) is threadedly connected to the lower end of the expansion nipple (5).

6. The swellable tubular casing hanger of claim 4, wherein, The lower end of the expansion pipe (4) and the upper end of the connecting nipple (9), and the lower end of the connecting nipple (9) and the upper end of the small sleeve (11) are connected through threaded structures, and the threaded structures between the expansion pipe (4) and the connecting nipple (9) and between the connecting nipple (9) and the small sleeve (11) have the same screw direction; the upper end of the expansion nipple (5) is provided with an upper joint used for threadedly connecting with the oil pipe nipple (3), the lower end of the expansion nipple (5) and the tension nipple (8) are connected through a threaded structure, the threads of the upper joint and the threads between the expansion nipple (5) and the tension nipple (8) have the same screw direction, and the threads of the upper joint and the threaded structures between the expansion pipe (4) and the connecting nipple (9) have the same screw direction.

7. The swellable tubular casing hanger of any of claims 1-6, wherein, The inflation pipe type casing hanger includes a plug assembly for displacing the plug in the casing assembly and the inner tube assembly, the plug assembly includes a large plug (12) connected to the lower end of the inner tube assembly, the large plug (12) is a hollow cylinder, the plug assembly further includes a small plug (2) for embedding into the cavity of the large plug (12) from top to bottom, the small plug (2) is used for displacing the plug in the inner tube assembly during embedding into the large plug (12) from top to bottom, the large plug (12) is used for displacing the plug in the casing assembly after embedding of the small plug (2), the large plug (12) and the small plug (2) constitute a sealing structure for sealing the casing assembly to prevent backflow of the plug below.

8. The swellable tubular casing hanger of claim 7, wherein, The large plug (12) is connected to the lower end of the inner tube assembly by a shear pin, the large plug (12) breaks the shear pin and moves downward after embedding of the small plug (2), the lower end of the casing assembly is connected to a flow limiting ring, the large plug (12) is provided with a self-locking ring which is clamped into the flow limiting ring when the large plug (12) moves downward to the position of the flow limiting ring.

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