A double anchor double packer tieback system for staged fracturing string

Abstract

The present invention discloses a double-anchored double-packing tieback system for a staged fracturing pipe string, comprising a first tieback plug, a tieback tube and a second tieback plug. The first tieback plug is provided with a first anchoring device, the first anchoring device comprises a locking slip, one end of the locking slip is provided with a plurality of locking grooves with one end opening and forming a simply supported beam structure, and the locking slip is also provided with a self-locking male buckle; a self-locking female buckle is provided on the inner wall of the tieback tube, the tieback tube is detachably connected to the locking slip through the locking groove of the locking slip, and is locked with the self-locking female buckle and the self-locking male buckle, the lower end of the tieback tube is connected to the lower end pipe string, and the lower end pipe string is provided with an anti-retraction slip and a packer in sequence from top to bottom; the upper end of the second tieback plug is connected to the lower end of the lower end pipe string, and the lower end of the second tieback plug is also anchored and connected with another tieback tube. The present invention adopts a double-anchoring design to realize the standby release and standby packing functions, improve the reliability of tool use, and reduce construction risks.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas well cementing and completion, and in particular to a double-anchor double-isolation tieback system for a staged fracturing pipe string. Background Art

[0002] Many tight oil and gas reservoirs in China are low-porosity, low-permeability gas reservoirs, highly heterogeneous and micro-fracture-developed reservoirs. Some oil and gas layers have the characteristics of multiple layers superimposed in the vertical direction, accompanied by bottom water, complex gas-water relationship, and thin reservoir barrier layer. As a result, when fracturing is used to transform the reservoir, artificial fractures are easy to penetrate the bottom cap layer and communicate with the bottom water, resulting in serious water discharge during production, which is easy to cause the whole wellbore of the horizontal well to be flooded, affecting the production capacity of a single well. In addition, there is also the problem that the horizontal well has been drilled, but the wellbore conditions do not meet the requirements for the entry of the open hole completion string, or the reservoir properties do not meet the technical requirements for the open hole completion transformation. In response to such mining problems, the method of perforating the reservoir transformation after the tail pipe cementing is generally adopted. However, the conventional tail pipe back connection has no anchoring device, and the sealing capacity is generally 25MPa, which cannot solve the uplift force generated by the fracturing construction on the back connection fracturing string and the high-pressure construction sealing requirements, and there are great risks in the construction process. Chinese patent publication number CN109899047A discloses a tieback fracturing method and an anchored removable tieback fracturing wellbore. The specific method is as follows: (1) connect the upper end of the liner hanger with the lower end of the sealing box, connect the upper end of the sealing box with the lower end of the tieback tube, and then lower them into the well; (2) use the liner hanger to cement the well. After the cement solidifies, connect the tieback plug with the tieback casing string, and lower the tieback plug downward to a set position; (3) press down the tieback casing string to insert the tieback plug into the tieback tube, and lock the upper pipe string with the lower liner hanger; (4) perform a wellhead pressure test and stabilize the pressure for a period of time. If there is no pressure drop and the tieback casing string does not rise, it means that the locking and sealing are normal; (5) start the fracturing operation; (6) after the fracturing operation is completed, lift the forward rotation tieback casing string, the tieback plug is separated from the tieback tube, lift the tieback casing string to remove the tieback plug, and the fracturing operation is completed. Although the structure is the same, this tool is prone to blockage during use and cannot be used for normal release operations, making it impossible to retrieve the tieback plug, and when the tieback plug is in an invalid anchoring state, it affects subsequent operations. At present, some blocks use a packer tail pipe hanger containing a tieback tube, hydraulic anchor, intubation packer and casing to the pressure wellbore at the wellhead, but the structure of the tieback pipe string is complex, and there are potential risks such as premature hanging, annular isolation failure and short casing bending and deformation. Summary of the invention

[0003] The purpose of the present invention is to provide a double-anchor double-isolation tieback system for staged fracturing tubing strings in response to the defects of the prior art. The double-anchor design can realize the standby release and standby isolation functions, improve the reliability of tool use, and reduce construction risks; it can solve the technical problems of complex structure, poor sealing and reliability of the tieback pipe string after tail pipe cementing; the tieback pipe string can be recycled and reused after fracturing, thereby improving resource utilization and saving costs; the tieback pipe string has a simple structure, which can ensure the full diameter of the tieback pipe string and the tail pipe string, and meet the large diameter requirements of subsequent production.

[0004] The technical solution of the present invention is: a double-anchor double-isolation tieback system for staged fracturing pipe string, comprising:

[0005] A first connection plug, wherein the first connection plug is provided with a first anchoring device, wherein the first anchoring device comprises a locking slip, wherein one end of the locking slip is provided with a plurality of locking grooves with one end open and forming a simply supported beam structure, and the locking slip is also provided with a self-locking male buckle;

[0006] A tie-back tube, wherein a self-locking female buckle is provided on the inner wall of the tie-back tube, the tie-back tube is detachably connected to the locking slip through the locking groove of the locking slip, and is locked with the self-locking male buckle through the self-locking female buckle, the lower end of the tie-back tube is connected with a conical pressure head, the inner surface of the lower end of the conical pressure head is connected to the lower end pipe column, and the lower end pipe column is provided with an anti-retraction slip and a packer from top to bottom, the anti-retraction slip comprises a slip tooth and a slip seat, the slip tooth sleeve is arranged on the outer side of the lower end pipe column, and the upper end inner surface of the slip tooth is provided with an inverted conical mating surface matching with the conical pressure head; the slip seat is located on the outer wall of the lower end pipe column, and the lower end of the slip tooth matches with the conical surface of the upper end of the slip seat;

[0007] The second return plug has an upper end connected to the lower end of the lower pipe column, and the lower end of the second return plug is also anchored and connected to another return sleeve.

[0008] Preferably, the first return connector and the second return plug both include an upper connector, an inverted bearing sleeve, a connector body and a horseshoe guide head which are threadedly connected in sequence from top to bottom, the locking slip sleeve is arranged on the inverted bearing sleeve, the inner wall of the lower end of the upper connector is provided with an upper limit step for preventing the locking slip from moving axially upward, the outer wall of the inverted bearing sleeve is provided with a lower limit step for preventing the locking slip from moving axially downward, and the two ends of the locking slip are located between the upper limit step and the lower limit step.

[0009] Preferably, a ridge for preventing the locking slip from circumferential rotation is provided on the outer wall of the inverted bearing sleeve, and the ridge is located in the locking groove of the locking slip.

[0010] Preferably, a plurality of sets of sealing vulcanization-based rings are provided on the outer wall of the lower part of the inverted bearing sleeve; a plurality of sets of sealing vulcanization-based rings are also provided on the lower part of the joint body; after the first return plug is inserted into the return tube, the sealing vulcanization-based rings on the inverted bearing sleeve and the sealing vulcanization-based rings on the joint body are respectively fitted with the inner wall of the return tube.

[0011] Preferably, each group of the sealing vulcanized base rings includes a base ring body and at least two rubber sealing rings; the rubber sealing rings are vulcanized on the outer walls at both ends of the base ring body; O-rings are provided between the outer wall of the inverted bearing sleeve and the inner wall of the sealing vulcanized base ring, and between the outer wall of the joint body and the inner wall of the sealing vulcanized base ring.

[0012] Preferably, the second anchoring device is an anti-retraction slip sleeved on the lower end pipe column.

[0013] Preferably, the locking slips are milled with 8 grooves with a width of 8-11 mm to form 8 simply supported beam structures.

[0014] Preferably, the self-locking female buckle is a tapered horse tooth buckle.

[0015] Preferably, an O-ring and a set screw are provided at the connection between the upper joint and the inverted bearing sleeve above the locking cava, an O-ring and a set screw are provided at the connection between the inverted bearing sleeve and the joint body; and a set screw is provided at the connection between the joint body and the horseshoe guide head.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. Easy to operate on site, and full-diameter high-pressure wellbore can be achieved after insertion;

[0018] 2. The seal of the hanger and the tieback seal both reach 70MPa, meeting the requirements of fracturing;

[0019] 3. The structure of the back-up pipe string is simple, the probability of risk is low, and it is safe and reliable;

[0020] 4. After the fracturing is completed, just lift it up and turn it forward to release it, which is convenient and quick to use on site;

[0021] 5. Double anchor design is adopted, with spare release and spare sealing functions;

[0022] 6. It can ensure that after the pressure is applied to the kava teeth, its upper and lower ends can expand outward at the same time, so as to better play the role of anchoring;

[0023] 7. The tie-back pipe column can be recycled and reused after fracturing, which improves resource utilization and saves well construction costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1This is a schematic diagram of a tie-back plug with a self-locking male buckle and anti-retraction slip;

[0025] Figure 2 It is a schematic diagram of the structure of the present invention;

[0026] Figure 3 This is a schematic diagram of an anti-retraction slip with a self-locking male buckle;

[0027] Figure 4 It is a schematic diagram of the structure of the sealing vulcanized base ring of the tie-back plug;

[0028] Figure 5 It is a schematic diagram of the structure after the return plug and the return tube are matched;

[0029] Figure 6 It is a schematic diagram of the structure of the anti-recoil slip.

[0030] In the figure: 1, upper joint, 2, O-ring, 3, set screw, 4, locking slip, 5, inverted bearing sleeve, 6, sealing vulcanized base ring, 7, upper limit step, 8, locking groove, 9, joint body, 10, horseshoe guide head, 11, first back-connection plug, 12, back-connection tube, 13, anti-retraction slip, 14, packer, 15, second back-connection plug, 16, rubber sealing ring, 17, base ring body, 18, lower end pipe string, 19, lower limit step, 20, ridge, 21, conical pressure head, 22, slip tooth, 23, slip seat. DETAILED DESCRIPTION

[0031] The present invention is further described below with reference to the accompanying drawings and embodiments.

[0032] Embodiment 1

[0033] Reference Figure 1-Figure 6 As shown, a double-anchor double-isolation tieback system for a staged fracturing string includes a first tieback plug 11, a tieback tube 12 and a second tieback plug 15.

[0034] Among them, a first anchoring device is provided on the first return plug 11, and the first anchoring device includes a locking slip 4. A plurality of locking grooves 8 with one end open and forming a simply supported beam structure are provided at one end of the locking slip 4. The locking grooves 8 can make the locking slip 4 deform when connected with the return tube 12, so as to facilitate entering the return tube 12. A self-locking male buckle is also provided on the locking slip 4.

[0035] A self-locking female buckle matching with the self-locking male buckle is provided on the inner wall of the return tube 12, so that when the locking slip 4 enters the return tube 12 through the deformation of the locking groove 5, the self-locking female buckle and the self-locking male buckle are locked, so that the return tube 12 and the first return plug 11 can be anchored.

[0036] The lower end of the tie-back tube 12 is connected with a conical pressure head 21, and the inner surface of the lower end of the conical pressure head 21 is connected with the lower end pipe string 18. The lower end pipe string 18 is provided with anti-retraction slips 13 and packers 14 from top to bottom. When the wellhead pressure test of 35MPa fails, the pipe string is pressed down to 30t, and the anti-retraction slips 13 and the expansion packer 14 are used to realize the setting and isolation, realize the backup isolation function, achieve the purpose of fracturing, and be safe and reliable. In addition, the anti-retraction slip 13 includes a slip tooth 22 and a slip seat 23. The slip tooth 22 is sleeved on the outside of the lower end pipe column 18, and the upper inner surface of the slip tooth 22 is provided with an inverted cone matching surface that matches the conical pressure head 21; the slip seat 23 is located on the outer wall of the lower end pipe column 18, the lower end of the slip tooth 22 matches the upper conical surface of the slip seat 23, and the upper inner surface of the slip tooth 22 matches the conical pressure head 21 through the inverted cone matching surface. The slip tooth 22 can be opened to play an anchoring role under the pressure of the conical pressure head 21. Moreover, since the upper and lower ends of the slip tooth 22 are respectively provided with cone matching, it can be ensured that after pressure is applied to the slip tooth 22, its upper and lower ends can expand outward at the same time, thereby better playing the role of anchoring.

[0037] The upper end of the second tie-back plug 15 is connected to the lower end of the lower pipe column 18, and the lower end of the second tie-back plug 15 is also anchored and connected to another tie-back tube. In this way, after the fracturing is completed, the first tie-back plug 11 and the hanger tie-back tube can be released by lifting and rotating forward, and the upper tie-back casing can be recycled and reused, saving costs. However, when the first tie-back plug 11 and the tie-back tube 12 are blocked and the release function cannot be realized, the standby release function can be realized by lifting and rotating the second tie-back plug 15 forward to prevent accidents.

[0038] Embodiment 2

[0039] A double-anchor double-isolation tieback system for a staged fracturing pipe string comprises a first tieback plug 11, a tieback tube 12 and a second tieback plug 15.

[0040] Among them, a first anchoring device is provided on the first return plug 11, and the first anchoring device includes a locking slip 4. A plurality of locking grooves 8 with one end open and forming a simply supported beam structure are provided at one end of the locking slip 4. The locking grooves 8 can make the locking slip 4 deform when connected with the return tube 12, so as to facilitate entering the return tube 12. A self-locking male buckle is also provided on the locking slip 4.

[0041] A self-locking female buckle matching with the self-locking male buckle is provided on the inner wall of the return tube 12, so that when the locking slip 4 enters the return tube 12 through the deformation of the locking groove 8, the self-locking female buckle and the self-locking male buckle are locked, so that the return tube 12 and the first return plug 11 can be anchored.

[0042] The lower end of the tie-back tube 12 is connected with a conical pressure head 21, and the inner surface of the lower end of the conical pressure head 21 is connected with the lower end pipe string 18. The lower end pipe string 18 is provided with anti-retraction slips 13 and packers 14 from top to bottom. When the wellhead pressure test of 35MPa fails, the pipe string is pressed down to 30t, and the anti-retraction slips 13 and the expansion packer 14 are used to realize the setting and isolation, realize the backup isolation function, achieve the purpose of fracturing, and be safe and reliable. In addition, the anti-retraction slip 13 includes a slip tooth 22 and a slip seat 23. The slip tooth 22 is sleeved on the outside of the lower end pipe column 18, and the upper inner surface of the slip tooth 22 is provided with an inverted cone matching surface that matches the conical pressure head 21; the slip seat 23 is located on the outer wall of the lower end pipe column 18, the lower end of the slip tooth 22 matches the upper conical surface of the slip seat 23, and the upper inner surface of the slip tooth 22 matches the conical pressure head 21 through the inverted cone matching surface. The slip tooth 22 can be opened to play an anchoring role under the pressure of the conical pressure head 21. Moreover, since the upper and lower ends of the slip tooth 22 are respectively provided with cone matching, it can be ensured that after pressure is applied to the slip tooth 22, its upper and lower ends can expand outward at the same time, thereby better playing the role of anchoring.

[0043] The upper end of the second tie-back plug 15 is connected to the lower end of the lower pipe column 18, and the lower end of the second tie-back plug 15 is also anchored and connected to another tie-back tube. In this way, after the fracturing is completed, the first tie-back plug 11 and the hanger tie-back tube can be released by lifting and rotating forward, and the upper tie-back casing can be recycled and reused, saving costs. However, when the first tie-back plug 11 and the tie-back tube 12 are blocked and the release function cannot be realized, the standby release function can be realized by lifting and rotating the second tie-back plug 15 forward to prevent accidents.

[0044] In addition, the first return plug and the second return plug both include an upper joint 1, an inverted bearing sleeve 5, a joint body 9 and a horseshoe guide head 10 which are threadedly connected in sequence from top to bottom. The locking cava 4 is sleeved on the inverted bearing sleeve 5. The inner wall of the lower end of the upper joint 1 is provided with an upper limit step 7 for preventing the locking cava 4 from moving axially upward. The outer wall of the inverted bearing sleeve 5 is provided with a lower limit step 19 for preventing the locking cava 4 from moving axially downward. The two ends of the locking cava 4 are located between the upper limit step 7 and the lower limit step 19. In this way, the locking cava 4 can be limited to move in the axial direction to prevent displacement when the pipe string is pressed down and fail to play an anchoring role.

[0045] Embodiment 3

[0046] A double-anchor double-isolation tieback system for a staged fracturing pipe string comprises a first tieback plug 11, a tieback tube 12 and a second tieback plug 15.

[0047] Among them, a first anchoring device is provided on the first return plug 11, and the first anchoring device includes a locking slip 4. A plurality of locking grooves 8 with one end open and forming a simply supported beam structure are provided at one end of the locking slip 4. The locking grooves 8 can make the locking slip 4 deform when connected with the return tube 12, so as to facilitate entering the return tube 12. A self-locking male buckle is also provided on the locking slip 4.

[0048] A self-locking female buckle matching with the self-locking male buckle is provided on the inner wall of the return tube 12, so that when the locking slip 4 enters the return tube 12 through the deformation of the locking groove 8, the self-locking female buckle and the self-locking male buckle are locked, so that the return tube 12 and the first return plug 11 can be anchored.

[0049] The lower end of the tie-back tube 12 is connected with a conical pressure head 21, and the inner surface of the lower end of the conical pressure head 21 is connected with the lower end pipe string 18. The lower end pipe string 18 is provided with anti-retraction slips 13 and packers 14 from top to bottom. When the wellhead pressure test of 35MPa fails, the pipe string is pressed down to 30t, and the anti-retraction slips 13 and the expansion packer 14 are used to realize the setting and isolation, realize the backup isolation function, achieve the purpose of fracturing, and be safe and reliable. In addition, the anti-retraction slip 13 includes a slip tooth 22 and a slip seat 23. The slip tooth 22 is sleeved on the outside of the lower end pipe column 18, and the upper inner surface of the slip tooth 22 is provided with an inverted cone matching surface that matches the conical pressure head 21; the slip seat 23 is located on the outer wall of the lower end pipe column 18, the lower end of the slip tooth 22 matches the upper conical surface of the slip seat 23, and the upper inner surface of the slip tooth 22 matches the conical pressure head 21 through the inverted cone matching surface. The slip tooth 22 can be opened to play an anchoring role under the pressure of the conical pressure head 21. Moreover, since the upper and lower ends of the slip tooth 22 are respectively provided with cone matching, it can be ensured that after pressure is applied to the slip tooth 22, its upper and lower ends can expand outward at the same time, thereby better playing the role of anchoring.

[0050] The upper end of the second tie-back plug 15 is connected to the lower end of the lower pipe column 18, and the lower end of the second tie-back plug 15 is also anchored and connected to another tie-back tube. In this way, after the fracturing is completed, the first tie-back plug 11 and the hanger tie-back tube can be released by lifting and rotating forward, and the upper tie-back casing can be recycled and reused, saving costs. However, when the first tie-back plug 11 and the tie-back tube 12 are blocked and the release function cannot be realized, the standby release function can be realized by lifting and rotating the second tie-back plug 15 forward to prevent accidents.

[0051] In addition, the first return plug and the second return plug both include an upper joint 1, an inverted bearing sleeve 5, a joint body 9 and a horseshoe guide head 10 which are threadedly connected in sequence from top to bottom. The locking cava 4 is sleeved on the inverted bearing sleeve 5. The inner wall of the lower end of the upper joint 1 is provided with an upper limit step 7 for preventing the locking cava 4 from moving axially upward. The outer wall of the inverted bearing sleeve 5 is provided with a lower limit step 19 for preventing the locking cava 4 from moving axially downward. The two ends of the locking cava 4 are located between the upper limit step 7 and the lower limit step 19. In this way, the locking cava 4 can be limited to move in the axial direction to prevent displacement when the pipe string is pressed down and fail to play an anchoring role.

[0052] A ridge 20 is provided on the outer wall of the inverted bearing sleeve 5 for preventing the locking slip 4 from circumferential rotation. The ridge 20 is located in the locking groove 8 of the locking slip 4. After the fracturing is completed, the pipe string can be lifted up and rotated back to achieve release. The ridge 20 can prevent the locking slip 4 from circumferential motion, thereby ensuring smooth release.

[0053] Embodiment 4

[0054] A double-anchor double-isolation tieback system for a staged fracturing pipe string comprises a first tieback plug 11, a tieback tube 12 and a second tieback plug 15.

[0055] Among them, a first anchoring device is provided on the first return plug 11, and the first anchoring device includes a locking slip 4. A plurality of locking grooves 8 with one end open and forming a simply supported beam structure are provided at one end of the locking slip 4. The locking grooves 8 can make the locking slip 4 deform when connected with the return tube 12, so as to facilitate entering the return tube 12. A self-locking male buckle is also provided on the locking slip 4.

[0056] A self-locking female buckle matching with the self-locking male buckle is provided on the inner wall of the return tube 12, so that when the locking slip 4 enters the return tube 12 through the deformation of the locking groove 8, the self-locking female buckle and the self-locking male buckle are locked, so that the return tube 12 and the first return plug 11 can be anchored.

[0057] The lower end of the tie-back tube 12 is connected with a conical pressure head 21, and the inner surface of the lower end of the conical pressure head 21 is connected with the lower end pipe string 18. The lower end pipe string 18 is provided with anti-retraction slips 13 and packers 14 from top to bottom. When the wellhead pressure test of 35MPa fails, the pipe string is pressed down to 30t, and the anti-retraction slips 13 and the expansion packer 14 are used to realize the setting and isolation, realize the backup isolation function, achieve the purpose of fracturing, and be safe and reliable. In addition, the anti-retraction slip 13 includes a slip tooth 22 and a slip seat 23. The slip tooth 22 is sleeved on the outside of the lower end pipe column 18, and the upper inner surface of the slip tooth 22 is provided with an inverted cone matching surface that matches the conical pressure head 21; the slip seat 23 is located on the outer wall of the lower end pipe column 18, the lower end of the slip tooth 22 matches the upper conical surface of the slip seat 23, and the upper inner surface of the slip tooth 22 matches the conical pressure head 21 through the inverted cone matching surface. The slip tooth 22 can be opened to play an anchoring role under the pressure of the conical pressure head 21. Moreover, since the upper and lower ends of the slip tooth 22 are respectively provided with cone matching, it can be ensured that after pressure is applied to the slip tooth 22, its upper and lower ends can expand outward at the same time, thereby better playing the role of anchoring.

[0058] The upper end of the second tie-back plug 15 is connected to the lower end of the lower pipe column 18, and the lower end of the second tie-back plug 15 is also anchored and connected to another tie-back tube. In this way, after the fracturing is completed, the first tie-back plug 11 and the hanger tie-back tube can be released by lifting and rotating forward, and the upper tie-back casing can be recycled and reused, saving costs. However, when the first tie-back plug 11 and the tie-back tube 12 are blocked and the release function cannot be realized, the standby release function can be realized by lifting and rotating the second tie-back plug 15 forward to prevent accidents.

[0059] In addition, the first return plug and the second return plug both include an upper joint 1, an inverted bearing sleeve 5, a joint body 9 and a horseshoe guide head 10 which are threadedly connected in sequence from top to bottom. The locking cava 4 is sleeved on the inverted bearing sleeve 5. The inner wall of the lower end of the upper joint 1 is provided with an upper limit step 7 for preventing the locking cava 4 from moving axially upward. The outer wall of the inverted bearing sleeve 5 is provided with a lower limit step 19 for preventing the locking cava 4 from moving axially downward. The two ends of the locking cava 4 are located between the upper limit step 7 and the lower limit step 19. In this way, the locking cava 4 can be limited to move in the axial direction to prevent displacement when the pipe string is pressed down and fail to play an anchoring role.

[0060] A ridge 20 is provided on the outer wall of the inverted bearing sleeve 5 for preventing the locking slip 4 from circumferential rotation. The ridge 20 is located in the locking groove 8 of the locking slip 4. After the fracturing is completed, the pipe string can be lifted up and rotated back to achieve release. The ridge 20 can prevent the locking slip 4 from circumferential motion, thereby ensuring smooth release.

[0061] A plurality of sets of sealing vulcanized base rings 6 are provided on the outer wall of the lower part of the inverted bearing sleeve 5; a plurality of sets of sealing vulcanized base rings 6 are also provided on the lower part of the joint body 9; after the first return plug 11 is inserted into the return tube 12, the sealing vulcanized base rings 6 on the inverted bearing sleeve 5 and the sealing vulcanized base rings 6 on the joint body 9 are respectively fitted with the inner wall of the return tube 12.

[0062] Each set of sealing vulcanized base rings 6 includes a base ring body 17 and at least two rubber sealing rings 16; the rubber sealing rings 16 are vulcanized on the outer walls at both ends of the base ring body 17; O-rings 2 are provided between the outer wall of the inverted bearing sleeve 5 and the inner wall of the base ring body 17, and between the outer wall of the joint body 9 and the inner wall of the base ring body 17. Each set of sealing vulcanized base rings 6 is annularly sealed by vulcanizing two rubber sealing rings 16 on the outer circle of a base ring body 17. This sealing form has a higher sealing pressure than the conventional V-ring sealing form, can withstand a pressure of 70MPa, and is not easy to damage. After multiple plug-in and pull-out of the reconnection tube, it can still be used. The gap between the inverted bearing sleeve 5, the joint body 9 and the sealing vulcanized base ring 6 is sealed by the provided O-ring 2.

[0063] Embodiment 5

[0064] A double-anchor double-isolation tieback system for a staged fracturing pipe string comprises a first tieback plug 11, a tieback tube 12 and a second tieback plug 15.

[0065] Among them, a first anchoring device is provided on the first return plug 11, and the first anchoring device includes a locking slip 4. A plurality of locking grooves 8 with one end open and forming a simply supported beam structure are provided at one end of the locking slip 4. The locking grooves 8 can make the locking slip 4 deform when connected with the return tube 12, so as to facilitate entering the return tube 12. A self-locking male buckle is also provided on the locking slip 4.

[0066] A self-locking female buckle matching with the self-locking male buckle is provided on the inner wall of the return tube 12, so that when the locking slip 4 enters the return tube 12 through the deformation of the locking groove 8, the self-locking female buckle and the self-locking male buckle are locked, so that the return tube 12 and the first return plug 11 can be anchored.

[0067] The lower end of the tie-back tube 12 is connected with a conical pressure head 21, and the inner surface of the lower end of the conical pressure head 21 is connected with the lower end pipe string 18. The lower end pipe string 18 is provided with anti-retraction slips 13 and packers 14 from top to bottom. When the wellhead pressure test of 35MPa fails, the pipe string is pressed down to 30t, and the anti-retraction slips 13 and the expansion packer 14 are used to realize the setting and isolation, realize the backup isolation function, achieve the purpose of fracturing, and be safe and reliable. In addition, the anti-retraction slip 13 includes a slip tooth 22 and a slip seat 23. The slip tooth 22 is sleeved on the outside of the lower end pipe column 18, and the upper inner surface of the slip tooth 22 is provided with an inverted cone matching surface that matches the conical pressure head 21; the slip seat 23 is located on the outer wall of the lower end pipe column 18, the lower end of the slip tooth 22 matches the upper conical surface of the slip seat 23, and the upper inner surface of the slip tooth 22 matches the conical pressure head 21 through the inverted cone matching surface. The slip tooth 22 can be opened to play an anchoring role under the pressure of the conical pressure head 21. Moreover, since the upper and lower ends of the slip tooth 22 are respectively provided with cone matching, it can be ensured that after pressure is applied to the slip tooth 22, its upper and lower ends can expand outward at the same time, thereby better playing the role of anchoring.

[0068] The upper end of the second tie-back plug 15 is connected to the lower end of the lower pipe column 18, and the lower end of the second tie-back plug 15 is also anchored and connected to another tie-back tube. In this way, after the fracturing is completed, the first tie-back plug 11 and the hanger tie-back tube can be released by lifting and rotating forward, and the upper tie-back casing can be recycled and reused, saving costs. However, when the first tie-back plug 11 and the tie-back tube 12 are blocked and the release function cannot be realized, the standby release function can be realized by lifting and rotating the second tie-back plug 15 forward to prevent accidents.

[0069] In addition, the first return plug and the second return plug both include an upper joint 1, an inverted bearing sleeve 5, a joint body 9 and a horseshoe guide head 10 which are threadedly connected in sequence from top to bottom. The locking cava 4 is sleeved on the inverted bearing sleeve 5. The inner wall of the lower end of the upper joint 1 is provided with an upper limit step 7 for preventing the locking cava 4 from moving axially upward. The outer wall of the inverted bearing sleeve 5 is provided with a lower limit step 19 for preventing the locking cava 4 from moving axially downward. The two ends of the locking cava 4 are located between the upper limit step 7 and the lower limit step 19. In this way, the locking cava 4 can be limited to move in the axial direction to prevent displacement when the pipe string is pressed down and fail to play an anchoring role.

[0070] A ridge 20 is provided on the outer wall of the inverted bearing sleeve 5 for preventing the locking slip 4 from circumferential rotation. The ridge 20 is located in the locking groove 8 of the locking slip 4. After the fracturing is completed, the pipe string can be lifted up and rotated back to achieve release. The ridge 20 can prevent the locking slip 4 from circumferential motion, thereby ensuring smooth release.

[0071] A plurality of sets of sealing vulcanized base rings 6 are provided on the outer wall of the lower part of the inverted bearing sleeve 5; a plurality of sets of sealing vulcanized base rings 6 are also provided on the lower part of the joint body 9; after the first return plug 11 is inserted into the return tube 12, the sealing vulcanized base rings 6 on the inverted bearing sleeve 5 and the sealing vulcanized base rings 6 on the joint body 9 are respectively fitted with the inner wall of the return tube 12.

[0072] Each set of sealing vulcanized base rings 6 includes a base ring body 17 and at least two rubber sealing rings 16; the rubber sealing rings 16 are vulcanized on the outer walls at both ends of the base ring body 17; O-rings 2 are provided between the outer wall of the inverted bearing sleeve 5 and the inner wall of the sealing vulcanized base ring 6, and between the outer wall of the joint body 9 and the inner wall of the sealing vulcanized base ring 6. Each set of sealing vulcanized base rings 6 is annularly sealed by vulcanizing two rubber sealing rings 16 on the outer circle of a base ring body 17. This sealing form has a higher sealing pressure than the conventional V-ring sealing form, can withstand a pressure of 70MPa, and is not easy to damage. After repeatedly plugging and unplugging the reconnection tube 12, it can still be used. The gap between the inverted bearing sleeve 5, the joint body 9 and the sealing vulcanized base ring 6 is sealed by the provided O-ring 2.

[0073] The anti-retraction slip 13 and the packer 14 can anchor it on the inner wall of the casing. The anti-retraction slip 13 and the packer 14 have a backup isolation function. If the second back-connection plug 15 passes the pressure test after anchoring, the packer 14 will not be expanded and sealed, and the upper and lower back-connection tubes can be released after fracturing; if the lower second back-connection plug 15 fails the pressure test after anchoring, it will continue to press down. Since the upper and lower ends of the slip teeth 22 are respectively provided with conical surfaces, it can be ensured that after pressure is applied to the slip teeth 22, its upper and lower ends can expand outward at the same time, so as to better play the role of anchoring. At this time, the packer 14 is expanded and sealed, and the backup isolation function is activated to achieve the purpose of fracturing. Therefore, it has double anchoring and double isolation functions.

[0074] The locking slip 4 is evenly milled with 8 grooves with a width of 8-11 mm along the circumferential direction to form 8 simply supported beam structures. The self-locking female buckle is a tapered tooth buckle. Under the action of external force, the simply supported beam structure of the locking slip 4 will be inserted into the corresponding tapered tooth buckle of the tie-back tube 12 to lock the upper pipe string with the lower liner hanger. At this time, the sealing vulcanized base ring 6 fits with the inner wall of the tie-back tube 12 to form a seal.

[0075] An O-ring 2 and a set screw 3 are provided at the connection between the upper joint 1 and the inverted bearing sleeve 5 above the locking slip 4, and an O-ring 2 and a set screw 3 are provided at the connection between the inverted bearing sleeve 5 and the joint body 9; a set screw 3 is provided at the connection between the joint body 9 and the horseshoe guide head 10.

[0076] Combined with the attached drawings, the working principle of the double anchor double packer tieback system of the staged fracturing string is introduced as follows: the on-site tail pipe hanger is hung, checked, slurry is replaced, and the central pipe is taken out. After the cement solidifies, the tail pipe tieback perforation fracturing is carried out. First, the double anchor double packer tieback system of the staged fracturing string is connected to the casing string, and after it is lowered to the designed position, the pipe string is pressed down by 5t. The simply supported beam structure of the locking slip 4 will be inserted into the corresponding tapered tooth buckle of the tieback tube 12 under the action of external force, and the upper pipe string and the lower tail pipe hanger are locked. At this time, the sealing vulcanized base ring 6 fits with the inner wall of the tieback tube 12 to form a seal.

[0077] At this time, a wellhead pressure test of 35MPa is carried out, and the pressure is stabilized for 1 hour. There is no pressure drop and the return pipe string does not move upward, indicating that the locking and sealing are normal. Since the return casing, the hanger and the plug can have the same inner diameter, a large diameter and high pressure bearing wellbore is provided, which is convenient for the subsequent fracturing operation. After the fracturing operation is completed, since the locking thread between the locking cava 4 and the return tube is a reverse thread connection, it is necessary to lift the forward pipe string, so that the first return plug 11 and the second return plug 15 can be separated from the return tube 12, with a spare release function. The return plug can be taken out by lifting the pipe string, and the fracturing operation is completed. If the first return plug 11 is blocked and the release function cannot be completed, the second return plug 15 can be used to complete the release, which is more flexible in operation and has good reliability.

[0078] If the wellhead pressure test at 35MPa fails, continue to press the tubing string down to 30t, expand and seal the packer, and perform another wellhead pressure test at 35MPa. Keep the pressure steady for 1 hour. If there is no pressure drop and the tie-back pipe string does not rise, it means that the locking and sealing are normal. After the fracturing operation is completed, lift the forward pipe string in the same way, take out the tie-back plug, and the fracturing operation is completed.

[0079] The present invention sets a self-locking thread matched with the tie-back anchor plug on the top of the hanger tie-back tube, and at the same time, the tie-back plug is provided with a locking slip 4 matched with the tie-back tube 12, and the locking slip 4 can be inserted into the tie-back tube 12 by pressing down to realize the anchoring of the tie-back pipe string; the tie-back plug adopts a sealing form of a sealing base ring to ensure that the sealing capacity in the tie-back tube 12 reaches 70MPa, which can not only ensure the simple structure of the tie-back pipe string and avoid the cumulative risk caused by too many units, but also realize the high-pressure sealing requirement in the tie-back wellbore, and after the fracturing is completed, the tie-back plug and the hanger tie-back tube can be released by lifting and rotating forward, so that the upper tie-back casing can be recycled and reused, saving costs; at the same time, the present invention has spare release and spare isolation functions. If the pressure test after the lower tie-back plug is anchored is qualified, the packer will not be expanded and sealed, and both the upper and lower tie-back tubes can be released after fracturing; if the pressure test after the lower tie-back plug is anchored is unqualified, the packer will be expanded and sealed, and the spare isolation function will be activated to achieve the purpose of fracturing.

[0080] The traditional horizontal well tail pipe tie-back fracturing process has a complex pipe string structure, many tools during tie-back, complex operation, high risk, and high cost, which does not conform to the current concept of low-cost mining. Therefore, the present invention solves the technical problems of complex structure of the tie-back pipe string after tail pipe cementing, poor sealing and reliability through the integrated design of cementing and completion tools; a double anchoring design is adopted to realize the standby release and standby isolation functions. After the tail pipe cementing tie-back is realized, a high-pressure wellbore is formed with the tie-back pipe string and the tail pipe string sealed and anchored in an integrated manner. At the same time, the tie-back pipe string can be recycled and reused after fracturing, which improves resource utilization and saves costs; the tie-back pipe string has a simple structure, with only a tie-back plug and a casing string, which can ensure the full diameter of the tie-back pipe string and the tail pipe string, meet the large diameter requirements of subsequent production, and have good economic and social benefits.

[0081] The present invention is not limited to the above-mentioned embodiments. Various changes can be made within the knowledge scope of those skilled in the art without departing from the spirit of the present invention. The changed contents still fall within the protection scope of the present invention.

Claims

1. A double anchor double packer tieback system for staged fracturing string, characterized in that: include: A first connection plug, wherein the first connection plug is provided with a first anchoring device, wherein the first anchoring device comprises a locking slip, wherein one end of the locking slip is provided with a plurality of locking grooves with one end open and forming a simply supported beam structure, and the locking slip is also provided with a self-locking male buckle; A tie-back tube, wherein a self-locking female buckle is provided on the inner wall of the tie-back tube, the tie-back tube is detachably connected to the locking slip through the locking groove of the locking slip, and is locked with the self-locking male buckle through the self-locking female buckle, the lower end of the tie-back tube is connected with a conical pressure head, the inner surface of the lower end of the conical pressure head is connected to the lower end pipe column, and the lower end pipe column is provided with an anti-retraction slip and a packer from top to bottom, the anti-retraction slip comprises a slip tooth and a slip seat, the slip tooth sleeve is arranged on the outer side of the lower end pipe column, and the upper end inner surface of the slip tooth is provided with an inverted conical mating surface matching with the conical pressure head; the slip seat is located on the outer wall of the lower end pipe column, and the lower end of the slip tooth matches with the conical surface of the upper end of the slip seat; A second return plug, wherein the upper end of the second return plug is connected to the lower end of the lower pipe column, and the lower end of the second return plug is also anchored and connected to another return sleeve; The first return plug and the second return plug both include an upper joint, an inverted bearing sleeve, a joint body and a horseshoe guide head which are threadedly connected in sequence from top to bottom. The locking slip sleeve is arranged on the inverted bearing sleeve. The inner wall of the lower end of the upper joint is provided with an upper limit step for preventing the locking slip from moving axially upward. The outer wall of the inverted bearing sleeve is provided with a lower limit step for preventing the locking slip from moving axially downward. The two ends of the locking slip are located between the upper limit step and the lower limit step.

2. A double anchor double isolation tieback system for staged fracturing string according to claim 1, characterized in that: A convex ridge for preventing the locking slip from circumferential rotation is provided on the outer wall of the inverted bearing sleeve, and the convex ridge is located in the locking groove of the locking slip.

3. A double anchor double isolation tieback system for staged fracturing string according to claim 1, characterized in that: A plurality of sets of sealing vulcanized base rings are arranged on the outer wall of the lower part of the inverted bearing sleeve; a plurality of sets of sealing vulcanized base rings are also arranged on the lower part of the joint body; after the first reconnection plug is inserted into the reconnection tube, the sealing vulcanized base rings on the inverted bearing sleeve and the sealing vulcanized base rings on the joint body are respectively fitted with the inner wall of the reconnection tube.

4. A double-anchor double-packer tieback system for a staged fracturing string according to claim 3, characterized in that: Each group of the sealing vulcanized base rings includes a base ring body and at least two rubber sealing rings; the rubber sealing rings are vulcanized on the outer walls at both ends of the base ring body; O-rings are provided between the outer wall of the inverted bearing sleeve and the inner wall of the sealing vulcanized base ring, and between the outer wall of the joint body and the inner wall of the sealing vulcanized base ring.

5. A double anchor double isolation tieback system for staged fracturing string according to claim 2, characterized in that: The locking slips are milled with 8 grooves with a width of 8-11 mm to form 8 simply supported beam structures.

6. A double anchor double isolation tieback system for staged fracturing string according to claim 1, characterized in that: The self-locking female buckle is a tapered horse tooth buckle.

7. A double anchor double isolation tieback system for staged fracturing string according to claim 1, characterized in that: An O-ring and a set screw are provided at the connection between the upper joint and the inverted bearing sleeve above the locking slip, an O-ring and a set screw are provided at the connection between the inverted bearing sleeve and the joint body; a set screw is provided at the connection between the joint body and the horseshoe guide head.

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