A sand-control tubing string capable of secondary fracturing and its sand-control fracturing method

Abstract

This invention discloses a sand control tubing string and sand control fracturing method capable of secondary fracturing, solving the technical problems of low fracturing efficiency and poor fracturing effect. The device includes a top packer assembly, a sand control fracturing assembly, and a sand-falling packer. Multiple sand control fracturing assemblies are provided, and the top packer assembly, multiple sand control fracturing assemblies, and sand-falling packers are connected by oil and gas screen pipes. The sand control fracturing assembly includes an isolation packer and a sand control assembly, and further includes: a screen sleeve assembly connected to the bottom of the sand control assembly; a sliding sleeve outer cylinder connected to the bottom of the screen sleeve assembly, with multiple production holes at the upper end and multiple fracturing holes at the lower end; and a fracturing sliding sleeve, vertically slidably disposed within the sliding sleeve outer cylinder, capable of sealing the production holes or fracturing holes. This invention can achieve sand control completion, reduce the risk of screen pipe damage during secondary fracturing operations, improve operational efficiency, and enhance fracturing effect.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas well development technology, specifically relating to a sand control tubing string capable of secondary fracturing and its sand control fracturing method. Background Technology

[0002] Currently, loose sandstone oil and gas reservoirs often face the problem of sand production at the bottom of the well during the exploitation process. For older wells that have been in operation for a period of time, severe formation sand production can lead to screen blockage or failure, affecting production and even causing the well to be abandoned. In this case, secondary fracturing and production enhancement operations need to be carried out in the older wells.

[0003] In related technologies, fracturing using screened tubing is commonly employed, followed by chemical or mechanical sand control after damage to the old screened tubing. This approach is prone to problems such as short sand control lifespan and small wellbore diameter, significantly impacting well quality and becoming a major obstacle to increased production in loose sandstone oil and gas reservoirs. Currently, some solutions utilize pre-fabricated fracturing sleeves in the completion string. While this avoids screened tubing fracturing, conventional tubing cannot effectively isolate different producing layers during fracturing, resulting in low efficiency and affecting fracturing effectiveness; therefore, improvements are needed. Summary of the Invention

[0004] In order to solve all or part of the above problems, the purpose of this invention is to provide a sand control tubing string capable of secondary fracturing and a sand control fracturing method thereof, which can realize the function of sand control well completion, and can reduce the risk of screen pipe damage, improve operation efficiency, and improve fracturing effect during secondary fracturing operations.

[0005] In a first aspect, the present invention provides a sand control tubing string capable of secondary fracturing, comprising a top packer assembly, a sand control fracturing assembly, and a sand settling packer arranged sequentially from top to bottom. Multiple sand control fracturing assemblies are provided, and the top packer assembly, the multiple sand control fracturing assemblies, and the sand settling packer are respectively connected by oil and gas screen pipes.

[0006] The sand fracturing control assembly includes:

[0007] Isolation packers are used to set and isolate oil wells;

[0008] A sand control assembly is connected to the bottom of the isolation packer and is used to fill the well with gravel;

[0009] The screen sleeve assembly is connected to the bottom of the sandproof assembly;

[0010] The outer sleeve is connected to the bottom of the screen sleeve assembly. The upper end of the outer sleeve has multiple production holes, and the lower end has multiple fracturing holes.

[0011] The fracturing sleeve is vertically slidably disposed inside the outer cylinder of the sleeve, and the fracturing service tool can control the vertical sliding of the fracturing sleeve and make the fracturing sleeve close the production hole or fracturing hole.

[0012] Optionally, a plurality of sealing rings are fixedly fitted on the fracturing sleeve to improve the sealing effect between the fracturing sleeve and the outer sleeve cylinder.

[0013] Optionally, a support groove is provided at the lower end of the fracturing sleeve, and a C-shaped locking ring is provided in the support groove. Limiting grooves are respectively provided at the middle and lower ends of the outer cylinder of the sleeve. The locking ring can be inserted into any of the limiting grooves to limit the fracturing sleeve, thereby achieving stable sealing of the production hole and the fracturing hole.

[0014] Optionally, each of the fracturing holes is sealed with a slotted metal plate, and when the fracturing service tool pressurizes the outer sleeve, the fracturing fluid can break through the slotted metal plate.

[0015] Optionally, the screen sleeve assembly includes:

[0016] The screen sleeve base tube is connected at the top to the sandproof assembly and at the bottom to the outer cylinder of the sliding sleeve.

[0017] The outer sleeve of the sieve sleeve is fixedly sleeved at the upper end of the sieve sleeve base tube;

[0018] A check valve is installed on the screen sleeve base tube, and the bottom of the screen sleeve outer cylinder is connected to the check valve;

[0019] An extension sleeve is connected at one end to the single-flow valve and at the other end to the outer cylinder of the sliding sleeve. An annular cavity exists between the extension sleeve and the outer cylinder of the sliding sleeve, and the plurality of production holes are respectively connected to the annular cavity.

[0020] The single-flow valve allows oil and gas in the well to enter the annular cavity only through the outer sleeve of the screen sleeve, and then enter the outer sleeve of the sliding sleeve through the production hole.

[0021] Optionally, the sand-proof assembly includes:

[0022] A sand-proof sleeve is connected to the bottom of the isolation packer, and the sand-proof sleeve is provided with sand-proof holes;

[0023] A sand-proof sliding sleeve is slidably fitted onto the sand-proof sleeve, and the filling service tool can control the vertical sliding of the sand-proof sliding sleeve to control the opening and closing of the sand-proof hole;

[0024] The extended screen tube is connected at the top to the sandproof sleeve via a positioning coupling and at the bottom to the corresponding screen sleeve base tube.

[0025] Optionally, the top sealing assembly includes:

[0026] Top packer, used to set and pack the wellhead;

[0027] The sand-filling assembly is connected at the top to the top packer and at the bottom to the corresponding oil and gas screen pipe, and is used to fill the wellbore with gravel.

[0028] Optionally, the sand-filling assembly includes:

[0029] A sand-filling sleeve is connected at the top to the top packer and at the bottom to the corresponding oil and gas screen pipe, and a sand-filling hole is provided on the sand-filling sleeve.

[0030] A sand-filling sliding sleeve is slidably fitted onto the sand-filling sleeve, and the filling service tool can control the vertical sliding of the sand-filling sliding sleeve to control the opening and closing of the sand-filling hole.

[0031] Optionally, the top of the top packer is connected to an oil and gas well casing.

[0032] In a first aspect, the present invention provides a sand-control fracturing method using the aforementioned sand-control tubing, comprising the following steps:

[0033] S1, the sand control tubing string is lowered, and the sand packer, top packer assembly and multiple isolation packers are set in the well to achieve the setting and sealing of the oil well;

[0034] S2, lower the fracturing service tool, and control the fracturing sleeve to move downward through the fracturing service tool, so that the fracturing sleeve closes all fracturing holes, so that multiple production holes are opened respectively;

[0035] S3, by filling the oil well with gravel through the sand control assembly, so that the space between two adjacent isolation packers is filled with gravel to achieve sand control operation;

[0036] S4. When performing secondary fracturing, select the target section, fill the sand inside the sand control tubing, and fill the remaining sand control tubing below the fracturing section to prepare for fracturing of the target section.

[0037] S5, the fracturing service tool is lowered into the sand control tubing string through the drill pipe or coiled tubing, and the fracturing service tool is used to control the fracturing sleeve to move upward, so that the fracturing sleeve closes all production holes, thereby opening multiple fracturing holes separately;

[0038] S6, fracturing fluid is pumped into the sand control tubing through fracturing service tools. The fracturing fluid enters the formation through the fracturing holes and performs secondary fracturing on the target section.

[0039] S7. After the secondary fracturing operation is completed, the fracturing service tool is used to control the fracturing sleeve to move downward, so that the fracturing sleeve closes all fracturing holes and opens multiple production holes. Then the fracturing service tool is removed.

[0040] S8, the oil and gas in the well replace the fracturing fluid and flush the sand and gravel out of the sand control string. At this time, the sand control string remains in its full-bore state before fracturing and production continues.

[0041] As can be seen from the above technical solution, the sand control tubing and sand control fracturing method provided by the present invention have the following advantages:

[0042] This device employs multiple sand control and fracturing assemblies, each containing a packer. These packers effectively isolate the well into multiple sections, separating different producing formations. This operation is simple and quick, improving both fracturing efficiency and effectiveness. Simultaneously, the sand control assembly fills the space between adjacent packers with gravel, and a sand-filling mechanism fills the space between the top packer and the uppermost packer with gravel, achieving sand control completion. Furthermore, this design allows the sand control tubing string to integrate sand control, fracturing, and production functions, increasing its versatility while reducing the operational difficulty and cost of sand control and fracturing operations.

[0043] Other features and advantages of the present invention will be set forth in the following description. Attached Figure Description

[0044] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the technical solutions of the present invention, and do not constitute a limitation on the technical solutions of the present invention.

[0045] Figure 1 This is a schematic diagram of the overall structure of the sand-control pipe column in an embodiment of the present invention;

[0046] Figure 2 This is a schematic diagram of the structure of the sand control tubing string being lowered into the oil well in an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of the sand-resistant fracturing assembly in an embodiment of the present invention;

[0048] Figure 4 for Figure 3 Enlarged view of region A in the middle;

[0049] Figure 5 for Figure 3 Enlarged view of region B in the middle;

[0050] Figure 6This is a schematic diagram showing the state of the fracturing service tool being lowered into the sand control tubing in an embodiment of the present invention.

[0051] Explanation of reference numerals in the attached figures:

[0052] 1. Oil and gas well casing; 2. Top packer assembly; 21. Top packer; 22. Sand packing assembly; 221. Sand packing sleeve; 222. Sand packing sliding sleeve; 3. Sand control and fracturing assembly; 31. Isolation packer; 32. Sand control assembly; 321. Sand control sleeve; 322. Sand control sliding sleeve; 323. Extension screen pipe; 33. Screen sleeve assembly; 331. Screen sleeve base pipe; 332. Screen sleeve outer cylinder; 333. Check valve; 334. Extension sleeve; 335. Annular cavity; 34. Sliding sleeve outer cylinder; 35. Production hole; 36. Fracturing hole; 37. Fracturing sliding sleeve; 4. Sand packer; 5. Oil and gas screen pipe; 6. Sealing ring; 7. Support groove; 8. Locking ring; 9. Limiting groove; 10. Slotted metal plate;

[0053] 100. Sand control tubing; 200. Fracturing service tools; 300. Fracturing tubing; 400. Fracturing packer; 500. Switching tools. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be arbitrarily combined with each other.

[0055] like Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 The figure shown is an embodiment of the present invention. This embodiment discloses a sand control tubing string 100 capable of secondary fracturing, including an oil and gas well casing 1, a top packer assembly 2, a sand control fracturing assembly 3, and a sand settling packer 4 arranged sequentially from top to bottom. The oil and gas well casing 1 is connected to the top of the top packer assembly 2. Multiple sand control fracturing assemblies 3 are provided. The top packer assembly 2, the multiple sand control fracturing assemblies 3, and the sand settling packer 4 are respectively connected by oil and gas screen pipes 5.

[0056] In one embodiment, such as Figure 1 , Figure 3 As shown, the sand control fracturing assembly 3 includes, from top to bottom, an isolation packer 31, a sand control assembly 32, a screen sleeve assembly 33, and a sliding sleeve outer cylinder 34. The isolation packer 31 is used to set and seal the oil well, and the sand control assembly 32 is used to fill the oil well with gravel to achieve sand control operation.

[0057] In one embodiment, such as Figure 3 , Figure 4, Figure 5 As shown, the upper end of the outer sleeve 34 has multiple production holes 35, and the lower end has multiple fracturing holes 36. The production holes 35 and fracturing holes 36 are arranged at equal intervals along the circumference of the outer sleeve 34. A fracturing sleeve 37 is vertically slidably disposed inside the outer sleeve 34, and the fracturing service tool 200 can control the vertical sliding of the fracturing sleeve 37 and make the fracturing sleeve 37 close the production holes 35 or fracturing holes 36.

[0058] The fracturing service tool 200 controls the fracturing sleeve 37 to slide vertically downwards, closing the fracturing orifice 36. At this time, the production orifice 35 is opened, allowing oil and gas to enter the tubing string through the production orifice 35, thus realizing the production function of the tubing string. Similarly, the fracturing service tool 200 controls the fracturing sleeve 37 to slide vertically upwards, closing the production orifice 35. At this time, the fracturing orifice 36 is opened, and fracturing operations can then be carried out to realize the fracturing function of the tubing string. In other words, the sand control tubing string 100 integrates fracturing and production.

[0059] In this embodiment, the sand control tubing 100 is equipped with multiple sand control fracturing assemblies 3, and each sand control fracturing assembly 3 includes an isolation packer 31. In other words, the oil well is isolated into multiple segments by multiple isolation packers 31, thereby achieving effective isolation between different production layers. Moreover, this operation is simple and quick, which can improve both fracturing efficiency and fracturing effect.

[0060] In one embodiment, such as Figure 3 , Figure 4 , Figure 5 As shown, multiple sealing rings 6 are fixedly fitted on the fracturing sleeve 37. The sealing rings 6 are tightly fitted to the inner wall of the outer sleeve cylinder 34 to improve the sealing effect between the fracturing sleeve 37 and the outer sleeve cylinder 34, thereby improving the sealing stability of the production hole 35 and the fracturing hole 36.

[0061] In one embodiment, such as Figure 3 , Figure 4 , Figure 5 As shown, a support groove 7 is provided at the lower end of the fracturing sleeve 37, and a C-shaped locking ring 8 is provided in the support groove 7. The locking ring 8 is made of elastic materials such as spring steel or manganese steel. At the same time, limit grooves 9 are provided at the middle and lower ends of the outer sleeve 34.

[0062] When the fracturing sleeve 37 moves upward and the locking ring 8 engages in the limiting groove 9 located in the middle of the fracturing sleeve 37, the fracturing sleeve 37 closes multiple production holes 35. At this time, one side of the locking ring 8 is located in the limiting groove 9, while the other side remains in the support groove 7, so that the locking ring 8 can limit the fracturing sleeve 37, reduce the risk of displacement of the fracturing sleeve 37, and thus achieve stable sealing of the production holes 35. Similarly, when the fracturing sleeve 37 moves upward and the locking ring 8 engages in the limiting groove 9 located at the lower end of the fracturing sleeve 37, the fracturing sleeve 37 closes multiple fracturing holes 36 to achieve stable sealing of the fracturing holes 36.

[0063] In one embodiment, such as Figure 3 , Figure 4 , Figure 5 As shown, each fracturing hole 36 is sealed with a slotted metal plate 10 to reduce the risk of gravel entering the outer sleeve 34. Simultaneously, when the fracturing service tool 200 pressurizes the outer sleeve 34, the fracturing fluid can rupture the slotted metal plate 10, thus affecting the normal operation of the fracturing operation.

[0064] In one embodiment, such as Figure 3 , Figure 4 , Figure 5 As shown, the screen sleeve assembly 33 includes a screen sleeve base tube 331. The top of the screen sleeve base tube 331 is connected to the sand prevention assembly 32, and the bottom is connected to the sliding sleeve outer cylinder 34. The screen sleeve outer cylinder 332 is fixedly sleeved at the upper end of the screen sleeve base tube 331. A one-way valve 333 is fixedly connected to the screen sleeve base tube 331, and the bottom of the screen sleeve outer cylinder 332 is connected to the one-way valve 333.

[0065] In one embodiment, such as Figure 3 , Figure 4 , Figure 5 As shown, an extension sleeve 334 is fitted onto the bottom end of the screen sleeve base pipe 331. The top end of the extension sleeve 334 is connected to a one-way valve 333, and the bottom end is connected to the outer sleeve cylinder 34. An annular cavity 335 exists between the extension sleeve 334 and the outer sleeve cylinder 34, and multiple production holes 35 are connected to the annular cavity 335. At the same time, the one-way valve 333 ensures that oil and gas in the well can only enter the annular cavity 335 through the screen sleeve outer cylinder 332, and then enter the outer sleeve cylinder 34 through the production holes 35.

[0066] In one embodiment, such as Figure 1 , Figure 3As shown, the sand control assembly 32 includes a sand control sleeve 321 connected to the bottom of the isolation packer 31, and the sand control sleeve 321 has sand control holes (not shown in the figure). A sand control sliding sleeve 322 is slidably fitted on the sand control sleeve 321, and the filling service tool can control the vertical sliding of the sand control sliding sleeve 322 to control the opening and closing of the sand control holes. At the same time, the bottom of the sand control sleeve 321 is connected to an extension screen tube 323 through a positioning coupling, and the bottom of the extension screen tube 323 is connected to the corresponding screen sleeve base tube 331.

[0067] In one embodiment, such as Figure 1 , Figure 2 As shown, the top packer assembly 2 includes a top packer 21 for setting and packing the wellhead, and the oil and gas well casing 1 is connected to the top of the top packer 21. The bottom of the top packer 21 is connected to a sand-filling assembly 22, and the bottom of the sand-filling assembly 22 is connected to a corresponding oil and gas screen 5. At the same time, the sand-filling assembly 22 is used to fill gravel into the wellbore.

[0068] In one embodiment, such as Figure 1 , Figure 2 As shown, the sand filling assembly 22 includes a sand filling sleeve 221. The top of the sand filling sleeve 221 is connected to the top packer 21, and the bottom is connected to the corresponding oil and gas screen pipe 5. The sand filling sleeve 221 has a sand filling hole (not shown in the figure). A sand filling slide sleeve 222 is slidably fitted onto the sand filling sleeve 221, and the filling service tool can control the vertical sliding of the sand filling slide sleeve 222 to control the opening and closing of the sand filling hole.

[0069] In this embodiment, the sand-proof sleeve 321 and the sand-filling sleeve 221 have the same structure. At the same time, the sand-proof sliding sleeve 322 and the sand-filling sliding sleeve 222 have the same structure and both adopt filling sliding sleeves. Using filling sliding sleeves and filling service tools to achieve gravel filling is the prior art and will not be described in detail here.

[0070] In this embodiment, the sand control tubing 100 is equipped with multiple sand control fracturing assemblies 3, and each sand control fracturing assembly 3 includes an isolation packer 31. In other words, the oil well is isolated into multiple segments by multiple isolation packers 31, thereby achieving effective isolation between different production layers. Moreover, this operation is simple and quick, which can improve both fracturing efficiency and fracturing effect.

[0071] Meanwhile, the sand control assembly 32 fills the space between two adjacent isolation packers 31 with gravel, and the sand filling mechanism fills the space between the top packer 21 and the uppermost isolation packer 31 with gravel, thereby achieving the sand control completion function.

[0072] Moreover, this design enables the sand control tubing 100 to combine sand control, fracturing, and production functions, achieving an integrated setup of the tubing, increasing the functionality of the tubing, and reducing the operational difficulty and cost of sand control and fracturing operations.

[0073] This embodiment also discloses a sand control fracturing method using the aforementioned sand control tubing 100, comprising the following steps:

[0074] S1, the sand control tubing string 100 is lowered, and the sand packer 4, the top packer assembly 2 and multiple isolation packers 31 are respectively set in the well to achieve the setting and sealing of the oil well;

[0075] S2, the fracturing service tool 200 is lowered into the sand control string 100 through the drill pipe or coiled tubing, and the fracturing service tool 200 controls the fracturing sleeve 37 to move downward, so that the fracturing sleeve 37 closes all fracturing holes 36, so that multiple production holes 35 are opened respectively.

[0076] S3, gravel is filled into the oil well through the sand control assembly 32, so that the space between the two adjacent isolation packers 31 is filled with gravel. At the same time, gravel is filled into the oil well through the sand filling assembly 22, and the space between the top packer 21 and the isolation packer 31 located at the topmost position is filled with gravel, so as to achieve the sand control completion function.

[0077] S4. When performing secondary fracturing, select the target layer and fill the sand control tubing 100 with sand to fill the remaining sand control tubing 100 below the fracturing layer, in preparation for fracturing the target layer. At this time, the one-way valve 333 can ensure that after the sand control tubing 100 is filled with sand, the gravel will not enter the outer cylinder of the screen sleeve 332 through the production hole 35.

[0078] S5, the fracturing service tool 200 is lowered into the sand control string 100 through the drill pipe or coiled tubing, and the fracturing service tool 200 controls the fracturing sleeve 37 to move upward, so that the fracturing sleeve 37 closes all production holes 35, so that multiple fracturing holes 36 are opened respectively.

[0079] S6, fracturing fluid is pumped into the sand control string 100 through the fracturing service tool 200. At this time, the slotted metal plate 10 of the fracturing hole 36 can prevent sand and gravel from entering the sand control string 100. As the fracturing fluid continues to be injected, the fracturing fluid is pressurized at the slotted metal plate 10 and breaks the slotted metal plate 10. Subsequently, the high-pressure liquid enters the formation and performs secondary fracturing on the target section.

[0080] S7. After the secondary fracturing operation is completed, the fracturing slide 37 is controlled to move downward by the fracturing service tool 200, so that the fracturing slide 37 closes all fracturing holes 36, so that multiple production holes 35 are opened respectively. Then the fracturing service tool 200 is taken out.

[0081] S8, the oil and gas in the well replace the fracturing fluid and flush the sand and gravel out of the sand control string 100. At this time, the sand control string 100 remains in its full-bore state before fracturing and continues production.

[0082] In one embodiment, such as Figure 3 , Figure 6 As shown, the fracturing service tool 200 includes a fracturing tubing string 300, on which a fracturing packer 400 is mounted, and the fracturing packer 400 can be seated on the screen sleeve base tube 331. Simultaneously, a switching tool 500, which is an expansion claw, is connected to the fracturing tubing string 300. Under hydraulic control, it expands outward and abuts against the inner wall of the fracturing sleeve 37, thereby driving the fracturing sleeve 37 to move vertically. At the same time, fracturing fluid can be discharged through the fracturing tubing string 300 to achieve pressurization operations. This service tool is existing technology and will not be described in detail here.

[0083] As can be seen from the above, the sand control pipe string 100 has a simple structure, low cost, and is easy to implement. During sand control and production, the fracturing sleeve 37 is in a closed state, that is, the fracturing sleeve 37 blocks the fracturing hole 36, which will not affect the construction and production. In addition, the locking ring 8 and the limiting groove 9 limit the cooperation to prevent accidental opening and closing and ensure the reliability of the operation.

[0084] Furthermore, the sand control fracturing method avoids the traditional fracturing method of perforating old screen tubes, keeping the screen tubes intact and the sand control performance unaffected. At the same time, after fracturing is completed, the fracturing sleeve 37 is closed, and the sand control tubing string 100 maintains its full bore, which is beneficial for oil and gas production and subsequent construction. Moreover, it can selectively repeat fracturing on any selected layer, providing high flexibility.

[0085] It should be noted that, unless otherwise stated, the technical or scientific terms used in this invention should have the ordinary meaning as understood by one of ordinary skill in the art.

[0086] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A sand-control tubular string capable of secondary fracturing, characterized in that, It includes a top packer assembly (2), a sand fracturing assembly (3), and a sand settling packer (4) arranged sequentially from top to bottom. Multiple sand fracturing assemblies (3) are provided. The top packer assembly (2), multiple sand fracturing assemblies (3), and the sand settling packer (4) are connected to each other through oil and gas screen pipes (5). The sand fracturing assembly (3) includes: Isolation packer (31), used to set and seal oil wells; Sand control assembly (32) is connected to the bottom of the isolation packer (31) and is used to fill the well with gravel; The screen sleeve assembly (33) is connected to the bottom of the sandproof assembly (32); The outer sleeve (34) is connected to the bottom of the screen sleeve assembly (33). The upper end of the outer sleeve (34) is provided with multiple production holes (35) and the lower end is provided with multiple fracturing holes (36). The fracturing sleeve (37) is vertically slidably disposed inside the outer sleeve cylinder (34), and the fracturing service tool can control the fracturing sleeve (37) to slide vertically and make the fracturing sleeve (37) close the production hole (35) or fracturing hole (36); The lower end of the fracturing sleeve (37) is provided with a support groove (7), and a C-shaped locking ring (8) is provided in the support groove (7). Limiting grooves (9) are respectively provided in the middle and lower ends of the outer sleeve (34). The locking ring (8) can be inserted into any of the limiting grooves (9) to limit the fracturing sleeve (37) and thus achieve stable sealing of the production hole (35) and the fracturing hole (36). Each of the fracturing holes (36) is sealed with a slotted metal plate (10), and when the fracturing service tool pressurizes the outer sleeve (34), the fracturing fluid can break through the slotted metal plate (10). The screen sleeve assembly (33) includes: The screen sleeve base tube (331) is connected to the sandproof assembly (32) at the top and to the sliding sleeve outer cylinder (34) at the bottom; The outer sleeve (332) of the sieve sleeve is fixedly sleeved at the upper end of the sieve sleeve base tube (331); A one-way valve (333) is installed on the screen sleeve base tube (331), and the bottom of the screen sleeve outer cylinder (332) is connected to the one-way valve (333); An extension sleeve (334) is connected at one end to the single-flow valve (333) and at the other end to the outer sleeve cylinder (34). An annular cavity (335) exists between the extension sleeve (334) and the outer sleeve cylinder (34), and multiple production holes (35) are respectively connected to the annular cavity (335). The single-flow valve (333) allows oil and gas in the well to enter the annular cavity (335) only through the outer sleeve of the screen sleeve (332), and enter the outer sleeve of the sliding sleeve (34) through the production hole (35).

2. The sand-control pipe string according to claim 1, characterized in that, Multiple sealing rings (6) are fixedly fitted on the fracturing slide sleeve (37) to improve the sealing effect between the fracturing slide sleeve (37) and the outer sleeve cylinder (34).

3. The sand-control pipe string according to claim 1, characterized in that, The sand-proof assembly (32) includes: A sandproof sleeve (321) is connected to the bottom of the isolation packer (31), and a sandproof hole is provided on the sandproof sleeve (321); The sand-proof sliding sleeve (322) is slidably sleeved on the sand-proof sleeve (321), and the filling service tool can control the sand-proof sliding sleeve (322) to slide vertically, so as to realize the control of the opening and closing of the sand-proof hole; The extended screen tube (323) is connected at the top to the sandproof sleeve (321) via a positioning coupling and at the bottom to the corresponding screen sleeve base tube (331).

4. The sand-control pipe string according to claim 1, characterized in that, The top sealing assembly (2) includes: Top packer (21) is used to set and pack the wellhead; The sand filling assembly (22) is connected at the top to the top packer (21) and at the bottom to the corresponding oil and gas screen (5), and the sand filling assembly (22) is used to fill gravel into the wellbore.

5. The sand-control pipe string according to claim 4, characterized in that, The sand-filling assembly (22) includes: The sand-filling sleeve (221) is connected to the top packer (21) at the top and to the corresponding oil and gas screen pipe (5) at the bottom, and a sand-filling hole is provided on the sand-filling sleeve (221). A sand-filling sliding sleeve (222) is slidably fitted onto the sand-filling sleeve (221), and the filling service tool can control the vertical sliding of the sand-filling sliding sleeve (222) to achieve control of the opening and closing of the sand-filling hole.

6. The sand-control pipe string according to claim 4, characterized in that, The top of the top packer (21) is connected to the oil and gas well casing (1).

7. A method for preventing sand fracturing, using a sand control tubing string according to any one of claims 1-6, characterized in that, Includes the following steps: S1, the sand control string (100) is lowered and the sand packer (4), the top packer assembly (2) and multiple isolation packers (31) are set in the well to achieve the setting and sealing of the oil well; S2, lower the fracturing service tool (200) and control the fracturing sleeve (37) to move downward through the fracturing service tool (200) so that the fracturing sleeve (37) closes all fracturing holes (36) so that multiple production holes (35) are opened respectively; S3, by filling the oil well with gravel through the sand control assembly (32), the space between two adjacent isolation packers (31) is filled with gravel to achieve sand control operation; S4. When performing secondary fracturing, select the target section, fill the sand inside the sand control tubing (100), and fill the remaining sand control tubing (100) below the fracturing section to prepare for fracturing of the target section. S5, the fracturing service tool (200) is lowered into the sand control string (100) through the drill pipe or coiled tubing, and the fracturing sleeve (37) is controlled to move upward through the fracturing service tool (200) so that the fracturing sleeve (37) closes all production holes (35) so that multiple fracturing holes (36) are opened respectively; S6, fracturing fluid is pumped into the sand control string (100) through the fracturing service tool (200), and the fracturing fluid enters the formation through the fracturing hole (36) and performs secondary fracturing on the target section; S7. After the secondary fracturing operation is completed, the fracturing sleeve (37) is controlled to move downward by the fracturing service tool (200) so that the fracturing sleeve (37) closes all fracturing holes (36) so that multiple production holes (35) are opened respectively. Then the fracturing service tool (200) is taken out. S8, the oil and gas in the well replace the fracturing fluid and flush the sand and gravel out of the sand control string (100). At this time, the sand control string (100) remains in full-bore condition as before fracturing and continues production.

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