Staged fracturing tool and construction method

Abstract

The invention provides a staged fracturing tool and a construction method, and belongs to the technical field of downhole tools. A step is arranged on the inner surface of the reducing coupling; a ball seat is mounted on the inner surface of the reducing coupling, the ball seat comprises a conical barrel, the conical barrel is of a conical barrel-shaped structure, and a connector is mounted on the first end face of the conical barrel; a first end face and a second end face are arranged on the outer surface of the conical cylinder, an expansion ring and a limiting ring are sequentially arranged on the outer surface of the conical cylinder from the second end face to the first end face, and a sealing ball is arranged on the inner surface of the conical cylinder in a sealing mode. Damage of anchoring teeth of a conventional bridge plug slip to the inner wall of a sleeve is effectively avoided, positive pressure of the slip to the sleeve is eliminated, multiple risks of sleeve deformation and later construction are reduced, and the problems that the bridge plug slips and fails to anchor due to the fact that the slip is not firmly anchored are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of downhole tools, and in particular relates to a staged fracturing tool and a construction method. Background Art

[0002] Due to the abundant amount and great development potential of tight oil and gas, shale oil and gas and other unconventional oil and gas resources, they are the main direction of energy succession. More than 90% of unconventional oil and gas development requires reservoir transformation measures to obtain relatively ideal production capacity. In recent years, with the research and continuous progress of domestic horizontal well staged fracturing technology, layered injection and production and horizontal well multi-stage fracturing technology have been widely used as core technical means for unconventional oil and gas reservoir transformation and effective increase in single well production, and have achieved significant production increase effects. Usually, during fracturing operations, bridge plugs are used to seal the downhole casing to isolate the target layer. The two technologies of bridge plug + cluster perforation and horizontal well multi-stage fracturing are the main technologies for the development of unconventional oil and gas resources. They can achieve the purpose of high-intensity, unlimited-level, and volume transformation, and are widely used at home and abroad.

[0003] After years of development, bridge plugs have evolved from cast iron drillable bridge plugs and composite drillable bridge plugs to soluble bridge plugs. The working principle of the bridge plug is that under the axial force of the downhole sealing tool, the bridge plug's slip expands and anchors to the inner wall of the casing, and the rubber sealing component is squeezed or expanded and deformed to fit the casing arm and locked, thereby achieving the sealing of the downhole casing and interlayer isolation. However, existing bridge plugs usually rely on high-strength anchor teeth embedded in the outer circle of the slip assembly to bite into the casing to achieve reliable anchoring and withstand the pressure during fracturing operations. Usually, the anchor teeth are made of alloy or ceramic self-dissolving materials. The high-strength anchor teeth need to bite into the inner wall of the casing to a certain depth, causing local damage to the inner wall of the casing, affecting the strength of the casing, and increasing the risk of casing deformation. Secondly, due to casing deformation or insufficient depth of the anchor teeth biting into the casing wall in different steel grades, it is easy to slip and anchor failure after the bridge plug is set and during the fracturing construction due to the action of high-pressure fluid, resulting in failure of the bridge plug seal and interruption of the fracturing operation. In addition, high-strength anchor teeth cannot dissolve underground, and a large number of anchor teeth are embedded in the casing arms or accumulated in the casing, which increases the complexity and risks of subsequent construction and flowback.

[0004] Therefore, there is a need for a dissolvable staged fracturing tool that is convenient for subsequent construction. Summary of the invention

[0005] In view of the above problems, the present invention provides a staged fracturing tool, comprising a casing connected by a reducer coupling; the inner surface of the reducer coupling is provided with a step;

[0006] The inner surface of the reducer coupling is provided with a ball seat, the ball seat comprises a cone, the cone is a conical cylindrical structure, a joint is provided on the first end surface of the cone; an expansion ring and a limit ring are provided on the outer surface of the cone in sequence from the second end surface to the first end surface, the limit ring is in contact with the joint;

[0007] After the cone is expanded, the outer surface close to the second end face is pressed against the inner wall of the reducer coupling or the inner wall of the casing to form an auxiliary seal; after the expansion ring is expanded, the diameter is larger than the inner diameter of the step, and the expansion ring contacts the upper surface of the step and establishes a seal; a sealing ball is installed on the inner surface of the cone, and the diameter of the sealing ball is smaller than the inner diameter of the casing and larger than the inner diameter of the first end face of the cone.

[0008] Furthermore, a boss is provided on the outer surface of the cone close to the second end surface; the maximum outer diameter of the boss is at least 0.5 mm smaller than the outer diameter of the joint.

[0009] Furthermore, a protrusion is provided on the outer surface of the cone cylinder to mesh with a groove provided on the inner surface of the expansion ring to establish a seal.

[0010] Furthermore, the outer surface of the cone is provided with helical teeth which mesh with the helical teeth provided on the inner surface of the expansion ring to establish a seal.

[0011] Furthermore, a protrusion is provided on the outer surface of the expansion ring to seal and contact with the inner surface of the reducer coupling or the inner surface of the casing.

[0012] Furthermore, a U-shaped fracture notch is provided on the inner side of the limiting ring; the outer diameter of the limiting ring is smaller than the inner diameter of the step, and the limiting ring is installed on the inner surface of the step.

[0013] Furthermore, the expansion ring is wedge-shaped as a whole, and arc-shaped chamfers are provided at both ends of the expansion ring. The outer diameter of the expansion ring should be at least 1 mm smaller than the outer diameter of the joint.

[0014] Furthermore, the staged fracturing tool also includes a sealing tool, the outer end of the sealing tool is connected to a sealing sleeve, the end of the sealing sleeve away from the sealing tool is connected to a conical push cylinder, the first end of the conical push cylinder is in contact with the inner surface of the conical cylinder; the inner end of the sealing tool is connected to a connecting core shaft, the connecting core shaft passes through the conical push cylinder, the conical cylinder and is threadedly connected to the joint.

[0015] Furthermore, the cone, expansion ring and sealing ball are all made of high elongation self-dissolving material, and the high elongation self-dissolving material is soluble magnesium alloy, soluble aluminum alloy or soluble magnesium-aluminum alloy.

[0016] A construction method, using the above-mentioned staged fracturing tool, comprises the following steps:

[0017] Install reducer collars between predetermined casings;

[0018] Install the ball seat on the reducer coupling; and radially expand the cone and expansion ring until they are close to the inner wall of the reducer coupling;

[0019] The sealing ball is placed, and the thrust of the fluid causes the sealing ball to fall into the inner hole at the upper end of the expanded cone cylinder and seal the inner hole of the cone cylinder;

[0020] The ground pump truck is started, the wellbore pressure is quickly increased and fracturing fluid and proppant are continuously injected to complete the fracturing.

[0021] Beneficial effects of the present invention:

[0022] 1. The present invention adopts a plugging method in which a reducer coupling is preset, and the cone and the expansion ring are radially deformed and expanded under the action of the axial force when they are installed, and then they are sealed in the reducer coupling. This effectively avoids the damage of the conventional bridge plug slip anchoring teeth to the inner wall of the casing, eliminates the positive pressure of the slip on the casing, reduces the deformation of the casing and many risks of later construction; and solves the problem of bridge plug slippage and anchor failure caused by unreliable slip anchoring.

[0023] 2. The cone, expansion ring and sealing ball of the present invention are made of high-elongation self-dissolving material, with a simple overall structure and low manufacturing cost. No special lowering and sealing construction process is required, and the full bore of the wellbore can be quickly restored after the operation. It can promote the iterative upgrade of large-scale volume fracturing tools, replace conventional soluble bridge plug staged fracturing, and promote the rapid development of staged fracturing tools in the direction of simple structure, low cost, fast dissolution, and no residue, providing strong technical support for the integrated design of geological engineering.

[0024] 3. The ball seat of the present invention has no residue after dissolution, and no continuous tubing drilling and plugging operation is required after fracturing construction, which can effectively solve the staged fracturing transformation problems of ultra-long horizontal wells, complex well conditions and special U-shaped wells.

[0025] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 A schematic diagram showing the position of the ball seat of the staged fracturing tool installed in the reducer coupling in Example 1 of the present invention is shown.

[0028] Figure 2 The schematic diagram shows the position of the adapter tool of the staged fracturing tool in Example 1 of the present invention before being connected to the ball seat and installed in the casing string.

[0029] Figure 3 The schematic diagram shows the position of the adapter tool of the staged fracturing tool in Example 1 of the present invention being connected to the ball seat and installed in the casing string.

[0030] Figure 4 The schematic diagram shows the position of the adapter tool of the staged fracturing tool in Example 1 of the present invention, which is connected to the ball seat and installed in the casing string, and before the ball seat is disconnected from the adapter tool.

[0031] Figure 5 A schematic diagram showing the position of the ball seat of the staged fracturing tool in Example 1 of the present invention installed in the casing string is shown.

[0032] Figure 6 The schematic diagram of the structure of the casing string of the staged fracturing tool in Example 1 of the present invention is shown.

[0033] Figure 7 A schematic structural diagram of the connection between the ball seat of the staged fracturing tool and the adapter tool in Example 1 of the present invention is shown.

[0034] Figure 8 A schematic structural diagram of a ball seat of a staged fracturing tool in Example 1 of the present invention is shown.

[0035] Fig. 9 A schematic structural diagram of a limit ring of a staged fracturing tool in Example 1 of the present invention is shown.

[0036] Fig.10 The schematic diagrams of various structural embodiments of the cone and expansion ring of the staged fracturing tool in Example 1 of the present invention are shown.

[0037] Fig.11 A schematic diagram of a preset reducer coupling for a pipe casing column in Example 1 of the present invention is shown.

[0038] Fig.12 A schematic diagram of the construction operation of the staged fracturing tool in Example 1 of the present invention is shown.

[0039] Fig.13 A schematic diagram showing the recovery of the full bore of the wellbore by dissolving the ball seat after the fracturing operation in Example 1 of the present invention is shown.

[0040] Fig.14 A schematic diagram showing the position of a ball seat of a staged fracturing tool in Example 1 of the present invention installed in another reducer coupling is shown.

[0041] Fig.15A schematic flow chart of the construction method in Embodiment 2 of the present invention is shown.

[0042] In the figure, 1, ball seat; 11, cone; 111, boss; 12, expansion ring; 13, limit ring; 14, joint; 15, screw; 16, sealing ball;

[0043] 2. Adapter tool; 21. Setting tool; 22. Setting sleeve; 23. Connecting mandrel; 24. Set screw; 25. Conical push cylinder;

[0044] 31. casing; 32. reducer coupling; 321. step;

[0045] 5. Pipe and casing string; 6. Oil and gas reservoir. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] like Figure 1 As shown, Figure 1 The schematic diagram shows the position of the ball seat of the staged fracturing tool installed in the reducer coupling in Example 1 of the present invention. Figure 1 , a staged fracturing tool, comprising a casing 31 connected by a reducer coupling 32; the inner surface of the reducer coupling 32 is provided with a step 321 (reference Figure 6 ); specifically, the reducer coupling 32 can adopt a thickened reducer coupling 32 to improve the connection strength and firmness; wherein the reducer coupling 32 has tapered threads at both ends, which are threadedly connected with the casing 31 at both ends respectively; through the conical surface transition, the angle of the conical surface is usually selected to be 20°~45°, and the preferred structure of the inner hole is: the inner hole at the large end has a certain length, which is at least 1.5 times the length of the ball seat 1; the pipe sleeve column 5 includes a casing 31 and a reducer coupling 32, and a reducer coupling 32 is connected between the casing 31 at the specified position for sealing.

[0048] refer to Figure 8, a ball seat 1 is installed on the inner surface of the reducer coupling 32, and the ball seat 1 includes a cone cylinder 11, which is a conical cylindrical structure, and the two ends of the cone cylinder 11 are respectively a first end face and a second end face, wherein the first end face is a small diameter end face, and the second end face is a large diameter end face; a joint 14 is installed on the small diameter end face of the cone cylinder 11; an expansion ring 12 and a limit ring 13 are installed on the outer surface of the cone cylinder 11 from the large diameter end face to the small diameter end face, and the limit ring 13 is in contact with the joint 14; the cone cylinder 11 is a conical cylindrical structure, which can be a cone cylinder with equal wall thickness or a structure with a thick upper end and a thin lower end, and the inner hole and the outer circle are respectively provided with conical surfaces, and the cone opening faces upward (reference Fig.10 , Fig.10 a is a diagram showing the matching of the cone 11 and the expansion ring 12, wherein the cone 11 is a cone of equal wall thickness, and a protrusion is provided on the outer surface of the cone 11 to mesh with a groove provided on the inner surface of the expansion ring 12; Fig.10 b is a diagram showing the coordination of the cone 11 and the expansion ring 12, wherein the cone 11 is a cone of equal wall thickness, and the outer surface of the cone 11 is provided with helical teeth that mesh with the helical teeth provided on the inner surface of the expansion ring 12; Fig.10 c is a diagram of the coordination of the cone 11 and the expansion ring 12, wherein the cone 11 is a cone of equal wall thickness, the outer surface of the cone 11 is provided with a protrusion which engages with a groove provided on the inner surface of the expansion ring 12, and the expansion ring 12 is provided with a protrusion on the side away from the cone 11 which contacts with the inner surface of the reducer coupling 32. Fig.10 d is a matching diagram of the cone 11 and the expansion ring 12, wherein the upper end of the cone 11 is thick and the lower end is thin, and a protrusion is provided on the outer surface of the cone 11 to mesh with the groove provided on the inner surface of the expansion ring 12 to establish a seal, and a seal and relative limitation are achieved between the expansion ring 12 and the cone 11 by providing a protrusion on the outer surface of the cone 11 to mesh with the groove provided on the inner surface of the expansion ring 12 or providing an oblique tooth on the outer surface of the cone 11 to mesh with the oblique tooth provided on the inner surface of the expansion ring 12 to establish a seal, so as to prevent the expansion ring 12 and the cone 11 from slipping on the contact surface, causing a poor seal or relative misalignment during use; a protrusion is provided on the side of the expansion ring 12 away from the cone 11 to contact the inner surface of the reducer 32).

[0049] refer to Fig.10 ,See Fig.10 a, Fig.10 c. Fig.10 d. The outer surface of the cone 11 is provided with a protrusion which meshes with the groove provided on the inner surface of the expansion ring 12. Fig.10 The outer surface of the cone 11 of b is provided with helical teeth which mesh with the helical teeth provided on the inner surface of the expansion ring 12; Fig.10 c. Fig.10 The expansion ring 12 of d is provided with a protrusion on the side away from the cone 11 to contact the inner surface of the reducer coupling 32.

[0050] After the cone 11 expands, the outer surface close to the second end surface is pressed against the inner wall of the reducer coupling 32 (refer to Figure 1 ) or on the inner wall of the sleeve 31 (reference Fig.14 , Fig.14 The reducer coupling 32 is convex outward and used to limit the ball seat 1) to form an auxiliary seal; when the cone 11 expands, the diameter of the expansion ring 12 after expansion is larger than the inner diameter of the step 321, and the expansion ring 12 contacts the upper surface of the step 321 and establishes a seal; the diameter of the sealing ball 16 is smaller than the inner diameter of the sleeve 31 and larger than the inner diameter of the small diameter end of the cone 11, and the sealing ball 16 is sealed and installed on the inner surface of the cone 11;

[0051] Specifically, the cone 11, the expansion ring 12 and the sealing ball 16 are made of a self-dissolving material with a high elongation.

[0052] Furthermore, the self-dissolving material used in the cone 11 has a high yield strength. The cone 11 can be made of a self-dissolving material with a high elongation and high yield strength, such as a soluble magnesium alloy, a soluble aluminum alloy, a magnesium-aluminum alloy, etc. with a high elongation and high yield strength, to ensure that it has a certain radial deformation capacity and can be uniformly expanded and deformed under the action of an axial force.

[0053] In the implementation of the present invention, a boss 111 is provided on the outer surface of the cone 11 near the large diameter end surface. It is the part with the largest diameter of the cone 11, and is used for the boss 111 to be pressed against the wall of the sleeve 31 after the cone 11 is expanded to form an auxiliary seal.

[0054] The maximum outer diameter of the boss 111 is 0.5mm-1.5mm smaller than the outer diameter of the joint 14; in one specific embodiment, a step groove is provided at the lower end of the cone cylinder 11 to cooperate with the joint 14, and the maximum outer diameter of the boss 111 at the upper end of the cone cylinder 11 should be 0.5mm smaller than the outer diameter of the joint 14 to prevent the boss 111 at the upper end of the cone cylinder 11 from contacting the inner wall of the sleeve 31 and wearing out prematurely during the rapid sliding of the ball seat 1 in the sleeve 31.

[0055] refer to Figure 1 , the inner diameter of the step 321 is consistent with the inner diameter of the casing 31. This ensures that the casing column 5 is of equal diameter. The inner holes of the expansion ring 12 and the limit ring 13 are both conical, and the angle of the cone surface is consistent with the angle of the outer circle of the cone cylinder 11, and they are placed in sequence at the lower end of the cone cylinder 11; the expansion ring 12 is wedge-shaped as a whole, and the upper and lower ends should be provided with arc chamfers, and must have good ductility and deformation capabilities; it is usually made of high elongation self-dissolving material, with an elongation of ≥25%, and can be uniformly expanded and deformed under the action of axial force but will not break; it is finally wedged into the gap between the cone cylinder 11 and the inner wall of the reducer 32, and is a key component of sealing; its outer diameter should be at least 0.5mm-3mm smaller than the outer diameter of the joint 14.

[0056] Furthermore, the gap finally wedged into the conical cylinder 11 and the inner wall of the reducer coupling 32 is a key component of sealing; its outer diameter should be at least 1 mm smaller than the outer diameter of the joint 14.

[0057] refer to Fig. 9 A U-shaped fracture notch is provided inside the limiting ring 13, and the limiting ring 13 will eventually break along the U-shaped fracture notch when the cone 11 expands. The limiting ring 13 is below the expansion ring 12 to axially position the expansion ring 12. The diameter of the limiting ring 13 is at least 12 mm smaller than the outer diameter of the expansion ring 12 to prevent it from contacting the small end of the inner hole of the reducer 32 in advance, thereby affecting the radial deformation of the cone 11 and the expansion ring 12. An arc groove is provided at any position of the circumference to serve as a fracture weak point of the limiting ring 13, which can be broken into a C shape when the cone 11 is radially deformed. The diameter of the limiting ring 13 is smaller than the inner diameter of the step 321, and the limiting ring 13 is directly opposite to the step 321.

[0058] refer to Figure 7 The joint 14 is provided with a large conical surface at a certain angle, and its taper can be in the range of 20° to 45° with the center line, which plays a guiding role. Its outer diameter should be at least 8mm smaller than the inner diameter of the sleeve 31 to ensure that the ball seat 1 slides smoothly in the sleeve 31. Furthermore, the outer diameter of the joint 14 should be 8mm smaller than the inner diameter of the sleeve 31.

[0059] The inner hole of the joint 14 is provided with a thread for connecting with the external thread of the connecting core shaft 23. The length of the internal thread of the joint 14 needs to be determined through strength calculation to obtain a certain tensile shear, that is: when the connecting core shaft 23 is subjected to a certain axial tension, the internal thread of the joint 14 is completely sheared, and the connecting core shaft 23 can be separated from the joint 14.

[0060] refer to Figure 7 The staged fracturing tool also includes a sealing tool 21, the outer end of the sealing tool 21 is connected to a sealing sleeve 22, the end of the sealing sleeve 22 away from the sealing tool 21 is connected to a conical push cylinder 25, the small diameter end of the conical push cylinder 25 is in contact with the inner surface of the cone cylinder 11; the inner end of the sealing tool 21 is connected to a connecting core shaft 23, the connecting core shaft 23 passes through the conical push cylinder 25, the cone cylinder 11 and is threadedly connected to the joint 14.

[0061] Specifically, the ball seat 1 is connected to the downhole sealing tool 21 through the adapter tool 2, and mainly comprises a sealing sleeve 22, a connecting core shaft 23, a tapered push cylinder 25, and a locking screw 24; wherein the sealing sleeve 22 is cylindrical, and an internal thread is provided at the upper end for external connection with the sealing tool 21, and at least two threaded holes are provided at the stop portion of the thread for installing the locking screw 24 to prevent the sealing sleeve 22 from rotating and disengaging; an internal thread is provided at the upper end of the connecting core shaft 23 for internal connection with the sealing tool 21, and an external thread is provided at the lower end for connection with the joint 14 of the ball seat 1, and the thread length should be greater than the internal thread length of the joint 14 to ensure that the thread is fully screwed in. The stepped surface at the upper end of the tapered push cylinder 25 abuts and cooperates with the lower end of the setting sleeve 22, and is positioned by more than 4 set screws 24 to prevent it from detaching. The inner hole at the upper end cooperates with the connecting core shaft 23, and the conical surface at the lower end cooperates with the outer conical surface of the cone cylinder 11. In the initial state, the lower end of the tapered push cylinder 25 is inserted into the upper end of the cone cylinder 11 to a certain depth. Under the axial force of the setting tool 21 (by pulling the inner shaft of the setting tool 21, the connecting core shaft 23 drives the joint 14 and then mobilizes the cone cylinder 11 and the expansion ring 12 to expand), the setting sleeve 22 transmits the axial force to the tapered push cylinder 25, and then gradually wedges into the inner hole of the cone cylinder 11 of the ball seat 1, so that the cone cylinder 11 and the expansion ring 12 expand radially until they are close to the inner wall of the reducer coupling 32. When the axial force reaches the shear force of the internal thread of the joint 14, the connecting core shaft 23 can be separated from the joint 14, and the ball seat 1 is expanded to the specified position.

[0062] In the above embodiment, another optional implementation is that the connecting core shaft 23 is connected to the joint 14 by means of a screw 15 , and the screw 15 is located in a hole of the joint 14 .

[0063] refer to Figure 1 The sealing ball 16 is spherical and made of fast-dissolving self-dissolving material. Its diameter depends on the inner diameter of the cone 11. After the bridge plug is set underground, the sealing ball 16 finally sticks to the conical surface of the inner hole at the large end of the cone 11 to block the inner hole. The contact point between the sealing ball 16 and the inner conical surface is in the upper half area. The sealing ball 16 should be larger than the minimum inner diameter of the cone 11 by more than 10-20mm. The sealing ball 16 should be 12mm larger than the minimum inner diameter of the cone 11.

[0064] Working principle:

[0065] A reducer collar 32 is pre-installed at a specific position of the wellbore. When the casing string 5 is lowered into the oil and gas well, the reducer collar 32 is connected at a specific position of the pre-set casing string 5, and the casing string 5 is lowered to the bottom of the well and cement slurry is injected for cementing. The connection position of the reducer collar 32 needs to be determined in combination with the wellbore fracturing transformation design plan. Finally, the wellbore with the preset reducer collar 32 is as follows: Fig.11 As shown, the reducer collars 32 are sequentially distributed at specific positions of the wellbore to contact the oil and gas reservoir 6 .

[0066] Lower the ball seat 1. During staged fracturing operations, Figure 2 As shown, the ball seat 1 is connected to the setting tool 21 on the ground through an adapter tool, and the tool string is lowered to a specific position of the bottom hole casing string based on the timely monitoring of the positioning instrument connected to the tool string by the gravity of the tool string and the thrust of the fluid. Then, the standard setting tool 21 on the tool string is started to apply a certain axial force. Under the axial force of the setting tool 21, the setting sleeve 22 transmits the axial force to the tapered push cylinder 25, and then gradually wedges into the inner hole of the tapered cylinder 11 of the ball seat 1 (as shown in FIG. Figure 3 As shown), the cone 11 and the expansion ring 12 are radially expanded until they are close to the inner wall of the reducer coupling 32 (as shown in FIG. Figure 4 As shown in the figure, when the axial force reaches the shear force of the internal thread of the joint 14, the connecting mandrel 23 can be separated from the joint 14, and the ball seat 1 is dropped at the designated inner hole of the reducer 32. After confirming that the ball seat 1 is successfully dropped, the tool string is lifted and perforated in sequence, and finally the tool string is pulled out of the wellhead (as shown in the figure). Figure 5 shown).

[0067] Ball-dropping and sealing. Before the fracturing operation begins, a sealing ball 16 is first dropped from the wellhead on the ground. The sealing ball 16 is quickly sent to the top of the ball seat 1 at the bottom of the well by the thrust of the fluid. The sealing ball 16 falls into the inner hole of the upper end of the expanded cone 11 and seals the inner hole of the ball seat 1. At the moment when the inner hole of the ball seat 1 is blocked, the pressure in the wellbore rises rapidly and is fed back to the ground instrument, so that it can be detected that the sealing ball 16 is successfully seated. Under the continued action of the fluid pressure, the sealing ball 16 slides downward a certain distance in the reducer coupling 32 along with the ball seat 1 until the expansion ring 12 of the ball seat 1 is compacted at the conical step 321 of the reducer coupling 32, thereby achieving complete sealing of the casing 31 or the wellbore by the ball seat 1 (such as Fig.12 shown).

[0068] Staged fracturing operation. After the ball seat 1 is completely blocked at the reducer 32, the surface pump truck group is started at the same time, the wellbore is quickly pressurized and the fracturing fluid and proppant are continuously injected to complete the fracturing of the layer. Fig.12 As shown, according to the above process, the whole wellbore staged fracturing operation can be performed by sequentially connecting, lowering, dropping the ball, and setting the ball seat 1.

[0069] The ball seat 1 dissolves. After the fracturing operation is completed, since the cone 11, expansion ring 12, limit ring 13, joint 14 and other components of the ball seat 1 are made of self-dissolving materials, they can dissolve quickly and automatically under certain temperature and mineralization conditions at the bottom of the well, and finally completely dissolve into fine powder residues. The material selection of each component needs to be optimized according to the actual well conditions to ensure that the ball seat 1 can effectively block the bottom of the well for more than or equal to 24 hours, and the complete dissolution time should be ≤120 hours. After all components are completely dissolved, the wellbore resumes its full diameter, such as Fig.13As shown, since the ball seat 1 as a whole does not have any insoluble matter, there will be no residue in the wellbore after dissolution, which will not affect subsequent construction and production.

[0070] Example 2

[0071] refer to Fig.15 A construction method, using the staged fracturing tool of Example 1, comprises the following steps:

[0072] Install a reducing collar 32 between predetermined casings 31;

[0073] Install the ball seat 1 onto the reducer coupling 32; and radially expand the cone 11 and the expansion ring 12 until they are close to the inner wall of the reducer coupling 32;

[0074] The sealing ball 16 is dropped into the inner hole of the upper end of the expanded cone cylinder 11 by the thrust of the fluid, and the inner hole of the cone cylinder 11 is blocked.

[0075] The surface pump truck is started to quickly increase the pressure of the wellbore and continuously inject fracturing fluid and proppant to complete the fracturing of the layer;

[0076] The cone 11, the expansion ring 12, the limit ring 13 and the joint 14 can dissolve by themselves without affecting the subsequent construction and production scheduling.

[0077] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A staged fracturing tool, characterized in that: It comprises a casing (31) connected by a reducing coupling (32); the reducing coupling (32) has a step (321) arranged on its inner surface; A ball seat (1) is installed on the inner surface of the reducer coupling (32), wherein the ball seat (1) comprises a cone (11), wherein the cone (11) is a conical cylindrical structure, and a joint (14) is installed on the first end surface of the cone (11); an expansion ring (12) and a limit ring (13) are installed on the outer surface of the cone (11) in sequence from the second end surface to the first end surface, and the limit ring (13) is in contact with the joint (14); After the cone (11) is expanded, the outer surface close to the second end face is pressed against the inner wall of the reducer coupling (32) or the inner wall of the sleeve (31) to form an auxiliary seal; after the expansion ring (12) is expanded, the diameter is larger than the inner diameter of the step (321), and the expansion ring (12) contacts the upper surface of the step (321) to establish a seal; a sealing ball (16) is installed on the inner surface of the cone (11) in a sealing manner, and the diameter of the sealing ball (16) is smaller than the inner diameter of the sleeve (31) and larger than the inner diameter of the first end face of the cone (11).

2. A staged fracturing tool according to claim 1, characterized in that: A boss (111) is provided on the outer surface of the cone (11) close to the second end surface; the maximum outer diameter of the boss (111) is at least 0.5 mm smaller than the outer diameter of the joint (14).

3. A staged fracturing tool according to claim 1, characterized in that: The outer surface of the cone (11) is provided with a protrusion which engages with a groove provided on the inner surface of the expansion ring (12) to establish a seal.

4. A staged fracturing tool according to claim 1, characterized in that: The outer surface of the cone (11) is provided with helical teeth which mesh with the helical teeth provided on the inner surface of the expansion ring (12) to establish a seal.

5. A staged fracturing tool according to claim 3 or 4, characterized in that: The outer surface of the expansion ring (12) is provided with a protrusion which is in sealing contact with the inner surface of the reducer coupling (32) or the inner surface of the sleeve (31).

6. A staged fracturing tool according to claim 1, characterized in that: A U-shaped fracture notch is provided on the inner side of the limiting ring (13); the outer diameter of the limiting ring (13) is smaller than the inner diameter of the step (321), and the limiting ring (13) is installed on the inner surface of the step (321).

7. A staged fracturing tool according to claim 1, characterized in that: The expansion ring (12) is wedge-shaped as a whole, and arc-shaped chamfers are provided at both ends of the expansion ring (12). The outer diameter of the expansion ring (12) should be at least 1 mm smaller than the outer diameter of the joint (14).

8. A staged fracturing tool according to claim 1, characterized in that: The staged fracturing tool also includes a sealing tool (21), the outer end of the sealing tool (21) is connected to a sealing sleeve (22), the end of the sealing sleeve (22) away from the sealing tool (21) is connected to a conical push tube (25), the first end of the conical push tube (25) is in contact with the inner surface of the conical tube (11); the inner end of the sealing tool (21) is connected to a connecting core shaft (23), the connecting core shaft (23) passes through the conical push tube (25), the conical tube (11) and is threadedly connected to the joint (14).

9. A staged fracturing tool according to claim 1, characterized in that: The cone (11), the expansion ring (12) and the sealing ball (16) are all made of a high-elongation self-dissolving material, and the high-elongation self-dissolving material is a soluble magnesium alloy, a soluble aluminum alloy or a soluble magnesium-aluminum alloy.

10. A construction method, using the staged fracturing tool according to any one of claims 1 to 9, characterized in that: The steps include: Installing a reducing collar (32) between predetermined casings (31); The ball seat (1) is mounted on the reducer coupling (32); and the cone (11) and the expansion ring (12) are radially expanded until they are in close contact with the inner wall of the reducer coupling (32); A sealing ball (16) is introduced, and the sealing ball (16) is caused to fall into the inner hole at the upper end of the expanded cone cylinder (11) by the thrust of the fluid, thereby sealing the inner hole of the cone cylinder (11); The ground pump truck is started, the wellbore pressure is quickly increased and fracturing fluid and proppant are continuously injected to complete the fracturing.

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