Reconstruction elastic ball seat refracturing method for repairing wellbore with casing pipe

Abstract

According to the casing subsidy wellbore reconstruction elastic ball seat refracturing method, an original perforation section is shielded through casing expansion pipe subsidy, and the method is similar to new well transformation; tool sand burying caused by communication of an upper layer and a lower layer due to poor well cementation quality outside the casing pipe is effectively prevented, and the problem that reverse circulation cannot be established due to well backwashing liquid leakage caused by formation pressure deficiency can be effectively solved; due to the fact that the ball seat throwing tool restrains the elastic ball seat in the ball seat throwing tool, the outer diameter of the elastic ball seat is reduced, the elastic ball seat can smoothly pass through hole shrinkage sections of all casing pipe subsidy in a shaft, infinite-level transformation can be achieved theoretically, the requirement for large-displacement fracturing can be met, and the construction efficiency can be greatly improved. The problem of repeated transformation of old wells of oil fields can be effectively solved, repeated fracturing of transformed layer sections can be completed, and meanwhile perforation and fracturing integrated operation of new sections can be completed.

Description

Technical Field

[0001] The invention belongs to the technical field of wellbore reconstruction of oilfield horizontal wells, and specifically relates to a method for repeated fracturing of an elastic ball seat for reconstructing a wellbore with casing supplementation, which is suitable for repeated fracturing transformation of horizontal wells with casing completion. Background Art

[0002] Existing re-fracturing methods include temporary plugging re-fracturing technology and transformation by using packers for isolation. Temporary plugging re-fracturing technology is to inject liquid or solid temporary plugging agent or temporary plugging ball into the original fracture to plug the original fracture, and then re-fractured the new perforated section or the unfractured perforated section by pumping fracturing fluid, which greatly increases the transformation volume and significantly improves the construction effect, thereby obtaining the maximum economic benefit. Figure 1 As shown, the horizontal well is repeatedly reformed and fractured because there are several reformed layers in the whole wellbore, so it is necessary to equip a hydraulic anchor 1 and use two packers, the upper K344 packer 2 and the lower K344 packer 4 to isolate the upper and lower parts of the construction layer for reformation.

[0003] For example, the patent application publication number CN109973067A discloses physical plugging of cracks by plugging particles, and then injecting cement to replace cement into the cracks by drillable plugging materials to achieve wellbore reconstruction, and then repeat fracturing construction. The above repeated fracturing technology, when adding temporary plugging balls or temporary plugging agents, due to the poor followability of temporary plugging balls or temporary plugging agents in liquids, may result in failure to block the liquid inlet channel, resulting in excessive transformation of the liquid inlet channel and excessive extension of some cracks, while other areas cannot be effectively transformed, resulting in poor plugging of the original cracks by the reconstructed wellbore, so that when repeat fracturing is performed, the flow direction of the pumped fracturing fluid is uncontrolled, and the ground cannot accurately know the fracturing layer section. In other words, due to insufficient plugging, the new repeated fracturing layer section cannot be accurately controlled, resulting in blindness in fracturing construction, and it is difficult to maximize the repeated transformation of the reservoir.

[0004] On April 22, 2022, the State Intellectual Property Office published an invention patent entitled "A method for repeated fracturing of shale gas horizontal wells", with a publication number of CN114382455A. This patent uses a repeated fracturing casing in conjunction with a packer to be lowered into the wellbore, which can cooperate with temporary plugging fluid to seal the fracture holes of the initial fracturing, and use the expansion seal of the packer to achieve complete isolation, thereby improving the sealing of the initial perforation holes, thereby improving the success rate of fracturing, and having the effect of improving the accuracy of repeated fracturing. This method can only be used for tubing and sandblasting injection and sand addition, and cannot achieve large-volume transformation. In addition, due to poor cementing quality, the two open layers outside the casing communicate, causing the injected liquid to flow back to the ground from the communication and burying the pipe string with sand, causing the drill to get stuck. In addition, when the reverse circulation operation is performed after the pressure is completed, the large absorption volume of the open layer causes the inlet and outlet displacement to be inconsistent and the sand cannot be brought out of the ground. Summary of the invention

[0005] The purpose of the present invention is to provide a method for repeated fracturing by regenerating an elastic ball seat by patching a wellbore with casing, so as to overcome the above-mentioned technical problems existing in the prior art.

[0006] To this end, the technical solution provided by the present invention is as follows: The method for repeated fracturing by casing-filling wellbore and recreating elastic ball seat comprises the following steps: Step 1) lowering the expansion pipe patching device to completely seal the original perforation section through the expansion pipe patching; Step 2) lowering the perforating string to perform perforating operations on the first section of the supplementary hole; Step 3) pulling out the perforating string to perform bare casing fracturing on the first section of the supplementary hole; Step 4) After the fracturing is completed, an elastic ball seat delivery tool is connected to the lower end of the perforating string, and a soluble ball is dropped into the tool to make the elastic ball seat shield the first section of the perforation patching, and then the perforating gun is used to perform the perforation operation of the second section of the perforation patching; Step 5) lifting the exit pipe string to perform bare casing fracturing on the second section of the supplementary hole; Step 6) Repeat steps 4) to 5) to complete all the plugging sections and the whole well construction is completed.

[0007] The expansion pipe patching device includes an expansion pipe, an expansion cone and a baffle, wherein the expansion cone and the baffle are respectively located at two ends of the expansion pipe, the expansion cone is connected to an oil pipe, the oil pipe passes through the baffle and is connected to the expansion cone, and a water hole is opened on the oil pipe near the expansion cone.

[0008] The elastic ball seat delivery tool comprises an outer cylinder and an elastic ball seat, wherein the elastic ball seat is arranged in the outer cylinder and the two are connected by a shear pin.

[0009] Step 1) The process of using the expansion tube to patch the original perforation section is as follows: the expansion tube patching device is lowered through the oil pipe to the casing position that needs to be patched, water is injected into the oil pipe to pressurize it, and water flows out from the water hole to expand the expansion tube, and the expansion cone moves upward and separates from the upper end of the expansion tube together with the baffle, and the patching is completed.

[0010] Step 4) The specific process is as follows: the perforating string drives the elastic ball seat delivery tool into the casing under the action of gravity. After reaching the predetermined position, the soluble ball is dropped, and then the perforating gun performs hydraulic sandblasting perforation. After the perforation is completed, the displacement is increased to cut the shear pin. At this time, the soluble ball pushes the elastic ball seat out of the outer tube, releasing its restraint force, and the elastic ball seat freely expands to a predetermined size so that it is close to the casing wall and sits on the upper end of the expansion tube patch.

[0011] The elastic ball seat is a "C-shaped" thin-wall cylinder, and the bottom is an elastic claw.

[0012] The perforating pipe string is threadedly connected with the elastic ball seat delivery tool through the perforating gun.

[0013] The displacement of the perforating gun for hydraulic sandblasting perforation is 2-2.5m 3 / min, after perforation, the displacement is increased to 3-3.5m 3 / min.

[0014] During the fracturing process, the upper end of the expansion tube provides support for the elastic ball seat. After the fracturing is completed, the soluble ball dissolves and disappears, achieving large-volume fracturing.

[0015] The beneficial effects of the present invention are: The invention shields the original perforation section through the casing expansion tube patch, which is similar to the reconstruction of a new well. It can effectively prevent the sand burial of tools caused by the communication between the upper and lower layers due to poor cementing quality outside the casing, and can also effectively solve the problem of reverse circulation failure caused by liquid leakage in the backwash well due to formation pressure deficit. Since the elastic ball seat placement tool constrains the elastic ball seat inside and reduces its outer diameter, it can smoothly pass through the reduced diameter sections of all casing patches in the wellbore. In theory, it can achieve unlimited-level reconstruction and meet the requirements of large-volume fracturing, so it can greatly improve construction efficiency.

[0016] The present invention constrains the outer diameter of the elastic ball seat through an elastic ball seat delivery tool so that it can smoothly pass through the multi-stage casing patch; after pre-setting, the soluble ball is firstly dropped and then perforated, and then the displacement is increased to push the elastic ball seat out through the soluble ball to release its constraint force, and the elastic ball seat freely expands to a predetermined size and fits tightly against the upper part of the wellbore pre-set casing patch to seal the patching section, effectively preventing the tool from being buried in sand due to the communication between the upper and lower layers caused by poor cementing quality on the outside of the casing; after fracturing is completed, the soluble ball dissolves, effectively solving the problem of reverse circulation failure due to backwash well liquid leakage caused by formation pressure deficit.

[0017] The elastic ball seat of the present invention is a "C-shaped" thin-walled cylinder, and the ball seat is mainly formed by the deformation of elastic materials. The rectangular groove at the bottom of the ball seat is an "elastic claw" design, which further enhances the seat-inducing function of the front end of the ball seat. During operation, the elastic ball seat is delivered to the casing compensation position by oil pipe transportation. The ball is first thrown in and hydraulic sandblasting is performed after the ball is in place. After the perforation is completed, the displacement is increased to make the ball seat lose its hand, and the ball pushes the ball seat downward to the reduced diameter of the casing compensation. At this time, the ball seat relies on its own elastic energy to force the outer diameter to expand and become larger, forming a size constraint to replace the cava structure for anchoring. The curling rebound test shows that the elastic ball seat can be repeatedly sealed more than 3 times under a pressure of 70MPa, which fully meets the construction requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of repeated fracturing of a conventional horizontal well; Figure 2 This is a schematic diagram of repeated fracturing of conventional horizontal wells; Figure 3 This is a schematic diagram of repeated transformation backwashing of conventional horizontal wells; Figure 4 is a schematic diagram of the original wellbore before repeated transformation in the embodiment; Figure 5 Schematic diagram of the wellbore after casing patching in the embodiment; Figure 6 It is the first section of the tubing transmission perforation and patching in the embodiment; Figure 7 It is the first section of the bare casing fracturing and hole repairing in the embodiment; Figure 8 The second stage of the ball-throwing hole and the elastic ball seat for setting the seal in the embodiment; Fig. 9 It is a schematic structural diagram of an implementation method of the elastic ball seat delivery tool in the embodiment; Fig.10 This is a schematic diagram of the second stage of drilling, fracturing and hole filling in the embodiment; Fig.11 Schematic diagram of the completion of the third stage of fracturing construction after the second stage of hole patching in the embodiment; Fig.12 It is a schematic diagram of the elastic ball seat structure; Fig.13 This is a schematic diagram of the expansion tube compensation device; Fig.14 It is a schematic diagram of the expansion cone going upward; Fig.15 This is a schematic diagram of the completion of the expansion tube subsidy.

[0019] In the figure: 1. hydraulic anchor; 2. upper K344 packer; 3. sandblaster; 4. lower K344 packer; 5. fourth perforation section; 6. third perforation section; 7. second perforation section; 8. first perforation section; 9. first perforation section; 10. tubing; 11. perforating gun; 12. outer cylinder; 13. elastic ball seat; 14. soluble ball; 15. shear pin; 16. second perforation section; 17. third perforation section; 18. water eye; 19. baffle; 20. expansion tube; 21. expansion cone. DETAILED DESCRIPTION

[0020] The following describes the implementation of the present invention through specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0021] The exemplary embodiments of the present invention are now described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0022] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0023] Example 1 This embodiment provides a method for repeated fracturing by using casing to patch a wellbore and recreate an elastic ball seat, comprising the following steps: Step 1) lowering the expansion pipe 20 patching device to completely seal the original perforation section through the expansion pipe 20 patching; Step 2) lowering the perforating string to perform perforating operation on the first section 9 of the supplementary hole; Step 3) pulling out the perforating string to perform bare casing fracturing on the first section 9 of the supplementary hole; Step 4) After the fracturing is completed, an elastic ball seat delivery tool is connected to the lower end of the perforating string, and a soluble ball 14 is dropped into the tool so that the elastic ball seat 13 shields the first section 9 of the perforation patching, and then the perforating gun 11 is used to perform perforation operations on the second section 16 of the perforation patching; Step 5) lifting the exit pipe string to perform bare casing fracturing on the second section 16 of the supplementary hole; Step 6) Repeat steps 4) to 5) to complete all the plugging sections and the whole well construction is completed.

[0024] Conventional horizontal wells are repeatedly stimulated by fracturing because there are several stimulated layers in the whole wellbore, such as Figure 1 As shown, it is necessary to equip the hydraulic anchor 1 with two packers, the upper K344 packer 2 and the lower K344 packer 4, to isolate the upper and lower parts of the construction layer for transformation. Therefore, only the oil pipe 10 and the sandblaster 3 can be used for injection and sanding, and large-volume transformation cannot be achieved. In addition, due to poor cementing quality, the two open layers outside the casing often communicate with each other (such as Figure 2 As shown in the figure, during backwashing, the backwash should be returned by the annular injection pipe, but the backwashing effect of each open layer section absorbing liquid is poor, which may cause the drill to get stuck (such as Figure 3 As shown in the figure), when reverse circulation operation is carried out after compaction, the large absorption volume of the opened layer section causes inconsistency in the discharge volume of the inlet and outlet, making it impossible to bring the sand out of the ground. Figure 1 It is a conventional horizontal well repeated fracturing double seal single card process construction method. Since the oil pipe 10 injection construction displacement is small, it is difficult to achieve large-scale fracturing. Figure 2 This is because horizontal well cementing is difficult and the quality of most cementing is poor. During the construction process of repeated fracturing double-seal single-card technology, casing external layer cross-linking often occurs. Figure 3 It is a transformation under the original wellbore. When the backwash well is pressed, the liquid is absorbed by the upper open layer in large quantities, resulting in poor backwash effect and increasing the risk of tool sticking.

[0025] The present invention shields the original perforation section through the casing expansion tube 20, which is similar to the reconstruction of a new well. It can effectively prevent the sand burial of tools caused by the communication between the upper and lower layers due to poor cementing quality outside the casing, and can also effectively solve the problem of reverse circulation failure caused by backwash well liquid leakage due to formation pressure deficit. Since the elastic ball seat placement tool constrains the elastic ball seat 13 inside it to reduce its outer diameter, it can smoothly pass through the reduced diameter sections of all casing subsidies in the wellbore. In theory, it can achieve unlimited-level reconstruction and meet the requirements of large-volume fracturing, so it can greatly improve construction efficiency.

[0026] Example 2 Based on Example 1, this example provides a method for repeated fracturing by regenerating an elastic ball seat by using a casing to supplement a wellbore. Fig.13 As shown, the expansion tube 20 compensation device includes an expansion tube 20, an expansion cone 21 and a baffle 19, wherein the expansion cone 21 and the baffle 19 are respectively located at two ends of the expansion tube 20, the expansion cone 21 is connected to the oil pipe 10, and the oil pipe 10 is connected to the expansion cone 21 through the baffle 19, and a water hole 18 is opened on the oil pipe 10 near the expansion cone 21.

[0027] Step 1) The process of the expansion tube 20 patching the original perforation section is as follows: the expansion tube 20 patching device is lowered through the oil pipe 10 to the casing position that needs to be patched, water is injected into the oil pipe 10 to pressurize it, and water flows out from the water hole 18 to expand the expansion tube 20, and the expansion cone 21 moves upward and separates from the upper end of the expansion tube 20 together with the baffle 19, and the patching is completed.

[0028] like Fig.14 As shown, the internal pressure of the expansion tube 20 increases when the oil pipe 10 is pressurized through the water hole 18, and the expansion tube 20 expands and fits closely to the casing wall. The expansion cone 21 enters the expansion tube 20, so that the expansion tube 20 further expands. At this time, the expansion cone 21 keeps moving upward.

[0029] like Fig.15 As shown, after the expansion cone 21 presses against the baffle 19, the wellhead is lifted up to separate the baffle 19 from the expansion pipe 20, so that the entire device is separated from the expansion pipe 20, and the casing patching is completed.

[0030] Example 3 Based on Example 1, this example provides a method for repeated fracturing by regenerating an elastic ball seat by patching a wellbore with casing. The elastic ball seat delivery tool comprises an outer tube 12 and an elastic ball seat 13. The elastic ball seat 13 is arranged in the outer tube 12 and the two are connected by a shear pin 15.

[0031] Elastic ball seat delivery tool such as Fig. 9 The elastic ball seat 13 is forcibly constrained in the outer cylinder 12 of the delivery tool (it is curled and inserted into the outer cylinder 12 by ground equipment) and fixed with a shear pin 15.

[0032] Elastic ball seat 13 Fig.12 As shown, it is a "C-shaped" thin-walled cylinder, and the ball seat is mainly formed by the deformation of elastic materials. The rectangular groove at the bottom of the ball seat is an "elastic claw" design, which further enhances the seat-inducing function of the front end of the ball seat. During operation, the elastic ball seat 13 is delivered to the casing compensation position by means of oil pipe 10. The ball is first thrown in and hydraulic sandblasting is performed after the ball is in place. After the perforation is completed, the displacement is increased to make the ball seat lose its hand, and the ball pushes the ball seat downward to the reduced diameter of the casing compensation. At this time, the ball seat relies on its own elastic energy to force the outer diameter to expand and become larger, forming a size constraint to replace the cava structure for anchoring. The curling rebound test shows that the elastic ball seat 13 can be repeatedly sealed more than 3 times under a pressure of 70MPa, which fully meets the construction requirements. Example 4 This embodiment takes YP48 well as an example to further illustrate the effect of the present invention.

[0033] The original wellbore Figure 4 As shown, there are originally four perforation sections: the fourth perforation section 5 , the third perforation section 6 , the second perforation section 7 and the first perforation section 8 .

[0034] The oil testing team completed the operations of clearing and washing the well as required, and sealed all the original four perforation sections by using the expansion pipe 20. Figure 5 shown.

[0035] Since the entire wellbore is in a fully closed state after being repaired, and the liquid cannot flow, other perforation methods cannot be used, such as Figure 6 As shown, the perforating gun 11 is carried by the oil pipe 10 and falls freely under the weight of the oil pipe 10 to the first section 9 for perforating. Figure 7 As shown, after the completion of the perforation repair, the perforating string is removed, and the first section 9 of the perforation repair is subjected to bare casing fracturing.

[0036] After the first stage 9 of the patching is completed, the perforating string (tubing 10 + perforating gun 11) is connected to the elastic ball seat delivery tool and lowered into the predetermined position in the casing. Figure 8 As shown in the figure, the outer tube 12 of the elastic ball seat delivery tool constrains the outer diameter of the elastic ball seat 13, so that it can smoothly pass through the upper casing compensation reduction section. After reaching the predetermined position, the soluble ball 14 is dropped. At this time, the perforating gun 11 starts hydraulic sandblasting perforation and performs perforation operation on the second section 16 of the compensation hole. Since the hydraulic sandblasting perforation displacement is 2.5m 3 / min, the pressure is 40MPa or less, and the shear pin 15 does not reach the shear pressure; after perforating, the displacement is increased to 3m 3 / min, the pressure rises to 50MPa, at which time the shear pin 15 is cut off, the soluble ball 14 pushes the elastic ball seat 13 away from the outer tube 12 of the delivery tool, and releases its restraint. The elastic ball seat 13 freely expands to a predetermined size so that it is close to the casing wall and sits on the upper end of the expansion tube 20, giving the elastic ball seat 13 a support force so that it will not move downward during the later fracturing process. Then the oil pipe 10, the perforating gun 11, and the outer tube 12 of the ball seat delivery tool are lifted out of the ground. Fig.10 As shown, the first section 9 of the lower patch hole is shielded, and the second section 16 of the patch hole is fractured. After the fracturing is completed, the soluble balls 14 automatically dissolve and disappear.

[0037] After the fracturing of the second section 16 of the patching hole is completed, the above process is repeated, and the elastic ball seat delivery tool is lowered through the perforating string to deliver the soluble ball 14, and the third section 17 of the patching hole is perforated; after the perforation is completed, the displacement is increased to release the constraint of the outer tube 12 on the elastic ball seat 13, and the elastic ball seat 13 is freely expanded to a predetermined size so that it is close to the casing wall and sits on the upper end of the expansion tube 20 to provide a supporting force for the elastic ball seat 13 so that it will not move downward during the subsequent fracturing process, and then the oil pipe 10, the perforating gun 11, and the outer tube 12 of the ball seat delivery tool are lifted out of the ground. The second section 16 of the patching hole at the bottom is shielded, and the third section 17 of the patching hole is fractured. After the fracturing is completed, the soluble ball 14 automatically dissolves and disappears, and the construction of the entire well is completed. Fig.11 shown.

[0038] The present invention reconstructs the original wellbore, making the wellbore clean and simple, effectively preventing the tool sand burial caused by the communication between the upper and lower layers due to poor cementing quality on the outside of the casing, and effectively solving the problem of reverse circulation failure due to backwash well liquid leakage caused by formation pressure deficit. It can also effectively solve the problem of repeated transformation of old wells in the oil field, and can complete the repeated fracturing of the transformed layer section, and can also complete the perforation and fracturing of the new section.

[0039] The above examples are merely illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. All designs that are the same or similar to the present invention fall within the protection scope of the present invention.

Claims

1. A method for repeated fracturing by using casing to supplement the wellbore and recreate an elastic ball seat, characterized in that: The following steps are involved: Step 1) lowering the expansion pipe patching device to completely seal the original perforation section through the expansion pipe patching; Step 2) lowering the perforating string to perform perforating operations on the first section of the supplementary hole; Step 3) pulling out the perforating string to perform bare casing fracturing on the first section of the supplementary hole; Step 4) After the fracturing is completed, an elastic ball seat delivery tool is connected to the lower end of the perforating string, and a soluble ball is dropped into the tool to make the elastic ball seat shield the first section of the perforation patching, and then the perforating gun is used to perform the perforation operation of the second section of the perforation patching; Step 5) lifting the exit pipe string to perform bare casing fracturing on the second section of the supplementary hole; Step 6) Repeat steps 4) to 5) to complete all the plugging sections and the whole well construction is completed.

2. The method for repeated fracturing by casing-padded wellbore reconstruction with elastic ball seat according to claim 1, characterized in that: The expansion pipe patching device includes an expansion pipe, an expansion cone and a baffle, wherein the expansion cone and the baffle are respectively located at two ends of the expansion pipe, the expansion cone is connected to an oil pipe, the oil pipe passes through the baffle and is connected to the expansion cone, and a water hole is opened on the oil pipe near the expansion cone.

3. The method for repeated fracturing by casing-padded wellbore reconstruction with elastic ball seat according to claim 1, characterized in that: The elastic ball seat delivery tool comprises an outer cylinder and an elastic ball seat, wherein the elastic ball seat is arranged in the outer cylinder and the two are connected by a shear pin.

4. The method for repeated fracturing by casing-padded wellbore reconstruction with elastic ball seat according to claim 2, characterized in that: Step 1) The process of using the expansion tube to patch the original perforation section is as follows: the expansion tube patching device is lowered through the oil pipe to the casing position that needs to be patched, water is injected into the oil pipe to pressurize it, and water flows out from the water hole to expand the expansion tube, and the expansion cone moves upward and separates from the upper end of the expansion tube together with the baffle, and the patching is completed.

5. The method for repeated fracturing by casing-padded wellbore reconstruction with elastic ball seat according to claim 3, characterized in that: Step 4) The specific process is as follows: the perforating string drives the elastic ball seat delivery tool into the casing under the action of gravity. After reaching the predetermined position, the soluble ball is dropped, and then the perforating gun performs hydraulic sandblasting perforation. After the perforation is completed, the displacement is increased to cut the shear pin. At this time, the soluble ball pushes the elastic ball seat out of the outer tube, releasing its restraint force, and the elastic ball seat freely expands to a predetermined size so that it is close to the casing wall and sits on the upper end of the expansion tube patch.

6. The method for repeated fracturing by casing-padded wellbore reconstruction with elastic ball seat according to claim 3, characterized in that: The elastic ball seat is a "C-shaped" thin-walled cylinder with an elastic claw at the bottom.

7. The method for repeated fracturing by casing-padded wellbore reconstruction with elastic ball seat according to claim 3, characterized in that: The perforating pipe string is threadedly connected with the elastic ball seat delivery tool through the perforating gun.

8. The method for repeated fracturing by casing-padded wellbore reconstruction with elastic ball seat according to claim 5, characterized in that: The displacement of the perforating gun for hydraulic sandblasting perforation is 2-2.5m 3 / min, after perforation, the displacement is increased to 3-3.5m 3 / min.

9. The method for repeated fracturing by casing-padded wellbore reconstruction with elastic ball seat according to claim 5, characterized in that: During the fracturing process, the upper end of the expansion tube provides support for the elastic ball seat. After the fracturing is completed, the soluble ball dissolves and disappears, achieving large-volume fracturing.

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