Suspended small cased well eccentric integrated double-pipe separated injection pipe column and separated layer water injection method thereof

Abstract

The invention discloses a suspended small cased well eccentric integrated double-pipe separated injection pipe column and a separated layer water injection method thereof, and aims to improve the later testing and adjusting success rate of small-diameter separated injection construction and prolong the separated injection validity period. The separate injection pipe column comprises an outer layer pipe and an inner layer pipe. The outer layer pipe comprises a conventional oil pipe, a double-flow-channel eccentric water distributor, an outer connecting sleeve, an adapter connector, a small-diameter oil pipe, a small-diameter packer, a double-acting injection valve, a small-diameter check valve, a screen pipe and a screwed plug which are sequentially connected from top to bottom. The inner-layer pipe comprises a first oil pipe connected to the lower inner end of the double-flow-channel eccentric water distributor and a rear-throwing ball type check valve. The layered water injection method comprises the steps of tripping in a tubular column, pressing and setting, measuring a water absorption index, putting a valve ball to control a water injection channel, and flushing a well. The method can achieve accurate layered water injection, improve the water injection efficiency and prolong the validity period of layered water injection, and is suitable for layered water injection operation of small cased wells.

Description

Technical Field

[0001] The present invention relates to a stratified water injection string, in particular to an eccentric integrated double-tube separate injection string for a suspended small cased well. The present invention also relates to a stratified water injection method for the eccentric integrated double-tube separate injection string for a suspended small cased well, belonging to the technical field of stratified water injection. Background Art

[0002] Separate layer water injection technology is an effective measure and means to improve interlayer conflicts and strengthen injection-production coordination, and has received considerable attention in oilfield development. However, as oilfield development deepens, the casing of oil and water wells is affected by factors such as formation sand production, corrosion, water injection, and changes in formation stress. The number of wells with casing damage has increased year by year. The number of wells shut down due to casing changes or unable to meet production requirements has continued to increase, damaging the previously relatively complete injection-production well network and causing serious losses in waterflooding reserves.

[0003] Repair techniques for damaged casing are primarily employed, including expansion sleeves, expansion sleeve milling, and small-diameter hanging casing. However, these treatments inevitably result in a reduction in pipe diameter. Existing, commonly used injection tools have difficulty navigating repair wells with passages smaller than 105 mm. To address this issue, slim-hole injection technology has been developed. By reducing the diameter of conventional injection tools and their associated testing tools to accommodate injection in casing repair wells, promising results have been achieved. However, field applications show a high initial success rate for small-hole injection testing, but this rate drops rapidly to 20%-30% in later stages. The majority of these failures occur at the downhole water distribution tools (small-diameter water distributors or small-diameter packers). This reduction significantly impacts the longevity of small-hole injection technology, and due to limitations imposed by the size of the repaired casing and the minimum tool performance requirements, a promising solution currently remains unproven.

[0004] Chinese patent publication number CN212535626U discloses a three-tube concentric stratified water injection string that requires only two runs of string to complete the string installation. However, its disadvantage is that it is only suitable for wells without casing damage, and is particularly inapplicable to small cased wells.

[0005] Chinese patent publication number CN103615223B discloses a concentric water distributor and a small-hole surface-adjustable stratified water injection string, which can achieve stratified water injection in 4-inch cased wells and belongs to single-tube concentric injection. The disadvantage is that it cannot meet the needs of small cased wells with a size of less than 4 inches.

[0006] Chinese patent publication number CN104453808B discloses a downhole injection method and injection string, which can be applied to highly deviated wells for easy testing. However, the string structure is complex, and the water distributor used differs from conventional distributors. Conventional flow rate and seal verification processes cannot be used, increasing the difficulty and investment of on-site operations. Summary of the Invention

[0007] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the invention of this application, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0008] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0009] The primary purpose of the present invention is to overcome the problems existing in the prior art and provide an eccentric integrated double-tube injection string for hanging small casing wells, which can improve the success rate of measurement and adjustment in the later stage of small-diameter injection construction and extend the effective period of injection.

[0010] In order to solve the above technical problems, the present invention provides a suspended small casing well eccentric integrated double-tube injection string, including an outer layer tube and an inner layer tube, the outer layer tube includes a conventional oil pipe, a dual-channel eccentric water distributor, an external connecting sleeve, a variable buckle joint, a small diameter oil pipe, a small diameter packer, a double-acting injection valve, a small diameter check valve, a screen pipe and a wire plug connected in sequence from top to bottom; the inner layer tube includes a first oil pipe connected to the lower inner end of the dual-channel eccentric water distributor and a rear-drop ball check valve.

[0011] Furthermore, the dual-channel eccentric water distributor includes an upper joint, a guide body, a guide sleeve, a guide pen tip, an upper outer tube, a guide cylinder, a double-layer plug, an integrated body, a plug, a positioning sleeve, an inner suspension sleeve, and a lower outer tube. The upper port of the upper outer tube is connected to the lower end external thread of the upper joint and sealed to each other, and the lower port of the upper outer tube is connected to the upper end external thread of the integrated body and sealed to each other.

[0012] Furthermore, the guide body is inserted into the lower inner cavity of the upper joint, and is threadedly connected to the upper joint and then welded and fixed; the guide pen tip is inserted into the guide sleeve, and after being connected and fixed together, it is inserted into the lower inner cavity of the guide body as a whole with the guide sleeve, and the lower end of the guide sleeve is bottom-connected and fixed to the upper end of the guide cylinder; the lower end of the guide cylinder is connected to the upper end of the integrated body, and the side wall of the guide cylinder is provided with a guide groove.

[0013] Furthermore, the integrated body is provided with a central channel and an axial side hole, and a double-layer plug is provided in the axial side hole; the upper side wall of the central channel is provided with an upper water inlet of the main body, and the upper water inlet of the main body is connected with the upper control water flow channel of the double-layer plug; the lower side wall of the central channel is provided with a lower water inlet of the main body, and the lower water inlet of the main body is connected with the lower control water flow channel of the double-layer plug.

[0014] Furthermore, the upper side wall of the axial side hole is provided with a first water outlet extending outward in a tangential direction, and the first water outlet is connected to the upper water outlet of the plug; the lower outer periphery of the integrated body is provided with a first lower thread, and a second lower thread with a reduced diameter is provided below the first lower thread. The lower part of the integrated body is provided with a lower flow channel extending axially and connected to the lower water outlet of the plug, and a second water outlet connected to the lower flow channel is provided on the outer wall between the first lower thread and the second lower thread.

[0015] Furthermore, the lower end of the integrated body is connected to the upper end of the lower outer tube through a first lower thread and sealed with each other, and the outer periphery of the lower end of the lower outer tube is provided with an external hanging thread; the lower end of the integrated body is also connected to the positioning sleeve through a second lower thread and sealed with each other; the upper port of the inner hanging sleeve is connected to the lower end external thread of the positioning sleeve and sealed with each other, and the outer periphery of the lower end of the inner hanging sleeve is provided with an internal hanging thread.

[0016] Furthermore, the end of the axial side hole of the integrated body and the end of the lower flow channel are sealed with a plug; the double-layer plug is an adjustable or cast-in-place nozzle core plug, and the upper control nozzle core and the lower control nozzle core are closed before entering the well.

[0017] Furthermore, the double-acting injection valve includes an outer tube and a lower joint connected from top to bottom, and a water outlet trough hole is provided in the middle and upper part of the outer tube; the upper end of the inner center tube is inserted into the inner cavity of the valve body, and the upper end of the inner center tube and the upper end of the valve body are connected and fixed by a first pin, and a conical step sealing surface with a wide upper part and a narrow lower part is provided on the upper part of the central channel of the inner center tube, and a radially through lower water inlet hole is provided below the conical step sealing surface, and a second seal is embedded below the outer port of the lower water inlet hole to achieve sealing with the inner wall of the valve body.

[0018] Furthermore, the outer wall of the inner center tube below the lower water inlet hole is provided with a movable groove extending vertically downward, and the lower part of the valve body is screwed with a second pin, the inner end of the second pin is embedded in the movable groove, and can slide up and down along the movable groove; the middle part of the valve body is provided with a valve body large diameter section, and the valve body large diameter section is located above the water outlet trough hole; the upper outer shoulder of the valve body large diameter section abuts against the bottom of the inner step of the outer tube, and the middle part of the valve body large diameter section is provided with a radially through lossless water outlet, and the upper and lower sides of the outer port of the lossless water outlet are respectively embedded with a first sealing ring and the inner wall of the outer tube to achieve sealing.

[0019] Furthermore, the lower outer wall of the inner center tube is provided with an inner center tube reduced diameter section, the lower end of the inner center tube reduced diameter section is connected to the internal thread of the lower joint and sealed with each other; the outer periphery of the inner center tube reduced diameter section is sleeved with a constant pressure spring, the constant pressure spring is inserted from the lower end of the inner center tube, the top of the constant pressure spring rests on the bottom of the gasket, the top inner edge of the gasket rests on the bottom of the top outer step of the inner center tube reduced diameter section, the top outer edge of the gasket is located below the inner step of the outer tube, and the lower end of the constant pressure spring rests on the upper end face of the lower joint.

[0020] Furthermore, the limit sleeve is sleeved on the outer periphery of the constant pressure spring and is located in the lower inner cavity of the outer tube, and the lower end of the limit sleeve rests on the inner step of the lower joint; the shear force of the first pin is greater than the sealing pressure of the small diameter packer by 2~3MPa, and the shear force of the second pin is greater than the larger of the normal water injection pump pressure and the shear force of the first pin by 2~3MPa.

[0021] Furthermore, the rear-throw ball-dropping one-way valve includes an upper sleeve, a lower sleeve and a pressure cap connected in sequence from top to bottom; the upper end of the limiting ring abuts against the lower end surface of the upper sleeve, and the lower end of the limiting ring abuts against the inner step of the lower sleeve; the circumference of the limiting ring is provided with a spring groove and a fixing hole that cooperate with the upper end of the check spring, and is fixedly connected to the check spring, and the check spring is wide at the top and narrow at the bottom; the fixing sleeve is sleeved on the outer periphery of the lower end of the valve seat and connected with a dislocation pin, and the whole is inserted from the lower port of the lower sleeve, the middle outer step of the valve seat abuts against the bottom of the middle inner step of the lower sleeve, and a conical step sealing surface is provided in the middle of the inner cavity of the valve seat, and the upper port of the conical step sealing surface is provided with an upper outer ring extending upward for limiting the check spring.

[0022] Another object of the present invention is to overcome the problems existing in the prior art and provide a stratified water injection method for a suspended small casing well, which can improve the success rate of measurement and adjustment in the later stage of small-diameter stratified injection construction and extend the effective period of stratified injection.

[0023] To solve the above technical problems, the present invention provides a stratified water injection method for a suspended small cased well, which adopts an eccentric integrated double-tube injection string for the suspended small cased well and comprises the following steps in sequence: S1. Run the plug, screen, small-diameter check valve, double-acting injection valve, small-diameter packer, and small-diameter tubing in sequence from bottom to top. Connect the small-diameter tubing in series, then run the variable-slip joint, external connection sleeve, and suspend at the wellhead. S2, insert the rear ball-drop check valve and the first oil pipe from bottom to top; S3. Connect the inner hanging thread of the double-channel eccentric water distributor to the first oil pipe and then lower it into the tank. Connect the outer hanging thread at the lower end of the double-channel eccentric water distributor to the outer connecting sleeve. S4. Continue to lower the conventional oil pipe to the wellhead, and connect the lower end of the conventional oil pipe to the dual-flow channel eccentric water distributor; S5. Pressurize and set packer: The injected water flows into the lower end of the outer pipe through the post-injection ball check valve, builds pressure, and the small-diameter packer is set; continue to pressurize. When the pressure exceeds the shear pressure of the first pin in the double-action injection valve, the pin is sheared off, the valve body moves downward until it stops moving when the second pin reaches the boundary of the moving groove; at this time, the lower end of the valve body contacts the upper end face of the packing ring, and the lower water inlet hole, the non-destructive water outlet, and the water outlet groove hole are connected, and the lower injection channel is opened.

[0024] Furthermore, the following steps are also included: S6. Measure the water absorption of the lower injection layer: Connect the pumping pipeline on the ground according to the injection process, record the water injection volume of the pump truck at different injection pressures per unit time, obtain the water absorption index of the lower injection layer, calculate the lower injection pressure P_down under the condition of meeting the injection allocation volume, and the maximum pump pressure does not exceed the shear force of the second pin during this process; S7. Insert the matching valve ball of the double-action injection valve. The valve ball falls onto the conical step sealing surface of the inner central pipe and closes the lower injection channel under the control and limit of the second pin; after lowering the measurement and adjustment instrument and docking it with the double-layer plug, control the ground to open the upper control nozzle core. At this time, the main body upper water inlet, the plug upper water inlet, the upper control nozzle core, the plug upper water outlet, and the first outer water outlet are connected, and the upper injection channel is opened.

[0025] Furthermore, the following steps are also included: S8. Measure the water absorption of the upper injection layer: Pump liquid on the ground, record the water injection volume of the pump truck at different injection pressures per unit time, obtain the water absorption index of the upper injection layer, calculate the upper injection pressure P_up under the condition of meeting the injection allocation volume, and the maximum pump pressure does not exceed the shear force of the second pin during this process; S9. If P_up < P_down: Backwash the well to discharge the matching valve ball of the double-action injection valve from the wellbore; insert the matching valve ball of the post-injection ball check valve. The valve ball falls onto the sealing surface of the valve seat and closes the inner pipe water injection channel; lower the measurement and adjustment instrument and dock it with the double-layer plug, and control the ground to close the upper control nozzle core; pressurize. When the pressure is greater than the shear force of the disengagement pin, shear it off. The valve ball pushes the valve seat to move downward until it contacts the bottom of the fixed sleeve. At this time, the lower end of the check spring just disengages from the outer ring of the upper end of the valve seat, and the check spring returns to its position. The claw type contracts inward, and its inner diameter is smaller than the valve ball to ensure that the valve ball is not washed out during well washing; lower the measurement and adjustment instrument and dock it with the double-layer plug, and control the ground to open the upper control nozzle core and the lower control nozzle core for normal water injection.

[0026] Furthermore, in S9: If Pup ≥ Pdown + the pressure difference of the well washing valve of the small-diameter packer: lower the measuring and adjusting instrument to connect with the double-layer plug, and the ground control will close the upper control nozzle; pressurize, and when the pressure is greater than the shear pressure of the second pin, it will be cut off; put in the matching valve ball of the rear-thrown one-way valve, the valve ball falls into the sealing surface of the valve seat, and the water injection channel of the inner pipe is closed; pressurize, and when the pressure is greater than the shear force of the dislocation pin, it will be cut off, and the valve ball pushes the valve seat down until it is connected with the bottom of the fixed sleeve. At this time, the check spring is just disengaged from the upper outer ring of the valve seat, the check spring returns to its position, and the claw shrinks inward. Its inner diameter is smaller than the valve ball, which ensures that the valve ball is not washed out during well washing; lower the measuring and adjusting instrument to connect with the double-layer plug, and the ground control will open the upper and lower control nozzles for normal water injection.

[0027] Furthermore, the method further includes the following steps: Well washing: The casing annulus is pressurized by water injection, the well washing channel of the small diameter packer is opened, the well washing channel of the small diameter check valve is opened, and the casing annulus well washing channel is established to achieve well washing. After the well washing is completed, the well washing channel of the small diameter packer is closed and stratified water injection is realized again.

[0028] Compared with the existing technology, the present invention has achieved the following beneficial effects: 1. The eccentric integrated double-tube injection string for hanging small cased wells realizes the function of full-well testing and adjustment without using the packer for testing and adjustment: Compared with the traditional eccentric small-diameter stratified water injection string, the eccentric integrated double-tube injection string for hanging small cased wells has the water distribution tools arranged above the casing damage reducing section, and the small-diameter packers are all arranged in the casing damage reducing section. During testing and adjustment, there is no need to use the small-diameter packer, which improves the success rate of testing and adjustment; 2. The eccentric integrated dual-tube injection string for suspended small cased wells is consistent with the testing and adjustment process of the eccentric integrated injection string. The internal diameter, guidance, positioning and adjustment design of the dual-channel eccentric water distributor are consistent with the eccentric integrated water distributor, eliminating the need to change the supporting testing and adjustment instruments and procedures. It has high on-site versatility, greatly reducing the cost and operational difficulty caused by equipment replacement and improving work efficiency. 3. The eccentric integrated double-tube injection string for hanging small cased wells can realize the water absorption index test of the upper and lower water injection layers, and can adjust the water injection throttling according to the different injection pressures of the upper and lower water injection layers, so that the well flushing valve of the packer under different pressure systems in the pipe is always in the closed state; 4. The eccentric integrated double-tube injection string for suspended small cased wells can achieve pre-throttling of the lower layer, meet the large pressure difference between the upper and lower layers (upper layer injection pressure > lower layer injection pressure) and adjust the water nozzle, reducing the risk of clogging due to insufficient opening of the water nozzle; extend the service life of the water injection string and reduce maintenance costs; 5. The eccentric integrated double-tube injection string for suspended small casing wells has three working states underground: water injection, injection stop and well washing. These three states can be used in a cycle automatically, reducing downtime and improving oilfield development efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive work. The drawings are provided for reference and explanation only and are not intended to limit the present invention. Among them: Figure 1 This is a structural diagram of the eccentric integrated dual-tube injection string for suspended small cased wells according to the present invention; Figure 2 for Figure 1 Schematic diagram of the structure of the double-channel eccentric water distributor; Figure 3 for Figure 2 Cross-section at AA in the middle; Figure 4 for Figure 2 Cross-section at the middle CC; Figure 5 for Figure 4 Cross-section at the middle BB; Figure 6 for Figure 1 Schematic diagram of the structure of the double-acting injection valve; Figure 7 for Figure 1 Schematic diagram of the center-rear ball-drop check valve structure; In the figure: 1. Conventional oil pipe; 2. Dual-channel eccentric water distributor: 2-1. Upper joint; 2-2. Guide body; 2-3. Guide sleeve; 2-4. Guide tip; 2-5. Upper outer tube; 2-6. Guide cylinder; 2-6-1. Guide groove; 2-7. Double-layer plug; 2-7-1. Upper water inlet of plug; 2-7-2. Upper control nozzle; 2-7-3. Upper water outlet of plug; 2-7-4. Lower water inlet of plug; 2-7-5. Lower control nozzle; 2-7-6. Lower water outlet of plug; 2-8. Integrated body; 2-8-1. Main body upper water inlet; 2-8-2. Main body lower water inlet; 2-8-3. First outlet; 2-8-4. Lower flow channel; 2-8-5. First lower thread; 2-8-6. Second lower thread; 2-8-7. Second outlet; 2-8-8. Auxiliary flow channel; 2-8-9. Axial offset hole; 2-8-10. Center channel; 2-9. Plug; 2-10. Positioning sleeve; 2-11. Internal suspension sleeve; 2-11-1. Internal suspension thread; 2-12. Lower outer tube; 2-12-1. External suspension thread; 3. External connecting sleeve; 4. Variable buckle joint; 5. Small diameter tubing; 6. Small diameter packer; 7. Double-acting injection valve: 7-1. Outer tube; 7-1-1. Water outlet slot; 7-2. Valve body; 7-2-1. Non-destructive water outlet; 7-3. Inner center tube; 7-3-1. Lower water inlet; 7-3-2. Movement slot; 7-3-3. Conical step sealing surface; 7-4. Gasket; 7-5. Constant pressure spring; 7-6. Limit sleeve; 7-7. Lower connector; 7-8. First pin; 7-9. Second pin; 7-10. First seal; 7-11. Second seal; 7-12. Third seal. 8. Small-diameter check valve; 9. Screen tube; 10. Threaded plug; 11. First oil pipe; 12. Rear-thrown ball-type check valve: 12-1. Upper outer sleeve; 12-2. Limiting ring; 12-3. Fastening screw; 12-4. Check spring; 12-5. Lower outer sleeve; 12-6. Valve seat; 12-7. Dislocation pin; 12-8. Fixing sleeve; 12-9. Pressure cap; 12-10. Valve ball. DETAILED DESCRIPTION

[0030] In the following description of the present invention, the terms "up", "down", "front", "back", "left", "right", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not mean that the device must have a specific direction.

[0031] In order to make the technical means, creative features, objectives and effects of the present invention easier to understand, the present invention is further described below with reference to specific figures. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention.

[0033] like Figure 1 As shown, the suspended small casing well eccentric integrated double-tube injection string of the present invention includes an outer layer pipe and an inner layer pipe. The outer layer pipe includes a conventional oil pipe 1, a dual-channel eccentric water distributor 2, an external connecting sleeve 3, a variable buckle joint 4, a small diameter oil pipe 5, a small diameter packer 6, a double-acting injection valve 7, a small diameter check valve 8, a screen pipe 9 and a wire plug 10 connected from top to bottom; the inner layer pipe includes a first oil pipe 11 connected to the lower inner end of the dual-channel eccentric water distributor 2, and a rear-drop ball check valve 12.

[0034] like Figure 2As shown, the dual-channel eccentric water distributor 2 includes an upper connector 2-1, a guide body 2-2, a guide sleeve 2-3, a guide tip 2-4, an upper outer tube 2-5, a guide cylinder 2-6, a double-layer plug 2-7, an integrated body 2-8, a plug 2-9, a positioning sleeve 2-10, an inner suspension sleeve 2-11, and a lower outer tube 2-12. The upper end of the upper outer tube 2-5 is externally threadedly connected to the lower end of the upper connector 2-1 and sealed therewith, while the lower end of the upper outer tube 2-5 is externally threadedly connected to the upper end of the integrated body 2-8 and sealed therewith.

[0035] The guide body 2-2 is inserted into the lower inner cavity of the upper joint 2-1, threadedly connected to the upper joint 2-1 and then welded to fix; the guide pen tip 2-4 is inserted into the guide sleeve 2-3, fixed together with the guide sleeve 2-3, and then inserted into the lower inner cavity of the guide body 2-2 as a whole, and the lower end of the guide sleeve 2-3 is connected to the bottom of the upper end of the guide cylinder 2-6 and fixed with bolts; the lower end of the guide cylinder 2-6 is bolted to the upper end of the integrated body 2-8, and the side wall of the guide cylinder 2-6 is provided with a guide groove 2-6-1.

[0036] The integrated body 2-8 is provided with a central channel 2-8-10 and an axial offset hole 2-8-9. A double-layer plug 2-7 is provided in the axial offset hole 2-8-9. When the double-layer plug 2-7 is placed, it slides toward the guide cylinder 2-6 through the guide tip 2-4 and is then guided into the axial offset hole 2-8-9 through the guide groove 2-6-1 on the side wall of the guide cylinder 2-6. Multiple auxiliary flow channels 2-8-8 are provided on the same circumference as the axial offset hole 2-8-9.

[0037] The upper side wall of the central channel 2-8-10 is provided with an upper water inlet 2-8-1 of the main body, which is connected with the upper control water flow channel of the double-layer plug 2-7; the upper control water flow channel includes the upper water inlet 2-7-1 of the plug, the upper control nozzle core 2-7-2 and the upper water outlet 2-7-3 of the plug.

[0038] The lower side wall of the central channel 2-8-10 is provided with a main body lower water inlet 2-8-2, which is connected with the lower water control channel of the double-layer plug 2-7; the lower water control channel includes the plug lower water inlet 2-7-4, the lower control nozzle core 2-7-5 and the plug lower water outlet 2-7-6.

[0039] The upper side wall of the axial offset hole 2-8-9 is provided with a first water outlet 2-8-3 which penetrates outwards along the tangential direction. The first water outlet 2-8-3 is communicated with the upper water outlet 2-7-3 of the plug.

[0040] A first lower thread 2-8-5 is provided on the outer periphery of the lower part of the integrated body 2-8, and a second lower thread 2-8-6 with a reduced diameter is provided below the first lower thread 2-8-5. The lower part of the integrated body 2-8 is provided with a lower flow channel 2-8-4 extending axially and connected to the lower water outlet 2-7-6 of the plug, and a second outflow outlet 2-8-7 connected to the lower flow channel 2-8-4 is provided on the outer wall between the first lower thread 2-8-5 and the second lower thread 2-8-6.

[0041] The lower end of the integrated body 2-8 is threadedly connected to the upper end of the lower outer tube 2-12 through a first lower thread 2-8-5 and sealed with each other. The outer periphery of the lower end of the lower outer tube 2-12 is provided with an external hanging thread 2-12-1.

[0042] The lower end of the integrated body 2-8 is also threadedly connected to the positioning sleeve 2-10 through a second lower thread 2-8-6 and sealed to each other; the upper port of the inner suspension sleeve 2-11 is externally threadedly connected to the lower end of the positioning sleeve 2-10 and sealed to each other, and the outer periphery of the lower end of the inner suspension sleeve 2-11 is provided with an inner suspension thread 2-11-1.

[0043] The end of the axial offset hole 2-8-9 of the integrated body 2-8 and the end of the lower flow channel 2-8-4 are connected by threaded sealing with a plug 2-9.

[0044] Double-layer plugs 2-7 are adjustable or replaceable nozzles. Using a double-layer plug is more convenient, and this embodiment also uses a double-layer plug. Before entering the well, the upper control nozzle 2-7-2 is closed, and the lower control nozzle 2-7-5 is closed. The central channel within the dual-channel eccentric water distributor 2 is the same as that of a conventional eccentric water distributor, measuring 46 mm in diameter.

[0045] like Figure 6 The double-acting injection valve 7 is shown, which includes an outer tube 7-1 and a lower joint 7-7 connected from top to bottom. A water outlet trough hole 7-1-1 is provided in the upper middle portion of the outer tube 7-1.

[0046] The upper end of the inner center tube 7-3 is inserted into the inner cavity of the valve body 7-2. The upper ends of the inner center tube 7-3 and the upper ends of the valve body 7-2 are connected and fixed by a first pin 7-8. The upper portion of the central channel of the inner center tube 7-3 is provided with a tapered step sealing surface 7-3-3 that is wide at the top and narrow at the bottom. Below the tapered step sealing surface 7-3-3 is a radially through-hole 7-3-1. A second seal 7-11 is embedded below the outer end of the lower water inlet hole 7-3-1 to achieve a seal with the inner wall of the valve body 7-2. The second sealing ring 7-11 is embedded in the upper and lower sides of the outer end of the lower water inlet hole 7-3-1 to ensure sealing. The outer wall of the inner center tube 7-3 below the lower water inlet hole 7-3-1 is provided with a movable groove 7-3-2 extending vertically downward. The lower part of the valve body 7-2 is screwed with a second pin 7-9. The inner end of the second pin 7-9 is embedded in the movable groove 7-3-2 and can slide up and down along the movable groove 7-3-2.

[0047] A large-diameter section of the valve body is provided in the middle of the valve body 7-2, and the large-diameter section of the valve body is located above the water outlet slot 7-1-1; the upper outer shoulder of the large-diameter section of the valve body abuts against the bottom of the inner step of the outer tube 7-1, and a radially through-destructive water outlet 7-2-1 is provided in the middle of the large-diameter section of the valve body. The upper and lower sides of the outer port of the lossless water outlet 7-2-1 are respectively embedded with first sealing rings 7-10 to achieve sealing with the inner wall of the outer tube 7-1.

[0048] The lower outer wall of the inner center tube 7-3 is provided with an inner center tube reduced diameter section. The lower end of the reduced diameter section is connected to the internal thread of the lower joint 7-7 and is sealed therewith. A constant pressure spring 7-5 is sleeved around the outer periphery of the reduced diameter section of the inner center tube. The constant pressure spring 7-5 is inserted from the lower end of the inner center tube 7-3. The top of the constant pressure spring 7-5 abuts against the bottom of the backing ring 7-4. The top inner edge of the backing ring 7-4 abuts against the bottom outer step of the top of the inner center tube reduced diameter section. The top outer edge of the backing ring 7-4 is located below the inner step of the outer tube 7-1. The lower end of the constant pressure spring 7-5 abuts against the upper end surface of the lower joint 7-7.

[0049] The limiting sleeve 7-6 is sleeved on the outer periphery of the constant pressure spring 7-5 and is located in the lower inner cavity of the outer tube 7-1, and the lower end of the limiting sleeve 7-6 rests on the inner step of the lower joint 7-7.

[0050] The shear force of the first pin 7-8 is 2-3 MPa greater than the setting pressure of the small diameter packer 6, and the shear force of the second pin 7-9 is 2-3 MPa greater than the larger of the normal water injection pump pressure and the shear force of the first pin 7-8.

[0051] like Figure 7 As shown, the rear ball-dropping check valve includes an upper outer sleeve 12-1, a lower outer sleeve 12-5 and a pressure cap 12-9 which are sequentially connected from top to bottom.

[0052] The upper end of the limiting ring 12-2 abuts against the lower end surface of the upper outer sleeve 12-1, while the lower end of the limiting ring 12-2 abuts against the inner step of the lower outer sleeve 12-5. The circumference of the limiting ring 12-2 is provided with a spring groove and a fixing hole that mate with the upper end of the check spring 12-4. The ring is fixed to the check spring 12-4 via a fastening screw 12-3. The check spring 12-4 is wide at the top and narrow at the bottom. The claw at the lower end of the check spring 12-4 faces inward. During installation, the claw is forced outward and engages the outer circumference of the upper outer ring of the valve seat 12-6.

[0053] The fixed sleeve 12-8 is sleeved on the outer periphery of the lower end of the valve seat 12-6 and connected with the dislocation pin 12-7. The whole is inserted from the lower port of the lower outer sleeve 12-5. The middle outer step of the valve seat 12-6 is against the bottom of the middle inner step of the lower outer sleeve 12-5. The middle part of the inner cavity of the valve seat 12-6 is provided with a bell mouth, i.e., a conical step sealing surface 7-3-3. The upper end of the conical step sealing surface 7-3-3 is provided with an upwardly extending upper end outer ring for limiting the check spring 12-4.

[0054] The lower end of the external connecting sleeve 3 is connected with a variable buckle joint 4 with a larger upper portion and a smaller lower portion. The upper end of the external connecting sleeve 3 is connected with the external hanging thread 2-12-1 at the lower end of the lower outer tube 2-12 of the double-channel eccentric water distributor 2.

[0055] The variable buckle joint 4 is downwardly connected to a small-diameter packer 6, a double-acting injection valve 7, a small-diameter check valve 8, a screen pipe 9, and a wire plug 10 which are connected in series via a small-diameter oil pipe 5.

[0056] The operation procedure and working principle of eccentric integrated double-pipe injection in suspended small casing wells are as follows: S1. From bottom to top, lower the wire plug 10, screen 9, small-diameter check valve 8, small-diameter tubing 5, double-acting injection valve 7, and small-diameter packer 6. Connect the small-diameter tubing 5 in series, then lower the variable-slip joint 4 and external connecting sleeve 3, and suspend at the wellhead. S2, insert the rear ball-type check valve 12 (valve balls 12-10 are not inserted) and the first oil pipe 11 from bottom to top; S3, the inner hanging thread 2-11-1 of the double-channel eccentric water distributor 2 is connected to the first oil pipe 11 and then lowered, and the outer hanging thread 2-12-1 at the lower end of the double-channel eccentric water distributor 2 is connected to the outer connecting sleeve 3; S4. Continue lowering the conventional oil pipe 1 to the wellhead, and connect the lower end of the conventional oil pipe 1 to the dual-flow channel eccentric water distributor 2; S5. Pressurization and setting: The injected water flows into the lower end of the outer tube through the rear ball-dropping check valve 12, and the pressure is applied, and the small-diameter packer 6 is set. The pressure is continued. When the pressure exceeds the shear pressure of the first pin 7-8 in the double-acting injection valve 7, the first pin 7-8 is sheared, and the valve body 7-2 moves downward until the second pin 7-9 reaches the boundary of the movable groove 7-3-2 and stops moving. At this time, the lower end of the valve body 7-2 contacts the upper end surface of the gasket 7-4, and the lower water inlet hole 7-3-1, the lossless water outlet 7-2-1 and the water outlet trough hole 7-1-1 are connected, and the lower injection channel is opened. S6. Measure the water absorption of the lower injection layer: Connect the pumping pipeline on the ground according to the injection process, record the water injection volume per unit time under different injection pressures of the pump truck, calculate the water absorption index of the lower injection layer, and calculate the lower layer water injection pressure P that meets the injection volume conditions (the maximum pump pressure does not exceed the shear force of the second pin 7-9); S7. Insert the matching valve ball of the double-acting injection valve 7. The valve ball falls into the conical step sealing surface 7-3-3 of the inner center tube 7-3, i.e., the bell mouth. Under the control limit of the second pin 7-9, the lower injection channel is closed. After the measuring and adjustment instrument is lowered and docked with the double-layer plug 2-7, the upper control nozzle 2-7-2 is opened by ground control. At this time, the upper water inlet 2-8-1 of the main body, the upper water inlet 2-7-1 of the plug, the upper control nozzle 2-7-2, and the upper water outlet 2-7-3 of the plug are connected to the first water outlet 2-8-3, and the upper injection channel is opened. S8. Measure water absorption of the upper injection layer: Pump liquid into the ground, record the water injection volume per unit time under different injection pressures of the pump truck, calculate the water absorption index of the upper injection layer, and calculate the upper layer water injection pressure Pup that meets the injection volume requirements (the maximum pump pressure does not exceed the shear force of the second pin 7-9); S9. If the upper injection pressure Pup < the lower injection pressure Pdown: backwash the well and discharge the valve ball of the double-acting injection valve 7 out of the wellbore; put in the matching valve ball 12-10 of the rear-drop check valve 12, and the valve ball 12-10 falls into the sealing surface of the valve seat 12-6, closing the water injection channel of the inner pipe; lower the measuring and adjusting instrument to connect with the double-layer plug 2-7, and the ground control closes the upper control nozzle 2-7-2; pressurize, when the pressure is greater than the shear force of the dislocation pin 12-7, the dislocation pin 12-7 is sheared, and the valve ball 12-10 pushes the valve seat 12-6 downward until it contacts the bottom of the fixed sleeve 12-8, at which time the lower part of the check spring 12-4 is released. The end is just separated from the upper outer ring of the valve seat 12-6, the check spring 12-4 returns to its position, the claw shrinks inward, and its inner diameter is smaller than the valve ball 12-10, to ensure that the valve ball 12-10 is not washed out during well washing; the measuring and adjustment instrument is lowered to dock with the double-layer plug 2-7, and the ground control opens the upper control nozzle 2-7-2 and the lower control nozzle 2-7-5 to inject water normally. At this time, the upper injection channel is the upper water inlet 2-8-1 of the main body → the upper water inlet 2-7-1 of the plug → the upper control nozzle 2-7-2 → the upper water outlet 2-7-3 of the plug → the first outer water outlet 2-8-3 → the annular space between the outer pipe and the casing → the upper injection layer.

[0057] The lower injection channel is the lower water inlet 2-8-2 of the main body → the lower water inlet 2-7-4 of the plug → the lower control nozzle 2-7-5 → the lower water outlet 2-7-6 of the plug → the lower flow channel 2-8-4 → the second outer water outlet 2-8-7 → the annular space between the positioning sleeve 2-10, the inner hanging sleeve 2-11 and the lower outer tube 2-12 → the annular space between the outer tube and the inner tube → the lower water inlet hole 7-3-1, the lossless water outlet 7-2-1 and the water outlet trough hole 7-1-1 of the double-acting injection valve 7 → the lower injection layer; at this time, there is no pressure loss when the lower layer is injected into the double-acting injection valve 7.

[0058] If the upper injection pressure P_up ≥ the lower injection pressure P_down + the differential pressure of the flushing valve of the small-diameter packer 6: Lower the survey and adjustment instrument to dock with the double-layer plug 2-7, and the ground control closes the upper control nozzle core 2-7-2; Apply pressure. When the pressure is greater than the shearing pressure of the second pin 7-9, the second pin 7-9 is cut off; Insert the matching valve ball 12-10 of the post-inserted ball-type check valve 12. The valve ball 12-10 falls onto the sealing surface of the valve seat 12-6 to close the inner-layer pipe injection channel; Apply pressure. When the pressure is greater than the shearing force of the dislocating pin 12-7, the dislocating pin 12-7 is cut off. The valve ball 12-10 pushes the valve seat 12-6 downward until it bottoms against the fixed sleeve 12-8. At this time, the check spring 12-4 just disengages from the upper outer ring of the valve seat 12-6, and the check spring 12-4 returns to its original position. The claws contract inward, and its inner diameter is smaller than the valve ball 12-10, ensuring that the valve ball 12-10 is not washed out during flushing; Lower the survey and adjustment instrument to dock with the double-layer plug 2-7, and the ground control opens the upper control nozzle core 2-7-2 and the lower control nozzle core 2-7-5 for normal injection. At this time, the upper injection channel is the main upper water inlet 2-8-1 → the upper water inlet 2-7-1 of the plug → the upper control nozzle core 2-7-2 → the upper water outlet 2-7-3 of the plug → the first outer water outlet 2-8-3 → the annular space between the outer layer pipe and the casing → the upper injection layer.

[0059] The lower injection channel is the main lower water inlet 2-8-2 → the lower water inlet 2-7-4 of the plug → the lower control nozzle core 2-7-5 → the lower water outlet 2-7-6 of the plug → the lower flow channel 2-8-4 → the second outer water outlet 2-8-7 → the annular space between the positioning sleeve 2-10, the inner suspension sleeve 2-11 and the lower outer pipe 2-12 → the annular space between the outer layer pipe and the inner layer pipe → the valve body 7-2 of the double-acting injection valve 7 pushes the constant pressure spring 7-5 to compress and move downward, exposing the water outlet slot hole 7-1-1 → the lower injection layer; At this time, the double-acting injection valve 7 acts as a throttle to ensure that the injection pressure P_up < P_down + the differential pressure of the flushing valve of the small-diameter packer 6 + the spring force of the constant pressure spring 7-5. During injection, the flushing valve of the small-diameter packer 6 is always closed, and there is no cross-layer; At the same time, under the throttling effect of the double-acting injection valve 7, the opening of the lower control nozzle core 2-7-5 can be larger. Especially for the situation where the pressure difference between P_up and P_down is large and the lower injection volume is small, relying solely on the throttling of the lower control nozzle core 2-7-5 to increase the pressure to meet the upper injection pressure P_up, the opening of the lower control nozzle core 2-7-5 will be very small and is easily blocked.

[0060] Flushing: Build pressure in the annulus between the tubing and the casing. The flushing channel of the small-diameter packer 6 is opened, and the flushing channel of the small-diameter check valve 8 is opened to establish the annulus flushing channel between the tubing and the casing to achieve flushing. After flushing is completed, the flushing channel of the small-diameter packer 6 is closed, and stratified injection is re-implemented.

[0061] When a 5.5" casing damaged well is repaired by hanging a Φ95mm small casing, the sizes of the conventional oil pipe 1, small diameter oil pipe 5, first oil pipe 11 and outer connecting sleeve 3 are Φ73mm, Φ60mm, Φ60mm and Φ95mm respectively.

[0062] The above description is only a preferred embodiment of the present invention, which shows and describes the basic principles, main features and advantages of the present invention, but does not limit the scope of patent protection of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. In addition to the above embodiments, the present invention may have other implementation modes without departing from the spirit and scope of the present invention. The present invention may also have various changes and improvements, and all technical solutions formed by equivalent replacement or equivalent transformation fall within the scope of protection required by the present invention. The scope of protection required by the present invention is defined by the attached claims and their equivalents. Technical features not described in the present invention can be achieved by or using existing technologies, and will not be described here.

Claims

1. A suspended small cased well eccentric integrated double-tube injection string, characterized in that: The invention comprises an outer layer pipe and an inner layer pipe, wherein the outer layer pipe comprises a conventional oil pipe (1), a dual-channel eccentric water distributor (2), an outer connecting sleeve (3), a variable buckle joint (4), a small-diameter oil pipe (5), a small-diameter packer (6), a double-acting injection valve (7), a small-diameter check valve (8), a screen pipe (9) and a wire plug (10) which are sequentially connected from top to bottom; and the inner layer pipe comprises a first oil pipe (11) connected to the lower inner end of the dual-channel eccentric water distributor (2) and a rear-drop ball check valve (12).

2. The eccentric integrated dual-tube injection string for suspended small cased wells according to claim 1 is characterized by: The dual-channel eccentric water distributor (2) comprises an upper joint (2-1), a guide body (2-2), a guide sleeve (2-3), a guide pen tip (2-4), an upper outer tube (2-5), a guide cylinder (2-6), a double-layer plug (2-7), an integrated body (2-8), a plug (2-9), a positioning sleeve (2-10), an inner hanging sleeve (2-11), and a lower outer tube (2-12). The upper end of the upper outer tube (2-5) is connected to the lower end of the upper joint (2-1) by external threads and are sealed to each other, and the lower end of the upper outer tube (2-5) is connected to the upper end of the integrated body (2-8) by external threads and are sealed to each other.

3. The eccentric integrated dual-tube injection string for suspended small cased wells according to claim 2 is characterized in that: The guide body (2-2) is inserted into the lower inner cavity of the upper joint (2-1), is threadedly connected to the upper joint (2-1), and is then welded and fixed; the guide pen tip (2-4) is inserted into the guide sleeve (2-3), and after being connected and fixed together, it is inserted into the lower inner cavity of the guide body (2-2) as a whole with the guide sleeve (2-3); the lower end of the guide sleeve (2-3) is bottom-connected and fixedly connected to the upper end of the guide cylinder (2-6); the lower end of the guide cylinder (2-6) is connected to the upper end of the integrated body (2-8), and the side wall of the guide cylinder (2-6) is provided with a guide groove (2-6-1).

4. The eccentric integrated dual-tube injection string for suspended small cased wells according to claim 2 is characterized in that: The integrated main body (2-8) is provided with a central channel (2-8-10) and an axial deviation hole (2-8-9), and a double-layer plug (2-7) is provided in the axial deviation hole (2-8-9); an upper water inlet (2-8-1) of the main body is provided on the upper side wall of the central channel (2-8-10), and the upper water inlet (2-8-1) of the main body is connected to the upper water control channel of the double-layer plug (2-7); and a lower water inlet (2-8-2) of the main body is provided on the lower side wall of the central channel (2-8-10), and the lower water inlet (2-8-2) of the main body is connected to the lower water control channel of the double-layer plug (2-7).

5. The eccentric integrated dual-tube injection string for suspended small cased wells according to claim 2 is characterized in that: The upper side wall of the axial deflection hole (2-8-9) is provided with a first water outlet (2-8-3) extending outward in a tangential direction, and the first water outlet (2-8-3) is communicated with the upper water outlet (2-7-3) of the plug; the lower outer periphery of the integrated body (2-8) is provided with a first lower thread (2-8-5), and a second lower thread (2-8-6) with a reduced diameter is provided below the first lower thread (2-8-5); the lower part of the integrated body (2-8) is provided with a lower flow channel (2-8-4) extending in the axial direction and communicated with the lower water outlet (2-7-6) of the plug; and a second water outlet (2-8-7) is provided on the outer wall between the first lower thread (2-8-5) and the second lower thread (2-8-6) and communicated with the lower flow channel (2-8-4).

6. The eccentric integrated dual-tube injection string for suspended small cased wells according to claim 2 is characterized in that: The lower end of the integrated body (2-8) is connected to the upper end of the lower outer tube (2-12) via a first lower thread (2-8-5) and sealed to each other, and the outer periphery of the lower end of the lower outer tube (2-12) is provided with an external hanging thread (2-12-1); the lower end of the integrated body (2-8) is also connected to the positioning sleeve (2-10) via a second lower thread (2-8-6) and sealed to each other; the upper end of the inner hanging sleeve (2-11) is connected to the lower end of the positioning sleeve (2-10) via an external thread and sealed to each other, and the outer periphery of the lower end of the inner hanging sleeve (2-11) is provided with an internal hanging thread (2-11-1).

7. The eccentric integrated dual-tube injection string for suspended small cased wells according to claim 2 is characterized in that: The ends of the axial side hole (2-8-9) of the integrated body (2-8) and the end of the lower flow channel (2-8-4) are sealed with a plug (2-9); the double-layer plug (2-7) is an adjustable or replaceable nozzle plug, and the upper control nozzle (2-7-2) and the lower control nozzle (2-7-5) are closed before entering the well.

8. The eccentric integrated dual-tube injection string for suspended small cased wells according to claim 1 is characterized in that: The double-acting injection valve (7) comprises an outer tube (7-1) and a lower joint (7-7) connected from top to bottom, wherein a water outlet trough hole (7-1-1) is provided in the middle and upper part of the outer tube (7-1); the upper end of the inner center tube (7-3) is inserted into the inner cavity of the valve body (7-2), and the upper end of the inner center tube (7-3) and the upper end of the valve body (7-2) are connected and fixed by a first pin (7-8); a tapered step sealing surface (7-3-3) which is wide at the top and narrow at the bottom is provided at the upper part of the central channel of the inner center tube (7-3), a radially penetrating lower water inlet hole (7-3-1) is provided below the tapered step sealing surface (7-3-3), and a second seal (7-11) is embedded below the outer end of the lower water inlet hole (7-3-1) to achieve sealing with the inner wall of the valve body (7-2).

9. The eccentric integrated dual-tube injection string for suspended small cased wells according to claim 8 is characterized in that: The outer wall of the inner central tube (7-3) below the lower water inlet hole (7-3-1) is provided with a movable groove (7-3-2) extending vertically downward; the lower part of the valve body (7-2) is screwed with a second pin (7-9); the inner end of the second pin (7-9) is embedded in the movable groove (7-3-2) and can slide up and down along the movable groove (7-3-2); the middle part of the valve body (7-2) is provided with a valve body large diameter section, and the valve body large diameter section is located above the water outlet slot hole (7-1-1); the upper outer shoulder of the valve body large diameter section abuts against the lower part of the inner step of the outer tube (7-1); the middle part of the valve body large diameter section is provided with a radially through lossless water outlet (7-2-1), and the upper and lower sides of the outer end of the lossless water outlet (7-2-1) are respectively embedded with first sealing rings (7-10) to achieve sealing with the inner wall of the outer tube (7-1) 10. The eccentric integrated dual-tube injection string for suspended small cased wells according to claim 8, characterized in that: The lower outer wall of the inner center tube (7-3) is provided with an inner center tube reduced diameter section, the lower end of the inner center tube reduced diameter section is connected to the internal thread of the lower joint (7-7) and sealed with each other; a constant pressure spring (7-5) is sleeved on the outer periphery of the inner center tube reduced diameter section, the constant pressure spring (7-5) is inserted from the lower end of the inner center tube (7-3), the top of the constant pressure spring (7-5) abuts against the bottom of the gasket (7-4), the top inner edge of the gasket (7-4) abuts against the bottom of the top outer step of the inner center tube reduced diameter section, the top outer edge of the gasket (7-4) is located below the inner step of the outer tube (7-1), and the lower end of the constant pressure spring (7-5) abuts against the upper end surface of the lower joint (7-7).

11. The eccentric integrated dual-tube injection string for suspended small cased wells according to claim 8, characterized in that: The limiting sleeve (7-6) is sleeved on the outer periphery of the constant pressure spring (7-5) and is located in the lower inner cavity of the outer tube (7-1), and the lower end of the limiting sleeve (7-6) abuts against the inner step of the lower joint (7-7); the shear force of the first pin (7-8) is greater than the setting pressure of the small diameter packer (6) by 2 to 3 MPa, and the shear force of the second pin (7-9) is greater than the larger of the normal water injection pump pressure and the shear force of the first pin (7-8) by 2 to 3 MPa.

12. The eccentric integrated dual-tube injection string for suspended small cased wells according to claim 1, characterized in that: The rear-drop ball check valve (12) comprises an upper outer sleeve (12-1), a lower outer sleeve (12-5) and a pressure cap (12-9) connected in sequence from top to bottom; the upper end of the limiting ring (12-2) abuts against the lower end surface of the upper outer sleeve (12-1), and the lower end of the limiting ring (12-2) abuts against the inner step of the lower outer sleeve (12-5); a spring groove and a fixing hole are provided on the circumference of the limiting ring (12-2) for matching with the upper end of the check spring (12-4), and the limiting ring (12-2) is fixedly connected to the check spring (12-4); the check spring (12-4) It is wide at the top and narrow at the bottom; the fixed sleeve (12-8) is sleeved on the outer periphery of the lower end of the valve seat (12-6) and connected with a dislocation pin (12-7), and the whole is inserted from the lower end of the lower outer sleeve (12-5); the middle outer step of the valve seat (12-6) abuts against the lower middle inner step of the lower outer sleeve (12-5); a conical step sealing surface (7-3-3) is provided in the middle of the inner cavity of the valve seat (12-6); and the upper end of the conical step sealing surface (7-3-3) is provided with an upper outer ring extending upward for limiting the check spring (12-4).

13. A stratified water injection method for a suspended small cased well, using the suspended small cased well eccentric integrated dual-tube separate injection string according to any one of claims 1 to 12, characterized in that: The steps are as follows: S1, from bottom to top, sequentially lower the wire plug (10), screen tube (9), small diameter check valve (8), double-acting injection valve (7), small diameter packer (6), and small diameter oil pipe (5); connect the small diameter oil pipe (5) in series, continue lowering the variable buckle joint (4), external connecting sleeve (3), and suspend at the wellhead; S2, inserting the rear ball-type check valve (12) and the first oil pipe (11) in sequence from bottom to top; S3, the inner hanging thread (2-11-1) of the double-flow channel eccentric water distributor (2) is connected to the first oil pipe (11) and then lowered, and the outer hanging thread (2-12-1) at the lower end of the double-flow channel eccentric water distributor (2) is connected to the outer connecting sleeve (3); S4, continue lowering the conventional oil pipe (1) to the wellhead, and connect the lower end of the conventional oil pipe (1) to the double-flow channel eccentric water distributor (2); S5. Pressurization and sealing: The injected water flows into the lower end of the outer tube through the rear ball-type check valve (12), and the pressure is applied, and the small-diameter packer (6) completes the sealing. The pressure is continued to be applied, and when the pressure exceeds the shear pressure of the first pin (7-8) in the double-acting injection valve (7), it is sheared off, and the valve body (7-2) moves downward until the second pin (7-9) stops moving when it reaches the boundary of the moving groove (7-3-2). At this time, the lower end of the valve body (7-2) contacts the upper end face of the gasket (7-4), the lower water inlet (7-3-1), the lossless water outlet (7-2-1) and the water outlet groove hole (7-1-1) are connected, and the lower injection channel is opened.

14. The stratified water injection method for a suspended small cased well according to claim 13, characterized in that: The following steps are also included: S6. Measure the water absorption of the lower injection layer: Connect the pumping pipeline on the ground according to the injection process, record the water injection volume per unit time under different injection pressures of the pump truck, calculate the water absorption index of the lower injection layer, and calculate the lower layer water injection pressure P that meets the injection volume conditions. During this process, the maximum pump pressure does not exceed the shear force of the second pin (7-9); S7. Insert the matching valve ball of the double-acting injection valve (7). The valve ball falls onto the conical step sealing surface (7-3-3) of the inner central pipe (7-3). Under the control and limit of the second pin (7-9), the lower injection channel is closed. After lowering the flow rate measuring and adjusting instrument to be docked with the double-layer plug (2-7), the upper control nozzle core (2-7-2) is controlled to open on the ground. At this time, the main body upper water inlet (2-8-1), the plug upper water inlet (2-7-1), the upper control nozzle core (2-7-2), the plug upper water outlet (2-7-3) and the first external water outlet (2-8-3) are connected, and the upper injection channel is opened.

15. The stratified water injection method for a suspended small cased well according to claim 14, characterized in that: It also includes the following steps: S8. Measure the water absorption of the upper injection layer: Pump liquid on the ground, record the water injection volume of the pump truck at different injection pressures per unit time, obtain the water absorption index of the upper injection layer, and calculate the upper layer water injection pressure P_up that meets the allocation injection volume condition. During this process, the maximum pump pressure does not exceed the shearing force of the second pin (7-9). S9. If P_up < P_down: Backwash the well to discharge the matching valve ball of the double-acting injection valve (7) from the wellbore. Insert the matching valve ball (12-10) of the post-insertion ball-type check valve (12). The valve ball (12-10) falls onto the sealing surface of the valve seat (12-6) to close the inner pipe water injection channel. Lower the flow rate measuring and adjusting instrument to be docked with the double-layer plug (2-7), and control the upper control nozzle core (2-7-2) to close on the ground. Apply pressure. When the pressure is greater than the shearing force of the dislocating pin (12-7), it is cut off. The valve ball (12-10) pushes the valve seat (12-6) to move downward until it bottoms against the fixed sleeve (12-8). At this time, the lower end of the check spring (12-4) just disengages from the outer ring at the upper end of the valve seat (12-6). The check spring (12-4) returns to its original position, and the claws contract inward. Its inner diameter is smaller than the valve ball (12-10) to ensure that the valve ball (12-10) is not washed out during well flushing. Lower the flow rate measuring and adjusting instrument to be docked with the double-layer plug (2-7), and control the upper control nozzle core (2-7-2) and the lower control nozzle core (2-7-5) to open for normal water injection.

16. The stratified water injection method for a suspended small cased well according to claim 15, characterized in that: In S9: If Pup ≥ Pdown + the pressure difference of the well flushing valve of the small diameter packer (6): the measuring and adjusting instrument is lowered and connected to the double-layer plug (2-7), and the ground control closes the upper control nozzle (2-7-2); the pressure is applied, and when the pressure is greater than the shear pressure of the second pin (7-9), it is sheared off; the matching valve ball (12-10) of the rear-throwing check valve (12) is put in, and the valve ball (12-10) falls into the sealing surface of the valve seat (12-6), closing the water injection channel of the inner pipe; the pressure is applied, and when the pressure is greater than the shear force of the dislocation pin (12-7), it is sheared off , the valve ball (12-10) pushes the valve seat (12-6) downward until it contacts the bottom of the fixed sleeve (12-8). At this time, the check spring (12-4) is just separated from the upper outer ring of the valve seat (12-6). The check spring (12-4) returns to its original position, and the claw shrinks inward. Its inner diameter is smaller than that of the valve ball (12-10), ensuring that the valve ball (12-10) is not washed out during well washing. The measuring and adjusting instrument is lowered and docked with the double-layer plug (2-7). The ground control opens the upper control nozzle (2-7-2) and the lower control nozzle (2-7-5) for normal water injection.

17. The stratified water injection method for a suspended small cased well according to claim 13, characterized in that: The following steps are also included: Well washing: The casing annulus is pressurized by water injection, the well washing channel of the small diameter packer (6) is opened, the well washing channel of the small diameter check valve (8) is opened, and the casing annulus well washing channel is established to achieve well washing. After the well washing is completed, the well washing channel of the small diameter packer (6) is closed and stratified water injection is realized again.

Images