A slim hole screen completion string and method of construction

Abstract

The application discloses a small-hole screen pipe completion string and a construction method, which comprises, from bottom to top, a well washing valve, a screen pipe, a sealing assembly and a circulating assembly connected in sequence; the circulating assembly comprises a sliding sleeve seat, the sliding sleeve seat is provided with a circulating hole, and the sliding sleeve seat is provided with an inner-outer double opening structure according to the position of the circulating hole. A soluble blank plate is further connected between the screen pipe and the sealing assembly. The application can avoid cement slurry pollution of oil and gas reservoirs, can save the cost of casing, cement and other materials, can save the construction period and operation cost, can effectively avoid the sealing assembly from being scratched, can effectively prevent cement slurry from leaking into the screen pipe section to pollute the oil layer, can provide a higher seat sealing pressure difference for the string packer, and can effectively avoid the problem of rubber ring falling in the cement injection process by a piston.

Description

Technical Field

[0001] This invention relates to the field of oil extraction technology, specifically to a small-bore screen completion string and its construction method. Background Technology

[0002] Currently, most of my country's old oilfields are gradually entering the high water-cut and ultra-high water-cut development phase, increasing the difficulty of development. Simultaneously, the extended development time and deepening development work have led to significant changes in the formation's fluid and pressure fields. Frequent oil and water well interventions and workovers, along with factors such as wellbore structure, completion and cementing quality, pipe materials, and corrosion, have resulted in increasingly poor technical conditions of the casing in oil and water wells, leading to continuous casing damage phenomena such as rupture, deformation, perforation, and breakage. Casing damage renders the corresponding controlled reserves of the oil well unusable, resulting in the loss of substantial recoverable reserves. Furthermore, casing damage prevents water injection wells from injecting water normally, hindering the replenishment of energy in the corresponding oil wells, making development plans impossible, and impacting the final recovery rate of the block. Sidetracking is an effective technical means to manage casing damage, especially horizontal sidetracking wells, which offer the technical advantages of low cost and large drainage area and high production rate.

[0003] Currently, the main completion methods for sidetracked horizontal wells include casing cementing, top-cementing of the screen, and tailpipe suspension. Among them, top-cementing of the screen is an open-hole screen completion method. The casing is inserted above and below the oil layer for cementing, while the screen is inserted below the oil layer without cementing. This method has the technical advantages of less reservoir contamination and a larger drainage area, and is therefore widely used.

[0004] Chinese Patent Application No. 200810238498.X discloses a "Drill-Free Cementing Method and String," including a completion casing, a rubber plug, a cement injector, an external packer, and a blind flange. The completion casing is run into the wellbore, and the lower part is sequentially connected to the cement injector, the external packer, and the blind flange. A rubber plug is placed inside the completion casing. The provided drilling-free cementing method uses a soluble material to make the blind flange. After cementing is completed, a designed amount of solution is injected to dissolve the blind flange. The method includes the following sequential steps: (A) running the completion string into the wellbore; (B) pressurizing and expanding the external packer; (C) well washing; (D) injecting a designed amount of cement slurry into the self-injecting cement injector; (E) releasing the rubber plug made of soluble material to the designed position; (F) injecting a designed amount of dissolving liquid to dissolve the blind flange made of soluble material, the rubber plug made of soluble material, and the soluble components on the cement injector; (G) waiting for it to set. The technology has the following problems: ① After cement injection, the cement injector needs to be closed with a rubber stopper, which may result in incomplete closure; ② There is a certain amount of cement residue between the blind plate and the rubber stopper, and the blind plate and the rubber stopper cannot be completely dissolved, requiring subsequent drilling and plugging operations; ③ The open-hole packer used for well completion is made of an expansion-type rubber sleeve, which is easily scratched by the well wall during the well running process, resulting in poor sealing and the screen section being prone to falling into the cement slurry and solidifying the oil layer.

[0005] Chinese patent application number 200910229932.2 discloses a "drill-free sand-control cementing string for open-hole horizontal wells," comprising an outer string and an inner string. The outer string includes an acid-washing and filling valve, a sand-control screen, an open-hole packer, an external positioning step, an external cement injector, and casing. The inner string includes tubing and an internal cement injector connected to it. The inner string is installed within the outer string, and the inner and outer strings are fixed and sealed together. First, the positioner is used to locate the open-hole packer and seal the packer annulus. Then, the positioner is raised to locate the cement injector, and the circulation hole is opened for cementing operations. Finally, the cement circulation hole is mechanically closed by the inner string, and the well is allowed to solidify. The technology has the following problems: ① It requires multiple positioning of the inner tubing string using a mechanical locator, which is a complex process with high positioning accuracy requirements and a low success rate; ② It requires a separate run of the inner tubing string, which increases operating costs and construction time; ③ The inner and outer tubing strings are sealed using a cup packer, which has poor sealing ability and is prone to cement slurry leakage; ④ The cement injector is closed mechanically, which has low reliability and is prone to failure to close tightly; ⑤ The open-hole packer is made of an expanding rubber sleeve, which is easily scratched by the well wall during the well running process, resulting in poor sealing and the screen section being prone to falling into the cement slurry and solidifying the oil layer.

[0006] Chinese patent application number 201110032469.X discloses "A half-stage cementing completion string and method thereof". The completion string includes an external packer, a stage collar and casing connected in sequence. A plug and a rubber stopper are placed in the external packer and stage collar. A positioning groove is provided on the inner wall of the external packer, and the positioning block of the plug is embedded therein. The cementing steps are as follows: lower the complete string, pressurize and set the external packer, increase the pressure to open the stage collar, circulate mud and then inject cement slurry, put in the rubber stopper, replace the pressure, close the stage collar, lower the retrieval spear to catch the plug, raise the retrieval spear to release the plug, take out the plug and rubber stopper, and wait for solidification. This can realize a cementing completion process without drilling and plugging the screen, and the diameter after completion is the same as the inner diameter of the casing. The technology has the following problems: ① The tool structure is complex, costly, and has low reliability; ② After cementing is completed, another trip of the retrieval string is required, and two trips of the string increase construction costs and operation cycle; ③ The requirements for controlling the cement setting time are high, otherwise the retrieval plug is prone to failure, increasing the risk of drilling plug failure; ④ The open-hole packer is made of an expansion-type rubber sleeve, which is easily scratched by the well wall during the well running process, resulting in poor sealing and the screen section easily falling into the cement slurry and solidifying the oil layer.

[0007] Chinese Patent Application No. 201711318126.3 discloses "An Integrated Cementing, Sand Control, and Completion String and Construction Method for Small Wellbore", which includes an outer string and a filling string placed inside it. The outer string includes a drill pipe string, a hanger, a tailpipe, a pressure seat, a cement injector, a packer, a partition plate, a screen pipe, a filling device, and a guiding device connected in sequence. The filling string includes a tubing string, a flushing string, and a filling docking device connected in sequence. The filling device and the filling docking device cooperate with each other. The string and construction method of this invention can realize the upper cementing and lower gravel filling screen pipe completion of small side-drilled wellbore, forming a sand barrier between the screen pipe and the open hole formation, and realizing the integrated cementing, sand control, and completion of small wellbore. The main construction steps are as follows: the outer tubing string is lowered to the predetermined position in the well, then pressure is applied to the outer tubing string, the hanger is mounted, and the expansion packer is used to seal the annulus. Pressure is continued until the cement injector opens, cement is injected for cementing, and a displacement plug is dropped to replace the cement slurry. The plug is then pressed at the pressure seat, and after setting, the displacement plug, pressure seat, cement injector, and separator are removed by the drill bit. The filling tubing string is then lowered and connected to the filling device to perform gravel filling operations, forming a gravel filling layer. This technology has the following problems: ① After cementing, a drill plug tubing string needs to be lowered for drilling and plugging. The vibration of the drill bit will affect the cement annulus, affecting the cementing quality; ② A separate drill plug tubing string is run, increasing operating costs and construction period; ③ The residual burrs formed after drilling and plugging are not smooth, which will affect the smooth lowering of the tubing string in subsequent operations; ④ The open-hole packer is made of an expansion-type rubber sleeve, which is easily scratched by the well wall during the well running process, resulting in poor sealing and the screen section easily falling into the cement slurry and solidifying the oil layer.

[0008] Therefore, in view of the problems existing in the above-mentioned patented technologies, it is necessary to invent a small-bore screen pipe completion string and construction method, so as to realize the cement injection completion process at the top of the screen pipe in a low-cost completion method with one run of the string in small wells such as sidetracking wells, achieve sand control and production, effectively manage casing damage wells, and quickly restore the production capacity of old wells. Summary of the Invention

[0009] To address the aforementioned deficiencies in existing technologies, the present invention aims to provide a small-bore screen completion string and construction method that can avoid cement slurry contamination of oil and gas reservoirs, save on the cost of casing, cement, and other materials, reduce construction time and operating costs, effectively prevent scratches on the sealing assembly, effectively prevent cement slurry from leaking into the screen section and contaminating the oil layer, provide a high setting pressure differential for the packer, and effectively avoid the problem of rubber ring detachment during piston cementing.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A small-bore well completion string includes a well-washing valve, a screen pipe, a sealing assembly, and a circulation assembly connected sequentially from bottom to top.

[0012] The circulation assembly includes a sliding sleeve seat with a circulation hole; the sliding sleeve seat has an inner and outer double opening structure for the circulation hole position.

[0013] A soluble blind plate is also connected between the screen tube and the sealing assembly.

[0014] The dual-opening structure includes an inner opening structure and an outer opening structure; the inner opening structure is located on the inner wall of the sliding sleeve seat, and the outer opening structure is located on the outer wall of the sliding sleeve seat.

[0015] The internal opening structure includes an opening sleeve; the opening sleeve can seal the circulation hole, and the opening sleeve is connected to the sliding sleeve seat through a pin, and the circulation hole can communicate with the pin;

[0016] The external opening structure includes a sliding sleeve; the sliding sleeve can seal the circulation hole.

[0017] The lower end face of the sliding sleeve has an inner conical surface, and the outer wall of the sliding sleeve seat has an outer conical surface. A spherical body is provided on the outer conical surface, and the inner conical surface and the spherical body form a rigid seal by compression.

[0018] The upper end of the sliding sleeve is connected to the spring sleeve, the spring sleeve is outside the spring sleeve, the lower end of the spring abuts against the upper end of the sliding sleeve, the upper end of the spring sleeve is connected to the upper connector, and the upper end of the spring abuts against the lower end face of the upper connector.

[0019] The outer wall of the spring sleeve and the inner wall of the sliding sleeve are simultaneously provided with corresponding limiting steps to prevent the sliding sleeve from continuing to descend.

[0020] The inner wall of the sliding sleeve seat is provided with a limiting step to prevent the opening sleeve from falling off.

[0021] The inner conical surface has a degree of 30 degrees.

[0022] The sealing assembly includes a support tube, a rubber sleeve assembly fitted on the outer wall of the support tube, and a hydraulic piston-driven sealing mechanism.

[0023] The rubber sleeve assembly includes a rubber sleeve, and the hydraulic piston drive sealing mechanism includes a hydraulic cylinder liner and a piston inside the hydraulic cylinder liner; the support tube has an inlet hole that communicates with the hydraulic cylinder liner;

[0024] The piston of the hydraulic piston-driven sealing mechanism axially compresses the rubber sleeve assembly, causing the rubber sleeve of the rubber sleeve assembly to expand radially.

[0025] The rubber tube includes an inner rubber tube and an outer rubber tube;

[0026] The upper outer circle of the support tube is fitted with a vulcanizing head, an inner rubber tube, and a sealing ring. An outer rubber tube is vulcanized on the outside of the inner rubber tube. The lower outer circle step of the vulcanizing head and the upper outer circle step of the sealing ring are respectively designed with a sawtooth or rectangular tooth structure, which are vulcanized together with the inner rubber tube and the outer rubber tube to form a double-layer rubber tube structure.

[0027] The inner rubber tube is made of soft rubber, and the outer rubber tube is made of hard rubber, with multiple "V" shaped grooves designed on the outer circumference; the sealing ring has a groove in the middle inner circumference.

[0028] The lower part of the inner circle of the hydraulic cylinder liner has a step, and the upper end face of the step is matched with the lower end face of the outer circle step of the piston. The lower end face of the step is designed with a groove to accommodate the locking ring. The lower part of the hydraulic cylinder liner is connected to the pressure cap through the inner circle thread. The upper end face of the pressure cap presses the locking ring into the groove to prevent it from retracting.

[0029] The piston has a locking thread on its outer circumference at the center, which works with the locking ring to prevent it from rolling back; the pressure cap is fixed to the piston by a control shear pin.

[0030] The soluble blind plate consists of a plate base, a plate core, and a pressure sleeve. After the pressure sleeve is connected to the plate base by threads, its upper end face presses the plate core against the inner circular step of the plate base. The outer circular step of the pressure sleeve and the outer circle of the plate core are respectively designed with sealing elements to form a seal with the inner circle of the plate base.

[0031] To achieve the above objectives, the present invention adopts the following technical solution:

[0032] A method for constructing a small-bore well completion string using a screen casing includes the following steps:

[0033] The piston of the hydraulic piston-driven sealing mechanism axially compresses the rubber sleeve assembly, causing the rubber sleeve of the rubber sleeve assembly to expand radially and seal.

[0034] Continue pressurizing inside the tubing string, open the sleeve, cut the open shear pin and move downwards to expose the circulation hole on the sliding sleeve seat. Hydraulically push the sliding sleeve to compress the spring and move upwards. At this time, the circulation hole is fully open, and a thorough well washing and circulation operation is carried out.

[0035] After the cement slurry has been quantitatively replaced, the pump is stopped. At this time, the sliding sleeve automatically returns to its original position under the action of the spring, and its lower inner conical surface presses against the arc-shaped outer circular step of the sliding sleeve seat to prevent the cement slurry in the annulus from flowing back. Then, the completion fluid is introduced to thoroughly flush the well.

[0036] The drill string is retrieved and the central tube of the hanger and its connected inner tube are brought out of the wellbore, enabling the cementing completion operation at the top of the screen pipe to be completed in one trip of the tubing string.

[0037] It also includes the following steps:

[0038] After well completion, the formation fluids fully dissolve the core of the soluble blind plate, and the completion tubing is connected to form an oil and gas production channel, enabling sand control and production using open-hole screen pipes.

[0039] Compared with the prior art, the present invention has the following advantages:

[0040] Cementing can be performed on the top of the screen pipe in newly drilled small wells. This can avoid cement slurry contamination of the oil and gas reservoir and save on the cost of materials such as casing and cement. The inner and outer tubing strings are run in one go. There is no need to run a separate drill plug string or inner tubing cementing string in the later stages of well completion. All well completion work can be completed in one run, saving construction time and operating costs.

[0041] The sealing assembly of this invention features an innovative design with inner and outer double-layer rubber sleeves and a compression sealing structure. The outer hard rubber sleeve can effectively prevent the sealing assembly from being scratched, while the inner soft rubber sleeve can maintain a long-lasting seal and effectively prevent cement slurry from leaking into the screen tube section and contaminating the oil layer.

[0042] The circulation assembly uses a throttle switch, which is simple and reliable in structure. After cement injection is completed, it automatically resets under the action of a spring, without the need for a separate shut-off action.

[0043] The entire completion string has a simple structure, leaves no steps after completion, and has a large inner diameter, which facilitates the smooth running of the string in subsequent operations.

[0044] The circulation assembly employs a double-opening piston design. The opening sleeve relies on the pressure movement generated by the piston area difference, coupled with pin control, to provide a high seat sealing pressure differential for the tubing packer. The throttling sleeve opening seal commonly uses a rubber ring with soft material sealing. The lower end of the throttling sleeve has a 30-degree chamfer that forms a rigid seal with the upper outer spherical surface of the lower connector. This effectively prevents the rubber ring from falling off during the piston cementing process, which could cause the sleeve to not close properly later, affecting the entire cementing operation and requiring rework, resulting in significant economic losses. The throttling sleeve's ability to self-adjust the opening channel area according to the injection pressure and displacement allows for more even injection of slurry into the casing's outer ring control area, effectively protecting the wellbore wall at the cementing site. The external return spring has an adjustable elasticity function, is easy to operate, and can meet the needs of different working conditions with varying load requirements. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the structure of a small-bore well screen completion string according to the present invention;

[0046] Figure 2 This is a schematic diagram of the sealing assembly and circulation assembly of a small-bore screen completion string according to the present invention.

[0047] In the diagram: 11 well-washing valve; 10 screen pipe; 9 soluble blind flange; 8 sealing assembly; 7 circulation assembly; 6 small wellbore; 5 inner pipe; 4 small casing; 3 hanger; 2 feed drill string; 1 technical casing;

[0048] 7.1 Upper connector; 7.2 Seal; 7.3 Spring sleeve; 7.4 Spring; 7.5 Sliding sleeve; 7.6 Sliding sleeve seat; 7.7 Circulation hole; 7.8 Opening sleeve;

[0049] 8.1 Sealing tube; 8.2 Vulcanizing head; 8.3 Support tube; 8.4 Outer rubber sleeve; 8.5 Inner rubber sleeve; 8.6 Sealing ring; 8.7 Liquid inlet; 8.8 Hydraulic cylinder liner; 8.9 Piston; 8.10 Anti-reverse thread; 8.11 Locking ring; 8.12 Pressure cap; 8.13 Control shear pin; 8.14 Lower connector;

[0050] 9.1 Plate base; 9.2 Plate core; 9.3 Pressure sleeve. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Example 1:

[0053] See appendix Figure 1 Taking a three-section small-bore completion as an example, the drilling string is run into the second-section technical casing 1, and the three-section small well 6 is drilled out. The completion string is run into the small well 6, which includes an inner tube 5. The screen pipe 10 in the completion string is run into the oil layer section and suspended on the technical casing 1 using the hanger 3. The sealing assembly 8 at the top of the screen pipe 10 expands to seal the wellbore annulus. After opening the circulation assembly 7, cement slurry is injected into the wellbore annulus above the sealing assembly 8 for cementing and completion. After the cementing is completed, the circulation assembly 7 automatically closes. After the hanger 3 is released, the residual cement slurry above the soluble blind plate 9 is flushed out of the wellbore using the inner tube 5 connected at the bottom and replaced with completion fluid. After the formation fluid dissolves the soluble blind plate 9, the screen pipe can be put into production for sand control.

[0054] A well completion string with a spool suspended from a screen and top cemented, comprising, from bottom to top: a well-washing valve 11 + a screen 10 + a soluble blind flange 9 + a sealing assembly 8 + a circulation assembly 7 + a small casing 4 + a hanger 3 + a drill string 2. The small casing 4 contains an inner tube 5, the upper part of which is connected and sealed to the central tube of the hanger 3, and the lower part extends to the upper part of the soluble blind flange 9. The well-washing valve 11 can also be a sand-control filling tool. The screen 10 can be one or more, and depending on the sand-control requirements, the screen 10 can be a perforated screen, a slotted screen, or a composite precision sand filter. The soluble blind flange 9 can be made of water-soluble or oil-soluble material. Depending on the wellbore diameter and the length of the sealing section, the sealing assembly 8 connected to the upper part of the soluble blind flange 9 can be one or more sets.

[0055] See appendix Figure 2The circulation assembly 7 consists of an upper connector 7.1, a spring sleeve 7.3, and a sliding sleeve seat 7.6 connected sequentially by threads. A sealing element 7.2 is designed at the threaded connection to achieve a seal. In use, the upper end of the upper connector 7.1 is connected to the small sleeve 4 via a sealing pipe thread. The upper part of the sliding sleeve seat 7.6 has an outer circular step, with a circulation hole 7.7 designed at the bottom of the step. An opening sleeve 7.8 is fitted inside the corresponding position. The opening sleeve 7.8 is fixed to the sliding sleeve seat 7.6 by an opening shear pin 7.9. Sealing elements 7.2 are designed on the outer circle of the opening sleeve 7.8 at both ends passing through the circulation hole 7.7 and the opening shear pin 7.9, respectively, to achieve a seal with the inner wall of the sliding sleeve seat 7.6. A sliding sleeve 7.5 is fitted onto the upper outer circle of the sliding sleeve seat 7.6, and the upper part of the sliding sleeve 7.5 has an inner circle... A step is fitted onto the outer circle of the spring sleeve 7.3. A spring 7.4 is installed between the lower end face of the upper connector 7.1 and the upper end face of the sliding sleeve 7.5. The lower end face of the sliding sleeve 7.5 is a conical structure, and the outer circle step of the sliding sleeve seat 7.6 is an arc structure. Under the action of the spring 7.4, the lower conical structure of the sliding sleeve 7.5 presses against the arc step of the outer circle of the sliding sleeve seat 7.6 to form a seal. A sealing groove is designed in the lower outer circle step of the spring sleeve 7.3, and a sealing element 7.2 is installed to form a seal with the inner wall of the sliding sleeve 7.5. An inner circle step is designed in the lower part of the sliding sleeve seat 7.6. When the opening sleeve 7.8 is opened and moves downward, it presses against the inner circle step of the sliding sleeve seat 7.6, just exposing the circulation hole 7.7.

[0056] The sealing assembly 8 consists of a sealing tube 8.1, a support tube 8.3, and a lower connector 8.14 connected sequentially by threads. Each threaded connection is equipped with a sealing element 7.2. The upper end of the sealing tube 8.1 is connected to the sliding sleeve seat 7.6 of the circulation assembly 7 via a sealing tube thread. The upper outer circumference of the support tube 8.3 is fitted with a vulcanizing head 8.2, an inner rubber sleeve 8.5, and a sealing ring 8.6. An outer rubber sleeve 8.4 is vulcanized around the inner rubber sleeve 8.5. The lower outer circumference step of the vulcanizing head 8.2 and the upper outer circumference step of the sealing ring 8.6 are respectively designed with serrated or rectangular tooth structures, which connect with the inner rubber sleeve 8.5 and the outer rubber sleeve 8.14. 4. The components are vulcanized together to form a double-layer rubber sleeve structure. A piston 8.9 is fitted between the support tube 8.3 and the hydraulic cylinder sleeve 8.8. The upper inner and outer circles of the piston 8.9 are designed with sealing grooves to install the sealing element 2, which forms a seal with the support tube 8.3 and the hydraulic cylinder sleeve 8.8 respectively. The upper end face of the piston 8.9 is tightly fitted with the lower end face of the sealing ring 8.6. At the corresponding contact positions of the two end faces, a liquid inlet hole 8.7 is opened on the support tube 8.3. Thus, a sealed pressure is formed between the lower end face of the sealing ring 8.6, the upper end face of the piston 8.9, and the inner wall of the hydraulic cylinder sleeve 8.8. Space; the lower part of the inner circle of the hydraulic cylinder liner 8.8 has a step, the upper end face of which mates with the lower end face of the outer circle step of the piston 8.9. The lower end face of the step is designed with a groove to house the locking ring 8.11. The lower part of the hydraulic cylinder liner 8.8 is connected to the pressure cap 8.12 through an inner circle thread. The upper end face of the pressure cap 8.12 presses the locking ring 8.11 into the groove to prevent it from retracting. The middle outer circle of the piston 8.9 is designed with a backlash thread 8.10, which mates with the locking ring 8.11 to prevent backlash. The pressure cap 8.12 is fixed to the piston 8.9 by a control shear pin 8.13. During initial installation and fixing, the inner rubber sleeve 8... 8.5 and the outer rubber sleeve 8.4 are not compressed and are in a freely unfolded state; a set of inner rubber sleeves 8.5 and outer rubber sleeves 8.4 are also fitted on the lower outer circle of the support tube 8.3, and are vulcanized together with the vulcanizing heads 8.2 at both ends to form a double-layer rubber sleeve structure. The upper end face of the upper vulcanizing head 8.2 simultaneously presses against the lower end face of the pressure cap 8.12 and the piston 8.9. The lower connector 8.14 is connected to the lower outer circle of the support tube 8.3 by threads, and its upper end face is pressed against the lower end face of the vulcanizing head 8.2. During initial assembly, both sets of double-layer rubber sleeve structures are not compressed and are in a freely unfolded state.

[0057] Example 2:

[0058] like Figures 1 to 2 As shown, the present invention provides a small-bore screen completion string, wherein the inner rubber sleeve 8.5 is made of soft rubber material and the outer rubber sleeve 8.4 is made of hard rubber material, and multiple "V" shaped grooves are designed on the outer circle; the middle inner circle of the sealing ring 8.6 is designed with a groove to place the sealing element 7.2 and the support tube 8.3 to maintain a seal, and the middle outer circle step is connected to the hydraulic cylinder sleeve 8.8 by threads, and is also designed with a sealing element 7.2 to form a seal with the inner wall of the hydraulic cylinder sleeve 8.8.

[0059] Example 3:

[0060] like Figures 1 to 2 As shown, the present invention provides a small-bore screen completion string, wherein the soluble blind plate 9 is composed of a plate seat 9.1, a plate core 9.2 and a pressure sleeve 9.3. After the pressure sleeve 9.3 is connected to the plate seat 9.1 by threads, its upper end face presses the plate core 9.2 against the inner circular step of the plate seat 9.1. The outer circular step of the pressure sleeve 9.3 and the outer circle of the plate core 9.2 are respectively designed with sealing elements 7.2, which form a seal with the inner circle of the plate seat 9.1.

[0061] Example 4:

[0062] like Figures 1 to 2 As shown, the present invention provides a small-bore screen completion string. During assembly, the upper connector 7.1 of the circulation assembly 7 is connected to the small casing 4 via a sealing pipe thread, and the lower part is connected to the sealing pipe 8.1 of the sealing assembly 8 via the sealing pipe thread of the sliding sleeve seat 7.6. One or more sets of sealing assemblies 8 can be connected according to the wellbore diameter and sealing requirements. The lowest set of sealing assemblies 8 is connected to the plate seat 9.1 of the soluble blind plate 9 via the lower connector 8.14. The internal space of the string above the soluble blind plate 9 forms a sealed space. Below the soluble blind plate 9, the screen pipe 10 and the well washing valve 11 are connected sequentially. The upper part of the small casing 4 is connected to the outer pipe of the hanger 3. An inner pipe 5 is installed inside the small casing 4. The upper part of the inner pipe 5 is connected and sealed to the central pipe of the hanger 3, and its lower part extends to the upper part of the soluble blind plate 9.

[0063] Example 5:

[0064] Construction Process: Taking a three-section small-bore completion as an example, the drilling string is run into the second-section technical casing 1, and the third-section small well 6 is drilled. The completion string is then run into the small well 6. From bottom to top, the completion string includes: a wash valve 11, a screen pipe 10, a soluble blind flange 9, a sealing assembly 8, a circulation assembly 7, a small casing 4, a hanger 3, and a feed drill string 2. The feed drill string 2 is connected to the hanger 3 at the top of the completion string. The screen pipe 10 in the completion string is run into the oil layer section. After the string is in place, the internal space of the string above the soluble blind flange 9 is a sealed space. Hydraulic pressure of 5MPa is applied to the feed drill string 2, and the hanger 3 is set, suspending the completion string on the technical casing 1. After inserting the drill string 2 and rotating it 30-50 times clockwise, reverse it and release the handle. After a successful test lift, return the tubing string and maintain the seal. Continue pressurizing to 7MPa-9MPa. The hydraulic pressure is transmitted through the inlet hole 8.7 to the action section formed by the inner and outer seals 7.2 of the sealing ring 8.6. The hydraulic force pushes the sealing ring 8.6 upward. The sealing ring 8.6 drives the hydraulic cylinder sleeve 8.8 upward through the thread. The hydraulic cylinder sleeve 8.8 drives the pressure cap 8.12 upward through the thread. The pressure cap 8.12 shears the control pin 8.13 and is no longer fixed to the support tube 8.3. The hydraulic force pushes the sealing ring 8.6 upward to squeeze the inner rubber sleeve 8.5 and the outer rubber sleeve 8.4 vulcanized double... The double-layer rubber sleeve structure expands outward under compression to seal the annulus between the completion string and the wellbore. Due to the "V"-shaped groove designed on the outer circumference of the outer rubber sleeve 8.4, the double-layer rubber sleeve structure forms multiple sealing contacts with the well wall using the "V"-shaped groove as the boundary, effectively improving sealing capacity. The "V"-shaped groove also effectively provides anti-creep performance, providing reliable wall gripping force when the rubber sleeve structure contacts the open hole well wall. Simultaneously, hydraulic pressure acts on the cross-section formed by the inner and outer seals 7.2 of the piston 8.9. The hydraulic force pushes the piston 8.9 downward, and the piston 8.9 pushes the vulcanizing head 8.2, which it contacts, downward. The invention employs a double-layer rubber sleeve structure. Under compression, the double-layer rubber sleeve expands outward to seal the annulus between the completion string and the wellbore. This sealing method is called "compression sealing." In contrast, the rubber sleeves used in the background technology employ "expansion sealing." These sleeves use inner and outer double layers with a steel strip lining. They expand outward by filling the internal sealing cavity with liquid, resulting in a large expansion ratio. However, they are easily scratched during well running, affecting the sealing effect. Compared to the "expansion sealing" rubber sleeve structure, the "compression sealing" rubber sleeve structure used in this invention uses hard rubber for the outer layer, which avoids scratching by the well wall during well running. The inner and outer rubber sleeves fully guarantee the sealing effect. When the sealing ring 8.6 and the piston 8.9 move relative to each other under hydraulic force, the locking ring 8.11 in the lower groove of the hydraulic cylinder liner 8.8 connected to the sealing ring 8.6 crawls on the anti-reverse thread 8.10 of the piston 8.9 and can only move upward relative to each other and cannot retract, thereby locking the relative displacement of the sealing ring 8.6 and the piston 8.9, ensuring the compression deformation of the upper and lower sets of double-layer rubber sleeves, and ensuring the sealing effect of the wellbore annulus.

[0065] The pressure inside the tubing continues to reach 18 MPa. Hydraulic pressure acts on the upper and lower end faces of the opening sleeve 7.8 of the circulation assembly 7. Because the outer circle of the opening sleeve 7.8 has a stepped structure, the hydraulic action surface formed on the upper end face is larger than that formed on the lower end face. Under the pressure difference created by the hydraulic pressure, the opening sleeve 7.8 shears the opening shear pin 7.9 and moves downwards until its lower end face rests on the inner circular step of the sliding sleeve seat 7.6. At this point, the circulation hole 7.7 on the sliding sleeve seat 7.6 is just exposed. Then, hydraulic pressure acts on the lower inner conical surface and the upper inner circular step surface of the sliding sleeve 7.5, pushing the sliding sleeve 7.5 to compress the spring 7.4 and move upwards. At this time, the circulation hole 7.7 is fully opened, the pressure inside the tubing decreases, and a thorough well-washing circulation operation is performed. Cement slurry is introduced from the drill string 2, and the cement slurry enters the completion tubing through the hanger 3 and the inner tube 5. Then, the cement slurry enters the wellbore annulus through the circulation hole 7.7. After quantitatively replacing the cement slurry, the pump is stopped. At this time, the sliding sleeve 7.5 automatically resets under the action of the spring 7.4, and its lower inner conical surface presses against the arc-shaped outer circular step of the sliding sleeve seat 7.6 to form a "line-surface" metal seal to prevent the backflow of cement slurry in the annulus. The drill string 2 is lifted up by 0.5m to 2m, so that the central tube of the hanger 3 is separated from the hanger 3 and a small annular channel (hereinafter referred to as "small annulus") is formed. At this time, a large displacement of completion fluid is injected into the drill string 2 to wash out the residual cement slurry in the inner tube 5 and the inner tube 5 connected to it from the wellbore through the upper "small annulus". After thorough washing, the drill string 2 is pulled out, and the central tube of the hanger 3 and the inner tube 5 connected to it are taken out of the wellbore, realizing the cementing completion operation of the top of the screen pipe in one trip of the tubing string.

[0066] After the designed completion time, the formation fluid will fully dissolve the core 9.2 of the soluble blind plate 9, and the completion tubing will be connected to form an oil and gas production channel, enabling sand control production with open hole screens. If the well washing valve 11 is designed as a filling tool, a filling tubing can also be run in to fill the outside of the tubing with gravel for sand control, thereby improving the sand control effect.

[0067] The small-bore screen completion string and construction method have significant application effects, mainly reflected in three aspects:

[0068] 1. A single tubing string can complete the cementing completion operation by suspending the stern tube above the screen pipe. On the one hand, stern tube suspension completion can save casing and cementing materials. On the other hand, screen pipe completion in the oil layer section can protect the oil and gas reservoir from cement slurry contamination. In the later production, it can save the cost of perforation and sand control in the pipe. A single tubing string operation can significantly reduce the completion cycle and operating cost.

[0069] 2. The innovative design of the inner and outer double rubber sleeve structure can not only prevent scratches during the well running process, but also ensure the long-term sealing of the annulus by using compression sealing. At the same time, the external "V" groove design can also improve the anti-creep capability of the tubing string and further improve the sealing effect of the rubber sleeve.

[0070] 3. The tools used with this completion string have a simple and reliable structure. After completion, the inner diameter is consistent with that of the casing, which facilitates the smooth running of the string in subsequent operations and reduces construction risks.

[0071] All components not discussed in detail in this application, as well as the connection methods of these components, are well-known technologies in this field. They can be directly applied and will not be elaborated further.

[0072] In this invention, the term "multiple" refers to two or more unless otherwise explicitly defined. The terms "install," "connect," "link," and "fix" should be interpreted broadly. For example, "connect" can be a fixed connection, a detachable connection, or an integral connection; "link" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0073] In the description of this invention, it should be understood that the terms "upper," "lower," "left," "right," "front," "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or unit referred to must have a specific orientation or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0074] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A small-bore well completion string, comprising a well-washing valve, a screen pipe, a sealing assembly, and a circulation assembly connected sequentially from bottom to top; characterized in that, The circulation assembly includes a sliding sleeve seat with a circulation hole; the sliding sleeve seat has an inner and outer double opening structure for the circulation hole; a soluble blind plate is also connected between the screen tube and the sealing assembly. The dual-opening structure includes an inner opening structure and an outer opening structure; the inner opening structure is located on the inner wall of the sliding sleeve seat, and the outer opening structure is located on the outer wall of the sliding sleeve seat; the inner opening structure includes an opening sleeve; the opening sleeve can seal the circulation hole, and the opening sleeve is connected to the sliding sleeve seat through a pin, and the circulation hole can communicate with the pin; the outer opening structure includes a sliding sleeve; the sliding sleeve can seal the circulation hole. The lower end face of the sliding sleeve has an inner conical surface, and the outer wall of the sliding sleeve seat has an outer conical surface. A spherical body is provided on the outer conical surface, and the inner conical surface and the spherical body form a rigid seal by compression. The inner conical surface has an angle of 30 degrees. The sealing assembly includes a support tube, a rubber sleeve assembly fitted on the outer wall of the support tube, and a hydraulic piston-driven sealing mechanism. The rubber sleeve assembly includes a rubber sleeve, and the hydraulic piston drive sealing mechanism includes a hydraulic cylinder liner and a piston inside the hydraulic cylinder liner; the support tube has an inlet hole that communicates with the hydraulic cylinder liner; The hydraulic piston drives the piston of the sealing mechanism to axially compress the rubber sleeve assembly, causing the rubber sleeve of the assembly to expand radially. The rubber sleeve includes an inner rubber sleeve and an outer rubber sleeve. A vulcanizing head, an inner rubber sleeve, and a sealing ring are fitted onto the upper outer circle of the support tube. The outer rubber sleeve is vulcanized outside the inner rubber sleeve. The lower outer circle step of the vulcanizing head and the upper outer circle step of the sealing ring are respectively designed with serrated or rectangular tooth structures, which are vulcanized together with the inner and outer rubber sleeves to form a double-layer rubber sleeve structure. The inner rubber sleeve is made of soft rubber material, and the outer rubber sleeve is made of hard rubber material, and multiple "V" shaped grooves are designed on its outer circle. The sealing ring has a groove in the middle inner circle. The lower part of the inner circle of the hydraulic cylinder liner has a step, and the upper end face of the step is matched with the lower end face of the outer circle step of the piston. The lower end face of the step is designed with a groove to accommodate the locking ring. The lower part of the hydraulic cylinder liner is connected to the pressure cap through the inner circle thread. The upper end face of the pressure cap presses the locking ring into the groove to prevent it from retracting. The piston has a locking thread on its outer circumference at the center, which works with the locking ring to prevent it from rolling back; the pressure cap is fixed to the piston by a control shear pin. The soluble blind plate consists of a plate base, a plate core, and a pressure sleeve. After the pressure sleeve is connected to the plate base by threads, its upper end face presses the plate core against the inner circular step of the plate base. The outer circular step of the pressure sleeve and the outer circle of the plate core are respectively designed with sealing elements to form a seal with the inner circle of the plate base.

2. The small-bore completion string according to claim 1, characterized in that, The upper end of the sliding sleeve is connected to the spring sleeve, the spring sleeve is outside the spring sleeve, the lower end of the spring abuts against the upper end of the sliding sleeve, the upper end of the spring sleeve is connected to the upper connector, and the upper end of the spring abuts against the lower end face of the upper connector.

3. The small-bore completion string according to claim 2, characterized in that, The outer wall of the spring sleeve and the inner wall of the sliding sleeve are simultaneously provided with corresponding limiting steps to prevent the sliding sleeve from continuing to descend.

4. The small-bore completion string according to claim 1, characterized in that, The inner wall of the sliding sleeve seat is provided with a limiting step to prevent the opening sleeve from falling off.

5. A construction method based on the small-bore screen completion string as described in claim 1, characterized in that, Includes the following steps: The piston of the hydraulic piston-driven sealing mechanism axially compresses the rubber sleeve assembly, causing the rubber sleeve of the rubber sleeve assembly to expand radially and seal. Continue pressurizing inside the tubing string, open the sleeve, cut the open shear pin and move downwards to expose the circulation hole on the sliding sleeve seat. Hydraulically push the sliding sleeve to compress the spring and move upwards. At this time, the circulation hole is fully open, and a thorough well washing and circulation operation is carried out. After the cement slurry has been quantitatively replaced, the pump is stopped. At this time, the sliding sleeve automatically returns to its original position under the action of the spring, and its lower inner conical surface presses against the arc-shaped outer circular step of the sliding sleeve seat to prevent the cement slurry in the annulus from flowing back. Then, the completion fluid is introduced to thoroughly flush the well. The drill string is pulled out and the central tube of the hanger and the inner tube connected to it are brought out of the wellbore, so that the cementing completion operation at the top of the screen pipe can be completed in one trip of the tubing string. It also includes the following steps: After well completion, the formation fluids fully dissolve the core of the soluble blind plate, and the completion tubing is connected to form an oil and gas production channel, enabling sand control and production using open-hole screen pipes.

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