Special well sand washing, filling and multifunctional completion pipe column and construction method

Abstract

The present application relates to a special well sand washing, filling multifunctional completion pipe column, including completion outer pipe column, completion inner pipe column; the completion outer pipe column includes push cylinder, outer central tube, lower cone, screen pipe, upper connecting cylinder, lower connecting cylinder, guide head; the push cylinder is sleeved on the outer wall of the outer central tube, the two ends of the lower cone are fixedly connected with the outer central tube and the screen pipe respectively, the other end of the screen pipe is fixedly connected with the upper connecting cylinder, the upper connecting cylinder is connected with the lower connecting cylinder through a closing structure, a one-way valve structure is installed between the lower connecting cylinder and the guide head; the outer central tube between the push cylinder and the lower cone is provided with a packer anchoring structure; the completion inner pipe column includes an upper joint and an inner central tube; the inner central tube is fixedly connected with the inner wall part of the upper joint, a piston is installed between the two, the inner central tube wall is provided with a liquid inlet hole, and a ball seat is installed on the inner wall of the inner central tube through a shear pin; the present application can realize downhole operation, sand washing, setting, well flushing, filling and releasing in one trip, simplifying the procedure and saving construction time.

Description

Technical Field

[0001] The invention belongs to the technical field of well completion tools, and in particular relates to a multifunctional well completion string for sand flushing and filling in special wells and a construction method. Background Art

[0002] During the multifunctional sand flushing and filling completion process for special wells, the ability to lower the tubing string into place in one go is crucial to wellbore safety and improving the success rate of the operation. In particular, the smooth lowering of the tubing string is crucial to the success rate of the subsequent gravel packing operation. Currently, in wells with severe sand production, the tubing string may encounter sand obstruction during lowering, preventing it from being lowered into place. The current solution is to remove the completion string, run a sand flushing tool to flush the sand and clean the well, and then run the completion string again. If the string still cannot be lowered into place, the sand flushing operation must be repeated. This results in a significant waste of time and money, and also makes the wellbore conditions more severe and irregular, hindering the subsequent gravel packing operation.

[0003] The invention patent "Horizontal Well Gravel Packing String and Pressure Control Valve Therefor," authorized on June 15, 2016, with authorization publication number CN 103362483B, primarily consists of tubing, an oil drain, a flushing pipe, a gravel packing tool, casing, and a screen. This technology suffers from the following major shortcomings: 1. The process is incapable of sand flushing operations, resulting in a high probability of tool obstruction during lowering and a low first-pass success rate. 2. The string structure is complex, and failure during operation would render the well useless and increase construction costs. 3. The process lacks a post-operation gravel spitting prevention device, potentially resulting in sand control failure. 4. The construction process is cumbersome, requiring two runs of the string to complete the gravel packing operation.

[0004] Therefore, based on these problems, a special well sand flushing and filling multifunctional completion string and construction method are provided, which can realize the operations of running, sand flushing, sealing, well washing, filling, and releasing in one trip. When the completion string encounters resistance during lowering, it can be run while sand flushing, which simplifies the procedure and saves construction time. It has important practical significance. Summary of the Invention

[0005] The present invention proposes a special well sand-flushing and filling multifunctional completion string and construction method that can complete operations such as running, sand flushing, sealing, well washing, filling, and releasing in one trip. When the completion string encounters resistance during lowering, it can be run while sand flushing, thus simplifying the procedure and saving construction time.

[0006] The present invention solves the technical problem by adopting the following technical solutions:

[0007] Multifunctional completion strings for special wells, including outer completion strings and inner completion strings;

[0008] The outer completion string includes a push tube, an outer center tube, a lower cone, a screen tube, an upper connecting tube, a lower connecting tube, and a guide head; the push tube is sleeved on the outer wall of the outer center tube, and the two are limited to each other in the axial reverse direction, the two ends of the lower cone are fixedly connected to the outer center tube and the screen tube respectively, the other end of the screen tube is fixedly connected to the upper connecting tube, the upper connecting tube and the lower connecting tube are connected by a closing structure, the lower connecting tube is fixedly connected to the guide head, and a one-way valve structure is installed in the cavity between the lower connecting tube and the guide head; a sealing anchoring structure is installed on the outer center tube between the push tube and the lower cone; the outer completion string is sleeved in the casing string;

[0009] The completion inner pipe string includes an upper joint, an inner center pipe, a small diameter pipe, and a butt pipe; one end of the inner center pipe is fixedly connected to the inner wall portion of the upper joint, a piston is installed between the outer wall of the inner center pipe and the inner wall of the upper joint, and a sealed cavity is formed between the piston, the inner center pipe, and the upper joint. A liquid inlet hole is provided on the inner center pipe wall corresponding to the sealed cavity, and a ball seat is installed on the inner wall of the inner center pipe through shear nails;

[0010] The inner completion string is located inside the outer completion string, and the two are fixedly connected by an inner center pipe and an outer center pipe; the butt joint can open the closing structure, and by throwing a ball to hold the pressure, the piston pushes the push cylinder to move, so that the isolation anchoring structure is opened, and the outer completion string is anchored on the inner wall of the casing string.

[0011] Furthermore, the isolation anchoring structure includes a sealing cylinder, an upper cone, and a suspension body; the sealing cylinder, upper cone, and suspension body are sequentially installed on the outer center tube between the push cylinder and the lower cone, the sealing cylinder is in sealing contact with the inner wall of the casing string, and the suspension body can move toward the inner wall of the casing string under the axial thrust of the upper cone.

[0012] Furthermore, the upper cone, the lower cone and the suspension body are all in contact through inclined surfaces.

[0013] Furthermore, the closing structure includes an upper sleeve, a closing seat, a torsion spring, and a closing cover. The two ends of the upper sleeve are fixedly connected to the upper connecting tube and the lower connecting tube respectively. The closing seat and the closing cover are fixedly connected to the two ends of the torsion spring respectively. The closing seat is an annular structure. The closing seat, torsion spring, and closing cover are located on the inner wall of the upper sleeve and are limited in the axial direction.

[0014] Furthermore, the one-way valve structure includes a lower sleeve, a one-way flow plug, a reset spring, and a flow plate; a flow hole is provided on the flow plate, and the two ends of the lower sleeve are fixedly connected to the lower connecting tube and the guide head respectively, and the flow plate is fixedly installed in the cavity of the lower sleeve, and the two ends of the reset spring are fixedly connected to the one-way flow plug and the flow plate respectively. In the initial state, the one-way flow plug is in close contact with one end of the lower connecting tube.

[0015] Furthermore, a first step structure is provided on the outer wall of the butt joint tube, and a second step structure is provided on the inner wall of the upper connecting tube. The first step structure and the second step structure cooperate with each other to achieve axial limitation of the butt joint tube.

[0016] Furthermore, the guide head is provided with an opening, and the one-way valve structure enables the fluid to flow from the outer central tube toward the guide head.

[0017] Furthermore, the upper joint is fixedly connected to the oil pipe string.

[0018] Furthermore, a plurality of sieve holes are provided on the side wall of the sieve tube.

[0019] The above-mentioned construction method of special well sand flushing and filling multifunctional completion string includes the following steps:

[0020] Hang the outer completion string at the wellhead, lower the inner completion string into the outer completion string, open the closing cap with the butt joint, and connect the inner center pipe and the outer center pipe to form a whole.

[0021] The inner completion string and the outer completion string are lowered into the well together. When sand is stuck, fluid is injected forward to flush the sand until the outer completion string is aligned with the oil layer.

[0022] Throwing soluble balls to set the seal to achieve isolation and anchoring;

[0023] Continue to pressurize and separate the inner completion string and the outer completion string;

[0024] The soluble balls dissolve automatically and gravel filling operations are carried out.

[0025] The advantages and positive effects of the present invention are:

[0026] When the completion string of the present invention is lowered and encounters obstacles, sand can be flushed while being lowered, ensuring that the completion string of the well with serious sand production is lowered into place at one time; the operation of lowering, flushing, sealing, well washing, filling, and releasing the string can be completed in one trip, which simplifies the procedure and saves construction time; the gravel filling tool is designed with a closing cover and a single-flow plug seat, both of which have anti-backflow functions, ensuring the sand blocking effect and preventing gravel from spitting back, which is safe and reliable; the string structure is simple and easy to operate, without complex parts, and low risk during construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that these drawings are designed for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless otherwise specified, these drawings are intended only to conceptually illustrate the structures described herein and are not necessarily drawn to scale.

[0028] Figure 1 A structure sectional view of the well completion outer pipe string of the special well sand washing and filling multifunctional completion pipe string provided by the embodiment of the present application is provided;

[0029] Figure 2 A structure sectional view of the well completion inner pipe string of the special well sand washing and filling multifunctional completion pipe string provided by the embodiment of the present application is provided;

[0030] Figure 3 A structure sectional view of the special well sand washing and filling multifunctional completion pipe string provided by the embodiment of the present application is provided;

[0031] Figure 4 A structure sectional view of the special well sand washing and filling multifunctional completion pipe string provided by the embodiment of the present application is provided;

[0032] Figure 5 A structure sectional view of the special well sand washing and filling multifunctional completion pipe string provided by the embodiment of the present application is provided; DETAILED DESCRIPTION

[0033] First of all, it should be noted that the specific structure, features and advantages of the present application will be specifically described below in an exemplary manner, however, all the descriptions are only for illustration, and should not be understood as any limitation on the present application. In addition, any single technical feature described or implied in the embodiments mentioned in the present application, or any single technical feature shown or implied in the drawings, can still continue to be combined or deleted between these technical features (or their equivalents), so as to obtain more other embodiments of the present application which can not be directly mentioned in the present application. In addition, in order to simplify the drawing, the same or similar technical features can only be marked in one place in the same drawing.

[0034] In the description of the present application, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship when the product of the present application is usually placed, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0035] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0036] The special well sand washing and filling multifunctional completion pipe string provided by the embodiment comprises a well completion outer pipe string and a well completion inner pipe string;

[0037] The completion outer string includes a push tube 7, an outer center tube 11, a lower cone 15, a screen tube 16, an upper connecting tube 20, a lower connecting tube 25, and a guide head 31; a plurality of screen holes are provided on the side wall of the screen tube, the push tube 7 is sleeved on the outer wall of the outer center tube 11, and the two are limited to each other in the axial reverse direction, the two ends of the lower cone 15 are fixedly connected to the outer center tube 11 and the screen tube 16 respectively, the other end of the screen tube 16 is fixedly connected to the upper connecting tube 20, the upper connecting tube 20 and the lower connecting tube 25 are connected by a closing structure, the lower connecting tube 25 is fixedly connected to the guide head 31, and a one-way valve structure is installed in the cavity between the lower connecting tube 25 and the guide head 31; an isolation anchoring structure is installed on the outer center tube 11 between the push tube 7 and the lower cone 15; the completion outer string is sleeved in the casing string 1;

[0038] The completion inner tubular string includes an upper joint 3, an inner center pipe 4, a small-diameter pipe 18, and a butt-joint pipe 19; one end of the inner center pipe 4 is fixedly connected to the inner wall portion of the upper joint 3, a piston 6 is installed between the outer wall of the inner center pipe 4 and the inner wall of the upper joint 3, and a sealed cavity is formed between the piston, the inner center pipe 4, and the upper joint 3. A liquid inlet hole 5 is provided on the wall of the inner center pipe 4 corresponding to the sealed cavity, and a ball seat 9 is installed on the inner wall of the inner center pipe 4 via shear nails 10; the upper joint is fixedly connected to the oil pipe string 2;

[0039] The inner completion string is located inside the outer completion string, and the two are fixedly connected by an inner center pipe and an outer center pipe; the butt joint 19 can open the closing structure, and by throwing a ball to hold the pressure, the piston pushes the push cylinder to move, so that the isolation anchoring structure is opened, and the outer completion string is anchored on the inner wall of the casing string.

[0040] Specifically, the isolation anchoring structure includes a sealing cylinder 12, an upper cone 13, and a suspension body 14; the sealing cylinder 12, the upper cone 13, and the suspension body 14 are sequentially installed on the outer center tube 11 between the push cylinder 7 and the lower cone 15, the sealing cylinder 12 is in sealing contact with the inner wall of the casing string, and the suspension body 14 can move toward the inner wall of the casing string under the axial thrust of the upper cone 13; it should be noted that the upper cone 13, the lower cone 15 and the suspension body 14 are in contact with the inclined surface, so that when the upper cone 13 pushes the suspension body 14 to move toward the lower cone 15, the suspension body 14 moves radially outward under the action of the inclined surface, thereby contacting and pressing with the inner wall of the casing string, and, in order to enhance the anchoring effect, it can be considered that the outer wall of the suspension body 14 is a rough surface.

[0041] The closing structure includes an upper sleeve 21, a closing seat 22, a torsion spring 23, and a closing cover 24. The two ends of the upper sleeve 21 are fixedly connected to the upper connecting tube 20 and the lower connecting tube 25, respectively. The closing seat 22 and the closing cover 24 are fixedly connected to the two ends of the torsion spring 23, respectively. The closing seat is an annular structure. The closing seat 22, the torsion spring 23, and the closing cover 24 are located on the inner wall of the upper sleeve 21 and are limited in the axial direction. The closing seat sleeve is arranged on the inner wall of the upper sleeve 21. When the docking tube 19 pushes open the closing cover 24, the closing cover 24 flips axially. When flipping, the torsion spring 23 is subjected to torque, and the closing seat 22 rotates freely around the torsion spring 23, thereby realizing multiple barrier-free opening or closing of the closing cover 24.

[0042] The one-way valve structure includes a lower sleeve 26, a one-way flow plug 27, a reset spring 28, and a flow plate 30; the flow plate 30 is provided with a flow hole 29, the two ends of the lower sleeve 26 are fixedly connected to the lower connecting tube 25 and the guide head 31 respectively, the flow plate 30 is fixedly installed in the cavity of the lower sleeve 26, the two ends of the reset spring 28 are fixedly connected to the one-way flow plug 27 and the flow plate 30 respectively, and in the initial state, the one-way flow plug 27 is in close contact with one end of the lower connecting tube 25.

[0043] A first step structure 1901 is provided on the outer wall of the butt joint tube, and a second step structure 2001 is provided on the inner wall of the upper connecting tube. The first step structure and the second step structure cooperate with each other to achieve axial limitation of the butt joint tube.

[0044] The guide head is provided with an opening 3101, and the one-way valve structure enables the fluid to flow from the outer central tube to the guide head.

[0045] Specifically, such as Figure 1As shown, the push cylinder 7 is connected to the outer step of the outer center tube 11 through the inner step at the lower end, and the two are clearance-matched and can move freely along the axial direction; the lower end face of the push cylinder 7 is pressed against the upper end face of the sealing cylinder 12, and the sealing cylinder 12 is sleeved on the outer center tube 11, and the two are clearance-matched. The lower end face of the sealing cylinder 12 is pressed against the upper end face of the upper cone 13, and the outer side of the sealing cylinder 12 is squeezed on the inner wall surface of the casing string 1, and the upper cone 13 is sleeved on the outer center tube 11, and the two are clearance-matched. The lower cone surface of the upper cone 13 is pressed against the upper cone surface of the suspension body 14, and the lower cone surface of the suspension body 14 is pressed against the upper cone surface of the lower cone 15. The lower cone 15 is connected to the outer center tube 11 through the upper end thread, and the lower cone 15 is connected to the screen tube 16 through the lower end thread. The screen tube 16 is connected to the upper connecting cylinder 20 through the lower end thread, and the upper connecting cylinder 2 0 is connected to the upper protective sleeve 21 through the lower end thread, the lower end surface of the upper connecting tube 20 is tightened against the upper end surface of the closing seat 22, and the closing seat 22 is set inside the upper protective sleeve 21, and the two are clearance fit. The closing seat 22 and the closing cover 24 are connected together by a torsion spring 23, and the closing seat 24 can rotate freely around the torsion spring. The upper sleeve 21 is connected to the lower connecting tube 25 through the lower end thread, and the lower connecting tube 25 is connected to the lower sleeve 26 through the lower end thread. The lower conical surface of the lower connecting tube 25 is tightened against the upper conical surface of the one-way flow plug 27, and the lower end surface of the one-way flow plug 27 is tightened against the upper end surface of the return spring 28. The lower end surface of the return spring 28 is tightened against the upper end surface of the flow plate 30. The flow plate 30 is installed inside the lower sleeve 26, and the two are threadedly connected. The lower sleeve 26 is connected to the guide head 30 through the lower end thread.

[0046] like Figure 2 As shown, the oil pipe string 2 is connected to the upper joint 3 through the lower end thread, and the pipe string is sent into the well through the oil pipe string 2. The upper joint 3 is connected to the upper end of the inner center pipe 4 through the inner side thread. The outer side of the upper end of the inner center pipe 4 is processed with a liquid inlet hole 5. A piston 6 is placed between the inner center pipe 4 and the upper joint 3. The ball seat 9 is placed inside the inner center pipe 4. The two are fixed together by shear nails 10. After the shear nails 10 are cut off, the ball seat 9 can move axially; the inner center pipe 4 is connected to the small inner diameter pipe 18 through the lower end thread, and the small inner diameter pipe 18 is connected to the butt pipe 19 through the lower end thread.

[0047] See attached Figure 3After the inner and outer completion strings are lowered to the predetermined positions, the soluble ball 8 is put in, and the soluble ball 8 falls on the upper end surface of the ball seat 9 to form a sealing cavity, pressurizing the inner completion string. The liquid flows in from the liquid inlet hole 5, pushing the piston 6 to move downward, and the piston pushes the push cylinder 7. The push cylinder 7 compresses the sealing cylinder 12, and the sealing cylinder 12 expands outward. The outer surface of the sealing cylinder 12 is squeezed together with the inner surface of the casing string 1 to achieve upper and lower isolation; at the same time, the sealing cylinder 12 pushes the upper cone 13 downward to move downward, and the upper cone 13 is pushed downward. The cone 13 pushes the suspension body 14 downward to move, and the suspension body 14 moves outward along the lower conical surface of the upper cone 13 and the upper conical surface of the lower cone 15, and finally bites into the casing string 1 to achieve anchoring; continue to pressurize, and when the pressure increases to a certain value, the ball seat 9 moves downward, shears the shear pin 10, and falls onto the internal step of the inner central pipe 4. At this time, the middle outer side of the inner central pipe 4 is separated from the inner side of the outer central pipe 11 by threads, and the corresponding completion inner string and completion outer string are separated; see the attached Figure 4 After a certain period of time, the soluble ball 8 dissolves and the internal diameter of the completion string is realized. At this time, gravel packing operation can be carried out. After the filling is completed, see the attached Figure 5 , which is the well structure left for special well completion.

[0048] The above-mentioned construction method of special well sand flushing and filling multifunctional completion string includes the following steps:

[0049] The outer completion string is hung at the wellhead, and the inner completion string is lowered into the outer completion string. The butt joint 19 opens the closing cover 24, and the inner and outer center pipes are connected to form a whole.

[0050] The inner completion string and the outer completion string are lowered into the well together. When sand is stuck, fluid is injected forward to flush the sand until the outer completion string is aligned with the oil layer 17;

[0051] Throwing soluble balls to set the seal to achieve isolation and anchoring;

[0052] Continue to pressurize and separate the inner completion string and the outer completion string;

[0053] The soluble balls dissolve automatically and gravel filling operations are carried out.

[0054] Specifically, firstly, the outer completion string is lowered and hung at the wellhead; next, the inner completion string is lowered, and the inner and outer strings are lowered into the well together. When sand is stuck, the sand can be flushed forward to remove the sand jam, and the strings are lowered to the predetermined position so that the screen 16 is aligned with the oil layer 17; a soluble ball 8 is dropped from the oil pipe string 2, and the soluble ball 8 sits on the upper end of the ball seat 9. After being pressurized to a certain pressure, the outer surface of the sealing tube 12 is squeezed together with the inner surface of the casing string 1 to achieve upper and lower isolation, and the suspension body 14 bites into the casing string 1 to achieve anchoring. Continued pressure releases the inner center pipe 4 and the inner center pipe 11, separating the corresponding inner and outer pipe strings. The soluble balls 8 automatically dissolve, allowing gravel packing to begin. Gravel-containing slurry is pumped into the tubing string 2. After passing through the inner pipe string, the slurry pushes open the one-way flow plug 27. The slurry bypasses the one-way flow plug 27, passes through the flow holes 29, the lower casing 26, and the guide head 31, and enters the annulus outside the screen 16. The gravel is then trapped outside the screen 16, forming a gravel pack layer 32. The liquid flows through the screen and into the space between the small-diameter pipe 18 and the screen 16. It then flows through the annulus between the inner center pipe 4 and the outer center pipe 11, and the annulus between the upper joint 3 and the casing string 1, returning to the surface. Gravel packing is complete. After the gravel packing is complete, the inner pipe string is removed.

[0055] After the above steps, the sand flushing and filling of special wells are realized, and the well completion and well retention structure is as follows: Figure 5 shown.

[0056] The above embodiments describe the present invention in detail, but the contents are only preferred embodiments of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. Multifunctional completion string for special wells, characterized by: Including outer completion string and inner completion string; The outer completion string includes a push tube, an outer center tube, a lower cone, a screen tube, an upper connecting tube, a lower connecting tube, and a guide head; the push tube is sleeved on the outer wall of the outer center tube, and the two are limited to each other in the axial reverse direction, the two ends of the lower cone are fixedly connected to the outer center tube and the screen tube respectively, the other end of the screen tube is fixedly connected to the upper connecting tube, the upper connecting tube and the lower connecting tube are connected by a closing structure, the lower connecting tube is fixedly connected to the guide head, and a one-way valve structure is installed in the cavity between the lower connecting tube and the guide head; a sealing anchoring structure is installed on the outer center tube between the push tube and the lower cone; the outer completion string is sleeved in the casing string; The completion inner pipe string includes an upper joint, an inner center pipe, a small diameter pipe, and a butt pipe; one end of the inner center pipe is fixedly connected to the inner wall portion of the upper joint, a piston is installed between the outer wall of the inner center pipe and the inner wall of the upper joint, and a sealed cavity is formed between the piston, the inner center pipe, and the upper joint. A liquid inlet hole is provided on the inner center pipe wall corresponding to the sealed cavity, and a ball seat is installed on the inner wall of the inner center pipe through shear nails; The inner completion string is located inside the outer completion string, and the two are fixedly connected by an inner central pipe and an outer central pipe; the butt joint can open the closing structure, and by throwing a ball to hold the pressure, the piston pushes the push cylinder to move, so that the isolation anchoring structure is opened, and the outer completion string is anchored to the inner wall of the casing string; The isolation anchoring structure includes a sealing cylinder, an upper cone, and a suspension body; the sealing cylinder, the upper cone, and the suspension body are sequentially mounted on the outer central tube between the push cylinder and the lower cone; the sealing cylinder is in sealing contact with the inner wall of the casing string; and the suspension body can move toward the inner wall of the casing string under the axial thrust of the upper cone; The upper cone, the lower cone and the suspension body are all in contact through inclined surfaces; The closing structure includes an upper sleeve, a closing seat, a torsion spring, and a closing cover. The two ends of the upper sleeve are fixedly connected to the upper connecting tube and the lower connecting tube respectively. The closing seat and the closing cover are fixedly connected to the two ends of the torsion spring respectively. The closing seat is an annular structure. The closing seat, torsion spring, and closing cover are located on the inner wall of the upper sleeve and are limited in the axial direction.

2. The multifunctional completion string for sand flushing and filling of special wells according to claim 1 is characterized in that: The one-way valve structure includes a lower sleeve, a one-way flow plug, a reset spring, and a flow plate; a flow hole is provided on the flow plate, and the two ends of the lower sleeve are fixedly connected to the lower connecting tube and the guide head respectively, and the flow plate is fixedly installed in the cavity of the lower sleeve, and the two ends of the reset spring are fixedly connected to the one-way flow plug and the flow plate respectively. In the initial state, the one-way flow plug is in close contact with one end of the lower connecting tube.

3. The multifunctional completion string for sand flushing and filling in special wells according to claim 1 is characterized in that: A first step structure is provided on the outer wall of the butt joint tube, and a second step structure is provided on the inner wall of the upper connecting tube. The first step structure and the second step structure cooperate with each other to achieve axial limitation of the butt joint tube.

4. The multifunctional completion string for sand flushing and filling in special wells according to claim 1 is characterized in that: The guide head is provided with an opening, and the one-way valve structure enables the fluid to flow from the outer central tube toward the guide head.

5. The multifunctional completion string for sand flushing and filling in special wells according to claim 1 is characterized in that: The upper joint is fixedly connected to the oil pipe string.

6. The multifunctional completion string for sand flushing and filling in special wells according to claim 1 is characterized in that: A plurality of sieve holes are provided on the side wall of the sieve tube.

7. The construction method of a special well sand flushing and filling multifunctional completion string according to any one of claims 1 to 6, characterized in that: The steps include: Hang the outer completion string at the wellhead, lower the inner completion string into the outer completion string, open the closing cap with the butt joint, and connect the inner center pipe and the outer center pipe to form a whole. The inner completion string and the outer completion string are lowered into the well together. When sand is stuck, fluid is injected forward to flush the sand until the outer completion string is aligned with the oil layer. Throwing soluble balls to set the seal to achieve isolation and anchoring; Continue to pressurize and separate the inner completion string and the outer completion string; The soluble balls dissolve automatically and gravel filling operations are carried out.

Images